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Magnetics, IEEE Transactions on

Issue 1  Part 2 • Date Jan. 1999

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Displaying Results 1 - 18 of 18
  • IEEE Magnetics Society Distinguished Lecturers for 1999-2000

    Page(s): 494 - 495
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    Freely Available from IEEE
  • IEEE Magnetics Society Distinguished Lecturers, 1980-1998

    Page(s): 496 - 497
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    Freely Available from IEEE
  • Effects of airgap and magnet shapes on permanent magnet reluctance torque

    Page(s): 536 - 542
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    This paper examines the permanent magnet reluctance torques produced by three different configurations of permanent magnet, airgap, and iron. These configurations are briefly described here as rectangular magnet/triangular airgap, rectangular magnet/sinusoidal airgap, and sinusoidal magnet/sinusoidal airgap. The analysis of the torques is achieved by developing analytical solutions. Equations for magnet reluctance torque are obtained by finding the derivative of the stored field energy with respect to position. The triangular airgap configuration is shown to produce a torque waveform which approximates a triangular waveform, and both the sinusoidal airgap configurations are shown to produce torque waveforms which approximate sinusoids View full abstract»

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  • Analysis of flux leakage in a brushless permanent-magnet motor with embedded magnets

    Page(s): 543 - 547
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    This paper analyzes the magnetic characteristics of brushless permanent-magnet motors with embedded magnets. It shows that the flux leakage has a substantial effect on the air gap flux density interacting directly with the armature current to produce torque. The flux leakage parameters η and λ are expressed analytically in terms of the magnetic material properties and the motor dimensions. They are essential quantities for the accurate prediction of the average flux densities within the air gap and the magnet. The finite element numerical method is adopted to verify the analytical model. For the numerical example in this paper, the average deviation between the finite element result and the analytical one is about 1-2%. This finding confirms the suitability of the analytical model for the design purpose. Although design is not particularly emphasized in this paper, one section gives a simple explanation of flux leakage considerations in magnet design View full abstract»

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  • Probable capacity of 3.5-inch magneto-optical disk using trilayer double-mask magnetically induced super-resolution media

    Page(s): 580 - 582
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    This paper discusses the probable capacity of 3.5-in magneto-optical (MO) disks using trilayer double-mask magnetically induced super resolution (MSR) media and a conventional optical system. We measured the bit error rate of the double-mask MSR media on a land/groove substrate with a track pitch of 0.6 μm. We obtained bit error rates as low as 1e-7 for a minimum bit length of 0.24 μm. The recording power margin was ±11.3% and the tilt margin was ±0.7°. These results indicate that a capacity of over 2.4 GB is possible for a 3.5-in MO disk using an optical head with a 685-nm laser diode having a lens numerical aperture of 0.55. The capacity corresponds to an areal density of 4.48 Gbit/in2 View full abstract»

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  • An artificial intelligence system for a complex electromagnetic field problem. II. Method implementation and performance analysis

    Page(s): 523 - 527
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    For pt. I see ibid., vol. 35, no. 1, p. 516-22 (1999). An artificial intelligence system has been developed to determine the electromagnetic field in the complex problem of a faulty overhead transmission line above earth and a buried pipeline. The amplitude and phase of the magnetic vector potential (MVP) in the earth around the pipeline neighborhood, including the pipeline itself, are calculated, The performance of the trained fuzzy logic system (FLS) described in Part I was tested extensively for various configurations of the above electromagnetic field problem, differing significantly from the cases used for training. The trained FLS parameters required to calculate the electromagnetic field by simple formulas are also presented View full abstract»

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  • An artificial intelligence system for a complex electromagnetic field problem. I. Finite element calculations and fuzzy logic development

    Page(s): 516 - 522
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    Artificial intelligence (AI) has been used to determine the electromagnetic field in the complex problem of a faulty overhead transmission line above earth and a buried pipeline. A suitable AI system for scaling finite element electromagnetic field calculations has been developed. This system was trained by using finite element calculations for configurations, i.e., cases having different distances between the overhead transmission line and the buried pipeline as well as different earth resistivities. The AI system may be used to calculate the electromagnetic field in new cases differing significantly from the cases used for training View full abstract»

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  • X-band characterization of anisotropic magnetic materials: application to ferrofluids

