Design Parameter Comparison for a Silicon-based Directional Low Drift Thermal Anemometer for Horticultural Applications

Vertical farms or controlled environment agriculture facilities are part of the solution to world hunger. This work focuses on improving the detection of air flow in such facilities to prevent leaf tip-burn and increase crop yields, by increasing the performance of a low-cost anemometer.

By optimizing and tuning key geometric design parameters, the sensitivity of a silicon-based combined calorimetric and hot-wire anemometer was increased. The electrical response in the relevant measurement range of 0 to 1 ms-1 is linear with a resolution of 0.05 ms-1 and a sensitivity of 23 µV / ms-1. Additionally, angle of attack measurements are now feasible without needing complicated sensor packaging or additional sensors due to the inherent presence of the heater. This heater acts as a secondary low-power hot-wire sensor (20mW) and was also improved in the optimization process.

The low-drift silicon-based sensor is fabricated in a p-type SOI process involving three plasma etches, one Si3N4 deposition and one wet release etch, resulting in a straightforward fabrication process without additional doping or metal deposition.

The optimization procedure combined with the simple fabrication process, paves the way for a drift-free, low-cost directional thermal anemometer which is calibrated for use in vertical farming sensor grids.