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Magnetics, IEEE Transactions on

Issue 5  Part 2 • Date Sept. 1998

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Displaying Results 1 - 22 of 22
  • Stochastic algorithms in electromagnetic optimization

    Page(s): 3674 - 3684
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (229 KB)  

    This paper gives an overview of some stochastic optimization strategies, namely, evolution strategies, genetic algorithms, and simulated annealing, and how these methods can be applied to problems in electrical engineering. Since these methods usually require a careful tuning of the parameters which control the behavior of the strategies (strategy parameters), significant features of the algorithms implemented by the authors are presented. An analytical comparison among them is performed. Finally, results are discussed on three optimization problems. View full abstract»

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  • Magnetic arrays and their resonant frequencies for the production of binary codes

    Page(s): 3765 - 3771
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    An array of cantilevers of varying lengths containing at least a layer of magnetic material has been fabricated to produce oscillations at the resonant frequencies of the cantilevers via magneto-mechanical coupling. The acoustic or magnetic fields resulting from the oscillations were detected using microphones or detection coils. The presence or absence of an oscillation at a given frequency of a preselected set of frequencies was used to represent a "1" or a "0", respectively, to create a binary code. The array can be designed and assembled to serve as a multibit magnetic tag. View full abstract»

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  • Physical limits of hyperthermia using magnetite fine particles

    Page(s): 3745 - 3754
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    Structural and magnetic properties of fine particles of magnetite are investigated with respect to the application for hyperthermia. Magnetic hysteresis losses are measured in dependence on the field amplitude for selected commercial powders and are discussed in terms of grain size and structure of the particles. For ferromagnetic powders as well as for ferrofluids, results of heating experiments within organic gels in a magnetic high frequency field are reported. The heating effect depends strongly on the magnetic properties of the magnetite particles which may vary appreciably for different samples in dependence on the particle size and microstructure. In particular, the transition from ferromagnetic to superparamagnetic behavior causes changes of the loss mechanism, and accordingly, of the heating effect. The maximum attainable heating effect is discussed in terms of common theoretical models. Rise of temperature at the surface of a small heated sample as well as in its immediate neighborhood in the surrounding medium is measured in dependence on time and is compared with solutions of the corresponding heat conductivity problem. Conclusions with respect to clinical applications are given View full abstract»

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  • Simple models and measurements of magnetically induced heating effects in ferromagnetic fluids

    Page(s): 3755 - 3764
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    This paper discusses several approximate analytic techniques for calculating power dissipation and forces in ferromagnetic fluids subjected to a spatially uniform but time varying magnetic field. This power dissipation results in a rising temperature in a ferrofluid sample. Several possible heating mechanisms in magnetic fluids have been investigated, including electromagnetic and hydrodynamic processes, and a simple method for prediction of power dissipation in a sample has been developed. Experimental results are given for an induction heating problem where it is shown that the power dissipation in a sample of ferrofluid cannot be explained by induction heating of the individual suspended particles. A simple viscous drag model is introduced which shows better agreement with measured power dissipation in the sample than an eddy current model for excitation frequencies under 1 MHz View full abstract»

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  • Analytical modeling of eddy-current losses caused by pulse-width-modulation switching in permanent-magnet brushless direct-current motors

    Page(s): 3728 - 3736
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    An analytical approach is developed to predict the inverter high frequency pulse width modulation (PWM) switching caused eddy-current losses in a permanent magnet brushless dc motor. The model uses polar coordinates to take curvature effects into account, and is also capable of including the space harmonic effect of the stator magnetic field and the stator lamination effect on the losses. The model was applied to an existing motor design and was verified with the finite element method. Good agreement was achieved between the two approaches. Hence, the model is expected to be very helpful in predicting PWM switching losses in permanent magnet machine design View full abstract»

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  • Thermal decay in high density disk media

