Journal of the Magnetics Society of Japan
Online ISSN : 1880-4004
Print ISSN : 0285-0192
ISSN-L : 0285-0192
Volume 29, Issue 5
Displaying 1-11 of 11 articles from this issue
Contributed Papers
Magnetic Recording
  • H. Yamada, R. Tsuchiyama, T. Shimatsu, I. Watanabe, H. Aoi, H. Muraoka ...
    2005 Volume 29 Issue 5 Pages 549-552
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    A cylindrical magnetic storage system was developed, using inclined-pad-type heads and perpendicular double-layered media with a CoPtCr-SiO2 recording layer. The inclined ABS (air-bearing surface) slider has an inclined leading pad formed on the leading edge of the slider and a trailing pad formed on the trailing edge of the slider to generate an air-bearing force. The fabricated head exhibits flying stability on a rotating cylindrical medium. A composite recording layer, CoPtCr-SiO2/Ru/Pt/Ta deposited on a rotating cylindrical substrate with a soft magnetic underlayer (SUL) shows high coercivity over 5 kOe, and squareness ratio of around 1, which are almost the same characteristics as the same composite recording layer on a conventional disk substrate with SUL. The fundamental read/write characteristics of CoPtCr-SiO2/CoZrNb perpendicular double-layered cylindrical media were measured using a merged-type GMR head with an inclined-pad-type slider designed for use with cylindrical media. The envelope of the head output did not show any modulation, large spike pulses, or thermal asperity associated with contact with the cylindrical medium. Isolated waveforms with sufficient symmetry were also obtained.
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Thin Films
  • K. Sunaga, M. Tsunoda, M. Takahashi
    2005 Volume 29 Issue 5 Pages 553-557
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    α' and γ'-Fe-N with various N contents were synthesized by using multilayer fabrication technique and the volume effect on magnetic moment for these phases was examined. The unit-cell volume of α' and γ' phases monotonously increases with increasing N content. In the case of α'-Fe-N, magnetic moment decreases with increasing unit-cell volume. This result is different from theoretical prediction. On the other hand, in the case of γ'-Fe-N, magnetic moment takes the maximum near the volume of bulk γ'-Fe4N. In particular, the magnetic moment drops drastically near the volume of bulk γ'-Fe4N, although unit-cell volume is almost same. This result is also different from the theory. Further experimental works including magnetic microstructural analysis are needed to answer these discrepancies.
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  • K. Kawabata, T. Kuroiwa
    2005 Volume 29 Issue 5 Pages 558-562
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    Thermal stability of submicron size permalloy thin films was investigated both by the Langevin LLG simulation and by the energy reconstruction method. The former gives the reversal time due to thermal fluctuation, and the latter, the potential energy profile of the films. The results were consistent with each other. The relation between the reversal time and energy barrier is well established by these methods. The magnetization behavior before reversal at finite temperature is visualized by a combination of these methods.
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Measurement and High-Frequency Devices
  • H. Kikuchi, K. Noguchi, T. Liu, K. Ara, Y. Kamada, S. Takahashi
    2005 Volume 29 Issue 5 Pages 563-566
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    Magnetic properties derived from major hysteresis loops are sensitive to the microstructures of iron-based steels and have therefore been used for nondestructive evaluation of degradation in ferromagnetic materials contained in structural components. A permeability obtained from an ac small field excitation may be a more useful parameter than one obtained from a major hysteresis loop from the viewpoints of electricity consumption and realtime measurement. In this paper, the relation between the ac permeability calculated from impedance measurements of coil elements and the ductile-brittle transition temperature (DBTT) and Vickers hardness of S15C steels is clarified. The possibility of nondestructive evaluation (NDE) using ac permeability measurements is also discussed.
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  • T. Saito, K. Tashiro, I. Sasada
    2005 Volume 29 Issue 5 Pages 567-570
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    Active compensation is studied for a multi-shell shield with an inner passive shell. We made a miniature shield consisting of four concentric magnetic shells, which has the same structure as our previously developed shielding system for a demonstration of MEG alpha-rhythm measurement. FINEMET rather than Permalloy was chosen as the material for the inner passive shell. We measured the amplitude and phase of the incoming magnetic field to the shielded area. It was found that the inner passive shell can help to suppress the phase difference between the observed field and the external field. A model for explaining this phenomenon is presented. We tried a simple feed-forward active compensation system for the shield, which consists of three canceling ring coils and a single monitoring flux-gate magnetometer. The axial shielding factor at 10 Hz, 10 μT was 300, and with active compensation a value of 12,000 was achieved.
