Microparticle Response to Two-Dimensional Streaming Flows in Rectangular Chambers Undergoing Low-Frequency Horizontal Vibrations

Manipulation of submicron-sized particles using second-order acoustic radiation forces at ultrasonic frequencies is hindered by the time-independent streaming flows. A similar phenomenon occurs when open fluid volumes are vibrated at low frequencies in the range of 100 Hz. The streaming phenomenon, in this lower-frequency range, is studied here by using horizontally actuated liquid-filled rectangular chambers. The formation of capillary waves at the liquid-air interface generates spatially varying flow fields in the bulk fluid, which can be used to collect particles at stable locations. However, the same spatial variation is the source of the streaming fields, which, under some conditions, can drag particles away from these stable locations. The governing equations for the second-order flow are derived and simulated, after which a particle-tracing algorithm is executed in the obtained flow field. Critical particle parameters are determined in multiple simulated chambers of different dimensions, with the aim of reducing the effect of the streaming field on the particle's movement. The simulation results are then applied experimentally to demonstrate the ability of this system to collect particles as small as 50 nm in diameter.