Showing papers in "IEEE Transactions on Magnetics in 1997"
TL;DR: The superparamagnetic limit on grain sizes may soon hinder progress in high density magnetic recording, and patterned media has been proposed as a means of overcoming this limit as discussed by the authors, but no clear path exists for implementation of a patterned medium recording system, it is nonetheless worth considering some of the system-level problems and possibilities that would be inevitably associated with such a system.
Abstract: The superparamagnetic limit on grain sizes may soon hinder progress in high density magnetic recording, and patterned media has been proposed as a means of overcoming this limit. Although no clear path exists for implementation of a patterned medium recording system, it is nonetheless worth considering some of the system-level problems and possibilities that would be inevitably associated with such a system. This paper examines some of these system-level issues, including implications for recording media, recording heads, and write-field pulse timing.
379 citations
TL;DR: In this article, the authors designed a thin wave absorber composed of the present material by introducing a low-permittivity area such as a free space into the present metal-containing material.
Abstract: Soft magnetic material has been produced in which flaky thin amorphous metal particles, about 2 /spl mu/m thick, are aligned in polymer in the direction perpendicular to electromagnetic wave propagation. This material yields a permeability two to three times higher than the spinel-type ferrite system in the quasi-microwave band. We have designed a thin wave absorber composed of the present material by introducing a low-permittivity area such as a free space into the present metal-containing material. This decreases the average permittivity, striking a balance between complex permeability and permittivity values, and thus reducing the reflection coefficient of the absorber. A thin (about 3-mm thick) wave absorber with a reflection loss of over 30 dB in the quasi-microwave band was successfully obtained when the free space region was 5% of the total volume.
212 citations
TL;DR: The goal of this review is to aid those working on numerical solutions of open boundary problems using the finite element method to gain perspectives on the variety of techniques presently available or being developed.
Abstract: This paper presents a review of finite element open boundary techniques for the computation of static and quasistatic electromagnetic fields. The underlying assumptions and ideas behind these techniques are outlined and explained. The advantages and shortcomings of each technique are discussed. The goal of this review is to aid those working on numerical solutions of open boundary problems using the finite element method to gain perspectives on the variety of techniques presently available or being developed. This review is also intended to facilitate the communication of numerical techniques between the low-frequency field computation community and those in the high-frequency community.
174 citations
TL;DR: In this article, the authors studied the GMI effect on a single-layer magneto-impedance film with a magnetic closed-loop structure and found that the sensitivity at 1 MHz is higher than that of single layer films of the same thickness by three orders of magnitude.
Abstract: Giant Magneto-Impedance (GMI) of films with a layered structure has been studied. They are Co-Si-B/Cu/Co-Si-B, Co-Si-B/Ag/Co-Si-B, and Fe-Co-Si-B/Cu/Fe-Co-Si-B with a magnetic closed-loop structure. They also have a certain magnetic configuration, for which the uniaxial anisotropy is perpendicular to both the driving current and the external field. Consequently, both reactance X and resistance R of the films change remarkably due to the external field in the frequency range from 100 kHz to 10 MHz, at which the GMI effect hardly appears in the single layer films of the same thickness. The conductivity difference between the outer and inner layers is important in order to achieve a high impedance change ratio in this frequency range. As a result, the ratios /spl Delta/Z/|Z/sub 0/|=(Z/sub maximum/-Z/sub [Hext=0]/)/Z/sub [Hext=0]/ of Co-Si-B/Ag/Co-Si-B films are 440% for a field of 9 Oe at 10 MHz, and the average sensitivity is 49%/Oe. Furthermore, /spl Delta/Z/|Z/sub 0/| of Co-Si-B/Cu/Co-Si-B and Co-Si-B/Ag/Co-Si-B films at 1 MHz is as much as 140%, and the average sensitivity reaches 15%/Oe. The sensitivity at 1 MHz is higher than that of single-layer magneto-impedance films of the same thickness by three orders of magnitude.
161 citations
TL;DR: In this paper, a new method employing the immune algorithm (IA) as the search method for the shape optimization of an electromagnetic device is presented, which is applied to the shape optimisation of a pole face of an electromagnet.
Abstract: A new method employing the immune algorithm (IA) as the search method for the shape optimization of an electromagnetic device is presented. The method is applied to the shape optimization of a pole face of an electromagnet. For the magnetic field analysis the finite element method is used. It is shown that the proposed method with the IA is very useful for the shape optimization of electromagnetic devices.
149 citations
TL;DR: In this paper, two new impedance models for planar coils on a magnetic substrate of finite thickness and a planar coil sandwiched between two substrates are described, based on the electrical conductivity of the magnetic material.
