Two-dimensional acoustic manipulation in air using interference of standing wave field by three sound waves

A number of small ultrasonic transducers were placed on a flat surface to form a directional ultrasonic sound source. A standing wave field with a hexagonal distribution of sound pressure like a honeycomb was formed when ultrasonic waves were superimposed from three directions using three of these sources. Small objects could be trapped at the nodes of the sound pressure in the sound field. When the phase of the three sources was changed, the sound pressure distribution shifted in the direction of the sound axis of the sources, and the objects trapped at the pressure nodes also shifted. For more stable object trapping, the ultrasonic transducers were placed on the inner wall of a semicylinder and the ultrasonic waves were focused to form a thin two-dimensional planar standing wave field. Three of these sources were used in the experiment, and it was possible to manipulate the objects more stably.