Acoustic micromanipulation using a multi-electrode transducer

Control of position of particles using acoustic radiation pressure in water was studied to develop non-contact micromanipulation technique. The radiation pressure traps particles suspended in water and forms agglomeration every half wavelength in an ultrasonic standing wave field. This paper describes a method to transport them in the transverse direction to the sound beam axis. The principle is based on the shift of sound field by driving selected elements of a multi-electrode transducer. The transducer was a rectangle 20 x 40 mm in size with fifteen electrodes of 20 x 2 mm. Driving a series of electrodes of the transducer, alumina particles were trapped at the nodes of the standing wave field. When the driving electrodes were switched sequentially, the standing wave field shifted laterally and the trapped particles moved to the corresponding nodal points. The resolution of transportation can be made smaller by reducing the size of electrodes. This suggests a new technique to manipulate micro-objects without contact using an ultrasonic standing wave field generated by a multi-electrode transducer.