Understanding the Influence of Film Thickness on rGO-Based Flexible Capacitive Leaf Wetness Sensors for In-Situ Agriculture Applications

Integrated plant disease management is pivotal in abating crop loss. For this purpose, leaf wetness sensors (LWSs) are widely used to measure the leaf wetness duration. This work focuses on fabricating the LWS on flexible polyimide substrates and understanding its sensor transfer characteristics using reduced graphene oxide (rGO) as the sensing film with varying thickness. For this purpose, three different concentrations, viz, 0.001 mg (Device A), 1 mg (Device B), and 10 mg (Device C) of rGO are dispersed in 0.5 mL deionized water, and these are drop-casted on the fabricated LWS. Subsequently, sensor properties such as response, recovery/recovery time, hysteresis, and temperature effects are studied. Initial laboratory readings demonstrate that the fabricated LWS response for devices A, B, and C is 607866%, 6541%, and 780%, sensing area wetness, respectively. Further, the response times for devices A, B, and C are 10, 15, and 6 s, respectively. Interestingly, the recovery times of devices A, B, and C are approximately 15, 16, and 2462 s, respectively. Further, it has been observed that over the temperature range of 30 °C–60 °C, the sensor response changes by 2%, 5%, and 17% for devices A, B, and C, respectively.