S. Yamaguchi

Kansai University, Suika, Ōsaka, Japan

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Publications (345)397.01 Total impact

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    ABSTRACT: A new antenna array is proposed in order to improve the sensitivity and complexity of microwave imaging diagnostics systems such as a microwave imaging reflectometry, a microwave imaging interferometer, and an electron cyclotron emission imaging. The antenna array consists of five elements: a horn antenna, a waveguide-to-microstrip line transition, a mixer, a local oscillation (LO) module, and an intermediate frequency amplifier. By using an LO module, the LO optics can be removed, and the supplied LO power to each element can be equalized. We report details of the antenna array and characteristics of a prototype antenna array.
    Review of Scientific Instruments 10/2014; 85(11). DOI:10.1063/1.4885471 · 1.58 Impact Factor
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    ABSTRACT: As a method of largely reducing the transmission loss in the electric power grid, superconducting direct current (DC) power transmission cable has been investigated. Using superconducting DC power transmission cables, large amounts of current and energy can be transferred compared to conventional copper cables. In this case, an alternating current (AC) is converted to DC and superposed AC which is known as ripple current, and the energy loss by the ripple current is generated. Therefore it is desired to estimate the energy loss density for the case of DC current and superposed AC current for a design of DC transmission cable system. In this study, the hysteresis loss for DC current of 2 kA rectified from 60 Hz alternating current is calculated using the Bean model, and coupling loss was also estimated. The diameter of the cable was 40 mm. The ripple currents generated by multi-pulse rectifiers, 6-pulse, 12-pulse, and 24-pulse were considered. It is found that the total AC loss including the hysteresis loss and the coupling loss is considerably smaller than the supposed heat loss of 0.5 W/m which is obtained with a newly developed cable.
    Physics Procedia 10/2014; DOI:10.1016/j.phpro.2014.09.080
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    ABSTRACT: In the 200 m high temperature superconducting (HTS) cable test facility at Chubu University, a coaxial power cable is used and composed of two BSCCO (Bi-2223) superconducting layers. The tapes are wound closely to reduce effects on the critical current of BSCCO at self-field. Accordingly, each superconducting layer has a different number of BSCCO tapes. Previously, we have investigated dependence of the critical current (Ic) on the gap in order to optimize the HTS DC cable design. We have been studying the effect on the performance of HTS tapes for the superconducting DC power cables by critical current measurements. In the present experiments several HTS tapes are used and set as a similar structure in the cable with a two-layer structure. The critical current of HTS tapes are measured against the gap between the tapes in the same layer. The experiments show the improvement of the critical current by optimizing the tape arrangements due to magnetic field interaction between the tapes. We will present the experimental results and discuss the design of the HTS DC cable.
    Journal of Physics Conference Series 05/2014; 507(2):022038. DOI:10.1088/1742-6596/507/2/022038
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    ABSTRACT: We constructed the 200 m class superconducting DC power transmission test facility (CASER-2) in 2010, and have carried out the cooling down and operation test. The 5th cooling down and operation test was carried out from August to November 2012. Long term current feeding was tested for a month with various currents and temperatures in the 5th test. From the long term current feeding test, the LN2 circulation was clearly affected by the operation of the cryogenic system and the atmosphere, not only by the operation DC current. It was also confirmed that the Peltier current leads worked effectively for the reduction of heat leak at the cable terminal.
    Journal of Physics Conference Series 05/2014; 507(3):032020. DOI:10.1088/1742-6596/507/3/032020
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    ABSTRACT: Carbon nanowalls (CNWs) are a nano-carbon material constructed with a few layers of graphene and thus may exhibit similar properties to graphene. We developed a self-alignment process for the creation of carbon nanowalls using graphoepitaxy, which can be used for the structural fabrication of field-effect transistors. We used Raman spectral mapping to study the mechanism of the self-alignment process. The dependence of growth on temperature and the use of Raman spectra enabled the observation of geometrical catalyst effects and the induction of defects for self-aligned regions. The same effects were observed when analyzing the dependence of deposition on time. For low-temperature growth, which corresponds to the initial growth, the growth of CNW flakes can be observed only on the edge of processed patterns. On the other hand, the self-alignment process should change the shape of the flakes, thereby affecting grain structures and inducing carrier scattering. The use of graphoepitaxy can therefore help in the initial growth, and then mainly induces defects in CNW films. Finally, these defects are cured with the overgrowth.
