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Magnetics, IEEE Transactions on

Issue 5 • Date May 2007

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Displaying Results 1 - 25 of 32
  • [Front cover]

    Page(s): C1
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    Freely Available from IEEE
  • IEEE Transactions on Magnetics publication information

    Page(s): C2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 1869 - 1870
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  • Surface and Interior Magnetic Domain Structures of \langle 110 \rangle Oriented Tb–Dy–Fe Alloy Rods

    Page(s): 1871 - 1874
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB) |  | HTML iconHTML  

    We investigated the surface and interior magnetic domains by using magnetic force microscopy for two types of Tb0.3Dy0.7 Fe1.95 crystal growing along the lang110rang direction: 1) crystals annealed at 673 K for 2 h in higher vacuum (5times10-5 Pa) and 2) crystals annealed at 723 K for 2 h in lower vacuum (5times10-3 Pa). For the former, we observed fine stripe-like domains at the surface. For the latter, we observed the interior domains of the specimen; these were also stripe-like, but with larger average width than the surface domains. X-ray diffraction patterns indicate the formation of a thin iron layer in the surface of the specimens annealed in the lower vacuum. The iron layer, as a "capping" layer, actually acts as a shielding layer for the stray fields emerging from the interior domains underneath, resulting in the wide interior domains View full abstract»

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  • Performance and Stability of Soft Magnetic Elements for Electronic Article Surveillance

    Page(s): 1875 - 1879
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    A simple figure of merit is proposed to compare the performance of soft magnetic elements for electronic article surveillance (EAS) applications. Annealing experiments were carried out to quantify the evolution of soft magnetic properties of amorphous-metal and Permalloy ribbons used in the library EAS industry. By fitting the kinetics of coercivity change to a simple model based on a uniformly distributed range of activation energies, the room-temperature kinetics of the amorphous elements is predicted View full abstract»

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  • Experimental Determination of the Nonuniform Shape-Induced Anisotropy Field in Thin Ni–Fe Films

    Page(s): 1880 - 1883
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (179 KB) |  | HTML iconHTML  

    We have determined the nonuniform distribution of the shape-induced magnetic anisotropy field for patterned thin films of Ni-Fe. To do this, we used integrated microstrip structures with different widths on identically patterned Ni-Fe cores to act as probes of the internal magnetic field. We verified the accuracy of the field profiles by comparing them with M-H loop measurements of the magnetic films View full abstract»

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  • Precision and Accuracy Study on Measurement of Soft Magnetic Properties Using DC Hysteresigraphs

    Page(s): 1884 - 1887
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    We report on an interlaboratory study on the precision and accuracy of determining dc soft magnetic properties, under the auspices of ASTM Committee A06 on Magnetic Properties. For certain quantities, the significant differences in the between-laboratory reproducibility results for high-permeability materials indicate that there is a need for improvement in the equipment and software procedures of measurement systems View full abstract»

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  • Analysis of Power Magnetic Components With Nonlinear Static Hysteresis: Proper Orthogonal Decomposition and Model Reduction

    Page(s): 1888 - 1897
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1122 KB) |  | HTML iconHTML  

    We applied the proper orthogonal decomposition (POD) method to extract reduced-order models to efficiently solve nonlinear electromagnetic problems governed by Maxwell's equations with nonlinear hysteresis at low frequency (10 kHz), called static hysteresis, discretized by a finite-element method. We used a new domain-wall-motion hysteresis model for Power MAgnetic Components (POMACs) in the finite-element potential formulation via an efficient implicit-inverse model calculation. We propose a rational method for the selection of snapshots employed in the POD, used in conjunction with a fixed-point method for the solution of nonlinear POMAC problems. The reduced simulation time and great flexibility of the reduced-order models, as applied to nonlinear POMAC systems, suggest that the procedure can be applied to other electromagnetic problems with nonlinear hysteresis View full abstract»

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  • Halbach Cylinders With Improved Field Homogeneity and Tailored Gradient Fields

    Page(s): 1898 - 1902
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    We show that designs based on Halbach cylinders with a linearly increasing inner bore radius can improve the magnetic field homogeneity or can be used to tailor the spatial variation of the field gradient. We compare our first design to those based on existing methods of increasing the field homogeneity and show that it achieves a twofold improvement in the homogeneity over the next best design. We also present a second design, which can achieve a region of constant field gradient, and a third design, which can produce a region in which the product of the field and field gradient is constant View full abstract»

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  • Designing Static Fields for Unilateral Magnetic Resonance by a Scalar Potential Approach

    Page(s): 1903 - 1911
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (458 KB) |  | HTML iconHTML  

