Study of laser-induced surface acoustic wave propagating on materials with machined surfaces based on wavelet analysis

The present paper is concerned with the calculation of the dispersion curves of surface acoustic waves (SAWs) propagation on materials with machined surfaces. Using a DPSS (Diode Pumped Solid State) laser as the excitation source, experiments are performed on the surfaces of silicon wafer, steel and aluminum alloy plates respectively. The theoretic analysis shows that the location of the wavelet coefficients peaks at different scales in time-frequency domain are related to the arrival times of surface acoustic waves with different frequencies. The wavelet transform using the Sym8 wavelet is applied to the time-frequency analysis of weakly-dispersive SAWs and the propagation velocities of SAWs with different frequencies are calculated by extracting relevant data. Combined with the nanoindentation experiments, the relationships between the variation trend of the SAWs' dispersion curves and the surface properties of the materials are analyzed. The repeatability of the experimental method and analysis method is also verified by multiple experiments on different materials, the results indicate that the dispersion curves of multiple groups of signals on the propagation path have good consistency.