    Japanese Journal of Applied Physics 04/2014; 53(5S1):05FD10. DOI:10.7567/JJAP.53.05FD10 · 1.06 Impact Factor
  • Norimasa Yamamoto, Satarou Yamaguchi, Tomohisa Kato
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    ABSTRACT: Recently, ingots of silicon carbide have been adapted to be sliced by the wire-cut electrical discharge machining. Fast slicing, and the reduction in the loss are important for slicing of the wafer. In this paper, characteristic features of the electric discharge machining in the ion-exchange water and the fluorine-based fluid were compared for these improvement. The discharge was caused by a pulse voltage applied to a ingot of silicon carbide and the wire in machining fluid, and the slicing was proceeded. As a result, improvement of surface roughness and kerf loss was confirmed, for the first time. In addition, the improving methods for fast slicing were considered.
    Materials Science Forum 02/2014; 778-780:767-770. DOI:10.4028/www.scientific.net/MSF.778-780.767
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    ABSTRACT: Nano-carbons such as carbon nanotubes and graphenes are very promising as next-generation materials, and field effect transistors (FETs) can be used with nano-carbon channels. In these nano-carbon materials, carbon nanowalls (CNWs) are constructed with a few layers of graphene and exhibit properties similar to those of graphene. We have developed a self-aligned process for CNWs using grapho-epitaxy. We have grown CNW channels on several line and space patterns fabricated by electron beam lithography and reactive ion etching. When the line and space pattern is suitable, self-aligned CNWs can be made by plasma-enhanced CVD. We also discuss the electrical properties (IDS-VDS characteristics) of the self-aligned CNW-FETs resulting from several growth temperatures and deposition times. [DOI: 10.1380/ejssnt.2014.225]
    e-Journal of Surface Science and Nanotechnology 01/2014; 12:225-229. DOI:10.1380/ejssnt.2014.225
  • Hisato Ohara, Jian Sun, Makoto Hamabe, Satarou Yamaguchi
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    ABSTRACT: A 200-m-long high-temperature superconducting (HTS) cable for dc power transmission, called CASER-II, was constructed at Chubu University using BSCCO tapes in 2010. The critical current of HTS tapes has been extensively studied against their layouts to improve the performance of HTS tapes in the cable. The multilayer structure of the tapes is needed to obtain a high current capacity. In the stacked tape conductors, the critical current of BSCCO tapes shows strong dependence on the current feeding directions between the tapes. The critical current is improved when the opposite-direction current is applied to them and reduced for the same-direction current feeding mode because of the strong magnetic field interaction between them. By using the ferromagnetic sheets, self-field of HTS tapes will be affected and may improve their critical currents. This technical paper presents the measurements of the critical currents of BSCCO tapes in the stacked conductors covered with the ferromagnetic sheets under different current feeding modes. We will present effects on the critical current of HTS tapes of the magnetic field from the currents applied to the neighboring tapes and the ferromagnetic sheets through the magnetic field analysis.
    IEEE Transactions on Applied Superconductivity 01/2014; 25(3):1-1. DOI:10.1109/TASC.2014.2373657 · 1.32 Impact Factor
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    IEEE Transactions on Applied Superconductivity 01/2014; DOI:10.1109/TASC.2014.2372632 · 1.32 Impact Factor
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    ABSTRACT: The vacuum insulation has been used for the thermal insulation of cryogenic pipes for the superconducting power transmission to reduce the heat leak from the environment at the room temperature to the low temperature parts. Since the cryogenic pipes, in particular, those for long distance power transmission, are considered to be thin long pipes, it might take a long time for evacuation. To estimate the evacuation time of the long cryogenic pipes, model calculations have been performed. According to the calculations, it is found that there is an optimum condition between the pumping speed, the diameter of the outer pipe and the length of the cryogenic pipe for efficient evacuation. It is also found that, if the outgassing is suppressed enough, the evacuation can be possible within 1 week even for the long cryogenic pipe with the length of 10 km. The reduction of outgassing is particularly important for the efficient evacuation.