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Power Magnetics
  • O. Ichinokura, J. Shida, K. Nakamura, T. Watanabe
    2005 Volume 29 Issue 5 Pages 571-576
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    A reluctance generator (RG) has various desirable features, including simple construction, high reliability, and low cost. Furthermore, it is suitable for an ultra-high-speed generator because the rotor of the RG is made of iron steel. However, the RG system is complicated, because it needs to detect the rotor position angle and requires a dc power supply for the driving circuit of the stator winding. For this reason, the RG has not been used in practical applications. In this paper, we propose a new RG with a permanent magnet in the stator yoke. The linkage flux of the stator winding from the permanent magnet changes with the salient-pole rotor. The experimental results obtained with a trial RG indicate that it has a very simple construction and high performance.
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  • K. Sasaki, H. Goto, T. Watanabe, H. J. Guo, O. Ichinokura
    2005 Volume 29 Issue 5 Pages 577-581
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    Switched reluctance motors (SRMs) have several desirable features, including simple construction, high reliability, and low cost. However, one of their drawbacks is higher torque ripple. Direct torque control (DTC) is considered a useful way of controlling the torque ripple. This paper presents an approach to the design and implementation of direct torque controller for SRM using digital signal processor (DSP) and field programmable gate arrays (FPGAs).
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  • S. Hasegawa, Y. Oshinoya, K. Ishibashi
    2005 Volume 29 Issue 5 Pages 582-588
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    This paper deals with a study of the elastic vibration control of an electromagnetic levitation steel plate. A new experimental apparatus that generates elastic vibration in a steel plate is proposed. Optimal control techniques were applied to two kinds of models, and the effect of suppression of the elastic vibration was investigated. One model is a simple one-degree-of-freedom system that treats the steel plate a rigid body, and the other is a comparatively complicated continuous model for the steel plate. To verify the usefulness of the two control systems, digital optimal control experiments were performed for a steel plate with free edges (800 mm×600 mm×0.3 mm). As a result, it was found that the control performance for elastic vibration was improved by using the control system for the continuous model in the theorized way.
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Biomagnetic and Medical Applications
  • M. Sekino, S. Ueno
    2005 Volume 29 Issue 5 Pages 589-593
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    Current distributions in transcranial magnetic stimulation (TMS) were calculated under various conditions and compared with the current distribution in electroconvulsive therapy (ECT) in order to find an optimum condition of TMS as an alternative to ECT. Current distributions in TMS were obtained for the following coil shapes and coil diameters: circular coils of 50 mm, 75 mm, 100 mm, 125 mm, and 150 mm, and figure-eight coils of 50 mm, 75 mm, 100 mm, and 125 mm. Stimulus parameters in TMS were evaluated using a performance function F which increases with the difference in the current distributions between ECT and TMS. The minimum value of F decreased with an increase in the coil diameter. In the case of a 150-mm circular coil, the performance function had a minimum value of 6.3 A2/m4 at a coil current of 29 kA, which corresponded to a magnetic flux density of 0.24 T. A coil position on the forehead and the use of a large circular coil gave better results.
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  • M. Soma, M. Sendoh, K. Ishiyama, K. Shoji, H. Watanabe, K. I. Arai
    2005 Volume 29 Issue 5 Pages 594-597
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    A magnetic micromachine for driving in a liver was fabricated. It consisted of a cylindrical permanent magnet, a cutting tip at the end of the magnet, and a spiral structure around the magnet. The magnet was magnetized in the direction of its diameter. When a rotating magnetic field was applied, the magnet was rotated by the magnetic torque, and the spiral structure produced a thrust force perpendicular to the rotation plane of the field. The micromachine was able to penetrate the liver of a swine and a bovine to a depth of 40-45 mm in 20-40 seconds. In addition, it was demonstrated that the driving direction of the micromachine could be controlled by changing the direction of the rotating magnetic field. The radius of a turn was 25 mm. These results show that the micromachine has great potential for medical applications such as local hyperthermia.
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  • M. Ogoshi, B. S. Kim, S. Kurokawa, K. Kumaki, K. Kobayashi, M. Yoshiza ...
    2005 Volume 29 Issue 5 Pages 598-602
    Published: 2005
    Released on J-STAGE: September 16, 2005
    JOURNAL OPEN ACCESS
    We performed three-dimensional vector measurement of magnetocardiograms (MCGs) for normal subjects and for a patient with Wolff-Parkinson-White (WPW) syndrome, using a three-dimensional second-order gradiometer connected to 39-channel SQUIDs, which can simultaneously detect magnetic field components perpendicular to the chest wall (Bz) and tangential to the chest wall (Bx, By). In order to discriminate the accessory pathway of WPW syndrome, Independent Component Analysis (ICA), having a time window (48 ms) for analysis, was applied to the MCG data of the WPW patient.
    ICA is a useful method for separating independent signals from overlapping signals. We succeeded in carrying out dynamic ICA by changing the analytical interval timewise, and in separating the excitement due to the WPW syndrome patient's accessory pathway from the normal pathway.
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