Broadband Attenuation Measurement for an Absorbing Plate

Abstract

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.