Design of acoustofluidic device for localized trapping.

State of the art acoustofluidics typically treat micro-particles in a multi-wavelength range due to the scale limitations of the established ultrasound field. Here, we report a spatial selective acoustofluidic device that allows trapping micro-particles and cells in a wavelength scale. A pair of interdigital transducers with a concentric-arc shape is used to compress the beam width, while pulsed actuation is adopted to localize the acoustic radiation force in the wave propagating direction. Unlike the traditional usage of geometrical focus, the proposed device is designed by properly superposing the convergent section of two focused surface acoustic waves. We successfully demonstrate a single-column alignment of 15-m polystyrene particles and double-column alignment of 8-m T cells in a wavelength scale. Through proof-of-concept experiments, the proposed acoustofluidic device shows potential applications in on-chip biological and chemical analyses, where localized handing is required.