Characteristics Of SAW Resonator Under Force Loaded On Substrate Surface

Surface acoustic wave (SAW) propagates on piezoelectric substrate surface,when the surrounding physical parameters (such as temperature, pressure, magnetic field, electric field, gas, etc.) change the physical characteristics of piezoelectric substrate and consequently the SAW propagation characteristics (such as velocity and loss) will be changed. In order to study the characteristics of SAW resonator under force loaded on the substrate surface, the theoretical analysis and experimental studies are conducted.This paper mainly includes the following aspects:①This paper first introduces the development of SAW technology, the classification and characteristics of SAW devices. Then it elaborates the development, classification, and characteristics of SAW sensors. Finally the physical configuration and sensing mechanism of one-port SAW resonator are analyzed.②Starting from the constitutive equation and motion equation of piezoelectric crystal, the SAW velocity is calculated by traditional Green function in free state, based on the piezoelectric coupling wave equation of the piezoelectric medium in free state. When force is exerted on the surface of the piezoelectric substrate, the elastic, piezoelectric and dielectric constants of the piezoelectric substrate will change, so the effective material coefficients are a function of the force. The piezoelectric coupling wave equation with force loaded on the substrate surface is deduced. Based on the general Green's function and the piezoelectric coupling wave equation with mechanical loading, SAW velocity with mechanical loading is deduced. With the formula of resonant frequencies, the variation relationship between the exerted force and resonant frequency of SAW resonator is obtained.③Through a force transfer mechanism, mass blocks are applied on the substrate surface, and generate forces along the directions either perpendicular to or parallel to SAW propagation direction. The resonant frequencies and losses of SAW resonators are measured by a network analyzer. When the back surface of the substrate is fixed, the experimental results show that there is a linear relationship between the force and resonant frequencies in SAW resonators, but there is no apparent relationship between force distribution and the resonant frequencies of SAW resonators. This is consistent with the numerical calculation results. By comparing the variation of Q values, it shows that the losses of SAW resonators are related to the force distribution.