A surface acoustic wave sensor terminal based on one-port resonator for contact stress measurement in slits

In a cramped slit with less than 0.5mm in width, the contact stress measurements in passive and wireless way face great challenges. In this paper, a sensing method based on surface acoustic wave (SAW) sensing principles is proposed to realize the goal. Specifically, a sensor terminal based on surface acoustic wave resonator (SAWR) is designed as a crucial part of the sensing system. The resonance frequency of SAWR is determined to be 1GHz and the size of SAWR is limited to 4×4×0.3mm. Then the SAW resonator is manufactured with photolithography technique. Moreover, a diaphragm structure is made up by covering a layer of support film with holes and the overall thickness of device is limited under 400 μm. Before the test, every single chip is examined under scanning electron microscope (SEM) to guarantee the integrality of electrodes. The bare chip is measured with vector network analyzer (VNA) and the resonator exhibited a good resonance at 990.03MHz and the quality factor Q is 15125. Furthermore, the loading test curve in 0-4MPa shows that the sensor has a good linearity with fitting related coefficient is 0.9966 and the frequency shift is 20.5kHz/MPa.