Anomalous behaviour of flexural waves in very thin immersed plates [acoustic wave sensors]

Numerical solutions for the characteristic equations of immersed plates are obtained for thin membranes of the type used for acoustic wave sensors. The results obtained for very small values of the f ×d (frequency times thickness) product reveal complex wave phenomena for the lowest-order flexural wave when its phase velocity falls below the longitudinal wave velocity in the surrounding fluids. Both Poisson´s ratio for the membrane medium and the ratio of the respective mass densities are shown to be the major factors controlling the anomalous region. The conditions under which the onset of this complex wave phenomenon occurs and the relevance to the design of acoustic wave sensors are discussed with the aid of computed results for both the flexural plate wave and the Scholte interface wave