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Magnetics, IEEE Transactions on

Issue 4 • Date July 2000

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Displaying Results 1 - 20 of 20
  • Eddy-current losses in magnetic conductors with abrupt magnetic transitions

    Page(s): 1962 - 1969
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    This paper presents an analysis of eddy-current losses in magnetic conductors with abrupt magnetic transitions. The study of the linear polarization of the magnetic flux is based on the Preisach model representation of eddy-current hysteresis. By using this representation, analytical formulas for the calculation of eddy-current losses in terms of simple experimental data are derived. The analysis of the circular polarization of the magnetic flux is carried out through the exact analytical solution of the corresponding nonlinear vector diffusion equation. It is shown that the f2 law for eddy-current losses has a universal character. View full abstract»

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  • Improvement in calculation of the self- and mutual inductance of thin-wall solenoids and disk coils

    Page(s): 1970 - 1975
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    The self-inductance expressions given by Yu and Han (1987) for air-core circular coils with rectangular cross sections, thin solenoids, and disk coils can be solved only by the numerical integration methods. We propose as an alternative a combined analytic and numeric approach. The approach brings some improvement in the calculations of self-inductance of thin-wall solenoids and disk coils that can be encountered in superconducting magnetic energy storage (SMES) problems. We also give a method for the calculation of mutual inductance of disk coils and of thin-wall solenoids. The results are obtained in an analytical form over the complete elliptic integrals of the first and second kind and Heuman's Lambda function. It is important to mention that the kernels of these integrals are always continuous functions on intervals of integration, so singularities are avoided. The results enable one to calculate the self-inductance and the mutual inductance of any thin air-core coil precisely and fast. For practical applications, the results are so simple to use that we recommend them to avoid the problems of solving the singular cases. View full abstract»

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  • Modulation noise in thin-film metallic media: elements of pulse/transition modulation theory

    Page(s): 2077 - 2090
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    This paper is a mathematical preliminary to a pulse/transition modulation theory in magnetic recording. Equations are given for single-tone pulse modulations of different types (pulse position, width, shape). The theory is applied to noise generation in thin-film metallic media. As longitudinal bit size becomes comparable to the grain size, medium noise manifests itself as significant errors in the traditional mapping of write current to media magnetization. Thus, noise has a character of random multidimensional modulation of pulse parameters of the magnetization derivative. Transition jitter in recording is followed by the transformation of double-sideband recording modulation into single-sideband readback modulation, because of the bandwidth limitation in the readback transducer. Readback output becomes modulated 50% in pulse amplitude and 50% in pulse position. The fluctuation of transition length in recording causes pulse shape modulation. This amounts to simultaneous pulse-width and pulse-amplitude modulations acting against each other, so that virtually no modulation sidebands are generated. The compensation process is hidden in the recording cycle and is not visible in the frequency domain of the readback signal. Therefore, the traditional technique of media noise measurement with a spectrum analyzer is flawed, because the analyzer is blind to pulse shape modulation, which is the dominant source of sampling errors in practical channels View full abstract»

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  • Damped gyromagnetic switching

    Page(s): 1976 - 1981
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    The gyromagnetic switching behavior of a single-domain grain or particle with uniaxial magnetocrystalline and shape anisotropy is solved analytically by the gyromagnetic torque equation using physically plausible Gilbert damping. The sole restriction is that the anisotropy easy axis and the applied field be collinear. The analytical solution for the magnetization switching time is then used to calculate precisely various phenomena which occur in pulsed-current stripline testing of magnetic recording storage media. Also, the analytic relationship between the polar and azimuthal angles of the magnetization during damped precession is derived View full abstract»

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  • New model for the computation of quasi-stationary fields due to arbitrary distributions of magnetic dipoles

    Page(s): 1990 - 1995
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    The quasi-stationary field of a magnetic dipole in free space is modeled by using the field due to a succession of dipoles oriented along any line between the poles of the original. Dipole, the two fields being identical everywhere except for the points on that line. By choosing appropriately the path of the equivalent string of dipoles, the resultant field due to the original dipole can be obtained from the superposition of fields with a simpler structure. In this paper, the proposed modeling method is illustrated for the quasi-stationary ac field of an arbitrarily located and oriented dipole in the presence of a conducting spherical shell, with the analytic expression of the field quantities derived in terms of single series, which are much more convergent than the double series in the expressions available in the literature. The model presented can be applied efficiently for analyzing eddy-current problems and electromagnetic shielding by various spherical, cylindrical, and planar structures in the presence of arbitrary distributions of electric current View full abstract»

