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Magnetics, IEEE Transactions on

Issue 2 • Date March 1993

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Displaying Results 1 - 25 of 187
  • Comments on "Analytical computation of magnetic vector potential from tetrahedral conductors" by G. Aiello et al

    Page(s): 1282 - 1283
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    The commenter presents a way to calculate the static magnetic vector potential and field of a polyhedral conductor with uniform current density that is simpler than the one given in the above-titled paper by G. Aiello et al. (ibid., vol.28, no.4, p.2045-50, Sept. 1992).<> View full abstract»

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  • Crack identification in metallic materials

    Page(s): 1861 - 1864
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    A novel formulation for the crack identification problem is proposed. In this formulation, cracks are regarded as the equivalent field or potential sources due to the discontinuity of conductivity at the crack positions. This means that crack identification problems are reduced to the inverse problems of searching for equivalent sources. The system equation of the inverse problems, derived by discretizing the integral equation, is successfully solved by the sampled pattern matching method. As a consequence, fairly good results are obtained even in the case of plural defect problems View full abstract»

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  • Method for determining relaxation factor for modified Newton-Raphson method

    Page(s): 1962 - 1965
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    In order to reduce the CPU time for the modified Newton-Raphson method which introduces a relaxation factor, the effect of the relaxation factor on the residual of the Galerkin method is examined in detail. It is shown that a relaxation factor which always provides convergent solutions can be easily searched. Various methods of searching for the relaxation factor to be used are compared View full abstract»

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  • Generation of intense magnetic fields with high homogeneity

    Page(s): 2064 - 2068
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    Various arrangements and geometries of air-core solenoids were investigated with a view to designing magnetic standards capable of producing magnetic fields in the range of 20-25 kG with a field homogeneity of 1 in 105 or better over a spherical volume of 1-in diameter. An analysis based on the method of zonal harmonics is presented. The effect of different coil geometries on field intensity and homogeneity is studied. In the case of the two-coil system, the effect of coil separation on field homogeneity is examined for various coil geometries. The method of adding compensating windings to the cylindrical solenoid for improving the field homogeneity is also investigated. The field homogeneity figures are computed for certain coil arrangements. The severe problem of cooling high-powered air-core solenoids is examined View full abstract»

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  • Self-sensing active magnetic levitation

    Page(s): 1276 - 1281
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    A magnetic levitation method that combines all the known advantages of active magnetic bearings in a self-sensing configuration is presented. The method realizes stable and well-damped levitation without any sensor hardware at the rotor. This is achieved by using the coil voltage of the magnetic bearing as system input (voltage instead of current amplifiers) and the current as system output. The resulting system is observable and controllable in the sense of control theory, allowing a magnetic bearing to be stabilized with a simple linear controller using current measurements alone. Several self-sensing bearings have been constructed. Their performance is comparable to systems with sensors, but hardware requirements and costs are substantially reduced. Experimental results are included View full abstract»

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  • An approach to modelling of magnetically excited forces in electrical machines

    Page(s): 2032 - 2035
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    A distinction is made between the vibrations produced by the fundamental current supplying the machine and the much smaller higher harmonic currents, with frequencies ranging into the kilocycles range. The small harmonic currents are emphasized. An appropriate mathematical modeling technique is presented. A mechanical model is selected based on modal analysis techniques. A method is developed for finding the driving force for each mode shape. This is illustrated with measurements on a permanent magnet machine. Experimental verifications of the model show the importance of a correct knowledge of eigenfrequencies and damping coefficients View full abstract»

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  • Use of the diffuse element method for electromagnetic field computation

    Page(s): 1475 - 1478
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    Application of the diffuse approximation to the posttreatment of electromagnetic field computations is investigated. This numerical method is very attractive since it does not require a mesh and leads to continuous estimates of the unknown function and its derivatives. The use of the diffuse element method to solve electromagnetic formulations is also considered. The implementation of the method into the finite element software FLUX3D is discussed. Numerical experiments are very encouraging View full abstract»

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  • An optimization procedure for electromagnetic confinement and levitation systems

    Page(s): 1758 - 1761
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    An automated optimal design method for the design of inductors for levitation or molten metal confinement is presented. It can modify the geometry of the inductor systems which produce the exciting electromagnetic field, until a specified performance is achieved. A number of constraints can be taken into account, related both to technical parameters, such as induction thickness and conductor cross-sections, and to designer choices aimed at directing the optimization process toward preferential solutions. Global and local equilibrium equations are used for levitation and confinement. The algorithm operates as a relaxation method, modifying the turn positions one at time, step by step. At every step the nonlinear inverse problem is linearized and solved as a least-square problem and the performance of the solution is checked. A second-order parabolic interpolation is used if the least-square solution is not satisfactory. Examples of applications are discussed View full abstract»

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  • Electromagnetic analysis of RFEC differential probes

