概要 / Overview
In our laboratory, against unknown mechanics of animal locomotion and nature phenomena, we try to clarify them by developing MEMS force sensors specialized for each target. Moreover, we would also like to give our research knowledge back to society as new industrial MEMS products.
Current working projects include:
MEMS力センサによる足裏反力 / Ground reaction forces using MEMS sensors
This study describes a micro force plate array for the simultaneous measurement of the anterior and vertical components of GRFs of multiple legs during the running motion of an ant. The proposed force plate, which consists of a 2000 μm × 980 μm × 20 μm plate base as the contact surface of an ant’s leg, and the supported beams with piezoresistors on the sidewall and surface are sufficiently compact to be adjacently arrayed along the anterior direction. Eight plates arrayed in parallel were fabricated on the same silicon-on-insulator substrate to narrow the gap between each plate to 20 μm. We compartmented the plate surface into 32 blocks and evaluated the sensitivities to two-axis forces in each block so that the exerted forces could be detected wherever a leg came into contact. The force resolutions in both directions were under 1 μN within ±20 μN. Using the fabricated force plate array, we achieved a simultaneous measurement of the GRFs of three legs on one side while an ant was running.
[Ref] H. Takahashi et.al., J. Micromech. Microeng., 2014.
[Ref] H. Takahashi et.al., Proc. of Transducers2017, 2017.
バイオロギングのためのセンサ開発 / Sensor development for biologging
Here we present an airflow sensor for seabird biologging. To attach the sensor to the biologging system, the sensor must be waterproof because seabirds dive into the seato prey on fish. In addition, the sensor must also be compact and have high sensitivity. Here, we propose a Pitot tube-type airflow sensor that satisfies these requirements. The proposed sensor is composed of MEMS piezoresistive cantilevers as sensing elements with high sensitivity and anodic alumina membranes with a nano-hole array as the waterproof elements with airflow penetration. The developed sensor responded sufficiently to airflow velocities from 2 m/s to 20 m/s. Inaddition, the sensor maintained its sensitivity after plunging into the water and returning to the air. Therefore, the proposed sensor can be utilized for practical seabird biologging.
[Ref] H. Takahashi et.al., Sens. Actuator A-Phys., 2018.
[Ref] T. Hagiwara et.al., Proc. of MEMS2019, 2019.
高感度MEMS力センサの工学応用 / New application of MEMS force sensors
We have developed a triaxial tactile sensor using piezoresistive beams. The sensor chip is composed of two pairs of sidewall-doped Si beams for shear stress sensing and one pair of surface-doped Si beams for normal stress sensing. The sensor chip is embedded in a silicone rubber. Because the simple beam structure can be fabricated easily, the proposed sensor is compatible with semiconductor device fabrication. The fabricated sensor was evaluated for normal and shear stress (0–400 kPa and 0–100 kPa, respectively). The responses of the corresponding beam pairs were found to be proportional to the magnitude of the applied stresses without the influence of the other stresses. The relationship between the angle of shear stress and the responses of each beam pair was also evaluated. Each beam pair detects only one axis’s shear stress and showed little reaction to the other axes’ shear stress. As a result, the proposed sensor can measure the three axial components of normal and shear stress independently. The actile sensor has been developed as a commercial device that a venture company "touchence" sells.
In addition, the fabricated differential pressure sensor can be applied to a variety of devices, such as airflow sensors, viscometers, angular acceleration sensors and so on.
[Ref] R. Wada and H. Takahashi, Jpn. J. Appl. Phys., 2020.
[Ref] H. Takahashi et.al., J. Micromech. Microeng., 2020.
新しいMEMSプロセスの構築 / Development of MEMS fabrication process
This work presents a self-focusing three-dimensional (3D) lithography based on refractive-indices changes of polyethylene glycol diacrylate (PEGDA) during photo-polymerization. Since the polymerization of PEGDA leads to increase in refractive index, the ultraviolet (UV) light rays in the PEGDA receives refraction effect during exposure, thus being focused and forming 3D photo-polymerized structures. Compared to the previous work, the present work enables to fabricate 3D structures using single UV exposure and theoretically estimate 3D features. We demonstrate the potential of the self-focusing 3D lithography by fabricating PEGDA microneedles and trapezoid-shaped microwells. Their structures well match to our theoretical estimation. Therefore, our theoretical approach can provide short route for on-demand, complicated 3D structures of refractive-indices-variable materials with single UV exposure.
[Ref] T. Sugimoto and H. Takahashi, Appl. Phys. Express, 2020.
[Ref] H. Takahashi et.al., Appl. Phys. Express, 2020.