Effect of homogenization on calculation of acoustic radiation force

Analytical methods for calculating acoustic radiation force are complicated by the presence of heterogeneity. For a multilayered sphere formed by biological substances having densities and compressibilities similar to those of the host fluid, the simplification provided by the Born approximation of the radiation force exerted by a 1-D standing wave was found by Jerome and Hamilton [JASA 150, 3417 (2021)] to be accurate via comparisons with the full solution by Wang et al. [J. Appl. Phys. 122, 094902 (2017)]. An alternative approximation based on replacing the layered sphere with a homogeneous effective medium, achieved by taking volume averages of the densities and compressibilities, was explored briefly by Gokani et al. [POMA 48, 045002 (2022)] in connection with particle sorting (acoustophoresis) in a microfluidic device that employs noncollinear plane waves. The present work explores the parameter range for which the simplification due to homogenization provides a reasonable approximation of the radiation force acting on layered spheres. Both 1-D standing waves and plane progressive waves are considered for the incident fields. Different densities and compressibilities of the layers are considered, as well as the ordering and thicknesses of the layers within the sphere. [CAC was supported by the ARL:UT McKinney Fellowship in Acoustics]