Zero Power Crop Water-Stress Detector Based on a Micromechanical Photoswitch Monitoring Leaf Transmittance Change

This paper reports on the first micromechanical photoswitch (MP) capable of detecting water-stress in a plant by monitoring its leaf's infrared transmittance change without consuming any electrical power in standby. The detection mechanism relies on the dependence of shortwave infrared (SWIR) transmittance on the leaf water relative content (RWC): lower the RWC, higher the transmitted IR power through the leaf. The detector selectively harvests this transmitted SWIR radiation to detect the water stress and generate a digitized output-bit. To achieve this, the proposed detector employs an MP with an integrated high-efficiency narrowband IR plasmonic absorber ( $\eta\sim 93\%$ , bandwidth ∼10%) matched to one of the water's spectral absorption bands ( $\lambda=1.47\mu m$ ). Here, we show that the MP can be tuned to detect different levels of water stress (RWC from 88% to 55%) by varying the applied bias voltage (between 5.91V and 5.76V), while keeping it dormant with zero-power consumption when the plant is healthy/non-water stressed.