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Magnetics, IEEE Transactions on

Issue 4 • Date April 2008

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Displaying Results 1 - 24 of 24
  • [Front cover]

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

    Page(s): C2
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  • Table of contents

    Page(s): 429 - 430
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  • Magnetic Anisotropy Dispersion in FeCo Films

    Page(s): 431 - 434
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (221 KB) |  | HTML iconHTML  

    We report on our study of magnetic and nonmagnetic parameters such as coercivity, anisotropy , magnetic dispersion, and stress on FeCo films of various thicknesses from 25 A to 500 A . We used 10 A Ru or NiFe seed layers for two sets of FeCo films. All films showed so-called hard-axis coercivity rocking, i.e., the hard-axis coercivity exhibits two local minima close to the nominal hard axis. Magnetic properties and stress change dramatically with FeCo thickness, but with little difference between the two types of seed materials. We found a correlation between the angular separation of the two local coercivity minima and easy-axis coercivity. The results stress the need to differentiate between two levels of dispersion, one at the microscopic and the other at the macroscopic level. View full abstract»

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  • Complex Magnetic Permeability and Dielectric Permittivity of Ferrites in Millimeter Waves

    Page(s): 435 - 437
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    We report a first-time study of complex magnetic permeability and dielectric permittivity of 99% pure powdered barium cobalt ferrite (Ba2Co2Fe12O22) and pure solid barium hexaferrite ceramics (BaFe12O19) in a broadband millimeter-wave frequency range. We performed transmittance measurements using a free-space quasi-optical millimeter-wave spectrometer, equipped with a set of high-power backward-wave oscillators as sources of tunable coherent radiation at each Q-, V-, and W-frequency band. We calculated frequency dependences of complex permittivity for both types of ferrites using analysis of recorded high-precision transmittance spectra and obtained frequency dependences of the magnetic permeability from Schlomann's equation for partially magnetized ferrites. View full abstract»

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  • Determination of Complex Permeability of Silicon Steel for Use in High-Frequency Modeling of Power Transformers

    Page(s): 438 - 444
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (314 KB) |  | HTML iconHTML  

    Information about frequency dependence of complex permeability of silicon steel is a vital input parameter in calculations of transformer winding inductance used for modeling high-frequency behavior (100 Hz-1 MHz). We present two ways of determining small signal complex permeability spectra in frequency domain and compare and discuss the results. The first method is based on an optimization procedure, in which inductance of a winding is measured and calculated by analytical formulas and finite-element modeling. The second method makes use of a single sheet tester. We show that the magnitude of effective permeability of the silicon steel laminations remains significant up to about 100 kHz. We also report on the effect of magnetic viscosity on complex permeability. View full abstract»

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  • Magnetic Force Calculation Between Thin Coaxial Circular Coils in Air

    Page(s): 445 - 452
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (235 KB) |  | HTML iconHTML  

    We present new and fast procedures for calculating magnetic forces between thin coaxial circular coaxial coils in air. The results are expressed in semianalytical form in terms of the complete elliptical integrals of the first and second kind, Heuman's Lambda function, and a term that must be solved numerically. These expressions are accurate and simple to use for several practical applications. We also describe a comparative method based on the filament technique. We discuss the computational cost and the accuracy of two methods and compare them with already published data. Results obtained by our two approaches are in excellent agreement with each other. They can be used in industrial electromagnetic applications such as electrodynamic levitation systems, linear induction launchers, linear actuators, and coil guns. View full abstract»

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  • Noncoaxial Inductance Calculations Without the Vector Potential for Axisymmetric Coils and Planar Coils

    Page(s): 453 - 462
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (605 KB) |  | HTML iconHTML  

