FEM-based analysis of micromachined calorimetric flow sensors

We present a summary of our computer-numeric investigations on calorimetric air-flow sensors considering two alternative measuring arrangements. For the sensor flush mounted to the wall of a rectangular duct, static flow transduction characteristics for both, the controlled-overtemperature and the constant-power operation mode, were derived from finite element based simulations. The simulation results are in good agreement with previous measurements. Additionally, we simulated the flush-mounted sensor response to step-like changes of the air-flow. Based on the model, one can understand the very specific features of the transient sensor signal. Guided by this knowledge, improved design rules for calorimetric flow sensors may be developed. In contrast, immersing a bare sensor chip into the fluid stream, which was the alternative approach studied, leads to improper transduction characteristics due to the formation of flow-vortices.