On transient ultrasonic waves in a homogeneous plate with thin superconducting coating layers

Transient guided waves excited by a line force applied on one surface of a plate with thin superconducting anisotropic layers deposited symmetrically on both surfaces of a core metallic material are considered here. The line of force is assumed to make an arbitrary angle to an axis of symmetry of the anisotropic layer. Thus, the displacement at any point in the plate has all the three components but it is independent of the coordinate parallel to the line force (taken as x2-axis). Attention is focused here on the coupling of the longitudinal and flexural motion with the horizontally polarized shear motion. It is shown that this coupling causes an interchange between longitudinal (or flexural) and shear horizontal modes at certain frequencies, which are not high. As a result, when the center frequency of a narrow band excitation is near one of the strong coupling frequencies the received signal has characteristic features that are quite different than for other frequencies. These features could be used to characterize in-plane anisotropy of the thin layers using transducers operating at moderate frequencies