Analysis of radiative absorption of acoustic Lamb waves in plates loaded with an inviscid non-conducting fluid.

The dependence of radiation losses into a liquid on the value of the displacement component U_3 normal to the plate on the surface of a piezoelectric plate was experimentally studied for Lamb waves of various orders. Waves whose phase velocity V_n in the plate are considered greater than the velocity of the longitudinal volumetric acoustic wave in the liquid V_l. It is shown that at small values of U3 there is no radiation into the liquid and the magnitude of radiation losses is close to zero even at V_n V_l; at large values of U_3, the magnitude of radiation losses is large and for Lamb waves in the YZ-LiNbO3 plate with a thickness normalized to the wavelength of 1.75 and frequency 16.97 MHz it reaches a value of 4 dB/mm, comparable to the radiative losses of surface acoustic waves in the same material.