Wide-range Load Sensor Using Vacuum Sealed Quartz Crystal Resonator for Simultaneous Biosignals Measurement on Bed

Monitoring of biosignals on a daily basis plays important roles for the health management of elderly. The monitoring system for the daily life, the system should not require the subjects to take special effort like wearing a sensor. We propose biosignals measurement using wide-range load sensor on the bed. The sensing system can detect the body weight, heartbeat and respiration simultaneously by just lying on the bed. We have developed load sensor using quartz crystal resonator (QCR load sensor) as wide-range load sensor. However, the measurement range was not sufficient for the simultaneous measurement of biosgnals on bed. To realize such sensing system, we propose a QCR load sensor utilizing vacuum sealing technology for expanding the measurement range. We improved the oscillation characteristics of the QCR by the vacuum sealing to stabilize the sensor output. Accordingly, the resolution of the sensor was improved. Moreover, the load capacity of the sensor was increased by improving the bonding strength of sensor structure. The fabricated sensor had a measurement range of 0.27 mN - 1180 N (4.4 × 106). This wide enough compared with the conventional force sensor (103 - 104).Also, we developed mechanically robust jig of QCR load sensor for practical use of QCR load sensor. We succeed in simultaneous measurement of weight, heart rate, and respiration rate using fabricated QCR load sensing system. The accuracy of heart rate and respiration rate measurement are 0.4 bpm (0.6 %) and 1.1 brpm (6.1 %), respectively, in standard deviation of error compared with ECG signal.