Stem-Clampable Frequency-Domain Electrical Impedance Sensor for Real-Time Monitoring of Plant Stem Water Content Dynamics

Abstract

Stem water content (SWC) is a critical indicator of plant physiological status, irrigation demand, and growth performance, yet its continuous, nondestructive measurement remains challenging. This study presents a clampable, multielectrode, frequency-domain-based electrical impedance sensor designed for real time, direct SWC monitoring in maize stems. The proposed device integrates eight spring-loaded electrodes with a floating-potential switching architecture, eliminating the need for a fixed ground reference and enabling robust electrical coupling to stems with irregular geometry. Two impedance-based sensing metrics—capacitance and phase angle—were systematically evaluated across multiple frequencies and validated against destructive gravimetric SWC measurements. Experimental results demonstrate that phase-angle-based impedance sensing provides superior robustness to electrode placement and stem heterogeneity, yielding lower prediction error and stronger correlation with gravimetric SWC than capacitance-based measurements. Furthermore, spatial averaging enabled by the multielectrode configuration further enhances measurement stability. These results establish a phase-angle-based, multielectrode impedance sensor as a distinct and reliable approach for continuous SWC sensing, offering a practical pathway toward direct monitoring of plant water status and the development of next-generation wearable plant sensors.