    We present a method for designing single-sided magnets suitable for unilateral magnetic resonance (UMR) measurements. The method uses metal pole pieces to shape the field from permanent magnets in a target region. The pole pieces are shaped according to solutions to Laplace's equation, and can be designed using a combination of analytical methods and numerical optimization. The design leads to analytical expressions for the pole piece shapes and magnetic field. Here, we develop the method in Cartesian, polar, and spherical coordinates, and discuss the merits of each system. Finite magnet size has a substantial effect on the field quality in many cases, according to our simulations. We found that in order to achieve a compact magnet in which the static field closely matches that specified, a full 3-D design approach is necessary. A magnet designed by our method produces a static field with a constant gradient over a region 2 cm in diameter and 2 mm thick. This leads to a compact cylindrical magnet just over 11 cm in diameter, topped with a single metal pole piece. The design is validated through simulation. The simulated field is found to agree closely with that specified analytically through the design procedure View full abstract»

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  • Simple Frequency Domain Model for Hysteresis and Eddy Currents in Cylindrical and Parallelepipedal Cores

    Page(s): 1912 - 1919
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    We develop a simple and approximate model for hysteresis and eddy currents in cylindrical magnetic cores. The model characterizes the core by the magnetic properties of its material (mu,psi0, and sigma) and its geometry (perimeter and area of cross section and core length). The model is compatible with common electrical simulators, such as spice, and allows a fast and approximate computation of both hysteresis and eddy-current power losses, impedance, flux, and field. We extended the model to parallelepipedal geometries, and we checked it by comparison to previous models and by experimentation View full abstract»

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  • A QR Accelerated Volume-to-Surface Boundary Condition for the Finite-Element Solution of Eddy-Current Problems

    Page(s): 1920 - 1933
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    We are concerned with the solution of time-dependent electromagnetic eddy-current problems using a finite-element formulation on three-dimensional unstructured meshes. We allow for multiple conducting regions, and our goal is to develop an efficient computational method that does not require a computational mesh of the air/vacuum regions. This requires a sophisticated global boundary condition specifying the total fields on the conductor boundaries. To meet this requirement, we propose a volume-to-surface boundary condition based on the Biot-Savart law. We found the Biot-Savart approach to be very accurate. In addition, this approach can be accelerated via a low-rank QR approximation of the discretized Biot-Savart law View full abstract»

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  • Planes of Continuous-Wave Oscillations From an Electron Nanocontact Spin-Transfer Device

    Page(s): 1934 - 1940
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (414 KB) |  | HTML iconHTML  

    We have found that the frequencies of continuous-wave (CW) microwave oscillations in nanocontact spin-transfer (ST) devices occur in well-defined planes of frequencies, as a function of the dc current bias, the direction of the magnetic field, and the magnitude of the magnetic field. The frequency, f, of these technologically significant peaks for each magnetic field direction is described empirically by the equation of a plane, f=a|Boarr|+bI+c, where |Boarr| is the magnitude of the magnetic field, I is the dc bias current, and a, b, and c are constants of the plane. The primary frequency plane described by this equation is accompanied by a smaller secondary plane. The empirical equation describing the primary plane serves as a guide for efficiently locating CW oscillations within the independent variable space View full abstract»

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  • Filter Capacity Predictions for the Capture of Magnetic Microparticles by High-Gradient Magnetic Separation

    Page(s): 1941 - 1949
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB) |  | HTML iconHTML  

    We present experimental and theoretical methods to predict maximum and working filter capacities for the capture of superparamagnetic microparticles through high-gradient magnetic separation (HGMS). For this, we employed various combinations of nine different HGMS filter matrices and two types of superparamagnetic microparticles. By calculating the separated particle mass per filter mesh area, we clearly demonstrated the influences of wire diameter and wire mesh spacing on the particle build-up density. Here, we introduce a simple experimental method for estimating average build-up densities in HGMS. Together with known physical parameters of the filter matrix and the background field, such average build-up densities allow good predictions of the operational working filter capacities View full abstract»

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  • Motor Core Iron Loss Analysis Evaluating Shrink Fitting and Stamping by Finite-Element Method

    Page(s): 1950 - 1954
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2299 KB) |  | HTML iconHTML  

    We describe a method to analyze the effects of shrink fitting and stamping on the mechanical stress distribution and iron loss in motor cores. Shrink fitting and stamping are important processes in manufacture of motor cores from electrical steel. The mechanical stress distribution is evaluated by a structural finite-element method, and the iron loss is evaluated by combined analysis of the electromagnetic field (by a finite-element method) and mechanical stress. The method clearly shows that the iron loss becomes larger as the width of the shrink fit increases, an effect borne out by experiment. In regard to the effect of stamping, calculation results again agree well with experimental data View full abstract»

