Mean-acoustic fields exerted on a subwavelength axisymmetric particle

TL;DR

This paper introduces a semi-analytical method to calculate mean-acoustic fields, including radiation force and torque, on subwavelength axisymmetric particles in fluids, validated against known solutions and applied to biological cells.

Contribution

A novel semi-analytical approach for computing mean-acoustic fields on arbitrarily shaped subwavelength particles in fluids, based on scattering coefficients derived from numerical solutions.

Findings

Method accurately matches exact solutions for rigid spheres in water.

Successfully applied to model red blood cells in blood plasma.

Provides a versatile tool for particle manipulation analysis.

Abstract

The acoustic radiation force produced by ultrasonic waves is the "workhorse" of particle manipulation in acoustofluidics. Nonspherical particles are also subjected to a mean torque known as the acoustic radiation torque. Together they constitute the mean-acoustic fields exerted on the particle. Analytical methods alone cannot calculate these fields on arbitrarily shaped particles in actual fluids and no longer fit for purpose. Here, a semi-analytical approach is introduced for handling subwavelength axisymmetric particles immersed in an isotropic Newtonian fluid. The obtained mean-acoustic fields depend on the scattering coefficients that reflect the monopole and dipole modes. These coefficients are determined by numerically solving the scattering problem. Our method is benchmarked by comparison with the exact result for a subwavelength rigid sphere in water. Besides, a more realistic case of a red blood cell immersed in blood plasma under a standing ultrasonic wave is investigated with our methodology.