Coupled mode behaviour in radiating membranes immersed in fluids

Radiation of acoustic waves into fluids from plate modes propagating in thin membranes has been shown to provide an efficient mechanism for air-coupled transducers. The real and imaginary parts of the propagation vector have been calculated with high accuracy for membranes of different materials radiating into air, as a function of frequency and membrane thickness. We have shown that mode coupling between the zeroth antisymmetrical plate mode (A₀) and the interface Scholte mode occurs over a range of fluid density and this coupling is the basis of anomalous behaviour of wave propagation in immersed membranes. Calculations of the acoustic power flow in the membrane and the fluid explain why the damping of the A₀ mode reaches a maximum value in the region where mode coupling occurs