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Magnetics, IEEE Transactions on

Issue 1 • Date Jan. 2010

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Displaying Results 1 - 25 of 29
  • [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): 1 - 2
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  • IEEE Magnetics Society Distinguished Lecturers for 2010

    Page(s): 3 - 6
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  • Spin-Polarized Transport Phenomena in Double Magnetic Tunnel Junctions Caused by Ferromagnetic CoFe Nanoparticles

    Page(s): 7 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (237 KB) |  | HTML iconHTML  

    We present some unusual spin-polarized transport phenomena in asymmetric double barrier magnetic tunneling junctions (ADBMTJs) with CoFe/AlOx/ferromagnetic nanoparticle (FM-NPs)/AlOx/Ta structures. The conductance curves and the magnetoresistance ratio clearly oscillate with applied bias voltage, indicating the presence of Coulomb blockade effects due to isolated ferromagnetic nanoparticles in the parallel configuration in the ADBMTJ. The oscillation period is about 1.5 mV at 2 K. View full abstract»

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  • Structural Stability and Magnetic Properties of the TbCu _{7} -Type SmCo _{x - 0.4} Ti _{0.4} (x = 5.0\hbox {\textendash }8.5) Alloys

    Page(s): 10 - 14
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (398 KB) |  | HTML iconHTML  

    We have studied the composition dependence, thermal stability, long-term stability at 500°C, and magnetic properties of the nanostructural TbCu7-type (1:7) Sm-Co-Ti alloys. We prepared the SmCox-0.4Ti0.4 alloys with a wide composition range from x = 5.0 to x = 8.5 by high-energy ball-milling, followed by annealing at 700-1100°C for 2 h. After annealing at 700°C, the powders with x = 7.0-8.5 showed a single 1:7 structure, while the powders with x = 5.0-6.5 presented the 1:7 plus CaCu5-type (1:5) structure. At an annealing temperature higher than 800°C, a minor Th2Zn17-type (2:17) phase precipitated in the matrix of the 1:7 phase. Intrinsic coercivity iHc exhibits a maximum of 2.3 T at room temperature and 0.4 T at 500°C in the x = 7.0 samples annealed at 700°C. The temperature coefficient of iHc seems stable as the Sm/Co ratio changes from 1/6.5 to 1/7.5. The coercivity decreased with increasing annealing temperature Ta, from 2.3 T at Ta = 700°C to 1.3 T at Ta = 1100°C, which is mainly attributed to the grain growth from 35 nm for Ta = 700°C to 1 ¿m for Ta = 1100°C. After holding at 500°C for up to 360 h, the microstructure and magnetic properties of the 1:7-type nanograin alloys remained almost unchanged, indicating a structurally and magnetically long-term stabilization at the potential high-temperature application environment. View full abstract»

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  • Temperature Dependence of Resistivity of Sintered Rare-Earth Permanent-Magnet Materials

    Page(s): 15 - 20
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (415 KB) |  | HTML iconHTML  

    We studied the resistivity of rare-earth permanent-magnet materials over the temperature range -40°C to +150°C. We investigated three different materials from four manufacturers, including Nd2 Fe14 B, SmCo5 , and Sm2 Co17 , and measured their resistivities and temperature coefficients. We found that rare-earth permanent-magnet materials show an anisotropic resistivity behavior. In fact, the resistivity anisotropy causes larger resistivity difference than the temperature variation within the range studied. In many applications, such as permanent-magnet motors, this behavior has to be taken into account in design. View full abstract»

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  • Implementation of the Preisach-Stoner-Wohlfarth Classical Vector Model

    Page(s): 21 - 28
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (921 KB) |  | HTML iconHTML  

    A useful vector magnetic model must accurately simulate both the magnitude and direction of the magnetization when a magnetic medium is subjected to a linear or rotating applied field. Such a model has been recently presented as the Preisach-Stoner-Wohlfarth (PSW) model. The Preisach model computes the magnitude of the magnetization; the Stoner-Wohlfarth model computes the direction of the magnetization. These two models are combined into the PSW model. The PSW model is now initially implemented in a two-dimensional vector classical Preisach model. The model is computationally efficient since the magnetization angle is accessed for all applied fields from a single lookup table, which is generated by a one-time Stoner-Wohlfarth computation. View full abstract»

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  • Elimination of Nonphysical Solutions and Implementation of Adaptive Step Size Algorithm in Time-Stepping Finite-Element Method for Magnetic Field–Circuit–Motion Coupled Problems

    Page(s): 29 - 38
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1229 KB) |  | HTML iconHTML  

