Magnetics, IEEE Transactions on - new TOC

Front cover

May 2013

IEEE Transactions on Magnetics publication information

May 2013

CEFC 2012 Chairman’s Foreword

May 2013

CEFC 2012 Publication Chairman’s Foreword

May 2013

CEFC 2012 Committee

May 2013

Generalized Magnetostatic Analysis by Boundary Integral Equation Derived From Scalar Potential

May 2013

The volume integral equation approach replaces the loop currents over the volume elements in magnetic material with the loop currents on the material surface to derive a boundary integral equation (BIE). The surface loop current is equivalent to the double layer charge, which offers an integral form of scalar potential to give the BIE. Once BIE has been solved, the loop current gives the magnetic flux density $B$ by Biot-Savart law. The BIE has many advantages such as giving accurate solutions and evaluating $B$ at edges and corners. But it has some severe drawbacks due to a multi-valued function of the excitation potential caused by the source currents and that is why its application has been restricted mostly to simply connected problem. This paper presents a novel generalized approach, which is applicable for solving generic problems such as multi-material, multiply connected and thin shielding problems.

Parallelization of Finite Element Analysis of Nonlinear Magnetic Fields Using GPU

May 2013

The acceleration of a nonlinear magnetic field analysis by parallelizing the finite element method (FEM) is examined using the graphics processing unit (GPU). It is shown that the speedup of the magnetic field analysis is realized by parallelizing the variable preconditioned conjugate gradient (VPCG) method. The Jacobi over-relaxation (JOR) method, conjugate residual (CR) method and conjugate gradient (CG) method are also applied in the variable preconditioning. The results of computations demonstrate that VPCG using the GPU significantly improve the performance. Especially, CG applied by variable preconditioned on GPU is 39 times faster than ICCG on a CPU.

Instantaneous Power Balance Analysis in Finite-Element Method of Transient Magnetic Field and Circuit Coupled Computation

May 2013

An instantaneous power balance analysis of time-domain finite-element method for transient 2-dimensional (2-D) magnetic field and electric circuit coupled computation is presented. Based on the principle of instantaneous power balance and the technique of matrix analysis, formulations for the computation of instantaneous reactive power, active power and eddy-current loss in solid conductors are put forward. The merit of the proposed algorithm is that the integration method for the loss computation is exactly the same as that for the system equations. Therefore, additional numerical errors arising from the integration in loss computation can be avoided. It clarifies the methods for eddy-current loss computation in solid conductors. The precise identification of instantaneous real power and reactive power is expected to pave the way for a new and accurate approach to extract the instantaneous ac resistances and inductances of the equivalent electric circuit. The concept of instantaneous power balance can also be used for force and torque computations.

Large-Scale Magnetostatic Domain Decomposition Analysis Based on the MINRES Method

May 2013

This paper describes a large-scale 3D magnetostatic analysis using the Domain Decomposition Method (DDM). To improve the convergence of an interface problem of DDM, DDM based on the Conjugate Residual (CR) method or the MINimal RESidual (MINRES) method is proposed. The CR or MINRES method improves convergence rate and shows stable convergence behavior in solving the interface problem, compared with the Conjugate Gradient (CG) method, and reduces the computation time for a large-scale problem with 100 million degrees of freedom.

A Stability Improvement Technique Using PML Condition for the Three-Dimensional Nonuniform Mesh Nonstandard FDTD Method

May 2013

We propose a technique to improve the stability of three-dimensional (3D) nonuniform mesh nonstandard FDTD (NS-FDTD) calculations. To mitigate the numerical instability arising from the connection of different-sized meshes, our method combines the usual interpolation fields and perfectly matched layer (PML) condition at mesh interfaces. We examine a connection for a mesh size ratio of 3:1, and show numerically that our technique improves the stability of 3D NS-FDTD calculation on nonuniform meshes. Our technique is also applied to analyze the fields around a periodic slot panel.

Nonlinear Magnetostatic Analysis by Unified BIE Utilizing Potential Gap Due to Loop Currents

May 2013

Since the line loop current is equivalent to the double layer charge, it gives an integral form of scalar potential. The segmental loop current on the interface between magnetic materials produces a potential gap, which works to give a boundary integral equation (BIE). By virtue of another potential gap due to a fictitious circulating current along the contour of cut-surface in the material, the excitation potential becomes single valued and the BIE becomes applicable to generic problems without any restriction. Regarding the nonlinear magnetic material as composed of segmental materials with different values of permeability, we get the same BIE for the nonlinear analysis as for the linear analysis. In order to check the adequacy and effectiveness of the nonlinear BIE, we solve a typical magnetostatic problem and compare the computed results with those by the conventional magnetic moment method.

Study of an Explicit Meshless Method Using RPIM for Electromagnetic Fields

May 2013

An explicit meshless method for analyzing electromagnetic fields is proposed in this paper. In the proposed method, the wave equation and the Lorentz gauge are discretized using the radial point interpolation method (RPIM) and Newmark's $beta$ method. The Taylor series expansion is also used to obtain an explicit scheme. The proposed method has been applied to the following examples: the magnetic field from a square coil, a Hertz dipole, and an eddy current in a thin plate. The potential of the proposed method has been confirmed through these examples.

Parallel Performance of Multithreaded ICCG Solver Based on Algebraic Block Multicolor Ordering in Finite Element Electromagnetic Field Analyses

May 2013

We present a parallel multithreaded incomplete Cholesky-conjugate gradient (ICCG) solver for a linear system derived from a finite element electromagnetic field analysis. Algebraic block multicolor ordering is introduced to parallelize the solver with a high cache hit ratio and convergence comparable to the sequential solver. We develop the parallel ICCG solver based on reordering with modification for electromagnetic field analyses involving external circuits. The numerical results from practical models show that a 2.6- to 3.8-fold speedup compared with the sequential solver is attained using eight cores.

RPCA-Based Noise Suppression in MEG Measurement for Improving Bio-Electromagnetic Source Estimation

May 2013

Magnetoencephalography (MEG) is a promising technology, which could be used in a variety of biomedical applications. However, MEG electromagnetic measurement is usually degraded by noise. Noise suppression in MEG measurement is particularly challenging because it is difficult to remove the noise and preserve the information components in the MEG data. In this study, a novel noise suppression method, based on robust principal component analysis (RPCA) technique, is presented and applied to the estimation of bio-electromagnetic field in source space for the first time. The proposed method gives a constrained optimization of MEG electromagnetic domain transformations such that the matrix of transformed MEG measurement can be decomposed as the sum of a sparse matrix of noise and a low-rank matrix of denoised data. Applying the proposed method to a number of simulations showed significant improvement of the result accuracy.

A Region-Based Approach for Investigating the Origin of Bioelectromagnetic Activities in MEG Source Space

May 2013

In the present study, we develop a region-based approach, which integrates a novel bioelectromagnetic source inverse technique, together with the use of connectivity analysis method, i.e., directed transfer function (DTF), in investigating the origin of activities in MEG source space. The results confirm that the proposed approach is a promising noninvasive tool for the bioelectric field analysis and biomedical applications. In particular, since the regions are defined according to criteria of functional requirements for biomedical applications, the result obtained by the proposed method is easier to understand and interpret, and moreover, the result also facilitates inter-subject comparisons of the source connectivity analysis.

Field Calculations for Magnetic Shielding: Fourier Modeling Extended With Mode-Matching Technique Applied on a Shield With Finite Dimensions

May 2013

In this paper, a semi-analytical model is derived to calculate the magnetic flux density around a magnetic shield with finite dimensions. The proposed modeling is based on Fourier modeling, which is extended with mode-matching. The described model has less than 0.2(%) error with respect to finite element modeling for the given configuration. Furthermore, the paper shows that assuming a magnetic shield with infinite dimensions introduces a significant error with respect to a magnetic shield with finite dimensions.

A Priori Error Indicator in the Transformation Method for Problems With Geometric Uncertainties

May 2013

To solve stochastic problems with geometric uncertainties, one can transform the original problem in a domain with stochastic boundaries and interfaces to a problem defined in a deterministic domain with uncertainties in the material behavior. The latter problem is then discretized. There exist infinitely many random mappings that lead to identical results in the continuous domain but not in the discretized domain. In this paper, an a priori error indicator is proposed for electromagnetic problems with scalar and vector potential formulations. This leads to criteria for selecting random mappings that reduce the numerical error. In an illustrative numerical example, the proposed a priori error indicator is compared with an a posteriori estimator for both potential formulations.

Accuracy Improvement of Extended Boundary-Node Method

May 2013

The extended boundary-node method (X-BNM) has been modified for improving the accuracy degradation due to the boundary shape and its performance has been numerically investigated by comparing with the standard one. For the case where the boundary shape is strongly concave, the results of computations show that the accuracy of the modified X-BNM is always higher than that of the standard one. In addition, the speed of the modified X-BNM is almost equal to that of the standard one. Therefore, it is found that the performance of the modified X-BNM is much superior to that of the standard one.

Solution of Large Stochastic Finite Element Problems—Application to ECT-NDT

May 2013

This paper describes an efficient bloc iterative solver for the spectral stochastic finite element method (SSFEM). The SSFEM was widely used to quantify the effect of input data uncertainties on the outputs of finite element models. The bloc iterative solver allows reducing computational cost of the SSFEM. The method is applied on an industrial nondestructive testing (NDT) problem. The numerical performances of the method are compared with those of the nonintrusive spectral projection (NISP).

A Quantum-Inspired Evolutionary Algorithm for Multi-Objective Design

May 2013

To explore the full potential of Quantum-inspired Evolutionary Algorithms (QEA) in multiobjective design optimizations, a vector QEA is proposed. To fulfill the two ultimate goals of a vector optimizer in finding and uniformly sampling the Pareto front of a multi-objective inverse problem, a fitness assignment formula to consider the number of improvements in the whole objective functions and the amount of the improvement in a specified objective function, as well as the use of a selection mechanism in choosing the so far searched best solutions, are proposed in this paper. The information sharing and the increment angle updating components of the scalar QEA have also been redesigned according to the characteristics of multi-objective inverse problems. Numerical results on two case studies are presented to validate the proposed vector QEA.

Large-Scale Simulation of Electromagnetic Wave Propagation Using Meshless Time Domain Method With Parallel Processing

May 2013

The large-scale simulation of the electromagnetic wave propagation using meshless time domain method (MTDM) is numerically investigated. Moreover, compute unified device architecture (CUDA) and OpenMP is adopted for parallelization technique to reduce the computation time. The results of computation show that the execution time of the time evolution calculation on GPU is 8.8 time faster than that of CPU. In addition, the execution time of the shape function generation procedure can be speedup about 7842 times by proposed scheme and OpenMP.

Quantum Cellular Automaton for Simulating Static Magnetic Fields

May 2013

This paper proposes a new quantum cellular automaton (quantum CA) for simulating macroscopic electromagnetic fields. The final target is to simulate the macroscopic electromagnetic fields on a quantum computer. In the proposal approach, Maxwell's historical model, which was explained the nature of electromagnetic fields in 1861, has been modified for a quantum CA model to simulate the electromagnetic fields. Then, a state transition rule for CA is determined by a strategy based on the quantum mechanics and the quantum computation theories. One of originalities of the proposed approach is that a system using quantum gates is superstructed to simulate magneto-static fields from currents. First, a modified Maxwell model for applying to quantum CA was shown. Second, by using the quantum computation theory, a quantum gate system to simulate the magnetic fields from currents was described. Finally, the proposed approach was applied to an example of magnetostatic field simulation.

Coupled Magneto-Mechanical Analysis Considering Permeability Variation by Stress Due to Both Magnetostriction and Electromagnetism

May 2013

A general model for the coupled analysis of magneto-mechanical systems is developed by minimizing the continuum energy functional of the system using the calculus of variation. This approach, which is in contrast with the traditional approach of minimizing after discretization, allows the use of strain and stress tensors, vector identities and the divergence theorem, and results in coupled governing equations of the system with three coupling terms; the magnetic stress tensor, the magnetostriction stress tensor, and the magnetostriction reluctivity. The model uses the information contained in the set of experimental magnetostriction curves dependent on stress to calculate the permeability variation due to stress. The governing equations are then discretized using the Galerkin method resulting in methods for the calculation of nodal magnetic and magnetostriction forces including the coupling effects. Finally the model is applied to a simple 2D problem and the flux density distributions using the proposed method and the traditional method of using experimental magnetization curves are compared.

Efficient Compression of 3-D Eddy Current Problems With Integral Formulations

May 2013

For the calculation of eddy current problems using integral formulations, compression techniques are needed due to the fully populated system matrix. As the system matrix is ill-conditioned, even low compression leads to very high errors and is in most cases unsolvable with classical iterative solvers like CG or GMRES. By using regularization techniques, the condition number is enormously reduced, so that high compression rates can be achieved. In this paper the efficiency of the Block Wavelet Compression combined with the Tikhonov regularization is shown by 3-D eddy current problems. The use of the so called Block Wavelet Compression is presented for the first time for eddy current problems using integral formulations.

Enhancing Quasi-Static Modeling: A Claim for Electric Field Computation

May 2013

Although electric field seems useless in non-conducting regions depicted within the quasi-static magnetic regime, its calculation appears necessary therein to: (i) improve the mesh quality required by eddy-current computation; and (ii) tackle the interplay between power transmission and its loss of integrity induced by higher frequencies. The discussion lies on a thermodynamic-oriented description of electromagnetism and a reversible interpretation of the Faraday's law. Energy efficiency challenges deserve such an attention.

High Resolution Numerical Electromagnetic Dosimetry Simulations Using a Coupled Two-Step Approach

May 2013

For numerical dosimetric simulations of complex electromagnetic human exposure situations the method of moments (MoM) is coupled with a finite integration time domain (FITD) scheme: The MoM simulation features a simple model of the body under test and computes the field distribution on a closed surface around the body. This field information is used to define equivalent sources on the surface for a full three-dimensional FITD simulation featuring a high-resolution body under test. First numerical results are presented for this novel approach.

Parameter Optimization and Study of Inverse J-A Hysteresis Model

May 2013

A method for parameter identification of J-A hysteresis model is presented. This method is based on combination of pattern search and nonlinear least square method. The B-H curve of different toroid and Epstein samples are obtained experimentally. The parameters of J-A model are determined by proposed parameter identification method. There is very good agreement between experimental data and predicted B-H curve for different extensive samples.

Improvement of the Preconditioned MRTR Method With Eisenstat's Technique in Real Symmetric Sparse Matrices

May 2013

The Incomplete Cholesky Conjugate Gradient (ICCG) method is widely used to solve indefinite algebraic equations obtained using an edge-based finite element method. However, when a linear solver based on the minimum residual is used, there is a possibility of reducing the elapsed time for a linear system. This paper shows the performance of the preconditioned minimized residual method based on the three-term recurrence formula of the CG-type (MRTR) method by comparing the MRTR method with the ICCG method for real symmetric sparse matrices. Furthermore, we intend to reduce computational costs by using Eisenstat's technique, and achieve more speed-up by applying a preconditioned residual to the convergence criterion.

Association of a PSO Optimizer With a Quasi-3D Ray-Tracing Propagation Model for Mono and Multi-Criterion Antenna Positioning in Indoor Environments

May 2013

This paper presents the association of a particle swarm optimization (PSO) optimization tool with a quasi-3D ray-tracing propagation model for both mono and multi-criterion antenna positioning in indoor environments. The association was applied for a typical wireless indoor system and showed to be an efficient tool to solve typical design antenna positioning problems.

GPU Acceleration of Finite Difference Schemes Used in Coupled Electromagnetic/Thermal Field Simulations

May 2013

The solution procedure of coupled electromagnetic-/thermal-simulations with high resolution requires efficient solvers. High performance computing libraries and languages like Nvidia's CUDA help in unlocking the massively parallel capabilities of GPUs to accelerate calculations. They reduce the time needed to solve real world problems. In this paper, the speed-up is discussed, which is obtained by using GPUs for coupled time domain simulations with finite difference schemes. A tailor-made implementation of the time consuming sparse matrix vector multiplication is shown to have advantages over standard CUDA-libraries like cuSparse.

Sizing of Wall Thinning Defects Using Pulsed Eddy Current Testing Signals Based on a Hybrid Inverse Analysis Method

May 2013

Quantitative non-destructive evaluation, especially sizing of piping wall thinning in nuclear power plants is still a difficult and urgent issue. In this paper, an inversion approach for PECT (pulsed eddy current testing) signals is developed based on ANN (artificial neural network) method at first for profile reconstruction of wall thinning, the sizing result of NN is then utilized as the initial value of the CG (conjugate gradient) inversion scheme to overcome the shortages of both the NN (accuracy problem) and CG (local minimum problem) methods. Several reconstruction examples using the proposed hybrid strategy indicate that the combination of NN and CG methods is rather effective for wall thinning reconstruction from PECT signals in view of both the robustness and sizing accuracy.

Lightning-Inverse Reconstruction by Remote Sensing and Numerical-Field Synthesis

May 2013

An inverse remote-sensing procedure is presented for reconstructing the spatial waveform of the lightning return stroke current throughout a numerical-field synthesis procedure, based on working regularization methods. The approach uses as input data the acquisition of time-domain recordings of the electric and/or magnetic field generated by the lightning current, at various locations on the ground and converts these signals into harmonics by Fourier decomposition. This combination between the proposed solving procedures and harmonic filtering yields numerical results that are in good agreement with the testing functions.

Usefulness of Fixed Point Method in Electromagnetic Field Analysis in Consideration of Nonlinear Magnetic Anisotropy

May 2013

In the electromagnetic field computation in consideration of nonlinear magnetic anisotropy, the solution by the Newton-Raphson method has some problems which are an asymmetric matrix and poor convergence characteristic. We applied the Fixed-Point method to the electromagnetic field computation in consideration of nonlinear magnetic anisotropy and examined the usefulness of the Fixed-Point method through comparing the Fixed-Point method with the ordinary Newton-Raphson method. The Fixed-Point method with a symmetric matrix is quite faster than the Newton-Raphson method with an asymmetric matrix. Therefore, the Fixed-Point method is a very useful technique in nonlinear magnetic anisotropy problems.

Real Time Simulation Method of Magnetic Field for Visualization System With Augmented Reality Technology

May 2013

In this paper, we propose a real-time visualization system utilizing Augmented Reality Technology for electromagnetics education. It gives an image of magnetic field generated by a bar magnet with a piece of iron in real-time, however the bar magnet and the piece of iron are represented by mock ones. In the newly proposed visualization system, these mocks are captured by a web camera, and mesh needed in the calculation of magnetic field is deformed. Subsequently, a finite element analysis is carried out in very short time and then the magnetic field is immediately visualized. Thereby, it is, in real-time, observable that magnetic flux lines generated by the bar magnet are attracted to a piece of iron. Moreover, when a user moves the mocks, the magnetic flux lines are immediately depicted according to the position of the mocks.

