Broadband attenuation measurement for an absorbing plate

This research demonstrates the effectiveness of combining laser ultrasonic and appropriate time-frequency signal analysis techniques for attenuation measurements of leaky Lamb waves. Laser ultrasonic techniques provide a non-contact, high-fidelity system of generating and detecting Lamb waves, which is critical for amplitude measurements. Time-frequency signal analysis techniques are used to study the dispersive behavior of Lamb waves and interpret broadband, transient signals. With a series of narrowband, bandpass filtering of time-domain signals from more than two positions, attenuation for each mode at specific frequencies can be calculated. This combined technique is tested with an aluminum plate with water half-space on one side. The experimental results show that the proposed technique captures changes in multi-mode attenuation over a broad frequency range, and the attenuation values are in good agreement with the results predicted by an analytical model where Lamb wave modes are well separated in the time-frequency domain.