    Page(s): 3786 - 3793
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    An experimental technique has been developed to accurately measure the time dependence of playback voltage due to the decay of recorded magnetization patterns. A “calibration” procedure is utilized to minimize the effect of magnetoresistive head sensitivity variations. This technique is applied to a systematic study of the dependence of the signal decay on recording bit density and magnetic layer thickness in longitudinal thin film media. A Neel-Arrhenius type model is introduced to calculate the degradation of a square wave magnetization pattern subject to thermal agitation. Because the equivalent external field which reduces the energy barrier is the time and spatially varying magnetostatic field produced by magnetic transitions, an iterative procedure is utilized to obtain the time dependent magnetization. The model takes into account distributions of grain volume and anisotropy axis. The calculation results are compared with the experimental data and good agreement is obtained View full abstract»

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  • Influence of thin amorphous sheets on the magnetic properties of laminated cores

    Page(s): 3696 - 3700
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    The electromagnetic properties of laminated cores assembled from grain oriented silicon steel sheets with the closer sheets from amorphous material placed among the silicon steel sheets were studied. A decrease of core loss of 4-6% was detected and the exciting current decreased by 20-50%. The improvement of the core performance was due to the decrease of the energy contribution of the magnetostatic fields to the total balance of the free energy of the core and due to the increase of its effective magnetic permeability after the redistribution of the magnetic flux in the corner regions View full abstract»

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  • Calculation of synchronous reactances of small permanent-magnet alternating-current motors: comparison of analytical approach and finite element method with measurements

    Page(s): 3712 - 3720
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    The synchronous reactances of permanent magnet (PM) motors have been determined using: (1) analytical method, i.e., form factors of the stator field (armature reaction factors), (2) finite element method (FEM), and (3) experimental tests on a special machine set. The analytical method is widely used in calculations of synchronous reactances of salient pole synchronous machines with electromagnetic excitation. Rotors of PM synchronous machines have more complicated structures, hence it is more difficult to predict accurately the magnetic field distribution in their airgaps in order to find the form factors of the stator field. Numerical methods of field analysis can easily solve this problem. The FEM can predict both the synchronous and mutual (armature reaction) reactances in the d and q axes. The leakage reactance can then be evaluated as a difference between synchronous and mutual reactances. As an example, a small, three-phase, four-pole motor with SmCo surface mounted PM's (three parallel magnets per pole), and mild-steel pole shoes has been investigated. Such a complicated rotor structure has been intentionally designed in order to be able to compare the advantages and disadvantages of the analytical method and the FEM. In the FEM, the reactances have been calculated using both the flux linkage and current/energy perturbation method. Synchronous reactances as functions of the stator current and load angle obtained analytically from the FEM modeling and from measurements have been compared View full abstract»

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  • Investigation of the permeability tensor of electrical steel sheet

    Page(s): 3667 - 3673
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    The permeability tensor is a mathematical model for the description of the electromagnetic behavior of electrical silicon iron steel sheet under two-dimensional magnetizing conditions. In this paper, an interpretation of the properties of this tensor is given, the investigation of the tensor elements from measurements under two-dimensional magnetizing conditions is described, and some examples of measurements and the corresponding permeability tensor elements are indicated View full abstract»

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  • Performance and implementation of adaptive partial response maximum likelihood detection

    Page(s): 3806 - 3815
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    Motivated by previous comparison work, a configuration for partial response maximum likelihood detection using the Viterbi algorithm (PRML/VA) detectors with adaptive target polynomials is examined. In this configuration, a mean-squared error decision feedback equalization (MSE-DFE) is used to adapt both the forward equalizer and the target channel for the Viterbi detector. The performance of this adaptive PRMLNA is analyzed and compared with other detection techniques. The issue of convergence speed is also studied View full abstract»

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  • Parametric modeling and control of a long-range actuator using magnetic servo levitation

    Page(s): 3689 - 3695
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    A mechatronic device based on magnetic servo levitation (MSL) is proposed for long range and wide bandwidth actuation. The force capability of this type of actuator can be significantly larger than a linear motor or voice-coil actuator of similar dimensions. A novel parametric model of the electromagneto-mechanical coupled system has been developed to describe its behavior over a large range of motion and frequency, as opposed to more conventional attractive force small-perturbation models. It also provides a convenient way of devising a feedback linearizing control scheme that eliminates the need for high biasing currents present in most magnetic bearing systems. This paper presents a feedback-linearized controller coupled with a Kalman filter as a first approach to solve the tracking problem for such an actuator. Good tracking performance have been found both in simulation and experiments View full abstract»

