Mozhaev V G, Weihnacht M
Faculty of Physics, Moscow State University, Russian Federation.
Ultrasonics. 2000 Jul;37(10):687-91. doi: 10.1016/s0041-624x(00)00019-6.
The extraordinary case of increase in velocity of surface acoustic waves (SAW) caused by electrical shorting of the surface of the superstrong piezoelectric crystal potassium niobate, KNbO3, is numerically found. The explanation of this effect is based on considering SAWs as coupled Rayleigh and Bleustein-Gulyaev modes. A general procedure of approximate decoupling of the modes is suggested for piezoelectric crystals of arbitrary anisotropy. The effect under study takes place when the phase velocity of uncoupled sagittally polarized Rayleigh waves is intermediate between the phase velocities of uncoupled shear-horizontal Bleustein Gulyaev waves at the free and metallized surfaces. In this case, the metallization of the surface by an infinitely thin layer may cause a crossover of the velocity curves of the uncoupled waves. The presence of the mode coupling results in splitting of the curves with transition from one uncoupled branch to the other. This transition is responsible for the increase in SAW velocity, which appears to be greater than its common decrease produced by electrical shorting of the substrate surface.
数值研究了超强压电晶体铌酸钾（KNbO₃）表面电短路导致表面声波（SAW）速度增加的异常情况。这种效应的解释基于将SAW视为耦合的瑞利模式和布勒斯廷 - 古利亚耶夫模式。针对任意各向异性的压电晶体，提出了一种模式近似解耦的通用方法。当未耦合的矢状极化瑞利波的相速度介于自由表面和金属化表面上未耦合的水平剪切布勒斯廷 - 古利亚耶夫波的相速度之间时，就会出现所研究的效应。在这种情况下，由无限薄的层进行表面金属化可能会导致未耦合波的速度曲线交叉。模式耦合的存在导致曲线分裂，并从一个未耦合分支过渡到另一个未耦合分支。这种过渡导致SAW速度增加，这似乎大于由衬底表面电短路通常产生的速度降低。
