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

none7This 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.mixedCappelli I.; Fort A.; Mugnaini M.; Panzardi E.; Pozzebon A.; Tani M.; Vignoli V.Cappelli, I.; Fort, A.; Mugnaini, M.; Panzardi, E.; Pozzebon, A.; Tani, M.; Vignoli, V

Autonomous Sensing Nodes for IoT Applications

The present doctoral thesis fits into the energy harvesting framework, presenting the development of low-power nodes compliant with the energy autonomy requirement, and sharing common technologies and architectures, but based on different energy sources and sensing mechanisms. The adopted approach is aimed at evaluating multiple aspects of the system in its entirety (i.e., the energy harvesting mechanism, the choice of the harvester, the study of the sensing process, the selection of the electronic devices for processing, acquisition and measurement, the electronic design, the microcontroller unit (MCU) programming techniques), accounting for very challenging constraints as the low amounts of harvested power (i.e., [μW, mW] range), the careful management of the available energy, the coexistence of sensing and radio transmitting features with ultra-low power requirements. Commercial sensors are mainly used to meet the cost-effectiveness and the large-scale reproducibility requirements, however also customized sensors for a specific application (soil moisture measurement), together with appropriate characterization and reading circuits, are also presented. Two different strategies have been pursued which led to the development of two types of sensor nodes, which are referred to as 'sensor tags' and 'self-sufficient sensor nodes'. The first term refers to completely passive sensor nodes without an on-board battery as storage element and which operate only in the presence of the energy source, provisioning energy from it. In this thesis, an RFID (Radio Frequency Identification) sensor tag for soil moisture monitoring powered by the impinging electromagnetic field is presented. The second term identifies sensor nodes equipped with a battery rechargeable through energy scavenging and working as a secondary reserve in case of absence of the primary energy source. In this thesis, quasi-real-time multi-purpose monitoring LoRaWAN nodes harvesting energy from thermoelectricity, diffused solar light, indoor white light, and artificial colored light are presented