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Magnetics, IEEE Transactions on

Issue 8 • Date Aug. 2007

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Displaying Results 1 - 25 of 36
  • [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): 3357 - 3358
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  • A New Thin-Film Permeameter for Measuring All Components of a Permeability Tensor

    Page(s): 3359 - 3362
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB) |  | HTML iconHTML  

    We describe a new permeameter to evaluate all components of a permeability tensor. The permeameter consists of a shorted microstrip line and a revolving coil, which can operate well up to 300 MHz. All muij r (i, j = x, y, and z) of a relative permeability tensor of a magnetic thin film were evaluated by the permeameter. The measurements show that the sample has large off-diagonal components compared with diagonal ones, indicating that the examination of such off-diagonal components by the permeameter can be used to design new devices with high accuracy. View full abstract»

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  • Indirect Susceptibility Mapping of Thin-Layer Samples Using Nuclear Magnetic Resonance Imaging

    Page(s): 3363 - 3367
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1393 KB) |  | HTML iconHTML  

    We measured and imaged magnetic field distributions of thin layers (2-D objects with negligible thickness) of biological and physical samples, by using nuclear magnetic resonance (NMR). The image represents the magnetic susceptibility distribution in the sample. We used a standard gradient echo imaging method, susceptible to magnetic field homogeneity, for detection. Since the physical and biological samples we investigated do not generate any NMR signal, we used a homogeneous phantom reference - a container filled with water - as a medium. The image acquired by this method is actually a projection of the sample properties onto the homogeneous phantom. The method can be applied in nanotechnology, microelectronics, and especially in the biological and medical sciences. View full abstract»

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  • Mutual Impedance of Cylindrical Coils at an Arbitrary Position and Orientation Above a Planar Conductor

    Page(s): 3368 - 3370
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB) |  | HTML iconHTML  

    We derive a closed-form expression for the mutual impedance due to eddy-current induction for a pair of cylindrical air-core coils with arbitrary position and orientation above a planar conductor. By extending a recently devised model for individual coils with an arbitrary tilt with respect to the surface, we obtain a remarkably simple result. We validated our model with measurements on a conductive plate. The results should be useful for designing new probe configurations and for evaluating the signals in eddy-current inspections when driver-pickup coil configurations are utilized. View full abstract»

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  • Ironless Loudspeakers

    Page(s): 3371 - 3374
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (166 KB) |  | HTML iconHTML  

    The paper notes the drawbacks of classical loudspeaker motors: the inductance varies with the coil's position, there is a reluctant effect, and eddy currents appear because of the iron in the motor. It then presents ironless structures of loudspeaker motors to eliminate these drawbacks. These structures are studied with the use of Coulomb's model of permanent magnets, which affords analytical calculations. Thus, a design can be optimized to create a uniform, high-level induction in the space where the coil moves. View full abstract»

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  • Numerical Analysis of Near-Field Magnetic Field for Automobile Electronic Key Systems

    Page(s): 3375 - 3379
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1390 KB) |  | HTML iconHTML  

    We propose a numerical method for analyzing near-field magnetic fields for automobile electronic key systems. The surface of an automobile body is divided into triangular patches and a modified inductance matrix formulation is employed. A large inductance matrix equation is solved using a block Gauss-Seidel method. A source magnetic field produced by a ferrite bar antenna is analyzed using a magnetic moment method to formulate a right-hand vector of the matrix equation. We have made a simplified automobile model and measured leakage of magnetic fields from windows of the model. Analyzed results agreed with the measured results with an error of 10%. View full abstract»

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  • An Analytical Determination of Eddy-Current Losses in a Configuration With a Rotating Permanent Magnet

    Page(s): 3380 - 3386
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    The paper presents a completely analytical method for determining the eddy currents in a cylindrical configuration. The configuration consists of a cylindrical permanent magnet rotating inside a conducting hollow cylinder (stator). The solution is obtained by solving a generalized form of the diffusion equation and applying the modified Bessel functions. The determination of the magnetic field in the air and in the stator, and the losses generated by the eddy currents, is completely analytical. The results are verified by finite-element software. View full abstract»

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  • Fringing Field Formulas and Winding Loss Due to an Air Gap

    Page(s): 3387 - 3394
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB) |  | HTML iconHTML  

