Experimental estimation of the transverse-wave backscatter coefficients for ultrasonic interrogation of weak scattering materials

Abstract

Estimation of a material’s ultrasonic scattering function is a preliminary step to the inverse problem of inferring the material properties from the scattering function. The necessary theory for backscatter coefficient estimation was recently formulated and then applied to the problem of longitudinal-wave backscatter coefficient estimation for weak scattering polycrystalline materials. The present work extends that approach and demonstrates its applicability to the estimation of transverse-wave backscatter coefficients for weak scattering materials whose backscatter coefficient is independent of depth and angle of interrogation. Backscattered ultrasonic signals were measured from a polycrystalline material using both focused and planar transducers operated broadband. Backscattered signals were measured for several measurement system configurations. The distributed scatterer measurement system response function power was calculated for each configuration based on volume integrals of velocity fields calculated using Gauss–Hermite polynomials. Backscatter coefficients were then estimated by removing the measurement system effects from the measured backscattered signals. Results are presented that show agreement between the frequency dependence of the backscatter coefficient estimates and the frequency dependence of the classically determined attenuation coefficient. The estimated transverse-wave backscatter coefficients are shown to be reasonably independent of water path, depth into the material, angle of incidence of the interrogation, and transducer type.