Development of E-tattoo Sensors for Monitoring of Plants Hydration Level

Information about hydration monitoring is of interest for plant care and their proper watering. On the other hand, the hydration monitoring of detached leaves is important for industry, such as tea production or tobacco processing, as it must be ensured that certain level of water content evaporates before some processing steps. In this paper we present a proof-of-concept e-tattoos for plant hydration levels monitoring. Forms of interdigital capacitor (IDC) and planar inductor-capacitor (LC) sensor were screen printed on tattoo paper and transferred to leaves of four types of plants (linden, fig, maple and Kalanchoe plant). Measurements of IDC impedance and resonant frequency of LC sensors were performed in laboratory environment, until leaves became totally dried. Capacitances of IDC and LC sensors were decreasing over time due to decay of water content in detached leaves, as the relative permittivity of the substrate between the fingers of IDC and LC sensors decreased. Consequently, the increase of IDC impedance modulus and increase in resonant frequency of LC sensors over time were observed.