Non linear electroacoustic effect in Lamb wave propagation in LiNbO3 plates

The nonlinear electroacoustic effect is investigated in the case of acoustic Lamb modes propagating in piezoelectric plates in the presence of a uniform bias electric field. A theoretical model is outlined, which shows how the effect can be interpreted is terms of the second and third order material constants. The strenght of the nonlinear interaction has been experimentally determined for several Lamb modes, propagating in YZ LiNbO plates by means of the measure of the change in phase velocity produced by the bias electric field. A strong dependence of the nonlinear effect on the acoustic mode and on the parameter /?h of the mode is shown. Most observed values of the nonlinear strenght were much higher than the ones measured in the case of surface waves.