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  • Impact of write equalization on high-density particulate recording systems

    Page(s): 2091 - 2097
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    Write equalization (WE), used extensively in tape recording systems, has offered many improvements to the recording channel. These include improved resolution, better overwrite, and reduced distortion. As linear density in these systems has increased with the use of thinner metal-particle (MP) media, which significantly improves read nonlinearity in magnetoresistive (MR) heads, it is not clear that the effects of the WE scheme are still advantageous. In this paper, the impact that WE has on high-density advanced particulate recording systems is investigated. It is found that surface roughness is much more detrimental to recordings using WE because of the higher frequency behavior and reduced channel output of the recording scheme View full abstract»

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  • Accuracy of expressions for the magnetic field of a ring head

    Page(s): 2073 - 2076
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    The Fourier method used by Fan has produced a representation of the field of a semi-infinite pole head consisting of a simple analytical approximation (Karlqvist field) plus an infinite series of correction terms. A method is developed in this paper by which other approximations to head fields have their infinite series of correction terms evaluated to make them exact. Expressions with only one correction term produced by Ruigrok and Szczech et al., are studied, and enhancement of them is shown to offer accurate approximations to the exact head fields View full abstract»

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  • Segregation of W in Nd-Fe-B magnets and its effects on coercivity

    Page(s): 2033 - 2036
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    The coercivity of sintered Nd22Fe71B7 magnets with the combined addition of Al and W was investigated to study the role of additive elements in improving the coercivity in the NdFeB system. It was found that the coercivity could be greatly enhanced by the Al and W combined addition. Microstructural studies show that the alloying element W would preferentially segregate on the surface region of the main phase grain when added into the magnets together with Al, leading to a significant enhancement of coercivity. Further, thermodynamic analysis reveals that the segregation of W could be attributed to inhomogeneous nucleating on the surface region of the main phase grains during cooling View full abstract»

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  • Identification method analyses for the scalar generalized moving Preisach model using major hysteresis loops

    Page(s): 1982 - 1989
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    A parametric identification strategy for the generalized moving Preisach model is presented. As it requires only the major hysteresis loop (to determine the distribution parameters) and the remanent major hysteresis loop (to determine the moving parameter), it is less sensitive to the presence of the usual experimental errors than other identification methods. The Preisach distribution function is considered to be in general a bivariate function. The method is verified on various commercial magnetic media View full abstract»

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  • Universal HSPICE macromodel for giant magnetoresistance memory bits

    Page(s): 2062 - 2072
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    Nonvolatile semiconductor storage using giant magnetoresistance (GMR) memory bits has the potential for revolutionizing both high-density and high-speed memory applications with devices exhibiting unlimited write endurance and very low write energy. This paper presents the first universal circuit macromodel for GMR memory bits. The macromodel is realized as a four-terminal subcircuit that emulates GMR bit behavior over a wide range of sense and word-line currents. It realistically models the nonlinear and hysteretic behavior of GMR memory bits, their transient thermal behavior, and the sense-current dependency of their write thresholds. The model is flexible and relatively simple: Ranges of the write/read currents and bit resistance values are incorporated as parameterized variables, and no semiconductor devices are used within the model View full abstract»

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  • Electromagnetic separation techniques in metal casting. I. Conventional methods

    Page(s): 2015 - 2021
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    Conventional methods for electromagnetic separation of small inclusions in metal casting are analyzed. The electromagnetic separation implies flotation of nonconducting inclusions in a conducting fluid (molten metal) by Archimedes' electromagnetic force, and their subsequent removal. The magnitudes of the separation force are calculated for the following methods: (1) separation by an electromagnetic induction coil; (2) separation by a traveling magnetic field; (3) pinch-effect separation; and (4) separation with superimposed current and superimposed magnetic field. Theoretically estimated force magnitudes appear on the order of the gravitation buoyancy force. They are not as high as observed in some laboratory-scale experiments. Power efficiency of the electromagnetic separation is studied with respect to the accompanying Joule heating of molten metal. A power efficiency coefficient is introduced to compare various separation techniques. Typically, this coefficient is very low, on the order of 10-4 and less for inclusions of 10-μm size in molten aluminum. The highest values of the power coefficient are obtained for the traveling magnetic field. The pinch-effect separation mechanism is found to be most energy-consuming. We found that the use of dc superconducting coils can drastically improve the power efficiency of an electromagnetic separation process if the injection current is used as the origin of the Lorentz force. This mechanism, as well as that of magnetohydrodynamic separation without superimposed current in very strong magnetic fields, are subjects of an upcoming publication View full abstract»

