論文 - 高橋　英俊

Sleep-mask-type pulse wave and respiration rate sensor using a MEMS-based differential pressure sensing element

T Kato, TV Nguyen, H Takahashi

IEEE Sensors Journal 24 （ 13 ） 20402 - 20410 2024年

ISSN  1530437X

　概要を見る

Noninvasive sensors have been widely used to measure pulse and respiratory waves, which are the primary measurement targets in sleep monitoring. Conventional noninvasive biometric sensing devices, including smartwatches, require the use of multiple sensing elements and face challenges in the direct and simultaneous measurement of pulse and respiratory waves. Recently, pressure sensors with micro-electromechanical systems (MEMS)-based sensing elements have attracted attention for their small size, high sensitivity, and broad applicability. These sensors detect minute vibrations on the body surface with changes in pressure for biometric sensing. In this study, we propose a sleep-mask-type sensor for sleep monitoring that measures pulse and respiratory waves. A MEMS differential pressure (DP) sensor chip serves as a sensing element, which is placed between two chambers, one open to the atmosphere and the other with a rubber membrane. The proposed sensor detects minute vibrations of the dorsal surface of the nose, which can be attributed to pulse and respiratory waves based on DP changes in the chambers. This article presents the design, fabrication, and evaluation of the sensor with respect to capturing vibrations during sleep. The application of frequency filtering to the measured raw data confirmed that the pulse and respiratory waveforms could be directly and simultaneously measured, thereby rendering the proposed sensor suitable for sleep monitoring.

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Single-step fabrication of a 6-axial force plate using an FDM 3D printer

Y Nakahara, H Takahashi

IEEE Sensors Journal 2024年

3D Printed Low Crosstalk 6-Axis Force Sensor Probe For Insects’ Jumping Force Measurement

Y Nakahara, H Takahashi

2024 IEEE 37th International Conference on Micro Electro Mechanical Systems …    837 - 840 2024年

ISSN  10846999

　概要を見る

This paper reports on a small 6-axis force sensor probe fabricated by a dual nozzle type fused deposition modeling (FDM) 3D printer. The proposed sensor probe consists of two coaxially connected PLA supporting structures in the out-of-plane and in-plane directions. Eight strain gauges are formed by electrically conductive PLA (EC-PLA) at the stress concentrations in each PLA structure in one dual-material print with automatic alignment. Thus, three-directional forces and three-directional moments can be measured with low crosstalk from the fractional resistance change of the eight strain gauges. The sensor probe can be produced and reproducibly and easily modified according to the measurement target. The fabricated sensor probe was calibrated and conducted to have 0.1 mN of force and 0.1 mNm of moment resolution with low crosstalk. Using the fabricated sensor probe, we demonstrated that the grasshopper's sheer vector jumping force was measured as 1 mN, assuming the sensor probe was a branch.

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Measurement of Ground Reaction Forces in Sprint Running Using Insoles With 6-Axis Tactile Sensors.

H TAKAHASHI, KENI SHIMAZAKI

デサントスポーツ科学 (Web) 45, 12-21 2024年

Liquid-immersion inclined-rotated exposure system for fabricating three-dimensional microstructures with large inclination angles

G Kagawa, H Takahashi

Journal of Micromechanics and Microengineering 34 (9), 095008 34 （ 9 ）  2024年

ISSN  09601317

　概要を見る

This study utilized liquid-immersion inclined-rotated ultraviolet lithography to fabricate three-dimensional (3D) microstructures. The maximum achievable inclination angles obtained through conventional inclined-rotated exposure (IRE) methods were limited by the significant refractive index differences in material. We proposed an IRE with liquid-immersion and adjustable mirrors, which enabled greater inclination angles with improved adjustability. Using liquid as a medium helped minimize the refractive index disparities between materials. We fabricated polydimethylsiloxane molds for micro suction cup (MSC) array sheets to evaluate the performance of the developed liquid-immersion IRE. The resulting MSC array sheets (10 mm2) with a suction cup diameter of 500 μm, achieved inclination angles up to 51°, approximately double those obtained with the conventional IRE method. In addition, the suction force of the fabricated MSC arrays were evaluated by pulling along the vertical, horizontal, and edge directions under wet conditions. The maximum measured suction force was 0.15 N, confirming the effectiveness of the proposed liquid-immersion IRE in fabricating 3D microstructures, as demonstrated by the fabricated MSC array sheets.