    The paper describes a simple treatment for the fringing fields of an air gap in the core of a magnetic component such as an inductor or a transformer. It verifies the derived analytical formulas for the fields by using numerical (finite-element) calculations. It then applies these formulas to the calculation of high-frequency eddy-current losses for two types of winding arrangements, both of which employ thin rectangular conductors. The rectangular conductors are commonly used in flex circuit windings, printed circuit windings, and thin-film windings. The two types of winding configurations are flat and barrel wound. Each behaves in a different way as a function of the position of the conductor. View full abstract»

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  • Characteristics of an Electrodynamic Wheel Using a 2-D Steady-State Model

    Page(s): 3395 - 3405
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    The mechanical rotation of a radially positioned permanent-magnet Halbach array above a conducting, nonmagnetic track induces eddy currents in the track that can inductively create suspension and propulsion forces simultaneously. The parameters that affect the performance of this electrodynamic wheel are studied using a 2-D steady-state finite-element method. Tradeoffs between the lift and thrust force performance are investigated and methods to improve the thrust efficiency are proposed. View full abstract»

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  • Comparison Between Finite-Element Analysis and Winding Function Theory for Inductances and Torque Calculation of a Synchronous Reluctance Machine

    Page(s): 3406 - 3410
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    This paper compares the prediction of two independent methods for calculating electromagnetic torque and inductances of a synchronous reluctance machine under linear condition. One method is based on winding function analysis (WFA) and the other on finite-element analysis (FEA). Both methods take into account the rotor geometry, the stator slot effects and the stator winding connections. The simulation results obtained by the WFA are compared with the ones obtained by two-dimensional FEA. It is shown that the two methods give approximately the same results but require different computation times. View full abstract»

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  • Design of Electrical Rotating Machines by Associating Deterministic Global Optimization Algorithm With Combinatorial Analytical and Numerical Models

    Page(s): 3411 - 3419
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (509 KB) |  | HTML iconHTML  

    This paper presents a new methodology of design of electrical rotating machines. The methodology is an extension of previous works of the second author. Indeed, associating combinatorial analytical models with exact global optimization algorithms leads to rational solutions of predesign. These solutions need to be validated by a numerical tool (using a finite-element method) before the expansive phase of hand-making a prototype. Such an automatic numerical tool for computing some characteristic values, such as the torque, was previously developed. The idea of this paper is to extend the exact global optimization algorithm by inserting the direct use of this automatic numerical tool. This new methodology makes it possible to solve design problems more rationally. Some numerical examples validate the usefulness of this new approach. View full abstract»

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  • Optimal Number of Stator Poles for Compact Active Radial Magnetic Bearings

    Page(s): 3420 - 3427
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB) |  | HTML iconHTML  

    We present a method for finding the optimal number of stator poles for active radial magnetic bearings that minimizes the stator outside diameter. We use magnetic circuit analysis to determine the number of turns of wire to generate the worst case load capacity within limits of coil currents and flux densities. Using the analysis, we developed six types of magnetic bearing for a given value of journal diameter. We found that 3-pole bearings yield the smallest outside diameter among the six types of bearing for a journal diameter less than 50 mm; however, all the bearings have almost the same outside diameter for a journal diameter larger than 200 mm. For an infinite-length bearing, the stator diameter is a linear function of the product of numbers of poles and coil turns. We applied a linear controller design method to a heteropolar 3-pole magnetic bearing that has nonlinear coupling between the orthogonal components of bearing force. With this controller, we successfully levitated a slender-rotor system and rotated it at 3571 rpm.This paper treats the optimal number of stator poles for active radial magnetic bearings in a sense of minimizing the stator outside diameter. The magnetic circuit analysis is used to determine the number of turns of wire to generate the worst case load capacity within limits of coil currents and flux densities. Owing to the analysis, six types of magnetic bearing are designed for a given value of journal diameter. The designed stator outside diameters show that 3-pole bearings are the smallest among the six types of bearing for a smaller value of journal diameter than 50 mm, and, however, all the bearing have almost the same outside diameter when a journal diameter is larger than 200 mm. For an infinite-length bearing, the stator diameter is a linear function of the product of numbers of poles and coil turns. A linear controller design method is applied to a heteropolar 3-pole magnetic bearing that has nonlinear coupling between the ortho- gonal components of bearing force. A slender-rotor system is successfully levitated by the designed controller and rotated at the speed of 3571 rpm. View full abstract»

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  • Iron Loss Model for Permanent-Magnet Synchronous Motors

    Page(s): 3428 - 3434
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (181 KB) |  | HTML iconHTML  

