EXPERIMENTAL-STUDY OF THE CONVERSION OF LAMB WAVES AT THE END OF AN IMMERSED PLATE

Three phenomena occurring when a propagating Lamb wave reaches the rig ht angle end of an immersed plate are experimentally studied. The stud y of the scattering of the incident Lamb wave into bulk waves in water allows us to establish a model permitting the description of this phe nomenon. The strength with which the incident Lamb wave is retroreflec ted (reflected into the same wave) backwards in the plate is quantifie d by the measurement of the retroreflection coefficient. This strength is compared to the one given by the extension of the Viktorov's crite rion. The last phenomenon studied concerns the conversion of the incid ent Lamb wave into other waves propagating backwards in the plate. Lam b waves, different from the incident one, are found to propagate backw ards in the plate. Non-guided waves are also observed. All these waves appear at a critical distance From the end of the plate. An interpret ation of the Lamb waves converted and of their distance of appearance is proposed, based on the description of the Lamb waves by the Debye s eries.