Lightweight soft sensor for droplets on plant leaves and other surfaces

Droplet sensing has crucial applications across many fields. For example, the effective arrival of droplets on plant leaves plays a vital role in representing the local conditions in plant ecosystems, ranging from rain and irrigation monitoring to analysis of agricultural spraying. Here, we present a soft, transparent, lightweight, and self-powered sensor that can be installed on plant leaves to measure impinging droplets of different sizes. The structure is fabricated by multilayer stacking of selected materials. The top layer contains an embroidered, patterned surface electrode that can be used to measure electrical signals due to liquid-solid surface charging when the droplet hits the device surface. Each droplet creates a characteristic current spike during interaction with the sensor materials and can be either directly read out in high frequency to obtain dynamic information on single droplets or analyzed in terms of average charges transferred to a sensing capacitor over larger periods. The devices allow to obtain droplet rates and information on the droplet size and could serve as sensors in smart and precision agriculture, spraying, and local, plant-level meteorology.