Characterization of the Response of Magnetron Sputtered In2O3−x Sensors to NO2

The response of resistive In2O3−x sensing devices was investigated as a function of the NO2 concentration in different operative conditions. Sensing layers are 150 nm thick films manufactured by oxygen-free room temperature magnetron sputtering deposition. This technique allows for a facile and fast manufacturing process, at same time providing advantages in terms of gas sensing performances. The oxygen deficiency during growth provides high densities of oxygen vacancies, both on the surface, where they are favoring NO2 absorption reactions, and in the bulk, where they act as donors. This n-type doping allows for conveniently lowering the thin film resistivity, thus avoiding the sophisticated electronic readout required in the case of very high resistance sensing layers. The semiconductor layer was characterized in terms of morphology, composition and electronic properties. The sensor baseline resistance is in the order of kilohms and exhibits remarkable performances with respect to gas sensitivity. The sensor response to NO2 was studied experimentally both in oxygen-rich and oxygen-free atmospheres for different NO2 concentrations and working temperatures. Experimental tests revealed a response of 32%/ppm at 10 ppm NO2 and response times of approximately 2 min at an optimal working temperature of 200 °C. The obtained performance is in line with the requirements of a realistic application scenario, such as in plant condition monitoring

QCM Measurements of RH with Nanostructured Carbon-Based Materials: Part 2-Experimental Characterization

In this series of two papers, the humidity sensing of a carbon nanotube (CNT) network-based material is transduced and studied through quartz crystal microbalance (QCM) measurements. To this aim, quartzes functionalized with different amounts of sensing material were realized, exposed to different humidity levels, and characterized. In this second paper, the experimental results are presented and discussed. The sensing mechanisms are elucidated exploiting the theory presented in the first paper of this series. The presented results show that the investigated material functionalization induces a large response of QCM to humidity in terms of resonant frequency even at low RH levels, with a sensitivity of about 12 Hz/%RH (at RH < 30% and room temperature and 10 ug of deposited SWCNT solution) and an increase in sensitivity in the high RH range typical of nanostructured film. Regarding the response in terms of motional resistance, a large response is obtained only at intermediate and high humidity levels, confirming that condensation of water in the film plays an important role in the sensing mechanism of nanostructured materials

A New Conditioning Method for PZT-Based Microsensors

A conditioning circuit able to simultaneously actuate and measure the output of an integrated MEMS cantilever mass-sensor fabricated in PiezoMUMPs technology is presented. The MEMS is a resonator with an embedded aluminum nitride (AlN) layer. The basic idea is to use the active layer properties to excite the device and simultaneously read the mechanical response by detecting the resonant frequency. In order to do this a suitable conditioning system has been developed, and a hybrid solution based on microelectronic devices has been realized. The proposed measurement system allows to detect the main parameters characterizing the electro-mechanical device response in real time, allowing the monitoring of the sensed quantity

Health monitoring of human breathing by graphene oxide based sensors

Monitoring of human health is of high importance to enable early detection of illness and improve the quality of life from diseases such as lung cancer or sleep apnea. Breath monitoring is highly interesting in this regard. Graphene oxide is one of the most studied materials for sensing applications and has exceptional properties like large surface area, mechanical stability, and tunable electrical properties. In this paper, we introduce a breath sensor made of a graphene oxide film. Graphene oxide dispersion was deposited on silver interdigitated electrode on flexible substrate, which was then thermally annealed to partially reduce the graphene oxide. The breathing signal was acquired by a digital oscilloscope and the data saved using a LabVIEW interface. The sensors show ultra low response time of less than one second and excellent repeatability. Impedance spectroscopy measurements were carried out at different humidity levels to characterize the sensor. The sensor impedance shows a high decrease by several orders of magnitudes by increasing the relative humidity. Sensitivity to humid air results from the high hydrophilicity of the graphene oxide due to its oxygen functional groups. The change of transport mechanism from Nyquist plot shows the change of the sensor impedance from the capacitive behavior to a semicircle of parallel resistance and capacitance. The high sensitivity of GO to humid air as well as the ultrafast response makes it suitable as a noninvasive and flexible breath-monitoring sensor