    Physica C Superconductivity 11/2013; 494:292-296. DOI:10.1016/j.physc.2013.04.042 · 1.11 Impact Factor
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    ABSTRACT: The loss energy density (AC loss) with ripple current is numerically calculated by finite element method for cylindrical and strip superconductors based on Irie-Yamafuji model in which the magnetic field dependence of the critical current density is taken into account for design of DC transmission cable system. It is confirmed that calculated result of the AC loss in the cylindrical superconductor with the ripple current agrees well with theoretical estimation which was reported in the previous work. On the contrary, the AC loss in the strip superconductor with the ripple current is obtained only by numerical calculation. It is found that the AC loss in the strip superconductor of the ripple current becomes larger than that without DC current at small ripple current amplitude, since the penetration depth of magnetic field becomes large. Therefore, it is recommended that strip superconductor is better to use as cylindrical hollow superconductor for DC transmission cable system to reduce the AC loss.
    Physica C Superconductivity 11/2013; 494:173-176. DOI:10.1016/j.physc.2013.04.075 · 1.11 Impact Factor
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    ABSTRACT: In the 200 m high temperature superconducting cable test facility, BSCCO tapes with the critical current of 160 A in self field are used for the two superconducting conductors corresponding to each polarity of DC power transmission. In order to improve the cable property by tape configuration, we have investigated the critical current of a BSCCO tape with different structures. Previous study shows that the critical current of BSCCO tape decreases by 15% for the 3-layer stack structure. However, the stack structures are needed to obtain high current capacity of a cable. Therefore we study the performance of BSCCO tape in the stacked tapes conductor. The insulated tapes are arranged in a tape-above-tape structure and different currents are applied to each tape. The critical current of the target sample is measured by the four probe method by immersing the samples into liquid nitrogen bath. The experiments show that the improvement and degradation of the critical current of BSCCO tape in the stacked conductor are observed under different current feeding mode due to the magnetic field interactions between the tapes. The critical current of BSCCO in the stacked conductor is enhanced by 50% to more than 230 A under the opposite-direction current feeding mode.
    Physica C Superconductivity 11/2013; 494:297-301. DOI:10.1016/j.physc.2013.04.031 · 1.11 Impact Factor
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    ABSTRACT: A self-cooling device has been developed by combining a commercial n-channel power metal-oxide-semiconductor field-effect transistor (MOSFET) and single-crystalline Sb-doped n-type or B-doped p-type silicon wafers in order to improve the heat removal or cooling quantitatively. The electric current dependence of the temperature distribution in the self-cooling device and the voltage between the source and drain electrodes have been measured to estimate the Peltier heat flux. We found that the average temperature is decreased for a power MOSFET in which an electric current of 50 A flows. In particular, the average temperature of the power MOSFET was decreased by 2.7°C with the n-type Si wafer and by 3.5°C with the p-type Si wafer, although an electric current of 40 A makes little difference. This certainly warrants further work with improved measurement conditions. Nonetheless, the results strongly indicate that such n-type or p-type silicon wafers are candidate materials for use in self-cooling devices.
