Y. Sato

Tohoku University, Japan

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Publications (9)8.39 Total impact

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    ABSTRACT: Residue-free dry etching of a photosensitive-polymer sacrificial layer using O-2/CF4/CO-plasma exposure is described for the fabrication of microelectromechanical-system (MEMS) devices. Energy dispersive X-ray spectroscopy reveals that O-2/CF4/CO-plasma exposure removes polymer sacrificial layers without leaving residue and severely damaging Au structures. Since the O-2/CF4/CO-plasma exposure hardly damages Au structures, this process is applicable for the removal of sacrificial layers for MEMS with Au structures.
    No preview · Article · Mar 2013 · ECS Transactions
  • Y. Sato · T. Ono · N. Sato · Y. Ogawa
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    ABSTRACT: This is a report on the first observations of auroral roar emissions near 4 times the ionospheric electron cyclotron frequency (fce) with a passive receiver installed in Svalbard, Norway. 4fce roar emissions were detected from 5.27 to 5.70 MHz during moderate geomagnetic disturbances in 22 days between May and September 2011 only from noon to evening, while no event occurred during the winter season. An analysis of a typical event shows that the electron density profile measured from EISCAT Svalbard dynasonde satisfies the condition that the upper frequency of the 4fce roar is nearly equal to both upper hybrid resonance frequency (fUH) and 4fce at 238-km altitude. These observations support the idea expanded from the most commonly-accepted generation mechanism of 2fce and 3fce roar: the origin of 4fce roar is upper hybrid waves favorably generated under the condition of fUH ˜ 4fce in the auroral F-region ionosphere.
    No preview · Article · Apr 2012 · Geophysical Research Letters
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    ABSTRACT: This paper describes a millimeter-sized electret vibrational energy harvester fabricated by a MEMS-based process for power generation enhancement. To increase current generation, we developed a new “slit-and-slider” structure with horizontal arrays and vertical protrusions. This structure enables us to increase an area and to narrow a gap of energy conversion in the limited size. The structure was fabricated by gold-electroplating. A lower chip with a movable part and an upper chip with a fixed part were aligned by chip-on-chip mounting. The device resonated around 1430 Hz with an acceleration amplitude of 6 m/s 2 . With an ethylene-tetrafluoroethylene
    No preview · Article · Jun 2011
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    ABSTRACT: This paper describes an RF-MEMS switch structure and its fabrication process for developing low-loss multiport RF switches that integrate multiple RF MEMS switches and CMOS control circuits. In our structure, RF MEMS switches and coplanar waveguides are seamlessly integrated, and they are suspended above a CMOS LSI to reduce the loss due to the lossy Si substrate. A gold multilayer stacking technique was used to fabricate the structures, and the STP technique was used to seal them for damage-free packaging. Switching operation of RF MEMS switches was achieved and low insertion loss of 0.07 dB/mm at 5 GHz was obtained for the suspended coplanar waveguides.
    No preview · Article · Jan 2011
  • Source
    Y. Sato · T. Ono · N. Sato · R. Fujii
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    ABSTRACT: This is a brief report on the first observation of polarization features and the source region of MF/HF auroral radio emissions emanating from the topside ionosphere. These emissions are called “Terrestrial Hectometric Radiation (THR)” and regarded as a counterpart of auroral roar and MF burst which are observable from the ground. THR typically occurs in either or both of two frequency bands near 1.5–2.0 MHz and 3.0–4.0 MHz, whose polarization features correspond to the L-O and R-X mode. The R-X mode, which has never been reported as auroral roar and MF burst, can be attributed to nonlinear coupling of two upper hybrid waves. The Akebono satellite observation shows THR emissions merge with upper hybrid waves in a frequency-time diagram under the matching condition fUH ∼ 2fce. This observation suggests that plasma instability enhances the upper hybrid waves under this condition, and then they are converted into MF/HF auroral radio emissions.
    Preview · Article · Jul 2010 · Geophysical Research Letters
