Effects of Lamb waves on ultrasonic bounded beam propagation

Schlieren imaging techniques are used to show that nonspecular bounded beam reflection effects occur when a Lamb surface wave is excited by an ultrasonic beam incident at the Lamb angle at both water/brass-plate/water and water/Plexiglas-plate/water interfaces. These observed nonspecular reflection effects are analogous to the nonspecular reflection effects occurring at liquid/solid interfaces when a Rayleigh surface wave is excited by mode conversion at the Rayleigh angle. In addition, nongeometrical bounded beam transmission effects are also observed at Lamb angles at liquid/solid-plate/liquid interfaces. Through a comparison of plane wave reflectivity theory and surface wave propagation theory at liquid/solid interfaces with the analogous theories at liquid/solid-plate/liquid interfaces, it is shown that the bounded beam reflection theory for liquid/solid interfaces can be extended to liquid/solid-plate/liquid interfaces. An additional interpretation of the existence and nonexistence of bounded beam effects at Lamb angles is presented in terms of the Lamb surface wave particle displacement parameter beta.