Journal articles: 'MOx sensor'

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Yurko, Gabriel, Javad Roostaei, Timothy Dittrich, Lanyu Xu, Michael Ewing, Yongli Zhang, and Gina Shreve. "Real-Time Sensor Response Characteristics of 3 Commercial Metal Oxide Sensors for Detection of BTEX and Chlorinated Aliphatic Hydrocarbon Organic Vapors." Chemosensors 7, no. 3 (August 27, 2019): 40. http://dx.doi.org/10.3390/chemosensors7030040.

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The objective of this study was to examine the sensor response characteristics of three commercial Internet of Things (IoT) compatible metal oxide (MOx) sensors in preparation for the development of field-scale sensor networks for the real-time monitoring of volatile organic compounds (VOCs) in indoor environments located in proximity to brownfield sites. Currently, there is limited examination of such sensor responses to relevant mixtures of target VOCs, such as the common petrochemicals benzene, toluene, ethylbenzene, and xylene (BTEX), as well as chlorinated aliphatic hydrocarbon (CAH) contaminants such as tetrachloroethylene (PCE) and trichloroethylene (TCE) which are frequently associated with deterioration of indoor air quality. To address this, a study of three commercial metal oxide (MOx) sensors (SGP30, BME680, and CCS811) was undertaken to examine the sensor response characteristics of individual components as well as mixtures of each of the target BTEX and CAH chemicals over relevant indoor air concentrations within the operating range of the MOx sensors (0–6000 ppb). Our investigation revealed similar response patterns to those previously reported for the thick film MOx sensor to most individual target VOCs, however, response trends for mixtures were more difficult to discern. In general, the MOx sensors we examined demonstrated similar magnitude responses to the CAHs as BTEX compounds indicating reliable detection of CAHs.

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Abdullah, Abdulnasser Nabil, Kamarulzaman Kamarudin, Latifah Munirah Kamarudin, Abdul Hamid Adom, Syed Muhammad Mamduh, Zaffry Hadi Mohd Juffry, and Victor Hernandez Bennetts. "Correction Model for Metal Oxide Sensor Drift Caused by Ambient Temperature and Humidity." Sensors 22, no. 9 (April 26, 2022): 3301. http://dx.doi.org/10.3390/s22093301.

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For decades, Metal oxide (MOX) gas sensors have been commercially available and used in various applications such as the Smart City, gas monitoring, and safety due to advantages such as high sensitivity, a high detection range, fast reaction time, and cost-effectiveness. However, several factors affect the sensing ability of MOX gas sensors. This article presents the results of a study on the cross-sensitivity of MOX gas sensors toward ambient temperature and humidity. A gas sensor array consisting of temperature and humidity sensors and four different MOX gas sensors (MiCS-5524, GM-402B, GM-502B, and MiCS-6814) was developed. The sensors were subjected to various relative gas concentrations, temperatures (from 16 °C to 30 °C), and humidity levels (from 75% to 45%), representing a typical indoor environment. The results proved that the gas sensor responses were significantly affected by the temperature and humidity. The increased temperature and humidity levels led to a decreased response for all sensors, except for MiCS-6814, which showed the opposite response. Hence, this work proposed regression models for each sensor, which can correct the gas sensor response drift caused by the ambient temperature and humidity variations. The models were validated, and the standard deviations of the corrected sensor response were found to be 1.66 kΩ, 13.17 kΩ, 29.67 kΩ, and 0.12 kΩ, respectively. These values are much smaller compared to the raw sensor response (i.e., 18.22, 24.33 kΩ, 95.18 kΩ, and 2.99 kΩ), indicating that the model provided a more stable output and minimised the drift. Overall, the results also proved that the models can be used for MOX gas sensors employed in the training process, as well as for other sets of gas sensors.

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Müller, Gerhard, and Giorgio Sberveglieri. "Origin of Baseline Drift in Metal Oxide Gas Sensors: Effects of Bulk Equilibration." Chemosensors 10, no. 5 (May 2, 2022): 171. http://dx.doi.org/10.3390/chemosensors10050171.

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Metal oxide (MOX) gas sensors and gas sensor arrays are widely used to detect toxic, combustible, and corrosive gases and gas mixtures inside ambient air. Important but poorly researched effects counteracting reliable detection are the phenomena of sensor baseline drift and changes in gas response upon long-term operation of MOX gas sensors. In this paper, it is shown that baseline drift is not limited to materials with poor crystallinity, but that this phenomenon principally also occurs in materials with almost perfect crystalline order. Building on this result, a theoretical framework for the analysis of such phenomena is developed. This analysis indicates that sensor drift is caused by the slow annealing of quenched-in non-equilibrium oxygen-vacancy donors as MOX gas sensors are operated at moderate temperatures for prolonged periods of time. Most interestingly, our analysis predicts that sensor drift in n-type MOX materials can potentially be mitigated or even suppressed by doping with metal impurities with chemical valences higher than those of the core metal constituents of the host crystals.

