Measurement models for ultrasonic nondestructive evaluation

The article reviews ways to use the electromechanical reciprocity relation to construct theoretical models of measurement processes in ultrasonic nond estructive evaluation. This relationship is important because it connects t he change in the voltages measured at the electrical terminal of the transd ucer to the perturbation in the mechanical wavefield caused by the change i n the propagation environment. It does so by mixing an unperturbed referenc e wavefield with one containing the perturbed wavefield. Two problems of pr ogressive difficulty are explored. We begin by investigating the imaging of a one-dimensional sinusoidal fluid-solid interface using a cylindrically f ocused beam and continue by developing a model of the imaging of the mechan ical properties of a two-dimensional, thin solid film using a confocal arra ngement of point-focused transducers. This last problem uses an approximati on to the thin solid film, which reduces its mechanical response to one sim ilar to that of a membrane. Integral relations are given that can be used t o form integral equations or to generate asymptotic approximations to the p article displacements and stresses in the film.