Thickness shear mode quartz crystal resonators with optimized elliptical electrodes
Ma Ting-Feng(马廷锋)a), Zhang Chao(张超)b)† , Jiang Xiao-Ning(江小宁)c), and Feng Guan-Ping(冯冠平)a)b)
a Department of Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, China; b Center for Information and Optomechatronics, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China; c Department of Mechanical & Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910, USA
Abstract Quartz crystal resonators (QCRs) with circular electrodes have been widely used for various liquid and gas sensing applications. In this work, quartz crystal resonators with elliptical electrodes were studied and tested for liquid property measurement. Mindlin's theory was used to optimize the dimension and geometry of the electrodes and a 5-MHz QCR with minimum series resistance and without any spurious modes was obtained. A series of AT-cut QCRs with elliptical electrodes of different sizes were fabricated and their sensing performances were compared to devices with circular electrodes. The experimental result shows that the device with elliptical electrodes can obtain lower resonance impedance and a higher Q factor, which results in a better loading capability. Even though the sensitivities of devices with elliptical and circular electrodes are found to be similar, the sensor with elliptical electrodes has much higher resolution due to a better frequency stability. The study indicates that the performance of QCRs with elliptical electrodes is superior to that of traditional QCRs with circular electrodes.
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