Reduction of Linear Subdomains for Non-Linear Electro-Quasistatic Field Simulations

May 2013

A method is presented that reduces the degrees of freedom (DoFs) in linear subdomains in transient non-linear electro-quasistatic (EQS) field finite-element method (FEM) simulations. The electro-quasistatic field model yields a suitable approximation to simulate high-voltage devices such as insulators or surge arresters featuring non-linear resistive field grading materials. These materials are usually applied as thin layers, i.e., they represent only a very small volume part in the overall model. Despite the application of unstructured FEM meshes, commonly most of the DoFs are located in the domain with constant material parameters. The non-linear subdomain is much smaller with respect to the number of DoFs than the part with constant materials. The application of model order reduction techniques, in particular proper orthogonal decomposition (POD), is proposed to minimize the DoFs in the linear subdomain of the simulation model. POD captures the dynamic in the linear subdomain. Large reduction factors can be achieved for low dynamic exterior domains, thus considerably reducing the computational costs. Numerical results are presented for an IEC norm surge arrester and a typical 11 kV insulator design with a field grading inlay.

Performance of 3-D Infinite Elements for High-Frequency Electromagnetic Fields

May 2013

The infinite elements for edge based finite-element methods (FEMs) have been shown effective for open boundary problems. In the infinite elements, electromagnetic fields are expressed in terms of radially decaying basis functions. On the other hand, the perfect matched layer has widely been used for FEMs for high-frequency problems. In this paper, numerical performance of both methods is comparably discussed. The numerical experiments show that the former has higher computational efficiency.

The Parallelized Automatic Mesh Generation Using Dynamic Bubble System With GPGPU

May 2013

An automatic mesh generation method employing a dynamic bubble system can provide a high-quality mesh for electromagnetic finite-element analysis. However, there is a problem in that it takes a very long time to compute the bubbles' movement when a mesh with a large number of elements is produced. It is possible to independently and simultaneously compute the bubbles' movement; therefore, the computation of the bubbles' movement is suitable for parallel computing. In order to shorten the computation time, the computation of the bubbles' movement is parallelized with the graphics-processing unit (GPU). We propose a dynamic bubble system parallelized with GPU. As a result, a reduction in computation time was achieved.

Magnetic Field Analysis in Far-Field Region by Infinite Edge Element With Boundary Surface Integration

May 2013

The electromagnetic phenomena intrinsically spread over the infinite space. Thus, the efficient handling of the open boundary is one of the main issues in the electromagnetic field computation. This paper proposes the infinite edge element method (IEEM) with the boundary surface integration to accurately obtain the magnetic field, i.e., the derivatives of vector potentials, in the far-field region.

Resolution of Nonlinear Magnetostatic Problems With a Volume Integral Method Using the Magnetic Scalar Potential

May 2013

An integral method using the magnetic scalar potential to solve nonlinear magnetostatic problems is developed. This method uses the range interactions between magnetizable elements and it is particularly well suited to compute field in the air domain which do not need to be meshed. The collocation and Galerkin approaches are presented and compared to solve the nonlinear magnetostatic equation. Both methods need the construction of full interaction matrices which may be computed with analytical formulae. A Newton-Raphson method, in which the interaction matrix must be built at each solver iteration, is used to solve the nonlinear formulation. A modified fixed point scheme, in which the interaction matrix is built only once, is also proposed. 3-D numerical examples are given and results of the different methods are compared.

A Vector Play Model for Finite-Element Eddy-Current Analysis Using the Newton-Raphson Method

May 2013

The differentiation of the vector hysteretic function represented by a vector play model is discussed for efficient nonlinear electromagnetic field computation using the Newton-Raphson method. The combination of the nonlinear finite-element method and the vector play model achieves accurate representation of the AC anisotropic magnetic property of nonoriented silicon steel sheet under rotational magnetic flux conditions. The proposed method is successfully applied to the eddy-current analysis of iron-cored inductors excited by a current or voltage source.

Geometrical Formulation of 3-D Space-Time Finite Integration Method

May 2013

A geometrical formulation of a space-time finite-integration (FI) method is studied for application in electromagnetic-wave propagation calculations. Based on the Hodge duality and Lorentzian metric, a modified relation is derived between the incidence matrices of space-time primal and dual grids. A systematic method to construct the Maxwell grid equations on the space-time primal and dual grids is developed. The geometrical formulation is implemented on a simple space-time grid, which is proven equivalent to an explicit time-marching scheme of the space-time FI method.

Model Reduction of Three-Dimensional Eddy Current Problems Based on the Method of Snapshots

May 2013

The model reduction based on the method of snapshots is applied to the finite element analysis of three-dimensional transient eddy current problems. It is known that accuracy of the reduced model highly depends on the number of snapshots. In this paper, we introduce a novel method which determines the adequate number of snapshots automatically. It is shown that the computational time can be reduced when using the model reduction based on the present method.

GMRES Solution of FEM-BEM Global Systems for Electrostatic Problems Without Voltaged Conductors

May 2013

This paper extends an iterative method to efficiently solve the global algebraic system of equations obtained by applying the hybrid FEM-BEM method to cases in which the field is due to charge distributions only, that is, when conductors with assigned potential (Dirichlet conditions) are not present. In the proposed approach, a conjugate gradient solver is used to solve the singular FEM equations, whereas the BEM equations are modified by means of the Gauss law.

A New Mesh Smoothing Method to Improve the Condition Number of Submatrices of Coefficient Matrix in Edge Finite Element Method

May 2013

A common mesh smoothing method strives to improve the shape quality of all elements. Generally a mesh consisting of only well-shaped elements is desired in finite element analysis. Although a perfect-shaped element yields short computation time, even a well-shaped element, whose shape is close to a regular polygon, sometimes prolongs the computation time of solving the system of equations derived with the edge-based finite element method. In this paper, we propose a new smoothing scheme of improving a convergence property of the system of equations by applying a common mesh smoothing method to some elements, which cause long computation time of the iterative solver. The proposed smoothing scheme utilizes the condition number of submatrices, into which coefficient matrix derived with the edge-based finite element method is subdivided, in order to choose ill-conditioned elements to be smoothed. As a result, the computation time is shortened applying a smoothing process only to the chosen ill-conditioned elements.

Electroquasistatic Field Simulation for the Layout Improvement of Outdoor Insulators Using Microvaristor Material

May 2013

A possible solution to locally reduce the high electric-field stress along the surface of outdoor insulators is to use the resistive field grading materials such as zinc–oxide microvaristor polymer compounds. This material is nonlinearly semiconductive and its conductivity depends on the electric-field intensity. In this paper, the field control effect of this material is demonstrated. Different configurations in order to optimize the layout of this material are compared. A case study is carried out for a 765-kV outdoor large-scale long rod polymeric insulator using different layouts of the microvaristor material. Electroquasistatic simulations are performed to evaluate the tangential electric-field distributions along the surface of the insulator for the dry clean surface condition and with a few single water droplets on the surface.

Natural Element Method Applied to Electromagnetic Problems

May 2013

In this paper, the natural element method (NEM), which is part of the meshless methods family, is used to solve electromagnetic problems. It is an interesting alternative to the finite element method. This method is based on the Voronoï diagram and the natural neighbors. These two concepts and the construction of the shape function are presented. The NEM shape functions are interpolant and linear on the boundary of the studied domain. This property allows a natural coupling with the finite element method. A 2D electrostatic example is studied. Results are compared to those obtained by FE method in order to illustrate the interest and the relevance of the new method. A second example of an electric machine is proposed in order to illustrate the ability of the NEM to be naturally coupled with FEM.

Natural Choice of Integration Surface for Maxwell Stress Tensor Computation

May 2013

The integration of the Maxwell stress tensor is a widespread technique for the calculation of total force acting on a body. Notwithstanding this technique has been investigated for many decades, the optimal choice of the integration surface is still an open problem. The aim of this paper is to contribute to the discussion, presenting a method for the automatic generation of the integration surface based on the dual discretization. Some benchmarks are studied to provide numerical evidence of the accuracy of the force calculation.

Residual Based a Posteriori Error Estimators for Harmonic ${\bf A}/\varphi$ and ${\bf T}/\Omega$ Formulations in Eddy Current Problems

May 2013

For eddy current problems, potential formulations are widely used nowadays. In this paper, residual based a posteriori error estimators are introduced to evaluate the discretization error in the finite element calculation in both case of ${bf A}/varphi$ and ${bf T}/Omega$ harmonic formulations. A device with eddy currents is studied in order to show the efficiency of the proposed estimators.

An Arbitrary Thick Shell Finite Element for Eddy-Current Dual Vector-Scalar Potential Formulations

May 2013

In many eddy current problems, surface impedance conditions are currently used to avoid the modelling of the skin depth in volumes. In the finite element method context, such conditions lead to surfaces elements at boundaries of massive conductors, or to shell elements representing thin layers, which unfortunately require a complex specific implementation in the codes. We propose here a new shell finite element easy to implement in the standard $({rm A}-varphi)$ and $({rm T}-{mitOmega})$ formulations. The advantage of this element is to be arbitrarily thick, so it takes into account some end-effects at its perimeter such as the connection between shell an 3D regions. The basic principles of the thick shell as well as a three-dimensional validation test dealing with a magnetic core-fault are presented.

Test Harness on a Preconditioned Conjugate Gradient Solver on GPUs: An Efficiency Analysis

May 2013

The parallelization of numerical simulation algorithms, i.e., their adaptation to parallel processing architectures, is an aim to reach in order to hinder exorbitant execution times. The parallelism has been imposed at the level of processor architectures and graphics cards are now used for general-purpose calculation, also known as “General-Purpose computation on Graphics Processing Unit (GPGPU)”. The clear benefit is the excellent performance over price ratio. Besides hiding the low level programming, software engineering leads to a faster and more secure application development. This paper presents the real interest of using GPU processors to increase performance of larger problems which concern electrical machines simulation. Indeed, we show that our auto-generated code applied to several models allows achieving speedups of the order of 10 $, times ,$.

Numerical Analysis of Negative Ion by Electrostatic Atomization Employing FEM and MPS Method

May 2013

This paper proposes a coupled method of 3-D finite element method (FEM) and Moving Particle Semi-implicit (MPS) method for the analysis of a negative ion that is produced by electrostatic atomization. In this method, the electric field is calculated by FEM and the fluid motion equation of a drop of water is calculated by the MPS method. The validity of this analysis method is verified by comparison with an experiment.

Analysis of the Disintegration of Charged Droplets Employing Boundary Element Method and Particle Method

May 2013

It is well known that an initially charged droplet disintegrates repeatedly into several tiny sibling droplets and one parent droplet if the charge exceeds a certain value defined by the Rayleigh Limit. Many researchers have experimentally verified this phenomenon in their works. However, it is difficult to estimate the number, charge and mass of the sibling droplets because the sizes of the droplets are generally very small. In this paper, a new coupled analysis method for the disintegration of dielectric charged droplets employing boundary element method (BEM) and particle method is proposed. The behavior of the droplet during disintegration is analyzed by means of this method.

Automatic Determination of Acceleration Factor Based on Residual and Functional in Shifted ICCG Method for 3-D Electromagnetic Field Analyses

May 2013

This paper describes new strategy for determining an optimal acceleration factor in the shifted incomplete Cholesky conjugate gradient (ICCG) method. Although a useful method focused on the maximum diagonal entry in the incomplete Cholesky (IC) preconditioner was already proposed, it cannot always provide the optimal acceleration factor. In this paper, we propose new automatic determination methods based on the minimization of the norms of the remainder matrix, the residual, and the functional in the shifted ICCG method and discuss its effectiveness in the 3-D electromagnetic field analyses using the edge-based finite element method. It is concluded that the proposed methods based on the minimization of the norm of the residual or the functional can determine an appropriate acceleration factor within the acceptable computational cost and improve the convergence property of the shifted ICCG method.

Multiobjective Cuckoo Search Algorithm Based on Duffing's Oscillator Applied to Jiles-Atherton Vector Hysteresis Parameters Estimation

May 2013

The parameter identification of hysteresis models is a fundamental task for correct hysteretic material simulation. In vector models, as the Jiles-Atherton (J-A) vector model, the parameter determination increases in complexity since one must solve a nonlinear system with a relative large number of variables. In these cases, fitting methods one of the most attractive solution. In this study, an improved multiobjective cuckoo search (IMCS) is introduced for the J-A parameters determination. The proposed IMCS based on the Duffing's oscillator to step size tuning is verified using data from a rotational single sheet tester in two-dimensional version. Numerical comparisons of IMCS with results using a multiobjective cuckoo search demonstrated that the performance of the IMCS is promising in parameters estimation. Furthermore, the proposed IMCS method can be easily extended to solve a wide range of multiobjective optimization problems.

Communication-Avoiding Krylov Techniques on Graphic Processing Units

May 2013

Communicating data within the graphic processing unit (GPU) memory system and between the CPU and GPU are major bottlenecks in accelerating Krylov solvers on GPUs. Communication-avoiding techniques reduce the communication cost of Krylov subspace methods by computing several vectors of a Krylov subspace “at once,” using a kernel called “matrix powers.” The matrix powers kernel is implemented on a recent generation of NVIDIA GPUs and speedups of up to 5.7 times are reported for the communication-avoiding matrix powers kernel compared to the standards prase matrix vector multiplication (SpMV) implementation.

Fast Block-Solution of PEEC Equations

May 2013

The study of electromagnetic structures with the partial element equivalent circuit usually requires the solution of the modified nodal analysis matrix. Due to the strong coupling between partial elements, standard circuit solvers are not efficient. In this work, an alternative method for the solution of the MNA system based on block partition of the final matrix is discussed and comparisons with two classic MNA formulations are presented.

Magneto-Mechanical Dynamic System Modeling Using Computer Code Chaining and Field Projections

May 2013

Complex systems involve several physical models such as magnetism, mechanics, and thermal science. Such models are divided into subproblems of different physical natures. Their resolutions require the development of specific computer programs, which is often complex and time consuming. Another approach is the use of dedicated software which are in this study linked together with the help of field projections. This reduces the weight of programming while improving the overall flexibility. This study will focus on magneto-mechanical system modelling in time domain. Starting from a transient analysis we will show that natural frequencies can be recovered with high accuracy. Discussions about the efficiency of time scheme and the coupling process are proposed.

Algebraic Second Order Hodge Operator for Poisson's Equation

May 2013

Algebraic methods, like the cell method or the finite integration technique are known to be effective in solving numerical problems, but they are limited to linear convergence, i.e., they exactly reconstruct constant fields inside the element. A few attempts in the literature have been aimed at extending the method to higher order, but results have not been completely satisfactory. This paper proposes a novel technique to extend the cell method to second order convergence. The consistency and convergence of the proposed approach are established by numerical results.

Analysis of a Permanent Magnet Machine for a High Power Density Taking Losses Into Consideration

May 2013

When a motor is running under a load condition, it is difficult to analyze and measure the diverse types of loss occurring in the motor. To address this problem, the analysis and the measurement methods that assess the losses in a motor under a load condition are proposed in this paper. In high power density types of motors, eddy current loss is the major type of loss. A three-dimensional finite element method has been used for the analysis of the eddy current loss, which requires the much time and effort in the design process. To solve this problem, in this study we propose an analytic method that can be used for the analysis of the eddy current loss. The proposed loss analysis and measuring methods for a permanent magnet motor under a load condition are validated using a prototype.

Consistent Modeling of Periodic Metasurfaces With Bianisotropic Scatterers for Oblique TE-Polarized Plane Wave Excitation

May 2013

In this paper, a new method for the consistent analysis of periodic metasurfaces with bianisotropic particles is introduced. The proposed technique combines a microscopic modeling approach at the level of the constituting meta-atoms with a macroscopic equivalent surface characterization, to unambiguously determine a set of surface susceptibilities that properly predict the reflection and transmission properties of the metasurface. Comparisons with alternative schemes and full-wave simulation results for bianisotropic scatterers, frequently utilized as building blocks of realistic metasurfaces, are provided in order to validate the featured algorithm.

Plasmon Mode Excitation on Graphene Layers via Obliquely-Incident Focused Wideband Pulses in Rigorous Time-Domain Algorithms

May 2013

In this paper, a family of 3-D finite-difference time-domain schemes is developed in order to investigate electromagnetic wave interactions in graphene arrangements. The novel algorithm excites the computational space through a modified total-field/scattered-field formulation with a focused wideband pulse of oblique incidence. In particular, the arbitrary incidence angle is attained via a set of three Euler angles, with the excitation scheme employed to generate surface plasmonic modes on graphene micro-ribbons. To this aim, the wavelength of surface waves as a function of frequency along with the magnitude of the exited field are extracted for the cases of normal and oblique incidence. It is, also, proven that by suitably rotating the focus pulse system, the excited plasmonic mode magnitude is increased. Numerical results, indicate the benefits of the proposed method.

A Novel Adaptive Mesh Finite Element Method for Nonlinear Magnetic Field Analysis

May 2013

A novel adaptive finite element method for the numerical simulation of magnetic fields with nonlinear materials is presented. The proposed method incorporates functions of both mesh refinement and mesh coarsening. Instead of explicitly eliminating unnecessary nodes in the mesh, the proposed mesh coarsening algorithm only needs a single mesh. The procedure is to apply constraints to those degrees of freedom with small estimated error. This process avoids solution interpolation errors due to changes from a fine mesh to a coarse mesh and can be implemented readily. The slave-master technique is adopted to eliminate the constrained degrees of freedom in the linear system, which has the same effect as mesh coarsening. Implementation details of the algorithm are presented and numerical examples are tested to showcase the effectiveness of the proposed method.

Extension of Time-Domain Finite Element Method to Nonlinear Frequency-Sweeping Problems

May 2013

Applications of magnetic-resonant wireless power transfer technology have been extensively researched because of its high efficiency, security and convenience. To recharge batteries, the induced ac voltage in the receiver coil of wireless systems must be rectified to dc, hence the power transfer systems are inevitably nonlinear. In this paper, a novel approach based on time-domain finite element method (FEM) is presented to analyze the nonlinear system in order to obtain frequency-sweeping solutions quickly. At the first step of the proposed method, the wireless power transfer system, excluding the rectifier circuit, will be equivalent to a voltage source and a general impedance at different frequencies. The equivalent circuit is then connected to the rectifier circuit. Numerical example being reported in this paper indicates that the results obtained using the proposed methodology are consistent with those obtained using traditional time-domain FEM method. If solutions at different operating frequencies are required, the proposed method can save a lot of computation time, because one just needs to solve the field problem using the time-domain FEM twice. From the numerical example on the performance analysis of the wireless power transfer system being studied, the computing time of the proposed time-domain method is only 2% of that required if traditional time-domain FEM method is used.

Acceleration of Field Computation Involving HTS

May 2013

The modeling of High Temperature Superconductor (HTS) devices has presented considerable challenges over the years. One of the main difficulties arises due to the high degree of non-linearity associated with the HTS materials. Iterative techniques are applied to deal with such nonlinearities, and construct computational prototypes and solvers. The conventional approaches such as the Newton-Raphson (NR) method, and the Successive Substitution (SS) method have been applied in the past but they have shortcomings of being unstable in certain scenarios, and at times, are very slow to converge. This paper presents a new algorithm which attempts to address these issues based on the ideas of the Aitken technique.

