Acoustic radiation- and streaming-induced microparticle velocities determined by microparticle image velocimetry in an ultrasound symmetry plane

摘要

We present microparticle image velocimetry measurements of suspended microparticles of diameters from 0.6nto 10 μm undergoing acoustophoresis in an ultrasound symmetry plane in a microchannel. The motion of thensmallest particles is dominated by the Stokes drag from the induced acoustic streaming flow, while the motionnof the largest particles is dominated by the acoustic radiation force. For all particle sizes we predict theoreticallynhow much of the particle velocity is due to radiation and streaming, respectively. These predictions includencorrections for particle-wall interactions and ultrasonic thermoviscous effects and match our measurements withinnthe experimental uncertainty. Finally, we predict theoretically and confirm experimentally that the ratio betweennthe acoustic radiation- and streaming-induced particle velocities is proportional to the actuation frequency, thenacoustic contrast factor, and the square of the particle size, while it is inversely proportional to the kinematicnviscosity.