An algorithm for the determination of coating properties from laser-generated and detected Rayleigh waves using wavelet analysis: Application to sputtered tantalum

We used single source and single detector laser-ultrasonic measurements to generate and detect Rayleigh waves on tantalum sputtered steel substrates. Group velocity dispersion curves were calculated from the single detected signals using wavelet techniques. Theoretical dispersion curves were calculated via the Achenbach and Keshava (AK) analysis. A simplex minimization technique between theory and experiment using known values for the substrate, allowed us to evaluate the coating parameters. The coating thickness was measured accurately with micrometers, and gives the most easily available comparisons with the output of the simplex method. The results using the straightforward wavelet method were compared with an adaptation thereof.