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Laser-Based Fabrication Process for Piezoresistive Cantilever Using Flash Laser Annealing

R Nakashima, T Kan, H Takahashi

2024 IEEE 37th International Conference on Micro Electro Mechanical Systems …    614 - 617 2024年

ISSN  10846999

　概要を見る

This paper reports a simple laser-based fabrication process for a piezoresistive cantilever involving flash laser annealing. The proposed process simultaneously realized a micro cantilever structure and an n-type piezoresistive sensing element by irradiating a dopant-coated Si wafer with a pulsed fiber laser. The fabricated sensors responded linearly to strain with a gauge factor over 10, a sufficiently useful value. The proposed process could serve as a rapid prototyping in MEMS processes involving semiconductor doping.

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Jumping dynamics of spherical shells driven by snap-through buckling

T Abe, S Shimizu, Y Nakahara, H Takahashi, G Ishigami, T Sano

APS March Meeting Abstracts 2024, B34. 014 2024年

Experimental validation of a wave-height sensor based on a MEMS piezoresistive cantilever and a waterproof film

K Shimada, T Kishimoto, H Takahashi

Japanese Journal of Applied Physics 63 (12), 128003 63 （ 12 ）  2024年

ISSN  00214922

　概要を見る

This paper presents a barometric pressure-sensing wave-height sensor that employs a microelectromechanical system piezoresistive cantilever, an air chamber, and a micromesh waterproof film. The developed sensor has a height resolution of less than 5 mm in the 0.01-10 Hz frequency band and a high time resolution with 100 Hz sampling rate. We conducted wave height measurements at sea using the developed sensor and compared its performance with that of a commercial global positioning system buoy-type wave-height sensor.

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Dual-Measurement Pitot Tube Type Airflow and Waterflow Speed Sensor for Seabird Biologging

K Shimada, T Kishimoto, H Takahashi

2024 IEEE SENSORS, 1-4 2024年

ISSN  19300395

　概要を見る

This study reports on a Pitot tube type airflow and waterflow speed sensor for seabird biologging. Due to seabirds' remarkable ability to traverse the sea and sky, biologging method, in which sensors are attached to animals, has been used to measure their locomotion under natural conditions. To evaluate seabird locomotion, a sensor was required that could be attached to a seabird and directly measure relative air speed and water speed. Here, we propose a sensor that incorporates a Pitot tube structure and a polytetrafluoroethylene porous film with air permeability and waterproof properties. We achieved the ability to switch the measurement principle between air and water using the same sensor element, enabling the measurement of different pressure ranges. The sensor demonstrated adequate responsiveness to airflow ranging from 0-10 m/s and waterflow from 0-1.6 m/s in experiments.

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Designing a bathymetric sensor using absolute pressure sensors arranged on a regular polyhedron

R Ando, K Shimada, T Kishimoto, H Takahashi

IEEE Sensors Letters 8 （ 8 ）  2024年

　概要を見る

In oceanic environments, compact underwater drones must determine their positional information, including water depth, to move autonomously because wireless communication underwater is challenging. However, current bathymetric sensors often lack high accuracy, energy efficiency, and cost-effectiveness. We propose a spherical bathymetric sensor that uses multiple absolute pressure sensor elements, allowing precise water depth measurement without being affected by dynamic pressure caused by waterflow as well as offering low energy consumption and cost-effectiveness. This sensor has a spherical design with 12 absolute pressure sensor elements arranged in a regular dodecahedron, connected by a flexible Kiri-origami circuit. The water depth is determined by compensating for waterflow-induced error using sensor data and linear regression. We evaluated our method using both simulations and experiments. The sensor reduced waterflow-induced errors to within 7.5 mm in simulations and 5 mm in a water tunnel at a speed of 2.0 m/s. By comparison, conventional methods without error compensation showed errors exceeding 100 mm under the same conditions. The sensor was also validated to predict depth at different depths, resulting in a 6.5 mm error. These results suggest that our proposed sensor can effectively measure water depth for compact underwater drones.