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  • Nonlinear AC response and noise of a giant magnetoresistive sensor

    Page(s): 2057 - 2061
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    We compare bridge voltage response measurements to ac magnetic fields from a giant magnetoresistive sensor with noise measurements on the same sensor. The small-signal response (for applied ac magnetic fields between 0.1 mOe rms and 30 mOe) is much less than is the slope of a dc voltage versus field curve, because of hysteretic effects. Noise statistics are used to estimate the size and number of the sites at which domain realignments occur near the response peak. Similar estimates are made by using fine-structure on the ac response curve. For ac fields of about 0.3 mOe rms, sharp spikes appear in the field-dependent response, giving rise to large harmonic distortion, varying in an irregular way with the ac amplitude. Domain sizes are estimated for the regions, giving these nonlinear response spikes, and for the domains, giving the magnetic noise, and a comparison based on a fluctuation-dissipation relation of the noise, and the response shows the importance of hysteresis View full abstract»

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  • Design of analog equalizers for partial response detection in magnetic recording

    Page(s): 2098 - 2108
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    Analog equalizers offer several advantages, such as high speed, small size, low power, and minimum delay, over sampled digital equalizers. (In this paper, the phrase analog equalizer refers to continuous-time equalizers having poles and zeros.) However, because of their feedback nature, their design often involves extensive search procedures. Recently, an analytical design technique based on equation-error formulation was proposed. In this paper, we study this approach for partial response (PR) equalization and show that it is quite sensitive to the choice of timing phase and it could result in quite suboptimal solution. We improve on it by using an iterative approach similar to that of Steiglitz and McBride. We also present a thorough simulation study to assess the performance loss incurred by low-order analog equalizers and produce performance charts that can be used for selecting the PR target for different channel characteristics. Application of this approach to multi-level decision feedback equalization detection is also discussed View full abstract»

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  • Micropumps based on alternating high-gradient magnetic fields

    Page(s): 2012 - 2014
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    A magnetic particle pumping scheme based on high-gradient magnetic fields is proposed, and its operation principle is demonstrated. The pumping action is generated by sequentially displacing the magnetic field distribution and its dragging force on the magnetic particles immersed in a solution. No mechanical moving parts are needed, and thus, the proposed system can provide a fast, reliable, and inexpensive way for on-chip biomedical testing and analysis application. In this paper, the analysis, design, and experimental results are described View full abstract»

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  • Analytically computing the flux linked by a switched reluctance motor phase when the stator and rotor poles overlap

    Page(s): 1996 - 2003
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    This paper develops an analytical model for the flux linked by a phase of a switched reluctance motor (SRM) starting with the basic laws for magnetic fields. Thus this model is not empirical nor does it require any data from the machine being modeled or any finite-element analysis results. The model is applicable to rotor positions where the stator and rotor poles overlap, and it includes iron saturation. This paper gives a detailed development of the analytical model including the approximations that are inherent to it and the justification for them. The analytical model for the flux linked by a phase is used to find the analytical equations of motion for the SRM. It is also used to obtain an analytical expression for the SRM's coenergy. Differentiating the coenergy with respect to rotor position, holding the current constant gives an analytical expression for the torque. Finally, this paper compares the analytical model's predictions to measured data from experimental machines View full abstract»

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  • Dynamic calculation of the responsivity of monodomain fluxgate magnetometers

    Page(s): 2052 - 2056
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    A model is presented describing the dynamic response of a single-domain fluxgate magnetometer over a wide range of operating conditions in terms of a single measurement of a hysteresis loop or the permeability of the fluxgate's ferromagnetic core. The model is based on the Landau-Lifshitz-Gilbert equation, which describes the dynamics of a coherently rotating ferromagnet. Measurements of the response of a permalloy thin-film fluxgate and a molybdenum-permalloy tube fluxgate demonstrate the accuracy and limitations of the model View full abstract»

