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Magnetics, IEEE Transactions on

Issue 6 • Date Nov. 2002

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Displaying Results 1 - 20 of 20
  • IEEE Magnetics Society Distinguished Lecturers for 2003

    Page(s): 3574 - 3576
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  • In memoriam Amikam Aharoni [1929-2002]

    Page(s): 3577 - 3578
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  • Author index

    Page(s): 3699 - 3731
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  • Subject index

    Page(s): 3731 - 3824
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  • Integral analysis of a magnetic field for an arbitrary geometry coil with rectangular cross section

    Page(s): 3589 - 3593
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (349 KB) |  | HTML iconHTML  

    The integral method can effectively analyze magnetic fields, but the traditional integral method can analyze only coils with regular geometries. Therefore, a new integral method was developed to calculate the three-dimensional (3-D) magnetic field created by an arbitrary geometry coil with a rectangular cross section using the local coordinate method and a 3-D coordinate transformation. However, when the field points are on the surface of the coil or the basic segment is the right angle trapezoidal prism, singularities occur that make the numerical analysis of the magnetic field more difficult. Thus, we present here some mathematical methods to eliminate the singularities to allow accurate numerical analysis of the magnetic field. We validate the integral method by comparing it with the analytical solutions for regular geometry coils. View full abstract»

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  • Electromagnetic NDE signal inversion by function-approximation neural networks

    Page(s): 3633 - 3642
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (829 KB) |  | HTML iconHTML  

    In the magnetic flux leakage (MFL) method of nondestructive testing commonly used to inspect ferromagnetic materials, a crucial problem is signal inversion, wherein the defect profiles must be recovered from measured signals. This paper proposes a neural-network-based inversion algorithm to solve the problem. Neural networks (radial-basis function and wavelet-basis function) are first trained to approximate the mapping from the signal to the defect space. The trained networks are then used iteratively in the algorithm to estimate the profile, given the measurement signal. The paper presents the results of applying the algorithm to simulated MFL data. View full abstract»

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  • Magnetic Barkhausen emission study in heat-treated Fe-Nb-Cu-Si-B alloy

    Page(s): 3669 - 3674
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB) |  | HTML iconHTML  

    Magnetic hysteresis and magnetic Barkhausen emission (MBE) parameters have been studied for as-received and annealed Fe72Nb4.5Cu1Si13.5B9 alloys. The coercivity rapidly decreased at the initial stage of annealing, in contrast to the slow change of root-mean-square voltage of Barkhausen emissions. The amplitude of the Barkhausen emission signal reduced almost to the background noise level at an intermediate annealing temperature, at which the material exhibited superior soft magnetic properties. Pulse height distribution of the MBE signal showed the existence of a large number of small amplitude pulses at the intermediate range of annealing, an indication that the magnetization process of the system is dominated by the rotation of the magnetization vector within a small volume of nanocrystalline particles. We explain the results by a random anisotropy model, assuming the exchange coupling between the Fe80Si20 nanograins of higher magnetic moment takes place through the magnetically weaker amorphous matrix. View full abstract»

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  • Identification of magnetic parameters by inverse analysis coupled with finite-element modeling

    Page(s): 3607 - 3619
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    We present a new approach for identification of the material electromagnetic parameters that are involved in electrothermal process simulations. We use inverse analysis techniques coupled with an induction heating finite-element model (FEM) and software developed in our laboratory. We describe here the direct induction heating FEM, the physical formulations, and the iterative identification procedure, and then present numerical tests and results. View full abstract»

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  • Circuit coupling method applied to bulk superconductors

    Page(s): 3661 - 3664
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    This paper presents a new finite-element method for including a bulk superconductor in an electrical circuit. The method solves simultaneously the finite-element equations of Aψ formulation and the circuit equations. At the same time, a power law defines the superconducting properties. The method then compares the classical homogeneous model of a Bi-2223 tape to a multifilament model. The results of a simulation of conductors carrying alternative current while subjected to an external ac field are presented. View full abstract»

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  • Topology optimization for reduction of vibration caused by magnetic harmonic excitation

    Page(s): 3643 - 3649
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    We apply the homogenization design method (HDM) to reduce the vibration level of a structure excited by magnetic harmonic force. We do this by obtaining the optimal material distribution of the structure to minimize the frequency response. We first use the Maxwell stress method to compute the magnetic force and then apply HDM for the optimization. Results show that the HDM can be used to minimize the frequency response. This method can also be applied to other rotary electrical devices such as motors and generators. View full abstract»

