Showing papers in "IEEE Transactions on Magnetics in 1989"
TL;DR: In this paper, the uniqueness of the vector potential is given special attention, and a numerically stable finite-element scheme that performs well at low and high frequencies, does not require an unduly high number of degrees of freedom, and is capable of treating multiple connected conductors is presented.
Abstract: Various magnetic vector potential formulations for the eddy-current problem are reviewed. The uniqueness of the vector potential is given special attention. The aim is to develop a numerically stable finite-element scheme that performs well at low and high frequencies, does not require an unduly high number of degrees of freedom, and is capable of treating multiple connected conductors. >
720 citations
TL;DR: In this paper, the relation between magnetic field annealing and magnetic properties in Fe-based alloys called FINEMET, composed of an ultrafine grain structure, have been studied.
Abstract: The relation between magnetic field annealing and magnetic properties in Fe-based alloys called FINEMET, composed of an ultrafine grain structure, have been studied. High-remanence-ratio B-H curves and flat B-H curves can be obtained by longitudinal-field and transverse-field annealing, respectively. The values of core loss and relative permeability of FINEMET alloys annealed in a magnetic field are similar to those of Co-based alloys, and they show excellent soft magnetic properties in the high-frequency range. The alloys annealed in longitudinal fields are suitable for saturable reactors and high-frequency transformers, and those annealed in transverse fields are suitable for choke coils. >
182 citations
TL;DR: In this paper, it was shown that edge elements, as vectorial finite-element approximations fields like e and h, can be used to solve scattering problems, which can be done in essentially two ways, according to which of the two fields d or b one most wishes to get in divergence-free form.
Abstract: It is shown that edge elements, as vectorial finite-element approximations fields like e and h, can be used to solve scattering problems. This can be done in essentially two ways, according to which of the two fields d or b one most wishes to get in divergence-free form. Apparent drawback of edge elements (due to the increased number of degrees of freedom in comparison with nodal elements) are more than compensated by economies due to greater sparsity. Moreover, they could help get rid of unwanted spurious modes when resonance frequencies of waveguides of complicated shape are computed. >
180 citations
TL;DR: In this article, the history, characteristics, and development trends of the most important particulate magnetic recording materials are reviewed, including acicular iron oxides, chromium dioxide, cobalt-modified iron oxide, acicular metal particles, and barium ferrite.
Abstract: After describing briefly the principles of magnetic recording and the manufacture of media, the author reviews the history, characteristics, and development trends of the most important particulate magnetic recording materials. These are acicular iron oxides, chromium dioxide, cobalt-modified iron oxides, acicular metal particles, and barium ferrite. A trend common to most of the materials is particle size reduction. >
172 citations
TL;DR: In this article, the authors argue that to realize the hypervelocity potential of plasma armature railguns, restrike must be eliminated, and they describe two promising approaches which are based on demonstrated technology.
Abstract: It is noted that conventional plasma armature railguns are limited to velocities of 6-8 km/s by arc restrike. The author argues that to realize the hypervelocity potential of plasma armature railguns, restrike must be eliminated. He describes two promising approaches which are based on demonstrated technology. The near-term solution is some form of circuit arrangement which eliminates current flow in the restrike arc. Both segmented and distributed configurations merit further development, but major issues of electrical and mechanical complexity must be addressed. For the longer term, the development of advanced ceramics coupled with measures to reduce armature power shows promise. Special attention will be required to inject projectiles at a velocity greater than the damage threshold and to perform the plasma armatures to avoid local bore damage. With restrike under control, the only plasma-related limitation will be viscous drag on the armature plasma. Recent MIDI-2 experiments with a hydrogen plasma armature have demonstrated armature velocities in excess of 30 km/s, so armature drag does not appear to be an issue in the 10-20 km/s velocity regime. >
133 citations
IBM1
TL;DR: In this article, the design, construction, and performance of miniature superconducting quantum interference device susceptometers is discussed, and simple expressions for S/sub n/ (spin sensitivity) in miniature SQUID susceptometers are developed and the implications of dimensional scaling explored.
Abstract: The design, construction, and performance of miniature SQUID (superconducting quantum interference device) susceptometers is discussed. Spins (in units of mu /sub beta /) per square root Hz has been identified as an important figure of merit. Simple expressions for S/sub n/ (spin sensitivity) in miniature SQUID susceptometers are developed and the implications of dimensional scaling explored. The details of several existing and proposed designs are reviewed, including versions that utilize commercial SQUIDs. With thin-film DC SQUIDs, S/sub n/ values of a few thousand spins/ square root Hz have already been obtained, and it is projected that values of a few hundred will be achieved soon. >
133 citations
131 citations
TL;DR: The ultracapacitor is composed of an inline stack of electrodes, which leads to an extremely low inductance device, and it exhibits interesting frequency dependence as mentioned in this paper, although its discharge characteristics and equivalent circuit are similar to those of dielectric capacitors.