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Martinez, Burgués, and Marco. "Fast Measurements with MOX Sensors: A Least-Squares Approach to Blind Deconvolution." Sensors 19, no. 18 (September 18, 2019): 4029. http://dx.doi.org/10.3390/s19184029.

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Metal oxide (MOX) sensors are widely used for chemical sensing due to their low cost, miniaturization, low power consumption and durability. Yet, getting instantaneous measurements of fluctuating gas concentration in turbulent plumes is not possible due to their slow response time. In this paper, we show that the slow response of MOX sensors can be compensated by deconvolution, provided that an invertible, parametrized, sensor model is available. We consider a nonlinear, first-order dynamic model that is mathematically tractable for MOX identification and deconvolution. By transforming the sensor signal in the log-domain, the system becomes linear in the parameters and these can be estimated by the least-squares techniques. Moreover, we use the MOX diversity in a sensor array to avoid training with a supervised signal. The information provided by two (or more) sensors, exposed to the same flow but responding with different dynamics, is exploited to recover the ground truth signal (gas input). This approach is known as blind deconvolution. We demonstrate its efficiency on MOX sensors recorded in turbulent plumes. The reconstructed signal is similar to the one obtained with a fast photo-ionization detector (PID). The technique is thus relevant to track a fast-changing gas concentration with MOX sensors, resulting in a compensated response time comparable to that of a PID.

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Samotaev, Nikolay, Konstantin Oblov, Anastasia Ivanova, Boris Podlepetsky, Nikolay Volkov, and Nazar Zibilyuk. "Technology for SMD Packaging MOX Gas Sensors." Proceedings 2, no. 13 (November 30, 2018): 934. http://dx.doi.org/10.3390/proceedings2130934.

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The perspective combination of laser micromilling technology and jet (aerosol) printing technologies for ceramic MEMS producing of microhotplate in the surface mounted device (SMD) package for the metal oxide (MOX) sensor is describing. There are discusses technological and economic aspects of small-scale production of gas MOX sensors. Experiments with laser micromilling of Al2O3 ceramics confirmed possibility to produce MEMS microhotplate for MOX gas sensor in SMD package with form-factor SOT-23. Developed technology process is close to 3D prototype philosophy—rapid, simple and cheap.

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Samotaev, Nikolay, Konstantin Oblov, and Anastasia Ivanova. "Laser Micromilling Technology as a Key for Rapid Prototyping SMD ceramic MEMS devices." MATEC Web of Conferences 207 (2018): 04003. http://dx.doi.org/10.1051/matecconf/201820704003.

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The flexible laser micromilling technology for ceramic MEMS producing of microhotplate in the surface mounted device (SMD) package for the metal oxide (MOX) gas sensors is describing. There are discusses technological and economic aspects of small-scale production of gas MOX sensors in comparison with classical clean room technologies using for mass production MEMS devices. The main technical factors affecting on using MOX sensors in various applications are presented. Current results demonstrate that using described technology possible to manufacturing all parts of MOX gas sensor in the SMD form-factor SOT-23 package type.

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Jaeschke, Carsten, Oriol Gonzalez, Johannes J. Glöckler, Leila T. Hagemann, Kaylen E. Richardson, Francesc Adrover, Marta Padilla, Jan Mitrovics, and Boris Mizaikoff. "A Novel Modular eNose System Based on Commercial MOX Sensors to Detect Low Concentrations of VOCs for Breath Gas Analysis." Proceedings 2, no. 13 (November 30, 2018): 993. http://dx.doi.org/10.3390/proceedings2130993.

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In this work, a new generation of eNose systems particularly suited for exhaled breath gas analysis is presented. The developed analyzer system comprises a compact modular, low volume, temperature controlled sensing chamber explicitly tested for the detection of acetone, isoprene, pentane and isopropanol. The eNose system sensing chamber consists of three compartments, each of which can contain 8 analog Metal Oxide (MOX) sensors or 10 digital MOX sensors. Additional sensors within the digital compartment allow for pressure, humidity and temperature measurements. The presented eNose system contains a sensor array with up to 30 physical sensors and provides the ability to discriminate between low VOC concentrations under dry and humid conditions. The MOX sensor signals were analyzed by pattern recognition methods.

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Wen, Wei-Chih, Ting-I. Chou, and Kea-Tiong Tang. "A Gas Mixture Prediction Model Based on the Dynamic Response of a Metal-Oxide Sensor." Micromachines 10, no. 9 (September 11, 2019): 598. http://dx.doi.org/10.3390/mi10090598.

