Frequency effects on microparticle motion in horizontally actuated open rectangular chambers

Abstract

The motion of a particle in a liquid subjected to periodic vibrations is determined by its interaction with the periodic (in time) and spatially varying first-order flow field and the ensuing second-order field. The dominating force either allows the particle to collect in stable locations or remain dispersed in the liquid bulk. In this work, we investigate the characteristics of a microparticle’s response to these first- and second-order effects across frequencies ranging from 100 Hz to 100 MHz. The movement of sedimented particles is analyzed through the simulation of capillary wave fields and acoustic wave fields in a horizontally actuated open rectangular chamber. The changing effect of the first-order field on the particle’s motion, from being the dominant mechanism at low frequencies to being ineffective at the higher frequencies, is demonstrated by considering time-averaged forces acting on the particle, over a cycle. Further, the time-averaged effects of the second-order field, termed as streaming field, are analyzed in both capillary-wave- and acoustic-wave-based collection mechanisms; this analysis provides valuable information regarding the minimum particle size that can be collected in a chamber, through the respective mechanisms. Intriguingly, it is observed that the collection of nanometer-sized particles requires excitation at either end of the frequency spectrum.