In Situ Leaf Water Status Sensor Using Resonant Tunneling Diodes as Terahertz Source and Sensor

This study presents a portable, compact, and cost-effective in situ monitoring device designed to monitor leaf water status through a terahertz (THz) source, THz sensor, and infrared array sensor. The innovation in the proposed device is the use of resonant tunneling diodes (RTDs) within THz sources and detectors operating at ~0.28 THz and using a low-cost system’s architecture that consists of an integrated signal generator and scope, coupled with associated hardware connected to a computer. This configuration enables signal acquisition and subsequent fast Fourier transform (FFT) processing to extract peak power values to determine the plant leaf’s water content and the leaf surface’s temperature using an infrared array sensor. Experimental analysis demonstrates that the proposed THz system exhibits a substantial correlation, with an R-squared value of approximately 0.97, when compared to moisture loss measurements obtained using a moisture analyzer. Furthermore, it effectively detects moisture loss within the range of 25%–85% and utilizes thermal images from an infrared sensor array to identify potential health issues in plants. Therefore, the device proposed in this work demonstrates a portable, in situ, nondestructive, and cost-effective solution tool for directly assessing water stress or drought conditions within a plant.