Abstract: The charge-storage mechanism and the design of the ultracapacitor are described. Based on a ceramic with an extremely high specific surface area and a metallic substrate, the ultracapacitor provides extremely high energy densities and exhibits low ESR (equivalent series resistance). The combination of low ESR and extremely low inductance provides the ultracapacitor with a very high power density and fast risetime as well. As a double-layer capacitor, the ultracapacitor is not constrained by the same limitations as dielectric capacitors. Thus, although its discharge characteristics and equivalent circuit are similar to those of dielectric capacitors, the capacitance of the ultracapacitor increases with the ceramic loading on the substrate and its ESR is inversely proportional to the cross-sectional area of the device. The ultracapacitor is composed of an inline stack of electrodes, which leads to an extremely low inductance device, and it exhibits interesting frequency dependence. The ultracapacitor principle has been extended to nonaqueous electrolytes and to a wide temperature range. >
130 citations
TL;DR: In this paper, the sensitivity versus a geometric or physical parameter and its use in an optimization process are presented, where the quasiNewton method is used to determine the direction of minimization, and the constraints of upper and lower bounds of parameters are treated by the penalty function.
Abstract: The calculation of the sensitivity versus a geometric or physical parameter and its use in an optimization process are presented. The 2-D finite-element method is used in the magnetic field calculation. The quasiNewton method is used to determine the direction of minimization, and the constraints of upper and lower bounds of parameters are treated by the penalty function. A cubic approximation method is used in the unidimensional minimization. Minimization of the current density (J/sub c/) while keeping the force desired for a relay model is presented as an example. >
128 citations
TL;DR: In this article, the authors carried out static and dynamic analyses of uniform one-dimensional arrays of ultrasmall tunnel junctions and found that correlated single-electron tunneling in the junctions of the array results in a behavior qualitatively similar to that of the Josephson transmission line.
Abstract: The authors carried out static and dynamic analyses of uniform one-dimensional arrays of ultrasmall tunnel junctions. The correlated single-electron tunneling in the junctions of the array results in a behavior qualitatively similar to that of the Josephson transmission line. In particular, external electric fields applied to the array edges can inject single-electron-charged solitons into the array interior. The shape of such a soliton and the character of its interactions with other solitons and the array edge are very similar to those of Josephson vortices (sine-Gordon solitons) in the Josephson transmission line. Under certain conditions, a coherent motion of the soliton train along the array is possible, resulting in generation of narrowband SET (single-electron tunneling) oscillations with frequency f=/e, where is the DC current flowing along the array. >
121 citations
TL;DR: In this article, the use of model-based parameter estimation based on rational function approximations is proposed to reduce the number of frequencies at which solutions or samples are required, and a sampling approach that uses frequency derivatives of the response and a novel analytical technique based on differentiating the moment method impedance equation is introduced.
Abstract: Two main ideas are introduced: (1) the use of model-based parameter estimation based on rational function approximations, which reduces the number of frequencies at which solutions or samples are required; (2) a sampling approach that uses frequency derivatives of the response and a novel analytical technique based on differentiating the moment method impedance equation, which provides derivative information in a time proportional to N/sup 2/ in contrast with the N/sup 3/ dependence in solving the original problem. Antenna input admittances are modeled using frequency samples and derivatives. The rational function model is shown to offer a large advantage over polynomial interpolation of a frequency response. Application of the frequency-derivative approach is demonstrated for problems having well-defined resonances such as a dipole antenna, and for more challenging problems having narrow resonances. >
IBM1
TL;DR: A measurement tool based on an in-plane rotating and saturating magnetic field and laser-beam-deflection technique, which is able to meet the requirements of more sensitive, reliable, and easy-to-use tools to monitor magnetostriction is described in this article.
Abstract: The drive in data storage technology towards utilizing magnetic films with lower magnetostriction (to reduce the magnetoelastic energy term) and reduced thickness has resulted in the requirement for more sensitive, reliable, and easy-to-use tools to monitor magnetostriction. A measurement tool based on an in-plane rotating and saturating magnetic field and laser-beam-deflection technique, which is able to meet these requirements, is described. The tool developed offers high accuracy, large dynamic range, long-term stability, simple sample insertion, and a fast, easy measurement procedure. With this tool, the measurement of small magnetostriction coefficients of thin soft-magnetic films can become a simple, fast, and reliable procedure, thus helping the development of magnetic thin-film production processes and routine composition control. >
TL;DR: In this article, an analytical model is developed for confined high-pressure discharges operating in a quasi-steady state in which the resulting plasma jet characteristics are steady at hydrodynamic timescales.
