Teppei Onuki

Improving an electret transducer by fully utilizing the implanted charge

Most of the countercharge in the conventional electret-based electromechanical transducer, where the electret is formed on a conducting or semiconducting substrate, is induced in the substrate. Here we introduce a type of electret transducer that contains a freestanding electret without a conducting substrate, thereby enhancing the electric field between the electret and the electrodes where the output current is generated. A measurement of the power output from an electromechanical transducer yielded approximately five times larger power when a freestanding electret film was used than when the same electret material was deposited on a conducting substrate.

Multichannel Photonic Crystal Wavelength Filter Array for Near-Infrared Wavelengths

Multichannel wavelength filters consisting of 2-D photonic crystal (PhC) for the near-infrared wavelength region (~800 nm) are demonstrated. The filter is a thin-film wavy multilayer structure and is fabricated by the autocloning method, which is based on a radio frequency bias sputtering process. Twelve long-pass-type filter regions are integrated on a common silica substrate. Sharp cutoff characteristics and almost equal channel spacing are experimentally verified. To precisely control the effective lattice constant of PhC, a modulated lattice structure on the substrate is utilized

Micro blender and separator using inner-vortex of droplet induced by surface acoustic wave

We report on a micro vortex in a droplet induced by surface acoustic wave acoustic streaming (SAW-AS), which is applicable as a stirrer in micro fluidic devices. Fine controllability of the flow rate in a micro vortex was revealed using two flow-tracking methods with colored aqueous fluids, or scattering laser beams by distributed particles. We performed two practical tasks of a micro stirrer as an on-chip blender and as a separator. Demonstrations results with a small concentrated blood specimen are also shown.

Low resistive copper films deposited using the ion beam sputtering method with an ultra-high purity target

Electric conductivities of copper thin films were investigated aiming toward low-loss metallization materials in energy-saving MEMS devices. The copper thin films were deposited with the goal of reducing impurities significantly and expecting to minimize scattering cross sections by relevant exclusion of scattering factors such as crystalline grain boundaries. Electron cyclotron resonance ion beam sputtering deposition (ECR-IBS) using an ultra-pure copper target was employed as the film process. Two indexes of the conductive properties, i.e. the resistivity at direct current and the mean free time extracted from optical transmission/reflection measurements at the plasma frequency, were employed in the evaluations and optimum conditions of the thin film processing were investigated. As a result, significant improvement in conductivity using the optimized conditions of temperature (430 K) and purity of the target (8N) was achieved for a thickness range of 10–300 nm.

A surface acoustic wave dynamics control device by grating structure

We have developed the dynamic controlling system of surface acoustic wave (SAW) using micro electromechanical structures, using a plate with periodic convex structures as a mechanical switch of the SAWs resonant condition. The effects of the geographical change on the substrate surface by the active control were investigated using the numerical analysis. And we verified the effect of spectrum shaping by the engraved grating structure, and the controlling effect of the resonant condition with the control plate on the grating structure experimentally.

Efficient Energy Harvesting from Irregular Mechanical Vibrations by Active Motion Control

A vibration-driven micropower generator with a high-Q mechanical resonator efficiently works under single-frequency vibration. However, the associated narrow operation frequency bandwidth tightly limits the power output under commonly observed wideband ambient vibrations. In this paper, we present a power-generation scheme in which the motion of an internal mass element is actively controlled. The control is such that the vibrating environment is forced to do the maximum possible work to the power generator. Electret-based energy conversion was analyzed as a means to realize the scheme, drawing on evidence from an experiment. We further analyzed the active control in general terms to reveal potential performance that is substantially above the conventional designs.

Radiative cooling using plasmon resonant nanostrips

We report on an attempt of cooling microsystem surface using a microminiatured heat sink. We also aim to enhance the outward heat flux from a microsystem surface via the radiation, optical (far infrared), and thermal properties of a copper nanostrip array that acts as a bandselective coupler; emitting heat on the surface as non-radiative electromagnetic components (phonon or plasmon polaritons at the surface). The emissivity was controlled with a nanostrip array designed as a pipe organ resonance (vertically) and 2nd Bragg resonance (horizontally), which generated a temperature gradient of 1.3 K across the substrate thickness when the other side of the substrate was heated to 42 °C from room temperature (26 °C).

MEMS Tunable Optical Filter Using Auto-Cloned Photonic Crystal

This paper proposes a novel MEMS tunable optical filter (TOF) using an auto-cloned photonic crystal (PhC). The auto-cloning method has great gains to fabricate multi-dimensional PhCs in productivity, flexibility and robustness. A two-dimensional PhC was fabricated by stacking Nb2O5and SiO2layers alternately keeping nano-scale periodic corrugations (190nm in pitch) formed on a substrate. This PhC was designed for splitting an incident light into the TM and TE modes at 500nm. Photonic band-gaps were changed by rotating the PhC and the transmittance of the TE mode was changed drastically at 420nm. The PhC was attached on the MEMS device (Eco Scan: Japan Signal) to control its angle of incidence. A resonance frequency of the MEMS structure was 183Hz and that rotation angle reached up to 40 degree. Switching characteristics of our MEMS-TOF were confirmed and its availability was demonstrated.

Rapid and nondestructive evaluations of conductivity by spectroscopic measurements at plasma edge

We report our evaluation of metallic material electric conductivity in terms of spectroscopic reflectometry at plasma edges for examining rapid and nondestructive micro components in microsystem. Conductivity (i.e., the mean free time of conduction electron) estimations were obtained through spectral measurements and fitting operations conducted with a theoretical model using copper and silver metal films. The validity of the Drude-Lorentz hybrid model and that of set parameters were confirmed and the mean free time was estimated by fitting with the peak height and the wavelength in the differential reflection spectrum as criteria. Significant differences in extracted conductivity values obtained through the process conditions (e.g., crystalline deficiency density and the existence of impurities) were recognized.

Study of surface plasmon polaritons near the photonic‐bandgap edge for interphotonic band switching devices

The photonic energy band structures near the bandgap edges of surface plasmon polariton in dielectric lattice structures on a smooth silver film were studied. At the bandgap edges, sharp changes of the surface plasmon polaritons transmittance arise owing to small changes in the refractive index around the lattice structure, which results in the band transition between the pass band and the stop band. On the analogy of ‘the phase transition’ between the surface plasmon polaritons conductive phase and the insulation phase, the surface plasmon polaritons phase diagram of the 1D lattice structure at a single frequency (λ≈ 780 nm) with parameters of the pitch and the refractive index of lattice were investigated. At the boundary, the most sensitive transition was found between the second pass band and the first stop band, with the ∼0.5 lattice filling factor. The surface plasmon polaritons phase state has been determined by far‐field observation using an optical microscope.