Numerical Pattern Identification—Application to Inductive Testing Method With Automatic Classifiers

May 2013

Automatic algorithms which include classifiers require effective systems of data acquisition, data modeling or other data source in order to create probability groups. Their role is to process the information to the basic structure of the model with a significant number of details. Owing to the differences between the probability groups, the classifier allocates the images to a selected class. At the same time the assessment of details' quality is created. The main topic of this article concerns the numerical modeling of a closed loop, generated from the study of the unbalanced voltage of the Maxwell bridge. It forms an image of material defects, determined by the numerical study of the sample and pattern that were analyzed in the work by changing the shape of a closed loop due to changes in size of the defect. The changes in the shape of the closed loops, as results of changes in the defect size were analyzed.

Coupled Field Modeling of Ferrofluid Heating in Tumor Tissue

May 2013

This work examines the method of magnetic fluid hyperthermia for breast cancer therapy. We develop a coupled-field model of ferrofluid transport and heating in tumor tissue. The finite element method (FEM) underpins our forward 3D electromagnetic—fluid dynamics-thermal model. The model uses anatomically precise multilevel geometry of the human breast, with known electrical properties of the tissues, and known speeds of blood and liquor in the breast vessels. We demonstrate the capabilities of the developed model on a real cancer sample acquired by a surgical procedure. The electrical properties of cancer and normal tissues are directly measured for the given sample. The thermal field results are verified by infrared thermograph imaging.

Modeling Ferroresonance Phenomena With a Flux-Current Jiles-Atherton Hysteresis Approach

May 2013

The ferroresonance phenomena in electrical power systems can cause very important quality and security problems. Although it has been extensively analyzed with different approaches since the birth of electrical systems, it still remains a challenge due the complexity of factors that can lead to the phenomenon. In this paper, a scalar Jiles-Atherton (JA) hysteresis model is applied to model a nonlinear ferromagnetic core allowing to analyze magnetic circuits, which can be in ferroresonant mode. It is used an inverse JA approach, which had originally the magnetic induction as its independent variable. The analysis here proposed applies a flux-current methodology to obtain a hysteresis behavior of a nonlinear inductor.

A Parallel FEM Matrix Assembly for Electro-Quasistatic Problems on GPGPU Systems

May 2013

This paper introduces a new matrix assembly algorithm for nonlinear problems that decomposes the problem into parts that are well suited for parallel computation on GPGPUs. It has the strength that recomputations in nonlinear entries of the stiffness matrices are embarrassingly parallel. The algorithm is used to solve electro-quasistatic problems. The proposed discretization includes the handling of Dirichlet and homogeneous Neumann boundary conditions.

Spread-Out Overlapping Sources by Independent Component Analysis for Location Positioning

May 2013

The problem of spread-out overlapping sensors and sources of electromagnetic fields is discussed, and the way to distinguished them having same amplitude, phase, and frequency is presented. The case of sources separated by small distance ${rm d}lllambda$ is studied. To do so, the method of independent component analysis is applied. In this work an algorithm based on maximizing the negentropy and symmetric orthogonalization is used. A measurement setup is proposed to construct the database for the algorithm. Two half wavelength dipoles, at 1.8 GHz, are considered as sources. A high gain broadband antenna is used to receive the incoming signals. The correlation coefficient is used to evaluate how much the estimated signals using the independent component analysis are similar to the originals signals. Correlation coefficient high as 0.98 is achieved for sources placed $lambda/10$ apart. The results obtained by independent component analysis are promising considering the complexity of the measurement setup and the proximity of sources.

High-Order Error-Optimized FDTD Algorithm With GPU Implementation

May 2013

This paper presents the development of a two-dimensional (2-D) finite-difference time-domain (FDTD) solver that features reliable calculations and reduced simulation times. The accuracy of computations is guaranteed by specially-designed spatial operators with extended stencils, which are assisted by an optimized version of a high-order leapfrog integrator. Both discretization schemes rely on error-minimization concepts, and a proper least-squares treatment facilitates further control in a wideband sense. Given the parallelization capabilities of explicit FDTD algorithms, considerable speedup compared to serialized CPU calculations is accomplished by implementing the proposed algorithm on a modern graphics processing unit (GPU). As our study shows, the GPU version of our technique reduces computing times by several times, thus confirming its designation as a highly-efficient algorithm.

Enhanced Thin-Wire Representation Models in a High-Order FDTD/TLM Method for Electrically Large Microwave Applications

May 2013

A compact class of general-radius thin-wire representation models combined with a 3-D high-order finite-difference time-domain/transmission-line matrix technique is developed in this paper for realistic large-scale microwave applications. Founded on an appropriately formulated set of telegrapher's equations via an error-controllable interpolation process, the new methodology efficiently approximates propagating waves along the radial direction of the wire and subdues artificial instabilities. Furthermore, through a nonoverlapping grid discretization algorithm, the hyperbolic character of Maxwell's laws is physically preserved and lattice reflection errors are extensively minimized. So, tilted and circular-loop wires of arbitrary orientation, pertaining to mesh axes, are accurately coupled with the hybrid method. These enhanced features are successfully validated by several composite media configurations.

Design of Least-Squares Time Integrators for Reliable FDTD Simulations

May 2013

Considering the importance of providing credible discrete models for Maxwell's equations, improved time integrators are constructed in this paper for reliable time-domain simulations of wave-propagation problems. The proposed design approach results in modified versions of high-order leapfrog processes that feature error-reducing behavior, in the sense that numerically-induced flaws are efficiently dealt with. Accuracy upgrade is accomplished via proper application of the least-squares technique, whereas the incorporation of optimized spatial expressions can further improve the wideband behavior. The combination of the proposed integrators with standard as well as optimized approximations in space is examined in numerical experiments, and it is shown that our treatment of time integration can contribute decisively to the foundation of reliable and efficient computational models.

Accuracy-Adjustable Nonstandard LOD-FDTD Schemes for the Design of Carbon Nanotube Interconnects and Nanocomposite EMC Shields

May 2013

The precise design of modern carbon nanoscale interconnects and EMC shields is presented in this paper via a nonstandard locally one-dimensional finite-difference time-domain algorithm. A key attribute of the new generalized technique is its frequency-dependent formulation in conjunction with an accuracy-adjustable meshing process to identify regions of smooth field variation and hence seriously reduce dispersion errors. In this way, the high-order unconditionally-stable method remains fully wideband and generates effective dual grids that allow the consistent analysis of complex carbon nanotube interactions with affordable resources. Numerical simulations, studying the performance features of various demanding applications in a wide frequency range, prove the advantages of the proposed schemes.

Determination of the Electrical Conductivity Tensor of a CFRP Composite Using a 3-D Percolation Model

May 2013

In this paper a percolation model is used to determinate the electrical conductivity tensor of one layer of carbon fiber composite. For this kind of material, fibers are randomly distributed in the resin. To take into account this distribution a virtual 3-D material model is developed and coupled with a homogenization method to overcome the scale factor problem. The electrical conductivity tensor is then used to simulate the induction heating of a multilayer composite.

A Simplified Domain Structure Model Exhibiting the Pinning Field

May 2013

A simplified domain structure model (SDSM) is developed as a building block with which to construct a physical macroscopic magnetization model exhibiting pinning-type hysteresis. The pinning field is represented by a stop hysteron. The proposed SDSM represents the vector magnetic property of a silicon steel sheet qualitatively. A preliminary analysis of the magnetization process described by the assembled SDSMs is reported, where the local demagnetizing field reduces the coercive force.

Non-Conforming Sliding Interfaces for Relative Motion in 3D Finite Element Analysis of Electrical Machines by Magnetic Scalar Potential Formulation Without Cuts

May 2013

This paper discusses non-conforming sliding interfaces for motion in combination with a magnetic scalar potential formulation. Lagrange multiplier are used to implement the relative motion of stator and rotor. The utilization of the specific Lagrange multiplier approach implies the application of a magnetic scalar potential formulation in 3D Finite Element (FE) modeling of electrical machines because up to the present a canonical definition of biorthogonal basis functions for the magnetic vector potential is not available.

Analysis of Transient Performance of Grounding System Considering Soil Ionization by Time Domain Method

May 2013

The grounding system is very important for lightning protection. If the lightning current is large enough, soil will be ionized, which will have a great effect on the transient performance of the grounding system. In this paper, an efficient time domain method is proposed to analyze the transient performance of the grounding system. The method takes account of nonlinear soil ionization, the shielding effect among electrodes, and frequency-dependent parameters all together. First, a frequency domain circuit model is set up based on a moment method coupling with circuit theory. Then, the model is approximated by a frequency-independent circuit model with the help of vector fitting method. Finally, the time-varying soil ionization is considered by making corresponding parameters time-varying when a time domain method is used to solve the circuit model. The method is validated by field test.

Influence of PCB and Connections on the Electromagnetic Conducted Emissions for Electric or Hybrid Vehicle Application

May 2013

This paper presents a fine modeling method for power module used in an Electric or Hybrid Vehicle (EHV) application. A time domain model is developed in order to predict conducted emissions. All parasitic elements of the power components constituting the power module are obtained by modeling, measuring or applying analytical formula. The influence of the Printed Circuit Board (PCB) and the connections of components on conducted emissions levels are shown here. The results obtained by the proposed models are compared with measurements results.

Magnetic Stimulation of the Spinal Cord: Experimental Results and Simulations

May 2013

This paper aims in interpreting the leg muscles responses recorded by electromyography during magnetic stimulation of the spinal cord by computing the electric field induced in the spinal cord and the nearby areas during this procedure. A simplified model of the spine was created and a Finite Difference Method algorithm was implemented in Matlab.

Homogenization of the Thin Dielectric Layers of Wound Components for the Computation of the Parasitic Capacitances in 2-D FE Electrostatics

May 2013

In this paper, we propose a homogenization procedure for the thin insulation layers that surround the conductors of wounded magnetic components. The dielectrics are replaced by a homogeneous medium with an equivalent permittivity, previously computed by solving two electrostatic problems on the cell scale, using the finite element method (FEM). The homogenized model is compared with the fine one (i.e., for which each layer is finely discretized), in terms of accuracy and computational burden.

Functional Magnetic Stimulation System and Pulsed Magnetic-Field Effect on Peripheral Nerve

May 2013

This paper studies a pulsed magnetic-field generator which provides a noncontact way for functional nerve stimulation. Each component of the device, such as charging circuit, discharging circuit, and control circuit, is described in detail. The feasibility of the device is verified by simulation and experiments. The magnetic field and the induced electric field are produced by a figure-8 coil under excitation of pulsed discharging current. According to the Schwarz model, the action potentials of nerve fiber are simulated, and the neural dynamic response is predicted.

A Multi-Slice Finite Element Model Including Distributive Capacitances for Wireless Magnetic Resonant Energy Transfer Systems With Circular Coils

May 2013

A multi-slice finite element model for wireless magnetic resonant energy transfer systems with circular spiral tape coils is presented. As the system is constructed using distributive capacitance, it is difficult to determine the parameters in the equivalent circuits analytically. To address the aforementioned problem, a multi-slice axisymmetric finite element method (FEM) is applied to analyze this wireless power transfer system. The merits of the proposed method are that three-dimensional FEM is not required and yet the distributive capacitances among the coils can be fully included in the proposed two-dimensional model. Compared with normal axisymmetric FEM without multi-slices, the proposed method can include the effect of distributive capacitance to produce more precise solutions. The proposed method is validated against experimental data.

Transient Thermal Analysis of an Eddy-Current Heated Conductor Applying FEM-DBCI

May 2013

A method is proposed for the computation of the transient heating of a conductor in which eddy currents flow, induced by time-harmonic source currents. The electrical field is assumed as unknown on a mesh of edge elements and is computed by a time-harmonic analysis. The heating power density inside the conductor is computed and a transient thermal analysis is started on the same mesh of nodal elements. This analysis is continued until the temperature-dependent electrical conductivity changes enough to require another time-harmonic eddy-current analysis. The combined procedure is iterated.

Magnetic-Thermal-Fluidic Analysis for Cooling Performance of Magnetic Nanofluids Comparing With Transformer Oil and Air by Using Fully Coupled Finite Element Method

May 2013

Magnetic-thermal-fluidic analyses were conducted to assess the cooling performance of magnetic nanofluids by comparing the performance with that of transformer oil and air using the fully coupled finite element method (FEM) considering the magnetoconvection phenomena. Magnetic nanofluids (MNFs) have been studied extensively for bio- and nanotechnology applications. In particular, some studies reported that the MNF has good characteristics for thermal management and electric insulation in experiments. With this motivation, this study focused on the cooling performance of MNFs including the experimental and numerical approaches. Until now, research on the cooling effect of MNF has focused mainly on heat propagation without any real magnetic system, in which the magnetic force plays a key role in driving fluidic flow. This flow driven by the magnetic force density was related to the magnetoconvection effect. To analyze this effect quantitatively, a coupled analysis technique should be developed using the magnetic-thermal-fluidic equations. To validate the cooling performance of MNFs numerically, the numerical results were verified by a comparison with those from the experimental tests in the air, transformer oil, and MNF. After confirming the numerical setup, some experiments were conducted with a vertical solenoid coil immersed in a MNF with different volume fractions of magnetic nanoparticles. The temperature at the inside part of the coil decreased dramatically by approximately 5$^{circ}$ C in the 7 vol. % MNF compared to the transformer oil. These temperatures were also predicted well using the proposed numerical setup.

Energy and Losses in Vector Thermal Aftereffect Model

May 2013

This work deals with some energy properties of a vector thermal aftereffect model, recently presented. The model can compute magnetization and magnetic losses using an extension in 2-D of a Preisach-type approach. Some properties of the model are presented and discussed. An experimental validation is also included.

Stochastic Nondestructive Testing Simulation: Sensitivity Analysis Applied to Material Properties in Clogging of Nuclear Powerplant Steam Generators

May 2013

A nondestructive testing procedure is currently used to estimate the clogging of tube support plates in French nuclear powerplant steam generators. A stochastic approach has been applied to the finite-element electromagnetic field simulation to evaluate the impact of material properties uncertainties on the monitoring signal. The polynomial chaos expansion method makes it possible to easily derive the Sobol decomposition which measures how much the variability of each input parameter affects the model output.

Virtual Voltage Method for Analyzing Shielding Current Density in High-Temperature Superconducting Film With Cracks/Holes

May 2013

An accurate numerical method is proposed for calculating the shielding current density in a high-temperature superconducting film containing defects. If the initial-boundary-value problem of the shielding current density is formulated by the $T$ -method, integral forms of Faraday's law on defect surfaces are also imposed as natural boundary conditions. However, the conditions are not satisfied exactly by a numerical solution and their residuals develop intolerably with a decrease in the film thickness. In order to resolve this problem, the following method is proposed: virtual voltages be applied along the defect surfaces as to have the natural boundary conditions numerically satisfied. A numerical code is developed on the basis of the proposed method, and the influence of a crack on the inductive method or the permanent-magnet method is numerically investigated.

Design and Analysis of High Temperature Superconducting Generator for Offshore Wind Turbines

May 2013

This paper presents the magnetic analysis and design of a high temperature superconducting generator (HTSG) for offshore wind turbines. High temperature superconducting (HTS) tapes form the rotor winding to produce a strong magnetic field when excited. This allows the generator to achieve high torque density with a compact size and light weight. Gearboxes can be removed for direct-drive operation to improve the reliability and efficiency of the offshore wind turbine. The lightweight and compact generator also helps reduce the construction cost. However, the high cost of HTS tapes should be considered and the reduction of the amount HTS material used should be carefully assessed. An HTSG is designed and analyzed for a 5 MW offshore wind turbine. The analysis involves several factors that affect the amount of HTS material utilized. The weight and volume of the HTSG is also considered in the design and analysis. Finite element analysis is employed for simulation of the HTSGs.

Axisymmetric Three-Dimensional Stress Distribution in a Hollow Cylindrical Bulk Superconductor

May 2013

In magnetization process by field cooling of a bulk high-Tc superconductor (HTS), stresses are induced by the Lorentz force between shielding currents and magnetic fields. Evaluation of the maximum stress during the magnetization is important from the viewpoint of the destruction of the bulk HTS. Stresses in a hollow cylindrical bulk HTS are numerically evaluated in the axisymmetric three-dimensional analysis. Shielding current distributions are obtained through a macroscopic numerical simulation with the Maxwell equations and the critical state model. Uniform trapped fields are discussed for piled bulk magnets. The stress distributions are obtained through numerical analysis with the finite-difference method. Maximum hoop stress is discussed for different boundary conditions of the bulk HTS.

Meander Line Antenna Design Using an Adaptive Genetic Algorithm

May 2013

This paper presents the optimization of a meander line antenna finite-element model by means of an adaptive genetic algorithm (GA). To search for optimal antenna configurations, the present method employs a GA with an adaptive method that adjusts the characteristics of its selection, crossover, and mutation operators in order to maintain a diverse set of high-quality candidate solutions during its execution. It is shown that the present method can find an optimal solution faster than the conventional GA. Moreover, the fitness values of the optimal solutions obtained by the present method are better than those obtained by conventional GA.

Metamaterial-Inspired Wire Antennas

May 2013

Three antennas for Wi-Fi 802.11n applications are presented. The first antenna is a dual-band antenna operating at the 2.4 GHz and the 5.5 GHz bands. This antenna is conceived from the zero-order resonating wire metamaterial antenna. By making a judicious choice for the capacitances and inductances of zero-order mode antenna, the new metamaterial-inspired wire antenna can resonate at two distinct frequencies. The simulated gain is 2 dBi and 4 dBi at lower and upper band, respectively. The two others designed antennas are the compact folded monopole antenna with 0.5 dBi gain, and the compact folded dipole antenna with 2 dBi gain. They were simulated using CST Microwave Studio full-wave simulator and measured.

Rotor Eccentricity Effect on Cogging Torque of PM Generators for Small Wind Turbines

May 2013

This paper discusses the effect of rotor eccentricity on cogging torque of a permanent-magnet (PM) generator applied to small wind turbines. The 1.4 kW radial-flux PM generator was designed to improve the start-up wind speed ($<$3 m/s) by reducing the cogging torque. Finite element analysis (FEA) is first used to simulate the generator for a range of eccentricities and their corresponding cogging torques. In experiment, the cogging torque of a prototype generator with a particular eccentricity of 0.25 mm (33% of the air-gap length) is measured and the result matched that of the FEA. This gives confidence in terms of using FEA for further studies. The relationship between the starting torque provided by turbine blades and the cogging torque is also discussed. From the simulation, it is found that the dynamic eccentricity can be detected by measuring the cogging torque waveform.

Characteristic of a Variable Inductor Using Magnetorheological Fluid for Efficient Power Conversion

May 2013

This paper proposes a new variable inductor for efficient power conversion which consists of the ferrite core and the gap filled with a magnetorheological fluid. Its main feature is to show a large inductance variation versus inductor currents even with a simple inductor structure and so it leads to improving light and intermediate load efficiency of power conversion systems compared with the conventional inductor with an air gap. To predict the characteristics of the variable inductor, the nonlinear magnetic permeability of the magnetorheological fluid used is accurately measured because the inductance value strongly depends on the magnetic nonlinearity of the fluid. With the obtained B-H curve, a 1 kVA variable inductor is designed and analyzed with three-dimensional finite element method taking into account the losses of the core and the fluid. Finally, to prove the feasibility and usefulness of the proposed inductor, a prototype inductor is fabricated and its experimental results are compared with numerical ones.