Abstract: Different physical processes in confined high-pressure discharges are analyzed. The energy transport inside the discharge tube yields a radial temperature profile which has sharp gradients only near the tube walls. The regime at which such discharges can operate at a steady state is determined. For a given discharge ablation rate and plasma pressure, the tube length is limited. An analytical model is developed for confined high-pressure discharges operating in a quasi-steady-state in which the resulting plasma jet characteristics are steady at hydrodynamic timescales. This model allows the calculation of all the discharge parameters, such as ablation rate plasma temperature, resistivity, density and pressure as functions of the slowly varying current and the tube dimensions. The scaling laws obtained in this model are important for determining the impedance matching between the discharge and the power source and upgrading the discharge energy in electrothermal launchers to hypervelocities. Good agreement is obtained between the analytical model and experimental results at energies up to 100 kJ. >
IBM1
TL;DR: In this paper, the concept of patterned longitudinal biasing as a means to suppress Barkhausen noise in narrow track MR (magnetoresistive) elements without under permeability degradation of the read region is discussed.
Abstract: The concept of patterned longitudinal biasing as a means to suppress Barkhausen noise in narrow-track MR (magnetoresistive) elements without under permeability degradation of the read region is discussed. This scheme also renders the performance of the read region relatively insensitive to the exact magnitude of the externally applied longitudinal bias, as long as this bias is large enough to ensure good longitudinal alignment of magnetization at the tail regions. This concept was demonstrated with Permalloy MR elements using patterned exchange biasing. Results show that these elements do indeed exhibit quiet and stable responses, but without the severe sensitivity reduction which is characteristic of MR elements under normal strong uniform longitudinal biasing. >
TL;DR: The Preisach (1935) model has been discussed and extended in papers concerned with ferromagnetic phenomena as discussed by the authors, and there is a growing interest in the preisach model as an object of mathematical study.
Abstract: The Preisach (1935) model has been discussed and extended in papers concerned with ferromagnetic phenomena. More recently, there is a growing interest in the Preisach model as an object of mathematical study. The author summarizes some of these results. Continuity properties and the inverse operator are discussed, and extensions to the so-called moving model are presented. >
TL;DR: New elements of the Rapid Single Flux Quantum (RSFQ) logic family have been designed, fabricated, and tested as mentioned in this paper, and all-Nb 14-layer 5 mu m technology using externally shunted tunnel junctions with j/sub c/=500 A/cm/sup 2/, I/sub C/R/sub s/=300 mu V, and B/subc/ >
Abstract: New elements of the rapid single flux quantum (RSFQ) logic family have been designed, fabricated, and tested. All-Nb 14-layer 5 mu m technology using externally shunted tunnel junctions with j/sub c/=500 A/cm/sup 2/, I/sub c/R/sub s/=300 mu V, and B/sub c/ >
TL;DR: In this paper, an extension to the harmonic solution of nonlinear magnetodynamic problems using the classical finite-element method is presented. But the results obtained by this algorithm are quite identical to those obtained by a step-by-step simulation.
Abstract: The nonlinear magnetodynamic model implemented in FLUX2D is improved in order to solve the field equations in an induction motor with a highly saturated slot isthmus. The resulting method is an extension to the harmonic solution of nonlinear magnetodynamic problems using the classical finite-element method. This extension applies the nonlinear Newton-Raphson algorithm in the same way as for magnetostatic problems, using the Jacobian matrix presented. The forces and torques obtained by this algorithm are quite identical to those results obtained by a step-by-step simulation. Applied to an industrial four-pole, squirrel cage induction machine, this method gives over the whole range of speed an error less than 5%. >
TL;DR: In this paper, two-dimensional and three-dimensional field distributions produced by permanent magnets (PMs) of a PMSM are obtained in analytical forms, based on the concept of magnetic charge and the method of images.
