In this study, we fabricated a flexible 3D mesh structure with periodic voids by using a 3D lithography method and applying it to a vibration energy harvester to lower resonance frequency and increase output power. The fabrication process is mainly divided into two parts: three-dimensional photolithography for processing a 3D mesh structure, and a bonding process of piezoelectric films and the mesh structure. With the fabricated flexible mesh structure, we achieved the reduction of resonance frequency and improvement of output power, simultaneously. From the results of the vibration tests, the meshed-core-type vibration energy harvester (VEH) exhibited 42.6% higher output voltage than the solid-core-type VEH. In addition, the meshed-core-type VEH yielded 18.7 Hz of resonance frequency, 15.8% lower than the solid-core-type VEH, and 24.6 μW of output power, 68.5% higher than the solid-core-type VEH. The advantage of the proposed method is that a complex and flexible structure with voids in three dimensions can be relatively easily fabricated in a short time by the inclined exposure method. As it is possible to lower the resonance frequency of the VEH by the mesh structure, use in low-frequency applications, such as wearable devices and house appliances, can be expected in the future.

A gravity gradiometer is an instrument to measure gravity gradients caused by local density variations. Gravity gradiometers can be used for surveys of soil moisture and exploration of underground resources. We are developing a portable gravity gradiometer, which is suitable for field measurements. In our gravity gradiometer, a pair of test masses set at different heights (separated by about 70 cm) in a vacuum tank is tossed up at the same time. The vertical gravity gradients are obtained by measuring differential acceleration between the test masses that are in free fall, using a Michelson interferometer.

In this study, we propose inclined micro-structures to trap single cells efficiently on micro-well arrays. We focused on the liquid flow in a well with a tapered wall and made a micro-well array with a channel structure by the rotated/inclined exposure method. In addition, we fabricated the well array having the tapered side-walls, and carried out cell trapping test using the fabricated micro-well array of an inversely tapered and a channel-attached models. We analyzed fluorescence microscope images obtained by the cell trapping tests and evaluated the cell trapping and the residual rates of the device. As a result, the proposed wells having the tapered side-walls keep a larger of the trapped cells than the conventional wells having the vertical side-walls. Moreover, the trapping structure having the flow channels is easier to immobilize the cells to the wells. The proposed principle of the channel structure is expected to raise the cell trapping rate.

In recent years, all kinds of electronic devices have been advanced and downsized with the development of micro/nano machining technology. Due to the downsizing of the electronic devices, high processing accuracy is required, and it is necessary to process complicated three-dimensional (3D) structures with high integration. In this study, we evaluated the angle controllability of 3D UV lithography to fabricate 3D microstructure. Firstly, we showed that it is possible to obtain the target angle of 3D microstructures by adjusting the UV exposure dose within the range of 0° - 38.7°. Secondly, we demonstrated the 3D lithography to correct the angle error caused by the UV light attenuation in thick photoresist. As a result of the demonstration, an angular error of a vertical side-wall in thick photoresist having the thickness of 200 μm exposed by the proposed method is 0.1 ° which is 1/10 or less of the conventional vertical exposure.

This paper proposes a bimorph piezoelectric vibration energy harvester (PVEH) with a flexible 3D meshed-core elastic layer for improving the output power while lowering the resonance frequency. Owing to the high void ratio of the 3D meshed-core structure, the bending stiffness of the cantilever can be lowered. Thus, the deflection of the harvester and the strain in the piezoelectric layer increase. According to vibration tests, the resonance frequency is 15.8% lower and the output power is 68% higher than in the conventional solid-core PVEH. Compared to the solid-core PVEH, the proposed meshed-core PVEH (10 mm × 20 mm × 280 μm) has 1.3 times larger tip deflection and the maximum output power is 24.6 μW under resonance condition at 18.7 Hz and 0.2G acceleration. Hence it can be used as a power supply for low-power-consumption sensor nodes in wireless sensor networks.

In recent years, self-powered sensor nodes for wireless sensor networks has been developed by energy harvester. Especially, vibration energy harvester (VEH) has attracted much attention because of the higher energy density, the simplicity of configuration, and the affinity with the micromachining technology. In this paper, we propose a piezoelectric VEH having 3D zigzag micro-structure as an elastic layer of cantilever in order to achieve lower resonance frequency than 10 Hz and improve power generation efficiency. In order to confirm the validity of the proposed piezoelectric VEH, we compared two kinds of VEHs (having 3D zigzag structure and solid flat plate as an elastic layer of a cantilever) by modal analysis and piezoelectric coupling analysis. As a result of modal analysis, the proposed 3D zigzag VEH lowers primary resonance frequency by 59%. Moreover, regarding the coupling analysis, the proposed VEH shows 1.6 times higher output electric power than flat plate one at each resonant condition.

Attempts to detect mass distribution changes, associated with volcanic activity, by measuring gravitational fields have been done since the 1920s in Japan. Measurement was done by using the gravity-variometer, such as the torsion balance on the Sakurajima volcano. In the early 1990s, Absolute Gravimeter (FG 5) of Micro-g LaCoste Company, which is simple to use and lightweight, became popular in field measurements. The absolute gravimeter has a resolution of 10 m/s level when used at a quite observation station. When observing volcanic activity with an absolute gravimeter, it is possible to estimate the height of the magma head from gravity change. However, the absolute gravimeter is sensitive to environmental disturbances, and the error is thought to mislead the height of magma head by several hundred meters. The instrument we are developing is a new gravity gradiometer. The gravity gradiometer can measure vertical gravity gradients with a resolution of 10 1/s level at an observation station with seismic vibration. In this gravity gradiometer, two test bodies are thrown upward at different heights in a vacuum tank at the same time, and the difference between the free fall acceleration of the two test bodies is obtained by a Michelson interferometer. Gravity is proportional to 1/r and the gravity gradient in the vertical direction is proportional to 1/r, where r is the distance between the gravitational source and the instrument. Therefore, the gravity gradiometer has a better sensitivity to nearby gravity sources, and is suitable for observation of the environmental disturbances, such as rainfall and groundwater fluctuation. Simultaneous observation of the absolute gravimeter and gravity gradiometer at the same observation station could allow us to estimate the displacement of the magma head more accurately. Assuming a simple volcano model, we have calculated the gravity change by Monte Carlo simulation for Mt. Asama and Sakurajima volcanos, and examined the usefulness of the simultaneous observation of the absolute gravimeter and gravity gradiometer. In this presentation, I will report the results of the simulation and discuss the optimum observation station for the absolute gravimeter and gravity gradiometer.

Many moving parts are on a microfluidic component in Micro Total Analysis System (μ-TAS) and Lab-on-a-chip. Conventional fabrication processes for moving and releasing parts are complex and laborious. Micro/nano-systems have been required to satisfy the integration, further miniaturization, and shortening fabrication process time for more complex application. In this paper, we propose a simple-structural micro-moving part having a magnetically-driven diaphragm made of a photosensitive nanocomposite for an easy integration method. The fabricated system generated the one-directional fluid flow evaluated by using image analysis with fluorescent microscope images.

In this paper, we examine the anxiety at utilizing wheelchair. When the human use wheelchairs, from the influence of environment, the human feel a sense of unease. In particular, when the human go down slopes using wheelchair, the human feel anxiety if the angle of slope is greater than thresholds, which is different depending on the person. If thresholds can estimate, we have possibility to make wheelchairs using which no one feels the anxiety. However the problem to estimate the threshold of angle to feel the anxiety is difficult. In this paper, we propose an estimation method of angle of threshold to feel the anxiety by using brain waves of the human in the case of going down slopes using wheelchair.