Abstract: High-frequency planar magnetic components, employing thin film and thick film technology, have become important components in applications, such as filters and switching converters, due to their ease of manufacture and reliability. In a previous paper, the authors established a frequency dependent impedance formula for planar coils on a magnetic substrate that is infinitely thick. In this paper, two new impedance models are described: the first is for planar coils on a magnetic substrate of finite thickness, and the second represents a planar coil sandwiched between two substrates. The models include the electrical conductivity of the magnetic material so that the effects of eddy currents, particularly at high frequencies, are taken into account. The eddy currents reduce the inductance and increase the losses associated with the device. The new impedance formulas are derived from Maxwell's equations. Simulations were carried out on a typical device, using finite element analysis, and the results validate the new formulas. This paper establishes the frequency limitations of lossy magnetic substrates.
148 citations
TL;DR: In this paper, the authors deal with mathematical models of magnetic hysteresis implemented by assembling hysterons of play and stop type, and compare their behaviors with experimental results. But they do not consider the effect of the stop-type model on the performance of the Preisach and Prandtl-Ishlinskii models.
Abstract: This paper deals with mathematical models of magnetic hysteresis implemented by assembling hysterons of play and stop type. A procedure for the identification of these models is described, and their behaviors are compared to experimental results. A comparison to the Preisach and Prandtl-Ishlinskii models is performed. It is shown that the Play-Type Model is a possible alternative to Preisach's algorithm, whereas the Stop-Type Model is apt to represent the inverse of Preisach's operator. Simulations adopting both models are reported and compared to experimental data. Moreover, an application to the analysis of a ferroresonant circuit is studied, both numerically and experimentally.
137 citations
TL;DR: In this article, a mathematical model is presented, together with a numerical scheme based on the Finite Element Method for axisymmetric geometries, and a comparison between results given by the code and experimental measurements is provided.
Abstract: This paper deals with numerical simulation of induction heating for axisymmetric geometries. A mathematical model is presented, together with a numerical scheme based on the Finite Element Method. A numerical simulation code was implemented using the model presented in this paper. A comparison between results given by the code and experimental measurements is provided.
124 citations
TL;DR: In this paper, the authors present a method for the calculation of the mutual inductance in the case of noncoaxial coupled coils, the characteristics of this inductance, and experimental results.
Abstract: The purpose of this paper is to determine the mutual inductance between two noncoaxial circular coils. In many cases, such as coil guns or tubular linear motors, one of them is fixed while the other one is moving, and if not supported, its axis may not coincide with that of the fixed coil. This paper presents a method for the calculation of the mutual inductance in the case of noncoaxial coupled coils, the characteristics of this inductance, and experimental results. The computation is based on complete elliptic integrals and on the mesh-matrix technique. The method enables one to obtain accurate results from a relatively simple procedure and calculation program.
106 citations
TL;DR: A formula is presented for computing the coupling between magnetic gears that is expressed as a finite sum of elementary functions and is well suited for parametric analysis.
Abstract: A formula is presented for computing the coupling between magnetic gears. This formula, which is based on two-dimensional analytical analysis, is expressed as a finite sum of elementary functions and is well suited for parametric analysis. It is demonstrated via application to a practical device and verified using finite element analysis (FEA).
99 citations
TL;DR: In this paper, a new magnetic field component yielding a dynamic magnetic loss is assumed and added to the magnetic field intensity of the dc magnetic hysteresis, which brings about the dependence of the frequency characteristics of the iron loss upon core size.
Abstract: Iron loss measurements of Mn-Zn ferrite cores up to the megahertz range are reported. Taking the dc magnetic hysteresis, the eddy, and displacement currents into account, magnetic and electric field distributions in the cores are computed with the cylindrical coordinates and Bessel functions. The computed iron loss due to the magnetic and electric fields is compared with the experimental value at different exciting frequencies. It is noted that the computed iron loss becomes considerably smaller than the experimental at high frequencies. In order to explain the difference between the computed and experimental iron losses, a new magnetic field component yielding a dynamic magnetic loss is assumed and added to the magnetic field intensity of the dc magnetic hysteresis. This assumption is verified by evaluating the iron losses in different size cores composed of the same ferrite material. Displacement current distribution in a ferrite core depends on the cross-sectional area of the magnetic flux path, which brings about the dependence of the frequency characteristics of the iron loss upon core size.
TL;DR: To make a more accurate prediction of performance possible, the air gap flux density and d, q axis inductances obtained by an analytical method are compensated by using the results from FEM studies.
