Showing papers in "IEEE Transactions on Magnetics in 1991"
TL;DR: In this article, permanent magnets can be made of composite materials consisting of two suitably dispersed ferromagnetic and mutually exchange-coupled phases, one of which is hard magnetic in order to provide a high coercive field, while the other may be soft magnetic, just providing a high saturation J/sub s/, and should envelop the hard phase regions to prevent their corrosion.
Abstract: It is proposed that permanent magnets can be made of composite materials consisting of two suitably dispersed ferromagnetic and mutually exchange-coupled phases, one of which is hard magnetic in order to provide a high coercive field, while the other may be soft magnetic, just providing a high saturation J/sub s/, and should envelop the hard phase regions in order to prevent their corrosion. A general theoretical treatment of such systems shows that one may expect, besides a high energy product (BH)/sub max/, a reversible demagnetization curve (exchange-spring) and, in certain cases, an unusually high isotropic remanence ratio B/sub r//J/sub s/, while the required volume fraction of the hard phase may be very low, on the order of 10%. The technological realization of such materials is shown to be based on the principle that all phases involved must emerge from a common metastable matrix phase in order to be crystallographically coherent and consequently magnetically exchange coupled. >
2,283 citations
TL;DR: In this paper, it was suggested that in many ferromagnetic materials there may occur particles distinct in magnetic character from the general matrix, and below the critical size, depending on shape, for which domain boundary formation is energetically possible.
Abstract: It is suggested that in many ferromagnetic materials there may occur particles distinct in magnetic character from the general matrix, and below the critical size, depending on shape, for which domain boundary formation is energetically possible. For such single-domain particles, change of magnetization can take place only by rotation of the magnetization vector. As the field changes continuously, the resolved magnetization may change discontinuously at critical values of the field. The character of the magnetization curves depends on the degree of magnetic anisotropy of the particle and on the orientation of easy axes with respect to the field. The magnetic anisotropy may arise from the shape of the particle, from magnetocrystalline effects, and from strain. A detailed quantitative treatment is given of the effect of shape anisotropy when the particles have the form of ellipsoids of revolution, along with a less detailed treatment for the general ellipsoidal form.
1,401 citations
Abstract: Fluxmetric (ballistic) and magnetometric demagnetizing factors N/sub f/ and N/sub m/ for cylinders as functions of susceptibility chi and the ratio gamma of length to diameter have been evaluated. Using a one-dimensional model when gamma >or=10, N/sub f/ was calculated for -1 >
472 citations
TL;DR: In this paper, the complex permeability and permittivity properties of ferrite-rubber composite material were investigated at X-band frequencies and their relationship with microwave absorbing properties were investigated.
Abstract: The complex permeability ( mu /sub r/) and permittivity ( epsilon /sub r/) spectra at X-band frequencies and their relationship with microwave absorbing properties are investigated in ferrite-rubber composite material. Multifrequency measurements of mu /sub r/ and epsilon /sub r/ are made by the reflection/transmission technique. The theoretical determination of matching frequency and matching thickness and minimum reflection loss can be made by plotting the observed mu /sub r/ and epsilon /sub r/ spectra on the solution map of wave-impedance-matching. It is found that a proper combination of mu /sub r/ and epsilon /sub r/ is necessary to produce the zero-reflection absorber at a given frequency and thickness. >
407 citations
TL;DR: In this article, the powder-in-tube method was used to fabricate BiPbSrCaCuO wires, and a prototype of a react & wind-processed coil was demonstrated using greater than 4m-long multifilamentary wires, which successfully produced enough magnetic field to rotate copper windings between steel cores.