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    ABSTRACT: This paper presents experimental proof of energy harvesting with MEMS-based vibrational devices. To clarify the effect of the coupling of vibration of MEMS devices and electrical field of electrets for current generation, a slit-and-slider structure was developed. This structure enables to combine the MEMS devices and electrets after their vibrational and electrical properties have been characterized separately. In the fabrication, the movable gold electrodes were released and then aligned by chip-on-chip mounting to face the fixed electrodes. A 1-mm-square electrode resonated around 1166 Hz with external vibration of a magnitude of acceleration of 1 m/s<sup>2</sup>. The surface and rear potentials of the electret were around -150 and +100 V, respectively. The coupling of the mechanical and electrical properties produced an AC current of 170 pA. The results pave the way to designing and fabricating small-sized vibrational energy harvesters.
    No preview · Conference Paper · Jul 2009
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    ABSTRACT: Recent ground-based observations have detected MF auroral radio emissions called MF burst and auroral roar. It is interpreted that origin of both emissions is upper hybrid waves generated in the ionosphere by auroral electrons. Some theoretical studies [e.g. Weatherwax et al., 2002] have proposed that MF burst which has a broad band spectrum is generated at an altitude of few hundred kilometers over a wide altitude range while auroral roar is excited in altitudes where a condition of fuh ~ nfce (n=2, 3) is met, which leads to its narrow band spectrum. The polarization spectrum observation at the Husafell observatory in Iceland, which started in 2005, revealed the polarization characteristics of 3fce roar and the relationship with energy of precipitating electrons [Sato et al., 2008]. However, occurrence rate is low because the observation site is located in the auroral zone. We install a new instrument for MF auroral radio emissions at Longyearbyen in Svalbard. The observation at Longyearbyen has several advantages: higher occurrence rate can be expected in the polar cap region, and simultaneous observations with EISCAT Svalbard Radar (ESR) and other ground-based observations can be easily obtained. The instrument consists of two types of observation systems. One is designed for the continuous observation of spectrum in a frequency range below 6 MHz. The other is designed to obtain waveform data in a frequency range below 4 MHz by an A/D converter with a sampling speed of 10MSPS. By using the wave form data, the arrival direction angle of a received radio wave can be estimated. In this presentation, we will introduce the purpose of the observation and the detail of the instrument, and report some initial results.
    No preview · Article · Dec 2008
  • Y. Sato · T. Ono · N. Sato · R. Fujii · H. Miyaoka · A. Kadokura
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    ABSTRACT: In order to study the generation and propagation processes of the MF auroral radio emissions (auroral roar and MF burst), a radio spectrograph ststem was installed at Husafell in Iceland (invariant latitude: 65.3deg). Within the observation period since late 2006, several MF auroral radio emissions have been detected. Based on our observation results, the polarization character of the MF bursts was consistent to the previous result by Shepherd et al. [1997], and identified that 3fce roar is L-O mode wave. It is suggested that auroral roar appears during magnetic storm recovery phase while MF burst is associated with aurora breakup. We compared the 3fce roar detected on May 23, 2007 with auroral image observed by the Polar/UVI and auroral particle observed by the DMSP/SSJ4 in the southern hemisphere. These image data show that the auroral oval has multilayer structure and the Husafell station is located between enhanced layers. In a region with relatively low energy electrons' precipitation (several 100 eV), MF radio waves can propagate to the ground because there is weak ionization in the D and E regions. Therefore, it is suggested that the auroral roar is generated by low energy electrons precipitating near the observation site and propagates downward to the ground. To understand the mechanism, the energy spectrum of precipitating electrons is the key parameter not only for plasma instability but also for ionization of low altitude region. This observation result shows important evidence. On the hypothesis that the frequency of auroral roar coincides with harmonics of fce in the source region, the observation frequencies of 3.1-3.5 MHz correspond to the altitude range of 550-880 km, and electron density should be more than 105/c.c. in this altitude range. It is less likely to occur in the polar ionosphere. When we introduce alternative hypothesis that the plasma instability occurs at (n+1/2)fce ESCH waves, the estimated altitude of the source region becomes 250-350 km. Thus, we have to reexamine the proposed generation mechanism of the MF auroral radio emissions.
    No preview · Article · Dec 2007

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