Battery-less HF RFID sensor tag for humidity measurements based on TiO2 nanoparticles

This paper shows the feasibility of a High Frequency RFID passive sensor tag equipped with a novel humidity sensor based on a Si substrate, properly functionalized with a solution of nanoparticles of TiO2 in order to increase its sensitivity. The characterization of the sensor is performed at variable humidity and using a properly designed front-end circuit. The reading circuit employed in the final prototype is tailored on the energy harvesting requirement. The obtained results prove that the solution conceived is satisfactory and that the sensor has good sensing properties in a large humidity range. The proposed system can be applied in the IoT framework in manifold monitoring scenarios, especially in humidity and soil moisture applications.