Abstract: Silver-sheathed BiPbSrCaCuO wires were fabricated using the powder-in-tube method. Critical current densities at 77.3 K were 4.7*10/sup 4/ A/cm/sup 2/ in a zero magnetic field, 3.1*10/sup 4/ A/cm at 0.1 T, and 1.1*10/sup 4/ A/cm/sup 2/ at 1 T. In liquid He, these wires can carry 1.03*10/sup 5/ A/cm/sup 2/ at 23 T. J/sub c/ and J/sub c/-B enhancements are due to grain-boundary improvements. Detailed investigation of J/sub c/-B characteristics in magnetic fields, especially increasing and decreasing fields, revealed that history effect behaviours caused by weak links disappeared with improvements of grain-boundary characteristics at both temperatures. It was observed that 1296 multifilamentary wires were capable of sustaining over 70% of J/sub co/ even after a strain of up to 0.66% repeated 10 times. Prototypes of coils and current leads were fabricated using 20-m-long wires. One coil showed critical currents of 54.2 A at 77.3 K and 367 A at 4.2 K. This coil generated a B/sub m/ of 142 G at 77.3 K and 876 G at 4.2 K. A prototype of a react & wind-processed coil was demonstrated using greater than 4-m-long multifilamentary wires, and it successfully produced enough magnetic field to rotate copper windings between steel cores.
341 citations
TL;DR: In this paper, an empirical model is presented that predicts the critical current density (J/sub c/) of Nb/sub 3/Sn wires under the combined effects of temperature, strain, and radiation damage.
Abstract: An empirical model is presented that predicts the critical current density (J/sub c/) of Nb/sub 3/Sn wires under the combined effects of temperature, strain, and radiation damage. The model, based on previous work of D.P. Hampshire et al. (1985) and J. W. Ekin (1980), predicts J/sub c/ with a reasonable degree of accuracy. The model can be used with a limited number of input parameters. eliminating the need for detailed characterization, particularly the difficult tasks of measuring critical current as a function of temperature and radiation damage.
266 citations
TL;DR: In this article, a dual-stage actuator was developed using a piezoelectric device for a magnetic disk drive with a high track density over 15 kTPI, where the head position was detected by an optical method using a dot-pattern etched on a disk.
Abstract: A dual-stage actuator has been developed using a piezoelectric device for a magnetic disk drive with a high track density over 15 kTPI. This actuator uses a VCM (voice coil motor) rotary actuator as a coarse actuator and a piezoelectric actuator installed in a head-arm as a fine actuator. The stroke of the fine actuator is 4.6 mu m, which is sufficient for a track pitch of 1.5 mu m at 17 kTPI. The head position is detected by an optical method using a dot-pattern etched on a disk. The authors describe the design of the dual-stage actuator, including structural analysis, its static and dynamic characteristics, the dual-stage feedback control system. Experimental results of tracking with high accuracy on a 3.5-in disk-drive unit are presented. >
250 citations
TL;DR: In this paper, a numerical finite element approach to magnetic flux distribution, coupled with a physical model of losses in ferromagnetic laminations under generic flux waveform, was used to estimate core losses in rotating electrical machines.
Abstract: Core losses in rotating electrical machines have been estimated through direct use of the standard Epstein loss data of the employed magnetic laminations, without introducing empirical correcting factors. The prediction is based on a numerical finite element approach to magnetic flux distribution, coupled to a physical model of losses in ferromagnetic laminations under generic flux waveform, which takes into account the specific role of the hysteresis and classical and excess loss components. An application has been made to the case of a 7.5-kW four-pole induction motor under no-load conditions. The predicted core losses turn out to be about 20% lower than the measured ones, a fact which points to an appreciable contribution of the rotor cage Joule losses and to the detrimental role played in the material properties by the residual and applied stresses introduced by lamination punching and core assemblage. >
226 citations
TL;DR: In this paper, a study of the magnetic behavior characteristic of a spin-glass, which has been examined for systems of ultrafine particles, is reported, and the results obtained support the suggestion of E. P. Wohlfarth (1977) that spinglass effects could arise from the clustering of impurity spins in the host material into ferromagnetic rich clusters.
