Experimental and analytical characterization of the 3D motion of particles in acoustofluidic devices

In this work we present an experimental and analytical study of the acoustophoretic motion of spherical polystyrene particles of different sizes. The primary aim is to understand the three-dimensional extension of the acoustic radiation force and the acoustic streaming-induced drag force and to examine the accuracy of analytical force predictions.

Polystyrene spheres with diameter of 0.5µm and 5µm were displaced under controlled conditions in a long straight rectangular acoustofluidic microchannel, actuated in its 2-MHz resonance mode, a transverse half-wavelength standing acoustic wave. Astigmatism Particle Tracking Velocimetry (APTV) was used to measure the three-dimensional trajectories, velocities and accelerations of the particles.

The experiments show how the acoustic radiation force dominates for the large 5-µm particles, whereas the drag force from the acoustic streaming dominates for the smaller 0.5-µm particles. The experimental 3D data is used to validate new theoretical predictions of the streaming velocity.