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 right angle end of an immersed plate are experimentally studied. The study of the scattering of the incident Lamb wave into bulk waves in water allows us to establish a model permitting the description of this phenomenon. The strength with which the incident Lamb wave is retroreflected (reflected into the same wave) backwards in the plate is quantified by the measurement of the retroreflection coefficient. This strength is compared to the one given by the extension of the Viktorov's criterion. The last phenomenon studied concerns the conversion of the incident Lamb wave into other waves propagating backwards in the plate. Lamb waves, different from the incident one, are found to propagate backwards in the plate. Non-guided waves are also observed. All these waves appear at a critical distance from the end of the plate. An interpretation of the Lamb waves converted and of their distance of appearance is proposed, based on the description of the Lamb waves by the Debye series.