Defect detection in thin plate by using focused lamb waves generated by laser

An arc array slit is used for generating the focused Lamb wave by laser, where spatially expanded Nd:YAG pulse laser is illuminated through the arc array slit on the surface of a sample plate to generate the Lamb wave of the same pattern as the slit. Then the generated Lamb wave is focused at the focal point of which distance from the slit position is dependent on the curvature of slit arc. The focusing effect enables to acquire higher intensity of water at the focus, better SNR in the received signal, and improved spatial resolution than when we use the conventional line array slit. In order to show the usefulness of the proposed method, experiments is carried out for the detection of the artificial linear and circular defects on a thin aluminum plate and proposed quantitative analysis of the defect size.