    Journal of Electronic Materials 10/2013; 43(6):604-. DOI:10.1007/s11664-013-2856-9 · 1.68 Impact Factor
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    ABSTRACT: We constructed a facility of a 200-m HTS power transmission test cable (CASER-II) in 2010. Generally, an HTS cable contracts about 0.3% when it is cooled from room temperature to liquid nitrogen (LN2) temperature. The contraction of the 200-m HTS cable corresponds to 0.6 m. In order to realize the HTS power transmission system, it is an essential issue to absorb the mechanical stress of the HTS cable during the cycles of cooling-down and heating-up. The CASER-II uses smooth pipes as the cryogenic pipe for the cable line to reduce the pressure drop of the liquid nitrogen flow, whereas the other HTS cables use corrugated pipes to absorb the mechanical stress. The CASER-II employed (1) the movable terminals at the cable end, and (2) the extendable bellows inserted in the cryogenic pipe, to absorb the contraction of 0.6 m in cooling cycles. Even at the 4th cooling-down test, no damage was observed in the CASER-II. Use of the smooth cryogenic pipe enabled low pressure drop with low LN2 flow rate, and negative pressure drop appeared at less than 5 L/sec of the LN2 flow rate. This negative pressure drop was caused by the LN2 flow assisted by siphon effect due to the difference of LN2 density along the cryogenic pipe line with elevation of 2.6 m.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):5400204-5400204. DOI:10.1109/TASC.2012.2235510 · 1.32 Impact Factor
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    ABSTRACT: Critical current of the high-temperature superconducting (HTS) tape is one of the important parameters for the application of power cables. After combination of the tapes in the cable, the self-field of the tape will be affected by the field from the other tapes, which will result in the degradation of the tape performance. Recently, a 200-m HTS cable test facility for dc power transmission and distribution has been constructed at Chubu University by using BSCCO tapes. In order to optimize the configuration of the HTS tapes in the cable, the effects on the critical current of the tape arrangements are investigated. In order to achieve high current capacity and efficiency of the cable, a multilayer configuration of the tapes is employed. This technical paper will present the measurements of the critical currents of the tape against the layer structures and the gaps between the HTS tapes. The critical current of the tape is measured by the four-probe method at liquid nitrogen temperature. We will present the effects on the critical current of the tape of the magnetic field from the currents applied to the neighboring tapes in the cable. An improvement of the critical current is observed, which suggests the design of DC HTS power cables regarding the tape arrangements may influence the cable property.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):5401104-5401104. DOI:10.1109/TASC.2012.2237495 · 1.32 Impact Factor
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    ABSTRACT: Heat leak from the current lead is the major source of power loss for superconducting (SC) magnets, motors and generators, and short distance SC power transmission lines. Therefore, reducing the heat leak from the current lead can improve the economy of the SC system and allow the use of SC systems commercially. The Peltier current lead was proposed and developed at Chubu University to reduce the electrical power consumption of the refrigerator. The heat leakage of the Peltier current lead saves almost 40%, but the power requirement of the refrigerator is still high. In order to realize greater power savings, the multistage current lead (MCL) and the gas-cooled MCL are proposed. The heat leakage reduction of the gas-cooled MCL depends on the characteristics of the cryogen and its pressure and the realization of high cost of performance and a high-temperature refrigerator. Here, we show the calculation results of the high-pressure effect of cryogen and discuss the performance of nitrogen trifluoride as cryogen.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):4802304-4802304. DOI:10.1109/TASC.2013.2243896 · 1.32 Impact Factor
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    ABSTRACT: Since self-cooling devices were first proposed, several materials have been tested for their suitability to be used in them. A self-cooling device requires a high Seebeck coefficient, a low electrical resistivity, and a high thermal conductivity. Here, we report experimental results for single-crystal silicon doped with boron. Samples were fabricated with carrier densities in the range of 2.0× 1015 to 1.6× 1019 cm-3, and their Seebeck coefficient and electrical resistivity were measured. Silicon with a carrier density of 1.6× 1019 cm-3 has a power factor of 4.8× 10-3 W/(K2m) at room temperature. The cooling capability of a self-cooling device was estimated using a one-dimensional model. The results suggest that a self-cooling device based on silicon with a high carrier density can have a higher heat removal performance than a conventional silicon power device of the same size.
