QUANTITATIVE BROAD-BAND ULTRASONIC BACKSCATTER - AN APPROACH TO NON-DESTRUCTIVE EVALUATION IN ACOUSTICALLY INHOMOGENEOUS MATERIALS

The use of a broadband backscatter technique to obtain the frequency dependence of the longitudinal-wave ultrasonic backscatter coefficient from a collection of scatterers in a solid is investigated. Measurements of the backscatter coefficient were obtained over the range 0. 1 less than ka less than 3. 0 from model systems consisting of dilute suspensions of randomly distributed crown glass spheres in hardened polyester resin. The results of these measurements agree well with theoretical prediction. Consequently, broadband measurements of the ultrasonic backscatter coefficient may represent a useful approach toward characterizing the physical properties of scatterers in intrinsically inhomogeneous materials such as composites, metals, and ceramics, and may represent an approach toward nondestructive evaluation of these materials.