Guided waves’ propagation in an elastic plate of linearly varying thickness

Abstract

Experimental studies of guided waves propagating in an elastic plate of linearly decreasing thickness are presented. The plate is embedded in water, and the mode’s excitation is achieved by means of an ultrasonic beam at a given incident angle. Measurements are done either with a receiving transducer or with a laser interferometer. In the first case, the amplitude of the leaking wave and its reemission angle are measured, while, in the second case, the normal acoustic displacement at the surface of the plate is obtained. Use of the surface wave analysis method then provides the dispersion curves of the propagating waves. For plates of small thickness slopes (one or two degrees), the interface waves are shown to behave mostly as generalized Lamb waves which adapt continuously to the varying thickness as they propagate. Evidence of waves propagating backward before having reached the plate end is shown. Mode’s conversions also occur, giving rise to intermodes’ branches in the dispersion plane.