    The time-stepping finite-element method (FEM) has become a powerful tool in solving transient electromagnetic fields. The formulation can include complex issues such as time harmonics and space harmonics, nonlinear magnetic property of iron materials, external circuit, and mechanical motion in the system equations. However, as the derivatives of physical quantities are usually unknown at the initial step of the time-stepping method, erroneous solutions might appear at the beginning of the transient process. To reduce the number of time steps, an adaptive step size algorithm can be used. In this paper, a method to eliminate the nonphysical or nonrealistic solutions at the start of the time-stepping finite-element analysis (FEA), when simulating the transient process of electric devices, is presented. A practical implementation of adaptive time step size algorithm for coupled problems is proposed. A matrix operation method, which can be understood clearly and implemented easily, that deals with matching boundary conditions in the study of mechanical motion, is also described. View full abstract»

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  • General Formulation of the Electromagnetic Field Distribution in Machines and Devices Using Fourier Analysis

    Page(s): 39 - 52
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1133 KB) |  | HTML iconHTML  

    We present a general mesh-free description of the magnetic field distribution in various electromagnetic machines, actuators, and devices. Our method is based on transfer relations and Fourier theory, which gives the magnetic field solution for a wide class of two-dimensional (2-D) boundary value problems. This technique can be applied to rotary, linear, and tubular permanent-magnet actuators, either with a slotless or slotted armature. In addition to permanent-magnet machines, this technique can be applied to any 2-D geometry with the restriction that the geometry should consist of rectangular regions. The method obtains the electromagnetic field distribution by solving the Laplace and Poisson equations for every region, together with a set of boundary conditions. Here, we compare the method with finite-element analyses for various examples and show its applicability to a wide class of geometries. View full abstract»

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  • Spatial Harmonic Expansion for Use With Magnetic Sensor Arrays

    Page(s): 53 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (718 KB) |  | HTML iconHTML  

    In order to reduce the effects of external magnetic fields on the accuracy of magnetic sensor measurements used for the reconstruction of ac electric currents flowing in massive parallel conductors, we use a spatial circular harmonic expansion of the magnetic scalar potential. Thanks to the linearity of the magnetic field problem with respect to the sources, we can then apply the least squares inversion and obtain the set of currents from the knowledge of the magnetic field data collected by the sensor array in the vicinity of the current carrying conductors. Furthermore, we can optimize the positions and the orientations of the magnetic sensors using D-optimality theory and particle swarm optimization. View full abstract»

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  • Microspeaker Diaphragm Optimization for Widening the Operating Frequency Band and Increasing Sound Pressure Level

    Page(s): 59 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (682 KB) |  | HTML iconHTML  

    We report on the optimization of a microspeaker diaphragm for widening the working frequency band between its first and second eigenfrequencies and increasing its sound pressure level (SPL). A metallic diaphragm produces a larger magnetic force and thus a higher sound pressure level; therefore a Ni-coating on a common poly ethylene naphthalene (PEN) diaphragm is appropriate. For the best diaphragm design, it is important to simultaneously optimize the diaphragm shape and the Ni-coating distribution on the top of the diaphragm. Since complete Ni-coating increases SPL but also reduces the frequency band, special attention must be paid to the Ni-coating. We solved the optimization problem by a two-step approach: standard shape optimization of a PEN diaphragm for widening the frequency band, followed by distribution optimization of the Ni material on the diaphragm. To facilitate the Ni distribution optimization, we formulated the problem as a special topology design optimization. Since the optimization requires a coupled analysis involving the electromagnetic field, mechanical vibration and sound radiation, the multiphysical system behavior should be properly modeled. After presenting the fundamental multiphysical equations, we provide shape and topology optimization procedures to find an optimal microspeaker diaphragm. We verified the validity of an optimized diaphragm configuration optimized by our method from a physical viewpoint. View full abstract»

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  • Multi-Slice Modeling in Circuit-Field Coupled Systems Using Finite-Element and Modified Nodal Analyses

    Page(s): 67 - 74
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1044 KB) |  | HTML iconHTML  

    We propose a systematic method for interfacing different 2-D low-frequency electromagnetic field slices and nonidentical multi-port circuit networks using finite-element (FE) and modified nodal analyses. Each independent field slice has its own length, geometry, materials, boundary conditions, and number of filamentary and massive conductors. Similarly, each multi-port circuit network can have different circuit elements, topology, and number of ports. As a result, field slices are not required to be successively connected, since multi-port circuit networks can exist between them. Thus, solutions for virtually any possible configuration of 2-D circuit-field coupled systems are possible. The number of slices and multi-port networks does not affect the general form of the final system of equations, which is symmetric for most practical cases. Although we developed the methodology for 2-D time-harmonic magnetic problems, it can be readily extended to the transient case. We analyzed an induction motor to test the proposed multi-slice FE approach and validated the results using the total short-circuit leakage reactance and commercial software (Flux2D). View full abstract»

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  • Inductance Calculations for Circular Coils of Rectangular Cross Section and Parallel Axes Using Bessel and Struve Functions

