Surface acoustic wave determination of subsurface structure

Surface acoustic wave dispersion curves were used to nondestructively estimate properly profiles in three industrially significant material systems; electrodeposited nickel on copper, induction hardened steel, and a nickel-copper-nickel sandwich. The estimation requires that an inverse problem be solved for measured dispersion data. To study the mathematical approach, simulated dispersion data were used to examine solution uniqueness, required computational time and data measurement accuracy. The results show that a fast, robust and unique estimate of industrial subsurface structures can be made as long as an a priori set of parametric relationships is established which span the possible configurations to be measured and constrain the problem. Under these conditions measured dispersion data were used to nondestructively predict the underlying material property profiles to within good agreement of their destructively measured values.