Characteristics of ultrasonic Lamb waves in 128° rotated Y-cutlithium niobate

摘要

The characteristics of ultrasonic Lamb waves propagating along thenX-direction of a 128° rotated Y-cut lithium niobate plate areninvestigated. The first higher-order antisymmetric mode, the A1n mode, is found to exhibit an anomalous behavior. The velocity ofnthis mode remains nearly constant for all values of h/Λ, where hnis the plate thickness and Λ is the acoustic wavelength. Thenparticle displacement of the mode tends towards that of a pure shearnhorizontal (SH) wave as the ratio h/Λ tends to zero. Thenelectromechanical coupling coefficient of the wave has a value ofnk2=0.78×10-2 at h/Λ≅0. Thencoupling decreases as h/Λ increases, becoming negligible fornh/Λ>1. The velocity and coupling coefficient of the mode havenbeen measured for various values of h/Λ, and are found to be innfair agreement with theoretical calculations