Two kinds of sensor systems for detecting gas trail (so-called plume) are discussed. One is the mobile robot with several kinds of sensors which can track the gas plume to search for a gas source. The other is the sensor network which can reveal the spatial and temporal behaviors of air-pollutant plumes in detail. The sensor network can also perform an automatic calibration to achieve a maintenance-free operation.

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In order to prevent catalyst layer collapse formed onto a porous silicon layer, a new method was developed. We have proposed a novel miniaturized fuel cell using monolithically fabricated silicon electrodes and power generation was verified though the output was small. Pore diameter and porosity of the porous silicon layer which works as a diffusion layer and a catalyst support layer was enlarged for easy penetration of electrolyte and fuel, but the porous layer was collapsed when the catalyst metals were deposited onto the porous layer. It is assumed that the porous layer shrinks because platinum, whose atomic size is smaller than the size of silicon, replaces silicon at equal stoichiometric ratio in a plating bath using Pt⁴⁺ ion. Pt²⁺ ion was mixed into the plating bath and the collapse of the porous layer was prevented.

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This paper describes trials to realize a MEMS-based polymer electrolyte fuel cell (PEFC) with Pt-loaded carbon electrodes. We first developed screen-printing technology to pattern Pt-loaded carbon electrodes on MEMS-based PEFCs. Iso-propyl alcohol (IPA) and dibutyl phthalate (DBP) were compared as the dispersion media of Pt-loaded carbon powder. We found that DBP-based paste had better screen-printability, and revealed the reason by measuring the relationship between the shear rate and viscosity of the pastes. Next, we applied the Pt loaded carbon paste to two types of MEMS-based PEFCs. One is the PEFC which uses porous SiO₂ as a gas diffusion layer. The Pt-loaded carbon paste was screen-printed on the Pt current collector which was sputter-deposited on the porous SiO₂. The obtained power density was only 70 μW/cm². The other type of MEMS-based PEFC is a thin film PEFC. A Pt-loaded carbon anode and cathode were screen-printed on a silicon/Pyrex glass support substrate. The obtained power density was 1.5 μW/cm². The low performance may be due to the low performance of the prepared Pt-loaded carbon, and/or the poor adhesion of the anode with the current collector and the PEM. For the thin film PEFC, the high resistance of the Pt-loaded carbon electrodes can be another reason, because there are no current collector on the Pt-loaded carbon electrodes.

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This paper describes a microvalve which is actuated by electrostatic force for the flow control of fuel in portable direct methanol fuel cell systems. The microvalve is fabricated by using standard MEMS fabrication techniques including photolithography, wet etching, thin film deposition and anodic bonding. The microvalve is equipped with a novel pressure-balance mechanism for normally-closed operation against pressurized fuel. The pressure-balance mechanism is composed of a pressure-balance tank whose pressure is adjusted to the same pressure as inlet by a soft corrugated diaphragm. This balanced pressure pushes the boss, which is supported by a soft actuator diaphragm, to close the microvalve, enabling a low driving voltage operation. By applying 100 V_dc, the microvalve controlled the flow rate of methanol up to maximum flow rate of 100 μl/min at an inlet pressure of 40 kPa. The microvalve is expected to miniaturize the fuel delivery system, and eventually increase the practical energy density of portable fuel cell systems.

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Binary optics is one of the effective methods to form three dimensional micro structure. In this study, Binary optics was applied to negative-tone photoresist of SU-8 with substrate penetration method, and three-dimensional structures with 16 levels were fabricated by 4 times exposure and development proceses. We also propose the new technique to generate mask patterns for binary optics by image-processing which dramatically reduces effort of designing mask pattern.

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