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Magnetics, IEEE Transactions on

Issue 3 • Date May 1990

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Displaying Results 1 - 18 of 18
  • Vector potential and magnetic field of current-carrying circular finite arc segment in analytical form. V. Polygon cross section

    Page(s): 1171 - 1180
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    For pt.IV see ibid., vol.MAG-20, p.2145-50 (1984). Analytical expressions for the components of the vector potential and magnetic field of a circular-arc segment of a current-carrying conductor of polygonal cross section and arbitrary azimuthal length are derived. The expressions developed consists of known analytical functions such as Jacobian elliptic functions and complete and incomplete elliptic integrals of the first, second, and third kind, which permit the formulation of a time-saving efficient computation algorithm. An example of application is given. The case of a beam with polygonal cross-section carrying a longitudinal current is also examined View full abstract»

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  • The effects of stress on a ferromagnet on a minor hysteresis loop

    Page(s): 1153 - 1156
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    Reversible and irreversible changes in magnetization due to stress on a minor hysteresis loop were studied at various magnetic field strengths. It was found that the irreversible changes were not always directed toward the principal anhysteretic, contrary to Jiles and Atherton's hypothesis (1986). Also, two different demagnetization methods were used within the minor loop to test the existence of postulated offset anhysteretic curves. The results of asymmetric demagnetizations seemed to support this suggestion View full abstract»

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  • Effect of order of stress and field application on changes in anhysteretic magnetization

    Page(s): 1157 - 1159
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    Differences between isostress anhysteretics and the zero stress anhysteretic are found to be of the same form but larger than magnetization changes induced by stress from an anhysteretic point. The latter are separated into reversible and irreversible parts, indicating that pinning impedes changes from an anhysteretic point, thus giving smaller changes than the differences between the isostress anhysteretics View full abstract»

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  • Image of static current loop over a superconducting sphere

    Page(s): 1137 - 1138
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    It is shown that the magnetic field of a static current loop with its axis radial to a superconducting sphere can be computed by replacing the sphere by a single image loop. This image solution is derived from the inversion of a point of charge by an equivalent sphere View full abstract»

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  • Study of the dynamic interaction of a domain wall with a pinning plane

    Page(s): 1139 - 1143
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    The motion of a domain wall under the action of an alternating magnetic field was studied during its interaction with a pinning plane. First and second harmonics of the electronic force were measured by a lock-in amplifier, using a computer-controlled system. Good agreement was obtained between theory and experiment. Therefore, results of these experiments were used to determine the characteristics of the pinning place in the sample. The optimal frequency and amplitude of the exciting field have been investigated using this effect and have been used to develop a magnetic sensor View full abstract»

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  • A design approach for actively shielded magnetic resonance imaging magnets

    Page(s): 1181 - 1188
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    A design basis for an actively shielded arrangement of coils is presented which results in an optimized magnet configuration suitable for magnetic resonance imaging (MRI). A random search technique is used to select configurations using the least amount of conductor, exhibiting the smallest level of field inhomogeneity, and resulting in the least level of stray field while meeting central field and size requirements. A computer program has been developed which incorporates this design approach. Magnetic configurations selected with the aid of this design tool are discussed View full abstract»

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  • Determination of lubricant film thickness on a particulate disk surface by atomic force microscopy

    Page(s): 1225 - 1228
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    The ability of the atomic force microscope (AFM) to measure the lubricant film thickness on the surface of particulate disks is demonstrated, and experimental results are presented. AFM measure the thickness of the lubricant film at a particular location on the disk surface with a lateral resolution of the order of the AFM tip radius, ~1000 Å. For an unused disk, 50-70 Å of lubricant thickness is found. After the disk has been in use for several years, the lubricant thickness decreases to 35-55 Å. In both cases, the lubricant is uniformly distributed on the disk surface, although somewhat more uniformly on the used disk. For all types of disks studied, most of the lubricant resides below the disk surface, presumably in the medium's porosity, with only a molecular thin film of lubricant on the surface View full abstract»

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  • High-frequency operation of a planar-type microtransformer and its application to multilayered switching regulators