Analysis of Inter-Turn Insulation of High Voltage Electrical Machine by Using Multi-Conductor Transmission Line Model

May 2013

In this paper, the inter-turn insulation of stator winding is comprehensively discussed. An equivalent circuit model and a multi-conductor transmission line (MTL) theory are established for the inter-turn voltage evaluation under the switching-impulse voltage, respectively. The distributed inductances are calculated by using small-signal analysis in finite element method (FEM) and the ac resistances of coils are analyzed considering the skin effect. The distributed capacitances of the coils are determined by using both electric field FEM and analytic equations. The electric potential distribution of inter-turn is calculated by the above two methods. The incident and reflect voltages are calculated by using the MTL model. The electric field of inter-turn calculated by using the FEM is presented. The FEM is used for the calculation of the inter-turn electric field distribution. The position where the inter-turn insulation may be more prone to breakdown is determined according to the result. Finally, the impact factors of inter-turn insulation including insulation materials and positions of failure in winding are analyzed in detail.

Fully Coupled Finite Element Analysis for Cooling Effects of Dielectric Liquid Due to Ionic Dissociation Stressed by Electric Field

May 2013

A fully coupled Finite Element Analysis (FEA) technique was developed and tested to validate the cooling effects of a dielectric liquid stressed by an electric field, resulting in the ionic dissociation phenomenon. Recently, electrohydrodynamics (EHD) techniques have been applied widely to enhance the cooling performance of electromagnetic systems by introducing gaseous or liquid media. The main advantage of EHD cooling is non-contact and low-noise resulting from smart control using an electric field. In addition, in some cases, the flow can be achieved using only a main electric field source not an extra one. The driving sources in EHD flow are ionization in the breakdown region and ionic dissociation in the sub-breakdown region. This study focused on dielectric liquid flow driven by the ionic dissociation phenomena, resulting in a cooling effect of the heat source. To build on this EHD phenomenon, fully coupled FEA, which consisted of the Poisson's equation for an electric field, Nernst-Planck equations for ions, and the Navier-Stokes equation for incompressible fluidic flow, was performed. To confirm the cooling effects, the developed velocities of fluidic flow were tested with the different applied voltages. In the sub-breakdown region, the effective velocity was approximately 2 m/s in the tip-sphere electrodes and a temperature drop of approximately 40$^{circ}$C was obtained in a numerical analysis model with a fluidic velocity of 1.96 m/s from the inlet.

Detent Force Reduction in Permanent Magnet Tubular Linear Generator for Direct-Driver Wave Energy Conversion

May 2013

In this paper, a quasi-Halbach magnetization structure of permanent magnet tubular linear generator (PMTLG) with bulged stators and auxiliary slots is proposed to reduce the detent force. In the meantime, the detent force for the structure of 9 PM poles 10 winding slots and the conventional one of 8 PM poles 12 winding slots is compared by using Fourier analysis and finite element analysis (FEA). The theoretical and FEA show that 87.18% detent force can be removed through changing the length of the bulged stator. Finally, a prototype is manufactured to verify that the detent force can be reduced efficiently by applying this method.

Research on a Tubular Primary Permanent-Magnet Linear Generator for Wave Energy Conversions

May 2013

A tubular primary-permanent magnet linear generator (TPPMLG), where both the magnets and armature windings are placed in the primary, is proposed for the sea-wave energy conversion. There is a simple structure on the secondary of the generator. Based on the model of proposed TPPMLG, the operation principle is analyzed. To investigate the electromagnetic characteristics and the unique advantages of the proposed generator, an optimized tubular secondary permanent-magnet linear generator (TSPMLG) is compared with the TPPMLG. Axisymmetrical dimensional finite-element method (FEM) is implemented to calculate the magnetic fields of the two generators and obtain the nonload and load performance. The results of finite-element analysis (FEA) indicate that the proposed generator has the advantages of sinusoidal voltage, minor detent force, high generating efficiency, and good performance at lower speed. Two prototypes are used to validate the results of FEA.

Numerical Analysis of Cold Crucible Induction Melting Employing FEM and MPS Method

May 2013

This paper proposes a coupled method of 3-D finite element method (FEM) and moving particle semi-implicit (MPS) method for the analysis of cold crucible induction melting. In this method, the magnetic field is calculated by FEM and the fluid motion equation of the molten metal and the thermal distribution in the molten metal are calculated by the MPS method. In this paper, the phase transformation of the metal is not considered. The effectiveness of this method is verified through the analysis of the molten metal behavior in the crucible.

Current Distribution Identification in Fuel Cell Stacks From External Magnetic Field Measurements

May 2013

This paper presents a new non invasive technique for fuel cell diagnosis. The method relies on the measurements of the magnetic field signature generated by a working fuel cell. Knowing the relationship between currents and magnetic field, it is possible to estimate the current density by solving an inverse problem. This problem being ill-posed, original current and sensors basis are proposed to improve the reconstruction process. The experimental set-up remains simple, based on few fixed sensors and shows a good efficiency.

2-D Discontinuous Galerkin Method for Streamer Discharge Simulations in Nitrogen

May 2013

This paper proposes a discontinuous Galerkin (DG) method combined with hierarchical reconstruction to simulate the fluid model of streamer discharges. To simulate the rapid transient streamer discharge process, a method with high resolution and high order accuracy is highly desired. Combining the advantages of finite volume and finite element method, DG is such a choice. A simulation of a double-headed streamer discharge in Nitrogen was performed using 2-dimensional fluid model. The preliminary results are quantitatively agreed with those obtained by finite volume method combined with moving mesh, indicating the potential of extending the method to general streamer simulations in complex geometries.

Calculation of the Ionized Field Around the DC Voltage Divider

May 2013

The space charges produced by the corona discharge of the DC voltage divider's high-voltage electrode can move under the effect of the electric field force, and parts of them can attach to the surface of the insulation sheds. Because of the influence of the space charges and the charges on the insulator sheds' surface, the electric field around has a big difference with the situation in the electrostatic field. In the paper, a 2-D axisymmetric upwind finite element method (upwind FEM) is used to calculate the electric field distribution on the surface of the DC voltage divider's insulation sheds. The space charge density inside the insulation sheds is set to be 0, and the charge density on the surface of the sheds is calculated by the iterative process. The ionized field of a 3-D sphere electrode model is calculated, and the 2-D axisymmetric upwind FEM is verified by comparing the numerical results with the analytical results. In the end the ionized field of the 500 kV voltage divider is calculated. The simulation results show that the existence of space charges affect evidently on the electric field distribution characteristic, and hence improve the uniformity of the electric field intensity along the sheds surface.

3-D FE Wire Modeling and Analysis of Electromagnetic Signatures From Electric Power Drive Components and Systems

May 2013

A 3-D finite-element (FE) optimized equivalent source numerical model for the analysis of low frequency electromagnetic field signatures in electric drives is proposed. An example electric drive system including a synchronous generator, an induction motor and power cables connecting a load is used to implement the model. The arrangement of the system setup is developed using a fully detailed 3DFE model to verify and compare with the results of the proposed equivalent source model. The proposed technique provides the exact field solution without large computational even with the presence of superposition. The equivalent source model (wire model) is created based on numerical techniques and physical theory of wave propagation. The superposition of the various components in this study is considered. The results of the proposed wire models match the results of the original models. For further verification, experimental results of the setup are compared with the numerical results. The importance of the proposed equivalent source is that it can be used for the evaluation of electromagnetic signatures and radiation patterns at the design stage. This enables performing various designs iterations to achieve compliant designs to electromagnetic compatibility standards. The proposed model can also be used for dynamic monitoring and diagnosing failures in the system.

Shielding Effectiveness of Composite Materials: Effect of Inclusion Shape

May 2013

The use of composite materials for electromagnetic shielding applications contributes to the effort of structure lightening in aerospace industry. In these materials the strong interaction between the electromagnetic field and the microstructure makes the standard numerical tools difficult to implement. Indeed these methods would involve an excessive number of degrees of freedom to describe details of the microstructure. An efficient way to overcome this problem is the use of homogenization techniques providing the effective properties of heterogeneous materials. These effective properties can then be introduced in standard numerical tools to estimate the behavior of shielding enclosures. A recent paper proposes an extension to microwave frequencies of quasistatic homogenization methods. It introduces a characteristic length for the microstructure in the case of a square array of circular 2-D conductive phases embedded in a dielectric matrix. In this paper, a method to identify this length parameter is proposed for random microstructures.

3-D Finite Element Analysis of Eddy Current in Laminated Cores of the Interior Permanent-Magnet Motor

May 2013

In this paper, a large-scale numerical analysis for eddy currents in laminated cores of an interior permanent-magnet motor is achieved. The eddy currents in the laminated cores caused by the axial flux are simulated by using the Earth Simulator, which is a vector-type parallel supercomputer.

3-D Modeling of Thermo Inductive Non Destructive Testing Method Applied to Multilayer Composite

May 2013

In this paper, a 3-D modeling of a thermo inductive nondestructing testing (NDT) technique applied to carbon fiber reinforced polymer (CFRP) composite is presented. A multiscale approach is used to calculate the electromagnetic and thermal field distribution. The relevance of the technique is then discussed for different positions of flaws and the optimal frequency is estimated.

Computation of Macroscopic Electromagnetic Properties of Soft Magnetic Composite

May 2013

This paper presents a new numerical method to compute the macroscopic electromagnetic properties of the soft magnetic composite (SMC). In present method, SMC is assumed to be composed of homogeneous magnetic bricks with periodicity. The macroscopic electromagnetic properties of SMC are obtained using the finite element method in which it is assumed that the homogenized energy is equal to that stored in a unit domain. We compare the macroscopic electromagnetic properties obtained by the present method with those obtained by Ollendorf's formula and magnetic circuit based on the nonmagnetic grain boundary model. It is shown that the three results are in good agreement when assuming constant permeability. It is also found that there are clear discrepancies among them due to magnetic saturations especially when the demagnetization coefficient is large.

Integration of a First Order Eddy Current Approximation With 2D FEA for Prediction of PWM Harmonic Losses in Electrical Machines

May 2013

Two-dimensional (2D) finite element models of electrical machines are known to over predict iron losses when modeling systems excited using pulse width modulation. This digest presents the integration of a simple first order 1D approximation of the eddy current distribution within the lamination into a 2D finite element model. Simulations of an induction machine under no-load conditions using standard 2D FEA methods and the proposed method are compared with test measurements. The proposed approach is shown to improve the accuracy of the predictions while reducing simulation time.

Influence of Steel Manufacturing on J-A Model Parameters and Magnetic Properties

May 2013

The influence that manufacturing processes have on electrical steel properties is investigated. The investigation is carried out by considering changes in measured electromagnetic quantities and the changes to parameters of a physics-based hysteresis model. The parameters of an inverse Jiles–Atherton hysteresis model are identified using nonlinear least square method and compared with measured data from steel samples that have undergone different stages of manufacturing. The results of the study may be used as a first step to the inclusion of manufacturing effects in models of electromagnetic devices.

Evaluation of Stray Load Losses in Cores and Secondary Conductors of Induction Motor Using Magnetic Field Analysis

May 2013

To develop further higher efficiency induction motors, the reduction of the stray load losses, which are the increase of loss in the load condition relative to that in no-load test condition, should be investigated by using the magnetic field analysis. However, the calculation of the stray load losses using the magnetic field analysis requires high computation cost due to consideration of the slot harmonics in the flux densities, and the large time constant. In this paper, to evaluate the stray load losses in the cores and the secondary conductors of induction motors using the two-dimensional (2-D) magnetic field analysis within practical computation cost, some useful techniques, to mention a few, the nonconforming technique and the simplified time-periodic explicit error correction method, are introduced. Then, the stray load loss of an actual induction motor without skew is evaluated by the developed 2-D magnetic field analysis. It is shown that the calculated no-load losses are almost the same with the measured one, and the stray load losses in the stator core and secondary conductors due to the harmonic components in the secondary current are large.

Homogenization Technique of Laminated Core Taking Account of Eddy Currents Under Rotational Flux Without Edge Effect

May 2013

A homogenization technique of a laminated core taking account of the eddy currents in the steel plates by combining a three-dimensional (3-D) solid core model with a one-dimensional (1-D) steel plate model has already been proposed. In this paper, to apply the proposed technique to a motor core, in which flux rotates, the 1-D eddy current analysis of the steel plate is expanded to a 3-D analysis. The proposed method is applied to a simple laminated core model under the rotational flux in the linear analysis. Then, the eddy current loss obtained from the developed method is compared with those obtained by the homogeneous solid core model with 1-D steel plate model and the real laminated core model. It is shown that error occurs by neglecting the edge of the model but the accuracy is much improved in the eddy current loss calculated by using the proposed method.

Loss Reduction of Reactor With Grain-Oriented Silicon Steel Plates

May 2013

To reduce the iron loss of a reactor stacked with non-oriented steel plates, we have proposed the method of loss reduction improving the iron core configuration using the magnetic field analysis taking account of the laminated structure by the homogenization technique. In this paper, the iron loss reduction method is expanded to a reactor stacked with grain-oriented steel plates. The magnetic field analysis taking account of the laminated structure and steel plate anisotropy using homogenization technique is developed. The flux concentration due to the laminated structure, steel plate anisotropy, and joint between the leg and yoke of the reactor is analyzed and relaxed by the improvement of the core and joint configurations. It is shown that the iron loss can be about 36% reduced by the improvements.

Analysis of the Magnetic Flux Distribution in a New Shifted Non-Segmented Grain Oriented AC Motor Magnetic Circuit

May 2013

This paper deals with a new AC electric motor magnetic circuit structure made of shifted non-segmented grain oriented steel laminations. The aim of the paper is to understand with a finite element approach the local distribution of the magnetic flux density inside shifted laminations as well as in the air-gaps between them. It is shown that the air-gap flux distribution is not trivial at all and very difficult to appreciate.

Magnetic Characteristic Analysis and Measurement of Vector Magnetic Property of a Non-oriented Electrical Steel Sheet Under High Magnetic Flux Condition

May 2013

In this paper, vector magnetic properties measurement and magnetic characteristics analysis of a non-oriented electrical steel sheet under high magnetic flux is presented. At first, the vector magnetic property of the non-oriented electrical steel sheet under the high magnetic flux condition is measured. Next relationships between the magnetic flux density vector $B$ and magnetic field strength vector $H$ of ring core model is simulated by using the database of measured vector magnetic property and a dynamic integration type E&S modeling. As the results, the difference of the maximum magnetic flux density $vert Bvert_{max}$, the maximum magnetic field strength $vert Hvert_{max}$ distribution and the local hysteresis loops in the ring core model is obtained by increasing the exciting voltage. In particular, it was clarified that $vert Hvert_{max}$ distribution and locus of $H$ vector was effected due to the magnetic anisotropy of the non-oriented electrical steel sheet strongly.

Equivalent Circuit Modeling of DC and AC Ferrite Magnetic Properties Using H-Input and B-Input Play Models

May 2013

An equivalent circuit model is proposed to represent ferrite magnetic properties under ac and dc fields phenomenologically, where the H-input and B-input play models are used to handle hysteretic property accurately and concisely. A slow magnetization component is extracted from measured ac and dc properties. Frequency dependence of the ac loss is represented by an equivalent resistance. The simulated ac and dc magnetic properties agree with the measured properties.

General Integral Formulation for the 3D Thin Shell Modeling

May 2013

In order to compute electromagnetic problems in presence of thin conductive and magnetic shells, a new integral formulation is proposed. Based on the principle of shell element, the formulation is general and enables the modeling of various problems for any skin-depth, avoiding the air region meshing. The formulation is validated thanks to an axisymmetric FEM and compared with another shell formulation implemented in a 3D FEM. Advantages and drawbacks of this new formulation are discussed.

Appraisal of Surrogate Modeling Techniques: A Case Study of Electromagnetic Device

May 2013

Simulations are successfully utilized to reproduce the behavior of complex systems in many knowledge fields. The computational effort is a key factor when high-cost simulations are required in optimization, principally, if the system to be optimized operates under uncertain conditions. In this context, surrogate modeling is useful to alleviate the CPU time. Hence, this paper presents a methodology to assess three surrogate techniques based on genetic programming (GP), a radial basis function neural network (RBF-NNs), and universal Kriging. These techniques are used in this paper to obtain analytical optimization functions that are accurate, fast to evaluate and suitable for interval robust optimization. The experiments were performed in a robust version of the TEAM 22 problem. The results show that the surrogate models obtained are reliable and appropriate for interval robust methods. The methodology presented is flexible and extensible to other problems in diverse fields of interest.

Fluctuation Frequency Analysis of the Barkhausen Signals Under Static and Dynamic Stresses

May 2013

Ferromagnetic materials are widely used for various artificial products such as cars, trains, ships. Because of its mechanical property, iron steel is most popular in use for frame materials. Nondestructive testing of iron steel is an extremely important way to maintain their mechanical reliability. As is well known fact, the Barkhausen signals are emitted from only the ferromagnetic materials having magnetic domain structures. Also this signal varies depending upon their past mechanical as well as radioactive stress histories. In the present paper, we have applied a generalized frequency fluctuation analysis to the Barkhausen signals to detect the various mechanical stresses. Surprisingly, it has been succeeded in clarifying that application of our frequency fluctuation analysis to the Barkhausen signals makes it possible to detect the two kinds of mechanical stress.

Reduction of PEEC Unknowns for 3D Metallic Plates in Magnetic Shielding

May 2013

This paper presented the PEEC models for 3D metallic plates with symmetry and/or anti-symmetry. These plates of concern were normally used for magnetic shielding, and were made of either conductive material or linear magnetic material. The distribution of both induced current and magnetization in the plates was examined, and the symmetrical and anti-symmetrical prosperities in typical shielding structures were identified. Reduced system matrix equations were provided. Using the loop analysis technique, the matrix equation can be reduced to one sixth approximately in size if these properties are fully taken into account. A shielding problem can be then solved at the reduced cost without loss of accuracy. The proposed modeling techniques have been tested numerically, and validated with a commercial FEM code.

Joint Modeling for Conductive Plates in Low-Frequency Magnetic Shielding

May 2013

Low-frequency magnetic shielding is usually made with finite-size metallic plates. The discontinuity on the shield is unavoidable, and degrades the performance of shielding. In this paper an equivalent circuit method was proposed to model the joint of conductive plates, and to evaluate the magnetic fields around the joint. The circuit equation using total cell current was presented. The modeling method was validated experimentally. Shielding performance of a shield against various joint parameters was also investigated. It is found that reasonable shielding performance can be achieved if the joint is provided with an adequate mating surface area and multiple fixing points.

Influence of Mechanical Boundary Conditions on Magnetoelectric Sensors

May 2013

Magnetic field sensors are an important application for magnetoelectric composite materials. In these devices the external magnetic field is converted into an electric voltage. The sensitivity of the sensor is known to depend on different factors, including geometrical and material parameters. This work deals with the modeling of the influence of mechanical boundary conditions on the sensitivity of magnetoelectric sensors.

