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We report the design and fabrication of a novel fiber optic bend sensor capable of measuring the bend direction and degree of curvature simultaneously. The sensor has a serial arrangement of two fiber Bragg gratings (FBGs) with two different reflection center wavelengths and similar asymmetrical cross sections with different etching faces on an independent single-mode fiber. These cross sections were fabricated by anisotropic reactive ion etching (RIE) using CF₄ plasma. The reflection center wavelengths of the two FBGs shifted sinusoidally with a phase difference of π/2 as a function of the bend direction under constant bend feeder displacement. Because it was shown that the reflection center wavelength shifted linearly as a function of the degree of curvature of an FBG with an asymmetrical cross section in our previous experiment, this sensor could be used to detect both the bend direction and the curvature from a pair of central reflection wavelength shifts for two FBGs. These experimental results were compared with theoretical values calculated from a strain of the core in an etched optical fiber.

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Recently, AT-cut quartz resonators have found widespread use as RF and high-sensitivity devices. In these applications, further miniaturization and high-frequency stability are required. To achieve a high quality (Q)-factor and high productivity, the authors have proposed a novel resonator shape in which the surface is machined as a three-dimensional stripe-like structure. This shape is called quasi-convex. In this paper, we discuss the design and fabrication of quasi-convex resonators to verify their effectiveness. First, with regard to the height of the convex part and the pitch of the quasi-convex pattern, the optimal resonator design is discussed on the basis of the results of a finite-element method simulation. Then, prototypes of the quasi-convex resonators fabricated by deep reactive-ion etching and micro electro-mechanical systems fabrication technology are presented. In our experiments, the highest Q-factor is obtained when the height ratio of the convex part was 5% and the pitch is 100 µm. In addition, the Q-factor of the quasi-convex resonators is seven times greater than that of ordinary plane-shaped resonators, as confirmed using vacuum equipment.

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A self-powered plant-health-monitoring sensor powered by a sap-activated battery that consists of two different types of metal electrodes and is activated by the sap of a vascular plant has been developed as an application for wireless biosensor networks. The battery consists of a galvanized iron nail inserted into a tree trunk and a stainless steel electrode planted in the soil nearby. Its output power is on the order of 1 µW. An intermittent-power-supply circuit with a divided-power-line structure, which separates the power line of a storage capacitor while it is discharging, makes it possible to charge the capacitor with an input power of around 1 µW and to supply power to a wireless transmitter with a power dissipation of a few milliwatts. To verify the effectiveness of the circuit scheme, a prototype sensor was fabricated and tested on a potted pachira tree. The sensor was able to transmit a signal about every 40 min over a distance of 5 m. We verified that the variation in the interval between transmitted signals depended on the water content of the soil around the tree.

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A tactile sensing system that measures normal and shear (triaxial) forces has been developed, and its characteristics such as linearity and crosstalk have been evaluated. Triaxial forces are estimated from the resistance changes of NiCr thin film strain gauge attached to three microcantilevers. The output voltage of the Wheatstone bridge that comprises a gauge film and three reference resistances is acquired using an A/D converter after amplification. Triaxial forces are calculated from the output voltages of three microcantilevers by simple matrix multiplication. Nonlinearity and crosstalk are less than 4% when the normal force applied is up to 1N and less than 10% when the shear force applied is up to 0.2N. Active touch sensing was demonstrated using an object having a striped profile measuring 0.1mm in height and 1mm in width.

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In this report, we propose a microfluidic device made of fused silica substrates and an optimized assay procedure for the device to reconstruct a motor protein system. The fabricated device is created using photolithography methods and bonding techniques to realize a minimum channel size of 4 µm in width and 2 µm in depth. The glass bonding process achieves good reproducibility by optimizing substrate cleaning processes, coating conditions, and the concentration of the sodium silicate solution. The assay sequence required to realize microtubule gliding in the channel without losing protein functionality is optimized to allow manipulation of the microtubule by applying an electric field. The average curvature of the microtubule trajectory is measured at 5.7±2.8 µm (N=3) at an electric field of 5 kV/m. The proposed device might have applications in micro total analysis systems.

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This paper presents the design and implementation of a MEMS activity sensor operating at less than 50 nW for monitoring of the simple health conditions of animals, particularly of chickens. The developed MEMS activity sensor includes a piezoelectric microcantilever, a low power comparator integrated with a CMOS multi-step voltage reference generator, and a counter. This system enables the realization of a wireless sensor node to work continuously for more than two years using a 1.55 V button battery weighing 0.5 g.

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This paper presents a novel receiver that simultaneously uses 50 channels to decrease the packet collision rate and can receive a packet without preamble; thus, the power consumption of a wireless sensor node during transmission can be reduced. In a multi-point monitoring system where one receiver receives data from several tens of thousands of nodes, a multiple-access problem arises. Because a wireless sensor node cannot have much power, solving the problem by improving the receiver and not using power in the node is desirable, such as employing a carrier-sense operation. The developed receiver enables the reception of packets from 10000 nodes without carrier-sense operation at approximately 1% packet collision rate.

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