    Iron losses in permanent-magnet synchronous machines form a larger portion of the total losses than in induction machines and, hence, more importance should be given to the iron losses. Previously, models have been presented for the calculations of these losses, but these models still rely on finite-element simulations to obtain correction factors, which are substantial, to apply to the theoretically derived formulas in order to obtain good agreement with the experimental data. This paper points out the source of this correction factor: the neglect of the excess eddy-current loss component. In many cases, this loss component dominates the total iron losses and needs to be incorporated in the theoretical considerations. The paper also provides a more complete model of iron loss, which greatly reduces the need for calculating the correction factors using the finite-element method (FEM). This more complete model reduces design time, especially when a number of candidate designs need to be analyzed. Otherwise, the calculation of the correction factors using FEM would be cumbersome, as the correction factors tend to be nonlinear. View full abstract»

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  • Design Consideration to Reduce Cogging Torque in Axial Flux Permanent-Magnet Machines

    Page(s): 3435 - 3440
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1106 KB) |  | HTML iconHTML  

    In designing new topologies for permanent-magnet machines based on rare earth magnets, it is necessary to diminish the undesired cogging torque. This paper presents a 3-D finite-element analysis to evaluate the effect of magnet shape and stator displacement on cogging torque reduction, for axial flux machines. It analyzes the final electromagnetic torque for the proposed configurations. Finally, it presents the resultant cogging torque waveform for a 5.0 kW prototype, based on our optimization techniques. View full abstract»

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  • Effects of the Slot Harmonics on the Unbalanced Magnetic Pull in an Induction Motor With an Eccentric Rotor

    Page(s): 3441 - 3444
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (111 KB) |  | HTML iconHTML  

    The slotting of electrical rotating machines creates slot harmonics of the air-gap magnetic flux density. These slot harmonics are the source of a nonnegligible part of the unbalanced magnetic pull (UMP). This paper presents analytical justifications for the use of a numerical impulse method to calculate the effects of the slot harmonics on the UMP. It uses the method to show that the force components due to the slot harmonics cannot be reduced easily. View full abstract»

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  • Mutual Coupling and Its Effect on Steady-State Performance and Position Estimation of Even and Odd Number Phase Switched Reluctance Motor Drive

    Page(s): 3445 - 3456
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1263 KB) |  | HTML iconHTML  

    In this paper, we analyze mutual coupling of switched reluctance (SR) motors with even and odd numbers of phases. We illustrate that SR motors with an even number of phases produce asymmetric mutual flux in different phases. On the other hand, an SR motor with an odd number of phases produces symmetric mutual coupling in all the phases. Then, we explain a practical way of measuring the mutual flux in SR motors and present the test results for an 8/6 pole, four-phase 4 kW motor. We simulated the performance of the SR motor with and without mutual flux, thereby demonstrating the effect of mutual flux on phase current, flux, and average torque. We verified the effect of mutual flux on position estimation by simulation and experiment. We show that appropriate correction for mutual flux may improve the accuracy of estimated position by 3deg, which will give better performance of the drive while driven without any shaft sensors. We also show that an SR motor with an odd number of phases is a better choice than one with an even number of phases because of its symmetric mutual coupling, its ability to utilize short flux paths, and the fact that it does not require costly bipolar excitation. View full abstract»

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  • Low-Temperature Annealing Effect of RF Inductor With FeNi-SiO2 Granular Film

    Page(s): 3457 - 3461
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    A low-temperature annealing process in vacuum is proposed to enhance the inductance of RF inductors with FeNi-SiO2 magnetic granular films. Due to the great improvement of soft magnetic property in the 200degC and 350degC annealed film, the inductance is enhanced by 9.6% (200degC) and 8.3% (350degC), respectively, compared with the case of as-deposited film inductor. The peak value of quality factor, which is 9.18 for the as-deposited film inductor, is also increased to 9.27 (200degC ) and 12.27 (350degC), respectively. View full abstract»

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  • Neural-Network-Based Model for Dynamic Hysteresis in the Magnetostriction of Electrical Steel Under Sinusoidal Induction

    Page(s): 3462 - 3466
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (534 KB) |  | HTML iconHTML  

    In this paper, we present a model for the dynamic hysteresis behavior of magnetostriction in electrical steel under sinusoidal induction. The model can be used for the numerical calculation of vibrations in magnetic cores. In order to keep the calculation time of the method to an acceptable level, we developed a neural-network-based model, which predicts magnetostriction loop shapes of the material under a limited set of circumstances but offers fast evaluation time. As an example, we apply the model to a grain-oriented electrical steel and present an error analysis. The model can be extended for use with nonsinusoidal induction. View full abstract»