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  • Armature reaction field and winding inductances of slotless permanent-magnet brushless machines

    Page(s): 3737 - 3744
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    The paper describes an improved two-dimensional (2-D) analytical model for predicting the winding inductances and the armature reaction field of slotless permanent magnet brushless machines. Results from the model are compared to those deduced from finite element analyses, existing one dimensional (1-D) and 2-D analytical models and measurements. It is shown that the radial thickness of the airgap winding can have a significant effect on both the winding inductances and the armature reaction field View full abstract»

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  • The effect of substrate bias on the properties of NiO/NiFe and NiO/CoFe exchange biased spin-valve sensors

    Page(s): 3772 - 3777
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    The effect of substrate bias applied during the deposition of NiO on the properties of unshielded NiO/Ni81Fe19 and NiO/Co87Fe13 biased spin-valve sensors was investigated. The addition of substrate bias of -40 V increased the blocking temperature Tb from 100-190°C for NiO/NiFe biased spin valves, and from 70-190°C for NiO/CoFe biased spin valves. The thermal stability upon anneal increased with substrate bias from 150-200°C for NiO/NiFe biased spin-valve sensors, and from 200-280°C for NiO/CoFe biased spin-valve sensors. At an operating temperature of 80°C, sensor magnetoresistance decreases 15% from its room temperature value for NiO/CoFe sensors where NiO was deposited under -40 V bias. At this temperature, the sensor transfer curves are well linearized and Barkhausen noise free. NiO films prepared with varying substrate bias were examined by atomic force microscopy (AFM) and X-ray diffraction. Substrate bias decreases surface morphology and grain size of NiO, which probably contributes to the observed improvement of blocking temperature View full abstract»

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  • Analytic analysis of single- and three-phase induction motors

    Page(s): 3721 - 3727
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    The analysis of single and multiphase induction motors continues to represent a challenge to researchers in computational electromagnetics due to the presence of rΩ×B electric fields. This contribution cannot be inserted into the Green's function for boundary element codes; finite difference and finite element approaches are forced to hard code these effects, compensating at high speeds with upwinding techniques. The direct computation of these affects using transfer relations in a linear environment offers an analytical backdrop both for benchmark testing numerical codes and for design assessment criteria. In addition to torque-speed predictions, the terminal relations and total power dissipation in the rotor are computed for an exposed winding three-phase and single-phase machine View full abstract»

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  • Inductance of a plunger-type magnet

    Page(s): 3685 - 3688
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    A new method, the power approximation of boundary conditions in connected regions, is used to solve the two-dimensional magnetic field problem within the window and the gap of the magnet, considering the core uniform saturated. Expressions of inductance and magnetic flux are given View full abstract»

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  • Laminated dual-axial anisotropy film for submicrometer-trackwidth thin-film heads

    Page(s): 3778 - 3782
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    A dual-axial anisotropy film which consists of two uniaxial sandwiches of Co91Nb6Zr3/SiO2/Co91 Nb6Zr3 with their easy axes orthogonally oriented, was fabricated by RF-sputtering using a water-cooled, magnetic substrate holder, for application in a new type of submicron trackwidth thin film head. The thermal stability of the induced uniaxial anisotropy of the film was studied by heat treatment in a magnetic field and subsequent magnetic measurements. The magnetic properties of the films before and after rotational field annealing (RFA) mere studied by their B-H loops and permeability spectrum along various directions in the film plane. It was found that the B-H loops of the as-deposited dual-axial film along either axis were the superposition of the easy axis and hard axis B-H loops of the two uniaxial sandwiches along that axis. The two uniaxial sandwiches appear to behave independently before RFA. In-plane isotropic B-H loops and isotropic permeability of 2640 at 10 MHz were obtained for the dual-axial films after RFA at 320°C. The small H k and the magneto-static interaction between the two sandwiches may be mainly responsible for the isotropic magnetic properties of the dual-axial film after RFA View full abstract»