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  • Analytical Modeling of a Permanent-Magnet Synchronous Machine in a Flywheel

    Page(s): 1955 - 1967
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    We develop an analytical model for a radial-flux external-rotor permanent-magnet synchronous machine (PMSM) without slots in the stator iron and with a shielding cylinder. The machine is part of an energy storage flywheel, to be used as the peak-power unit in a hybrid electric passenger bus. To reduce the induced no-load losses due to the high rotational speed of the flywheel, the slots in the stator are made not of iron but of a nonmagnetic plastic material. This results in an air gap winding with a stator yoke consisting of stacked circular laminations. The analytical model includes the effect of the winding distribution on the field, the fact that it is in the air gap, and the effect of the eddy-current reaction field of the shielding cylinder. The two-dimensional magnetic field is solved in six defined machine layers and useful machine quantities are derived directly from it, leading to the machine voltage equation. We built a prototype flywheel machine. The locked-rotor machine resistance and inductance predicted by the analytical model was compared with the experimentally determined values. The values showed good agreement, thereby validating the analytical model of the machine View full abstract»

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  • Minimizing Thrust Fluctuation in Moving-Magnet Permanent-Magnet Brushless Linear DC Motors

    Page(s): 1968 - 1972
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    We present the results of our research on the factors that cause thrust fluctuation in moving-magnet-type permanent-magnet brushless DC linear motors (PMBLDCLM). We combined Fourier transforms and finite-element models to obtain the power spectra of three components of the detent force. We developed a method of optimizing magnet width to minimize the detent force on the basis of harmonic analysis. To verify this method, we designed several motor models with different magnet widths and analyzed them by finite-element methods. The calculations and experimental results prove that thrust fluctuation of the motor can be effectively reduced with our method View full abstract»

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  • Pulse Shape Improvement in Core-Type High-Voltage Pulse Transformers With Auxiliary Windings

    Page(s): 1973 - 1982
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    High-voltage pulsed power technologies are rapidly emerging as a key to efficient and flexible use of electrical power for many industrial applications. One of the most important elements in high-voltage pulse-generating circuit technology is the transformer, generally used to further increase the pulse output voltage level. However, its nonideal behavior has significant influence on the output pulse shape. The most attractive winding configuration for high-voltage, the core-type transformer with primary and secondary on different core legs, is seldom used in pulsed applications, because of its weak magnetic coupling between windings, which would result in a slow-rising output voltage pulse. This paper shows that auxiliary windings, suitably positioned and connected, provide a dramatic improvement in the pulse rise time in core-type high-voltage pulse transformers. The paper derives a mathematical model and uses it to describe the observed behavior of the transformer with auxiliary windings. It discusses experimental results, obtained from a high-voltage test transformer associated with a high-voltage pulse generating circuit, and the simulation results obtained from the numerical evaluation of the developed differential equations implemented in Matlab and taking into account the measured transformer parameters View full abstract»

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  • Computation of Parameters of Power Transformer Windings for Use in Frequency Response Analysis

    Page(s): 1983 - 1990
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2931 KB) |  | HTML iconHTML  

    We present a 3-D model for calculating magnetic fields in a power transformer and the effective parameters (inductance and resistance) of its windings. The transformer is representative of large transformers with power ratings ranging from hundreds of kilovolt amperes to hundreds of megavolt amperes. The model accounts for anisotropic frequency-dependent properties of the laminated transformer core and eddy currents in the steel sheets. We discuss the results of the calculations performed in the frequency range 10 Hz-10 MHz, and show that the largest variations of both the magnetic field and parameters of the windings take place at frequencies below ~10 kHz and, at frequencies higher than 1 MHz, the magnetic core does not significantly affect the variation of the effective parameters View full abstract»

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  • Evaluation of Surface Impedance Models for Axisymmetric Eddy-Current Fields

    Page(s): 1991 - 2000
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB) |  | HTML iconHTML  

    We have investigated the range of validity of the perfect electric conductor and of the standard Rytov-Leontovich impedance boundary condition models for the analysis of axisymmetric eddy-current problems. Using these models, we derived approximate expressions for the magnetic vector potential, field quantities, Joule losses, and forces for conducting spheroids placed in external nonuniform magnetic fields produced by coaxial circular turns carrying currents varying sinusoidally with time. We compared our numerical results for the magnetic field intensity at the conductor surface, power losses, and forces (for both prolate and oblate spheroidally shaped conducting objects) with the results from analytical expressions obtained by applying the exact boundary conditions. While the simpler perfect conductor model can be employed only when the electromagnetic depth of penetration is much smaller than the smallest local radius of curvature, the results obtained by using the standard surface impedance model for conducting prolate and oblate spheroids of various axial ratios are in good agreement with the exact results for skin depths of about 1/5 of the semi-minor axis for electromagnetic forces and for skin depths less than 1/20 of the semi-minor axis for Joule losses View full abstract»

