Detection of Suspicious Mass on Structures by Acoustical Waves

Analysis of scattered Lamb waves in thin plates and shells, with an added foreign mass on their surface, was performed. Waves were generated in a range of frequencies, up to 80 kHz, by an impact loading. The responses were detected by full-field and point-wise optical methods. Pulse holointerferometry and pulse electronic speckle patterns interferometry techniques were used to visualize the interaction of the Lamb waves with the added foreign mass. Double-channel laser vibrometry was used to record the velocity history within the proximity of the added foreign mass. It was shown that frequency analysis of the recorded waveforms was more convenient than time domain analysis when investigating the response in the thin-walled structures. The proposed method is applicable to search for suspicious masses (e.g. explosive devices) added to the structures.