Load sensor using quartz crystal resonator for detection of biological signals

Abstract

High sensitive, wide-measurement range, and small sized load sensors was developed by using AT-cut quartz crystal resonator (QCR). The quartz crystal generates a charge which is proportional to the external force. Since it has high sensitivity and excellent temperature stability, it has been used for various sensors. Especially, QCR has superior characteristic for static load sensing in nature. However, QCR is fragile and easily broken by the stress concentration. Moreover, a retention mechanism is required to transmit the load efficiently, and we have to fix the QCR firmly while avoiding horizontal force. Miniaturization of the retention mechanism is quite difficult to develop, since fabrication and assembly process is complicated. We have proposed miniaturized sensor element by using microfabrication. The QCR load sensor had enormously wide range of force sensing over 104 N. The objective of this study is to improve the resolution of load measurement and stabilization of sensor output for detection of biological signals. We fabricated QCR sensor whose sensitivity is 896 Hz/N. We succeeded in detection of biological signals (breath, heartbeat) by using proposed QCR load sensor.