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  • Numerical Modeling of Iron Yoke Levitation Using the Pinning Effect of High-Temperature Superconductors

    Page(s): 2001 - 2008
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    A ferromagnetic material can be levitated by the pinning effect of a field-cooled superconductor. This paper presents two methods for modeling this effect: 1) an approximate calculation to determine the relationship between attractive force and air gap at both room temperature and superconductive temperature (77 K) and 2) a novel way of modeling the pinning effect by a finite-element method (FEM). A comparison of analytical and FEM results with experimental results verifies the validity of the methods. The methods can be used to estimate the system's behavior when the cylindrical yoke is replaced by a ring yoke. The stiffness of the system will increase by 70% (to 5.3 N/mm) when a ring yoke with the same surface area is used instead of a cylindrical yoke View full abstract»

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  • Intelligent Adaptive Backstepping Control System for Magnetic Levitation Apparatus

    Page(s): 2009 - 2018
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    We propose an intelligent adaptive backstepping control system using a recurrent neural network (RNN) to control the mover position of a magnetic levitation apparatus to compensate for uncertainties, including friction force. First, we derive a dynamic model of the magnetic levitation apparatus. Then, we suggest an adaptive backstepping approach to compensate disturbances, including the friction force, occurring in the motion control system. To further increase the robustness of the magnetic levitation apparatus, we propose an RNN estimator for the required lumped uncertainty in the adaptive backstepping control system. We further propose an online parameter training methodology, derived by the gradient descent method, to increase the learning capability of the RNN. The effectiveness of the proposed control scheme has been verified by experiment. With the proposed adaptive backstepping control system using RNN, the mover position of the magnetic levitation apparatus possesses the advantages of good transient control performance and robustness to uncertainties for the tracking of periodic trajectories View full abstract»

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  • Design and Load/Unload Performance of Hard Disk Drive Suspension Integrated With Shape Memory Alloy Thin Film

    Page(s): 2019 - 2024
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (729 KB) |  | HTML iconHTML  

    We propose a new load/unload (L/UL) suspension featuring shape memory alloy (SMA) thin film and demonstrate its effectiveness through the L/UL simulation. We estimated the mechanical properties of the SMA with respect to the material phases by experiment and designed the proposed suspension by considering the vibration modes related to the L/UL performance. In order to effectively verify the effectiveness of the proposed suspension, we designed the suspension to have similar L/UL performance to that obtained from the conventional suspension when the SMA film is not activated. After analyzing the L/UL design parameters of the proposed suspension when the SMA is activated, we examine the relative performance of the conventional and proposed suspensions by L/UL simulation by comparing the vibration motions of the slider and the minimum gap size between the disk and slider View full abstract»

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  • Off-Track and Azimuth Angle Effects in Perpendicular Replay

    Page(s): 2025 - 2028
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    We investigated the effects of transition curvature on T50 and Vp-p for a shielded giant magnetoresistive (GMR) element reading a single, isolated transition recorded on a perpendicular medium in the presence of a soft magnetic underlayer. We considered displacement and rotation of the read head relative to the recorded track and a range of read head geometries. The curvature of the transition adversely affects T50, which also increases with azimuth angle. Both T50 and Vp-p decrease as either the GMR element or the element-side shield spacing is reduced View full abstract»

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  • Nonrepeatable Run-out Rejection Using Online Iterative Control for High-Density Data Storage

    Page(s): 2029 - 2037
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    The spectra of disturbances and noises affecting precise servo positioning for ultrahigh-density storage in future hard disk drives are time-varying and remain unknown. In this paper, we propose an online iterative control algorithm that sets the measured position error signal (PES) into the servo system to achieve high track densities by minimizing the square of the H2-norm of the transfer function from nonrepeatable run-out (NRRO) disturbances to the true PES. It is not necessary to solve any algebraic Riccati equations and linear matrix inequalities. The algorithm constructs an online repeatable run-out estimator to extract NRRO components for gradient estimates, thereby preventing the controller parameters from being trapped in a local minima. Experimental results on a PC-based servo system for a spinstand show an improvement of 22% in 3sigma NRRO and suppression of baseline NRRO spectrum 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