Abstract: This paper presents an optimal design method to maximize the efficiency of the interior permanent magnet synchronous motor. To do this, the efficiency of the motor is taken as the objective function, and the genetic algorithm is used as the optimization algorithm to find the optimal design variables of the objective function. To make a more accurate prediction of performance possible, the air gap flux density and d, q axis inductances obtained by an analytical method are compensated by using the results from FEM studies.
TL;DR: In this paper, the collector current of an Al/AlO/sub x/sub y/emitter, the spin-valve base and an nSi collector was measured by measuring a collector current, which was found to change more than 200% under application of magnetic field.
Abstract: Hot electron transport across an Fe/Au/Fe spin valve was examined by measuring a collector current of a hot electron transistor which was composed of an Al/AlO/sub x/ emitter, the spin-valve base and an nSi collector. The collector current changed more than 200% under application of magnetic field. The magnitude of this change decreased monotonously with emitter voltage, and no anomaly was observed at the voltage (/spl sim/1.5 V) corresponding to the sharp peak in the density of states of the minority spin bands in Fe.
TL;DR: Pulsed power requirements for electric guns are described and preferred technologies for energy storage and pulse compression are discussed in this article, but alternative technologies that may offer some operational benefits are also discussed.
Abstract: Pulsed power requirements for electric guns are described and preferred technologies for energy storage and pulse compression are discussed. Primary approaches are rotating machines and capacitor based, pulse-forming networks, but alternative technologies that may offer some operational benefits are also discussed. These include linear magnetic flux compressors, cryogenically cooled, high-temperature superconducting inductors, novel dielectrics for energy storage, and pulsed magnetohydrodynamic (MHD) generators.
TL;DR: In this paper, the magnetic viscosity and activation volume of elongated /spl alpha/Fe particles in alumite were investigated at room temperature for an anodized aluminum oxide film.
Abstract: Particle size effects on the magnetic viscosity and activation volume were studied at room temperature for elongated /spl alpha/-Fe particles in alumite (Fe nanowires in an anodized aluminum oxide film). Both magnetic viscosity and activation volume are strongly dependent on the particle diameter, but independent of the particle length. The magnetization reversal mechanism of elongated /spl alpha/-Fe particles in alumite films is discussed. The activation volume may represent the size of the magnetic switching unit propagating along the particle length during the non-uniform magnetization reversal.
TL;DR: In this article, a family of sensitive, stable and low power consumption MI micro magnetic sensors are constructed using a CMOS IC multivibrator circuit, in which a sharp pulse train current is applied to an amorphous wire to cause the skin effect.
Abstract: A family of sensitive, stable and low power consumption MI micro magnetic sensors are constructed using a CMOS IC multivibrator circuit, in which a sharp pulse train current is applied to an amorphous wire to cause the skin effect. A micro field sensor having a resolution of 10/sup -6/ Oe with a full scale (FS) of /spl plusmn/1.5 Oe and a nonlinearity of less than 0.2%, a cut-off frequency of /spl sim/200 kHz, and a power consumption in the oscillation circuit of 0.5/spl sim/5 mW is obtained using a zero-magnetostrictive FeCoSiB amorphous wire of 30 /spl mu/m diameter and 2 mm length. A differential field sensor is also constructed using a pair of amorphous wires suitable for detection of a localized held with the resolution of 10/sup -4/ Oe cancelling uniform disturbance fields such as terrestrial field. Non-contact sensing of a magnetic card surface field was demonstrated.
TL;DR: In this paper, an analytical approach based on a two-dimensional electromagnetic field analysis in polar coordinates is developed to predict the commutation losses in a permanent magnet brushless dc (PMBD) motor.
Abstract: An analytical approach based on a two-dimensional electromagnetic field analysis in polar coordinates is developed to predict the commutation losses in a permanent magnet brushless dc (PMBD) motor. These losses are essentially the eddy-current losses induced in the PMBD motor's rotor magnets and core and are caused by the rotor sweeping of the stationary stator magnetic field before each current commutation due to inverter switching takes place. The approach is applicable to motor constructions with either magnet segments or a magnet ring and able to deal with ill-conditioned cases. The model was applied to an existing motor and good agreement (within 11%) with the finite element method was achieved.
TL;DR: In this article, the induced electromotive force (EMF) across a coil above a half-space conductor and of the magnetic field on the coil axis were compared with experiments.