Abstract: A study of the magnetic behavior characteristic of a spin-glass, which has been examined for systems of ultrafine particles, is reported. The results obtained support the suggestion of E. P. Wohlfarth (1977) that spin-glass effects could arise from the clustering of impurity spins in the host material into ferromagnetic rich clusters. All the results are explained on the basis of the Neel superparamagnetic (blocking) model. The results obtained show that the behavior of fine particle systems is similar to that of certain spin-glass alloys (e.g., Au/Fe alloys). This result supports the idea that spin-glass alloys can be interpreted on the basis of a blocking model. >
180 citations
TL;DR: In this paper, a series array of 100 DC SQUIDs has been fabricated using trilayer Nb-AlO/sub x/-Nb junctions, which produces an output voltage swing of several millivolts across the array.
Abstract: A series array of 100 DC SQUIDs has been fabricated using trilayer Nb-AlO/sub x/-Nb junctions. The SQUIDs are modulated with a common flux bias line and produce an output voltage swing of several millivolts across the array. The large output voltage will allow direct connection to room temperature electronics without the transformer coupling and resulting frequency limitations commonly associated with DC SQUID amplifiers. A bandwidth of DC to at least 175 MHz for a 100-SQUID array has been measured. The series array will be used as the output stage for a multistage integrated SQUID amplifier.
166 citations
TL;DR: In this paper, a green tape with an excellent J/sub c/ was prepared by doctor-blade casting and a partial melt process, and a highly textured microstructure was formed during slow cooling between 890 and 870 degrees C.
Abstract: Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ textured tapes with an excellent J/sub c/ were prepared by doctor-blade casting and a partial melt process. A green tape, composed of Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ powder and an organic formulation, was laid on a silver foil and heat-treated. A highly textured microstructure was formed during slow cooling between 890 degrees C and 870 degrees C. X-ray diffraction and scanning-electron-microscope observation indicated that initially an oriented Bi/sub 2/Sr/sub 2/Cu/sub 1/O/sub x/ structure forms by growth from the melt, and it subsequently transforms to the Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ phase. A grain alignment was significantly enhanced in the oxide layer with a thickness less than 20 mu m. Silver dissolved in the oxide from the substrate also plays an important role in the grain alignment by lowering the melting point of the oxide. The T/sub c/ of a tape could be increased to 89 K by quenching from 870 degrees C. The J/sub c/ was 1.3*10/sup 4/ A/cm/sup 2/ at 77 K, 0 T and 1.4*10/sup 5/ A/cm/sup 2/ at 4.2 K in a high magnetic field of 25 T.
TL;DR: In this paper, a method for computing high-frequency ferrite core losses in the magnetic component for arbitrary voltage waveforms is presented, which requires only a few material parameters as input.
Abstract: A practical method is presented for computing high-frequency ferrite core losses in the magnetic component for arbitrary voltage waveforms. The model presented requires only a few material parameters as input. To calculate ferrite hysteresis losses, a model based on empirical rules is employed. For high-frequency eddy current losses, a built phenomenon is assumed. It is demonstrated that the hysteresis model reproduces all of the important known features of the soft ferrites. These features include hysteresis loop shapes for low- and high-field excitations, the nonlinear permeability behavior, and hysteresis loss dependence on the amplitude of the exciting field. It is found that the total calculated core loss as a function of frequency and flux density correctly describes the observed soft ferrite behavior. The theoretical results are compared with available data for two commercial ferrites, and good agreement is found up to fairly high frequencies ( approximately 500 kHz). >
TL;DR: In this paper, a melt-powder-melt-growth (MPMG) process was proposed for bulk Y-Ba-Cu-O superconductors, which results in high J/sub c/ for bulk superconductor.
Abstract: The authors report a melt-powder-melt-growth (MPMG) process which results in high J/sub c/ for bulk Y-Ba-Cu-O superconductors. The Y-Ba-Cu-O pellets or powders are melt quenched. The quenched plates are crushed into powder and mixed well. The powder is then compacted into desired shapes, remelted, and slowly cooled in a thermal gradient. When the starting composition is changed from the 1:2:3 stoichiometry toward the Y/sub 2/BaCuO/sub 5/
TL;DR: Attention is given to the hybrid nature of the PRML channel; many channel functions are implemented using a combination of both analog and digital circuits.
