Characterization of thin films using numerical inversion of the generalized Lamb wave dispersion relation

Abstract

A numerical inversion procedure based on the simplex algorithm was implemented and tested for the dispersion relation of generalized Lamb waves propagating in a thin film on a semi-infinite substrate. This procedure allows for the determination of up to three parameters of the thin film (transverse elastic wave velocity, density, and thickness). Continuous wave scanning acoustic microscopy was used to measure the dispersion curves of surface waves in a gold film sputtered on a fused silica substrate. The inversion of the data yielded the thickness of the gold film, a Young’s modulus of 80.55 GPa and a Poisson coefficient of 0.418.