Takashi Genda

Charging Method of Micropatterned Electrets by Contact Electrification Using Mercury

This paper describes a new charging method for micropatterned electrets. The charging is based on contact electrification, and is performed by dipping an electret into mercury. By this method, 0.5-µm-thick silicon-dioxide electrets whose surfaces were treated by hexamethyldisilazane (HMDS) and a fluorinated silane coupling agent were charged up to -50 and -80 V, corresponding to a seventh and a forth of the dielectric breakdown limitation, respectively. Micropatterned electrets with line-and-space features were also charged near the surface charge density of the unpatterned electret, but a part of the charges disappeared from both edges of the electrets. The charge stability was propotional to the square of the electret width. This suggests that the charge stability is not dominated by the electret bulk property, but by surface conduction. To reduce the surface conduction, surface modification by the fluorinated silane coupling agent is effective, improving the charge stability by 100 times compared with HMDS treatment.

High power electrostatic motor and generator using electrets

For application to a micro-machined gas turbine, we first designed the motor/generator using electrets. Theoretical calculation confirmed that the motor/generator generates 30.4 W at a rotational speed of 1 Mrpm after its electrode design is optimized. Next, we proposed a novel circuit using LC resonance for the generator, which can avoid the charging-discharging loss of the parasitic capacitance. And we confirmed that the circuit could generate over 80% output of the theoretical maximum. Lastly, we developed an electret-charging equipment using Corona discharge. Using it, an electret was charged, showing the average surface voltage of 354 V and the standard deviation of 16 V.

Development of Microturbocharger and Microcombustor for a Three-Dimensional Gas Turbine at Microscale

A microscale gas turbine is under development at Tohoku University in Japan. Current objective of the project is to reveal the performance of the gas turbine at microscale with optimum aerodynamic shape. Therefore the engine to be tested will be fabricated by machining using a micro-5-axis end mill to realize three-dimensional modeling. The first step of the development has been split into the development of microturbocharger and microcombustor, to prevent the problem of the heat flow effect pointed out in the previous study [1]. The heat flow from the combustor to compressor will become relatively large at microscale, and this will degrade the performance of the compressor. The goal of the first step of the development is to achieve the required performance of the components to realize the gas turbine cycle, without the heat effect. Those are, 62% compressor efficiency, 870,000 rpm shaft rotating speed, and the self sustained combustion. A microscale turbocharger has been designed. The compressor impeller of diameter 10mm is expected to produce a pressure ratio of 3, and 68% compressor adiabatic efficiency. The bearings to realize the design rotational speed are hydrodynamic type gas bearing. Fabrication of the herring-bone grooves have been attempted, and successfully formed on a cylindrical surface by new etching procedure. A technique to fabricate three-dimensional turbine impellers at microscale by powder sintering of ceramics has been demonstrated. A semi-microcombustor has been fabricated and shown successful performance by burning hydrogen fuel.Copyright

High power electrostatic motor with micropatterned electret on shrouded turbine

The paper describes the fabrication process of a shrouded turbine and surface modification using fluorinated silane coupling agents to stabilize the charges of a silicon-dioxide electret. The shrouded turbine was fabricated by cavity-through etching, which is deep reactive ion etching (DRIE) through a wafer having cavities made by DRIE and fusion bonding. By using this process, a shrouded turbine with little eccentricity was obtained without damaging the inner structures such as blades and flow ways. Charge stability of electrets was deteriorated by miniaturizing the size. The charge deterioration was caused by leakage current through the surface. To decrease the surface conduction, the surface was terminated by fluorine with silane coupling agents. As a result, the charge stability of a silicon-dioxide electret was improved 100 times compared with HMDS (hexamethyldisilazane) treatment.

Micro-patterned electret for high power electrostatic motor

This paper describes the charging method of a micro-patterned electret for a high power electrostatic motor. By applying contact electrification using mercury to electret charging, charging to 5 /spl mu/m-wide micro-patterned electret was achieved. But, 0.9 /spl mu/m-wide edges of the electret is not charged due to discharge at the edges. Using this method, a silicon-dioxide electret with 0.5 /spl mu/m thickness was charged up to a charge density of about -100 V//spl mu/mSiO/sub 2/ with fair repeatability.

Three-Dimensional Micromachining of Silicon Nitride for Power Microelectromechanical Systems

This paper describes a 3-dimensional micromachining process of silicon nitride microcomponents for power microelectromechanical systems (power MEMS). This process is summarized as nitridation (reaction-sintering) of spark-plasma-sintered Si powder compacts after micromilling. Using this process, we have fabricated 2- and 3-dimensinal Si3N4 micro-turbine rotors for micro-gas turbines with a diameter of 5 and 9 mm, respectively. The shrinkage of a workpiece was within 1 % during reaction-sintering. X-ray diffraction analysis revealed the nitridation of the Si powder compact and the formation of α- and β-Si3N4 by reaction-sintering. The reaction-sintered samples have 87 % density compared with that of pressure-less sintered Si3N4 and 77 % bending strength compared with that of the commercially-available reaction-sintered Si3N4 ceramics.