有限长叉指换能器激发表面波及体波声场的数值模拟

Numerical simulation of SAW and BAW modes in the surface excited by finite-length IDT

采用数值方法,模拟了有限长叉指换能器(IDT)在半无限大压电晶体中激发的表面波和体波声场在晶体界面上的分布情况。在数值模拟所得结果的基础上,将频率域内的位移分量做傅立叶反变换得到时间域内声波脉冲振幅随时间的分布,并对界面上三个位移分量含有的声波模式进行分析,其中场位移分量1沿波的传播方向,位移分量2为平行于IDT指条方向,位移分量3沿基片表面法线方向。分析结果表明,界面上各位移分量中除Rayleigh波外,还含有不同比例的体波成分。其中,在位移分量1和位移分量3中占主要成分的是准纵波,在位移分量2中占主要成分的是准慢切变波。它们均按照指数方式在表面上进行传播衰减,其中准慢切变波的衰减速度小于准纵波的衰减速度。IDT指条数相对较多时的体波振幅要大于指条数相对较小时的体波振幅,且在距离IDT较近的范围内IDT指条数相对较多时体波衰减更快。

Simulations of acoustic fields on the surface of semi-infinite piezoelectric crystal, excited by finite-length IDT including surface acoustic waves and bulk waves, are made using numerical tools. With inverse Fourier transform of displacement components in the frequency domain, the distribution of acoustic wave pulse amplitude over time can be obtained. By analyzing the acoustic wave modes in three displacement components on the surface, some information can be found. It should be explained that, the first displacement component follows the wave propagation direction, the second in parallel with the fingers of the IDT, and the third along the direction of the surface normal. The results show that there are different kinds and scales of bulk wave modes beside Rayleigh mode in three displacement components. Quasi-longitudinal wave is the main mode in the first and third displacement components. Meanwhile, quasi-slow shear wave occupies a large part in the second displacement component on the surface. Two kinds of bulk waves transmit and attenuate exponentially on the surface separately, but the quasi-slow shear wave is lower than quasi-longitudinal wave in attenuation speed. Amplitudes of the three bulk wave modes in the IDT with more fingers are greater than those in the IDT with fewer fingers, and have high attenuation speed near the IDT.