Multilayered material characterization by the Lamb wave lens

The Lamb wave lens excites only one of the possible leaky modes in a multilayered structure at a time by generating conical wavefronts at a fixed incidence angle. In multilayered structures, correct interpretation of the acoustic images requires identification of the layer or interface which is responsible for a particular mode. The Poynting vetor, which is a measure of acoustic energy flow, can be used for this purpose. Calculated and measured curves for a layered material with different interface conditions at a wide frequency range are presented. The variation of Poynting vector components for different frequencies and interfaces as a function of depth and lateral position is calculated. The lateral component of the Poynting vector shows that particular modes are predominantly present in one of the layers or interfaces.