Ultrasonic micromixer for microfluidic systems

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Abstract
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/spl times/6 mm/spl times/0.15 mm) was etched on the Si side for oscillation. The ultrasonic vibration originated from a bulk piezoelectric PZT ceramic (5 mm/spl times/4 mm/spl times/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/spl times/6 mm/spl times/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 /spl mu/l/min) and water (5 /spl mu/l/min) were mixed effectively when the PZT was excited.

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