Miniaturised Prandtl tube with integrated pressure sensors for micro-thruster plume characterisation

A miniaturised Prandtl-tube sensor incorporating a 6 mm long 40 μm diameter microchannel with integrated pressure sensors has been realised. The sensor has been designed for the characterisation of rarefied plume flow from a MEMS-based monopropellant propulsion system for high-accuracy attitude control of satellites. The 4.5 × 2.5 mm sensor chip incorporates 400 mbar full-scale capacitive pressure sensors. The capacitive pressure transducer is created by merging several microchannels into a rectangular pressure membrane, with outward-facing comb-fingers hinging on the microchannel sidewall. Additionally, thermistors can measure the temperature profile on the Prandtl tube and an integrated Pirani sensor can optionally measure vacuum pressures below 10 mbar. An electronics board and stainless steel probe, from which only the Prandtl tube protrudes has been realised. Initial plume measurements of dynamic pressure on the Prandtl tube have been obtained by flowing air from a metal tube with 0.7 mm diameter, demonstrating the feasibility of the miniaturised Prandtl-tube sensor.