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Magnetics, IEEE Transactions on

Issue 5 • Date Sept. 1997

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Displaying Results 1 - 18 of 18
  • Mutual inductance of noncoaxial circular coils with constant current density

    Publication Year: 1997 , Page(s): 4303 - 4309
    Cited by:  Papers (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    The purpose of this paper is to determine the mutual inductance between two noncoaxial circular coils. In many cases, such as coil guns or tubular linear motors, one of them is fixed while the other one is moving, and if not supported, its axis may not coincide with that of the fixed coil. This paper presents a method for the calculation of the mutual inductance in the case of noncoaxial coupled coils, the characteristics of this inductance, and experimental results. The computation is based on complete elliptic integrals and on the mesh-matrix technique. The method enables one to obtain accurate results from a relatively simple procedure and calculation program. View full abstract»

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  • Anisotropy in three-phase transformer circuit model

    Publication Year: 1997 , Page(s): 4319 - 4326
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (804 KB)  

    In this paper, an important discussion of transformer design and modeling is given. Anisotropy effects of the transformer laminations have been stressed in the light of the investigation of a three-phase three-limb transformer T-joint. Three simple T-joint modeling schemes accounting for the lamination anisotropy are proposed. The fundamental result is that the flux lines remain almost parallel to the rolling direction (RD), except in a small area around the T-joint. Therefore, transformer yokes and limbs have been divided into longitudinal elements according to the RD. Reluctances related to these elements are connected according to the magnetic circuit coupling and yield a new transformer circuit model. A good agreement is obtained between computed and measured transient currents. Furthermore, the new transformer model enables some localized analysis. The computed localized fluxes and loci of flux density vectors near to the T-joint exhibit a satisfactory agreement with many results based on FEM or experimental investigations View full abstract»

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  • Designing with null flux coils

    Publication Year: 1997 , Page(s): 4327 - 4334
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    Null flux were suggested by Danby and Powell in the late 1960's as a useful means for realizing induced lift with little drag. As an array of alternating magnets is translated past a set of null flux coils, the currents induced in these coils act to vertically center the magnets on those coils. At present, one Japanese MAGLEV system company and two American-based companies are employing either null flux or flux eliminating coils in their design for high speed magnetically levitated transportation. The principle question addressed in paper is: what is the proper choice of coil length to magnet length in a null flux system? A generic analysis in the time and frequency domain is laid out with the intent of showing the optimal design specification in terms of coil parameters View full abstract»

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  • Magnetic properties and microstructure of Fe-O and Co-O thin films

    Publication Year: 1997 , Page(s): 4363 - 4366
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    Iron oxide and cobalt oxide thin films were prepared by reactive DC magnetron sputtering in a mixture of Ar and O2 gases. The stoichiometry of the oxide films was studied as a function of the amount of O2 during deposition. Sputtering conditions, including dc power and oxygen-to-argon ratio, were found which allowed pure FeO, Fe 3O4, α-Fe2O3, CoO, and Co3O4 films to be fabricated. The microstructure of the films, and especially the grain shape and size distribution, were quite different for oxide films with different stoichiometry. The crystallographic axes of Fe-O films were randomly oriented in contrast to Co-O films in which a strong <111> texture was found. A strong ferromagnetic-like behavior was observed in FeO and α-Fe2 O3 films, in contrast to the well-established antiferromagnetic behavior in bulk. The reason for this anomalous behavior is attributed to clusters of defects in FeO films and uncompensated surface spins in α-Fe2O3 films. A large shift (3800 Oe) was observed in the low temperature hysteresis loop of a field cooled sample consisting of 50% Co and 50% CoO. A similar but less pronounced effect was observed in FeO and α-Fe2O3 films. This result is believed to be caused by a strong exchange coupling between the ferromagnetic and antiferromagnetic constituents in these composite films View full abstract»

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  • Giant magneto-impedance effect in layered thin films

    Publication Year: 1997 , Page(s): 4367 - 4372
    Cited by:  Papers (74)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (940 KB)  

