A miniature microclimate thermal flow sensor for horticultural applications

Closely packed plant canopies have a negative influence on the uniformity of conditioned air and therefore induce physiological disorders inside plant production systems. Real-time leaf-level flow measurements help to improve the microclimate. This application needs a small and low-cost flow sensor for a flow regime up to 1 m s ⁻¹ . The chip that is presented in this paper consists of five suspended heavily p-doped silicon beams with resistors integrated in the tip. A fluid flow along these tips causes a temperature difference between the resistors by convective heat transfer, enabling calorimetric flow sensing. The 4.4 mm by 3.6 mm sensor is realized in a three-mask versatile fabrication process. The sensor shows a range of 1m s ⁻¹ to 3 m s ⁻¹ for air with a maximum sensitivity of 1.8 mV m ⁻¹ s and a standard deviation-based accuracy of 3.6 cm s ⁻¹ . The sensor design is easily scalable in theory, hence, a redesign will be made with a slightly lower flow range to fully meet the requirements for the application.