    This paper presents an exact method for calculating the mutual inductance between a general axisymmetric coil and a second planar coil consisting of either a disk coil or a planar loop of essentially arbitrary shape. The approach is based directly on the magnetic field rather than the vector potential . The paper gives detailed results for two circular loops, a circular loop and an elliptic loop, and a circular loop and an annular disk coil. The method can be extended to cover the cases where all these loops and coils are extruded in the axial direction to give the corresponding solenoids. The method is also applicable to calculations for nuclear radiation detectors. View full abstract»

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  • Plane Wave Model for the Electromagnetic Behavior of SiFe Alloys

    Page(s): 463 - 472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (833 KB) |  | HTML iconHTML  

    We present a model that evaluates in the frequency domain the magnetic behavior of laminated SiFe alloys caused by a magnetic field imposed at the material edge. The model is based on plane wave theory describing how an electromagnetic wave penetrates a material. As the nonlinear material with hysteresis can cause harmonic frequency components of the field and induction inside the material, the model takes into account several harmonics simultaneously by applying the harmonic balance principle. The plane wave model is solved iteratively with a classical Preisach model as constitutive law. We compare the model with a time domain finite-element model and with measurements on a ring core and find a good correspondence. The CPU time is low if only a few harmonics are considered and if the nonlinearity of the material is rather mild. View full abstract»

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  • Analysis of the Convergence of the Fixed-Point Method Used for Solving Nonlinear Rotational Magnetic Field Problems

    Page(s): 473 - 478
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (385 KB) |  | HTML iconHTML  

    The fixed-point method has not been widely used for solving nonlinear electromagnetic field problems, except for the hysteretic problem, for which it is the prevailing method. The method converges stably with a slow rate, exactly opposite to the Newton-Raphson method, which can easily suffer from instability, but which, if it converges, does so remarkably fast. In this paper, we analyze the convergence of the fixed-point method, examine the barriers behind the slow convergence, and show how to overcome them. The analysis has proved fruitful and provided sound techniques for speeding up the convergence of the fixed-point method. We have given special attention to the 2D and 3D problems and devised a general formula for the fastest convergence. We used a time-stepping finite-element formulation to test the convergence of the fixed-point method and compare it to the Newton-Raphson method. We investigated certain factors including the time-step size in magnetic field simulations of two rotating electrical machines. View full abstract»

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  • Dipolar Interaction Between Amorphous Microwires

    Page(s): 479 - 484
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    We present a model for the description of the magnetostatic interaction between two glass-coated amorphous microwires with positive magnetostriction. We report the results of dipolar field calculations based on this model as well as results of measurements on microwires with their ends separated. We also calculated the switching field variation with fluctuations in microwire dimensions. Experimental results show an insignificant dipolar interaction between two microwires placed next to each other, provided that their ends are bent and separated at a certain distance. Calculated results are in good agreement with the experimental ones. View full abstract»

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  • Methods of Assembling Large Magnetic Blocks From NdFeB Magnets With a High Value of ({\rm BH})_{\max } and Their Influence on the Magnetic Induction Reached in an Air Gap of a Magnetic Circuit

    Page(s): 485 - 491
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB) |  | HTML iconHTML  

    We have investigated methods of assembling large magnetic blocks from NdFeB magnets with a high value of the maximum energy product, and inserting these blocks into magnetic circuits. We found that the magnetic induction in the middle of an air gap between large opposing magnetic blocks in a closed magnetic circuit depends, in addition to other parameters, on the basic method of assembling these magnetic blocks. We compared two methods of assembly, differing in the direction in which magnetic plates approach each other. When being moved toward each other during the assembly by Method 1, magnets first repel each other. In the case of low coercivity of the magnet material, this results in their partial demagnetization. However, by using the new Method 2, where the magnets keep attracting throughout their movement together, it is possible to eliminate partial demagnetization. View full abstract»

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  • Influence of High Temperature Superconducting Transformer Geometry on Leakage Magnetic Field

    Page(s): 492 - 496
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1064 KB) |  | HTML iconHTML  