Human Breathing Monitoring by Graphene Oxide Based Sensors

Non-invasive monitoring of human health is of a high importance for early detection of illnesses and improving life quality. Breath monitoring is important for detection of severe diseases such as lung cancer or sleep apnea. In this work, we introduce a breath sensor based on a graphene oxide film deposited on silver interdigitated electrode and a flexible substrate. The graphene oxide film was then thermally annealed to partially reduce the graphene oxide. The measurements of sensor impedance carried out at different humidity levels show a high decrease by several orders of magnitudes by increasing the relative humidity. Sensitivity to humid air results from the high hydrophilicity of the graphene oxide due to its oxygen functional groups. The change of transport mechanism from Nyquist plot shows the change of the sensor impedance from the capacitive behavior to a semicircle of parallel resistance and capacitance. The sensors show an ultrahigh sensitivity to humidity at high humidity values, a very low response time of less than one second and an excellent repeatability of the measurements. For tracking human breathing, the reaction on natural breathing was acquired by a digital oscilloscope together with an IoT mobile application to visualize the results in real time and store them for further processing. The sensor performance shows that it is suitable as a noninvasive and flexible breath-monitoring sensor system. The proposed sensor can be a step to flexible and cheap wearable sensors for detection of human breath and hazardous breath airborne such as COVID-19

Performance Analysis of a Humidity Sensor Based on a Microresonator Functionalized with TiO2Nanoparticles

This article proposes a novel humidity sensor based on a low-frequency micromachined electromechanical resonator functionalized with nanoparticles of TiO2 deposited on a preparation layer of Al2O3 nanoparticles. Using a low-frequency resonator allows for obtaining a better immunity to the nonidealities of the conditioning electronics components and minimizes the degradation of the resonator quality due to the deposition of the sensing material. In this article, a relationship is derived between the sensor construction parameters, the obtainable sensor resolution, and the requirements in terms of resolution and accuracy of the measurement system, showing the applicability of such sensors in the context of low-cost, low-power distributed sensing systems. An ad hoc characterization system allowed for characterizing the proposed sensor, proving that this solution is viable and requires a simple preparation route and that the sensor has satisfactory performance in a large humidity range. It was shown that the sensitivity can be increased simply by repeating the TiO2 nanoparticle deposition obtaining at least an increase of the relative sensitivity of 5 ppm/1% RH at each deposition step

Black powder flow monitoring in pipelines by means of multi-hop LoRa networks

The aim of this paper is to present a LoRa-basedarchitecture to be used to monitor the formation of Black Powder(BP) in gas pipelines. The proposed network architecture isbased on a multi-hop linear topology that allows to deploy amonitoring infrastructure that can be used to cover extremelylong pipeline structures thanks to the wide transmission rangeof the LoRa technology. Together with the network architecture,a novel protocol based on nodes synchronization and very lowduty-cycling is proposed, in order to reduce power consumptionand then to ensure long life-time to the whole monitoringinfrastructure. The network is expected to be used to detect BPflow in gas pipelines: for this application scenario, a measurementsystem based on electrostatic monitoring is presented. Thissystem is integrated onto a sensor node composed of low powercomponents, in order to reduce power consumption and thenincrease as much as possible the node life time

Measurement System Based on Electrostatic Sensors to Detect Moving Charged Debris with Planar-Isotropic Accuracy

We present a measurement system capable to detect and reconstruct the trajectory of moving charged debris expelled with the exhaust gases or circulating in the lubricating oil of engines, aero-engines, or gas turbines. The measurement technique is based on a circular array of three electrostatic sensors used to estimate the trajectory, the charge, and the velocity of a moving charged particle. We discuss methods to process the information provided by the sensors, combining physical models and the geometrical characteristics of the sensor array, providing a theoretical characterization of the measurement accuracy, which is shown to be not dependent on the direction of the particle motion with respect to the sensor placement. The information obtained with the measurement system can be used to reject false positives when the sensors and the front-end electronics are used in noisy environments

Modeling the conductivity response to NO2 gas of films based on MWCNT networks

This work proposes a model describing the dynamic behavior of sensing films based on functionalized MWCNT networks in terms of conductivity when exposed to time-variable concen-trations of NO2 and operating with variable working temperatures. To test the proposed model, disordered networks of MWCNTs functionalized with COOH and Au nanoparticles were exploited. The model is derived from theoretical descriptions of the electronic transport in the nanotube net-work, of the NO2 chemisorption reaction and of the interaction of these two phenomena. The model is numerically implemented and then identified by estimating all the chemical/physical quantities involved and acting as parameters, through a model fitting procedure. Satisfactory results were obtained in the fitting process, and the identified model was used to further the analysis of the MWCNT sensing in dynamical conditions