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Cylindrical-Shaped Waterflow Vector Sensor Using Multiple Absolute-Pressure Sensors and Polynomial-Regression Models

K Shimada, T Kishimoto, H Tanaka, H Takahashi

IEEE Sensors Journal （Institute of Electrical and Electronics Engineers (IEEE)）  24 （ 23 ） 38822 - 38834 2024年

ISSN  1530437X

　概要を見る

With the growing interest in leveraging sensor technology for sustainable and efficient aquaculture, the measurement of ocean currents is considered a critical aspect of fish-cage environment monitoring. Conventional ocean-current sensors are typically large with high-energy consumption. Thus, they fall short of the specific demands for monitoring fish cages, which require the installation of multiple sensors in a small area. In this study, we developed a compact waterflow-vector sensor equipped with six absolute-pressure sensor elements. These elements measure the pressure on the surface of a cylinder-like housing. Through the application of fourth-degree polynomial regression, the pressure data are transformed into 2-D water-velocity and direction measurements. We fabricated a sensor based on a design informed by simulations and conducted circulating water-tunnel experiments using the fabricated sensor. Polynomial-regression models were constructed and validated from the experimental pressure output, and the models achieved an estimation accuracy of 0.21 m/s in velocity and 10° in direction within a 2.0 m/s range. Thus, our proposed sensor demonstrates the potential for monitoring sea currents in aquaculture.

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Airflow sensor using standing laser-induced graphene cantilevers

K Ohara, R Nakashima, H Takahashi

IEEE Sensors Journal 24 (7), 9585-9592 24 （ 7 ） 9585 - 9592 2024年

ISSN  1530437X

　概要を見る

Various animals in nature, particularly insects, possess sensory hairs that can detect minute fluid forces. Numerous airflow sensors, inspired by these insect sensory hairs, have been developed using silicon-based microelectro-mechanical systems (MEMS) technology. However, the intricate fabrication process and the challenge of integrating shape-controlled sensing elements on the same substrate have posed significant obstacles. On the other hand, laser-induced graphene (LIG) has emerged as a promising material for various physical sensors due to its high sensitivity as a piezoresistive material and its simplicity of production. Polyimide (PI), the most commonly used material for LIG formation, is thermoplastic, enabling the creation of 3-D shapes with ease. In this study, we propose a single-axis airflow sensor with upright LIG cantilevers. The process involves the use of an ultraviolet (UV) laser to cut a PI substrate into cantilever shapes and a CO2 laser to form LIG sensing elements. Subsequently, thermal deformation is employed to bend the cantilevers at right angles. The resulting sensor measures 25 × 25 mm at its base and stands at a height of 10.2 mm. Wind tunnel experiments validated the sensor s performance, showing a quadratic increase in response with wind velocity ranging from 2 to 12 m/s, consistent with theoretical expectations. Furthermore, the baseline shift observed with repeated wind application was significantly small. This approach holds great promise for the development of airflow sensors inspired by sensory hairs of insects.

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MEMS highly sensitive and large-area force plate for total ground reaction force measurement of running ant

H Takahashi, S Kohyama, T Takahata, I Shimoyama

Journal of Micromechanics and Microengineering 34 (4), 045006 34 （ 4 ）  2024年

ISSN  09601317

　概要を見る

Terrestrial insects exhibit agile manoeuvrability while running. However, the ground reaction force (GRF) in small insects remains poorly understood owing to its size and acting force. Here, we present a force plate for the measurement of total GRF during the running motion of ants with a force on the order of several tens of μN. The proposed force plate consists of a sufficiently large plate for several step cycles and four supporting cantilevers with highly sensitive piezoresistive elements. The plate and sensor chips were fabricated separately and combined during postprocessing. Two sizes of force plates were designed and fabricated for a large ant (Camponotus japonicas) and small ant (Messor aciculatus) with force resolution less than 1 μN. The developed force plates were calibrated by applying vertical forces at 32 points on the plate. Using the fabricated force plate, we measured the total GRF over several step cycles as the ant ran along the plate. Consequently, it was suggested that the ant ran with small vibrations in the direction of gravity.

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Triaxial Force Plate with High Speed and Resolution Line Scan Camera for Sampling Moiré Method

Y Nakahara, O Nomura, H Takahashi

2024 IEEE SENSORS, 1-4 2024年

ISSN  19300395

　概要を見る

This study reports on a force sensing method to enable high-time resolution triaxial measurement by analyzing line-scan camera images through a prism using the sampling moire method (SM). It is well-known that conventional SM accurately measures the in-plane displacement of grid pattern images. Recently, it was reported that by combining SM with a prism, a force sensor capable of triaxial measurement can be realized. However, in the case of area scan cameras, high-time resolution is usually a trade-off with the number of pixels, which determines accuracy. Here, we combined a line scan camera with a high frame rate of 26 kHz and a wide view in the horizontal direction with an inclined pattern to achieve high independence three axes measurement.