    Leakage magnetic fields in high temperature superconducting (HTS) transformer windings reduce the critical current and increase the ac losses in HTS tapes. Moreover, because of the anisotropic properties of the HTS tapes, the influence of the radial component of the leakage field on critical current and ac losses is much stronger than that of the axial one. For these reasons, leakage magnetic fields must be carefully considered in HTS transformer design. In this paper, we report a study of the influence of the core structure and the winding configuration on the leakage field by the finite-element method (FEM), and offer some suggestions for reducing the maximal radial component of leakage field to make the HTS transformer more efficient. View full abstract»

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  • A Miniature Short Stroke Linear Actuator—Design and Analysis

    Page(s): 497 - 504
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    We report a newly developed miniature short stroke tubular linear permanent-magnet actuator for robotic applications. Compared to a rotary-to-linear mechanism, the linear actuator has the advantages of efficiency, thrust control, and compact size in generating linear motion. We optimized the electromagnetic force of the actuator analytically by selecting appropriate dimensions and then predicted the force produced by the winding currents by the finite-element method under the brushless dc excitation scheme. We analyzed the actuation performance by dynamic modeling of the actuator. We constructed and tested a prototype on a specially designed test bench to verify the design. Finally, we analyzed and measured the end effect on the magnetic force due to the limited length of the stator core and translator. View full abstract»

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  • Noninvasive Procedure for Improving Efficiency of Three-Phase Induction Motors

    Page(s): 505 - 515
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (350 KB) |  | HTML iconHTML  

    In developing countries, three-phase squirrel cage induction motors, even though with load equal to their name plate rating, may operate at low efficiencies. This may be because their winding parameters are not optimized for lower running cost. To ascertain the cause, it is necessary to know the stator winding data and compare it with the results of the design. If a deviation exists, the winding is improper. However, it may be possible to improve efficiency by rewinding the motor. We propose a noninvasive procedure to determine the following winding data: number of parallel circuits in a phase, number of turns per coil, and conductor area. The procedure includes a new iterative algorithm for determining these winding data. We discuss experimental investigations to validate the proposed procedure and to test its effectiveness in energy conservation. We outline the usefulness of the procedure for designers and the advantages it offers to service providers and educational institutions. View full abstract»

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  • Characterization of Surface-Breaking Cracks Using One Tangential Component of Magnetic Leakage Field Measurements

    Page(s): 516 - 524
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1183 KB) |  | HTML iconHTML  

    We propose a procedure for full characterization of rectangular surface-breaking cracks based on measurements of only one tangential component of the magnetic field with the magnetic flux leakage (MFL) technique. The parameters of interest include orientation, length, and depth of the cracks. We assume that the length and the depth of the investigated cracks are much larger than the crack width, so that the variation of the MFL response with respect to the width is negligible. Our procedure employs fast direct methods that provide reliable estimation of the crack parameters in three separate consecutive steps. We propose denoising and correction techniques as well. We confirmed the accuracy of the methods by simulations based on the finite-element method (FEM) as well as by experimental MFL observations. A procedure is proposed for full characterization of rectangular surface breaking cracks based on measurements of only one tangential component of the magnetic field with the magnetic flux leakage (MFL) technique. The parameters of interest include orientation, length and depth of the cracks. We assume that the length and the depth of the investigated cracks are much larger than the crack width such that the variation of the MFL response with respect to the width is negligible. The proposed procedure employs fast direct methods which provide reliable estimation of the crack parameters in three separate consecutive steps. De-noising and correction techniques are proposed as well. The accuracy of the proposed estimation methods is examined via simulations based on the finite element method (FEM) as well as experimental MFL data. View full abstract»

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  • Shock Resistance of a Disk-Drive Assembly Using Piezoelectric Actuators With Passive Damping