    Japanese Journal of Applied Physics 05/2013; 52(5):4201-. DOI:10.7567/JJAP.52.054201 · 1.06 Impact Factor
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    ABSTRACT: Carbon nanotubes (CNTs) have many interesting properties for nano devices such as high sensitive sensors or noise enhanced nonlinear devices. A field effect transistor (FET) structure is one of the key features for these applications, and the control of noise in FETs is important for the actual operation of the application. Several origins of noise have been proposed, and defects and/or surface adsorption of molecules seem to be dominant for the 1/f type noise in CNTs. To study the origins of noise, the diameter dependence of noise properties was studied. We analyzed the noise properties in CNTs using noise spectroscopy with different fabrication parameters or ambient environments. We observed the crossover of noise properties in CNTs, which involved transition between different origins of noise depending on their diameter. Additionally, noise spectroscopy was used to observe such crossover between air and vacuum environments. We can control noise intensity using the gate voltage, and noise properties can be controlled by the fabrication parameters. These phenomena are useful for the stochastic operation of CNT-FETs.
    Applied Surface Science 02/2013; 267:101–105. DOI:10.1016/j.apsusc.2012.08.003 · 2.54 Impact Factor
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    ABSTRACT: Peltier Current Lead (PCL) is a key device which was developed to decrease heat penetration into DC superconducting system. We had been developed 100 A-class PCL. This PCL was employed in the demonstration test of DC superconducting transmission system in Chubu University (CASER-2) and confirmed operating stably. We have developed prototype of 1 kA-class PCL. In this paper, we report the performance of the prototype of 1 kA-class PCL.
    Physics Procedia 01/2013; 45:317–320. DOI:10.1016/j.phpro.2013.05.031
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    ABSTRACT: Progress in micro- to millimeter-wave technologies have made possible advanced diagnostics (imaging) for various applications, such as, plasma diagnostics, radio astronomy, alien substance detection, airborne and spaceborne imaging radars called as synthetic aperture radars, living body measurements. In this report we focus on the reflectometric (radar) techniques applied to plasma diagnostics and biomedical measurement.
    Electromagnetic Theory (EMTS), Proceedings of 2013 URSI International Symposium on; 01/2013

Publication Stats

2k Citations
397.01 Total Impact Points

Institutions

  • 2008–2014
    • Kansai University
      • • Department of Pure and Applied Physics
      • • Faculty of Engineering Science
      Suika, Ōsaka, Japan
  • 2002–2014
    • Chubu University
      • • Center of Applied Superconductivity and Sustainable Energy Research
      • • Department of Electrical Engineering
      Касугай, Aichi, Japan
    • High Energy Accelerator Research Organization
      Tsukuba, Ibaraki, Japan
  • 1969–2010
    • Tohoku University
      • Institute for Materials Research
      Japan
  • 2009
    • National Research Institute for Earth Science and Disaster Prevention
      Ibaragi, Ōsaka, Japan
  • 2006–2009
    • Sony Corporation
      Edo, Tōkyō, Japan
  • 1994–2006
    • National Institute for Fusion Science
      • Department of Helical Plasma Research
      Tokitsu-chō, Gifu, Japan
    • Fujitsu Ltd.
      • Fujitsu Laboratories
      Kawasaki Si, Kanagawa, Japan
  • 2002–2005
    • Chiba Institute of Technology
      Tiba, Chiba, Japan
  • 1968–2004
    • The University of Tokyo
      • Division of New Materials Science
      Tōkyō, Japan
  • 1998–2003
    • Nagoya Institute of Technology
      • Department of Materials Science and Engineering
      Nagoya, Aichi, Japan
  • 2001
    • Kyoto University
      • Department of Physics II
      Kioto, Kyōto, Japan
  • 1998–1999
    • The Graduate University for Advanced Studies
      • Department of Fusion Science
      Миура, Kanagawa, Japan
  • 1997–1999
    • Matsusaka University
      Matsusaka, Mie, Japan
  • 1984–1998
    • Nagoya University
      • Department of Energy Engineering and Science
      Nagoya, Aichi, Japan
  • 1974–1978
    • Sendai University
      Sendai, Kagoshima, Japan