Microwave-based leaf wetness detection in agricultural wireless sensor networks

Leaf wetness monitoring is significant for many agricultural applications, e.g. plant disease prevention. It is strictly related to the appearance of downy mildew, one of the most disruptive plant disease, especially for vine-grapes. Leaf wetness is usually measured using electronic devices, which detect the presence of water on equivalent leaves by measuring the dielectric constant (capacitive sensors) or the electrical resistance (resistive sensors) of their upper surface. Here an alternative solution, suitable for integration into microwave sensor nodes, is presented. The presence of humidity is detected measuring the reflection coefficient of microwave aperture antennas covered with plastic porous film. The feasibility of the solution is proven by some preliminary laboratory measurements.