Acoustic radiation force and torque on spheroidal particles in an ideal cylindrical chamber.

Abstract

In this article, the acoustic radiation force and torque exerted on a small spheroidal particle immersed in a nonviscous fluid inside an ideal cylindrical chamber is theoretically investigated. The ideal chamber comprises a hard top and bottom (rigid boundary condition) and a soft or hard lateral wall. By assuming that the particle is much smaller than the acoustic wavelength, analytical expressions of the radiation force and torque caused by an acoustic wave of arbitrary shape are presented. Unlike previous results, these expressions are given relative to a fixed laboratory frame. The model is showcased for analyzing the behavior of an elongated metallic microspheroid (with a 10:1 aspect ratio) in a half-wavelength acoustofluidic chamber with a diameter of a few millimeters. The results show that the radiation torque aligns the microspheroid along the nodal plane, and the radiation force causes a translational motion with a speed of up to one body length per second. Finally, the implications of this study on propelled nanorods by ultrasound are discussed.