声表面波与声板波激发特性对比研究

通过沉积在压电基片表面的叉指换能器可在基片上激发出声波。以部分波理论为基础，引入表面有效介电常数方法来对比研究压电基片上激发的声表面波和声板波，并通过实验证明了理论分析方法的有效性。特定切向和传播方向的压电晶体只能激发出一种声表面波模式，而其声板波则具有多种模式，且各高阶模式只有当基片厚度与声波波长之比大于某一特定值时才会出现。随着基片厚度增大，声板波各高阶模式的传播速度和机电耦合系数减小，两种低阶模式的传播速度则趋近于声表面波相应值。受基片背面的电学边界条件影响，其中一种低阶模式的机电耦合系数随着基片厚度增大而趋近于声表面波相应值，另一种低阶模式的机电耦合系数则接近于零。根据上述研究结果可以确定叉指电极激发声表面波或声板波的条件及两种声波之间的关系。


Comparative Study on Excitation Characteristics of Surface Acoustic Wave and Acoustic Plate Mode Wave

On the basis of the partial wave theory, the surface effective permittivity method was introduced to analyze the excitation characteristics of surface acoustic wave (SAW) and acoustic plate mode wave (APM), and the experiments verified the effectivity of the theoretical study. The results show that only one SAW mode can be excited on the piezoelectric substrate under certain cut orientation and propagation direction, while the APMs have multiple modes. Furthermore, the high-level modes can be excited only when the ratio of the substrate thickness to the acoustic wavelength is bigger than a certain value. With the increase of the substrate thickness, the propagation velocities (v) and electro-mechanical coupling coefficients (k²_s) of the APM high-level modes both decrease. Both propagation velocities of the two APM low-level modes approximate to that of SAW when the substrate thickness increases. As to the electro-mechanical coupling coefficients, one is close to that of SAW, but the other approximates to zero. Additionally, the electrical boundary conditions of the substrate’s back side will influence the APM low-level modes’ tendency to SAW. From these studies we get a conclusion about how to excite SAW or APM by IDT and the corresponding relationship of the two acoustic waves.