Effect of an electric field on the propagation velocity of surface acoustic waves in piezo-electric media

The propagation velocity of surface acoustic waves in piezoelectric materials is affected by the presence of a bias electric field. This effect can be theoretically described by introducing into the constitutive piezo- electric equations non linear terms involving second and higher order constants of the material. In the present paper , a theoretical model is proposed which permits to evaluate surface acoustic wave (SAW) velocity in presence of a uniform electric field under the simplifying assumption of small amplitude acoustic waves. The dependence of the urface acoustic wave velocity on the strenght of the applied electric field has been calculated for surface acoustic waves propagating along Z direction of a Ycut LiNbO crystal under an electric field applied along Y direction. Theoretical values of the fractional velocity changes ersus applied electric field are reported and compared with experi- mental results.