Design and Experimental Analysis of Time Domain Reflectometry-Based Chipless RFID Soil Moisture Sensor

This paper presents the design and experimental analysis of a novel, cost-effective, and robust soil moisture sensor based on a non-conventional Time Domain Reflectometry (TDR) technique integrated with chipless Radio Frequency Identification (RFID) technology. The proposed sensor operates without relying on complex circuitry or expensive components, making it ideal for deployment in resource-constrained settings. By leveraging amplitude variation in the TDR signal, the sensor accurately detects soil moisture levels while eliminating the need for power-intensive electronics. The key contributions of this work include the development of a compact sensing structure capable of providing precise volumetric moisture measurements across varying soil types, the implementation of a validated calibration technique that relates TDR amplitude variations to dielectric constant values, enabling the determination of volumetric soil moisture content. Additionally, the sensing structure is designed to target a defined soil depth, enabling precise moisture profiling within its validated sensing zone. Experimental results demonstrate a minimum sensitivity of 15 dB/m<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub>, equivalent to 1.5 dB per 10% variation in volumetric moisture content, ensuring reliable measurements even at extreme sensing depths. This advancement addresses challenges in cost, complexity, and environmental adaptability, offering a significant step toward improved irrigation systems and sustainable agricultural practices.