Acoustic standing waves have been widely used in trapping, patterning, and manipulating\nparticles, whereas one barrier remains: the lack of understanding of force conditions on particles\nwhich mainly include acoustic radiation force (ARF) and acoustic streaming (AS). In this paper,\nforce conditions on micrometer size polystyrene microspheres in acoustic standing wave fields\nwere investigated. The COMSOL�® Mutiphysics particle tracing module was used to numerically\nsimulate force conditions on various particles as a function of time. The velocity of particle movement\nwas experimentally measured using particle imaging velocimetry (PIV). Through experimental and\nnumerical simulation, the functions of ARF and AS in trapping and patterning were analyzed.\nIt is shown that ARF is dominant in trapping and patterning large particles while the impact\nof AS increases rapidly with decreasing particle size. The combination of using both ARF and\nAS for medium size particles can obtain different patterns with only using ARF. Findings of the\npresent study will aid the design of acoustic-driven microfluidic devices to increase the diversity of\nparticle patterning.
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