Ultrasonic micro-degassing device

The design, fabrication and evaluation of a micro-degasser are described. The intended use of the device is in portable dialysis systems. Degassing processes were based on ultrasound induced cavitation. The pattern of the degassing chamber was formed in a glass wafer and that of the gas-venting channels were formed in a silicon wafer. The entire flow path network was encapsulated by the anodic bonding of the Si to the glass wafer. A diaphragm (6 mm/spl times/6 mm/spl times/0:1 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 49 kHz square wave at 100 V (peak-to-peak). The gas venting channels (2 /spl mu/m width and 2.7 /spl mu/m depth) were hydrophobically passivated using a chemical. Cavitation occurred in a degassing chamber (6 mm/spl times/6 mm/spl times/0.02 mm) when the Si oscillating diaphragm was driven by the PZT. Water was used to demonstrate the degassing process. The entire process was recorded using a microscope equipped with a video camera. The gas bubbles were vented effectively and no gas bubbles flowing out of the degassing chamber with water were observed.