    Page(s): 568 - 572
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    A simple, fast method of characterization of anisotropic magnetic materials uses a nonreciprocal X-band rectangular cell. The material may be a solid, powder, or magnetic liquid. A network analyzer measures the scattering parameters, and an original numerical processing routine computes the permeability tensor components. Two anisotropic magnetic materials have been characterized: a ferrofluid made with magnetite particles suspended in a hydrocarbon and a barium iron oxide powder. The knowledge of permeability behavior of magnetic liquids is important in designing specific nonreciprocal microwave devices. Experimental results are in good agreement with the proposed theoretical simulated model View full abstract»

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  • Comparison of the torque of flat airgap synchronous couplings versus the magnetization direction of the magnets

    Page(s): 548 - 556
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    A study of flat airgap synchronous couplings uses the analytical formulas of the tangential and radial components of the force between two permanent magnets. These formulas are applied to compare the torque transmitted by three different structures of flat airgap couplings. In the first, the magnets have a radial magnetization direction with respect to the rotation axis. This direction is tangential to the rotation axis in the second structure and parallel to the rotation axis in the third where the force Is computed with a semi-analytical method. The torque of the different couplings is studied and compared. The dependence of the torque on various parameters such as the number of pole pairs and the width, length, and depth of the magnets is also investigated. The analytical and semi-analytical methods used afford efficient optimization of the coupling structure with full compliance with practical and economic constraints View full abstract»

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  • Performance comparison of modified multilevel decision feedback equalization detectors

    Page(s): 594 - 604
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    Multilevel decision feedback equalization (MDFE) is a detection scheme that was developed for (1,k) coded recording channels. The user signal-to-noise ratio required to achieve a chosen bit error rate (BER) of 1e-6 has been shown to be about 1.9 dB more than that of the maximum likelihood lower bound for a Lorentzian channel at user density 2.5. Recently, an advanced version of MDFE, called M2DFE, was proposed. By using computer simulations, the BER of M2DFE has been shown to improve by about 1 dB compared to MDFE. In this paper, we first discuss the various aspects of M2DFE design and then present its theoretical analysis. Using the analysis, we show how the two critical parameters in the design are to be chosen for optimum performance. We also propose a modified M2DFE detector, which exploits the noise correlation at the slicer input, to improve the BER performance as well as reduce error propagation considerably. These MDFE detectors are then compared for their BERs and error propagation performances View full abstract»

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  • Linearizing magnetic bearing actuators by constant current sum, constant voltage sum, and constant flux sum

    Page(s): 528 - 535
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    For each controlled axis, two identical electromagnets are usually used to provide a net scalar force of changeable sign. Each magnet has a winding on it and is mostly premagnetized, leading naturally to a configuration in which the currents through the two windings sum to a positive constant value while each individual one varies. Apart from this prevailing constant current sum (CCS) configuration, constant voltage sum (CVS) of the driving voltages and constant flux sum (CFS) of the resultant fluxes provide two additional constant-sum scenarios. CFS is shown to be realizable by a simple nonlinear state feedback of only displacement and current. It is also shown that with CFS the state equations of the plant are linear. CVS is derived by approximation to CFS and is shown to yield a more linear plant than CCS. These constant-sum configurations are compared in terms of closed-loop performance, where for every considered aspect of performance CVS is shown to be better than CCS and CFS is the best. As to the complexity, CVS is the least complex and CFS is the most complex. While CFS is shown to be a candidate for high-performance applications, it is suggested that the widely accepted CCS be replaced by CVS in practice because of its better performance and lower complexity. Finally, problems and additional choices in implementation are discussed View full abstract»

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  • Effect of a conducting shield on the inductance of an air-core solenoid

    Page(s): 508 - 515
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    A magnetostatic integral equation for the current induced by a solenoidal inductor in the conducting wall of a closed, perfectly conducting cylindrical shield was solved by the method of moments and point matching. The induced current was then used to determine the self-inductance of the solenoid. A chart of the ratio of the shielded inductance to that in free space was produced to aid in the design of practical air-core inductors. In addition, Wheeler's well-known formula for the free-space inductance of a single-layer solenoid was shown to be sufficiently accurate to serve as a basis for the design of practical coils if the effect of the shield, available from the chart, is included View full abstract»

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  • Energy stored in permanent magnets

