Three-dimensional acoustic micromanipulation using four ultrasonic transducers

Non-contact micromanipulation is a fundamental technique in micromachine technology. Previously, we proposed a new manipulation technique to transport particles two-dimensionally using an ultrasonic standing wave field generated by three transducers, whose sound beam axes were arranged with an angle of 120° in a plane. The present paper describes an advanced technique to manipulate particles three-dimensionally using four transducers. The transducers were settled at each corner of a regular triangular pyramid with their soundbeam axes crossing at the center of the pyramid. All transducers were driven at the same frequency, and a standing wave field was generated in the crossing region. When polystyrene particles were poured with a pipette into the sound field, the particles were trapped at the node of the sound pressure in the central region of the sound field. Changing the phase of one transducer out of four, the trapped particles were transported along the sound beam axis of the transducer. Combining each movement along the four sound beam axes, three-dimensional non-contact manipulation of a particle was accomplished