Abstract: Describes the channel architecture, IC technology, and integration solutions used in implementing the IBM 0681 disk drive data channel. A brief description of the 0681 disk drive is given along with a block representation of the data channel. Particular focus is placed on the major channel functions: equalization, data coding and detection, gain and timing recovery, and write circuitry. Both the analog and adaptive digital equalizer sections used in the channel are described. The 0681 channel uses an IBM mixed-mode IC technology to implement all channel functions. This IC process is illustrated, along with the partial-response maximum-likelihood (PRML) chip layout. Attention is also given to the hybrid nature of the PRML channel; many channel functions are implemented using a combination of both analog and digital circuits. >
TL;DR: In this paper, a prototype 3.5-in diameter hard disk drive with a track density of 17 kTPI was used to minimize the reduction in the physical clearance between the medium and the head.
Abstract: Developments of magnetic head, recording medium, positioning, and signal processing technologies made it possible to perform magnetic recording at an areal density of 2 Gb/in/sup 2/ on a prototype 3.5-in diameter hard disk drive. A track density of 17 kTPI, which is comparable to or even greater than that used in optical storage systems, is used to minimize the reduction in the physical clearance between the medium and the head. The authors outline the system and its component technologies. The read/write characteristics of the 3.5-in prototype disk system are also reported. >
TL;DR: In this article, the microwave surface impedance of high-T/sub c/ superconductors is studied and the frequency, temperature, and field dependence of the surface resistance R/sub s/ and the temperature dependence of field penetration depth lambda are discussed on the basis of a two-fluid model.
Abstract: The available data on the microwave surface impedance Z/sub s/ of high-T/sub c/ superconductors from more than 30 laboratories around the world are reviewed to show the frequency, temperature, and field dependence of the surface resistance R/sub s/ and the temperature dependence of the field penetration depth lambda . The data are discussed on the basis of a two-fluid model and are compared with results from the classical superconductors Nb and Nb/sub 3/Sn. At temperatures above 0.8 T/sub c/, Z/sub s/ values of classical and high-T/sub c/ superconductors show strong similarities and are in close agreement with the Mattis-Bardeen theory. The comparatively very high R/sub s/ of the cuprates at 4.2 K, however, is indicative of a high density of unpaired charge carriers. The lowest values for R/sub s/ and lambda obtained until now with epitaxially grown YBa/sub 2/Cu/sub 3/O/sub 7- delta / films are 16 mu Omega at 4.2 K and 10 GHz and 140 nm, respectively. Such films are required for high RF field applications. Polycrystalline samples show a strong field dependence of R/sub s/. The highest magnetic surface field without R/sub s/ deterioration achieved so far on single crystals of YBa/sub 2/Cu/sub 3/O/sub 7- delta / is about 100 G.
TL;DR: In this article, a two-step annealing procedure is used with a partial melting of the wire core, the melt having a composition near Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 6+x/ on cooling, as revealed by XRD (X-ray diffraction) measurements.
