声表面横波压力传感器的电极质量负载效应分析方法

An analytical method of electrodes mass load effect for surface transverse wave pressure sensor

针对声表面横波（Surface Transverse Wave,STW）压力传感器,提出了一种考虑叉指电极质量负载的有限元和微扰理论结合分析方法。首先构建包含叉指电极的有限元模型,通过计算电极表面的面电荷得到器件的等效输入导纳,由导纳谐振点处提取STW传播声场,然后根据微扰理论,由STW传播声场以及压力引起的传感器结构的应力应变,得到包含电极质量负载影响的STW传感器的灵敏度。以一种基于ST-90°X石英材料的点压式STW压力传感器为例进行了理论计算,电极厚度为0.17 μm和0.21 μm时,计算灵敏度分别为-54.9 kHz/bar和-21.7 kHz/bar,说明电极质量负载对于传感器有较大影响。制作电极厚度为0.17 μm的传感器进行测试,得到-57 kHz/bar的压力灵敏度,实验结果和理论结果吻合,证明计算方法的有效性。

A method combining perturbation theory and finite element method （FEM） with mass load effect considered, is proposed to analyze surface transverse wave （STW） pressure sensor. The proposed method firstly build a FEM model including the inter-digital transducers （IDT） structure, in which the admittance of IDT is calculated by the current on the electrodes at different frequencies. From the resonation point of calculated admittance the STW acoustics field can be obtained. Then with the stress and strain induced by pressure, and the STW acoustics field, the sensitivity of STW sensors is calculated by tile perturbation theory, which would take into account the mass load effect of IDT. An example of STW pressure sensors based on ST-90°X Quartz with pressure forced on one point is analyzed. The theoretical sensitivity with IDT＇s thickness of 0.17 gm and 0.21 μm is -54.9 kHz/bar and -21.7 kHz/bar respectively, which indicates that the mass load of IDT has great influence on the pressure sensitivity. Sensor with IDT＇thickness of 0.17 μm is manufactured and tested, the experimental sensitivity is -57 kHz/bar. The theory coincides with experiment, which demonstrates the validity of the proposed method.