Nabeshima Taiga, Nguyen Thanh-Vinh, Takahashi Hidetoshi
Department of Mechanical Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kouhoku-ku, Yokohama 223-8522, Kanagawa, Japan.
Sensing System Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba 305-8564, Ibaraki, Japan.
Micromachines (Basel). 2022 Apr 19;13(5):645. doi: 10.3390/mi13050645.
Wearable sensor devices with minimal discomfort to the wearer have been widely developed to realize continuous measurements of vital signs (body temperature, blood pressure, respiration rate, and pulse wave) in many applications across various fields, such as healthcare and sports. Among them, microelectromechanical systems (MEMS)-based differential pressure sensors have garnered attention as a tool for measuring pulse waves with weak skin tightening. Using a MEMS-based piezoresistive cantilever with an air chamber as the pressure change sensor enables highly sensitive pulse-wave measurements to be achieved. Furthermore, the initial static pressure when attaching the sensor to the skin is physically excluded because of air leakage around the cantilever, which serves as a high-pass filter. However, if the frequency characteristics of this mechanical high-pass filter are not appropriately designed, then the essential information of the pulse-wave measurement may not be reflected. In this study, the frequency characteristics of a sensor structure is derived theoretically based on the air leakage rate and chamber size. Subsequently, a pulse wave sensor with a MEMS piezoresistive cantilever element, two air chambers, and a skin-contacted membrane is designed and fabricated. The developed sensor is 30 mm in diameter and 8 mm in thickness and realizes high-pass filter characteristics of 0.7 Hz. Finally, pulse wave measurement at the neck of a participant is demonstrated using the developed sensor. It is confirmed that the measured pulse wave contains signals in the designed frequency band.
为实现对生命体征（体温、血压、呼吸频率和脉搏波）的连续测量，穿戴时对佩戴者造成最小不适的可穿戴传感器设备已在医疗保健和体育等各个领域的众多应用中得到广泛开发。其中，基于微机电系统（MEMS）的差压传感器作为一种用于测量伴有轻微皮肤收紧的脉搏波的工具而受到关注。使用带有气室的基于MEMS的压阻悬臂作为压力变化传感器能够实现高灵敏度的脉搏波测量。此外，由于悬臂周围的空气泄漏，传感器附着到皮肤上时的初始静压在物理上被排除，这起到了高通滤波器的作用。然而，如果这种机械高通滤波器的频率特性设计不当，那么脉搏波测量的基本信息可能无法得到反映。在本研究中，基于空气泄漏率和腔室尺寸从理论上推导了传感器结构的频率特性。随后，设计并制造了一种带有MEMS压阻悬臂元件、两个气室和一个与皮肤接触的膜片的脉搏波传感器。所开发的传感器直径为30毫米，厚度为8毫米，并实现了0.7赫兹的高通滤波器特性。最后，使用所开发的传感器展示了对一名参与者颈部脉搏波的测量。证实所测量的脉搏波包含设计频带内的信号。
