Extensions of the Born Approximation for Acoustic Radiation Force and Torque to Inhomogeneous Objects and Progressive Spherical Waves
* Presenting author
A simple volume integral based on the Born approximation was developed for the acoustic radiation force and torque exerted by a plane standing wave on objects of arbitrary shape [Jerome et al., J. Acoust. Soc. Am. 145, 36-44 (2019)]. The principal restriction is that their material properties are similar to those of the surrounding fluid, in which case the approximation is reasonably accurate for objects with dimensions up to about one wavelength. Results were presented for spheres, cylinders, and prolate spheroids with homogeneous material properties. Here, closed-form expressions based on the Born approximation are presented for spheres and cylinders with compressibility and density that vary either linearly or discretely within the object. The expressions reveal the dependence of the radiation force and torque on the position and orientation of the object with respect to an incident standing wave. Second, the validity of the Born approximation for the radiation force on a homogeneous compressible sphere as a function of its distance from the center of a diverging or converging spherical wave is assessed by comparing the closed-form expression obtained in the Born approximation with the full solution based on spherical harmonic expansion of the incident and scattered fields.