A compact passive air flow regulator for portable breath diagnostics

This work reports on a compact flow regulator designed to maintain a steady flow during breath diagnostics. The fabricated device consists of six in-plane moving pistons that restrict the flow through six flow orifices, controlling comparatively large air flows up to 50 ml/s at a pressure range of 1-2 kPa on a chip of only 2×2×4 mm³. The device is fabricated from three wafers, including an SOI wafer, using standard silicon micromachining and only three masks. The in-plane design also allows for scaling of the flow and pressure range by changing the thickness of the handle wafer and device layer. Experimental evaluation of the prototype shows that flow rate is regulated close to the dictated requirements for FENO asthma monitoring.