    Page(s): 1849 - 1852
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    A differential probe (DP) for defect detection in the remote field eddy current (RFEC) technique is proposed. The analysis of the DP response to a sinusoidal steady-state excitation and a sinusoidal pulse excitation has been carried out by an equivalent network model, which allows easy modeling of axisymmetric defects. In the case of a sinusoidal steady-state excitation, the possibility of having clearer defect detection with respect to the conventional phase shift output, exploiting the phase shift between the induced signals in the two pickup coils, is shown. The differential output signal is equally sensitive to outer and inner defects, while the signal amplitude decreases as the distance between the coils increases. In the case of a sinusoidal pulse excitation, the differential configuration allows defect detection, but the transient nature of the induced voltages presents the phase shift effect, and the differential probe output amplitude is lower than the conventional one View full abstract»

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  • Magnetic field of an asymmetric ring head with an underlayer

    Page(s): 2069 - 2072
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    The fringe field of an asymmetric ring head with an underlayer is obtained using conformal mapping techniques. The Schwartz-Christoffel transformation is used to determine the magnetic field distribution around the head poles, and an analytical field equation is obtained. It is found that an asymmetric ring head with an underlayer is highly suitable for perpendicular recording View full abstract»

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  • A neural behavior estimation by the generalized correlative analysis

    Page(s): 1389 - 1394
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    The authors propose an approach to magnetoencephalogram (MEG) analysis. The problem of obtaining the current signal flow in the brain reduces to the inverse problem, the governing equation of which is written in an integral form. The authors propose a generalized correlative analysis method based on the Cauchy-Schwarz relation to solve the system equation derived from the governing equation. As a result, they have succeeded in estimating current signal flows in the human brain. A comparison between the conventional single dipole model and generalized corrective analyses has demonstrated that the proposed method is far superior to the conventional one View full abstract»

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  • On the nonlinear eddy current field coupled to the nonlinear heat transfer

    Page(s): 1546 - 1549
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    A semianalytical algorithm including the Fourier transform, the quasi-Newton iteration, and Galerkin's finite element method has been developed to solve the eddy current field problem and the coupled heat transfer problem in the presence of a metallic slab. The field dependence of the magnetic permeability and the temperature dependence of the electric and thermal conductivities of the heated slab are considered. The results are reasonable and consistent with the real operating conditions in industrial processing View full abstract»

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  • A non-isothermal device simulator for MOSFET analysis

    Page(s): 2047 - 2050
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    A nonisothermal semiconductor device simulator is developed which solves not only the conventional drift-diffusion equations but also the energy balance and heat flow equations to account for nonequilibrium transport phenomena and lattice temperature effects. The results are compared with the conventional drift-diffusion model. In order to reduce computation time, the heat flow equation is solved by an iterative scheme where this equation is solved only once during three cycles of the iteration loop. It is found that heat generation abruptly increases in the vicinity of the drain and the channel interface, and the lattice temperature shows a localized increase of about 20° in a MOSFET with a channel length of 0.3 μm, under a bias of VG= VD=3.0 V. The electron density distribution spread is broader than with that of the drift-diffusion model-that is, the channel depth becomes wider than in a conventional case View full abstract»

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  • A circuit approach to field computation

    Page(s): 1294 - 1300
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    Many design objectives can be expressed more directly in terms of circuit parameters, such as capacitance and inductance, than in terms of the field vectors E and B. A simple, although radical, change is suggested to provide a closer link between the field and circuit views. The electric potential φ and magnetic vector A are defined, in energy terms, as the primary field quantities, and they are visualized as measures of the capacitance and inductance, respectively. E and B become auxiliary symbols denoting derivatives, so that the customary roles of the potentials and field vectors are reversed. Some of the practical advantages of the change are examined and are illustrated by example View full abstract»

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  • Novel boundary element analysis for 3-D eddy current problems

    Page(s): 1520 - 1523
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    The authors consider a boundary-element method (BEM) using edge elements for 3-D eddy current problems. The eddy current region is formulated only by means of the electric field intensity E, while the free space is formulated only by the magnetic field intensity H. In each region, both unknown variables are expressed independently of each other. By physical consideration and the appropriate boundary-element discretization, these physical quantities can be connected on the interface with ease View full abstract»

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  • 3-D adaptive mesh refinement using nonconforming elements

    Page(s): 1479 - 1482
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    The conventional method of analysis for nonconforming mesh with 3-D brick elements is improved in order to avoid the error due to the multiapproximation of potential. The method of adaptive mesh refinement using the nonconforming elements is described, and it is applied to a nonlinear magnetostatic model. It is shown that the error in potential at a nonconforming node due to multiapproximation can be avoided by improving the conventional method of analysis for the nonconforming mesh. The accuracy of the flux density using the novel adaptive mesh refinement scheme is improved compared with that using an ordinary conforming mesh with the same number of unknowns. Although the proposed method needs about twice as much CPU time as the conventional method, the mesh can be created automatically View full abstract»

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  • A survey of numerical methods for transient eddy current problems

