RF-based Split Ring Resonator with Cellulose Nanofiber for Soil pH Sensing

Monitoring the soil pH for farming is a crucial step for evaluating soil health thereby optimizing agricultural yield. This study presents a novel soil pH sensing system utilizing a split-ring resonator (SRR) structure with a cellulose nanofiber (CNF) scaffold as its sensing material. The CNF scaffold, characterized by its elevated surface area, conductivity, and responsiveness to environmental fluctuations, functions as an efficient medium for detecting alterations in soil pH by modifying the dielectric properties of the sensor system. The SRR functions as a highly sensitive microwave resonator that facilitates real-time observation of pH variations through the alteration of its resonant frequency. The interaction of soil samples with differing pH levels with the CNF scaffold alters the material's dielectric constant, resulting in a measurable frequency shift in the SRR response. RF characterisation technology addresses the shortcomings of previous technologies, such as electrochemical sensors, especially for thin materials (thickness < 0.2 mm), where standard devices like Episilometers are ineffective. Experimental validation reveals a significant association between soil pH levels and resonant frequency alterations, confirming the system's reliability and sensitivity.