Control of position of a particle using a standing wave field generated by crossing sound beams

Non-contact control of position of a particle using an ultrasonic standing wave field in water has been studied experimentally. Although a standing wave field generated between a transducer and a reflector makes it possible to trap particles at nodes of the sound pressure distribution and to transport them by changing frequency, the method has several problems such as resonance of the sound field. The present paper describes a method to generate a standing wave field by two transducers whose sound beam axes are crossing to each other without using a reflector. Since the sound field does not resonate, it is stable for any frequency changes. When a particle was put in the region of the crossing sound beams, it was trapped at nodes of the sound pressure. By changing the phase difference between the transducers, the trapped position shifted. By assigning slightly different frequency to each transducer, transportation at constant speed was realized. It is possible to extend this scheme into two or three-dimensional manipulation by adding more transducers.