Control of a particle flow in a microchannel using ultrasound

Noncontact micro manipulation technique is needed in micromachine technology, biotechnology and so on. Using a standing wave field of ultrasound, it is possible to trap and manipulate small objects at nodes of a sound pressure distribution. In the present paper, a sound wave was generated by a transducer far from a microchannel, and propagated into a microchannel on a glass plate, where a standing wave field was formed. When the liquid water containing alumina particles was injected into the microchannel, the particles flowed along several layers in the flat microchannel. When a half circular space with a branched microchannel were added in the center of the microchannel and the frequency of the ultrasound was swept, the exit channel of the particle flow can be occasionally controlled. Using a curved reflector, a high sound pressure field is formed in a small area in order to stably push the particles.