Ai Ueno

Soft-X-ray-charged vertical electrets and its application to electrostatic transducers

A novel charging method for vertical electrets in narrow gaps using soft X-rays has been developed. Electrets can be charged up to the depth 20∼30 times of the gap opening. With the present charging technology, MEMS electret transducers can be fabricated using a single wafer without assembling process. We demonstrate performance of vertical electrets using early prototype of in-plane accelerometer. Under 18.7 µmp-p external oscillation at 500 Hz, 30 mV output has been obtained without external bias voltage. Surface potential for 80 µm-deep vertical electrets is estimated to be 52 V.

Parylene-based active micro space radiator with thermal contact switch

Thermal management is crucial for highly functional spacecrafts exposed to large fluctuations of internal heat dissipation and/or thermal boundary conditions. Since thermal radiation is the only means for heat removal, effective control of radiation is required for advanced space missions. In the present study, a MEMS (Micro Electro Mechanical Systems) active radiator using the contact resistance change has been proposed. Unlike previous bulky thermal louvers/shutters, higher fill factor can be accomplished with an array of electrostatically driven micro diaphragms suspended with polymer tethers. With an early prototype developed with parylene MEMS technologies, radiation heat flux enhancement up to 42% has been achieved.

Triple-walled gold surfaces with small-gaps for nonresonance surface enhanced Raman scattering of rhodamine 6G molecules

To increase the intensity of Raman scattering with surface enhanced Raman scattering (SERS) effect, the authors proposed the triple-walled gold (Au) structures on silicon (Si) substrate. High aspect ratio Au nanowalls with nanogaps were realized by two different techniques. One is layer by layer technique. The other is standing high aspect ratio Au wall fabrication technique. Finally, 50 nm-thick Au standing walls and 50 nm gaps were obtained. Through the comparison of bare Si substrate, Au film, single-walled Au structures, and triple-walled Au structures in SERS intensity with 0.020 wt. % rhodamine 6G molecules, it was revealed that the SERS intensity from triple-walled Au structure was 50 times higher than that from Au film. The enhancement factor (EF) of our proposed SERS chip was estimated as 4.7 × 106. The proposed method will allow us to realize multiwalled Au structure, which can increase EF efficiently.

Study on the correlation between Solid Oxide Fuel Cell Ni-YSZ anode performance and reduction temperature

The influences of reduction temperature on the initial performance and shorttime durability of nickel-yttria-stabilized zirconia composite solid oxide fuel cell anode were investigated. Anode microstructures before and after operation were quantitatively analyzed by three-dimensional reconstruction based on focused ion beam-scanning electron microscopy technique. The anode reduced at 500 oC showed the worst initial performance and stability in operation and the anode reduced at 800 oC showed the smallest polarization resistance. The anode reduced at 1000 oC showed the most stable performance with polarization resistance enhanced with operation. It is found that higher reduction temperature leads to dense nickel and enhances nickel-yttria-stabilized-zirconia interfacial bonding, which can inhibit nickel sintering and improve the composite anode stability in long-time operation.

Electrostatically-driven active space radiator using near-field thermal radiation

Radiation control is crucial to maintain the operation temperature of satellites under varying irradiation of sunlight. Bulky heat exchangers with heat pipe or thermal louvers/shutters with a low fill factor previously proposed are not suitable for next-generation small satellites. In the present study, we propose an array of electrostatically-driven MEMS diaphragms for active control of thermal radiation using the near-field effect. In between Au and Cu surfaces at 300K, simulated effective emittance drastically increases from 0.1 to 0.8 when the gap is smaller than 0.4 µm. We have also designed and successfully microfabricated a prototype of the MEMS radiators.