    Page(s): 525 - 532
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    Current dual-stage actuator design uses piezoelectric patches only, without passive damping. In this paper, we propose a dual-stage servo system using enhanced active-passive hybrid piezoelectric actuators. Because they incorporate passive damping, the proposed actuators will improve the existing dual-stage actuators, giving them higher precision and better shock resistance. We report finite-element analyses of different types of piezoelectric actuators in a disk arm assembly under external shock and vibration. We modeled the viscoelastic damping layers in the hybrid actuators with the Prony series, whose parameters we determined from the dynamic frequency data of a nomograph. In the analyses, a shock impulse (175 g, 1 ms half sine) and a vibration impulse (350 g and 1 ms full sine) are applied at one end of the base, while the other end of the base is fixed. We evaluated and compared the responses of the disk arm assembly with different configurations of the piezoelectric actuators. The simulation results show that the enhanced active-passive hybrid actuator design would reduce the residual in-plane vibration induced during the shock, resist liftoff motion, and reduce the impact damage when the head slaps. View full abstract»

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  • Two-Dimensional Equalization/Detection for Patterned Media Storage

    Page(s): 533 - 539
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (635 KB) |  | HTML iconHTML  

    Although patterned media storage (PMS) is a promising candidate for ultrahigh-capacity magnetic data storage, as the capacity of PMS increases, the bit error rate (BER) performance of the system is degraded by increased two-dimensional intersymbol interference (2D-ISI), which results from intertrack interference (ITI), intersymbol interference (ISI), and noise. To improve the system performance under these adverse effects and to increase the capacity, in this paper, we propose to use and/or devise two-dimensional equalization/detection techniques: iterative decision feedback detection (IDFD) and two-dimensional generalized partial response equalization, which is optimized in minimum mean square error (MMSE), followed by one-dimensional Viterbi algorithm (2D-GPR/1D-VA). We evaluate the performance of the proposed methods by using numerical experiments under different amounts of 2D-ISI and noise. Simulation results suggest that under high storage density, the performance of the IDFD is improved by using more iterations and that under the same computational load, 2D-GPR/1D-VA performs better than IDFD. 2D-GPR/1D-VA, therefore, is a good candidate for ultrahigh-capacity PMS. View full abstract»

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  • Modified Damping Scheduling Proximate Time Optimal Servomechanism for Improvements in Short Strokes in Hard Disk Drives

    Page(s): 540 - 546
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (683 KB) |  | HTML iconHTML  

    Proximate time-optimal servomechanism (PTOS) has been widely used as a point-to-point motion control algorithm in many control systems, especially in hard disk drives, because of its simplicity and good performance. A great deal of research for improving PTOS has been reported; however, most of it is complex or needs a time-consuming tuning process. Damping scheduling PTOS (DSPTOS), which maintained the simplicity of PTOS and showed faster settling in long strokes by scheduling a closed-loop damping coefficient, was proposed previously. In this paper, we propose a modified DSPTOS which can schedule a closed-loop damping coefficient not only in long strokes, but also in short strokes. The proposed algorithm improves seek and settling performances significantly in short strokes. The effectiveness of the proposed algorithm is verified through simulations and real-time experiments. Consequently, we achieved over a 25% settling time improvement for a short stroke (10 tracks). View full abstract»

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  • A New Data Allocation Method for Parallel Probe-Based Storage Devices

    Page(s): 547 - 554
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (773 KB) |  | HTML iconHTML  

    We present a new data allocation method for probe-based storage devices that use multiple, simultaneously accessed parallel data fields. Our method uses blocks of data of unequal length for allocating a sector in the various storage fields. The amount of data stored in each field depends on the sector's offset from the beginning of the allocation round and on the storage field used. Numerical results demonstrate the storage efficiency improvement that is achieved by the proposed method. We show that this method can be applied to atomic force microscopy-based probe storage devices. View full abstract»

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    Page(s): 555
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    Page(s): 556
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  • IEEE Magnetics Society Information

    Page(s): C3
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    Page(s): C4
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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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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology