Papers - Takahashi, Hidetoshi

Open planar acoustic notch filter using a film-integrated Helmholtz resonator array

F Mizukoshi, H Takahashi

Japanese Journal of Applied Physics 62 (3), 034002 (Japanese Journal of Applied Physics)  62 ( 3 )  2023.03

ISSN  0021-4922

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Acoustic filters are used to transmit or attenuate noise in a specific frequency band. However, previous acoustic filters consisting of rigid structures generally required a large housing of a size equivalent to the wavelength, limiting their downsizing. This study presents an open planar acoustic notch filter using a film-integrated Helmholtz resonator (HR) array. A film divides the HR chamber and resonates with the HR. The film-integrated HR array filter achieved smaller housing dimensions than a no-film HR array filter with the same notch frequency. The transmittance of the film-integrated HR array was theoretically calculated using the transfer matrix method. The calculated spectra were very similar to the simulation results. The notch frequency of the film-integrated HR array filter was 4.04, 0.74 kHz lower than a no-film HR array filter. The design and analysis of the acoustic filter presented should motivate further development of advanced acoustic filters.

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Sensitivity characteristics of a waterproof airflow sensor based on a MEMS piezoresistive cantilever and nanohole array

T Hirayama, Y Kazoe, H Takahashi

Japanese Journal of Applied Physics 62 (2), 026503 (Japanese Journal of Applied Physics)  62 ( 2 )  2023.02

ISSN  0021-4922

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This paper presents the sensitivity characteristics of a microelectromechanical systems (MEMS) piezoresistive cantilever and nanohole array used in a waterproof airflow sensor. Previously, a Pitot tube-type waterproof airflow sensor was developed for seabird biologging. Built-in MEMS piezoresistive cantilevers are used as the differential pressure sensing elements. The waterproof function is achieved using nanohole arrays via Laplace pressure. However, the mechanism underlying sensitivity reduction when nanohole arrays are attached is unclear. Here, we experimentally and theoretically verified that the specific constant, which determines the airflow rate through the cantilever and nanohole array, affects sensitivity reduction. An airflow sensor with a small sensitivity reduction was achieved based on the calculated results using appropriate cantilever and nanohole arrays. We demonstrated that the proposed method for estimating sensitivity reduction is useful for designing waterproof airflow sensors using cantilever-type differential pressure sensor elements.

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Spiral Spring-Supported Force Plate with an External Eddy Current Displacement Sensor

Y Kawasaki, H Takahashi

Actuators 12 (1), 16 (Actuators)  12 ( 1 )  2023.01

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This study proposes a force plate with a planar spring and an eddy current displacement sensor to measure the ground reaction force (GRF) of a small insect and reveal its motion characteristics. The proposed force plate comprises a circular aluminum plate, four aluminum springs symmetrically connected to the plate, and an eddy current displacement sensor under the plate. The diameter and thickness of the fabricated plate were 8 and 0.1 mm, respectively. The spring width was 0.4 mm. When a force is applied to the plate, the plate moves vertically downward. Then, an eddy current displacement sensor detects the plate displacement without contact. The applied force can be measured using Hooke’s law. The proposed force plate has the advantages of ease of fabrication and cost-effectiveness. The central displacement variation and resonant frequency of the designed springs were evaluated by simulation. Then, we calibrated the fabricated force plate to obtain the sensitivity variation and resonant frequency. The experimental results suggest that the proposed force plate can effectively measure the GRF of a small insect.

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Highly Sensitive Low-Frequency-Detectable Acoustic Sensor Using a Piezoresistive Cantilever for Health Monitoring Applications

Y Okamoto, TV Nguyen, H Takahashi, Y Takei, H Okada, M Ichiki

Scientific reports 13 (1), 6503 (Scientific Reports)  13 ( 1 )  2023

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This study investigates a cantilever-based pressure sensor that can achieve a resolution of approximately 0.2 mPa, over the frequency range of 0.1–250 Hz. A piezoresistive cantilever with ultra-high acoustic compliance is used as the sensing element in the proposed pressure sensor. We achieved a cantilever with a sensitivity of approximately 40 times higher than that of the previous cantilever device by realizing an ultrathin (340 nm thick) structure with large pads and narrow hinges. Based on the measurement results, the proposed pressure sensor can measure acoustic signals with frequencies as low as 0.1 Hz. The proposed pressure sensor can be used to measure low-frequency pressure and sound, which is crucial for various applications, including photoacoustic-based gas/chemical sensing and monitoring of physiological parameters and natural disasters. We demonstrate the measurement of heart sounds with a high SNR of 58 dB. We believe the proposed microphone will be used in various applications, such as wearable health monitoring, monitoring of natural disasters, and realization of high-resolution photoacoustic-based gas sensors. We successfully measured the first (S1) and second (S2) cardiac sounds with frequencies of 7–100 Hz and 20–45 Hz, respectively.

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Thin Glass Micro Force Plate Supported by Planar Spiral Springs for Measuring Minute Forces

T Kiriyama, K Shimazaki, R Nakashima, H Takahashi

Micromachines 14 (5), 1056 (Micromachines)  14 ( 5 )  2023

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Microforce plates are indispensable tools for quantitatively evaluating the behavior of small objects such as tiny insects or microdroplets. The two main measurement principles for microforce plates are: the formation of strain gauges on the beam that supports the plate and the measurement of the deformation of the plate using an external displacement meter. The latter method is characterized by its ease of fabrication and durability as strain concentration is not required. To enhance the sensitivity of the latter type of force plates with a planar structure, thinner plates are generally desired. However, brittle material force plates that are both thin and large and can be fabricated easily have not yet been developed. In this study, a force plate consisting of a thin glass plate with a planar spiral spring structure and a laser displacement meter placed under the plate center is proposed. The plate deforms downward when a force is exerted vertically on its surface, resulting in the determination of the applied force using Hooke’s law. The force plate structure is easily fabricated by laser processing combined with the microelectromechanical system (MEMS) process. The fabricated force plate has a radius and thickness of 10 mm and 25 µm, respectively, with four supporting spiral beams of sub-millimeter width. A fabricated force plate featuring a sub-N/m spring constant achieves a resolution of approximately 0.01 µN.

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Neural network-based airflow vector sensor using multiple MEMS differential pressure sensors

K Haneda, K Matsudaira, H Takahashi

IEEE Access 11   40978 - 40987 2023

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As airflow information is significant in various fields, several airflow measurement devices have been developed. Differential pressure (DP)-type sensors, including pitot tubes, are extensively used because they can directly measure dynamic pressure due to airflow. However, this method has a disadvantage in that it is difficult to measure some wind directions because of the non-monotonic pressure distribution around the device. This study proposes a compact sphere airflow vector sensor using a neural network model that compensates for nonmonotonicity. It consists of three built-in microelectromechanical system (MEMS)-based DP sensor elements that simultaneously measure the DPs around the spherical sensor housing. The measured DPs are converted into 2D wind speed and direction using a neural network. The network model was trained using the simulated output of each sensor, and it was confirmed that the proposed design guideline contributed to achieving high accuracy. An airflow sensor was fabricated on the basis of the designed model. A network model was trained using the sensor responses in a wind tunnel experiment. The wind speed and direction accuracies obtained by the neural network model for 2-10 m/s and 0°-359° were 0.24 m/s and 3.62°, respectively. Finally, we demonstrated a drone flight test by attaching the calibrated sensor to a toy drone. This study is expected to contribute to realizing highly accurate low airflow measurement devices.

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Multi-Mems Differential Pressure Sensor Elements-Based Airflow Sensor with Neural Network Model

K Haneda, K Matsudaira, H Takahashi

2023 IEEE 36th International Conference on Micro Electro Mechanical Systems … (Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS))  2023-January   499 - 502 2023

ISSN  1084-6999

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This paper reports a compact spherical airflow sensor using multi-MEMS differential pressure (DP) sensor elements. Three built-in MEMS sensors simultaneously measure the DP around the spherical housing structure so that the measured DPs are converted into 2D wind direction and speed. The sensor outputs are converted into wind direction and speed by neural network. We attached the calibrated sensor to a toy drone as a demonstration. Then, it was confirmed that the output corresponding to wind direction and speed was measured when a crosswind was applied during flight.