Abstract: Eddy-current nondestructive evaluation commonly carried out using single frequency time harmonic excitations, but a pulsed excitation offers a simple and effective alternative. The pulse signals have been calculated for a probe coil whose current rises and falls exponentially, approximating a square wave when the exponential time constant is small. Predictions of the induced electromotive force (EMF) across a coil above a half-space conductor and of the magnetic field on the coil axis have been compared with experiments. The comparison shows excellent agreement between theory and experiment.
TL;DR: In this article, a 3D finite element scheme for eddy-current non-destructive evaluation (NDE) problems is described that calculates directly the perturbation of the electromagnetic field due to defects in metallic specimens.
Abstract: A new three-dimensional (3-D) finite element scheme for eddy-current nondestructive evaluation (NDE) problems is described that calculates directly the perturbation of the electromagnetic field due to defects in metallic specimens. The computational costs of such problems are usually very high using available finite element schemes, and the new scheme is supposed to lower these costs. The basic concept, the direct calculation of the field distortion due to the flaw, is provided for rather general defects, but the detailed finite element scheme is discussed for zero-conductivity flaws. The source terms of the formulation are determined from the unperturbed field, and the impedance change due to a defect can be calculated as an integral over the flaw. A finite element scheme for solving problems with crack-type defects is also presented as a limiting case of the formulation for zero-conductivity flaws. Solutions of a benchmark problem from the testing electromagnetic analysis methods (TEAM) workshop series (problem number 15/2) and of tube problems with artificial slots are presented and compared to experimental data.
TL;DR: In this article, a time-stepping two-dimensional (2-D) eddy-current finite element method, based on multislice technique, is described to study the steady-state operation and the starting process of skewed rotor induction machines.
Abstract: Normally a complicated three-dimensional (3-D) approach is needed to study the field pattern of induction machines with skewed rotor bars. In this paper, a time-stepping two-dimensional (2-D) eddy-current finite element method, based on multislice technique, is described to study the steady-state operation and the starting process of skewed rotor induction machines. The fields of the multislices are being solved en bloc simultaneously, and thus, the effects of the eddy current and saturation can be taken into account directly. New forms of the governing equations for the multislice model are derived, which allow the meshes of multislices to be taken as one 2-D mesh so that the algorithm is very similar to that of general 2-D problems. Special techniques required for the mesh generation in the multislice model and the salient structures of the software are also described. The results obtained by using the program being developed have very good correlation with test data.
TL;DR: In this paper, a combination of transient magnetic field (FEM) analysis and harmonic analysis was used to estimate the electromagnetic force of an induction motor in order to reduce the noise of the motors.
Abstract: The electromagnetic force due to slot combination has a strong influence on acoustic noise from induction motors. When both the vibration mode and natural frequency of the stator correspond to those of the electromagnetic force, the stator causes a resonance which results in a loud noise. Therefore, it is necessary to estimate accurately the electromagnetic force before acoustic noise can be reduced. The force is calculated numerically by a combination of transient magnetic field FEM analysis and harmonic analysis by using a Fourier series expansion. The moving of the rotor and eddy currents are also taken into account in the FEM method. The acoustic noise from three types of motors is measured to verify the developed method. The simulated frequency and space harmonic order of the electromagnetic force are in good agreement with the measured frequency and vibration mode.
TL;DR: In this paper, the authors examined transmission /sup 57/Fe Mossbauer spectroscopy (TMS), conversion X-ray (CXMS) and conversion electron (CEMS) data for both bulk and nanocrystalline samples, indicating similar cation distributions near the surface of nanoparticles.
Abstract: The synthesis of nanocrystalline zinc ferrite (ZnFe/sub 2/O/sub 4/) has been accomplished by a variety of chemical and mechanochemical techniques. An enhanced magnetization, 4-5 times that of bulk zinc ferrite, is observed for the nanoparticles regardless of the synthesis method. The hypothesis that the enhanced magnetization is due to partially inverted nanocrystalline zinc ferrite has been examined by transmission /sup 57/Fe Mossbauer spectroscopy (TMS), conversion X-ray Mossbauer spectroscopy (CXMS) and conversion electron Mossbauer spectroscopy (CEMS). Both TMS and CXMS data indicate differences in local structure between bulk and nanocrystalline samples, however they do not suggest that the samples are partially inverted. CEMS data are similar for both bulk and nanocrystalline samples, indicating similar cation distributions near the surface of nanocrystalline and bulk particles.
TL;DR: In this paper, a 3D finite element analysis (FEA) model for axial-field permanent-magnet motors is presented, based on a three-dimensional analytical analysis and expressed in terms of a finite sum of elementary functions.
