Rapid acoustophoretic motion of microparticles manipulated by phononic crystals

We present the acoustophoretic motion of microparticles simultaneously driven by the acoustic streaming induced drag force (ASF) and acoustic radiation force (ARF) on a phononic crystal plate (PCP). A much faster acoustophoresis can be achieved via a PCP than a traditional standing wave in bulk and surface acoustic wave devices. The mechanism is attributed to the significantly enhanced ASF and ARF originating from the resonant excitation of a nonleaky zero-order antisymmetric Lamb mode intrinsically in the plate, which generates the highly localized field vertical to the surface and periodic field parallel to the surface. We also demonstrate the transition from the ASF dominated acoustophoresis to ARF dominated acoustophoresis as a function of particle size. The predicted trajectories and velocity of acoustophoretic particles by the proposed finite element model are in reasonable agreement with experimental phenomena. This study would aid the development of simple, scalable, integrated, and disposable phononic crystal based acoustofluidic systems for biomedical applications such as rapid mixing, cell trapping, sorting, and patterning.