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.

Monitoring of biosignals plays important roles in health management in daily life. Especially, the sensing method of biosignals, which does not require special efforts such as restraining people or wearing the sensors to measure them, is really important to maintain monitoring activities of people. We call such method what a sensing way should be for monitoring of biosignals as casual sensing methods. Previously, we have developed highly sensitive and wide-measurement-range load sensors based on measuring frequency shift of quartz crystal resonator (QCR) as the sensing principal. We have integrated the load sensor into a chair, and measure the load when people just sit on it. Since the load sensor has wide measurement range of 105order, multi-biosignal; heartbeat, respiration, and body motion under the weight-loaded environment can be measured from load information. Thus, people can casually monitor the biosignals by sitting on the chair. However, the previous sensing system required us to measure the frequency shift of one-Hz order in tens-MHz of the resonant frequency of a QCR. In this case, the sensing system requires a expensive frequency counter, and it is not suitable for daily use situation such as in-home sensing. In this paper, we presents the detection of multi-biosignal method using a newly developed load sensing system which utilizes the developed frequency counter unit. In order to measure the frequency shift of one-Hz order in tens-MHz of the resonant frequency, we use a differential method of signal for two QCRs with an electrical signal-mixing circuit. By using the method, we can reduce the required measurement range for frequency from tens-MHz to tens-kHz. The load sensing performances were evaluated, and the results showed that the sensitivity and withstand load were 2.9 [mN] and 300 [N], respectively. Finally, we demonstrated the measurement of multi-biosignal by using constructed system, and succeeded in detecting respiration, heartbeat, and body motion.

We present a super wide-measurement range load sensor with high-durability for multi-biosignal sensing in daily life. We employed quartz crystal resonator (QCR) load sensor with super wide range (from 6 × 10-5to 30 [N]) for sensing of biosignals ranging from mN order (e.g. heartbeat) to 100 N order (e.g. body motion). Furthermore, we implemented an outer case which makes the sensor durable against unexpected loads in practical use. The outer case increased the durability of the sensor 88 times higher than the sensor without outer case. Finally we succeeded in simultaneous sensing of heartbeat (≈ 100 [mN]) and body motion (≈ 25 [N]) with identical sensor.

A load sensor with high sensitivity, a wide measurement range, and a small size was developed by using an AT-cut quartz crystal resonator (QCR). The quartz crystal generates a charge that is proportional to the external force. Because it has high sensitivity and excellent temperature stability, it has been used for various sensors. In particular, a QCR has an inherently superior static-load-sensing characteristic. However, a QCR is fragile and easily broken by a stress concentration. Moreover, a retention mechanism is required to efficiently transmit the load, and it is necessary to fix the QCR firmly to avoid a horizontal force. Moreover, it is very difficult to miniaturize the retention mechanism because the fabrication and assembly process is complicated. We previously proposed a miniaturized sensor element that was developed using microfabrication. The QCR load sensor had an enormously wide force-sensing range of greater than 104N. However, the output was easily affected by a change in the parasitic capacitance around the QCR. The objective of this study was to improve the load-measurement resolution and stabilize the sensor output for application to biological signal detection. We fabricated a QCR sensor with a sensitivity of 973 Hz/N and succeeded in detecting multiple biological signals (respiration, heartbeat, and posture) with using proposed QCR load sensor.