Novel Thermal Flow Sensors Based on a Wheatstone Bridge Read-out

A novel thermal flow sensor transduction method is presented combining advantages of the calorimetric and the hot-film transduction principle. Four thin-film germanium thermistors are embedded in the silicon-nitride membrane acting as heat sources and as temperature sensors simultaneously. These devices operate in a Wheatstone bridge. The voltage across the bridge as well as the total dissipated power serves as output quantities. Two sensor configurations with different arrangement of the membrane thermistors were examined experimentally. Moreover, we investigated the influence of different layouts on the rise time, the sensitivity, and the usable flow range by means of two-dimensional finite element simulations.