Miniature valveless ultrasonic pumps and mixers

Miniature acousto-fluidic devices are described that operate as pumps without valves in channel widths of millimeters and below. These devices can also be configured to produce mixing in low-Reynolds-number flows. The prototypes are based on radio-frequency, ultrasonic piezoelectric transducers that exert a directed body force on the fluid via acoustic attenuation. The process is a type of acoustic streaming termed quartz wind. In microfluidics applications, this mechanism has the advantages of insensitivity to the chemical state of the fluid or walls and greatly reduced crosstalk in a multichannel system. The observed pump flow velocities are on the order of 1 mm/s in 1.6 x 1.6 mm(2) channels and with a calculated maximum backpressure that can be pumped against of 0.13 Pa. Due to the low backpressure, quartz wind devices are not competitive pumps for open-loop and high-impedance microfluidics systems but could find application in pumping in low-impedance planar and closed-loop systems and for mixing in reservoirs and channels. Published by Elsevier Science B.V.