    Page(s): 505 - 507
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    There has been some confusion over the energy stored in a permanent magnet, with many texts and some finite element packages giving incorrect values. We demonstrate the correct formulation, under both normal operation and partial demagnetization, and discuss the physical meaning of stored energy in a permanent magnet View full abstract»

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  • Observation of magnetic domain structure and switching in barium ferrite thin films

    Page(s): 583 - 593
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    Magnetic domain structure and switching mechanism were investigated in individual barium ferrite grains with sizes ranging from 0.5-7 μm. Magnetic force microscopy (MFM) was used to image grains in sputtered Pt-doped barium ferrite thin films. The switching thresholds of the different grains were measured by applying successively larger magnetic fields to the sample and observing which grains switched. Application of a field to as-annealed samples swept out multidomain structures at a field of Hini≈1000 Oe, which was relatively independent of grain size. It was found that, after the grains had been saturated, a different field Hrev had to be applied to saturate the grain in the opposite direction in large size grains (about 4 μm) Hini≈Hrev; whereas for grains with sizes of 1-3 μm, Hrev varies from approximately equal to Hini to many times larger. Domain wall motion was found to dominate the reversal process in grains larger than 4 μm, as suggested by discontinuous magnetization jumps and an inverse-cosine angular dependence of Hrev. Reversal in grains with sizes between 0.5 and 1 μm is believed to be dominated by incoherent rotation, as indicated by the angular dependence of Hrev View full abstract»

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  • Ball bearing and rolling cylinder motors

    Page(s): 562 - 567
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    The speed-current characteristic for electrically conducting cylinders has been measured while rolling on parallel rails, current flowing from rail to rail through the cylinders. The characteristic is similar to that of the ball bearing motor. A heavy load can be carried by the rolling cylinders, but there is a minimum current below which the rollers come to a standstill. In the case of stainless steel rollers the load increases with this minimum current at the rate of 2.8 kg/A. However, for carbon rollers the load is proportional to the square of the current, as predicted by electromagnetic theory, rising at the rate of 1.8× 10-2 kg/A2. As an alternative to the electromagnetic theory, a model based upon thermal expansion is also discussed View full abstract»

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  • Susceptibility profile in soft magnetic wires

    Page(s): 573 - 579
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    The local susceptibility profile is here proved to be a reliable source of unique information about the internal domain structure and the local magnetization process. In the present work, the profile is studied for a series of magnetically soft amorphous wires having different magnetostriction constants and exhibiting various domain structures. The presence of closure domain structures near the ends of the wires is confirmed. These domains appear regardless of the value of the magnetostriction constant. They reduce the stray field energy and strongly enhance the local values of susceptibility View full abstract»

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  • Modeling the effects of torsional stress on hysteretic magnetization

    Page(s): 498 - 504
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    Opposite torques applied axially to a polycrystalline ferromagnetic rod result in tensile and compressive stresses acting perpendicularly at the rod surface at 45° to the rod axis. These stresses affect the magnetization of the rod when a magnetic field is applied parallel to the rod axis. It is shown how one can formulate the magnetomechanical hysteresis model so as to treat this special case of biaxial stress and take into account the effect of opposite torques on the magnetic properties of the rod. Variation of hysteresis parameters such as coercive field, remanent flux density, differential permeability at the coercive field, and hysteresis loss as a function of applied torque are determined from the model. In the model, the torque is applied first and then the field is cycled to give hysteresis loops. It is found that the torque dependence of the magnetic properties is different, depending on what is chosen for Hmax, the maximum value of the applied magnetic field H. The best parameter to use for tracking the torque is found to be Hc at saturation or near saturation, since that parameter shows an almost linear decrease with the applied torque View full abstract»

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  • Nonoriented electrical steel sheet with low iron loss for high-efficiency motor cores

    Page(s): 557 - 561
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    A new material was studied for high-efficiency motor cores that need higher magnetic flux density, lower iron loss, and lower mechanical hardness. Excessively high Si content tends to decrease magnetic flux density of nonoriented electrical steel sheets. The composite addition of rare-earth metals (REM) and Al into molten steel was found to make inclusions coarse and remarkably improve grain growth during stress relief annealing, which resulted in decreased iron loss. A new nonoriented electrical steel sheet (50RMA350) with Si, Al, and REM has been successfully developed to give a higher efficiency to inverter drive model motors than a conventional material View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology