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Magnetics, IEEE Transactions on

Issue 3 • Date May 1994

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Displaying Results 1 - 18 of 18
  • Application of a perturbation method to the solution of eddy current testing problems

    Page(s): 1247 - 1252
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    This paper presents an analytical solution for the change of the impedance of a double conductor line due to eddy currents induced in presence of an infinitely long horizontal cylindrical flaw with vertically symmetric cross-section. The solution, found by a perturbation method, is applicable in the case the conductivities of the flaw and of the surrounding material do not differ by much. Numerical results for flaws of circular and elliptic cross-sections are presented View full abstract»

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  • High spatial-resolution domain-observation of longitudinal thin film media by spin-polarized scanning electron microscopy

    Page(s): 1327 - 1330
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    A noise generating mechanism is studied by observing recorded bits of two kinds of high-density recording media, in the 50-140 kFCI range, that produce different levels of noise. The noise power is found to be mainly correlated with the zigzag wavelength of the bit boundary View full abstract»

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  • A two-dimensional measuring equipment for electrical steel

    Page(s): 1253 - 1257
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    The technical aspects of two-dimensional measuring equipments for electrical steel are described. The choice of the appropriate field sensors and the important point of the control of B&oarr;(t) are described. The equipment described is designed to measure the two-dimensional properties of square shaped single sheets of all qualities of electrical steel covering the technical frequencies and induction ranges of the major applications. The equipment is useful for the manufacturers of electrical steel to control the texture of their material and for designers of machines to know about the properties of the material under two-dimensional excitation, which in case of rotational flux conditions are different from the one-dimensional properties measured with the Epstein frame or single sheet testers View full abstract»

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  • Effect of annealing on magnetization process of Ni3-xFe 1+x (-0.2<x<0.2) alloys

    Page(s): 1331 - 1335
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    The magnetocrystalline anisotropy, the magnetostriction and the structure-sensitive properties in the magnetization process were studied in the ordered and disordered states of specimens between 70.1 wt% Ni and 79.7 wt% Ni. The single crystals were cooled at the rate of 1 K/day to obtain the fully ordered state. Magnetization curves and hysteresis loops were measured using picture frame specimens. The magnetocrystalline anisotropy and the magnetostriction were also measured in disc specimens. New experimental results obtained in the order state are considerably different from those obtained by previous investigators. The difference is attributed to the degree of order and the magnetic properties of the previous investigators are those of a partially ordered state View full abstract»

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  • Oblique-field annealing effect for in-plane magnetic anisotropy of soft magnetic Co-Nb-Zr thin films

    Page(s): 1336 - 1339
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    The effect of annealing in a magnetic field applied obliquely to the surface of soft magnetic thin films has been investigated. This annealing method was found to be extremely effective to control in-plane magnetic anisotropy without a change of annealing temperature and to suppress local anisotropy dispersion. For sputtered amorphous Co85.5Nb8.9Zr5.6 thin films, it has been found that the in-plane uniaxial anisotropy energy was varied from 250 J/m3 to near zero with the coercive force Hc less than 6.5 A/m by changing the oblique-field annealing angle α. Experimental values of in-plane anisotropy energy agreed well with calculated ones predicted from α and intrinsic anisotropy induced by quasi-directional ordering. These films showed good high frequency characteristics for applying to miniaturized inductive devices View full abstract»

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  • Magnetic properties and texture of sputtered Fe/Fe3O4 multilayer films

    Page(s): 1316 - 1323
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    Polycrystalline Fe/Fe3O4 multilayers have been fabricated with varying Fe/Fe3O4 ratios, period (bilayer) thickness, number of periods, and deposition sequence. The films were deposited by RF magnetron sputtering. The coercivity was found to vary in a nonlinear fashion between that of Fe and Fe3 O4. For selected multilayer geometries, the coercivity can be increased beyond that of single-layer Fe and Fe3O4 films. The magnetic saturation was observed to follow a linear mixture rule. These results suggest that a multilayer approach is useful for designing magnetic thin films and may allow fabrication of new materials for recording media applications. A secondary result was the ability to obtain highly textured polycrystalline films of both Fe and Fe3O4 on amorphous substrates for selected multilayer geometries. The texture results, which may be generally applicable, suggest that relatively thin multilayers of only a few periods may provide a means to control polycrystalline film texture on amorphous substrates View full abstract»

