Battery-less HF RFID sensor tag for soil moisture measurements

This article shows the feasibility of a high-frequency RFID passive sensor tag equipped with sensors based on a thin-film circuit on a Si substrate for the measurement of soil moisture. Three tags embedding different sensing systems compliant with the energy harvesting requirements were developed. The used sensors were previously characterized with the aim of tailoring an adequate electronic front-end. All the typical solutions for soil moisture detection were implemented: a fringe capacitance sensor, a soil impedance sensor, and finally a humidity sensor based on functionalization with TiO2 nano particles. The obtained results prove that the conceived solution is satisfactory and that the sensors have good sensing properties. The proposed system can be applied within the Internet of Things (IoT) framework in manifold monitoring scenarios of soil moisture sensing.