Two-dimensional acoustic micromanipulation using three ultrasonic transducers

Stable control of positions of a small object in water was studied using acoustic radiation pressure to develop a noncontact micromanipulation technique. Although an ultrasonic standing wave field generated between a transducer and a reflector makes it possible to trap particles in water at nodes of the sound pressure distribution and to transport them, this method has several problems such as instability in the control of positions. This paper describes a method to generate a standing wave field without a reflector; the field is generated with three ultrasonic transducers whose sound beam axes are arranged with an angle of 120° to each other. When polystyrene particles were placed into the sound field, they were trapped at the nodes in the central region of the field. When the phase of one of the transducers was changed, the particles moved along the sound beam axis of that transducer. It is possible to transport them two-dimensionally by controlling the phases of two transducers