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  • Steady-state performance analysis of permanent magnet synchronous motors including space harmonics

    Page(s): 1306 - 1315
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    This paper describes the method for the analysis to obtain steady-state currents and torques of permanent magnet synchronous motors including space harmonics. A time-stepping finite element technique including the rotor movement is proposed, where both terminal voltage and load angle are given as the known values. In simulating the rotor movement, the suitable rotation step to take account of the effects of space harmonics, is determined. The agreement between calculated and measured results of the synchronous performance in an experimental motor is good View full abstract»

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  • A least squares method for fitting head fields by parametric equations

    Page(s): 1301 - 1305
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    Models of magnetic recording systems generally require the field of the record head to be calculated. In the interests of speed a simple, but accurate, analytic expression is desirable. In this paper the method of minimization of squared residuals is used to obtain parameters defining a parametric approximation to the head field. As an example parameters are obtained which give best fits to finite pole tip head fields produced by conformal mapping. It is found that a good set of parameters is obtained by separately characterizing the infinite pole length head field and correction terms due to the outer pole edges evaluated at the medium surface. The same method could be used to fit measured data or fields obtained using numerical models View full abstract»

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  • A problem related to Earnshaw's Theorem

    Page(s): 1324 - 1326
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    An alternative to Earnshaw's Theorem, based on perturbation theory, is discussed that predicts the stable or unstable behavior of classical electromagnetic physical systems in a two dimensional situation View full abstract»

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  • Design of shielded quadrupolar gradient coils for magnetic resonance microscopy by simulated annealing

    Page(s): 1242 - 1246
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    A novel design for shielded, magnetic pulsed field gradients with transverse geometry is presented. The gradients are intended for use in NMR microscopy and localized spectroscopy. The integrated coil design is based on simulated annealing (SA) optimization and results in well shielded coil sets of high linearity and sensitivity. The design approach is a flexible one and is amenable to the design of gradients in a variety of configurations View full abstract»

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  • Spectral estimation for a magnetostrictive magnetic field sensor

    Page(s): 1274 - 1290
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    Recently there has been increasing concern regarding the effects of low-frequency magnetic fields on humans and livestock. A portable magnetometer is essential for monitoring the field dose encountered. There are some devices currently available for this purpose which use the induced EMF technique. The field sensitivity for these devices depends on the number of turns of coil used. This limits the minimum size of devices with reasonable performance. The magnetometer considered in this paper overcomes this size limitation by using a highly magnetostrictive material, Terfenol-D, as the magnetic field sensor. The primary focus of this paper is to determine the magnetic field spectral characteristics using digital signal processing. A survey of spectral estimation techniques are presented, followed by their application to the Terfenol-D magnetic field signal. The estimators are compared using data obtained from a magnetometer hardware prototype. Using these methods it was possible to detect signal for a field strength of 20 milligauss View full abstract»

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  • A new technique of noise reduction for large aspect magnetoresistors

    Page(s): 1263 - 1266
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    A large aspect (width to thickness ratio) magnetoresistive sensor operated with an alternating transverse biasing is characterized by high sensitivity and reduced temperature drift. However, it has little demagnetizing anisotropy to maintain a single domain state so noisy behavior often results. A constant longitudinal field can be used to reduce this noise but at the expense of reduced sensitivity. A new unipolar a.c. longitudinal biasing technique is presented which allows the full sensitivity to be achieved whilst significantly reducing magnetic noise and hysteresis View full abstract»

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  • Off-track spacing loss of shielded MR heads

    Page(s): 1267 - 1273
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    The side-reading of a finite track-width shielded MR head is investigated both analytically and numerically. The head field (potential) utilized in a reciprocity calculation is obtained, and its Fourier transform is derived in semi-analytic forms. The off-track MR head response to a longitudinally magnetized micro-track and finite-width track is calculated from these results. Estimations on off-track spacing loss are undertaken for two types of shielded MR heads: finite track-width flush MR sensor and shields, and finite-width MR sensor with infinitely wide shields View full abstract»

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  • Compact extended algorithms for elliptic integrals in electromagnetic field and potential computations. II. Elliptic integral of third kind with extended integration range

