Backscattering enhancements associated with antisymmetric Lamb waves confined to the edge of a circular plate: Direct and holographic observations

Significant backscattering enhancements occur for thin circular plates tilted close to the coupling angle for the second antisymmetric leaky wave, the a 1 wave. Imaging the surface of the plate using acoustic holography shows that the mechanism responsible for this enhancement is associated with the excitation of a leaky wave that is confined to the edge of the plate. This “circumferential” wave couples to the incident field at the top and bottom of the plate and travels around the plate with a group velocity that is much slower than that of the a 1 wave. This circumferential wave may be a whispering gallery mode associated with the a 1 wave or a higher order flexural edge wave.