    Page(s): 1711 - 1716
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    The efficiencies of different time-stepping schemes and associated algebraic system solvers for transient eddy current computations are assessed. For 2-D problems, the direct methods nested dissection (ND) and quotient minimum degree (QMD) are shown to be preferable to the incomplete Cholesky conjugate-gradient (ICCG) method, provided enough memory is available. The multilevel preconditions (MP) method is highly efficient for magnetically homogeneous problems both in 2-D and 3-D. The efficiency of multilevel methods for inhomogeneous problems, although proven theoretically, needs further practical investigation View full abstract»

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  • Electromagnetic field computations by the hybrid FE-BE method using edge elements

    Page(s): 1487 - 1490
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    The authors present a hybrid finite-element (FE) and boundary-element (BE) method using edge elements for an open-boundary 3-D electromagnetic problem. In this method, the modified magnetic vector potential A* and the magnetic field intensity H are adopted as the physical quantities. The appropriate BE discretization described makes it easy to couple the BE region with the FE region through the transformation of unknown variables. Several practical applications of this method to 3-D eddy current problems are presented. The calculated values agree well with the experimental results View full abstract»

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  • Design of single-sided linear induction motor using the finite element method and SUMT

    Page(s): 1762 - 1766
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    The optimization of the design variables of a single-sided linear induction motor (SLIM) using the finite-element method (FEM) and the sequential unconstrained minimization technique (SUMT) is presented. Thrust is taken as an objective function in order to maximize thrust under a constant current drive, and seven independent design variables and nine constraints are chosen. As a result, pole pitch/airgap and pole pitch/aluminum depth for the best design are determined. Thrust is increased by 30% under a constant current of 12 A, so that the input current can be reduced to 10.5 A for necessary starting thrust because thrust is proportional to I2 View full abstract»

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  • Automatic mesh generation for h-p adaption

    Page(s): 1894 - 1897
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    In p-adaption, the density of degrees of freedom is controlled by adjusting the polynomial order of the finite elements. An ideal mesh is therefore as coarse as possible, subject to the constraint that the elements are not too thin. An algorithm capable of producing such meshes is described. The algorithm adds nodes to the mesh in a way which avoids thin triangles. It can also work in conjunction with a specified node density, and is therefore suitable for combined h-p adaptation. Sample meshes are presented for a dielectric waveguide structure, and an electric machine View full abstract»

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  • Computation of 3-D magnetostatic fields using a reduced scalar potential

    Page(s): 1329 - 1332
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    Some improvements to the finite element computation of static magnetic fields in three dimensions using a reduced magnetic scalar potential are presented. Methods are described for obtaining an edge element representation of the rotational part of the magnetic field from a given source current distribution. When the current distribution is not known in advance, a boundary value problem is set up in terms of a current vector potential. An edge element representation of the solution can be directly used in the subsequent magnetostatic calculation. The magnetic field in a DC arc furnace is calculated by first determining the current distribution in terms of a current vector potential. A 3-D problem involving a permanent magnet as well as a coil is solved, and the magnetic field in some points is compared with measurement results View full abstract»

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  • Another approach to the electromagnetic deceleration

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    An alternative method is suggested for solving the differential equation that approximates the electromagnetic deceleration of metallic spheres. Specifically, the author suggests an alternative method to the Runge-Kutta-Nystrom numerical solution which may be more convenient in some cases View full abstract»

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  • The calculation of 3D high-frequency electromagnetic fields during induction heating using the BEM

    Page(s): 1566 - 1569
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    A numerical 3-D-calculation method for the simulation of the electromagnetic field for different applications of high-frequency induction heating is developed. The calculation program uses the boundary-element method (BEM) and runs on an efficient personal computer. The setup to be considered is divided into groups of bodies with specific material properties which allow the formulation of simplified conditional equations for the electric vector potential at the surfaces of the setup components. Some examples of numerically calculated high-frequency current distributions indicate the efficiency of the program developed View full abstract»

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  • An electromagnetic inverse problem solver for radar: aircraft rotation and tilt measurement

    Page(s): 1767 - 1770
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    A Doppler radar is used to obtain the velocity, altitude, and distance of an aircraft with respect to the radar coordinates. It is shown that the reflected electromagnetic fields picked up by the receiver antenna also contain information on the rotation angle and tilt angle of the aircraft, which could be obtained using a maximum-likelihood estimation algorithm. The electromagnetic signal processing unit estimates the angles of rotation and tilt and the radius of the target modeled as a cylinder using the scattered magnetic field. Specific results showing the application of the estimator are given View full abstract»

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  • Modified surface impedance boundary conditions for 3D eddy current problems

    Page(s): 1826 - 1829
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    The concept of modified surface impedance boundary conditions (IBCs) is extended to three-dimensional eddy current problems. Approximate expressions for the modified surface impedances near sharp edges and corners are given. The validity of the expressions is examined by solving test problems using the method of fundamental solutions. The results given by the approximate expressions are compared with the true values of surface impedances obtained from the full region solution (i.e., without the use of IBCs), and those agree well with the latter View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology