Acoustic Lateral Recoil Force and Stable Lift of Anisotropic Particles

TL;DR

This paper investigates the acoustic forces and torques on anisotropic particles, revealing novel lateral recoil force and stable lift phenomena that could enhance particle manipulation and sorting in biomedical applications.

Contribution

It introduces the concepts of lateral recoil force and stable acoustic lift for anisotropic particles, expanding understanding beyond spherical particle models.

Findings

Discovery of lateral recoil force orthogonal to incident wave

Identification of conditions for stable acoustic lift

Potential applications in biomedical particle sorting

Abstract

Acoustic forces and torques are of immense importance for manipulation of particles, in particular in biomedical applications. While such forces and torques are well understood for small spherical particles with lowest-order monopole and dipole responses, the higher-order effects for larger anisotropic particles have not been properly investigated. Here we examine the acoustic force and torque on an anisotropic (spheroid) particle and reveal two novel phenomena. First, we describe the lateral recoil force, orthogonal to the direction of the incident wave and determined by the tilted orientation of the particle. Second, we find conditions for the stable acoustic lift, where the balanced torque and force produce a stable lateral drift of the tilted particle. We argue that these phenomena can bring about new functionalities in acoustic manipulation and sorting of anisotropic particles including biological objects such as blood cells.