A MEMS-based passive air flow regulator for handheld breath diagnostics

This paper reports on a passive MEMS-based flow regulator designed to maintain a steady flow during asthma diagnostics. A prototype consisting of six in-plane moving pistons that restrict the flow through six flow orifices has been fabricated from three wafers using standard silicon micromachining. The in-plane design enables relatively large flows and tuning of the flow and pressure range to specific application requirements by changing a wafer thickness. In particular, for FENO asthma monitoring, regulatory guidelines specifies that measurements should be made at steady flow of approximately 50 ml/s and within a pressure range of 1–2 kPa. Experimental evaluation of the prototype shows that the flow rate is controlled within a dynamic pressure range of 770 Pa compared to only 430 Pa for a dummy structure and that it can be achieved on a chip measuring only 2 mm × 2 mm × 4 mm. The evaluation also showed that condensation of exhaled air that expectedly occurs in the flow regulator at room temperature can be eliminated by local heating of the device to 40 °C.