IEEJ Transactions on Fundamentals and Materials
Online ISSN : 1347-5533
Print ISSN : 0385-4205
ISSN-L : 0385-4205
Volume 140 , Issue 6
Showing 1-10 articles out of 10 articles from the selected issue
Paper
  • Takeshi Musha, Hiroshi Inujima
    2020 Volume 140 Issue 6 Pages 306-311
    Published: June 01, 2020
    Released: June 01, 2020
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    The optical rotation angle sensor is characterized in that it is excellent in resolution and angle detection accuracy, and the magnetic sensor is characterized in that it is resistant to foreign matter such as dust and dirt, and that it is possible to achieve low power consumption, small size, and low cost of the sensor, as compared with the optical sensor. However, in the magnetic type, in order to obtain a high resolution as compared with the optical type, it is necessary to make the magnetization period of the magnet fine, so the magnetic rotation angle sensor has the difficulties compared with the optical type.

    This time, for magnetic rotation angle detection, we carried out a feasibility study by magnetic field simulation and principle verification experiments on a technique of extracting signals of two frequencies from one signal detection track by modulating a magnetic field from a magnet with a slit of a magnetic material, and this paper reports the result.

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  • Takeshi Ishida, Yuki Kobayashi, Yukihiro Tozawa, Osamu Fujiwara
    2020 Volume 140 Issue 6 Pages 312-317
    Published: June 01, 2020
    Released: June 01, 2020
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    Electrostatic discharge (ESD) immunity testing for consumer or industry electronic equipment is specified by the International Electrotechnical Committee (IEC) as IEC 61000-4-2, and has to be in compliance with both the tests of contact and air discharges. Contact discharge testing is most often used due to good repeatable testing results, despite the fact that air discharge testing can impose on equipment severe electromagnetic stresses of a few times larger discharge current peaks and faster rise-time in comparison with contact discharge testing. This is because air discharge testing results are significantly affected by many factors such as a test voltage, an approach speed, electrode surface conditions and climatic conditions. For this reason the IEC standard is unable to identify any specific current waveform for air discharges and thus provide its calibration procedure. Nevertheless, this standard is still mandatory testing for making a decision to pass or fail. In this study, as aiming to validate the usefulness of compliance test using ESD generators by contact discharges, current waveforms measured for air discharges to sphere and cone electrodes at an approach speed of 40 mm/s are shown at test voltages of 2 kV to 15 kV. The first peak current waveforms for air discharges to sphere electrodes at an approach speed of 80 mm/s are also exhibited under various different climatic conditions. Unstable air discharge phenomena and variations in the current waveforms are demonstrated in comparison with contact discharges. Results indicate that the first current peaks of contact discharges fall between the maximum and minimum of first current peaks caused by air discharges, and the rise times are between the fastest and the slowest rising slopes of air discharges. These findings show the usefulness of contact discharges as immunity compliance testing because they stably provide more moderate waveforms compared to those for air discharges.

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  • Haruki Ejiri, Takashi Fujii, Akiko Kumada, Kunihiko Hidaka
    2020 Volume 140 Issue 6 Pages 318-324
    Published: June 01, 2020
    Released: June 01, 2020
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    The initiating process of vacuum breakdown is still unknown despite the efforts of many researchers in the long history of vacuum insulation. This paper reports the results of Particle-In-Cell Monte Carlo Collision simulation of the electrons, positive ions, and neutrals in the vicinity of an emitter on the cathode. The radius of the emitter re, the temperature of the emitter T, product of macroscopic electric field and electric field enhancement factor βEmac, and the electric field enhancement factor β itself are used as the parameters. In some combinations of the parameter values, the distort of electric field and the increase in current are observed as the result of the following positive feedback: field emission, positive ion generation, electric field enhancement by approach of positive ions, and increase in field emission electrons. All parameters affect whether the current increase or not. The radius of the emitter re is a key parameter that determines the occurrence of the current increase. This is because the density of the neutrals in the region where ionization occurs becomes larger with re. Necessary conditions to occur the current increase are the field emission current in the order of 0.1 μA or more and the line integral neutral density along z-direction at the center of the emitter in the order of 1017 /m2 or more.

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  • Yasutomo Otake, Takahiro Umemoto, Ryosuke Kondo, Masaharu Fujii, Hyeon ...
    2020 Volume 140 Issue 6 Pages 325-330
    Published: June 01, 2020
    Released: June 01, 2020
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    To investigate the breakdown mechanism in oil/PB composite insulation systems applied to power transformers, we have measured the electric field in partial discharge occurrence by the application of lightning impulse voltage using the electric field measurement system by electro-optical Kerr effect. It has confirmed that the system has sufficient time response for the measurement of the electric field during lightning impulse application. In the oil/PB composite insulation system, which has multi oil gaps, we could have confirmed the increase of the electric field of the other gaps when the partial discharge occurred in one of the oil gaps. Furthermore, we have confirmed that the obtained optical phase shift is similar to estimated value by electric field simulation.

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  • Mitsuru Sakakibara, Satoru Muto, Manabu Okuda, Yoshiaki Adachi, Gen Ue ...
    2020 Volume 140 Issue 6 Pages 331-337
    Published: June 01, 2020
    Released: June 01, 2020
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    Magnetoencephalography (MEG) requires a magnetically shielded room (MSR) for protection against very slow and micro magnetic noise. An index called initial permeability, µi, is generally used to evaluate the performance of high-quality magnetic shielding materials. However, the measurement conditions, such as the magnetic strength and frequency of the µi, are not suitable for an MEG magnetic shield; further, the effect of background geomagnetism (DC magnetic field) is not considered. In this paper, we propose incremental permeability, µΔ, as an index to evaluate a magnetic shield for very low-frequency micro magnetic field fluctuations. In addition, the µΔ measurement system is described in detail. The measurement conditions of the magnetic strength and frequency were set at 1 to 0.001A/m and 3 Hz, respectively. We experimentally confirmed that geomagnetism does not have much influence on the measurement of µΔ. Lastly, the effectiveness of this evaluation method was demonstrated via results obtained for three different samples.

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Letter
  • Hirofumi Sanada, Naofumi Wada, Megumi Takezawa, Hiroki Matsuzaki
    2020 Volume 140 Issue 6 Pages 338-339
    Published: June 01, 2020
    Released: June 01, 2020
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    Under the theme of raising the efficiency of white-collar business tasks using software robots, we performed a study of industry-academia bidirectional learning in which project leaders from a university and a company acquire knowledge and gain practical experience in a collaborative manner. An application for automating a certain routine task was successfully developed using Python and related libraries while the project leaders exchanged opinions and information. The end result was a mutually beneficial.

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  • Tomoyuki Nagano, Sadao Masamune, Akio Sanpei
    2020 Volume 140 Issue 6 Pages 340-341
    Published: June 01, 2020
    Released: June 01, 2020
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    This paper presents the active control system for Resistive Wall Mode (RWM) stabilization in the low-aspect-ratio Reversed Field Pinch (RFP) machine RELAX. In magnetic confinement fusion research, RWM is MHD instability that degrades plasma confinement, and the stabilization of RWM is an important research issue. In the RFP machine RELAX with the aspect ratio of 2, RWM of m/n = 1/2 mode grows from when the discharge time exceeds 1.5 ms, and limits the discharge time. In RELAX, a control system using saddle coil array and on-off control have applied for RWM stabilization. It is confirmed that the system works as design, and as a result, the discharge time has been extended from ~3.0 ms to ~4.0 ms.

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