A Battery-Less UHF RFID Sensor for Soil Moisture Monitoring

Soil moisture monitoring is essential for optimizing irrigation strategies, enhancing crop yields, and conserving water resources in precision agriculture. Traditional sensing methods often rely on battery-powered devices, which require maintenance and periodic replacement. This work introduces a batteryless ultrahigh frequency radio frequency identification (UHF RFID) soil moisture sensor that leverages RFID technology and an interdigitated capacitor (IDC) for capacitive sensing. The proposed sensor integrates a meandered dipole antenna and an EM4152 RFID chip, enabling wireless monitoring of soil Volumetric Water Content (VWC) without the need for an external power source. The sensor’s performance is validated through controlled soil moisture experiments, where capacitance readings are correlated with reference measurements from the commercial TEROS 10 soil moisture sensor. The sensor was tested and calibrated using three different soil types: sandy, clay, and a commercial combo substrate. The results demonstrate strong linear correlations with TEROS 10 measurements across all soil types, with coefficients of determination of R2 = 0.9648 (sandy), R2 = 0.9512 (clay), and R2 = 0.9444 (combo). Furthermore, tests conducted at varying water contents and a read range of up to 3.5 meters validate the sensor’s robustness across different soil conditions. The findings highlight the potential of battery-less RFID-based sensing for sustainable and maintenance-free soil moisture monitoring in agricultural applications.