Ultrasound-induced acoustophoretic motion of microparticles in three dimensions

TL;DR

This paper develops a comprehensive 3D analytical model for microparticle motion in microchannels under ultrasound, incorporating wall effects and validated by experiments and simulations, advancing precise control in acoustophoretic applications.

Contribution

It introduces a new analytical framework for 3D microparticle motion in microchannels that accounts for side wall effects, validated by experiments and numerical simulations.

Findings

The model accurately predicts particle trajectories in 3D.

Experimental results agree with theoretical predictions.

Quantitative calibration of acoustic energy density was achieved.

Abstract

We derive analytical expressions for the three-dimensional (3D) acoustophoretic motion of spherical microparticles in rectangular microchannels. The motion is generated by the acoustic radiation force and the acoustic streaming-induced drag force. In contrast to the classical theory of Rayleigh streaming in shallow, infinite, parallel-plate channels, our theory does include the effect of the microchannel side walls. The resulting predictions agree well with numerics and experimental measurements of the acoustophoretic motion of polystyrene spheres with nominal diameters of 0.537 um and 5.33 um. The 3D particle motion was recorded using astigmatism particle tracking velocimetry under controlled thermal and acoustic conditions in a long, straight, rectangular microchannel actuated in one of its transverse standing ultrasound-wave resonance modes with one or two half-wavelengths. The acoustic energy density is calibrated in situ based on measurements of the radiation dominated motion of large 5-um-diam particles, allowing for quantitative comparison between theoretical predictions and measurements of the streaming induced motion of small 0.5-um-diam particles.