Abstract
Abstract Highly sensitive, wide-measurement-range compact load sensors are desirable for various applications, including measurement of biosignals, manipulation and stiffness measurement of cells, and so on. Conventional load sensors are highly sensitive but have relatively small measurement ranges. A load sensor using an AT-cut quartz crystal resonator (QCR) has superior characteristics such as, high accuracy, improved strength under compressive stress, long-term stability, and compact size. However, a retention mechanism is required to firmly support the QCR because the QCR is easily broken by stretching and bending motions. Conventional machining processes are not suitable for further miniaturization of the sensor. Even if the retention mechanism were miniaturized, the assembly process is complicated. In this paper, we propose a novel design and fabrication method for a load sensor using the QCR. Using microfabrication and bonding, the assembly process was simplified. We demonstrate the feasibility of a miniaturized QCR load sensor whose volume is 24.6 mm3 (width is 4 mm, height is 5.6 mm, depth is 1.1 mm). The experimental results showed that the nonlinearity and hysteresis were 0.94% F.S. and 1.68% F.S., respectively. Additionally, sensitivity of the sensor was 1458 Hz/N. We improved the sensitivity and stability of the sensor; the fluctuation was 0.04 mN over a period of 1 min. Moreover, the effects of the temperature change were evaluated. The temperature and the sensor output were linear within the range of 20°C–50°C.
Highlights
Sensitive, wide-measurement-range, compact load sensors are desirable in many fields, such as the medical field and biological fields
To realize a high-performance load sensor with both high sensitivity and a wide measurement range, we focused on the quartz crystal resonator (QCR)
We aim to improve the QCR load sensor with regard to miniaturization and sensitivity to increase its number of effective applications
Summary
Wide-measurement-range, compact load sensors are desirable in many fields, such as the medical field and biological fields. Load sensors have employed different methods, such as the use of strain gauges [1,2], piezoelectric vibration [3,4], and capacitance changes [5]. To realize a high-performance load sensor with both high sensitivity and a wide measurement range, we focused on the quartz crystal resonator (QCR). The resonant frequency of a QCR changes with high linearity depending on the external force [6,7]. Quartz crystals have high strength under compressive stresses [8]. A high-resolution and wide-measurement-range load sensor can be realized using the QCR
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