LAUSR

Abstract Particles or cells in suspension and exposed to ultrasonic waves experience an acoustic radiation force ( F R ) which, under certain conditions, drives them toward positions of acoustic equilibrium. In this paper, we present a three-dimensional model of the particle motions within the acoustic field generated by ultrasonic standing waves. This model allows a theoretical study of the three-dimensional F R induced by a standing acoustic wave in a microfluidic chamber with rectangular geometry on micrometer-sized spherical particles. The approach models the agglomeration process and the behavior of particle clusters in the acoustic field. To achieve this, expressions for the 3D F R are obtained as the time-average of a gradient of the acoustic potential established within the chamber with two different sets of boundary conditions. The particle motion under the action of this force was analyzed assuming a non-viscous fluid and a particle size much smaller than the acoustic wavelength. The 3D force expressions were used in a simulation employing an optimized Forest–Ruth algorithm to derive the dynamics of N spherical particles. This work provides novel results that predict some particle motion toward chamber or channel walls and the formation of pearl-chain aggregates within channels. These particle movements and the aggregate formation process were observed experimentally in an acoustic device built to assess the validity of the theoretical predictions.