Yuichi Murozaki

Wide Range Load Sensor Using Quartz Crystal Resonator for Detection of Biological Signals

High-sensitive, wide-measurement range, and small-sized load sensor was developed 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. In particular, 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 off axis force. Miniaturization of the retention mechanism is quite difficult to develop, since fabrication and assembly process is complicated. We have proposed a miniaturized sensor element using microfabrication. The QCR load sensor had enormously wide range of force sensing over 104. However, output of previous sensor changes easily by parasitic capacitance change around QCR. The objective of this paper is to improve the resolution of load measurement and stability of sensor output for detection of biological signals. We fabricated QCR sensor whose sensitivity is 973 Hz/N. We succeeded in detection of multiple biological signals (breath, heartbeat, and posture) using proposed QCR load sensor with high stability.

Microfabrication of wide-measurement-range load sensor using quartz crystal resonator

We successfully established a wafer level fabrication process of the quartz crystal resonator (QCR) load sensor using atomic diffusion bonding. The proposed sensor has three-layer structures; two Si-hold layers and a quartz layer. Using microfabrication and atomic diffusion bonding, the assembly process was simplified. The fabrication process enables further miniaturization of the QCR sensor due to the simplified assembling method. The fabricated sensor is easily integrated in the outer package and can be designed the measurement range. Finally, we succeeded in multi-biosignals (heartbeat, body motion) detection using fabricated QCR sensor and the outer case.

Wide-range load sensor using quartz crystal resonator for biological signal detection

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 104 N. 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.

Improvement of the Measurement Range and Temperature Characteristics of a Load Sensor Using a Quartz Crystal Resonator with All Crystal Layer Components

Monitoring multiple biosignals, such as heart rate, respiration cycle, and weight transitions, contributes to the health management of individuals. Specifically, it is possible to measure multiple biosignals using load information obtained through contact with the environment, such as a chair and bed, in daily use. A wide-range load sensor is essential since load information contains multiple biosignals with various load ranges. In this study, a load sensor is presented by using a quartz crystal resonator (QCR) with a wide measurement range of 1.5 × 106 (0.4 mN to 600 N), and its temperature characteristic of load is improved to −7 Hz/°C (−18 mN/°C). In order to improve the measurement range of the load, a design method of this sensor is proposed by restraining the buckling of QCR and by using a thinner QCR. The proposed sensor allows a higher allowable load with high sensitivity. The load sensor mainly consists of three layers, namely a QCR layer and two holding layers. As opposed to the conventional holding layer composed of silicon, quartz crystal is utilized for the holding layers to improve the temperature characteristic of the load sensor. In the study, multiple biosignals, such as weight and pulse, are detected by using a fabricated sensor.

Detection of multi-biosignal using a quartz crystal resonator based wide range load sensor with compact frequency counter

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 105 order, 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.

Cellular force measurement by load sensor using quartz crystal resonator

We present a force sensor with high-sensitivity and high-rigidity using quartz crystal resonator (QCR) for cellular force measurement. We integrated miniaturized QCR load sensor into cantilever utilizing the principal of leverage for improvement of sensing sensitivity. We show the measurement results of the cellular force using constructed sensing system.

Miniaturization of wide-range QCR load sensor for biosignal sensing

It is highly required to long-term monitoring of the biosignals under unbouded and non-invasive condition for health and safe management. Thus, we present biosingnal sensing by the miniaturized load sensing system using a quartz crystal resonator (QCR). We show a method of miniaturization of the sensing system and also measurement results of the biosignal sensing in a chair.

Protection of wide-range QCR load sensor using robust outer case for stable detection of biosignals

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 × 10-5 to 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.

Robust packaging of QCR load sensor for biosignal detection

We present a super wide-measurement range load sensor with high-durability for multi-biosignal sensing in daily life. We employ quartz crystal resonator (QCR) load sensor with super wide range (from 6 × 10-5 to 30 [N]) for sensing of biosignal ranges from mN order (e.g. heartbeat) to 100 N order (e.g. body motion). Furthermore, we implement an outer case to make the sensor durable against unexpected loads in practical use. The outer case increase 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.

Load sensor using quartz crystal resonator for detection of biological signals

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.