    Page(s): 75 - 81
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (318 KB) |  | HTML iconHTML  

    A simple method for calculating the mutual and self inductances of circular coils of rectangular cross section and parallel axes is presented. The method applies to non-coaxial as well as coaxial coils, and self inductance can be calculated by considering two identical coils which coincide in space. It is assumed that current density is homogeneous in the coil windings. The inductances are given in terms of one-dimensional integrals involving Bessel and Struve functions, and an exact solution is given for one of these integrals. The remaining terms can be evaluated numerically to great accuracy using computer packages such as Mathematica. The method is compared with other exact methods for the coaxial case, and with a filamentary method for the non-coaxial case. Excellent agreement was found in all cases, and the exact method presented here agrees with another exact coaxial method to great numerical accuracy. View full abstract»

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  • Three-Dimensional Magnetohydrodynamic Calculation for Coupling Multiphase Flow in Round Billet Continuous Casting Mold With Electromagnetic Stirring

    Page(s): 82 - 86
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (393 KB) |  | HTML iconHTML  

    A 3-D combined finite element-finite volume for magnetohydrodynamic (MHD) calculation method considering the coupling flow field, heat transfer, and inclusion trajectory was developed, and the flow characteristics of molten steel and inclusion trajectory in round billet mold using electromagnetic stirring (EMS) were numerically investigated. The calculation results of magnetic field and temperature in the mold are in a good agreement with the measured data. The influence of EMS on the turbulent flow and temperature in the mold is estimated by the model, which shows that EMS has an obvious effect on the flow and temperature distribution of molten steel, and the macrostructure of the billet. View full abstract»

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  • Using Embedded Dynamic Random Access Memory to Reduce Energy Consumption of Magnetic Recording Read Channel

    Page(s): 87 - 91
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB) |  | HTML iconHTML  

    Although the performance of a magnetic recording read channel can be improved by employing advanced iterative signal detection and coding techniques, the method nevertheless tends to incur significant silicon area and energy consumption overhead. Motivated by recent significant improvement of high-density embedded dynamic random access memory (eDRAM) towards high manufacturability at low cost, we explored the potential of integrating eDRAM in read channel integrated circuits (IC) to minimize the silicon area and energy consumption cost incurred by iterative signal detection and coding. As a result of the memory-intensive nature of iterative signal detection and coding algorithms, the silicon cost can be reduced in a straightforward manner by directly replacing conventional SRAM with eDRAM. However, reducing the energy consumption may not be trivial. In this paper, we present two techniques that trade eDRAM storage capacity to reduce the energy consumption of iterative signal detection and coding datapath. We have demonstrated dDRAM's energy saving potential by designing a representative iterative read channel at the 65 nm technology node. Simulation shows that we can eliminate over 99.99% of post-processing computation for dominant error events detection, and achieve up to a 67% reduction of decoding energy consumption. View full abstract»

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  • Media Corrosion: Not Just an Overcoat Problem

    Page(s): 92 - 94
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (205 KB) |  | HTML iconHTML  

    This paper demonstrates that electrochemical impedance spectroscopy combined with atomic force microscopy analysis can successfully characterize the coverage ability of an overcoat on perpendicular magnetic recording media. Rougher media, brought about by lower surface energy oxide segregants, can adversely impact the overcoat integrity. The role of the capping layer, and its ability to somewhat planarize the overall structure, is also discussed. View full abstract»

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  • Capacity Approaching Run-Length-Limited Codes for Multilevel Recording Systems

    Page(s): 95 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (350 KB) |  | HTML iconHTML  

    We propose two constructions for multilevel run-length-limited (RLL) block codes for which the rates are very close to the capacity. For each code construction, we propose a variation that has the advantage of low complexity of encoding and decoding. We conducted a simulation to see the combined effect of channel coding and our proposed RLL coding over an optical recording channel. View full abstract»

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  • Comparison Between Viterbi Detectors for Magnetic Recording Channels Based on Regressive and Autoregressive Noise Models

    Page(s): 105 - 111
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (206 KB) |  | HTML iconHTML  

    A recent work presents a regressive noise model for the data-dependent correlated noise, at the output of a magnetic recording channel detector. We have generalized this channel model, considering digital equalization and a more efficient correlation matrix, in order to make a comparison with the usual detector in a more realistic environment. Simulation results show that the regressive detector performs better when the number of trellis states is lower than needed, while both approaches are comparable when the number of states matches the channel memory. View full abstract»

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  • An Improved Magnetic Equivalent Circuit Model for Iron-Core Linear Permanent-Magnet Synchronous Motors

    Page(s): 112 - 120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (874 KB) |  | HTML iconHTML  

