Beyond the single-scattering assumption for analysis of diffuse ultrasonic scattering experiments

Abstract

Characterization of diffuse ultrasonic scattering is challenging because accurate models require assumptions about the degree of scattering. Most previous research has focused on the single-scattering regime in which rays are assumed to scatter only once before detection. In this presentation, scattering effects beyond single scattering are examined with a focus on polycrystalline materials. The contribution of the second scattering within the response is quantified with respect to measurement parameters and sample properties. The results show that single-scattering models are appropriate for weakly scattering materials, such as aluminum, for a wide range of experiments and grain sizes. However, stronger scattering materials are predicted to have significant components beyond single-scattering for certain measurement parameters even in the Rayleigh regime. Experimental results for a steel alloy are used to verify model predictions. The experimental work shows the domain for which the doubly-scattered response becomes significant as well as the limitation at which the double scattering model is no longer applicable. The results can be used to predict the applicable frequency range for each level of scattering for a given experimental configuration. Finally, the impact of the higher-order scattering is discussed with respect to the detection of defects within a heterogeneous medium.