Analysis of Magnetic Field for Power Transmission Line With Multiple AC Singular Currents by Coupling of Fourier Series Expansion and FEM

May 2013

The central characteristic of line current problems with AC power transmission lines and overhead trolley lines are that the source region of conductors is extremely small compared with the entire analytical region. This is a problem with singular point sources in two-dimensional space that creates computational difficulties whit the standard finite element method. This paper proposes an accurate and efficient method for magnetic field calculations for such electric lines, which couples the analytical method and finite element formulation. The analytical solution is expressed as a Fourier series. Unknowns of finite elements at the boundary between the current and finite element regions are coupled with Fourier series coefficients. The boundary conditions are used to derive a coupled system equation expressed in matrix form. The proposed algorithm is validated using a test model of a three-phase two-circuit transmission line. The results are compared with the measured one.

Numerical Modeling of Capacitive Effects in HF Multiwinding Transformers—Part I: A Rigorous Formalism Based on the Electrostatic Equations

May 2013

This paper is the first part of a work which aims at proposing a global approach for the numerical modeling of parasitic capacitances in high-frequency multiwinding transformers. In this first part, various capacitive circuits of $n$-winding magnetic components are presented. Careful attention is paid to the definition of a rigorous mathematical formalism based on the electrostatic equations, valid for any number of windings. The numerical identification of the proposed circuits is discussed in a companion paper.

Numerical Modeling of Capacitive Effects in HF Multiwinding Transformers—Part II: Identification Using the Finite-Element Method

May 2013

This paper is the second part of a work which aims at proposing a global approach for the numerical modeling of parasitic capacitances in high-frequency multiwinding transformers. In this part, we focus on the numerical identification using the finite-element method (FEM) of the capacitive circuits which have been introduced in a companion paper in the same issue. An original procedure based on the FEM in 2-D electrostatics is first presented. The validity of the 2-D approximation is thereafter discussed, and a new method which consists in solving two successive 3-D models (an electrokinetic problem in the windings and an electrostatic one in the dielectrics) is then exposed. The two methods are illustrated and experimentally validated on a three-winding transformer.

A Novel Approach to Investigate the Quantitative Impact of Harmonic Currents on Winding Losses and Short Circuit Forces in a Furnace Transformer

May 2013

A novel approach based on the finite element method is proposed to calculate accurately the winding losses and short circuit forces caused by harmonic currents in a furnace transformer. The technique derives the appropriate partial differential equation required to determine the harmonic currents. The technique is validated by its application to a benchmark furnace transformer where experimental results demonstrate the accuracy of the developed technique. The contribution of harmonic currents to winding losses is shown to be significant in the benchmark furnace transformer, whereas the contribution of harmonic currents to short-circuit forces is limited.

Application of an Improved Multi-Conductor Transmission Line Model in Power Transformer

May 2013

In this paper, a new multi-conductor transmission line (MTL) method is introduced to analyze the voltage distribution of power transformer windings, including inserted capacitance continuous winding and duplex winding, under lightning overvoltage excitation. This new MTL model may take into account electromagnetic induction between windings. The influences of copper screen tapes on the MTL parameters are discussed. The terminal conditions of single winding including screen tape differ from those of duplex windings, which have to be carefully considered. The results are compared with the traditional equivalent circuit model, revealing that the new model may provide detailed accurate voltage distribution on each turn of the windings.

Three-Dimensional Eddy Current Loss Modeling in Steel Laminations of Skewed Induction Machines

May 2013

The effects of skewing on the loss behavior of a megawatt rated slip-ring induction machine are studied. The iron loss evaluation is performed by postprocessing the field solution obtained from a multi-slice finite element model. A novel method to compute the three-dimensional eddy current distribution in the steel sheets is employed for the eddy current analysis. The iron loss models are validated against no-load iron loss measurements. Simulation results under load show that skewing leads to a highly non-uniform iron loss distribution along the machine length. The sum of the iron and copper losses increases slightly compared to a machine with straight rotor bars.

An Analytical Model for the Effect of Multiaxial Stress on the Magnetic Susceptibility of Ferromagnetic Materials

May 2013

The magnetic permeability of magnetic materials highly depends on mechanical stress. Stress state is usually multiaxial and has a significant effect on the performance of electromagnetic devices. In this paper a three-parameter analytical model for the stress dependent permeability of magnetic materials is proposed, based on a simplified energetic description of magneto-elastic behaviour. The proposed approach also provides a new equivalent stress for magnetic behaviour in the low-field and low-stress regime.

Iron Losses, Magnetoelasticity and Magnetostriction in Ferromagnetic Steel Laminations

May 2013

The interdependence of iron losses and magnetoelasticity in ferromagnetic laminations is studied by numerical simulations. For the simulations, a finite-element model for the eddy currents in the lamination is coupled to a constitutive magnetomechanical material law. We demonstrate how the experimentally apparent rate-dependency of magnetostriction partly results from the comparison of the local surface magnetostriction to the average flux density supplied through the sheet. The average flux density is a global quantity and lags behind the local surface magnetostriction due to the skin effect of the eddy currents. Accurate modeling of the skin effect also shows that in addition to the hysteresis losses, the eddy-current losses also change as a result of applied mechanical stress, contrary to some earlier discussions in the literature.

A Study on the Deperming of a Ferromagnetic Material by Using Preisach Model With $M\hbox {-}B$ Variables

May 2013

In this paper, a study on the demagnetization of ferromagnetic materials is conducted based on both experiments with magnetic treatment facility (MTF), which is a miniaturized experimental model, and numerical analysis methods in which the static magnetic finite-element method and Preisach model are combined. The magnetic hysteresis phenomenon inside ferromagnetic materials is effectively mimicked by means of Preisach model. However, owing to the use of $Mhbox{-}H$ variables, Preisach model generally bears numerical instability during repetitive computations. A Preisach model with $Mhbox{-}B$ variables is proposed in this paper to resolve the numerical instability. From the proposed Preisach model with $Mhbox{-}B$ variables, analysis results that were tantamount to those from the general Preisach model with $Mhbox{-}H$ variables were obtained. Numerical instability was also resolved by the proposed model. Furthermore, the discrepancy was practically negligible between the experimental result from a practical demagnetization process and the numerical analysis result from the proposed Preisach model with $Mhbox{-}B$ variables, under the same conditions.

Computational Homogenization for Laminated Ferromagnetic Cores in Magnetodynamics

May 2013

In this paper, we investigate the modeling of ferromagnetic multiscale materials. We propose a computational homogenization technique based on the heterogeneous multiscale method (HMM) that includes both eddy-current and hysteretic losses at the mesoscale. The HMM comprises: 1) a macroscale problem that captures the slow variations of the overall solution; 2) many mesoscale problems that allow to determine the constitutive law at the macroscale. As application example, a laminated iron core is considered.

Proposal of Electromagnetic Inspection Method of Tensile Strength in Steel Without Influence of Lift-Off Between Steel and Inspection Probe

May 2013

A tensile strength of steel material is measured by a tension-testing machine. It is a destructive inspection, and it is necessary to prepare a large size specimen. The conductivity of the steel with high tensile strength becomes large, and its permeability becomes small. Then, the nondestructive estimation of the tensile strength in the steel is possible by using the difference of the electromagnetic properties. The inspection method of the tensile strength in the steel is proposed using an alternating electromagnetic field. The signal, however, is also influenced by the change of the distance (lift-off: $L$o) between the steel and an electromagnetic probe. In this paper, the inspection method for measuring the tensile strength which is not affected by the lift-off $L$o is proposed by examining the performance of the method using the 3-D edge-based hexahedral nonlinear FEM.

Adaptive Weighted Expected Improvement With Rewards Approach in Kriging Assisted Electromagnetic Design

May 2013

The paper explores kriging surrogate modelling combined with expected improvement approach for the design of electromagnetic devices. A novel algorithm based on the concept of rewards is proposed, tested and demonstrated in the context of TEAM Workshop Problem 22. Balancing exploration and exploitation is emphasized and robustness of the design considered.

A Global Optimization Algorithm for Electromagnetic Devices by Combining Adaptive Taylor Kriging and Particle Swarm Optimization

May 2013

This paper presents an efficient optimization strategy which employs adaptive Taylor Kriging and Particle Swarm Optimization (PSO). In this method, the objective function of electromagnetic problem is interpolated by using adaptive Taylor Kriging, in which the covariance parameter is obtained by Maximum Likelihood Estimation (MLE). And then, PSO is used to search for optimal solutions of electromagnetic problem. The proposed algorithm is verified its validity by analytic functions and TEAM (Testing of Electromagnetic Analysis Method) problem 22.

A Surrogate Genetic Programming Based Model to Facilitate Robust Multi-Objective Optimization: A Case Study in Magnetostatics

May 2013

A common drawback of robust optimization methods is the effort expended to compute the influence of uncertainties, because the objective and constraint functions must be re-evaluated many times. This disadvantage can be aggravated if time-consuming methods, such as boundary or finite element methods are required to calculate the optimization functions. To overcome this difficulty, we propose the use of genetic programming to obtain high-quality surrogate functions that are quickly evaluated. Such functions can be used to compute the values of the optimization functions in place of the burdensome methods. The proposal has been tested on a version of the TEAM 22 benchmark problem with uncertainties in decision parameters. The performance of the methodology has been compared with results in the literature, ensuring its suitability, significant CPU time savings and substantial reduction in the number of computational simulations.

A Quantum-Based Particle Swarm Optimization Algorithm Applied to Inverse Problems

May 2013

To balance exploration and exploitation searches in order to prevent premature convergences in Particle Swarm Optimization (PSO) algorithms, an improved Quantum-based PSO (QPSO) algorithm is proposed with an ultimate goal of preserving the simplicities of available QPSOs. The improvements include the design of diversification and intensification phases, searching mechanisms and a strategy to shift away from the worst solutions. The proposed QPSO are compared to available optimizers on two case studies to showcase its merits.

Topology Optimization for a Dielectric Optical Cloak Based on an Exact Level Set Approach

May 2013

This paper proposes a topology optimization method for a dielectric optical cloak that provides results that are perfectly free from intermediate materials, based on a level set boundary expression and the Finite Element Method. The finite element mesh is re-generated to fit the iso-surface of the level set function at every iterative step, to remove intermediate materials, so that the obtained optimal structure consists of only two materials, the dielectric material and air. First, the level set-based topology optimization is formulated and a topology optimization algorithm is proposed for the exact level set approach. Next, design requirements for the dielectric optimal cloak device are clarified and an objective functional for the design is formulated. The proposed method is then applied to a simple numerical problem to illustrate its effectiveness.

An Ant Colony Algorithm for Both Robust and Global Optimizations of Inverse Problems

May 2013

To address the computational inefficiencies of available robust oriented optimizers, a fast optimal algorithm based on ant colony optimization (ACO) algorithm for both robust and global optimizations of inverse problems is proposed. In the proposed algorithm, the structures of the algorithm are redesigned, and methodologies for efficient computations of the robust performance parameters are proposed. Numerical results are reported to positively showcase the merits of the proposed algorithm.

Level Set-Based Topology Optimization for the Design of an Electromagnetic Cloak With Ferrite Material

May 2013

This paper presents a structural optimization method for the design of an electromagnetic cloak made of ferrite material. Ferrite materials exhibit a frequency-dependent degree of permeability, due to a magnetic resonance phenomenon that can be altered by changing the magnitude of an externally applied dc magnetic field. Thus, such ferrite cloaks have the potential to provide novel functions, such as on-off operation in response to on-off application of an external magnetic field. The optimization problems are formulated to minimize the norm of the scattering field from a cylindrical obstacle. A level set-based topology optimization method incorporating a fictitious interface energy is used to find optimized configurations of the ferrite material. The numerical results demonstrate that the optimization successfully found an appropriate ferrite configuration that functions as an electromagnetic cloak.

A Multiobjective Firefly Approach Using Beta Probability Distribution for Electromagnetic Optimization Problems

May 2013

Current research on optimization methods is increasingly focused on biology-inspired metaheuristics as efficient tools for the solution of many electromagnetic optimization problems. The firefly algorithm (FA) is an algorithm of this class, and is based on the idealized behavior of the flashing characteristics of fireflies. In FA, the flashing light can be represented in such a way that it is associated with the objective function to be optimized, which makes it possible to formulate a biology-inspired algorithm. This paper briefly introduces the basics of FA and its multiobjective version (MOFA) and proposes a novel multiobjective variant which uses the beta probability distribution (MOBFA) in the tuning of control parameters, which is useful to maintain the diversity of solutions, as well as the use of crowding-based archiving of the Pareto solutions. Numerical results refer to a simple analytical benchmark as well as a multiobjective constrained brushless dc motor design problem, both showing that the resulting MOBFA algorithm outperforms the standard one.

Multiobjective Optimization of Post Insulator Based on Dynamic Population Size

May 2013

Most of the existing optimization algorithms use fixed size of population. We propose a dynamic population size throughout the optimization process applied on the numerical model of a medium voltage post insulator. Our modified PSO algorithm enables change population in any iteration of optimization process. It is desired to reduce the population size because of a decreasing calculation time. The results of a modified PSO algorithm are compared with a similar modified differential evolution algorithm. Algorithm PSO is suitably modified in order to operate with the principle of the Pareto nondominancy using dynamic population size.

Binary-Based Topology Optimization of Magnetostatic Shielding by a Hybrid Evolutionary Algorithm Combining Genetic Algorithm and Extended Compact Genetic Algorithm

May 2013

Topology optimization using the binary information of magnetic material is one of the most attractive simulations for the conceptual design of electrical machines. Heuristic algorithms based on random search allow engineers to define general-purpose objects with various constraint conditions. However, it is difficult for topology optimization to realize a practical solution without island and void distribution. In this paper, we propose a hybrid evolutionary algorithm that is composed of a genetic algorithm (GA) and extended compact GA (ECGA). We verify the effectiveness of the proposed algorithm on the binary topology optimization problem for the design of magnetostatic shielding.

An Improved Differential Evolution Algorithm Adopting $\lambda$ -Best Mutation Strategy for Global Optimization of Electromagnetic Devices

May 2013

The differential evolution (DE) algorithm has almost ten different variants according to a trial vector generation strategy. The trial vector generation strategy has a significant effect on the performance of the DE algorithm. The selection of a suitable mutation strategy, however, is difficult because of the differences in the convergence speed and diversity. This paper proposes an improved differential evolution algorithm adopting a new mutation strategy, “${rm DE}/lambda-{rm best}/1$,” to increase the performance of global optimization. The suggested mutation strategy guides the population to the feasible region of various constraint optimization problems. The validity and numerical efficiency of the developed method was investigated through a comparison with conventional DEs on well known benchmark functions and Testing Electromagnetic Analysis Methods (TEAM) problem 22.

A Novel Approach for Free-Form Optimization in Engineering Design

May 2013

The paper presents a novel approach for a gradient-less free-form optimization of engineering problems. The main feature of the approach is that it enables optimization of the engineering problems without calculation of an adjoint problem. This provides a fast and robust optimization of 3-D problems in practical engineering. In this paper we present the basic idea behind this technique followed by the example of the indirect optimization of the TEAM benchmark problem No. 25.

Multiguiders and Nondominate Ranking Differential Evolution Algorithm for Multiobjective Global Optimization of Electromagnetic Problems

May 2013

The differential evolution (DE) algorithm was initially developed for single-objective problems and was shown to be a fast, simple algorithm. In order to utilize these advantages in real-world problems it was adapted for multiobjective global optimization (MOGO) recently. In general multiobjective differential evolutionary algorithm, only use conventional DE strategies, and, in order to optimize performance constrains problems, the feasibility of the solutions was considered only at selection step. This paper presents a new multiobjective evolutionary algorithm based on differential evolution. In the mutation step, the proposed method which applied multiguiders instead of conventional base vector selection method is used. Therefore, feasibility of multiguiders, involving constraint optimization problems, is also considered. Furthermore, the approach also incorporates nondominated sorting method and secondary population for the nondominated solutions. The propose algorithm is compared with resent approaches of multiobjective optimizers in solving multiobjective version of Testing Electromagnetic Analysis Methods (TEAM) problem 22.

An Improved Robust Optimization Algorithm: Second-Order Sensitivity Assisted Worst Case Optimization

May 2013

The demand of performance robustness against the uncertainty in design variables is required during the optimization process. From the viewpoint of fast robustness evaluation for the electromagnetic problem, based on the worst case scenario approximation and design sensitivity analysis, a new robust optimization algorithm, the sensitivity-assisted worst case optimization (SA-WCO), is developed. In order to keep higher accuracy of the robustness prediction, the second-order sensitivity implemented by the hybrid direct differentiation-adjoint variable method is introduced into the robustness assessment. The performance and robustness of the proposed SA-WCO algorithms are investigated through a numerical experiment with the TEAM Problem 22.

Reflector Texturing Design of a Thin Film Solar Cell in a Specific Wavelength Range Using Topology Optimization

May 2013

For a thin film solar cell, proper light trapping is commonly requested for the purpose of increasing the absorbing efficiency in the silicon absorbing layer. This study aims to suggest a design method for a thin film solar cell using topology optimization so that the overall efficiency increases in a specified wavelength range from 700 nm to 800 nm. For the efficient energy translation, extending the wave-path length and raising the efficiency are inevitable. The bottom transparent conducting oxide (TCO) layer shape is designed so that the propagating wave reflects on the surface and it satisfies the total internal reflection condition at the top TCO layer.

A Practical Approach for the Global Optimization of Electromagnetic Design of 3-Phase Core-Type Distribution Transformer Allowing for Capitalization of Losses

May 2013

A new approach which integrates multiple nonlinear constrained optimization algorithms in conjunction with an improved heuristic algorithm is presented. The approach includes capitalization of losses in the global design optimization process of three-phase oil-immersed distribution transformers. In addition, the proposed technique incorporates finite element-based electromagnetic analysis for losses, short circuit impedance and forces, in order to assess the globally optimum design produced by the approach against design specifications. We present practical results from a range of distribution transformers designed using existing techniques and the new approach. The practical results demonstrate the significant improvements in design when compared with existing techniques.

Novel Gamma Differential Evolution Approach for Multiobjective Transformer Design Optimization

May 2013

The differential evolution (DE) algorithm is a simple but powerful population-based stochastic search technique for solving global optimization problems. DE consists of three main operations: mutation, crossover and selection. The advantages of DE are simple structure, ease of use, speed and robustness. However, to achieve optimal performance with DE, time consuming parameter tuning is essential as its performance is sensitive to the choice of the mutation and crossover values. In this paper, a novel DE algorithm (NDE) based on truncated gamma probability distribution function is proposed for solving multiobjective optimization problems as the design of transformers. Simulations of transformer design optimization (TDO) demonstrate the effectiveness of the proposed optimization algorithm. The simulation results show that, compared with other multiobjective DE algorithm, the proposed NDE is able to find better spread of solutions with better convergence to the Pareto front and preserve the diversity of Pareto solutions more efficiently.