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  • Practical equalizer for a perpendicular magnetic disk

    Page(s): 3684 - 3688
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (381 KB) |  | HTML iconHTML  

    We have developed a readback equalizer for a perpendicular magnetic disk with a commercial anisotropic magnetoresistive head for use with a PR4ML read channel with 8-9 coding. The transfer function of the perpendicular magnetic disk, derived by Fourier analysis, has a phase lag of 90° from that of the longitudinal magnetic disk. We defined the parameters of the equalizer by simulation. The equalized readback signal nearly satisfied Nyquist's first criterion. Using resistor-capacitor circuits that correspond to the simulated function, we obtained a byte-error rate of below 10-7. Comparing the effect of incorporating PR4 or PR1 as part of the equalizer, we observed that PR4 gave a lower bit-error rate than PR1. Thus, PR4 is an effective detection method for a perpendicular magnetic disk. It is suitable not only for longitudinal magnetic disks, but also for perpendicular magnetic disks. View full abstract»

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  • Minimum-volume coil arrangements for generation of uniform magnetic fields

    Page(s): 3579 - 3588
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB) |  | HTML iconHTML  

    This paper describes an optimization method for designing electromagnetic coil arrangements that generate uniform magnetic fields. The method can accurately and efficiently determine an arrangement that minimizes the volume of the coils. An important advantage of the method is that the solutions it generates are guaranteed to be global minimums. The method may be useful for designing large superconducting magnets, since their cost depends strongly on the amount of superconducting wire required. It is also shown that the method can be applied to minimize the power consumption of resistive magnets. View full abstract»

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  • Data continuation for the explicit solution of an inverse biomagnetic problem

    Page(s): 3620 - 3632
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (844 KB) |  | HTML iconHTML  

    This paper considers the problem of data continuation for an explicit identification method for electric dipoles situated in a conductor, and shows that the magnetic field measured over a part of a closed surface (which encloses the conductor) can be analytically continued to the rest of the surface. Such a continuation problem has a unique solution for an arbitrarily shaped conductor and observation surface. The paper proposes two straightforward methods for the continuation - the spherical harmonic expansion and the integral equation approach - and presents continuation examples for the case of a single dipole in a spherical conductor with the data measured on a part of a spherical observation surface. The spherical harmonic expansion method works well when the field is continued relatively far from the conductor and when the measured data are clean; however, the spherical harmonic expansion fails when the data are noisy. On the other hand, the integral equation approach, although it suffers from numerical integration errors, shows a much better continuation with quite noisy data. (A method to reduce the numerical integration errors is proposed.) The latter approach is also much more accurate than the spherical harmonic expansion for continuing the field in the proximity of the conductor. Finally, the paper discusses the applicability of both methods to an explicit identification method. View full abstract»

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  • Magnetostatic field of a conductor of semicircular cross section in a highly permeable half-space: exact analytic solution for infinite permeability with perturbative correction

    Page(s): 3594 - 3606
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    Poisson's equation for the magnetic vector potential is solved using complex Fourier (Laplace) transforms in bipolar coordinates, the natural system for the subject two-dimensional geometry. The source is a dc current uniformly distributed over the semicircular cross section of a long conductor that is buried in, and flush with, the otherwise planar boundary of an infinitely permeable material. Exact closed-form potentials are obtained in the conformal mapping of the Neumann boundary value problem that characterizes the case of an infinitely permeable magnetic medium. One term of a perturbative correction that accounts for finite permeability is constructed for both the uniform source distribution and for the associated Green's function. View full abstract»

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  • Extension of winding function theory for nonuniform air gap in electric machinery

    Page(s): 3654 - 3657
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    This paper extends the winding function theory for nonuniform air gap in rotating electric machinery. It shows that the winding function differs from that used in the symmetrical case, although several papers employ the uniform air-gap winding function to study electric motor performance under fault conditions. The extended theory will be particularly helpful in the study of squirrel-cage induction motors with a nonuniform air gap such as that caused by eccentricity of the rotor and stator. View full abstract»

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  • Magnetic recording configuration for densities beyond 1 Tb/in2 and data rates beyond 1 Gb/s

