Analysis of laser-generated Lamb waves with wavelet transform

Multimode laser-generated Lamb wave signals were processed using the wavelet transform. Lamb waveforms were acquired in a 1.6 mm thick aluminum plate containing defects simulated by machined notches with depths of 25%, 50% and 75% of the thickness. The characteristics of the Lamb modes after interacting with the various notches were studied. The amplitude of dominant modes was not sensitive to the notch depths. However, shifting of Lamb modes in time or frequency and the presence of a different number of modes observed from the wavelet analysis of signals from defect-free and defective regions provide an effective way for detecting defects. The results indicate that wavelet transform is an extremely useful tool for analysis of multimode Lamb waves for the inspection of plate-like structures.