Abstract: Two-dimensional and three-dimensional field distributions produced by permanent magnets (PMs) of a permanent-magnet linear synchronous motor (PMLSM) are obtained in analytical forms, based on the concept of magnetic charge and the method of images. The determination of electromagnetic forces and parameters of this type of a motor is examined. The proposed method and the resulting simplified formulas are useful for the design and analysis of PMLSMs as well as for other types of PM motors. Calculated results compare favorably with the experimental results, and thus validate the assumptions and the analysis. >
TL;DR: In this paper, a finite-element procedure is presented for calculation of the frequency-dependent resistances and inductances and of the capacitances of a multiconductor cable taking account of skin and proximity effects.
Abstract: A finite-element procedure is presented for calculation of the frequency-dependent resistances and inductances and of the capacitances of a multiconductor cable. The inductances and resistances are evaluated taking account of skin and proximity effects. The capacitances are obtained by integrating the Laplace equation. The procedure permits analysis of systems having extremely complex geometric configurations and also diverse insulating materials with different dielectric characteristics. The resistance, inductance, and capacitance values obtained agree with the values obtained, in simple cases, by an exact analytical solution. >
TL;DR: An overview of the compulsator research is presented in this paper, including a brief history of the device, electromagnetic and mechanical design considerations, status of machines currently in operation and under development, and future technology.
Abstract: An overview of compulsator research is presented, including a brief history of the device, electromagnetic and mechanical design considerations, status of machines currently in operation and under development, and future technology. The compulsator appears to have great potential as a power supply for a variety of fields including fusion, industrial applications, directed energy weapons, low-frequency sound sources, and electromagnetic launch (EML) technology. Several machines have been built and tested, successfully demonstrating the principle of operation and showing that a compact rotating machine, operating at high efficiency, can provide a series of appropriate high current pulses without the necessity of complicated conditioning and switching networks. >
TL;DR: In this article, a new type of thin-film head on silicon (IC head) for high-density magnetic recording was developed, which is based on the intensive use of semiconductor equipment and silicon material.
Abstract: In order to achieve a breakthrough in advanced head fabrication cost and performance, a new type of thin-film head on silicon (IC head) for high-density magnetic recording was developed. This technology is based on the intensive use of semiconductor equipment and silicon material. The authors discuss the fabrication cost, head structure, and design and compare them with those of conventional thin-film heads made on ceramic substrates. Fabrication processes and technical details for realizing heads and sliders in the same process line by techniques similar to those used by semiconductor manufacturers are given. It is concluded that the IC head offers many advantages over the conventional thin-film head due to its mass production and low fabrication cost. >
TL;DR: In this article, three kinds of corrosion tests, a humidity test, an autoclave test, and a salt spray test, were performed on a sintered magnet treated with nickel plating.
Abstract: Three kinds of corrosion tests, a humidity test (80 degrees C, 90% RH), an autoclave test (120 degrees C, 2 atm saturated with water vapor), and a salt spray test (35 degrees C, 5% NaCl), were performed on a sintered magnet treated with nickel plating. For comparison, samples with epoxy resin coating, Al ion plating, and without coating were also exposed to the corrosion test. After specified periods of corrosion testing, the permanent flux loss of the remagnetized sample was measured. Changes in appearance were also observed. It was found that the epoxy resin coating could not prevent the penetration of moisture in the humidity and autoclave tests because of its hygroscopic properties. The nickel plating and Al ion plating withstood the humidity and autoclave tests reasonably well, but they suffered slight corrosion in the salt spray test. It is concluded that the use of nickel plating can provide high corrosion resistance and low cost of production. >
TL;DR: In this paper, a complex analysis of the nonlinear diffusion problem in ferromagnetic materials under steady-state excitation is presented, where the relative permeability is assumed to be constant in time but different from point to point and is related to the B-H characteristic curve with the help of the stored magnetic co-energy density.
Abstract: A complex analysis of the nonlinear diffusion problem in ferromagnetic materials under steady-state excitation is presented. The problem is solved by considering an equivalent fictitious material where the relative permeability is assumed to be constant in time but different from point to point and is related to the nonlinear B-H characteristic curve with the help of the stored magnetic co-energy density. Eddy current losses are calculated in a one-dimensional thick steel plate. A comparison made with results obtained from the classical step-by-step method shows a good agreement. >
TL;DR: In this paper, a superconductive current-biased variable-delay transmission line structure is proposed, which is capable of operating up to terahertz in the frequency domain.