    Giant Magneto-Impedance (GMI) of films with a layered structure has been studied. They are Co-Si-B/Cu/Co-Si-B, Co-Si-B/Ag/Co-Si-B, and Fe-Co-Si-B/Cu/Fe-Co-Si-B with a magnetic closed-loop structure. They also have a certain magnetic configuration, for which the uniaxial anisotropy is perpendicular to both the driving current and the external field. Consequently, both reactance X and resistance R of the films change remarkably due to the external field in the frequency range from 100 kHz to 10 MHz, at which the GMI effect hardly appears in the single layer films of the same thickness. The conductivity difference between the outer and inner layers is important in order to achieve a high impedance change ratio in this frequency range. As a result, the ratios ΔZ/|Z0|=(Zmaximum-Z[Hext=0])/Z [Hext=0] of Co-Si-B/Ag/Co-Si-B films are 440% for a field of 9 Oe at 10 MHz, and the average sensitivity is 49%/Oe. Furthermore, ΔZ/|Z0| of Co-Si-B/Cu/Co-Si-B and Co-Si-B/Ag/Co-Si-B films at 1 MHz is as much as 140%, and the average sensitivity reaches 15%/Oe. The sensitivity at 1 MHz is higher than that of single-layer magneto-impedance films of the same thickness by three orders of magnitude View full abstract»

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  • Preparation of magnetic fluids with particles obtained in microemulsions

    Publication Year: 1997 , Page(s): 4359 - 4362
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    Ternary mixtures of organic solvent, surfactant, and aqueous solution forming a single phase are used for the synthesis of magnetic particles of magnetite. These particles, washed and covered with oleic acid, were stabilized in a carrier liquid, producing a magnetic fluid. X-ray diffraction, transmission electron microscopy, and magnetic measurements of the particles, and the prepared liquid are reported View full abstract»

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  • A simple apparatus for the measurement of the Cotton-Mouton effect in particulate suspensions

    Publication Year: 1997 , Page(s): 4349 - 4358
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (920 KB)  

    An apparatus has been constructed for the practical realization of the Cotton-Mouton effect in colloidal suspensions. Measurements of the magnetically induced birefringence in such media, using a medium power argon-ion laser operating at a wavelength of 515 nm, have been made for variable magnetic field intensities up to 2.5 T. Data have been recorded on the four pure liquids-nitrobenzene, carbon disulphide, acetone, and benzene. The system has been primarily designed for studies on colloidal media for which the Cotton-Mouton effect can be large, thereby requiring relatively low intensity magnetic fields. Data for bentonite and vermiculite are reported, which demonstrate the ease and validity of such measurements for colloid characterization. These are the first known data on suspensions of vermiculite clay. Furthermore, the influence of any stray Faraday effect is examined View full abstract»

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  • Magnetic field of curvilinear asymmetric and symmetric single heads

    Publication Year: 1997 , Page(s): 4373 - 4380
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The magnetic fields of eleven curvilinear asymmetric and symmetric single heads are computed along a plane a short distance in front of them. A generalized Schwarz-Christoffel theory is used in order to accommodate the curved shape of the heads. The components of dimensionless magnetic fields in each case are displayed graphically View full abstract»

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  • Vector-potential boundary-integral evaluation of eddy-current interaction with a crack

    Publication Year: 1997 , Page(s): 4287 - 4294
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    In eddy-current nondestructive evaluation, an excitation coil, used to induce current in a conductor, changes impedance in the presence of a crack. The impedance change can be calculated from a knowledge of the coil parameters, the excitation frequency, and the crack geometry. Two boundary integral formulations of the problem are compared. The first formulation uses an electric field integral equation, and the second expresses the magnetic vector potential in integral form using an integral kernel with a weaker singularity. The vector potential formulation, presented here for the first time, leads to a more complicated equation but has a singular kernel that is easier to deal with. In addition, the new approach opens up a number of possibilities for further analytical developments. An example calculation is performed for a long, surface-breaking crack, and the results are compared to available analytical solutions. Very good agreement is found between the numerical solution of the integral equation and the analytical results View full abstract»

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  • Low magnetic field measurement by a separated NMR detector using flowing water

    Publication Year: 1997 , Page(s): 4345 - 4348
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    Using polarized flowing water, NMR detection at a high field region separated far away from the measured field was investigated to estimate ranges and conditions for a wide-range magnetometer. We obtained the Lorentzian-type NMR signal with the full-half-maximum width of 320 nT and the S/N ratio of 10.5, and measured the magnetic field from several mT down to a few μT with the same enhancement of signals by a separated NMR detector View full abstract»

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  • Study of an extended partial-response, class IV, channel for digital magnetic recording

    Publication Year: 1997 , Page(s): 4392 - 4404
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1064 KB)  

    In this work, we study an EPR-IV system for high density digital recording and compare it to the PRML recording system. A combinatorial optimization technique that uses the simulated annealing algorithm in conjunction with a descent method is employed for optimization of partial response (PR) equalizers. The gradient algorithm to track variations of timing phase for the EPR-IV channel is investigated. Also, a generalized Viterbi algorithm is used for detecting the EPR-IV system. Simulation results demonstrate that at high recording density, a coding gain over the PRML system can be obtained for the EPR-IV system with a comparable complexity View full abstract»