Optimization of 3-D Magnetic Circuit of Linear Oscillatory Actuator for Diaphragm Blower

May 2013

The efficiency and materials cost of a linear oscillatory actuator (LOA) for a diaphragm blower depends on the design of magnetic circuit. Therefore, it is necessary to optimize the magnetic circuit in order to develop a high efficiency and low price LOA by employing the magnetic field analysis method and an optimization method. In this paper, the 3-D multi-objective optimization of LOA with large magnetic force and small magnet volume is carried out using the combined 3-D finite element method (FEM), evolution strategy (ES), and particle swarm optimization (PSO).

3-D Optimization of Ferrite Inductor Considering Hysteresis Loss

May 2013

This paper presents three-dimensional shape optimization of inductors for the dc-dc converters, in which the nonconforming voxel-based finite element method (FEM) is employed to realize fast FE mesh generation during the optimization. The operating point of the inductor under the bias current condition, which is estimated from the circuit analysis, is obtained by nonlinear FE analysis. Then, the FE equation linearized around the operating point is solved being coupled with the circuit equation to obtain the magnetic fields in the inductor. The hysteresis loss is computed from the Steinmetz formula. Validity of the field computation is tested by comparing the numerical results with measured data. The multiobjective optimization of the inductor shapes is performed to minimize the winding resistance and hysteresis loss. It is shown that the present method can effectively find the Pareto solutions which can lead to improvement in the efficiency of the dc-dc converter.

Shape Optimization of Double Antenna for Long Range Passive UHF-Band RFID

May 2013

The passive RFID tag, which receives energy for its operation from electromagnetic waves radiated by RFID readers, changes the antenna impedance to modulate the back scattering waves caught by the reader. For this reason, during the back-scattering communication, the energy received by the RFID tag much reduces due to the impedance mismatch. To resolve this problem, the double antenna system which consists of receiving and sending antennas has been proposed. In this paper, the double antenna shapes are optimized on the basis of FDTD analysis and genetic algorithm to maximize the communication distance.

New Reliability-Based Robust Design Optimization Algorithms for Electromagnetic Devices Utilizing Worst Case Scenario Approximation

May 2013

In order to deal with main targets of design methodologies subject to uncertainties in design variables: reliability and robustness, the reliability-based robust design optimization (RBRDO) is developed by integrating the performance robustness and constraint feasibility into a single optimization model. A new RBRDO algorithm is proposed based on the worst case scenario approximation for robustness assessment and the sensitivity-assisted Monte Carlo simulation method for effective reliability calculation. Furthermore, one multi-objective RBRDO formulation is suggested. Overall, an electromagnetic application-superconducting magnetic energy storage device (TEAM Problem 22) is used to investigate performances of the proposed RBRDO methods.

Optimal Needle Positioning for Electrochemotherapy: A Constrained Multiobjective Strategy

May 2013

A multiobjective optimization method is used to design a treatment planning based on electrochemotherapy (ECT). A penalty function technique is coupled to NSGA algorithm in order to identify the constrained Pareto front, so preventing unfeasible solutions.

A Hybrid Optimal Design Strategy of Wireless Magnetic-Resonant Charger for Deep Brain Stimulation Devices

May 2013

A hybrid optimal design strategy for wireless magnetic-resonant charger of deep brain stimulation devices is presented. It is proposed that a differential evolution algorithm with discrete variables (turn numbers of coils) and constrains (induced current and voltage in the load loop) is used to design the wireless power transfer system. The variables which normally include the sizes of the load coil, receiver coil, transmitter coil, source coil and capacitances are analyzed in the optimization study. Analytical formulas are embedded in the numerical optimization to speed up the convergence of the searching process. The designed receiver can receive enough power to recharge a 3.7 V circular button-type nickel-metal hydride rechargeable battery which can be implanted into the patients' skull. The performance of the designed system has been verified experimentally.

Study on Optimal Design Based on Direct Coupling Between a FEM Simulation Model and L-BFGS-B Algorithm

May 2013

This paper investigates the capability of a Quasi-Newton optimization algorithm, the L-BFGS-B one, to reduce the drawbacks of the direct coupling with FEM models. After a short description of the L-BFGS-B algorithm, the authors have tested it to the TEAM Workshop Problem 25. L-BFGS-B algorithm issues linked to FEM estimation of the objective function have been analyzed. Finally the authors present the results of an electromagnetic device optimal design, using a large number of parameters (47).

A Fuzzy-Based Taguchi Method for Multiobjective Design of PM Motors

May 2013

This paper describes a design optimization based on the fuzzy-based Taguchi method coupled with finite element analysis (FEA). The proposed approach takes advantage of both the Taguchi method and a fuzzy rule based inference system, which forms a robust and practical methodology in tackling multiobjective optimization problems. The proposed methodology is applied to the optimization design of a surface-mounted permanent magnet (SPM) motor. The experimental results confirm the validity of the proposed method.

Ultrathin Metamaterial Screens With Nonuniform Patches for Reflectivity Reduction From Metallic Surfaces

May 2013

This paper presents a class of ultrathin metamaterial screens for microwave reflectivity reduction from metallic surfaces. The screens consist of a highly conductive sheet with periodic patterns on top of a thin grounded lossy substrate. The periodic patterns of the screens are composed of nonuniform patches. It is found that the considered screens exhibit about 60% larger working bandwidth than those with uniform patches. A simple analytical equivalent circuit is also derived for mechanism understanding and quick design for the screens.

Design of a Novel Electrical Continuously Variable Transmission System Based on Harmonic Spectra Analysis of Magnetic Field

May 2013

A novel electrical continuously variable transmission (E-CVT) system is presented and analyzed based on harmonic spectra analysis of magnetic fields. Two rotors and one stator are integrated within one electric machine so as to keep the whole system compact. The main merits of this proposed torque transmission machine are its brushless structure, improved torque density, reduced stator end winding length, and reduced copper loss. The operating principle of the machine is described and its steady-state and transient performances are analyzed using time-stepping finite element method (TS-FEM). FEM results are used to confirm and validate the superior performance of the proposed machine.

A Novel Mesh Morphing Technique for Large Shape Deformation and Its Application to Optimal Design Problems

May 2013

In the process of finding the optimal solution by parameter sweeping analysis for optimal shape design problems, the silhouette of the device to be optimized usually needs to be changed many times. To avoid the tedious and time-consuming mesh regeneration process when the shape parameters change, a parameterized mesh technique is adopted in this paper. In the proposed method, the new coordinates of the nodes and their displacement vectors can be obtained instantly because all nodes are associated with the design parameters. To eliminate inverted elements in case of large shape deformation, a smart edge swapping technique is proposed. The edge swapping process is based on the nodal displacement vectors and the edge facing the displacement vector of the node is to be swapped. The parameterized mesh technique is fully described and examples are also given to showcase the effectiveness of the proposed method.

Cogging Torque Optimization of Flux-Switching Transverse Flux Permanent Magnet Machine

May 2013

In this paper, cogging torque characteristics in both single-phase and three-phase flux switching transverse flux permanent magnet machines (FS-TFPMM) are analyzed by 3-D finite element method (FEM). It is found that the cogging torque of the FS-TFPMM is significantly influenced by the ratios of stator and rotor core circumferential widths to pole pitch, $k_{s}$ and $k_{r}$. When $k_{r}>1-k_{s}$, the cogging torque waveform has additional two zero-crossing points, whilst its amplitude is significantly reduced. The optimal ratios of $k_{s}$ and $k_{r}$ are selected to reduce the cogging torque and to maximize the permanent magnet flux linkage. A 380 W three-phase prototype is designed, manufactured, and tested to verify the optimization.

Optimization Methods of Torque Density for Developing the Neodymium Free SPOKE-Type BLDC Motor

May 2013

In this paper, we propose a method for optimizing the torque density to develop a SPOKE-type brushless direct current (BLDC) motor that does not require the use of a neodymium permanent magnet. Recently, the price of neodymium magnets has increased significantly owing to the rising prices of rare-earth minerals. Therefore, here we developed a method to maximize the torque density by using ferrite magnets instead of neodymium magnets. The proposed model was inserted into the auxiliary magnets in the center of a rotor after changing the existing interior permanent magnet-type BLDC motor to a SPOKE-type motor, and the effective air-gap flux density $(B_{g})$ was maximized. We also developed an optimization tool to determine the volume of a magnet that would generate the maximum torque at a SPOKE-type motor structure including an auxiliary magnet. We manufactured a SPOKE-type motor designed using these optimization tools. Finally, we compared and analyzed finite element method simulation results and experimental results.

Coupled Computation of Electric Motor Design and Control Parameters Based on Ant Colonies Speed Trajectory Optimization

May 2013

The multiplicity of operational and technical specifications, characterizing the design of electric drives, favors the application of coupled computation techniques. When the combined optimization of steady-state and transient-state operation is required in terms of energy efficiency versus speed performance, the coupled computation of electric motor design and control parameters can be utilized. In this paper, a particular electric motor design technique is introduced, based on the simultaneous optimization of motor steady-state performances and speed controller transient responses. The proposed methodology has been applied for the optimization of a Permanent Magnet Synchronous Machine (PMSM) drive and offered practical reduction of the complex optimization criterion cost when compared to the decoupled approach. Implementation of the resulting drive system has been undertaken, and overall performance improvements have been experimentally validated.

Optimization of High-Speed Motors Considering Centrifugal Force and Core Loss Using Combination of Stress and Electromagnetic Field Analyses

May 2013

A shape optimization method by using combination of stress and electromagnetic field analyses has been developed for the design of high-speed motors. In the stress analysis, the mechanical stress caused by centrifugal force in the rotor is estimated. In the electromagnetic field analysis, the loss and torque of the motor are estimated. The permeability and the core-loss coefficients used in the electromagnetic field analysis are modified due to the results of the stress analysis. The validity of the optimization is confirmed by the measurement of a prototype motor. The measured and calculated results are found to be in good agreement. The proposed method is useful for high-speed motor designs.

Shape Optimization of Induction Machines by Using Combination of Frequency- and Time-Domain Finite Element Methods

May 2013

A shape optimization method has been developed in order to obtain advanced designs of induction machines within practical computational time. In the proposed method, the frequency- and time-domain adaptive finite element methods (FEMs) are combined. The frequency domain FEM is used to obtain initial potentials for the acceleration of the time-domain FEM, which estimates the characteristics of the machines. The experimental verification is carried out in order confirm the validity of the analysis. An advanced design of a cage induction motor is obtained by using the proposed method.

Cogging Torque Optimization of Axial Flux Permanent Magnet Motor

May 2013

The conventional climb method is difficult to apply for the multimodal and multi-dimensional optimization problem. To solve this problem, the improved climb method is proposed in this paper. The proposed algorithm can mitigate the time for the optimization and increase the reliability for the optimization. The proposed algorithm is verified through the optimization of an axial flux permanent magnet motor.

Rotor Shape Optimization of Interior Permanent Magnet BLDC Motor According to Magnetization Direction

May 2013

This paper proposes the optimization of an anisotropic ferrite magnet shape and magnetization direction to maximize back-EMF of IPM BLDC motor. Firstly, four different models of general magnet shapes are selected, and then FEM analysis is carried out with four different magnetization directions for each of four models. The best magnet shape and magnetization direction from each model are selected as an initial model for optimization. Secondly, based on the initial model, optimization design for maximum back-EMF and minimum cogging torque and THD is performed. Finally, validity and superiority of the optimization design are confirmed by manufacturing the prototype motor and performing the experiment.

Optimal Shape Design of Rotor Slot in Squirrel-Cage Induction Motor Considering Torque Characteristics

May 2013

Induction motors are widely used in various industrial applications with different torque-speed characteristics. Since the configuration of the rotor slot has a great impact on the electromagnetic torque-speed characteristics, a design optimization process is necessary to improve the motor performance of the induction motor. The material boundaries of the rotor slot are represented by a level set function, and a voltage driven time-harmonic field analysis is performed to estimate the characteristics of the induction motor. An optimization problem is formulated to maximize the torque at one speed either a rated or starting condition constrained by the torque at other speeds, starting currents and efficiency. A level set equation with an augmented Lagrangian method is derived to find the optimal design. Optimal results are achieved by updating the sequential changes of the material region driven by the shape derivative. The design flexibility of the proposed method is confirmed to obtain National Electrical Manufacturers Association (NEMA) designs satisfying different torque characteristics.

Min-Max Univariate Dynamic Encoding Algorithm for Searches (uDEAS) and Its Application to Optimal Design of Electric Machines

May 2013

Optimal design of Interior Permanent Magnet Synchronous Machines (IPMSM) is to obtain the global design optimum in association with the characteristic analysis investigating nonlinear magnetic saturation based on Finite Element Analysis (FEA). Since characteristic analysis occupies most part of the convergence time, the number of objective function must be called minimally. Hence, in this paper, MuDEAS is newly implemented in order to compensate the excessive computation time and the reliability of convergence to the global optimum. MuDEAS has been verified through a benchmark function and applied to the optimal design of IPMSM for maximizing Maximum Torque Per Ampere (MTPA) indentified with FEA.

Optimal Rotor Shape Design of a Concentrated Flux IPM-Type Motor for Improving Efficiency and Operation Range

May 2013

In this paper, an optimal design for a concentrated flux interior permanent magnet (CFIPM) motor is proposed to improve efficiency and obtain a wide operation range simultaneously. For enhancement in efficiency in the constant torque region, the saliency ratio is increased with respect to the initial model. Two points, 3000 rpm (based speed) in the constant torque region and 7000 rpm (maximum speed) in the constant power region, are chosen so as to compare the torque in our design with that of the initial model. A 2D-finite element method (FEM) was used to calculate the inductances of the d-axis and q-axis with a change in the CFIPM rotor shape. In the optimal design, the Kriging method based on Latin hypercube sampling (LHS) and a genetic algorithm (GA) were employed. The validity of the optimal design was verified by 2D-FEM and current vector control.

Intelligent MADS With Clustering and Elastic Net and Its Application to Optimal Design of Interior PM Synchronous Machines

May 2013

Optimal design of the electric machines is interlinked with the optimization algorithm for obtaining the quantitative optimum and numerical analysis of electric machines for the objective function. The optimization algorithm is required to evaluate the objective function minimal times since numerical analysis of the electric machines consumes a lot of time. In this paper, intelligent MADS with a clustering and elastic net is newly adopted for the optimal design of electric machines to raise the reliability of the global optimization and fast convergence time. In particular, the proposed algorithm is employed to the optimal design of the interior permanent-magnet PM synchronous machine minimizing torque ripples, which has been regarded as one of the complicated design problems.

Analysis of Radiated EMI and Noise Propagation in Three-Phase Inverter System Operating Under Different Switching Patterns

May 2013

In this paper, a numerical model using the finite-element (FE) method was used to predict the electromagnetic interference (EMI) generated by 325-V, 5-kW power inverter, supplying a variable three-phase load. A comparative analysis was performed to evaluate the effects of different switching patterns on the radiated and conducted EMI levels. An experimental setup was arranged to validate the simulation results. The proposed approach is suitable for prediction of radiated and conducted EMI generated by power converters. This helps reduce the post prototype EMC testing cost by minimizing redesign and modifications of final converter product.

Extended Anisotropic Layer Theory for Electrical Machines

May 2013

The Anisotropic Layer Theory (ALT) has been extensively used for electric machine analysis, due to its ability to take finite iron permeability into account globally. However, the effect of the slot openings, which are often present in slotted electrical machines, is neglected. In this work, an extension of the ALT to account for slot openings is proposed. The classical ALT is combined with the Harmonic Modeling Technique (HMT) for slotted structures by assuming infinitely permeable tooth tips. A semi-analytical solution is described for the classical and the extended ALT model. The results of the semi-analytical models are compared to Finite Element Analysis (FEA) results.

Analysis of Magnetizing Process of a New Anisotropic Bonded NdFeB Permanent Magnet Using FEM Combined With Jiles-Atherton Hysteresis Model

May 2013

This paper proposes an algorithm to analyze the magnetizing process of a new anisotropic bonded NdFeB permanent magnet (PM) which is magnetized by a capacitor discharge impulse magnetizing fixture. In the algorithm, the magnetic field analysis and the prediction of the residual magnetic flux density are achieved by using the transient finite element method (FEM) incorporating the scalar Jiles-Atherton (J-A) hysteresis model. The validity of the suggested method is demonstrated by applying to a 4-pole ring-type anisotropic bonded NdFeB PM and comparing the numerical results with the experiment ones.

Study on Starting Performance of Ni-Mn-Ga Magnetic Shape Memory Alloy Linear Actuator

May 2013

This paper describes the startup performance of a linear actuator made from Ni-Mn-Ga magnetic shape memory alloy, which is driven by an external magnetic field and a return spring. This actuator produces large displacements compared with conventional magnetostrictive materials. However, it is difficult to control due to the hysteresis of Ni-Mn-Ga. The strain and magnetic field intensity characteristics of Ni-Mn-Ga are simplified and modeled for the simulation. A transient electromagnetic field—structural coupled analysis of the startup performance of the actuator is conducted using the 3-D finite element method. The results are verified by carrying out measurements on a prototype.

Novel Electromagnetic Actuator Using a Permanent Magnet and an Inter-Locking Mechanism for a Magnetic Switch

May 2013

The solenoid magnetic actuator has been widely used as an actuator for MS (magnetic switch). Thus, conventional MSs continuously consume electrical power to maintain a closed state. To address this problem, an innovative structure which uses a permanent magnet to generate holding force in the closed state without electrical power is suggested in this paper. Further, the permanent magnet is dedicated to the opening operation and the closing operation by means of its magnetic force. In other words, an eco-friendly MS is proposed in this research. However, this structure has a critical problem in that, if unexpected external force is applied to the MS when in the open state, the MS returns to the closed state by the force of the permanent magnet and remains in the closed state, causing an unintended operation of the load. To solve this problem, a novel inter-locking mechanism is proposed. Hence, we termed the proposed novel MS the MSPI (magnetic switch using a permanent magnet and an inter-locking system). In addition, analysis and design methods for the MSPI are proposed in this paper. The usefulness of the MSPI and the accuracy of the analysis and design methods are confirmed through an experiment.

Analysis of 2-Degree of Freedom Outer Rotor Spherical Actuator Employing 3-D Finite Element Method

May 2013

To drive a conventional motor drive system, the number of degrees of freedom needed has to be equal to the number of actuators employed, and this causes the system to be larger and heavier. To solve these problems, the development of a spherical actuator which can rotate around multi axes is being conducted. In this paper, we propose a new spherical actuator with an outer rotor to produce higher torque density and describe the control method for open loop drive. Static torque and dynamic characteristics of the actuator are clarified by employing 3-D finite element method and are verified from experimental results of a prototype.

Proposal of a Two Movers Linear Oscillatory Actuator for Active Control Engine Mounts

May 2013

Active control engine mounts employing linear oscillatory actuators are mounted onto automobiles to reduce the frame vibration and noise. In conventional ACMs, the electric power consumption is high, and we clarify the causes of the high electric power consumption by dynamic simulation. Moreover, we propose a new LOA with two movers. The operational principle is described and the effectiveness of the ACM is verified using dynamic simulation.

