Design Parameters for the Housing of Two-Dimensional Air Flow Sensors

Micro machined sensors for the 2-D measurement of air flow magnitude and direction achieve very high sensitivity. The housing required for the protection of the sensor membrane greatly reduces the sensitivity for low velocities and induces deformation of the angle response. The first critical design factor is the gap height between the sensor surface and the protecting cover plate. The second is the layout of the necessary mounting bars to hold the cover. Several laboratory tests were conducted to evaluate and compare the influence of these factors. Best results were achieved by replacing the initial four needles holding the cover with a high number of wedge-shaped fins. The final sensor with improved housing was able to measure air flow in cooled fruit warehouses between 0.1 and 2 m/s with a 2% deviation from an ideal sinusoid angle dependency.