Axial acoustic radiation torque of a Bessel vortex beam on spherical shells.

The present paper investigates the interaction of an acoustic Bessel vortex beam centered on a viscoelastic polyethylene sphere and spherical shells filled with air or water immersed in nonviscous water and mercury, and the induced axial acoustic radiation torque (ART) resulting from the transfer of angular momentum. Closed-form series expansions for the axial ART are derived for the case of progressive, standing, and quasistanding waves. The ART is shown to be the result of acoustic absorption inside the particle's material. Numerical predictions shown in the form of two-dimensional (2D) plots illustrate the theory, and reveal new properties related to the ART of Bessel vortex beams. Potential applications are in particle rotation and manipulation. Other applications, such as the characterization of fluids from induced angular accelerations (produced by the ART) and containerless processing, may benefit from the analysis developed here.