センサ・マイクロマシン部門誌（論文誌E）では，英語の論文・レターのみを集めた「英文特集号」を試みており，前回（2014年3月号）に引き続き，本誌2015年3月号を発行する運びとなりました。ここで，初めて，本企画をお知りになった方もいらっしゃ

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This paper presents an electrostatic vibration energy harvester with a bipolar-charged electret for high output power and for low electrostatic force. In conventional electrostatic energy harvesters, electrets are charged by monopolar charge (mainly by negative) with a high potential for large power harvesting. We propose a bipolar charging method in order to form an electret, which not only has negative charge but also positive charge. The electrostatic energy harvester, with a size of 13×12×1.2 mm³, was fabricated and charged by a -250-V monopolar potential and by a ±250-V bipolar potential. The maximum output power of the monopolar- and bipolar-charged harvester is 3.1 µW and 9.8 µW, respectively with an applied acceleration of 7 g at 352 Hz with a 0.9-MΩ load resistance. The output power is 9 µW at 1.4 g and the maximum effectiveness against the velocity-damped resonant-generator (VDRG) limit is 2.5%. By using the bipolar-charged electret, the high output power obtained from the high charging potential was compared to a conventional harvester charged by the monopolar method. Further, using the finite element method (FEM) analysis, we determined that the electrostatic force that prevents harvesting mass movement is significantly reduced on the bipolar-charged electret. The electrostatic forces under static conditions along the vertical and horizontal directions obtained through the FEM analysis were reduced to 15% and 20%, respectively, from those of the monopolar-charged electret.

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A micro-assembly technique for microstructures using a silicon clip mechanism is developed for a time-of-flight scanning force microscope (TOF-SFM) probe with an electrostatically driven actuator. Microsprings formed by deep reactive-ion etching are used for the clip micromechanism. Cantilever-shaped microelements for the TOF-SFM are handled by a manipulator, and the microgap between the microspring and opposite wall is expanded by pulling the microspring using a microneedle. Then, the microelement is inserted into the micromechanism, and is clipped by releasing the microspring. After assembly, all microelements are fixed with a conductive glue. Electrostatic actuation of the cantilevered microelement is demonstrated. This technique is advantageous in the fabrication of complex three-dimensional microstructures.

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This paper describes a magnetic tactile sensor with Indium antimonide (InSb) Hall elements that enables multifunctional tactile sensing devices to detect normal contact forces and temperature. InSb Hall elements are generally used as magnetic sensors. The proposed sensor consists of two InSb Hall elements and a magnet that are embedded in silicone rubber, which functions as artificial skin. Here, the normal contact force is detected by the variation in distance between the Hall elements and the magnet. The temperature characteristics of the InSb Hall elements depend on the bias circuit to generate the Hall voltage. Two output Hall voltages driven by two kinds of bias circuits are measured in the normal contact force range from 0 to 90 N, and for a temperature range of 0 to 50°C. The inverse response surfaces that are used to identify the normal contact force and temperature are formulated using experimental results. The results obtained show that it is possible to detect normal contact force and temperature by obtaining two kinds of Hall voltages.

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Two types of sensing systems for ion balance control, based on potential measurement and current measurement, were proposed and investigated. MOSFETs were used in both types of systems as key devices. The detection limits and response times of both systems were experimentally compared. The potential measurement type of system is superior in regard to the detection limit, and the current measurement type of system is superior in regard to the response time. The type of system should be appropriately chosen depending on the semiconductor manufacturing objective.

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In this work, we present a new design involving a microheater-integrated quartz crystal microbalance (QCM) array for thermal desorption spectroscopy. Each QCM consists of two electrodes to excite thickness-shear-mode (TSM) vibrations on the crystal back side and one microheater to increase the temperature on the crystal front side. The resonance frequency was stable when a voltage was applied to the microheater. Carbon microparticles were coated on one of the QCMs for gas adsorption, and its frequency change during the temperature increase was calculated by subtracting the frequency change of an untreated QCM. The proposed QCM array was employed to separate ethanol from methanol. The separation was successful, as confirmed via thermal desorption spectra calculated by differentiating the resonance frequency change with respect to time.

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An effective method to decrease the operational power of an MEMS plasma source in a vacuum ultraviolet light source is described. The floating electrode has been introduced to promote power efficiency during discharging. Furthermore, it was observed that shielding a major part of the floating electrode further enhanced its power saving capability. The ignition and sustaining powers are 5 W and 4.5 W, respectively. The power values are lower than those reported for an inductively coupled micro-plasma source with the bulk setup.

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This paper presents an equivalent circuit model of an electrostatic energy harvester for a SPICE circuit simulator. The output power and impedance of the proposed model are approximated by using a simplified model of a voltage-controlled capacitor. The relationship between the capacitance and the electrode position is calculated by FEM analysis by taking the fringing effect into account; this relationship is applied to a sub-circuit model for the SPICE simulator. Further, the results of this study show that the output waveform and the optimal resistance obtained using the SPICE simulator correspond with the measurement results. In addition, the operation of a harvesting system connected with a commercially available power management IC is demonstrated.

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