Analysis of a Vernier Motor with Concentrated Windings

May 2013

This paper describes the operating principle and the performance analysis of the surface-permanent-magnet-type vernier motor with concentrated windings using finite element method analysis. To satisfy the structural relationship of $Z_{2}=Z_{1}pm p$ , the number of auxiliary teeth in the stator, pole pairs in the rotor and winding pole pairs are chosen as $Z_{1}=12$, $Z_{2}=11$ and $p=1$ respectively. With this setup which operates at a gear ratio of 1/11, the cogging torque tends to be lower and therefore the output torque contains only smaller ripples. The iron loss computation and the efficiency calculation employing the two-frequency method are also investigated. Estimation of the iron loss has clarified that the hysteresis loss was dominant in the laminated core and that the magnet eddy current loss increased dramatically at higher speeds due to the rotating magnetic field.

Feedback Control of the 2-DOF Actuator Specialized for 2-Axes Rotation

May 2013

Recently many multi-degree-of-freedom actuators have been proposed and we ourselves have proposed a 2-degree-of-freedom spherical actuator. In this paper a feedback control method is proposed, and the dynamic operating characteristics under feedback control are computed using 3-D finite element method analysis. In addition, in order to verify the simulation results, experiments using a prototype are carried out.

Design Considerations in Actuators for Aerospace Applications

May 2013

In this paper, a comparative optimal design of actuators for aerospace applications based on induction-machine (IM) and permanent-magnet machine (PMM) technologies is undertaken by means of a combined electromagnetic and thermal evaluation. Initially, 3-D time-stepping finite-element analysis is employed for the determination of the actuators' basic dimensional and operating characteristics. As the actuator thermal constraints constitute a key feature of the respective systems, the proposed configurations are compared on the basis of equal thermal evacuation. Both configurations considered are in a next step optimized regarding the mean torque and torque ripple through the application of a specific optimization procedure employing Taguchi's methodology in conjunction with an extended Rosenbrock's method accounting also for the machine operation cycle. Resulting IM and PMM optimal configurations have been validated through manufactured prototypes, illustrating the effectiveness of the proposed optimization algorithm presenting, however, complementary advantages for aerospace applications.

Amplitude Control Method of Linear Resonant Actuator by Load Estimation From the Back-EMF

May 2013

This paper proposes a feedback control method for a linear resonant actuator (LRA), in which an external load estimated from two signals of the back-EMF is used as a target voltage in PID control. From the estimated load, it becomes possible to obtain an arbitrary amplitude of the mover. The effectiveness of this method was verified through FEM analysis.

Design and Simulation of a Five Degrees of Freedom Active Control Magnetic Levitated Motor

May 2013

A novel magnetically levitated motor which has the ability to control five degrees of freedom was proposed. The proposed magnetic levitated motor uses a radial bearing-less motor to control both radial translation motion and rotation, and an axial magnetic bearing to control both axial translation and tilting motion. Moreover, stators were installed on the inner side of the rotor, such that the flux path of the axial magnetic bearing and radial bearing-less motor are partially-shared. Therefore, the proposed magnetic levitated motor is small, while achieving five degrees of freedom active control. The prototype device was designed using FEM. According to this analysis, the device had sufficient magnetic force to control the rotor within a designed airgap of ${pm}$ 0.6 mm. Moreover, simulated dynamic characteristics showed good response performance of the proposed maglev system.

Dynamic Analysis of an Independently Controllable Electromagnetic Spherical Actuator

May 2013

We have been developing electromagnetic spherical actuators capable of three-degree-of-freedom rotation. However, these actuators require complex control because rotation around one axis interferes with rotation around another. In this paper, we propose a new 3-DOF actuator where the 3-axes can be independently controlled, and the basic structure and the operating principle of the actuator are described. Then the dynamic performance under position feedback control is analyzed employing 3D-FEM and the effectiveness of this actuator is clarified.

The Analysis of Permanent Magnet Double-Sided Linear Synchronous Motor With Perpendicular Arrangement

May 2013

In this paper, a new linear synchronous motor—permanent magnet double-sided linear synchronous motor with perpendicular arrangement (PMDLSM), was proposed. This motor was designed to account for the drawbacks of conventional linear motors, such as the problems with normal force and end effects. It was designed by analyzing the detent force and the thrust of different models, and optimizing the design variables of the machine. The characteristics of the perpendicular PMDLSM were analyzed by finite element method, and a comparison of the results was made in the experiments.

Design Considerations for Coreless Linear Actuators

May 2013

Linear permanent magnet synchronous motors are often used in applications where a high accuracy is needed. This paper investigates the influence of the key design parameters on the performance of a linear actuator with vertically magnetized magnets and a magnet array with quasi-Halbach magnetization. The performance is modeled by means of analytical expressions of the three-dimensional magnetic field components and optimal design ratios and guidelines are established.

Cogging Force Reduction of Double-Sided Linear Flux-Switching Permanent Magnet Machine for Direct Drives

May 2013

This study proposes a double-sided linear flux-switching permanent magnet machine for direct drives in precision servo applications. The method of asymmetry distribution of stator teeth (ADST) is introduced to reduce the cogging force. Moreover, cogging force, back-EMFs, and thrust force are calculated by using finite element analysis. In addition, the performance comparison is carried out to verify the accuracy and effectiveness of the method of cogging force reduction. Finally, the experiment confirms the reasonability and feasibility of the ADST method.

A Multiobjective Approach for Designing the Rotor of Brushless Motors

May 2013

This paper presents a multiobjective formulation for the topological design of synchronous motors. The developed torque of a motor is broken into two components: the torque due to the permanent magnet excitation and the torque due to the magnetic reluctance. In addition, topological gradients of the two torque components as objective functions are derived respectively using an adjoint variable method. Instead of simply maximizing the total torque, these two torque components are treated as different objectives in the design, thus a Pareto front of different topologies of rotor design can be achieved.

Coupled Field-Circuit Estimation of Operational Inductance in PM Synchronous Machines by a Real-Time Physics-Based Inductance Observer

May 2013

This paper presents a new real-time inductance estimation method for 3-phase permanent magnet synchronous machine (PMSM), utilizing a physics-based inductance observer. The mathematical modeling, stability analysis, and transient analysis of the observer are developed and described in details. The inductance of a 3-phase, 250 W, radial flux PMSM was calculated by an electromagnetic field-circuit based finite-element analysis with motion. The numerical results are compared with the experimental results obtained from the developed inductance observer. The results show excellent agreement in steady state operating conditions.

A Novel Parallel Motor Winding Structure for Bearingless Motors

May 2013

A novel winding structure without separated suspension winding has been proposed for bearingless motors. The proposed winding structure basically has two parallel paths in three-phase motor windings. One three-phase winding path has a neutral point in general, but another three-phase winding path is connected to a suspension inverter, which injects currents for suspension force generation. Additional suspension windings are not needed in the stator slots, because the two parallel path windings are used for both torque and suspension force generation. In the proposed winding structure, speed induced voltages are cancelled each other so that no speed induced voltage is induced at suspension terminals.

Comparison of the Test Result and 3D-FEM Analysis at the Knee Point of a 60 kW SRM for a HEV

May 2013

The maximum torque values in computer analysis and experiment in the switched reluctance motor (SRM), having competitive torque density and efficiency with respect to the rare-earth permanent magnet motor employed in the 2009 Toyota Prius, have been compared. The SRM is highly saturated to provide the maximum torque for a short time; thus, the torque value tends to have considerable error of 15% even in the 3D FEM analysis with respect to experimental result because of the incomplete material setting. A comparison of the flux-linkage and current is also provided for consideration. The results of the 2D-FEM and 3D-FEM analysis as well as a test machine are presented. The maximum torque in the 3D-FEM analysis is shown to be within errors of 5.0% with respect to that in the test machine.

Cogging Torque Minimization and Torque Ripple Suppression in Surface-Mounted Permanent Magnet Synchronous Machines Using Different Magnet Widths

May 2013

Permanent magnet synchronous machines are vulnerable to significant amounts of torque ripple if they are not carefully designed. Even though minimizing cogging torque can help reduce the torque ripple, but can not definitely give rise to a low level torque ripple. This paper presents a simple solution for minimizing the cogging torque and suppressing operation torque ripple simultaneously. The principle of that simple solution is illustrated, where a magnet with different width is used so that the flux density distribution in the machine is substantially changed. The magnet widths for minimizing cogging torque are obtained by using an analytical model. The influence of magnet widths on operation torque ripple and average operation torque is examined by using Finite Element Analysis (FEA) which gives more preciseness to calculations. It is found that the cogging torque and operation torque ripple can be greatly reduced, but with slight average output torque reduction. At last, the Unbalance Magnetic Pull (UMP) is examined, indicating that the presented method can substantially increase the UMP due to the asymmetric distribution of magnets.

Relative Permeability in a 3D Analytical Surface Charge Model of Permanent Magnets

May 2013

The analytical surface charge model is used to calculate the magnetic field of magnets in 3D in an unbounded domain. The method combines high accuracy with a short calculation time. However, in the classical method the relative permeability of the magnet is assumed to be equal to air. This introduces an error in the resulting magnetic field strength. In this paper the permeability of the magnet is taken into account in the form of a redistribution of magnetic surface charge. As such, an exact solution for the magnetic field at low relative permeability is obtained. The interaction force between two magnets is calculated using the newly obtained expressions for the magnetic field and compared with FEM and measurements.

Computations of Magnetic Field Anomalies in Synchronous Generator Due to Rotor Excitation Coil Faults

May 2013

The paper presents an approach to model shorted turns in rotor excitation winding of synchronous generator using finite element analysis. It enables detailed examination of magnetic field at several operating conditions under healthy and faulty states which are difficult or even impossible to carry out by available measurement methods in industrial environment. It is confirmed that an extensive analysis should be performed to assure accurate healthy/faulty state predictions, since the level of diagnostic signal is considerably influenced by a combination of many machine design and operating parameters.

A Performance Study on a Permanent Magnet Spherical Motor

May 2013

To realize the multi-Degree-of-Freedom (multi-DOF) movement, researches on spherical motor have been conducted in many countries. The Spherical motor has a 3-DOF, whose shaft can not only rotate as rotary motor but also tilt in the 2-DOF space. Researches on spherical motor will greatly contribute to 3-DOF systems, because spherical motor can reduce the size and weight of 3-DOF systems. This paper studies a new type of spherical motor that has rotating coils and tilting coils. Also, the current function depending on shaft angles is proposed. Finally, the torque is calculated corresponding to different shaft angles and rotating speeds. Moreover, these performances are validated via experiments.

Investigation of V-Shaped Line Start Permanent Magnet Motors Based on Reactance Effect

May 2013

This paper presents an investigation into the effect of the reactance on a V-shaped line start permanent magnet motor. Five rotor designs with different V-shaped angles are utilized for exploring motor characteristics with the reactance. Performances such as back electromotive force, $d$- and $q$-axis reactance, loading capability and efficiency are simulated and analyzed by the torque model and a time stepped two-dimensional finite element software application. According to the comparison, the variations of output behaviors with $d$- and $q$-axis reactance can be described. Moreover, the design which features both excellent synchronization capability and high efficiency was verified by experiment on a prototype.

Design of Homopolar Consequent-Pole Bearingless Motor With Wide Magnetic Gap

May 2013

A wide magnetic gap bearingless motor is required in canned pumps and chambers in the semiconductor manufacturing process. In two-axis actively regulated bearingless motors, having the wide magnetic gap causes decreases in radial magnetic suspension force, axial restoring force, and tilting restoring torque, as well as in rotational torque. In radial actively positioned bearingless motors, the passive stiffness of the axial and tilting movements is one of main concerns. In this paper, a homopolar consequent-pole bearingless motor has been improved with wide magnetic gap. Design improvement of the permanent-magnet arrangement is presented with a 3-D finite-element method analysis. The proposed structure of the homopolar consequent-pole bearingless motor is shown to enhance the passive stiffness and the radial suspension force as well as the rotating torque.

An Analytical Approach for a High Speed and High Efficiency Induction Motor Considering Magnetic and Mechanical Problems

May 2013

This paper deals with the analysis techniques of a high speed and high efficiency 10 kW, 30,000 rpm rated induction motor. The induction motor has been analyzed by time-varying magnetic finite element method and the test results show that there is a possibility that the motor could be used in a high speed spindle system application. All analysis techniques are introduced to develop a high speed and high efficiency induction motor made by copper die casting. The analysis techniques are composed of magnetic analysis considering losses and input current (PWM and sinusoidal), structural analysis of rotor and stator, 3-D rotordynamic analysis and 3-D CFD. All performances of the prototype are successfully verified.

Experiment and Analysis for Effect of Floating Conductor on Electric Discharge Characteristic

May 2013

In this paper, we present a numerical analysis method for analyzing the discharge characteristic with the presence of a floating conductor. Space charges generated during the discharge process can accumulate on the surface of the floating conductor, or be emitted from its surface. An intensification of the electric field around the floating conductor is affected by those space species. Therefore, it is important to calculate the space-charge distributions considering the surface charge on a floating conductor because the discharge occurs at the floating conductor, which is placed around the cathode. An axial symmetry finite-element model is used to analyze this floating conductor discharge system, and Poisson's equation is coupled with the hydrodynamic drift-diffusion equation to calculate space charge distributions. Fowler–Nordheim electron emission is employed for the boundary condition at conductor surfaces. The analysis results show the variation of the electric field due to the space charges and the surface charge density on the floating conductor. Experiments using corona generators are carried out, and the current data obtained show the space charge generated by the presence of a floating conductor.

Development of a Large Diameter Motor for Turret Application

May 2013

This paper proposes an outer rotor and spoke type longitudinal flux direct-drive machine with advantages such as high precision, robustness, reliability, no backlash and a simple structure for large diameter turret applications. This paper deals with the optimum design using Latin hypercube sampling (LHS) with the many design variables of the developed motor. The effective design variables are selected by screening using an analysis of means (AMOM). This paper presents an optimum design for maximum torque and efficiency with the constraints of torque ripple ratio and maximum current using response surface methodology (RSM). The simulation results are compared with the experiment, and are within a 5% deviation of each other in the second prototype. All design performances of the second prototype are verified successfully. The predicted optimum design performances are consistent with the simulation results with a maximum error of 0.283%.

Analysis for Fault Detection of Vector-Controlled Permanent Magnet Synchronous Motor With Permanent Magnet Defect

May 2013

This paper analyzes the characteristics of a vector-controlled permanent-magnet synchronous motor (PMSM) with a permanent-magnet defect. A method for the diagnosis of the demagnetization of the permanent magnet in PMSM is proposed. In the proposed method, the magnetic field is calculated by the finite-element method, and then the flux linkage and $d$ and $q$ axis inductances are calculated. They are introduced into the block diagram of the drive and control system. We have manufactured interior permanent-magnet motors, where one of four magnets is reduced by 10% and 20% in order to imitate the demagnetization. It is shown that the Fourier and wavelet results are in good agreement with the measured ones. This paper shows that the stator current and stator voltage using the proposed method are useful for the fault detection of demagnetized permanent magnet.

Effect of Magnetic Property in Bridge Area of IPM Motors on Torque Characteristics

May 2013

This paper investigates the deterioration effect of magnetic properties on the performance of an interior permanent magnet synchronous motor (IPMSM). It is well known that the magnetic property of an electrical steel sheet is deteriorated by stress, which results in a decrease in efficiency of electric machines in general. In this paper, by making good use of the deterioration of magnetic properties, the performance improvement of IPMSMs due to the reduction of leakage flux in a rotor is examined. As a result, it is verified that cogging torque can be decreased by half by deteriorating magnetic property in bridge area in a rotor without reducing average torque and increasing iron loss at load condition.

Torque Density of Radial, Axial and Transverse Flux Permanent Magnet Machine Topologies

May 2013

Torque density of radial, axial and transverse flux machine topologies is investigated. A 10-kW, 200-rpm motor is chosen as a test case. Radial and axial flux motors that fulfill the key specifications of the selected test case are designed employing in-house analytical dimensioning tools and MATLAB genetic multi-objective optimization. Rather simple numerical approach is taken to study the transverse flux motor. A 20-pole-pair radial flux motor is found to outperform its axial and transverse flux counterparts in terms of torque density.

Current Harmonics Loss Analysis of 150-kW Traction Interior Permanent Magnet Synchronous Motor Through Co-Analysis of $d\hbox {-}q$ Axis Current Control and Finite Element Method

May 2013

In this study, the losses due to the time-harmonic current in a permanent magnet synchronous motor (PMSM) are calculated through a co-analysis of the time harmonics using a space vector pulse width modulation (SVPWM) inverter. PMSM is typically used as a control motor. The current in the PMSM contains harmonics because the inverter voltage is not sinusoidal, and as a result, losses occur. These losses have a negative effect on the synchronous motor performance, which is vulnerable to heat. Therefore, for efficiency and performance evaluation of the PMSM, it is necessary to consider a co-analysis of the time harmonics. In this study, we present a co-analysis method for a PMSM designed for buses and compare the analysis results with those of the current source analysis in order to verify the significance of the co-analysis. In particular, it is observed that the difference in the eddy current losses in the PM individually determined with the current source analysis and co-analysis is approximately 500%. For validating this study, the experimental equipment is established, and it can be confirmed that the experimental results are close to the co-analysis results.

Multistatic Reluctance Network Modeling for the Design of Permanent-Magnet Synchronous Machines

May 2013

This paper deals with an original design methodology of permanent-magnet synchronous machines using multistatic reluctance-network (RN) modeling. Traditionally, RN models are based on using $d$ -$q$ axis components in order to calculate the fundamental values of the torque and the back-electromotive force (emf). In this study, the RN permits an angular rotation between the rotor and stator to thereby extract the magnitude of the harmonics which are necessary for better optimization results. Besides, three different methods of calculation of the air-gap reluctances are presented and applied to the RN. Then, simulation results are compared to finite-element analysis (FEA) in order to finally determine the best method. Ultimately, the proposed model shows precise and very fast results making it suitable for geometry optimization and to help designers obtain a better sense of machine behavior.

Analysis and Experimental Study of Permanent Magnet Machines With In-Situ Magnetization

May 2013

This paper evaluates the performance of surface-mounted permanent-magnet (PM) machines with anisotropic rare-earth magnets magnetized using its own stator windings. The magnets in this process (often called in-situ magnetization) are magnetized after complete assembly. For manufacture of PM machines using this process, part of the magnet may suffer from weaker magnetization due to the magnetizing flux pattern, in particular on the two sides of the anisotropic magnets. The machine performance can thus be affected and needs to be evaluated. The current required to sufficiently magnetize the machine should be carefully studied. In this paper, both finite element analysis and experiments on prototype PM machines manufactured with in-situ magnetization are used. The concentrated and distributed winding machines are both considered. The results show that distributed winding machines can magnetize the rotors more easily than concentrated winding ones. Also, it is found that a magnetizing field of 2.5 times coercivity allows the machine back EMF magnitude to achieve the levels of pre-magnetized cases.