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Liquid-Immersion Inclined-Rotated UV Lithography for Micro Suction Cup Array

G Kagawa, H Takahashi

2023 IEEE 36th International Conference on Micro Electro Mechanical Systems … (Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS))  2023-January   610 - 612 2023

ISSN  1084-6999

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This paper reports liquid-immersion inclined/rotated UV lithography for fabricating micro suction cups. Microstructures such as micro suction cups have been applied in various applications. However, the conventional fabrication method had limitations in suction force due to the insufficient inclination angle. We proposed liquid-immersion to inclined/rotated exposure (IRE), enabling greater microstructure inclination angles. IRE equipment was developed to fabricate PDMS micro suction cup arrays. The experimental inclination angle reached 51°, nearly doubling the conventional IRE method.

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Lig-Based Triaxial Tactile Sensor Utilizing Rotational Erection System

R Nakashima, N Nakamura, TG Sano, E Iwase, H Takahashi

2023 IEEE 36th International Conference on Micro Electro Mechanical Systems … (Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS))  2023-January   221 - 224 2023

ISSN  1084-6999

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This paper reports a laser-induced graphene (LIG)based triaxial tactile sensor utilizing rotational erection system (RES). The proposed process realizes a sensing element with a piezoresistive layer by irradiating a polyimide (PI) film with two types of lasers only once each. Furthermore, the sensing element formed with origami/kirigami method maintains a three-dimensional structure by applying a single external force. The prototype triaxial tactile sensor fabricated by the proposed fabrication process responded independently to normal and shear forces.

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Highly Sensitive Wave Height Sensor with MEMS Piezoresistive Cantilever and Waterproof Membrane

T Hirayama, H Takahashi

2023 IEEE 36th International Conference on Micro Electro Mechanical Systems …    760 - 762 2023

ISSN  1084-6999

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Triaxial tactile sensor using RES structure and standing LIG cantilevers

R NAKASHIMA, T SANO, N NAKAMURA, E IWASE, H TAKAHASHI

センサ・マイクロマシンと応用システムシンポジウム (CD-ROM) 40, 3-4  2023

Triaxial piezoresistive force sensor probe with high sensitivity and stiffness using 3D notch structure

H Takahashi, Y Takei, K Noda, K Matsumoto, I Shimoyama

Journal of Micromechanics and Microengineering 33 (12), 125005 (Journal of Micromechanics and Microengineering)  33 ( 12 )  2023

ISSN  09601317

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This paper proposes a microelectromechanical system triaxial piezoresistive force sensor probe with high sensitivity and stiffness. The sensor probe is composed of a cantilever and four supporting beams. Two of the four beams had horizontal notch parts at the root, and sidewall-doped piezoresistors were utilised to detect the in-plane deformation. There was a vertical notch at the root of the remaining two beams and a surface-doping piezoresistor in one beam to detect the out-of-plane deformation. Thus, the proposed sensor probe measures the three directional forces applied to the cantilever tip with high sensitivity and stiffness owing to the corresponding piezoresistive notch structures. We demonstrate a fabrication process that forms the notch structure and the surface and sidewall doping methods. Our fabricated device was confirmed capable of measuring triaxial forces with a force resolution at the sub-micro-Newton level.

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Single step fabrication of a triaxial force plate using 3D printer

Y NAKAHARA, H TAKAHASHI

センサ・マイクロマシンと応用システムシンポジウム (CD-ROM) 40, 5-31  2023

Simple hearing test utilizing a soundproofing headphone with acoustic filters

F Mizukoshi, N Oishi, H Takahashi

Biomedical Engineering Advances 6, 100102  2023

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Airflow Sensor Using MEMS Differential Pressure Sensors and Neural Network

KENEI MATSUDAIRA, K HANEDA, T KISHIMOTO, H TAKAHASHI

センサ・マイクロマシンと応用システムシンポジウム (CD-ROM) 40, 5-30  2023

MEMS 6-axis force sensor chip for spike pins in athletic sports shoes

H Takahashi, H Ishido, A Nakai, T Takahata, K Matsumoto, I Shimoyama

Sensors and Actuators A: Physical 363, 114702 363 2023

ISSN  09244247

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This study reports a microelectromechanical system (MEMS) sensor for evaluating the force acting on the spike pins of athletic sports shoes. The ground reaction force (GRF) of the human sole is a crucial factor in understanding running mechanics. In short-distance sprints, running is achieved by biting the ground using shoe spikes. However, it is difficult to evaluate the forces acting on such spike pins because of their small size. In this study, a MEMS sensor chip that could measure the 6-axis forces was embedded in an actual spike-pin-shaped structure, and the fabricated spike pin was attached to athletic shoes. By utilizing four pairs of surface- and sidewall-doped beams as sensing elements, the 6-axis force acting on the pin can be measured regardless of the force distribution when the pin bites into the track. We demonstrated that the force distribution could be measured using three sensors developed during running. The vertical force on each pin exceeded 100 N. Furthermore, it was observed that higher propulsive forces were exerted on all the spike pins in the first step compared to the second step or later steps. Therefore, the proposed method can be used to evaluate running mechanics using spike pins in athletic sports shoes.

