Diffraction of Lamb waves at the end section of a plate

An experimental study is presented of the diffraction of Lamb waves at the end section of a plate imbedded in water. The amplitude of the diffracted wave is plotted versus angle of diffraction for different Lamb modes. The S modes have maxima of diffraction in their direction of propagation, as opposed to A modes that are associated with minima of diffraction in their direction of propagation. For all modes, the diffraction pattern is symmetric about the direction of propagation of the incident (Lamb) wave, and the peaks associated with maxima of the diffracted amplitude widen as the angle of observation increases. Those results are in good agreement with those obtained by a simple calculation of interferences between two sources, the relative phases of which are determined by the type (A or S) of diffracting Lamb wave.