Velocity Measurement of Lamb Waves With Laser Ultrasonics

Abstract

The group velocities of multimode's Lamb waves are simultaneously measured by the phase spectrum method. Multimode's Lamb waves in an aluminum plate of 2.0 mm thickness were generated by the Q-switched Nd : YAG laser. The Lamb waves were received at two different distances using a laser interferometer. The analysis using by the phase spectrum method and moving average enables to measure to the dispersion curves of various modes. The measured dispersion curves agree well with the theoretical dispersion curves in velocity range from 2000 to 3000 m/s and in the frequency×thickness range from 2.0 to 18.0 MHz mm. This method may be effective for detection of various defects in thin plates.