TiO2 nanoparticles coating has been proven to be an extremely performing sensing material for relative humidity (RH) measurements. The chemical activity of TiO2 toward water vapor adsorption and the very large surface to volume ratio typical of nanostructures are ideal characteristics for the development of RH fast and sensitive sensors. Different sensor technologies can be used in conjunction with this material to realize devices with satisfactory performance. In this paper, the authors aim to describe and discuss the main different possible choices and highlight the advantages and disadvantages, and linking them both to the underlying mechanism of water adsorption on the TiO2 sensing layer and to the modification of the electrical behavior due to the water adsorption. In particular, the authors start from results obtained by depositing TiO2 nanoparticles on a novel MEMS microbalance operating at low frequency, which allows to sense only the adsorbed water mass, and they exploit the sensor output to obtain a dynamic model of the water adsorption. They also link these results to those obtained with a Quartz Crystal Microbalance (QCM) functionalized with the same material operating at 10 MHz as a part of an oscillator. Finally, they establish a link with the results obtained by an RH impedance sensor, which exploits the same active material and the same deposition technique. With this sensor technology, the conductive and electrical behavior of the sensing and adsorbed films play a role. The whole work tries to unravel the different phenomena that contribute to the response of RH sensors not only based on TiO2 nanoparticles but also, more generally, based on nanostructured metal oxide materials.

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Direct measurements of aeolian sand transport on coastal dunes and beaches is of paramount importance to make correct decisions about coast management. As most of the existing studies are mainly based on a statistical approach, the solution presented in this paper proposes a sensing structure able to orient itself according to wind direction and directly calculate the amount of wind-transported sand by collecting it and by measuring its weight. Measurements are performed remotely without requiring human action because the structure is equipped with a ZigBee radio module, which periodically sends readings to a local gateway. Here data are processed by a microcontroller and then transferred to a remote data collection centre, through GSM technology. The ease of installation, the reduced power consumption and the low maintenance required, make the proposed solution able to work independently, limiting human intervention, for all the duration of the expected experimental campaign. In order to analyze the cause-effect relationship between the transported sand and the wind, the sensing structure is integrated with a multi-layer anemoscope-anemometer structure. The overall sensor network has been developed and tested in the laboratory, and its operation has been validated in field through a 48 h measurement campaign.

The aim of this paper is to present the viability of an energy-harvesting system prototype, based on thermoelectric generators (TEGs), to be embedded in a Long-Range Wide Area Network (LoRaWAN)-based wireless sensor node, allowing continuous quasi-real-time data transmission even for low temperature gradients and for frequent transmissions. To this end, an RFM95x LoRa module is used in the system. The energy management of the entire node is achieved by exploiting a nano power boost charger buck converter integrated circuit, which allows power extraction from the energy-harvesting source and, at the same time, regulates the charging/discharging process of a Li-Po battery that supplies the wireless node. The first phase of the project was dedicated to understanding the electrical characteristics of the TEG. A series of tests were performed to study the open circuit voltage, the current and the power generated by the TEG at different temperature gradients. Following this first phase, tests were then set up to study the charging/discharging process of the battery by changing two crucial parameters: the temperature between the faces of the TEG and the frequency of the transmissions performed by the transceiver. Experimental results show a positive balance for the battery charging at different conditions, which suggests two important conclusions: first of all, with high temperature gradients, it is possible to set relatively high transmission frequencies for the LoRaWAN module without discharging the battery. The second important consideration concerns the operation of the system at extremely low temperature gradients, with a minimum of 5 °C reached during one of the measurements. This suggests the usability of thermoelectric energy-harvesting systems in a wide range of possible applications even in conditions of low temperature gradients.

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