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Dive into the research topics where Yasushi Koyama is active.

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Featured researches published by Yasushi Koyama.


Applied Physics Express | 2013

Oscillations up to 1.40 THz from Resonant-Tunneling-Diode-Based Oscillators with Integrated Patch Antennas

Yasushi Koyama; Ryota Sekiguchi; Toshihiko Ouchi

Oscillations from 1.02 to 1.40 THz were observed at room temperature from resonant-tunneling-diode (RTD)-based oscillators with integrated patch antennas by improving the mesa structure and tuning the length of the antenna and the feed point location of the RTD. A two-step post structure realized a reduction of series resistance of the RTD, and the oscillation frequency significantly increased with the feed point closer to the center of patch antenna at around 1 THz. Experimental results agreed well with the analysis.


Applied Physics Letters | 2010

Subterahertz oscillations from triple-barrier resonant tunneling diodes with integrated patch antennas

Ryota Sekiguchi; Yasushi Koyama; Toshihiko Ouchi

We report on subterahertz oscillations of resonant tunneling diode oscillators with an integrated patch antenna. The device consists of an InGaAs/InAlAs triple-barrier resonant tunneling diode and a patch antenna on an InP substrate. Current-voltage characteristics indicate a peak current density of 280u2002kA/cm2, with a peak-valley ratio of about 3 at room temperature. An oscillation frequency of 517 GHz was observed at room temperature through Fourier transformed infrared spectroscopy. The results agree with electromagnetic analysis.


Journal of Infrared, Millimeter, and Terahertz Waves | 2014

Terahertz Imaging System for Medical Applications and Related High Efficiency Terahertz Devices

Toshihiko Ouchi; Kousuke Kajiki; Takayuki Koizumi; Takeaki Itsuji; Yasushi Koyama; Ryota Sekiguchi; Oichi Kubota; Kodo Kawase


Archive | 2004

Deflector, method of manufacturing deflector, and charged particle beam exposure apparatus using deflector

Haruhito Ono; Masatake Akaike; Kenji Tamamori; Futoshi Hirose; Yasushi Koyama; Atsunori Terasaki; Kenichi Nagae; Yoshinori Nakayama


Archive | 2009

Electromagnetic-wave oscillator

Yasushi Koyama; Takeaki Itsuji; Toshihiko Ouchi


Archive | 2012

Waveguide, method of manufacturing the same, and electromagnetic wave analysis apparatus

Yasushi Koyama


Archive | 2011

Optical frequency converter

Yasushi Koyama; Kousuke Kajiki


Archive | 2008

RESONANT TUNNELING STRUCTURE

Yasushi Koyama; Ryota Sekiguchi


Archive | 2007

IMAGE PROCESSOR, CONTROL METHOD OF IMAGE PROCESSOR, AND PROGRAM FOR IMPLEMENTING THE SAME

Yasushi Koyama; Hiroyuki Ogino; 泰史 小山; 宏幸 荻野


Archive | 2010

OSCILLATION CIRCUIT HAVING NEGATIVE RESISTANCE ELEMENT AND OSCILLATOR USING THE OSCILLATION CIRCUIT

Yasushi Koyama; Ryota Sekiguchi

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