    Page(s): 3675 - 3683
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    A new magnetic recording system is evaluated that includes the single-pole head, a new medium design, and the soft underlayer of perpendicular recording. The proposed medium consists of perpendicular grains with anisotropy directions tilted optimally about 45° with respect to the perpendicular direction. Here, focus is on the tilt angle at 45° in the crosstrack direction, including a small but typical dispersion. The write pole consists of a tapered-neck single-pole head with a very small throat height that yields maximized write fields without increased edge track degradation. The advantages of tilted perpendicular recording are discussed using theoretical and numerical micromagnetic analyses. This design achieves a much higher signal-to-noise ratio (SNR) than conventional recording, because it is less sensitive to medium orientation distributions and, for the same thermal decay, can utilize media with much smaller grain sizes. The switching speed is much more rapid due to increased recording torque. Estimated recording limits for tilted perpendicular recording with a medium-jitter SNR of 17 dB are beyond densities of 1 Tb/in2 and data rates of 1 Gb/s. View full abstract»

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  • Numerical model of electromagnetic stirring for continuous casting billets

    Page(s): 3658 - 3660
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (521 KB) |  | HTML iconHTML  

    This paper introduces a numerical model of an electromagnetic rotary stirrer based on the finite-element model. Such stirrers are used to improve the quality of continuously cast steel, particularly billets and blooms. The method determines the magnetic flux density profile and compares it to experimental measurements. In addition, it calculates the Lorentz force field as a function of the stirrer position, the current applied, and the frequency. The stirrer position at the end of the mold affects the profile symmetry of the force, creating a z component of the force. With this model, it will be possible to simulate the fluid dynamics effects in the molten steel. View full abstract»

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  • Effects of rare-earth element substitution on magnetostrictive properties of polycrystalline Tb-Dy-Fe alloys

    Page(s): 3665 - 3668
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    Magnetostrictive properties of (Tb0.5Dy0.5)1-xRExFe1.9 (x=0-0.05, RE=Y, Ce, Sm, Gd, Ho, Yb) polycrystalline compounds were studied. Each rare-earth element formed a RE-Fe2 Laves compound with a different lattice spacing. Corresponding to this difference, (Tb0.5Dy0.5)0.95RE0.05Fe1.9 alloys showed a variation in lattice spacing as a result of the substitution of rare-earth elements and the prestress dependence of magnetostriction changed noticeably. In the case of Y, Sm, and Gd substitution, which showed greater lattice spacing than that of the Tb0.5Dy0.5Fe1.9 alloy, the prestress dependence and maximum magnetostriction decreased. On the other hand, in the case of Ce, Ho, and Yb substitution, which showed a decrease in lattice spacing, the conspicuous prestress dependence was the same as that of the Tb0.5Dy0.5Fe1.9 alloy and the maximum magnetostriction was greater than that of the latter alloy. View full abstract»

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  • Mostly analog disk drive read channel with practical depth-of-two fixed delay tree search

    Page(s): 3689 - 3698
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1001 KB) |  | HTML iconHTML  

    A new read-channel arrangement for use with d=1 codes equalizes the input to extended partial response IV (EPR4) for clock recovery, and follows this with a new realization of a fixed delay tree search with decision feedback detector with search depth of two. The detector and a discrete-time phase detector for clock recovery share a five-tap finite-impulse response forward equalizer. Clock recovery from EPR4 is fast, while forward and feedback equalizers need no adaptation of tap weights. The read channel, originally developed for a rate-4/5 X{101} code, is extended to the more efficient rate-6/7 maximum-transition-run (MTR) codes. The detector consists of a conventional decision feedback equalizer, assisted by an error-correction circuit to sense and eliminate the major error events, thus performing as well as tree search with depth of two. With MTR code, the read channel outperforms EPR4 with Viterbi detection by 1 dB. View full abstract»

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  • Influence of an aperture on the performance of a two-degree-of-freedom iron-cored spherical permanent-magnet actuator

    Page(s): 3650 - 3653
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB) |  | HTML iconHTML  

    This paper describes a computational and experimental study of a two-degree-of-freedom spherical permanent-magnet actuator equipped with an iron stator. In particular, it considers the effect of introducing an aperture in the stator core to facilitate access to the armature. The resultant magnetic field distribution in the region occupied by the stator windings, the net unbalanced radial force, and the resulting reluctance torque are determined by three-dimensional magnetostatic finite-element analysis. The predicted reluctance torque is validated experimentally, and its implications on actuator performance are described. 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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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology