Anomalous propagation characteristics of evanescent waves

An analysis is done of the crossing of a forbidden region in a thin plate b y a backward propagating Lamb wave: the refraction/reflection effects under gone by the coupled modes produced at each boundary of the forbidden region are taken into consideration, as well as the penetration of the backward w ave as an evanescent wave. The outcome of the acoustic perturbation is anal ysed for a few angles of incidence and experiments are performed that confi rm the theoretical predictions. (C) 2000 Elsevier Science B.V. All rights r eserved.