Interplays between elastic particles in an ultrasonic standing wave

Separated particles are agglomerated only by the secondary radiation force when trapped at the pressure node. However, the mechanism behind this phenomenon remains unclear. Here, interplays among elastic particles in a trapping process induced by an ultrasonic standing wave are numerically and experimentally investigated. The effects of multi-scattering on particle movement are analyzed by solving the comprehensive acoustic-structure interactions. The theoretical calculations well explain the observed inter-particle behaviors in experiments when they are at or approaching the pressure nodes. Ultrasonic trapping of 100 μm silica particles is experimentally showcased, and the result agrees well with the prediction.