Ultrasonic micromixer for microfluidic systems

This paper describes the design, fabrication and evaluation of an active micromixer for continuous flow. Mixing occurs directly from ultrasonic vibration. The intended use of the device is for integrated microchemical synthesis systems or for micro total analysis systems. The patterns of inlets, outlet and mixing chamber were formed in glass. The entire flow path was encapsulated by anodic bonding of a Si wafer to the glass. A diaphragm (6 mm x 6 mm x 0.15 mm) was etched on the Si side to prevent ultrasonic radiation from escaping to the other parts of the device. The ultrasonic vibration originated from a bulk piezoelectric lead-zirconate-titanate (PZT) ceramic (5 mm x 4 mm x 0.15 mm). The PZT was adhered on the diaphragm and was excited by a 60 kHz square wave at 50 V (peak-to-peak). Liquids were mixed in a chamber (6 mm. x 6 mm x 0.06 mm) with the Si oscillating diaphragm driven by the PZT. A solution of uranine and water was used to evaluate the effectiveness of mixing. The entire process was recorded using a fluorescent microscope equipped with a digital camera. The laminar flows of the uranine solution (5 ml/min) and water (5 ml/min) were mixed continuously and effectively when the PZT was excited. The temperature rise of our device was 15 degreesC due to the ultrasonic irradiation. (C) 2001 Elsevier Science B.V. All rights reserved.