    Page(s): 1204 - 1209
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    The operation of a multilayered microtransformer composed of planar zig-zag coils and amorphous magnetic film is described. The transformer has a maximum efficiency of 77.5%. Its equivalent circuit is approximated by the parallel connection of the winding inductance and of the stray capacitance. Variable magnetic coupling is obtained between the primary and secondary windings by shifting the relative position of the two coils. The microtransformer is used in a magnetically controlled multilayered switching regulator. The regulator has an output of 1.4 W and an efficiency of 24%. The magnetization loss in the circuit is the same as that of the semiconductors. A two-output-type multilayered switching regulator is also proposed that has an acceptably good output characteristic at each port even though a common magnetic film is used View full abstract»

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  • Magnetic properties of anisotropic Sr-La system ferrite magnets

    Page(s): 1144 - 1148
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    An experiment was carried out to investigate the effect of La2O3 on the magnetic and physical properties of strontium ferrite magnets. It was found that the La2O3 addition to SrO-6Fe2O3 (stoichiometric composition) was very useful in stabilizing the magnetoplumbite structure and that these ferrites of the Sr-La system had excellent permanent-magnet properties. Various compositions were tested, and the optimum conditions for making magnets and some properties of typical specimens were determined. The semisintering condition was 1250°C for 1 h in oxygen, and the sintering condition 1300°C for 0.5 h in oxygen. Magnetic and physical properties are presented and discussed. The [(SrO)0.143(Fe2O3)0.857]98 (La2O3)2 compound magnet exhibited the highest value of (BH)max, and this value was equivalent to or higher than that of ordinary Ba and Sr ferrites View full abstract»

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  • A new algorithm for coupled solutions of electric, magnetic and mechanical systems in dynamic simulation of solenoid actuators

    Page(s): 1189 - 1197
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    An algorithm is presented for the simultaneous solutions of the coupled electric, magnetic, and mechanical problems in the dynamic simulation of a solenoid actuator. The transient nonlinear field in the coupled problem is analyzed using the finite-element (FE) method, which considers the effects of saturation, eddy current, and armature movement in the actuator. The nonlinear electronic circuit is represented by equivalent circuit equations that are coupled to the FE equations and are solved simultaneously with them in an iterative manner. Dynamic responses of the solenoid actuator predicted by using this algorithm agree closely with experimental results. The advantage of this method is that its principle is applicable to general types of power electronic devices. With suitable modifications, it can be used to simulate the dynamic responses of power-electronic-controlled electric machines View full abstract»

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  • Wavelength response of ring-type head with arbitrary gap depth

    Page(s): 1213 - 1216
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    In 1953 Westmijze found analytic solutions for the fields and wavelength responses of ring-type-head models with zero and infinite gap depths and demonstrated that the wavelength responses for these two extreme cases are substantially different. A model two-dimensional electromagnet that is equivalent to a more general ring-type-head model that takes into consideration a final gap-depth value is considered. It is shown that the Westmijze head models are actually two specific cases of this more general model. Using the theory of complex analytic functions, the gap between the two Westmijze models is bridged and an analytic solution for the wavelength response of a ring-type head with an arbitrary gap depth is derived. Graphs of the responses calculated for several gap depths are presented. These graphs illustrate that the gap depth has no practical effect on wavelength response as long as the ratio of pole thickness to gap size exceeds 0.5. However, further decrease of this ratio causes considerable changes in wavelength responses View full abstract»

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  • Comparison of ring and pole head magnetic fields

    Page(s): 1229 - 1232
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    Idealized mathematical models of the magnetic fields generated by ring and single-pole heads are examined. In each case, more accurate Fourier coefficients than have been published previously are provided. However, the main purpose is to consider, in a more rigorous manner than has been presented before, the correspondence between the fields of ring and pole heads. Ranges of parameters and areas of the domain are identified for which the fields are almost identical. In the region of each geometry occupied by the recording medium, the similarities were less clear View full abstract»

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  • Transient eddy current analysis for generalized structures using surface impedances and the fast Fourier transform

    Page(s): 1164 - 1170
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    Surface impedances have primarily been utilized in eddy current problems, where the skin depth is small compared to the conductor thickness being modeled. Their use is extended to arbitrary-thickness conductors. In addition, the authors investigated modeling different shapes as combinations of slabs. In particular, a cylinder was emulated as a polygon of slabs to verify the versatility of the technique. The application to sinusoidal steady-state problems is straightforward. Of greater interest is the extension to the transient problem. A solution was sought via the fast Fourier transform. With the surface impedance method, the calculation of each frequency solution is fast; the overhead required in setting up the problem, albeit the integral or finite-element matrix is geometry-dependent only, and need be performed but once. The calculation of the transient response of a cylinder placed in an exponentially decaying field is computed and compared to analytic results. Some discussion is given on the benefits of breaking up the excitation field into parts that start and end at the same level View full abstract»