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  • Assessment of the Stress Sensitivity of Magnetostriction in Grain-Oriented Silicon Steel

    Page(s): 3467 - 3476
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (586 KB) |  | HTML iconHTML  

    This paper describes a novel, versatile system for measuring the stress sensitivity of magnetostriction of Epstein strips of grain-oriented electrical steel, an analysis of results of measurements on several grades of commercial material, and an attempt to relate their stress sensitivity characteristics to material properties. The maximum value of peak magnetostriction under applied stress is proportional to the strip gauge for both conventional and high permeability grades of material. A model explains the contributions of retained stress and stress due to the forsterite coatings on grain-oriented silicon steel. This model can be used to correlate the thickness of the fosterite coating to its calculated coating stress. It is also possible to separate the effect of the phosphate and forsterite coatings. Both types of coating set up a longitudinal stress in the steel in proportion to their thickness. View full abstract»

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  • Zero-Power Magnetic Levitation Using Composite of Magnetostrictive/Piezoelectric Materials

    Page(s): 3477 - 3482
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1146 KB) |  | HTML iconHTML  

    We present a zero-power magnetic levitation technique using a composite of magnetostrictive and piezoelectric materials. The composite is bonded to iron yokes with an attached permanent magnet, by which the magnetic force exerted on movable yoke via air gap is controlled by the applied voltage on the piezoelectric material. The magnetic force control is based on the inverse magnetostrictive effect of the magnetostrictive material, i.e., the magnetization is varied with mechanical stress. The advantage of the composite is zero power consumption, because no current flows in static operation as a result of the capacitive property of the piezoelectric material. This feature will be useful in high-precision stage or conveyor systems using magnetic levitation where heat generation and power consumption should be avoided. The zero power characteristic of the composite is valid at any reference gap or load, whereas that of the conventional electromagnetic type is valid only at the equilibrium gap. We performed two levitation experiments: one using the composite to demonstrate the zero power advantage, and the other combining the composite to adjust the bias gap and electromagnet to stabilize the motion of the levitated yoke. The composite driven by a small dc-dc converter successfully varied the gap and maintained it constant with zero power consumption. View full abstract»

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  • Finite-Element Computation of Magnetic Force Densities on Permeable Particles in Magnetic Separators

    Page(s): 3483 - 3487
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (819 KB) |  | HTML iconHTML  

    Magnetic force densities are computed by differentiation of the magnetic energy density distribution obtained by finite-element analysis. The computed forces on small permeable particles are shown to agree reasonably well with a classical formula by Oberteuffer. The method is applied to both planar separators and axisymmetric magnetic separators, including those used for biomolecular screening. View full abstract»

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  • Effect of the Magnetic Dipole–Dipole Interaction on the Capture Efficiency in Open Gradient Magnetic Separation

    Page(s): 3488 - 3493
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    In magnetic separation, the magnetic dipole-dipole (DD) interaction between particles has an important effect on the capture efficiency. By producing transient particle agglomerations, this interaction can considerably speed up the separation process. To take into account adequately this effect in ferromagnetic particle random dispersion, we have developed a modeling approach. The approach is based on the coupling of the magnetic force equation and a local homogenizing model for the material magnetic permeability. To verify the efficiency of the proposed approach on one hand and to estimate the effect of the DD interaction on the particle capture on the other hand, we consider a problem of open gradient magnetic separation (OGMS). We also conducted a limited experimental verification of the transient agglomeration for fine ferromagnetic particles. View full abstract»

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  • Bulk Nanocrystalline SmCo6.6Nb0.4 Sintered Magnet With TbCu7-Type Structure Prepared by Spark Plasma Sintering

    Page(s): 3494 - 3496
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (631 KB) |  | HTML iconHTML  

    We prepared bulk nanocrystalline SmCo6.6Nb0.4 sintered magnet material by spark plasma sintering technique. X-ray diffraction patterns show that the magnet exhibits a stable TbCu7 structure. Transmission electron microscopy indicates that the microstructure of the magnet is composed of SmCo6.6Nb0.4 single-phase grains with an average grain size of 30 nm. Magnetic measurement shows that under a 7 T magnetic field, the coercivity of the magnet reaches as high as 2.8 T; the saturation magnetization and the remanence are 69.6 and 51.4 emu/g, respectively. The magnet exhibits good thermal stability with the coercivity of 0.48 T at 773 K, and the coercivity temperature coefficient beta of -0.169%/K. 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