Acoustic radiation force and torque on objects with continuous and discrete inhomogeneity

Abstract

At the Fall ASA meeting in 2019, the Born approximation was extended to acoustic radiation force and torque on objects of arbitrary shape with spatially varying density and compressibility [Proc. Meet. Acoust. 39, 045007 (2020)]. This model is applied here to a standing plane wave incident on objects either with continuously varying material properties or composed of connected homogeneous regions with different material properties. The approximation for inhomogeneous objects is subject to the same restrictions on incident field structure, scatterer size, and material contrast as for homogeneous objects. Results are presented for cylinders with a variety of strongly asymmetric inhomogeneity distributions. Closed-form expressions are obtained for a sphere with material properties that vary linearly with distance from its center and for a sphere surrounded by concentric spherical layers. Results for the latter case are shown to be in close agreement with existing theory for the radiation force on a nucleated cell modeled as a multilayered compressible sphere [Wang et al., J. Appl. Phys. 122, 094902 (2017)]. The Born approximation thus proves convenient for determining radiation force and torque on soft objects with both arbitrary shape and inhomogeneity. [TSJ was supported by the ARL:UT McKinney Fellowship in Acoustics.]