Ultrasonic micromixer for microfluidic systems

This paper describes the design, fabrication and evaluation of an active micromixer. Mixing occurs directly from ultrasonic vibration. The intended use of the device was for integrated micro chemical synthesis systems or for micro total analysis systems. The pattern of inlets, outlet and mixing chamber were formed in glass. The whole flow path was encapsulated by anodic bonding of a Si wafer to the glass. A diaphragm (6 mm×6 mm×0.15 mm) was etched on the Si side for oscillation. The ultrasonic vibration originated from a bulk piezoelectric PZT ceramic (5 mm×4 mm×0.15 mm), which was excited by a 60 kHz square wave at 50 V (peak-to-peak). Liquids were mixed in a chamber (6 mm×6 mm×0.06 mm) with the Si oscillating diaphragm driven by the PZT. A solution of uranine and water were used to evaluate the mixing effectiveness. The entire process was recorded using a fluorescent microscope equipped with digital camera. The laminar flows of uranine solution (5 μl/min) and water (5 μl/min) were mixed effectively when the PZT was excited