We present micro-PIV measurements of suspended microparticles of diameters
from 0.6 um to 10 um undergoing acoustophoresis in an ultrasound symmetry plane
in a microchannel. The motion of the smallest particles are dominated by the
Stokes drag from the induced acoustic streaming flow, while the motion of the
largest particles are dominated by the acoustic radiation force. For all
particle sizes we predict theoretically how much of the particle velocity is
due to radiation and streaming, respectively. These predictions include
corrections for particle-wall interactions and ultrasonic thermoviscous
effects, and they match our measurements within the experimental uncertainty.
Finally, we predict theoretically and confirm experimentally that the ratio
between the acoustic radiation- and streaming-induced particle velocities is
proportional to the square of the particle size, the actuation frequency and
the acoustic contrast factor, while it is inversely proportional to the
kinematic viscosity.Comment: 11 pages, 9 figures, RevTex 4-