Abstract: Bi-2212/Ag phi 1-mm round untextured wires have been produced with critical current densities of 1200 A/cm/sup 2/ at 77 K, 0 T and up to about 2.0*10/sup 4/ A/cm/sup 2/ at 4.2 K in magnetic fields beyond 20 T. In order to achieve this, a two-step annealing procedure is necessary with a partial melting of the wire core, the melt having a composition near Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 6+x/. On cooling, the Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 6+x/ phase appears at 880 degrees C, as revealed by in situ XRD (X-ray diffraction) measurements. Long-term annealing at 840 degrees C leads to the transformation of this phase into the Bi/sub 2/Sr/sub 2/Ca/sub 1/ Cu/sub 2/O/sub 8+x/ phase. The alkaline earth cuprate (Sr,Ca) /sub 14/Cu/sub 24/O/sub approximately=40/ and CuO occur as major extraneous phases. Helically shaped samples yield a lower j/sub c/ between 3*10/sup 3/ and maximum 1.0*10/sup 4/ A/cm/sup 2/ at 4.2 K, 10 T. Cracks due to thermal expansion mismatch with the sample holder and remaining inhomogeneities along the wire are responsible for these lower values. From I-V curves measured at 4.2 K, n-values were determined to be 20 to 25 in the interesting very-high-field region beyond 20 T. Bi-2223/Ag highly textured thin tapes yield an appreciably higher j/sub c/ of 2.6*10/sup 4/ A/cm/sup 2/ at 77 K, 0 T. Temperature-dependent measurements of j/sub c/ as a function of magnetic field B yielded onset of significant flux creep above 20 K, limiting the range of application in magnet technology to the temperature range up to 20 K unless an additional more effective pinning mechanism is introduced.
TL;DR: A customized version of SPICE3b is developed which incorporates a Josephson junction model, and a margin analysis command has been added, allowing operating ranges to be determined for an arbitrary circuit with a minimum of simulation.
Abstract: SPICE3 is the most recent version of the circuit simulator SPICE from the University of California, Berkeley. Unlike its predecessors, SPICE3 is written in the C programming language, and is designed for interactive use under a modern multitasking operating system. The Berkeley distribution of SPICE3 lacks support for Josephson junctions. As a consequence, the author has developed a customized version of SPICE3b.1 which incorporates a Josephson junction model. The model supports control current modulation, as well as fifth-order polynomial description of the quasiparticle current suitable for NbN junctions. In addition, a margin analysis command has been added, allowing operating ranges to be determined for an arbitrary circuit with a minimum of simulation. Further enhancements include the addition of a second graphics post-processor with new features and display, as well as debugging and streamlining of the original code. The program is currently configured to run on an IBM/Intel 386 compatible computer with Weitek coprocessor, under DOS extender software. The modifications to SPICE3 are described, and some of the issues involved in simulating Josephson circuits are also addressed. The features and philosophy of the SPICE3 program are discussed, and sample results presented.
TL;DR: In this paper, a modified solution for minor loops is presented which retains the features of D.C. Jiles and D.L. Atherton's original motor loops, but only requires knowledge of the initial point on each portion of the loop to obtain the solution.
Abstract: The reason for the failure of the differential equations to yield physical minor loops involved in the magnetization in ferromagnetic materials is explained. A modified solution for minor loops is presented which retains the features of D.C. Jiles and D.L. Atherton's (1983) original motor loops, but only requires knowledge of the initial point on each portion of the loop to obtain the solution. This yields a general differential equation formulation for the Jiles-Atherton theory that can be used with circuit simulations having arbitrary excitations and initial conditions for ferromagnetic components. >
TL;DR: The relationship between the statistical distribution of the particle coercivity and the high density magnetic recording characteristics was investigated in this paper, where it was shown that a sharper PCD resulted in better recording performance, particularly in perpendicular recording media.
Abstract: Most magnetic recording media are composed of magnetic crystalline particles having inherent coercivity originating from crystalline and shape anisotropies. The relationship between the statistical distribution of the particle coercivity and the high density magnetic recording characteristics was investigated. In order to estimate the width of the particle coercivity distribution (PCD) in a medium, a method in which the PCD can be obtained from M-H major and minor curves. The PCD correlates strongly with the coercivity squareness and the switching field distribution, and needs no compensation for the demagnetizing field, even in perpendicular recording media. It was shown that a sharper PCD resulted in better recording performance, particularly in perpendicular recording media. >
TL;DR: Inverse problem methodology is extended, through the more difficult geometric differentiation of finite-element matrices, to identify the location, material, and value of unknown sources within an inaccessible region using exterior measurements.
