Detection of Small Water Droplets on Flexible Leaf Wetness Sensor Considering the Effect of Spatiotemporal Variation

Leaf wetness sensors (LWSs) are employed widely for plant disease management. However, a key challenge for LWS during in situ measurements is detecting small water droplets at various stages of plant growth. Spatiotemporal variation leads to changes in the stem angle or the leaf canopy may exhibit bending due to environmental factors or physical trauma. A flexible electronic LWS deployed under such a scenario needs to detect the small water droplets. Thus, in this work, reduced graphene oxide (rGO)-coated LWS is fabricated on a flexible polyimide substrate. Considering the spatiotemporal effect on fabricated LWS, we have examined the efficacy of LWS by varying the water droplets from $0.5~\mu $ L (small) to $500~\mu $ L (bulk) and changing the angle (from 0° to 90°) and bending the sensor in both inward and outward directions under both laboratory and field conditions. Lab measurements indicate that the sensor response at 0°, 45°, and 90° is approximately 4400%, 3000%, and 90%, respectively, at 1 kHz when only a 0.5- $\mu $ L water droplet is drop-casted. Furthermore, the sensor response for a 0.5- $\mu $ L water droplet during inward and outward bending is approximately 5500% and 7900%, respectively, when the sensor is bent by 3 cm from its initial position. During the field measurements, it is observed that the fabricated LWS is able to detect 0.5- $\mu $ L water droplets at angles of 0°, 45°, and 90°. Likewise, fabricated LWS detects small water droplets of $0.5~\mu $ L when subjected to inward and outward bending during in situ measurements.