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  • Influence of uniaxial elastic stress on power spectrum and pulse height distribution of surface Barkhausen noise in pipeline steel

    Page(s): 1160 - 1163
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    Barkhausen noise (BN) measurements were made on a half-section of a pipe under tensile and compressive isostress. The RMS BN voltage was found to increase with increasing tensile stress and to decrease with increasing compressive stress. Pulse-height distribution analysis and power density spectral analyses were performed on the BN data. These analyses revealed that the BN events with large amplitudes occur in the presence of tensile stress, while events with small amplitude occur under compressive stress. The power of the BN spectrum increased or decreased, respectively, with increasing tension and compression. While the exact mechanism responsible for the shift in BN pulse height distribution is not yet clear, the authors suggest that it may be related to stress-induced changes in domain size, magnetization distribution, and/or the clustering behavior of domain walls View full abstract»

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  • Constant-current versus constant-voltage VCM drive analysis

    Page(s): 1217 - 1224
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    A voice-coil-motor (VCM)-driven actuator is analyzed for both constant-current and constant-voltage drive operation. Through the use of dimensional analysis, the solutions to the two drive methods are directly compared. This allows for quick evaluation of an actuator design. The analysis compares the actuator performance parameters, including seek time, switching time, and maximum angular velocity. The relationship between constant-current and constant-voltage drive is shown to depend on the value of a dimensionless parameter. For actuators with low values of this parameter (<1.43), the current is not back-EMF limited when constant-voltage drive is used. It is shown that such actuators have the same seek time for the same average power dissipated in the coil, regardless of which drive approach is chosen. Therefore, a single equation was derived to describe power generated at the source for both constant-current and constant-voltage drives. The ratio of average power generated at the source average power dissipated in the coil is equal to the ratio of source voltage to stall voltage. A given actuator dissipating the same power in the coil will always have a lower stall voltage and a higher peak voltage if constant-current drive is used instead of constant-voltage drive View full abstract»

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  • Application of a new orthogonal-flux-type amorphous core to high-frequency parametric inverters and three-phase measuring transformers

    Page(s): 1198 - 1203
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    The fundamentals of a parametric oscillator using an orthogonal-flux-type amorphous core are described, and several applications are proposed. The parametric oscillator circuit has a power-conversion efficiency of 42% and automatic overcurrent protection. The flux distribution calculated by the finite-element method (FEM) suggests that the discharge of a tuning capacitor generates a circulating flux in a leg of the core. The parametric oscillator, a self-oscillating invertor using a Royer circuit, shows an efficiency of 47% at 18.5 kHz and offers overcurrent protection. As a separately controlled parametric inverter, it operates at a frequency of 74 kHz and shows an efficiency of 14% at the maximum output power of 11 W. It can also be used as a potential transformer and as a current transformer in a three-phase system View full abstract»

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  • Recording characteristics of electroless-plated perpendicular recording flexible disks with a perpendicular head

    Page(s): 1210 - 1212
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    Perpendicular magnetic recording using a main-pole-driven perpendicular head was tested using electroless-plated flexible disks. Soft magnetic NiFeP films, also produced by electroless plating, were used as an underlayer of a perpendicular recording medium in this test. Two types of flexible double-layer media, composed of an electrodeless-plated CoNiReP film with two types of NiFeP underlayers with a coercivity of 2 and 5.5 Oe, were fabricated, and their recording characteristics were measured. A recording density value of 75 kFRPI was obtained for the medium with the softer magnetic 2-Oe underlayer, about twice as high a value as that for the medium with the 5.5-Oe underlayer View full abstract»

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  • An investigation of anisotropy of cobalt-surface-modified iron oxide magnetic particles

    Page(s): 1149 - 1152
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    Surface treatment experiments on nonstoichiometric iron oxide are described, along with a theoretical analysis which suggests that the uniaxial anisotropy of cobalt-surface-modified iron oxide particles is not induced by the magnetic field of the inner core of iron oxides, but rather is due to the shape anisotropy being larger than the magnetocrystalline anisotropy of imperfectly crystallized CoFe2 O4. It is concluded that the crystalline imperfection of CoFe2O4 on the outer layer of iron oxides particles decreases the magnetocrystalline anisotropy and limits the enhancement rate of the coercivity of cobalt-surface-treated iron oxide particles 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