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Two-dimensional waterflow sensor using multiple absolute pressure sensors

K Shimada, T Kishimoto, H Tanaka, H Takahashi

2023 IEEE SENSORS, 1-4  2023

ISSN  19300395

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This study reports a two-dimensional (2D) waterflow sensor for marine aquaculture. In recent years, environmental monitoring has been widely developed in marine aquaculture. Among these monitoring, ocean currents are one of the important factors in capturing the inflow of hypoxic water into fish cages. However, there were no low-power, simple waterflow sensors that could be adapted to fish cages. Here we propose a waterflow sensor using with a cylindrical housing and an array of six absolute pressure sensor elements to measure 2D waterflow velocity around a fish cage. 2D waterflow velocity is calculated via a polynomial regression model of the responses of six pressure sensors and sensor tilt angle. By constructing the model for each tilt angle, the developed sensor responded with sufficient sensitivity to waterflow velocities from 0.4 to 2.0 m/s.

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Pressure sensor with a corrugated structure utilizing LIG sensing element

R Oda, R Nakashima, H Takahashi

2023 22nd International Conference on Solid-State Sensors, Actuators and …    1601 - 1603 2023

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This paper reports on a pressure sensor with a corrugated structure utilizing a laser-induced graphene (LIG) strain gauge. A concentrically expanding corrugated structure is formed on a polyimide (PI) film by a UV laser. A LIG layer, which function as a piezoresistor, is directly formed by a CO2 laser to the outermost circumference of the corrugated structure. Using two different-types laser processing, a highly sensitive pressure sensor is easily realized. Here we theoretically and experimentally show the proposed method usefulness by evaluating the sensor response.

Pitot-Type Waterflow Sensor Logger for Relative Waterflow Velocity Measurement of a Sea Turtle

T Kishimoto, R Saito, H Tanaka, M Naruoka, K Kuroda, K Sato, ...

2023 22nd International Conference on Solid-State Sensors, Actuators and …    698 - 701 2023

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This study presents a waterflow sensor logger for sea turtles. Many sensors have been attached to wild animals via the biologging method for animal ecological analysis. However, it is not easy to measure the relative waterflow velocity of marine animals with a conventional sensor due to marine debris and algae. Furthermore, there are limited examples of measurements for sea turtles. Here, we proposed a Pitot-type waterflow sensor logger. The sensor logger achieves both resistance to algae and marine debris and pressure resistance because of the Pitot-type waterflow sensor structure. Attaching the sensor logger to a sea turtle's carapace will make long-term velocity measurement possible. The fabricated sensor logger responded stably to waterflow and measured actual sea turtle's swimming as waterflow velocity.

Pitot Tube Type Compact Waterproof Airflow Sensor for Seabird Biologging

T Hirayama, T Kishimoto, H Takahashi

2023 IEEE SENSORS, 1-4  2023

ISSN  19300395

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In this study, a waterproof airflow sensor is proposed for seabird biologging. Biologging, in which a sensor is directly attached to an animal to record its behavior, has attracted much attention to assess the animal's locomotion performance. Among them, it has been focused to evaluate the flight performance of seabirds. An airflow sensor becomes a powerful tool to measure the self-induced flight velocity of a seabird, however, the sensor is also required to have water pressure resistance. Here we propose a Pitot tube type compact waterproof airflow sensor with micromesh filters for seabird biologging. The Pitot tube structure with built-in the differential pressure sensor element realized a compact and robust sensor performance. The micro-mesh filter was attached to the air inlets to achieve high water pressure resistance. The developed sensor responded with high sensitivity to pressures up to 100 Pa and airflow up to 10 m/s without any loss of sensitivity caused by the filter.

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