Abstract: Inverse problem methodology is extended, through the more difficult geometric differentiation of finite-element matrices, to identify the location, material, and value of unknown sources within an inaccessible region using exterior measurements. This is done through the definition of an object function that vanishes at its minimum when the externally measured electric field matches the electric field given by an assumed configuration that is optimized to match measurements. The method is demonstrated by identifying the shape, permittivity, charge, and location of an electrostatic source through exterior measurement. The procedure is then extended to eddy current problems for the identification of the location and shape of cracks in metallic structures. An example demonstrates that when dealing with eddy current problems the least squares object function used by others has multiple local minima so that gradient methods have to be combined with search methods to identify the one absolute minimum. Procedures are also given for handling situations with no cracks and overdescribed cracks. >
TL;DR: In this paper, the energetic behavior of two samples of soft magnetic materials fed by inverters has been studied and the authors dealt with the increase of the iron losses due to a nonconventional voltage supply.
Abstract: The energetic behavior of two samples of soft magnetic materials fed by inverters has been studied. The authors dealt with the increase of the iron losses due to a nonconventional voltage supply. Six-step and PWM (pulse width modulated) inverter output voltages have been selected as the excitation waveforms for the samples under test. Extensive experimental results of high-quality grain-oriented silicon steel and amorphous-alloy-wound core samples are presented. A detailed description of the testing procedure is shown. The results are quite informative and quantify the iron-loss increase with nonsinusoidal supply in comparison with the results obtained by the standard tests (sinusoidal supply and Epstein method). The comparison can give useful indications to electromagnetic-device designers about the derating factors for the different magnetic materials that have to be used in designing devices fed by static power sources. >
TL;DR: In this paper, a four-pole reluctance synchronous machine with additional two-pole windings was constructed and the contribution of these inductances to the radial force production was established.
Abstract: A four-pole reluctance synchronous machine with additional two-pole windings was constructed. The additional winding currents produce the radial force to act as a magnetic bearing. Expressions for the machine inductance functions are given. Inductance functions with respect to the eccentric displacement of the rotor were measured. The contribution of these inductances to the radial force production is established.
IBM1
TL;DR: In this article, a novel method for measuring the bit position shift induced by neighboring transitions, known as nonlinear bit shift, is developed, which is based on special bit patterns which do not contain a specific frequency component when written without nonlinear bits shift.
Abstract: A novel method for measuring the bit position shift induced by neighboring transitions, known as nonlinear bit shift, is developed. The technique is based on special bit patterns which do not contain a specific frequency component when written without nonlinear bit shift. The presence of nonlinear bit shift will result in the appearance of this component and the amount of bit shift can be determined from its intensity. In the present work, a pattern that is insensitive to disturbances from certain unwanted effects such as the hard-transition shift, the positive-negative write current asymmetry, and the magnetoresistive head positive-negative readback asymmetry is used. Experimental results from the proposed method are in good agreement with those obtained by measuring pulse positions in the time domain. >
TL;DR: In this article, a discrete-time modeling of transition-noise dominant channels is considered, which facilitates performance analysis of various sample-data detection schemes, based on the proposed channel description method in the presence of transition noise, expressions for signal-to-total noise power ratios associated with a few selected detection schemes are derived.
Abstract: Discrete-time modeling of transition-noise-dominant channels is considered which facilitates performance analysis of various sample-data detection schemes. Based on the proposed channel description method in the presence of transition noise, expressions for signal-to-total-noise-power ratios associated with a few selected detection schemes are derived. Under the assumption of a Lorentzian step response and perfect equalization, a comparison is made among different detectors based on the signal-to-noise ratio figure-of-merit evaluated as a function of linear density. >
TL;DR: The development of the SQUID as the most sensitive instrument known for the measurement of changes in magnetic flux has presented new opportunities for its use for nondestructive evaluation (NDE) of electrically conducting and ferromagnetic structures.
