Acoustic radiation force and radiation torque on Rayleigh particles

Abstract

In this work, the acoustic radiation force and radiation torque exerted by an arbitrary shaped wave on a spherical particle in the Rayleigh approximation (i.e. the incident wavelength is much smaller than the particle dimensions) are discussed. The host fluid in which the particle is suspended is assumed to be inviscid. Expressions for the force and the torque are obtained in terms of the incident acoustic fields, namely pressure and particle velocity. As it turns out, the obtained radiation force expression represents a generalization of Gor'kov's formula [Sov. Phys. Dokl. 6, 773-775 (1962)]. Moreover, the radiation torque can be expressed in terms of the incident Reynolds' stress tensor. The method is applied to calculate both radiation force and radiation torque produced by Bessel beams. It is demonstrated that only the first-order Bessel vortex beam generates radiation torque on a particle placed in the beam's axis. In addition, results involving off-axial particles and Bessel beams of different order are illustrated.