Born approximation of acoustic radiation force and torque on inhomogeneous objects

The Born approximation developed previously to model acoustic radiation force and torque exerted on homogeneous compressible objects of arbitrary shape [Jerome et al., J. Acoust. Soc. Am. 145, 36-44 (2019)] is extended to include objects that are inhomogeneous. The same general restrictions apply to this extended model, mainly that the incident field is not too similar to a progressive plane wave, that the material properties of the object do not differ substantially from those of the surrounding fluid, and that the size of the object is not much larger than a wavelength. Two applications of the model are presented, one for objects consisting of connected homogeneous regions with different material properties, and the other for objects with continuously varying material properties. Calculations are presented for spheres, finite cylinders, and prolate spheroids.