Defect detection using a scanning laser source

Surface breaking defects are identified using a scanning laser source. A Q‐switched Nd‐YAG laser is used as a non‐contact source of ultrasound and an electromagnetic acoustic transducer (EMAT) employed as detector. For a thin plate, an increase in frequency content of the received wave is observed when the laser spot is situated directly over the defect. Time‐frequency analysis using a Wigner transform has enabled individual Lamb wave modes to be identified, while propagation of Lamb waves through aluminium sheet is studied by finite element analysis.