    The aim of this work is to establish an accurate yet simple method for predicting flux density distribution and iron losses in linear permanent-magnet synchronous motors (LPMSMs) for iterative design procedures. For this purpose, an improved magnetic equivalent circuit for calculation of the teeth and yoke flux densities in the LPMSMs is presented. The magnetic saturation of iron core is considered by nonlinear elements and an iterative procedure is used to update these elements. The armature reaction is also taken into account in the modeling by flux sources located on the teeth of motors. These sources are time dependent and can model every winding configuration. The relative motion between the motor primary and secondary is considered by wisely designing air gap elements simplifying the permeance network construction and preventing permeance matrix distortion during primary motion. Flux densities in different load conditions are calculated by means of the proposed model. The effects of saturation and armature reaction on the flux density distribution are shown in detail. Using these flux densities, iron losses in the motor are examined and its variations versus motor parameters are then studied. All results obtained by proposed model are verified by finite-element method based on an extensive analysis. View full abstract»

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  • Air-Gap Flux Density Distortion and Iron Losses in Anisotropic Synchronous Motors

    Page(s): 121 - 126
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    The anisotropy of the rotor of the synchronous reluctance motor (sometimes assisted by permanent magnets) causes a high content of flux density harmonics. These harmonics cause flux density fluctuations in the stator iron teeth, and thus iron losses. These losses increase with the motor speed and are independent of the main flux, that is, they exist even during the flux-weakening operations. An analytical model, validated by finite-element analysis, shows the dependence of flux density harmonic content on the rotor geometry. Therefore, this model is adopted to individuate the flux-barrier geometry so as to minimize the stator iron losses. View full abstract»

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  • A Quantitative Comparative Analysis of a Novel Flux-Modulated Permanent-Magnet Motor for Low-Speed Drive

    Page(s): 127 - 134
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1709 KB) |  | HTML iconHTML  

    A novel low-speed flux-modulated (FM) permanent-magnet (PM) motor that breaks the traditional design rule, which stipulates that the number of stator pole pairs and the number of rotor pole pairs must be the same, is proposed. The FM motor has a special physical structure with iron segments in the air gap to modulate the magnetic field. In the design, the free space between adjacent stationary iron segments also acts as ventilating ducts to help improving the heat dissipation and ventilation of the motor. Its cogging torque is very small. In this paper, a rule for comparing the power density of electric motors is proposed. The performance of the FM motor is compared with those of a magnetic-geared PM motor, a traditional PM motor, and a fractional-slot PM motor by using magnetic field finite-element analysis. View full abstract»

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  • Reduction of Cogging Force in Linear Permanent-Magnet Generators

    Page(s): 135 - 140
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB) |  | HTML iconHTML  

    Although linear permanent-magnet generators (LPMGs) are widely used for converting wave energy into electrical energy, they suffer from large cogging force. The cogging force causes oscillatory output power, which shortens lifetime and increases the maintenance costs of the generators. To reduce this force in the generator, we have designed and simulated a three-phase LPMG for direct wave energy conversion and predicted its performance using the finite-element method. We studied the influence of different design parameters on the cogging force and minimized this force by varying the proposed parameters. The results obtained confirm a large reduction in the cogging force and an enhancement in the generator performance. View full abstract»

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  • Transformer Core Parameter Identification Using Frequency Response Analysis

    Page(s): 141 - 149
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB) |  | HTML iconHTML  

    We present a novel model-based approach for parameter identification of a laminated core, such as magnetic permeability and electrical conductivity, of power transformers on the basis of frequency response analysis (FRA) measurements. The method establishes a transformer core model using the duality principle between magnetic and electrical circuits for parameter identification with genetic algorithms. We use reference input impedance frequency responses, calculated by a well-known lumped parameter model of a three-phase transformer and finite-element computations, to analyze identification accuracy of the method. The results verify the ability of the approach to accurately identify the core lamination parameters with respect to the reference values. The approach can be used for parameter identification of a demagnetized core with known geometrical parameters when the core lamination samples are unavailable for experimental tests. The approach can also be employed for transformer core modeling and FRA result interpretation at low frequencies. View full abstract»

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  • Investigation of Self-Excitation and Discharge Processes in an Air-Core Pulsed Alternator

    Page(s): 150 - 154
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (662 KB) |  | HTML iconHTML  

    The air-core pulsed alternator has advantages in the application of pulsed power region, such as in electromagnetic launchers. The self-excitation and discharge processes in an air-core alternator are more complicated than traditional iron-core generators. In this paper, a mathematical model of an air-core pulsed alternator is built and several critical problems are analyzed, such as the conditions for successful self-excitation, the time needed for self-excitation, the waveforms of electromagnetic torque, discharge current and load voltage, and the compensation action during discharge, the effect of triggered angles, the rotational speed curve, and the energy reclaiming. Investigation of self-excitation and discharge processes in an air-core pulsed alternator is helpful for understanding the operation principle, predicting the performance, and analyzing and designing the system. 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