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

TL;DR

This paper provides analytical expressions for acoustic radiation force and torque on spheroidal particles in an ideal cylindrical chamber, revealing how particles align and move under acoustic waves, with implications for nanorod propulsion.

Contribution

It introduces new analytical formulas for radiation force and torque on spheroids in an ideal chamber, considering arbitrary wave shapes and fixed laboratory frame analysis.

Findings

Radiation torque aligns spheroids along nodal planes.

Radiation force induces translational motion up to one body length per second.

Model applicable to nanorod propulsion using ultrasound.

Abstract

We theoretically investigate how the acoustic radiation force and torque arise on a small spheroidal particle immersed in a nonviscous fluid inside an ideal cylindrical chamber. The ideal chamber comprises a hard top and bottom (rigid boundary condition), and a soft or hard lateral wall. By assuming the particle is much smaller than the acoustic wavelength, we present analytical expressions of the radiation force and torque caused by an acoustic wave of arbitrary shape. Unlike previous results, these expressions are given relative to a fixed laboratory frame. Our 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 few millimeters diameter. The results show 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. At last, we discuss the implications of this study to propelled nanorods by ultrasound.