Analysis of scattering from dual-frequency Incident beam interaction

Abstract

The characterization of acoustically inhomogeneous structures insonified by dual-frequency acoustic beams is undertaken. A layer of microbubble contrast agents is included to improve the resolution of the scattered field. Of particular interest is the identification of characteristic sizes of volume scatterers and their principal orientations by measurement of their acoustic signatures in the exterior field. The inclusion of bubble contrast agents has shown to enhance the directional pattern of the back-scattered field generated from the difference frequency source created by the nonlinear interaction of the incident beams. However, the sensitivity of the scattered field to variations in the contrast parameter and spatial orientation requires computation to be carried out in a high-dimensional parameter space that includes the difference wavenumber, angle of incidence, acoustic nonlinearity parameter, and several microbubble parameters. A fast computation of the exterior field is carried out using a monopole expansion of the Green's function that separates the source and observation coordinates. The exterior field is sampled and analyzed in the aforementioned system parameter space to identify the weighted combination of parameters that serve as a minimum representation for detecting the changes in the medium parameters through measurements of the exterior scattered field.