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Transparent glass force plate with CrN strain gauges featuring a notch structure

R Oda, Y Okamoto, R Nakashima, Y Takei, H Takahashi

Journal of Micromechanics and Microengineering 35 (1), 015005 2024年

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Three-Dimensional Shape Optimized Seesaw-Type Force Sensor Fabricated with a Micro-Scale 3D Printer

S Sato, Y Nakahara, G Kagawa, M Asai, H Takahashi

2024 IEEE SENSORS, 1-4 2024年

ISSN  19300395

　概要を見る

This paper proposes a force sensor that utilizes three-dimensional (3D) shape optimization and 3D printing technology. Introduction of micro-scale 3D printing technology have simplified the fabrication processes of microdevices with complex geometries. At the same time, there have also been advancements in the optimization of 3D structures to achieve desirable performances. This study combined these two technologies to develop a force sensor for measuring the force of a soft actuator. The force sensor combines a typical probe geometry with a laser displacement sensor. Due to the millimeter-order scale of the sensor, the low rigidity of the resin material causes undesired torsional deformation. Through 3D shape optimization, a beam design with more than 70 % torsional displacement reduction was achieved without changes in spring constant. Furthermore, a beam printed by a micro-scale 3D printer showed elasticity. The relationship between the input force and laser displacement sensor output showed linear characteristics, indicating its suitability as a force sensor.

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Stretchable Pulse Wave Sensor with a Laser-Induced Graphene-Formed Kirigami Structure

S Oya, T Kato, G Kagawa, R Nakashima, H Takahashi

2024 IEEE SENSORS, 1-4 2024年

ISSN  19300395

　概要を見る

This paper reports on a stretchable laserinduced graphene (LIG) pulse-wave sensor based on a kirigami structure. The proposed sensor is fabricated by embedding a stretchable sensor element using the kirigami structure into an elastic material. The polyimide-based sensor element is formed by UV and CO2 laser irradiation, and the stretchable LIG strain gauges detect skin vibrations caused by pulse waves with high sensitivity. The proposed sensor could be stretched by up to 7.5 mm, and the sensitivity increased 27 times in the stretched state. Furthermore, the fabricated sensor was able to measure the pulse waves. Therefore, the proposed sensor shows potential as a stretchable wearable sensor for measuring pulse waves with high sensitivity.

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Snap and Jump: How Elastic Shells Pop Out

T Abe, I Hashiguchi, Y Nakahara, S Kobayashi, R Tarumi, H Takahashi, ...

arXiv preprint arXiv:2410.08525 2024年

Sensitivity characteristics of a wave height sensor based on a MEMS piezoresistive cantilever and waterproof film

T Hirayama, H Takahashi

Japanese journal of applied physics 63 (2), 026505 63 （ 2 ）  2024年

ISSN  00214922

　概要を見る

This paper presents the frequency characteristics of a barometric pressure-sensing wave height sensor employing a MEMS piezoresistive cantilever and a micromesh waterproof film. The proposed sensor exhibited mechanical bandpass filter characteristics owing to air leakage around the cantilever and film. Consequently, high robustness can be achieved if the frequency is designed to match the wave range. We theoretically and experimentally verified that the frequency response is influenced by the film’s chamber volume and permeability constant. We demonstrated that the proposed frequency-response model helps design a waterproof wave height sensor using a cantilever-type differential pressure sensor.

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Sampling Moiré Method Force Plate Utilizing Smartphone Camera

O Nomura, A Ogawa, H Takahashi

IEEE Sensors Letters 8 （ 8 ）  2024年

　概要を見る

Ground reaction force (GRF) is a significant factor for evaluating foot biomechanics, and force plates (FPs) are commonly employed for assessment. Conventional FPs feature an integrated design of a supporting structure and sensor elements but face the challenges of high cost and limited customizability. Recently, high-resolution triaxial force measurements have been conducted using a prism and sampling moiré (SM) method within an optical experimental setup. Herein, we propose an FP that utilizes a commercial smartphone and the SM method. The proposed design simplifies the FP configuration, which comprises mechanical spring structures, a simple optical setup, smartphone, and smartwatch. We constructed a prototype FP of 200 mm × 400 mm capable of force resolution under 1 N. Camera images from the smartphone displayed two inclined grating images (GIs) via the prism, accurately reflecting vertical force applications. In the experiment, the developed FP measured the GRF in a manner similar to that of a commercial FP during human walking. The proposed method is practical for developing high-performance FPs.

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