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  • A new target and detector for high-density magnetic recording channels

    Publication Year: 1997 , Page(s): 4385 - 4391
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    A new equalization target for the high-density magnetic recording channel is proposed based on the PR1 partial response combined with decision feedback. A detector for the new target is developed and shown to allow practical implementation. The performance of the detector is assessed through analysis and simulation. It is shown that the detector is suitable for channel recording densities of 3 bits per PW50 View full abstract»

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  • Flux distributions near boundaries of magnetizable shells

    Publication Year: 1997 , Page(s): 4295 - 4302
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    The singular behavior of magnetic fields near the boundary curves of thin-walled structural members such as soft ferromagnetic plates or open shells is explored. Employing the concept of magnetic surface flux and results from potential theory, together with some reasonable assumptions concerning modeling and nonlinear magnetizability, explicit expressions and field plots are obtained. The paper includes a discussion on “forces of magnetic origin” in the present context View full abstract»

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  • Commutation-caused eddy-current losses in permanent-magnet brushless DC motors

    Publication Year: 1997 , Page(s): 4310 - 4318
    Cited by:  Papers (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    An analytical approach based on a two-dimensional electromagnetic field analysis in polar coordinates is developed to predict the commutation losses in a permanent magnet brushless dc (PMBD) motor. These losses are essentially the eddy-current losses induced in the PMBD motor's rotor magnets and core and are caused by the rotor sweeping of the stationary stator magnetic field before each current commutation due to inverter switching takes place. The approach is applicable to motor constructions with either magnet segments or a magnet ring and able to deal with ill-conditioned cases. The model was applied to an existing motor and good agreement (within 11%) with the finite element method was achieved View full abstract»

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  • Optimization of guideway coil dimensions for a magnetic levitation system

    Publication Year: 1997 , Page(s): 4335 - 4344
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (780 KB)  

    A fast computer code that generates currents and forces for multiple magnetic levitation (MAGLEV) vehicle coils over a discrete guideway of arbitrary geometry has been developed, tested, and verified. A study of coil dimensions for overlapping loops, ladders, and discrete loops has been conducted to determine the optimal guideway design. A parameter known as “figure of merit” has been defined to assist in evaluating the level of “merit” for a particular track configuration. From this, it has been discovered that, for most cases, ladder tracks are a better configuration over both overlapping and discrete loops. On closer inspection, it was also discovered that an aspect ratio of unity for the dimensions of a ladder track yields the best overall results View full abstract»

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  • Effect of anisotropy field magnitude distribution on signal-to-noise ratio

    Publication Year: 1997 , Page(s): 4381 - 4384
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    Recording performance is analyzed by a micromagnetic model in two thin film media with different distribution width of the anisotropy field magnitude. With the same Mrδ, the magnetic properties of the two media are almost the same except that the switching slope S* is larger for the medium with narrower distribution. The signal-to-noise ratio (SNR) is calculated for both media versus recording densities. The SNR at recording densities 4800-9000 flux reversals per millimeter is 5-8 dB smaller in the medium with a broad anisotropy magnitude distribution than the SNR in the medium with a sharp distribution View full abstract»

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  • Recording performance of a giant magnetoresistive head on a perpendicular multilayer medium

    Publication Year: 1997 , Page(s): 4411 - 4412
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    The magnetic recording characteristics of a giant magnetoresistive spin-valve head in combination with a perpendicular disk medium have been measured. The disk medium contains a 30-nm-thick Pt/CoCrTa multilayer displaying low noise and high remanence. A pulse width of 172 nm, a signal to noise ratio of 31 dB, and a rolloff D50 point of 120 kFCI were achieved. The parametric data and window margin testing show this recording system can support recording storage density of 3.5 Gbits/in2 using a simple peak detect channel at a data rate of 65 Mbits/s View full abstract»

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  • Rapid computation of static fields produced by thick circular solenoids

    Publication Year: 1997 , Page(s): 4405 - 4410
    Cited by:  Papers (31)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    A straightforward method is proposed for computing the magnetic field produced by a circular coil that contains a large number of turns wound onto a solenoid of rectangular cross section. The coil is thus approximated by a circular ring containing a continuous constant current density, which is very close to the real situation when wire of rectangular cross section is used. All that is required is to evaluate two functions, which are defined as integrals of periodic quantities; this is done accurately and efficiently using trapezoidal-rule quadrature. The solution can be obtained so rapidly that this procedure is ideally suited for use in stochastic optimization. An example is given, in which this approach is combined with a simulated annealing routine to optimize shielded profile coils for NMR 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