Abstract: The authors present a device concept for a superconductive current-biased variable-delay transmission line structure which is capable, in principle, of operating up to the terahertz regime. The device makes use of the change in kinetic inductance of superconductors with transport current. The relevant material figures of merit for optimum performance of such a device are defined, and suitable candidate materials are identified. The device concept has been tested in niobium technology, where temperature-dependent changes in the inductance are easily achieved. Preliminary measurements on the temperature and current dependence of niobium transmission line resonators operating in the 1-20 GHz range are presented. The expected DC bias current variable delay has not yet been observed, but niobium is not expected to be the optimum material for such an effect. Suggested improvements include the use of more favorable materials, such as amorphous alloys and oxide superconducting films, and the use of modified microstrip geometries where a closer approach to the depairing critical current density should be possible. >
TL;DR: In this article, a finite-element method for the calculation of the frequency-dependent series impedances of underground power cables is described, which are needed for the analysis of electromagnetic transients in power systems.
Abstract: A finite-element method for the calculation of the frequency-dependent series impedances of underground power cables is described. These impedances are needed for the analysis of electromagnetic transients in power systems. A technique based on the perturbation concept is used to reduce the size of the solution region inside the poorly conducting earth. The impedances of buried single-core and pipe-type cables are calculated, and the results are compared with those from analytical formulas. >
TL;DR: In this article, conditions required for in situ growth of YBaCuO thin films by reactive electron-beam evaporation have been explored, and three sources of activated oxygen (atomic oxygen from microwave discharge, plasma generated by electron beams, and an ion beam) were compared.
Abstract: Conditions required for in situ growth of YBaCuO thin films by reactive electron-beam evaporation have been explored. Three sources of activated oxygen (atomic oxygen from microwave discharge, plasma generated by electron beams, and an ion beam) were compared. The best results so far were obtained with atomic oxygen. Epitaxial films with high critical currents were grown on SrTiO/sub 3/ [100] and [110], Al/sub 2/O/sub 3/ (1102), and MgO [100] at 600 degrees C. Evaporation rates were controlled with a rate monitor using atomic absorption. >
TL;DR: In this paper, a general three-dimensional computational model of ferrite-core eddy-current probes has been developed for research and design studies in nondestructive evaluation.
Abstract: A general three-dimensional computational model of ferrite-core eddy-current probes has been developed for research and design studies in nondestructive evaluation. The model is based on a volume integral approach for finding the magnetization of the ferrite core excited by an AC-current-carrying coil in the presence of a conducting workpiece. Using the moment method, the integral equation is approximated by a matrix equation and solved using conjugate gradient techniques. Illustrative results are presented showing the impedance characteristics and field distributions for practical eddy-current probe configurations. >
TL;DR: In this article, the authors measured the magnetic field H' at the center of a hollow of sintered Y-Ba-Cu-O superconductor as a function of applied field H, temperature, tube length, and tube wall thickness.
Abstract: The authors have measured the magnetic field H' at the center of a hollow of sintered Y-Ba-Cu-O superconductor as a function of applied field H, temperature, tube length, and tube wall thickness. The maximum field that can be shielded H/sub sh/ agrees with the value calculated from the critical state model using the measured critical-current density J/sub c/. The maximum trapped field H/sub tr/ in the tube, on decreasing H to zero, exceeds H/sub sh/ by as much as a factor of two, and large enhancements in J/sub c/ are observed in the decreasing field. These phenomena are identified with intragranular flux pinning present only after H has exceeded H/sub c1/ of the grains. Finite tube length does not affect the H/sub tr//H/sub sh/ ratio appreciably. H/sub sh/ depends approximately on the square root of the wall thickness. >
TL;DR: In this paper, the microstructural effect of Al addition was studied by transverse electron microscopy assisted by energy dispersive X-ray analysis, and a systematic change in the wetting behavior of the liquid phase, at sintering temperature, was detected.
Abstract: The coercivity of Nd-Fe-B sintered magnets has been improved by Al additions. To study the microstructural effect of Al addition, two types of investigation were formed: (1) the change in the wetting behavior of the liquid phase, at the sintering temperature, was studied by measurements of the wetting angle; and (2) the microstructural changes resulting from Al additions were studied by transverse electron microscopy assisted by energy dispersive X-ray analysis. A systematic change was detected that depended on the kind of Al addition, i.e., metallic or as Al/sub 2/O/sub 3/. >
TL;DR: In this article, a two-dimensional finite-element model for the magnetic and temperature fields in a railgun is presented for several rail and armatures designs, and a molybdenum armature is identified as candidates for future solid armature testing.
Abstract: Velocity limits of a solid armature in a railgun are the result of temperature and internal forces which surpass the yield strength of the material. A two-dimensional finite-element model for the magnetic and temperature fields in a railgun is presented for several rail and armatures designs. Copper rails and a molybdenum armature are identified as candidates for future solid armature testing. All simulations are performed for a 1/2-inch-square-bore railgun. >