A Novel Two-Phase Permanent Magnet Synchronous Motor Modeling for Torque Ripple Minimization

May 2013

This paper proposes a novel two-phase, two-pole, permanent magnet synchronous motor (PMSM) with dual U-core stator structure for torque ripple minimization. The proposed motor is modeled based on the conventional single-phase U-core PMSM with approximate output power and core dimension. Torque ripple in the novel motor can be reduced significantly due to 90 $^{circ}$ electrical angle phase shift in two sets of magnet pairs and 90$^{circ}$ shift in two-phase excitation currents. Characteristics of both PMSMs such as back-EMF, cogging torque and electromagnetic torque are analyzed and compared by using the 3-D finite element analysis (FEA). As shown in the result, the cogging torque and torque ripple in the novel two-phase PMSM are efficiently reduced with sinusoidal back-EMF waveform and reasonable current density value. The validity of both PMSM models is also verified by the comparison between simulated and experimental measured results.

Magnetic Circuit Modeling of Brushless Doubly-Fed Machines With Induction and Reluctance Rotors

May 2013

This paper presents a magnetic circuit modeling (MCM) technique for analysis of the brushless doubly-fed machine (BDFM). Two rotor types are considered: the induction type and the reluctance type. The flux density in both the stator and rotor can be calculated by the developed MCM. This is particularly beneficial to the BDFM with the induction rotor since the generated rotor currents may saturate the rotor or stator and this is difficult to foresee at the design stage due to the complex flux patterns in the machine. A coupling factor is proposed to determine the flux coupling between the stator and rotor teeth of the induction type of BDFM. Saturation is also considered in the MCM. Finite element analysis is used to verify the analytical results.

Design of a Powder-Aligning-Fixture for a 4-Pole Anisotropic Bonded Nd-Fe-B Ring-Type Permanent Magnet

May 2013

A powder-aligning-fixture of anisotropic bonded Nd-Fe-B magnetic powder is designed to make a 4-pole polar anisotropic ring-type permanent magnet (PM). Magnetic performance of anisotropic bonded Nd-Fe-B PM under various aligning magnetic field intensities was investigated through analyses using equivalent magnetic circuit and 2-D finite element method (FEM). A cylinder-type bonded Nd-Fe-B PM having 4-pole polar anisotropy is realized by using the powder-aligning-fixture through an optimal design.

Quantification of Uncertainty in the Field Quality of Magnets Originating from Material Measurements

May 2013

A challenge in accelerator magnet design is the strong nonlinear behavior due to magnetic saturation. In practice, the underlying nonlinear saturation curve is modeled according to measurement data that typically contain uncertainties. The electromagnetic fields and in particular the multipole coefficients that heavily affect the particle beam dynamics inherit this uncertainty. In this paper, we propose a stochastic model to describe the uncertainties and we demonstrate the use of generalized polynomial chaos for the uncertainty quantification of the multipole coefficients. In contrast to previous works we propose to start the stochastic analysis from uncertain measurement data instead of uncertain material properties and we propose to determine the sensitivities by a Sobol decomposition.

Convergence Stabilization of E&S Vector Hysteresis Model Incorporated With Finite Element Analysis of Electrical Machines

May 2013

This paper presents a convergence stabilization method of E&S vector hysteresis model when it is combined with nonlinear finite element analysis (FEA). In order to ensure the stable convergence, an additional nonlinear iterative procedure with a relaxation method is incorporated with the conventional nonlinear FEA, and adaptive determination of relaxation factor during the nonlinear iteration is suggested. The effectiveness of the suggested method is verified through a comparison of the numerical results from the suggested and conventional methods.

The Development of Industrially-Relevant Computational Electromagnetics Based Design Tools

May 2013

The paper reviews the development of two branches of analysis tools, i.e., magnetic circuits and field solvers, and their implementation with an industrial design process for low frequency electromagnetic devices. The current state of the art is described along with the rationale for the current research work being carried out. The slow uptake of advanced analysis tools by industrial designers is examined and reasons given. The impact of manufacturing processes on the structure of design tools is considered. A development roadmap is developed with the goal of creating advanced industrial tools which will reduce the need for physical prototypes and thus reduce the overall cost of electromagnetic devices both in design and manufacture.

A Novel Dual-Permanent-Magnet-Excited Machine for Low-Speed Large-Torque Applications

May 2013

This paper proposes a novel dual-permanent-magnet-excited (DPME) machine, in which two sets of permanent magnets (PMs) are employed, one on stator and the other on rotor. Bi-directional field modulation effect (BFME) is artfully engaged to guarantee the effective coupling between the magnetic field excited by the armature windings and those excited by the two sets of PMs. Machine configuration and its operating fundaments are elaborated. Finite element analysis demonstrates that the proposed DPME machine can offer much higher torque capability than its existing counterparts, which allows it a strong competitor for low-speed large-torque applications.

Power Balanced Electromagnetic Torque Computation in Electric Machines Based on Energy Conservation in Finite-Element Method

May 2013

Time stepping finite-element method can be used to compute the electromagnetic torque on the rotor of electric machines. During calculation, the magnetic field equations are solved for finding the field distribution, and Maxwell stress tensor method is usually used for force distribution. However, the solutions from the two different sets of mathematical systems cannot guarantee the energy input and output of the system are balanced. In some cases unrealistic results may occur in that, for example, the calculated efficiency is higher than 100%. In particular, the accuracy of force computation is largely dependent on the mesh qualities and relative position changes along the integration path. In this paper, an algorithm of power balanced torque computation based on considerations of energy conservation is presented. The main salient merit of this method is that it guarantees the input energy and output energy are balanced as the rotor moves, and the computed torque is less sensitive to mesh quality and position changes.

Calculation and Analysis of Rotor Eddy Current Loss of Permanent Magnet-Inductor Hybrid Excited Synchronous Generator

May 2013

The rotor eddy current losses of a Permanent Magnet-Inductor Hybrid Excited Synchronous Generator (PMIHESG) are calculated by applying numerical computation method. The steady-state temperature fields of the PMIHESG are calculated by three dimensions FEM. The predicted rotor eddy current losses are validated by measuring temperature. The significant conclusions include: the vortex center of the rotor eddy current on the Homopolar Inductor (HI) section of the PMIHESG appears on the side of the rotor salient pole close to the field coil. The eddy current density on the side of the rotor salient pole far away from the field coil is smaller than that close to the field coil. The two dimensions method may be improper to study the eddy current loss of the HI section. Under the same axial length, the rotor eddy current loss of the HI section is much more than that of the Permanent Magnet (PM) section.

Air Gap Flux Density Waveform Design of Surface-Mounted Permanent Magnet Motor Considering Magnet Shape and Magnetization Direction

May 2013

The flux density waveform in the air gap of a surface-mounted permanent magnet motor demonstrates key design information such as the back electromotive force, cogging torque and torque waveform. To achieve a sinusoidal back electromotive force waveform, zero cogging torque and zero total ripple torque, the most important point to be considered is the elimination of higher harmonics in the air gap flux density. In this paper, the harmonics of the air gap flux density waveform is reduced by designing the magnet shape and magnetization direction using the level set based design optimization method. Multiple level set functions are employed to express several magnet segments with different magnetization directions. To control geometry complexity and improve the ease of manufacturing, a modified phase field model is implemented. The reaction-diffusion equation is solved to update the level set functions by the design sensitivity. A practical example shows that the optimal shapes of a permanent magnet with different magnetization directions can effectively mitigate the harmonics of the air gap flux density waveform.

Design and Analysis of a Spoke Type Motor With Segmented Pushing Permanent Magnet for Concentrating Air-Gap Flux Density

May 2013

This paper proposes a new design of a SPOKE-type permanent magnet brushless direct current (BLDC) motor by using pushing magnet. A numerical analysis is developed to calculate the maximum value of air-gap flux density. First, the analytical model of the SPOKE-type motor was established, and Laplace equations of magnetic scalar potential and a series of boundary conditions were given. Then, the analytical expressions of magnet field strength and magnet flux density were obtained in the air gap produced by ferrite permanent magnets. The developed analytical model was obtained by solving the magnetic scalar potential. Finally, the air-gap field distribution and back-electromotive force of spoke type machine was analyzed. The analysis works for internal rotor motor topologies, and either radial or parallel magnetized permanent magnets. This paper validates results of the analytical model by finite-element analysis as well as with the experimental analysis for SPOKE-type BLDC motors.

Torque-Speed Characteristics Analysis of a Magnetic-Geared Motor Using Finite Element Method Coupled With Vector Control

May 2013

This paper describes the torque-speed characteristics of a magnetic-geared motor with permanent magnets only on the high-speed rotor. This magnetic-geared motor has inherent overload protection characteristics, and the rotor slips under overload condition. The characteristics are determined by using finite element analysis under vector control. The analysis results are then verified by carrying out measurements on a prototype.

Analysis of Hysteresis Motor Starting Torque Using Finite Element Method and Scalar Static Hysteresis Model

May 2013

A method for the analysis of high-speed hysteresis micromotor by using a magnetostatic field solution and Piece-Wise-Linear (PWL) model of scalar static hysteresis is presented. The solution of the magnetic field in the active layer of the hysteresis motor is performed by a two steps approach: nonlinear on the whole motor domain and hysteretic on the rotor one, the two solutions are coupled by boundary conditions. The main aim of the work is to evaluate the effect of the hysteresis of the hard magnetic material (Vicalloy 52KF7) on the magnetic field distribution, on the hysteresis losses and to provide comparison with experiments.

A New Exponential Reaching Law of Sliding Mode Control to Improve Performance of Permanent Magnet Synchronous Motor

May 2013

Permanent magnet synchronous motor (PMSM) is a typical nonlinear multivariable coupled system. It is sensitive to the load disturbance and the changing of motor parameters such as stator inductance. Magnetic-field distribution is observed by finite element analysis, and inductance parametric variations are obtained. To improve dynamic quality of PMSM control system, a new exponent reaching law is proposed. The results demonstrate that the novel speed controller can improve dynamic response performance and robustness characteristics of PMSM drive.

Time-Domain Parallel Finite-Element Method for Fast Magnetic Field Analysis of Induction Motors

May 2013

This paper investigates the effectiveness of the time domain parallelization in magnetic field analyses of practical electric machines. We propose an efficient procedure to parallelize transient as well as steady-state analyses by generalizing the formulation of the parallel time-periodic finite element method. The proposed method is called the time domain parallel finite element method (TDPFEM) because it can be applied to both transient and steady-state analyses. Additionally, we derive a special condition of the slip to reduce computational costs for steady-state analyses of induction motors by using a half-cycle polyphase time-periodic condition.

Analysis on Correlation Between Cogging Torque and Torque Ripple by Considering Magnetic Saturation

May 2013

The correlation effect between cogging torque and torque ripple of an interior permanent magnet synchronous motor is analyzed in this paper by considering magnetic saturation in the core. Cogging torque is generated because of the reluctance variation between rotor magnets and stator teeth which are independent of any current. By contrast, torque ripple is generated because of the reaction field and by inputting currents such as cogging torque. However, the motor, having high cogging torque, does not always generate high torque ripple because of the magnetic saturation effect in the core. Therefore, extracting cogging torque component from torque ripple at rated torque generation should be conducted by considering magnetic saturation effect. The technique used to extract cogging torque from torque ripple is proposed by analyzing relative permeability in the core via finite element method.

Conference Author Index

May 2013

IEEE Magnetics Society Information

May 2013

IEEE Transactions on Magnetics institutional listings

May 2013

Magnetics, IEEE Transactions on - new TOC

Front cover

IEEE Transactions on Magnetics publication information

Table of Contents

CEFC 2012 Chairman’s Foreword

CEFC 2012 Publication Chairman’s Foreword

CEFC 2012 Committee

Generalized Magnetostatic Analysis by Boundary Integral Equation Derived From Scalar Potential

Parallelization of Finite Element Analysis of Nonlinear Magnetic Fields Using GPU

Instantaneous Power Balance Analysis in Finite-Element Method of Transient Magnetic Field and Circuit Coupled Computation

Large-Scale Magnetostatic Domain Decomposition Analysis Based on the MINRES Method

A Stability Improvement Technique Using PML Condition for the Three-Dimensional Nonuniform Mesh Nonstandard FDTD Method

Nonlinear Magnetostatic Analysis by Unified BIE Utilizing Potential Gap Due to Loop Currents

Study of an Explicit Meshless Method Using RPIM for Electromagnetic Fields

Parallel Performance of Multithreaded ICCG Solver Based on Algebraic Block Multicolor Ordering in Finite Element Electromagnetic Field Analyses

RPCA-Based Noise Suppression in MEG Measurement for Improving Bio-Electromagnetic Source Estimation

A Region-Based Approach for Investigating the Origin of Bioelectromagnetic Activities in MEG Source Space

Field Calculations for Magnetic Shielding: Fourier Modeling Extended With Mode-Matching Technique Applied on a Shield With Finite Dimensions

A Priori Error Indicator in the Transformation Method for Problems With Geometric Uncertainties

Accuracy Improvement of Extended Boundary-Node Method

Solution of Large Stochastic Finite Element Problems—Application to ECT-NDT

A Quantum-Inspired Evolutionary Algorithm for Multi-Objective Design

Large-Scale Simulation of Electromagnetic Wave Propagation Using Meshless Time Domain Method With Parallel Processing

Quantum Cellular Automaton for Simulating Static Magnetic Fields

Coupled Magneto-Mechanical Analysis Considering Permeability Variation by Stress Due to Both Magnetostriction and Electromagnetism

Efficient Compression of 3-D Eddy Current Problems With Integral Formulations

Enhancing Quasi-Static Modeling: A Claim for Electric Field Computation

High Resolution Numerical Electromagnetic Dosimetry Simulations Using a Coupled Two-Step Approach

Parameter Optimization and Study of Inverse J-A Hysteresis Model

Improvement of the Preconditioned MRTR Method With Eisenstat's Technique in Real Symmetric Sparse Matrices

Association of a PSO Optimizer With a Quasi-3D Ray-Tracing Propagation Model for Mono and Multi-Criterion Antenna Positioning in Indoor Environments

GPU Acceleration of Finite Difference Schemes Used in Coupled Electromagnetic/Thermal Field Simulations

Sizing of Wall Thinning Defects Using Pulsed Eddy Current Testing Signals Based on a Hybrid Inverse Analysis Method

Lightning-Inverse Reconstruction by Remote Sensing and Numerical-Field Synthesis

Usefulness of Fixed Point Method in Electromagnetic Field Analysis in Consideration of Nonlinear Magnetic Anisotropy

Real Time Simulation Method of Magnetic Field for Visualization System With Augmented Reality Technology

Reduction of Linear Subdomains for Non-Linear Electro-Quasistatic Field Simulations

Performance of 3-D Infinite Elements for High-Frequency Electromagnetic Fields

The Parallelized Automatic Mesh Generation Using Dynamic Bubble System With GPGPU

Magnetic Field Analysis in Far-Field Region by Infinite Edge Element With Boundary Surface Integration

Resolution of Nonlinear Magnetostatic Problems With a Volume Integral Method Using the Magnetic Scalar Potential

A Vector Play Model for Finite-Element Eddy-Current Analysis Using the Newton-Raphson Method

Geometrical Formulation of 3-D Space-Time Finite Integration Method

Model Reduction of Three-Dimensional Eddy Current Problems Based on the Method of Snapshots

GMRES Solution of FEM-BEM Global Systems for Electrostatic Problems Without Voltaged Conductors

A New Mesh Smoothing Method to Improve the Condition Number of Submatrices of Coefficient Matrix in Edge Finite Element Method

Electroquasistatic Field Simulation for the Layout Improvement of Outdoor Insulators Using Microvaristor Material

Natural Element Method Applied to Electromagnetic Problems

Natural Choice of Integration Surface for Maxwell Stress Tensor Computation

Residual Based a Posteriori Error Estimators for Harmonic and Formulations in Eddy Current Problems

An Arbitrary Thick Shell Finite Element for Eddy-Current Dual Vector-Scalar Potential Formulations

Test Harness on a Preconditioned Conjugate Gradient Solver on GPUs: An Efficiency Analysis

Numerical Analysis of Negative Ion by Electrostatic Atomization Employing FEM and MPS Method

Analysis of the Disintegration of Charged Droplets Employing Boundary Element Method and Particle Method

Automatic Determination of Acceleration Factor Based on Residual and Functional in Shifted ICCG Method for 3-D Electromagnetic Field Analyses

Multiobjective Cuckoo Search Algorithm Based on Duffing's Oscillator Applied to Jiles-Atherton Vector Hysteresis Parameters Estimation

Communication-Avoiding Krylov Techniques on Graphic Processing Units

Fast Block-Solution of PEEC Equations

Magneto-Mechanical Dynamic System Modeling Using Computer Code Chaining and Field Projections

Algebraic Second Order Hodge Operator for Poisson's Equation

Analysis of a Permanent Magnet Machine for a High Power Density Taking Losses Into Consideration

Consistent Modeling of Periodic Metasurfaces With Bianisotropic Scatterers for Oblique TE-Polarized Plane Wave Excitation

Plasmon Mode Excitation on Graphene Layers via Obliquely-Incident Focused Wideband Pulses in Rigorous Time-Domain Algorithms

A Novel Adaptive Mesh Finite Element Method for Nonlinear Magnetic Field Analysis

Extension of Time-Domain Finite Element Method to Nonlinear Frequency-Sweeping Problems

Acceleration of Field Computation Involving HTS

Numerical Pattern Identification—Application to Inductive Testing Method With Automatic Classifiers

Coupled Field Modeling of Ferrofluid Heating in Tumor Tissue

Modeling Ferroresonance Phenomena With a Flux-Current Jiles-Atherton Hysteresis Approach

A Parallel FEM Matrix Assembly for Electro-Quasistatic Problems on GPGPU Systems

Spread-Out Overlapping Sources by Independent Component Analysis for Location Positioning

High-Order Error-Optimized FDTD Algorithm With GPU Implementation

Enhanced Thin-Wire Representation Models in a High-Order FDTD/TLM Method for Electrically Large Microwave Applications

Design of Least-Squares Time Integrators for Reliable FDTD Simulations

Accuracy-Adjustable Nonstandard LOD-FDTD Schemes for the Design of Carbon Nanotube Interconnects and Nanocomposite EMC Shields

Determination of the Electrical Conductivity Tensor of a CFRP Composite Using a 3-D Percolation Model

A Simplified Domain Structure Model Exhibiting the Pinning Field

Non-Conforming Sliding Interfaces for Relative Motion in 3D Finite Element Analysis of Electrical Machines by Magnetic Scalar Potential Formulation Without Cuts

Analysis of Transient Performance of Grounding System Considering Soil Ionization by Time Domain Method

Influence of PCB and Connections on the Electromagnetic Conducted Emissions for Electric or Hybrid Vehicle Application

Residual Based a Posteriori Error Estimators for Harmonic ${\bf A}/\varphi$ and ${\bf T}/\Omega$ Formulations in Eddy Current Problems

A Study on the Deperming of a Ferromagnetic Material by Using Preisach Model With $M\hbox {-}B$ Variables

An Improved Differential Evolution Algorithm Adopting $\lambda$ -Best Mutation Strategy for Global Optimization of Electromagnetic Devices