This work presents a project overview and recent research results for the MEMS Rotary Engine Power System project at the Berkeley Sensor & Actuator Center of the University of California at Berkeley. The research motivation for the project is the high specific energy density of hydrocarbon fuels. When compared with the energy density of batteries, hydrocarbon fuels may have as much as 20x more energy. However, the technical challenge is the conversion of hydrocarbon fuel to electricity in an efficient and clean micro engine. A 12.9 mm diameter Wankel engine will be shown that has already generated 4 Watts of power at 9300rpm. In addition, the 1mm and 2.4 mm Wankel engines that BSAC is developing for power generation at the microscale will be discussed. The project goal is to develop electrical power output of 90milliwatts from the 2.4 mm engine. Prototype engine components have already been fabricated and these will be described. The integrated generator design concept utilizes a nickel-iron alloy electroplated in the engine rotor poles, so that the engine rotor also serves as the generator rotor.

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This paper describes the design of an electrostatic motor/generator using electrets and its circuit. By using electrets which generate permanent electric field on a rotor, higher power than that of conventional types is expected. We revealed that the maximum power is obtained from the motor/generator when the ratio of the gap to the width of electrodes is optimized at 0.6. And we estimated that 30.4 W output is obtained from the motor/generator with a 6mm diameter rotor at a rotational speed of 1 Mrpm by applying 200 V to 3 µm electrode gap. To use this output, however, a circuit which escapes loss due to charging/discharging cycle of a parasitic capacitance at the stator electrode is essential. We designed a novel circuit using inductor-capacitor (LC) resonance, and confirmed that over 80% of theoretically-ideal output is available using this circuit.

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This paper describes two works on a miniature fuel cell for portable application: (1) Demonstration of the conceptual prototype of a borohydride fuel cartridge, and (2) Prototyping of a 4-cell-stacked miniature polymer electrolyte fuel cell (PEFC) by sand blasting. The borohydride fuel cartridge consists of aqueous solution of sodium borohydride (NaBH₄), a catalyst for hydrolysis reaction of the fuel (BH₄^- + 2H₂O → 4H₂ + BO₂^-), and a hydrogen separation membrane of porous PTFE (polytetrafluoroethylene). The hydrogen separation membrane seals the fuel and reactant, securing users from their leakage. We confirmed the feasibility of this fuel cartridge by experiments. The miniature PEFC consists of two glass-based current collector plates, and a MEA (membrane electrode assembly) with cell interconnections and a gas seal. Four 7×7 mm single cells are placed in 27.5 mm square area, and electrically connected in series. The current collector plate was fabricated by photolithography and sand blasting, which are preferable for mass-production. The miniature PEFC was tested using hydrogen as fuel, and an output of 0.5 mW/cm² was obtained from a single cell.

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We report a MEMS-based fuel reformer for supplying hydrogen to micro-fuel cells for portable applications. A combustor and a reforming chamber are fabricated at either side of a suspended membrane structure. This design is used to improve the overall thermal efficiency, which is a critical issue to realize a micro-fuel reformer. The suspended membrane structure design provided good thermal isolation. The micro-heaters consumed 0.97W to maintain the reaction zone of the MEMS-based fuel reformer at 200°C, but further power saving is necessary by improving design and fabrication. The conversion rate of methanol to hydrogen was about 19% at 180°C by using evaporated copper as a reforming catalyst. The catalytic combustion of hydrogen started without any assistance of micro-heaters. By feeding the fuel mixture of an equivalence ratio of 0.35, the temperature of the suspended membrane structure was maintained stable at 100°C with a combustion efficiency of 30%. In future works, we will test a micro-fuel reformer by using a micro-combustor to supply heat.

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A reciprocating engine was designed for a micro power generator. It is expected to be used for a portable micro power generator with high energy density. The proposed reciprocating engine has the spring system, which is composed of opposite-pistons supported by an elastic spring. Combination of resonance of the spring system by the combustion pressure and an induction coil generates electricity due to generated voltage. Working cycle analysis, structural analysis, vibration analysis, and generated voltage calculations were carried out. Adopting H₂ gas as a fuel and Si as a structural material, the theoretical output was found to be 41 mW under the conditions that compression ratio is 5, the maximum combustion temperature is 850 K and resonance frequency of the spring system is 582 Hz.

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This paper presents a simple new configuration for a switched capacitor type C-V converter based on a charge balance principle for a differential capacitance sensor and its simulation results. The new converter was devised and realized using only one operational amplifier, nine CMOS switches and an oscillation circuit. It was shown that the offset output due to the input offset voltage of an operational amplifier can be ideally reduced to zero with an appropriate additional switch configuration. By using a P-Spice circuit simulator, the offset cancellation scheme and proper transient response were confirmed for possible parasitic capacitances concerned in a typical differential capacitance sensor. In addition, a P-Spice system simulation based on analog behavioral models enabled us to reliably estimate the operation of an electro-mechanical system with the C-V converter statically and dynamically, where the electrostatic force acting on a movable electrode was taken into account.

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An on-chip signal conditioning CMOS Integrated Circuit on Si (111) was fabricated for use in multi-point neural activity recording. The two-dimensional (2D) micro-Si probe array for neural activity recording sensor can be fabricated on the IC by Vapor-Liquid-Solid (VLS) growth method. However, the circuit has to be fabricated on Si (111) wafer because micro-Si probe is grown perpendicularly only on Si (111) wafer. Proper process conditions were established for fabrication of CMOS on Si (111). The circuits include 8×8 array of signal conditioning pixels with two 8-bit shift registers as 2D scanning circuits and a frequency divider. It is found from evaluated results of the fabricated circuits on Si (111) that CMOS circuits can be formed on Si (111) with enough performance. The output signal is detected from the selected pixel with the circuit. Increasing the potential at the selected pixel, the output signal increases in proportion to the potential. It has been confirmed that circuits on Si (111) are possible to be realized and available for image-recording sensor of neural activity.

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We have developed an X-ray lithography simulation system X3D (Moving Mask Deep X-ray Lithography Simulation System for 3-Dimensional Fabrication) for the first time, that is tailored to simulate the fabrication process of 3-dimensional microstructures using the M²DXL (Moving Mask Deep X-ray Lithography) technique. The newly developed X3D can simulate the progress of developed PMMA surface with developing time using chemical dissolution rate data as a function of dose energy. The simulation system consists of three modules: mask generation, exposure, and development. The exposure module calculates a dose energy distribution over a PMMA using a mask pattern and its movement pattern, and then converts this dose energy to a dissolution rate of PMMA. The development module adopted a "Fast Marching Method" to calculate the resultant 3D shape of the PMMA. In this paper, a new experimental method to determine dissolution rate as a function of dose energy that dominates the simulation accuracy was proposed. An experimental procedure of the new experimental method, the determined dissolution rate, and verification of the measured results are presented.

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One of the essential factors in ITS (Intelligent Transportation Systems) that needs to be considered is to improve ambient safe driving for vehicles on a slippery road. This letter proposes a new detection technique for slipping vehicle’s wheels based on measuring the magnetic patterns of a magnetized rotated wheel by on-board vehicle induction magnetometer. The data of the magnetic patterns of a slipping wheel that has been collected by both observation method and computer-based simulation method has been compared and evaluated. The results demonstrate that our new sensor capable to provide a practical device for future ITS

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