Acoustic Lamb wave-electric field nonlinear interaction in yz-LiNbO3

The nonlinear electroacoustic effect has been investigated for acoustic Lamb wave propagation in a Y Z LiNbO3 plate under a uniform bias electric field. A theoretical model is briefly outlined, which shows how the effect can be interpreted in terms of second and third order material constants. The strength of the nonlinear interaction has been experimentally evaluated through measurements of the change in phase velocity of Lamb modes produced by the bias field. The experiments were performed in the frequency range 8-33 MHz on most of the Lamb modes excited in a 1.25-mm-thick plate by an interdigital transducer with a periodicity ?=0.396 mm. The results evidence a strong dependence of the nonlinear effect on the order and symmetry of the analyzed modes.