Abstract: A formula is presented for computing the field in axial-field permanent-magnet motors. The formula is based on a three-dimensional (3-D) analytical analysis and is expressed in terms of a finite sum of elementary functions. It is readily programmed and ideal for parametric studies of field strength. It is also well suited for parallel processing and could be developed into a motor model for real-time performance simulations. It is applied here to a practical motor geometry and verified by the use of 3-D finite element analysis (FEA).
TL;DR: In this paper, a trapezoidal-rule quadrature is used to compute the magnetic field produced by a circular coil that contains a large number of turns wound onto a solenoid of rectangular cross section.
Abstract: A straightforward method is proposed for computing the magnetic field produced by a circular coil that contains a large number of turns wound onto a solenoid of rectangular cross section. The coil is thus approximated by a circular ring containing a continuous constant current density, which is very close to the real situation when wire of rectangular cross section is used. All that is required is to evaluate two functions, which are defined as integrals of periodic quantities; this is done accurately and efficiently using trapezoidal-rule quadrature. The solution can be obtained so rapidly that this procedure is ideally suited for use in stochastic optimization. An example is given, in which this approach is combined with a simulated annealing routine to optimize shielded profile coils for NMR.
TL;DR: The precalculation of a claw-pole alternator is presented based on the example of a prototype with additional permanent magnets, based on a three-dimensional magnetostatic field computation.
Abstract: Numerical procedures were developed for the calculation and design optimization of claw-pole alternators. Based on a three-dimensional (3D) magnetostatic field computation, the output performance, efficiency, local and global forces are computed and compared to measurements. The precalculation of a claw-pole alternator is presented based on the example of a prototype with additional permanent magnets.
TL;DR: The proposed hybrid optimization procedure was found to be efficient in most of the applications and the strengths of both techniques are used at different stages of the search.
Abstract: Genetic algorithms (GAs) have been successfully applied to optimization problems in a variety of applications in electromagnetics. In this paper, GAs are used along with a gradient-based direct search technique. The proposed hybrid optimization procedure was found to be efficient in most of the applications. The strengths of both techniques are used at different stages of the search. A magnetizer example is presented to show the effectiveness of the proposed technique.
TL;DR: In this paper, a small brushless DC motor with cogging torque reduction methods is discussed and applied to the optimum design of the armature pole shape, and the results are compared.
Abstract: Cogging torque reduction methods are discussed and applied to the optimum design of a small brushless DC motor. Because the cogging torque has a close relation with the distribution of the magnetization, the magnetizing system for permanent magnets is analyzed numerically by using the time-stepping finite element method. Based on the remnant magnetic flux densities, the cogging torque is computed by using finite element analysis. Optimum design of the armature pole shape is then carried out using design sensitivity analysis and an evolution strategy whose design variables are based on the harmonic balance method, and the results are compared. With these design results, sample motors are constructed and cogging torques are measured. By comparing the computational and experimental results, the problems in the usage of the numerical design method are discussed.
TL;DR: In this paper, the effects of Al oxidization time, Al thickness and annealing temperature on the tunnel properties were investigated, and changes of between 10 and 15% were observed in the resistance.
Abstract: We fabricated ferromagnetic tunnel junctions with naturally oxidized Al barriers, and investigated the effects of Al oxidization time, Al thickness and annealing temperature on the tunnel properties. Changes of between 10 and 15% have been observed in the resistance, and in some junctions, the MR ratios increase by annealing at 250 to 300/spl deg/C. The Ni-Fe/Co/Al-AlO/sub x//Co/Ni-Fe/Fe-Mn/NiFe junction showed a 24% spin-valve-like MR change after annealing at 300/spl deg/C for one hour.
TL;DR: In this paper, a homogenization technique for harmonic Maxwell equations in a composite periodic medium is given, which consists in using the finite element method to solve Maxwell equations with adequate periodicity conditions on a "basic cell" of the structure.
Abstract: A homogenization technique for harmonic Maxwell equations in a composite periodic medium is given. This technique consists in using the finite element method to solve Maxwell equations with adequate periodicity conditions on a "basic cell" of the structure. We describe this "cell problem" and report on numerical results for some cell structures.
TL;DR: In this paper, a mixture of organic solvent, surfactant, and aqueous solution was used for the synthesis of magnetic particles of magnetite, which were stabilized in a carrier liquid, producing a magnetic fluid.
Abstract: Ternary mixtures of organic solvent, surfactant, and aqueous solution forming a single phase are used for the synthesis of magnetic particles of magnetite. These particles, washed and covered with oleic acid, were stabilized in a carrier liquid, producing a magnetic fluid. X-ray diffraction, transmission electron microscopy, and magnetic measurements of the particles, and the prepared liquid are reported.