Hiroshi Toshiyoshi

Bio: Hiroshi Toshiyoshi is an academic researcher from University of Tokyo. The author has contributed to research in topics: Microelectromechanical systems & Surface micromachining. The author has an hindex of 38, co-authored 498 publications receiving 6232 citations. Previous affiliations of Hiroshi Toshiyoshi include Centre national de la recherche scientifique & Toshiba.

Electrostatic micro torsion mirrors for an optical switch matrix

Abstract: We have developed a new type of compact optical switch using silicon micromachining technique. Torsion mirrors (300 /spl mu/m/spl times/600 /spl mu/m) supported by thin polysilicon beams (16 /spl mu/m wide, 320 /spl mu/m long, and 0.4 /spl mu/m thick) are arranged in a 2/spl times/2 matrix (total size 3 mm/spl times/5 mm, t 0.3 mm). The mirrors are independently attracted by electrostatic force of applied bias voltage to redirect the incident light in a free space. Using collimated beam fibers for optical coupling, we obtained small insertion loss (/spl les/-7.66 dB), considering the length of a light path (/spl ges/10 mm), a large switching contrast (/spl ges/60 dB), and small crosstalk (/spl les/-60 dB). The fabrication yield was higher than 80% thanks to the newly developed releasing technique that used a silicon oxide diaphragm as an etch-stop layer and as a mechanical support in the process. Holding voltage (/spl les/50 V) was lower than the voltage to attract the mirror (100/spl sim/150 V) because of the hysteresis of angle-voltage characteristic of electrostatic operation.

Light actuation of liquid by optoelectrowetting

Abstract: Optical actuation of liquid droplets has been experimentally demonstrated for the first time using a novel optoelectrowetting (OEW) principle. The optoelectrowetting surface is realized by integrating a photoconductive material underneath a two-dimensional array of electrowetting electrodes. Contact angle change as large as 308 has been achieved when illuminated by a light beam with an intensity of 65 mW/cm 2 . A micro-liter droplet of deionized water has been successfully transported by a 4 mW laser beam across a 1 cm � 1 cm OEW surface. The droplet speed is measured to be 7 mm/s. Light actuation enables complex microfluidic functions to be performed on a single chip without encountering the wiring bottleneck of two-dimensional array of electrowetting electrodes. Published by Elsevier Science B.V.

Integrated Broadband Microwave and Microfluidic Sensor Dedicated to Bioengineering

Abstract: This paper presents an innovative high-frequency- based biosensor, which combines both microwave detection and microfluidic network for time-efficient and accurate biological analysis. It is composed of a coplanar waveguide with a microfluidic channel placed on top. With the help of an appropriate de-embedding technique and modeling of the measurements, the relative effective permittivity of human umbilical vein endothelial cells has been evaluated successfully. Furthermore, experiments have been performed with the sensor on various cell concentrations in suspension, which validates its use in bioengineering applications such as cell quantification and counting in solution. This sensor requires no direct contact or use of labels on the cells, contrary to other usual types of biosensors (optical, mechanical or dc/low-frequency-detection-based ones).

Experimental investigation of radiative thermal rectifier using vanadium dioxide

Abstract: Vanadium dioxide (VO2) exhibits a phase-change behavior from the insulating state to the metallic state around 340 K. By using this effect, we experimentally demonstrate a radiative thermal rectifier in the far-field regime with a thin film VO2 deposited on the silicon wafer. A rectification contrast ratio as large as two is accurately obtained by utilizing a one-dimensional steady-state heat flux measurement system. We develop a theoretical model of the thermal rectifier with optical responses of the materials retrieved from the measured mid-infrared reflection spectra, which is cross-checked with experimentally measured heat flux. Furthermore, we tune the operating temperatures by doping the VO2 film with tungsten (W). These results open up prospects in the fields of thermal management and thermal information processing.

Bistable nanowire for micromechanical memory

Abstract: We present a micromechanical device designed to be used as a non-volatile mechanical memory. The structure is composed of a suspended slender nanowire (width: 100 nm, thickness: 430 nm, length: 8 to 30 ?m) clamped at both ends. Electrodes are placed on each side of the nanowire to (1) actuate the structure during the data writing and erasing mode and (2) determine its position by measuring the capacitive bridge in the reading mode. The structure is patterned by electron beam lithography on a pre-stressed thermally grown silicon dioxide layer. When later released by plasma etching, the stressed material relaxes and the beam buckles by itself to a position of lower energy. These symmetric bistable Euler beams exhibit two stable deformed. This paper presents the microfabrication process and analysis of the static buckling of nanowires. Snapping of these nanowires from one stable position to another by mechanical or electrical means will also be discussed.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Microfluidics: Fluid physics at the nanoliter scale

Abstract: Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.