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  • “Transition” and “statistical” noises in an ideal recording medium

    Page(s): 3816 - 3817
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (36 KB)  

    In a recent paper concerning the potential advantages and otherwise of patterned magnetic recording media, White et al. (1997) refer to “transition” and “statistical” noises. In this brief note, it is pointed out that in the case of an ideal recording medium, these two noises stem from identical statistical considerations View full abstract»

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  • Flying height measurement using frustrated total reflection: determination of the reflectivities by the least-squares method

    Page(s): 3783 - 3785
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (72 KB)  

    A new method for determining reflectivities in flying height measurement of a slider using frustrated total reflection (FTR) sensor is evaluated. The method is based on the fact that the reflectivity of FTR has different dependence on flying height for P-polarized light and S-polarized light. The flying height of a slider on a glass disk was measured both by an FTIP sensor using this method and by a traditional flying height tester. The results agree with each other with an error of less than 3 nm View full abstract»

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  • Bit errors due to channel modulation of media jitter

    Page(s): 3799 - 3805
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    Recording media written-in transition jitter noise can limit magnetic recording systems. Read channel intersymbol interference (ISI) modulates media jitter in a head/disk/channel, attenuating jitter at low linear density due to classical ISI but amplifying at high density. This paper assesses whether jitter modulation is significant in typical disk drive peak detect (PD) and partial response (PR) channel design, where maximum linear bit density is sought at a specified bit error rate (BER). Experimental isolated pulse data, transition noise, and electronic noise measurements from a 65 mm head/disk recording design are used as inputs to a Matlab simulation of PD and PR Lorentzian channel low pass and boost filters, PD differentiator filter, PR digital filter, and PD/PR bit detectors. The goal of such models is optimizing the designable PD and PR channel parameters for realistic maximum linear density prediction. However their complexity obscures the jitter modulation contribution, which is demonstrated here by the shift in the EER versus density curves, when the jitter modulation is mathematically turned off. Jitter modulation is thereby shown to be significant but not dominant in (1,7) PD density limits. About an order of magnitude BER loss due to jitter modulation can occur at typical PD linear channel bit densities P50/T≈2. Jitter amplification in PD channels can occur at channel density 3.8 (above usable PD limits). PR channels only amplify media jitter, degrading EER by about an order of magnitude at typical (0, k) PR4 densities, and degrading timing channel accuracy twice as fast as channel density increases. Lorentzian isolated pulse (ISOP) modeling is compared to recording physics mathematical pulses, and simulation statistical validity checks are made View full abstract»

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  • New transformer model including joint air gaps and lamination anisotropy

    Page(s): 3701 - 3711
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    A new three phase transformer model is presented in this paper, taking into account air gaps, saturation, core losses, and lamination anisotropy. The flux distribution in a straight overlap joint has been investigated using a lumped circuit model. It is shown that the actual air gap varies largely between an upper and a lower limit as a function of core saturation. Therefore, mitered joints have been modeled using a new concept of an equivalent variable air gap. This consists of defining the length of an equivalent air gap as a function of the instantaneous value of the flux in the laminations. A new approach to the core loss modeling is highlighted. It is characterized by a nonlinear conductance placed in parallel with the saturated magnetizing inductance. Furthermore, transformer yokes and limbs have been divided into longitudinal elements according to the rolling direction to take into account the lamination anisotropy effects. The transient and steady state behaviors of the transformer model have been tested. A good agreement is obtained between computed and measured results View full abstract»

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  • Isolated pulse distortion and medium noise analysis for submicrometer-width narrow-track recording

    Page(s): 3794 - 3798
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    Isolated pulse shapes and medium noise are analyzed for narrow track recording by micro-magnetic simulation. Low density recording is simulated and studied with thin film heads of widths 1.5, 1.0, and 0.5 μm. Isolated pulse shape for a 0.5 μm width recording is severely distorted compared with that for a wide recording. A formula for the PW50 of an isolated pulse is empirically obtained. For a fixed gap length, the first null in the spectrum shifts to lower frequency with a smaller head width. Increases in total noise power are sensitive to narrower heads, especially in the submicron region of the head width 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