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  • Open-loop pulsed hysteresis graph system for the magnetization of rare-earth magnets

    Page(s): 2042 - 2051
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    An open-loop pulsed hysteresis graph system can magnetize and characterize ceramic and rare-earth permanent magnets such as neodymium, samarium cobalt, and alnico of cylindrical and rectangular shapes. The prototype system relies on an air-core excitation coil with an inner diameter of 3 cm and a length of 10 cm. A pulsed power supply provides a transient current pulse of up to 9000 A into the air-core coil. The pulse duration is typically on the order of 15 to 20 ms. In addition, a pair of Helmholtz coils records the applied magnetic field strength, whereas a local coil, tightly wound around the permanent magnet, records the magnetic flux density in the sample. Both fields are electronically acquired, digitized, and processed in a digital computer to obtain the hysteresis graph response of the sample. The processing takes into account the demagnetization field due to the open-loop system configuration. This paper presents the system concept in terms of the hardware and software realizations. An integral part of the data processing is calculation of the demagnetization factors that are needed to correct for the open-loop magnetization arrangement. Furthermore, a finite-element postprocessing procedure corrects for the influence of eddy currents in highly conductive samples. In tests of the prototype system with ceramic and neodymium permanent magnet samples, the pulsed field predictions compare favorably against reference data and dc hysteresis graph measurements of samples of low conductivity. Even for high-conductivity samples such as alnico, good agreement can be achieved through suitable post processing steps View full abstract»

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  • Model of power soft MnZn ferrites, including temperature effects

    Page(s): 2022 - 2032
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    This paper describes a model for simulating the behavior of soft MnZn. This model takes into account both hysteresis and dynamic phenomena. The temperature is introduced using behavioral laws. In fact, the following model requires only few parameters. It estimates iron losses and characteristics, such as B(H), φ(t), and the induced electromotive force. The obtained results are compared with measured data for three soft MnZn ferrites currently used in power electronics. The comparison found good agreement in a wide range of operating frequencies for temperatures ranging from 40 to 140°C View full abstract»

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  • Syntheses and magnetic properties of Nd3Co13-xNixB2 borides

    Page(s): 2037 - 2041
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    The effect of substitution of Ni for Co in the borides Nd3 (Co13-xNix)B2 (x=0, 1, 2, 3, 4, 5) on the crystal structure and magnetic properties has been investigated. The lattice parameter a decreases while c increases with increasing x in the range 0⩽x⩽5. The Curie temperature and saturation magnetic moment per formula unit in Nd3(Co13-xNix)B2 decrease monotonically as the Ni concentration increases. We have observed spin-reorientation transitions at temperatures that decrease monotonically with increasing Ni concentration. It is noteworthy that the substitution of Ni has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, leading to the change of easy magnetization direction of Nd3(Co13-x Nix)B2 compounds from basal plane to the c axis at room temperature when x⩾2. The magnetic phase diagram of the Nd3(Co13-xNix)B2 borides is given, and the behavior of magnetocrystalline anisotropy is analyzed by the single ion model View full abstract»

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  • Magnetomechanics of internal-dipole, Halbach-array motor/generators

    Page(s): 2004 - 2011
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    The magnetomechanical behavior of internal-dipole, Halbach-type magnet arrays is analyzed for application as a motor/generator (M/G) with an energy-storage flywheel that is suspended by low-stiffness bearings. Scaling laws for the maximization of torque are derived as a function of geometry. The optimal geometry is relatively insensitive to gap and stator design and occurs approximately at a ratio of inner to outer diameter of the array of 0.8. Values are found for the angular extent of each phase of the stator coil that minimize the stiffness. The negative stiffness of the internal-dipole array is calculated for several manufacturable configurations and is shown to provide an upper limit on the available torque of the M/G according to the positive stiffness of the bearings. Experimental results are reported for an internal-dipole array used as a M/G for a flywheel suspended by a bearing consisting of a permanent-magnet assembly levitated over an array of high-temperature superconductors. Results show that the system is stable and that idling losses are low 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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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology