Depth profiling of coating by laser ultrasonic technique

Functionally graded materials (FGMs) show great potential, and the development of new FGMs will lead to materials that have properties not achievable with homogeneous materials. The dispersion curves of surface acoustic wave propagating in coating structures are investigated using the reflection and transmission coefficient method. It's found that the dispersion curves are sensitive to the transverse wave velocity, but they are not very sensitive to the longitudinal wave velocity and density. Genetic algorithms adopted to handle the inverse problem. The object function is established based on experimental phase velocity and the theoretical one. The reconstructed depth-profiling of material properties agrees well with the experimental ones.