Abstract: The development of the SQUID as the most sensitive instrument known for the measurement of changes in magnetic flux has presented new opportunities for its use for nondestructive evaluation (NDE) of electrically conducting and ferromagnetic structures. The preliminary studies of this application within the past few years are reviewed in order to serve as an introduction to those that follow. It includes early work by the author that explored the ability of a SQUID to detect defects in a buried pipe and to detect fatigue in steel structures. Studies designed to find defects in North Sea oil platforms and corrosion currents are covered, as well as more recent work in mapping the magnetic field above a current-carrying circuit board. The future of SQUID-based NDE is discussed.
TL;DR: In this paper, the authors presented a generalization of the classical Preisach model which handles coupled magnetic and mechanical hysteresis. But this model is not suitable for the case of magnetostrictive materials such as Terfenol-D.
Abstract: The authors present a generalization of the classical Preisach model which handles coupled magnetic and mechanical hysteresis. Magnetostrictive materials are known to have hysteresis with respect to both magnetic field H and mechanical stress lambda . To test the validity of the model, experiments where the two components H and lambda have been verified in many different ways have been performed on Terfenol-D and compared to results computed from the model. Some of these results are presented. This stress-dependent model is found to have an accuracy comparable to that of the classical Preisach model. >
TL;DR: In this article, a bearingless induction motor with additional windings in the stator slots is proposed to produce radial magnetic forces, which control the position of the rotor shaft, when magnetic fluxes from the two-pole windings cause an imbalance in the revolving magnetic field of the four pole windings.
Abstract: A bearingless induction motor with additional windings in the stator slots is proposed. Additional two-pole windings were wound with the conventional four-pole windings to produce radial magnetic forces. These forces, which control the position of the rotor shaft, are produced when magnetic fluxes from the two-pole windings cause an imbalance in the revolving magnetic field of the four-pole windings. Inductance functions were measured to derive the machine inductance matrix expression, and from this matrix the radial force and current relationships were found. Control circuits were designed and fabricated for a test machine. This test machine was successfully driven by the control circuits. A bearingless induction motor was successfully operated at speeds up to 6000 r/min. >
TL;DR: In this article, conditions for obtaining a high degree of texturing in Ag-sheathed tapes were found, yielding J/sub c/ values up to 17.500 A/cm/sup 2/ at 77 K, 0 T.
Abstract: The critical current density of Ag-sheathed (Bi,Pb)-Sr-Ca-Cu-O tapes with thicknesses below 0.2 mm exhibiting the 2223 phase has been systematically studied for various compositions and oxygen contents of the surrounding atmosphere. Various sequences of the final thermochemical treatment leading to a textured structure were also examined. Conditions for obtaining a high degree of texturing in Ag-sheathed tapes were found, yielding J/sub c/ values up to 17.500 A/cm/sup 2/ at 77 K, 0 T. A major factor for the improvement of J/sub c/ by the present cold deformation approach was the thickness of the 2223 layer, which should be smaller than 20 mu m. Due to the large number of parameters involved in the optimization of this system and to the complex formation conditions, a substantial further increase of J/sub c/ in the 2223 phase is still expected. This is particularly important in view of the use of 2223 tapes at 4.2 K and at high magnetic fields.
TL;DR: In this article, an explanation of the giant magnetoresistance effect observed in some magnetic superlattices is given in terms of an equivalent network of resistors, which leads to a simple analytic formula that relates the magnetore-sensitivity to the spin-dependent electron mean-free paths and thickness of the magnetic and nonmagnetic layers in the super-lattice.
Abstract: An explanation of the giant magnetoresistance effect observed in some magnetic superlattices is given in terms of an equivalent network of resistors. The model leads to a simple analytic formula that relates the magnetoresistance to the spin-dependent electron mean-free paths and thickness of the magnetic and nonmagnetic layers in the superlattice. The formula is used to study the giant magnetoresistance of Co/Cu and Fe/Cr superlattices, and is also used to predict the most favorable values of parameters for a large magnetoresistance effect. >