Design and Analysis of a Novel UHF RFID Soil Moisture Sensor for Smart Farming

This work presents the design, analysis and experimental validation of a novel chip-based Ultra High Frequency Radio Frequency Identification (UHF RFID) sensing system designed for soil moisture measurement. The presented sensing resonator is integrated with Alien Higgs-3 IC having an impedance of 27.40-j200.9Y and operates at 915 MHz. The resonator is superimposed with a Kapton Polyimide sheet that acts as the smart sensing material for moisture detection. The proposed design is fabricated and tested in sandy soil with varying moisture levels. Variation of moisture content leads to changes in dielectric properties of the soil which is indicated by a consistent reduction in Received Signal Strength Indicator (RSSI) values. The change in RSSI further correlates to a consistent change in the impedance value of the sensor. Calibration curves establishing a relationship between RSSI levels and impedance are plotted against the known volumetric soil moisture content. This curve will be utilized to determine unknown soil moisture content in practical scenarios.