    Page(s): 1236 - 1241
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    Electromagnetic field and potential computations on elements with curved contours in boundary and volume integral methods (BEM, VIM) require evaluation of a number of Jacobian complete and/or incomplete elliptic integrals of all the three kinds for the same modulus but different angles depending upon the arc length and the angle coordinate of the field point. Up to now they have been evaluated individually repeating the same algorithms a number of times. To reduce such redundant computations, as in Part I for elliptic integrals of first and second kind, a new compact algorithm based on Bartky's transformation is developed in the present paper for the elliptic integral of third kind with an extended integration range -π⩽a⩽π. Computational accuracy and time-saving are discussed View full abstract»

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  • Route to chaos of a domain wall with vertical Bloch lines

    Page(s): 1233 - 1235
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    A route to chaos of a domain wall in a thin magnetic garnet film is investigated numerically using Slonczewski's equation of motion for a periodic drive field with its amplitude treated as a control parameter. The route to chaos consists of alternatively occurring ranges of quasiperiodic and periodic wall motion. In the neighborhood of the lower limit of chaotic range the symptoms of intermittency and fractal character of the boundary of basins of attraction were found View full abstract»

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  • Modelling the asymmetry of the recorded transition zone in digital magnetic recording

    Page(s): 1296 - 1300
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    A vector model of the recorded transition zone for digital magnetic recording is used to incorporate asymmetric transition profiles, non-constant recording contours and both longitudinal and perpendicular components of magnetization into a channel model. These factors all contribute to the asymmetry of the recording zone and hence the asymmetry of replay pulses and the associated nonlinear channel phase response. The use of the model for evaluation of channel spectra is examined. In particular it is found that good fits to experimental results for a typical recording channel are provided by a linear recording contour in conjunction with an arctangent transition profile. This model is useful for inclusion in a full digital magnetic recording system model since analytic expressions are available for both the replay pulse and its spectrum View full abstract»

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  • A novel magnetic suspension cum linear actuator system for satellite cryo coolers

    Page(s): 1258 - 1262
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    Stirling cycle cryogenic coolers have been widely used for device cooling in satellites. Various types of magnetic bearings and linear actuators find application in such systems. The most widely used configurations have two-axis-radially-active suspension stations placed at either end of a reciprocating shaft in the compression and expansion sections. Separate or integral linear motors are provided in each section for axial shaft movement. It may be noted that such configurations are rather complicated and less reliable because of the presence of numerous electro-mechanical components, sensors and electronic servo channels. In this paper, a simple and reliable scheme is suggested which axially stabilizes and linearly perturbs the piston so that the need of a separate motor for axial actuation can be totally dispensed with. The piston is radially supported by passive repulsive bearings. In the axial direction, a servo actuator `balances' the piston and also actuates it bi-directionally. Implementation of this `bearing cum motor theme', reduces the number of electromechanical and electronic components required to operate the system and hence minimizes the chances of system failure. Apart from this, the system's power consumption is reduced and efficiency is improved as electrical heating losses caused by quiescent-operating currents are removed and electromagnetic losses on the moving parts are minimized. The necessary system parameters have been derived using finite element analysis techniques. Finally, the proposed design is validated by computer-aided system simulation View full abstract»

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  • Aging effect on coercivity of iron oxide thin films

    Page(s): 1291 - 1295
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Changes in magnetic properties for Fe3-xx O4 (x: oxidation degree) thin films made by reactive sputtering and subsequent heat treatments have been examined under room temperature aging and constant temperature annealing. Aging causes variations in coercivity of insufficiently oxidized films which have a specific resistance of less than 1×101 Ω·cm, while the coercivity of γ-Fe2O3 (x=1/3) did not change. This phenomenon did not depend on additive elements or preparation method. Other magnetic properties such as saturation magnetization, residual magnetization, squareness ratio and coercive squareness, were not affected by aging for any Fe3-x xO4 composition. The activation energy for a coercivity change is 0.72-0.95 eV near room temperature for films with a specific resistance below 1×101 Ω·cm. It was confirmed that only the coercivity varied at 20°C, while both coercivity and the degree of oxidation changed with annealing at 100°C 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