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Metal-oxide (MOX) gas sensors are widely used for gas concentration estimation and gas identification due to their low cost, high sensitivity, and stability. However, MOX sensors have low selectivity to different gases, which leads to the problem of classification for mixtures and pure gases. In this study, a square wave was applied as the heater waveform to generate a dynamic response on the sensor. The information of the dynamic response, which includes different characteristics for different gases due to temperature changes, enhanced the selectivity of the MOX sensor. Moreover, a polynomial interaction term mixture model with a dynamic response is proposed to predict the concentration of the binary mixtures and pure gases. The proposed method improved the classification accuracy to 100%. Moreover, the relative error of quantification decreased to 1.4% for pure gases and 13.0% for mixtures.

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Palacín, Jordi, Eduard Clotet, and Elena Rubies. "Assessing over Time Performance of an eNose Composed of 16 Single-Type MOX Gas Sensors Applied to Classify Two Volatiles." Chemosensors 10, no. 3 (March 19, 2022): 118. http://dx.doi.org/10.3390/chemosensors10030118.

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This paper assesses the over time performance of a custom electronic nose (eNose) composed of an array of commercial low-cost and single-type miniature metal-oxide (MOX) semiconductor gas sensors. The eNose uses 16 BME680 versatile sensor devices, each including an embedded non-selective MOX gas sensor that was originally proposed to measure the total volatile organic compounds (TVOC) in the air. This custom eNose has been used previously to detect ethanol and acetone, obtaining initial promising classification results that worsened over time because of sensor drift. The current paper assesses the over time performance of different classification methods applied to process the information gathered from the eNose. The best classification results have been obtained when applying a linear discriminant analysis (LDA) to the normalized conductance of the sensing layer of the 16 MOX gas sensors available in the eNose. The LDA procedure by itself has reduced the influence of drift in the classification performance of this single-type eNose during an evaluation period of three months.

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Francioso, Luca, Pasquale Creti, Maria Concetta Martucci, Simonetta Capone, Antonietta Taurino, Pietro Siciliano, and Chiara De Pascali. "100 nm-Gap Fingers Dielectrophoresis Functionalized MOX Gas Sensor Array for Low Temperature VOCs Detection." Proceedings 2, no. 13 (November 13, 2018): 1027. http://dx.doi.org/10.3390/proceedings2131027.

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Present work reports the fabrication process and functional gas sensing tests of a 100 nm-gap fingers DiElectroPhoresis (DEP) functionalized MOX (Metal OXide) gas sensor array for VOCs detection at low temperature. The Internet of Things (IoT) scenario applications of the chemical sensing-enabled mobiles or connected devices are many ranging from indoor air quality to novel breath analyser for personal healthcare monitoring. However, the commercial MOX gas sensors operate at moderate temperatures (200–400 °C) [1], and this limits the mobile and wearable gadgets market penetration. Nanogap devices may represent the alternative devices with enhanced sensitivity even at low or room temperature. A nanogap electrodes MOX gas sensor array functionalized with 5 nm average size SnO2 nanocrystals with positive dielectrophoresis technique is presented. The single sensor active area is 4 × 4 µm2. The devices exhibited about 1 order of magnitude response at 100 °C to 150 ppm of acetone.

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Palacín, Jordi, Elena Rubies, Eduard Clotet, and David Martínez. "Classification of Two Volatiles Using an eNose Composed by an Array of 16 Single-Type Miniature Micro-Machined Metal-Oxide Gas Sensors." Sensors 22, no. 3 (February 1, 2022): 1120. http://dx.doi.org/10.3390/s22031120.

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The artificial replication of an olfactory system is currently an open problem. The development of a portable and low-cost artificial olfactory system, also called electronic nose or eNose, is usually based on the use of an array of different gas sensors types, sensitive to different target gases. Low-cost Metal-Oxide semiconductor (MOX) gas sensors are widely used in such arrays. MOX sensors are based on a thin layer of silicon oxide with embedded heaters that can operate at different temperature set points, which usually have the disadvantages of different volatile sensitivity in each individual sensor unit and also different crossed sensitivity to different volatiles (unspecificity). This paper presents and eNose composed by an array of 16 low-cost BME680 digital miniature sensors embedding a miniature MOX gas sensor proposed to unspecifically evaluate air quality. In this paper, the inherent variability and unspecificity that must be expected from the 16 embedded MOX gas sensors, combined with signal processing, are exploited to classify two target volatiles: ethanol and acetone. The proposed eNose reads the resistance of the sensing layer of the 16 embedded MOX gas sensors, applies PCA for dimensional reduction and k-NN for classification. The validation results have shown an instantaneous classification success higher than 94% two days after the calibration and higher than 70% two weeks after, so the majority classification of a sequence of measures has been always successful in laboratory conditions. These first validation results and the low-power consumption of the eNose (0.9 W) enables its future improvement and its use in portable and battery-operated applications.

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Ravichandran, Siddharth, Chockalingam Thiagarajan, and Ponnusamy Senthil Kumar. "pH Sensitivity Estimation in Potentiometric Metal Oxide pH Sensors Using the Principle of Invariance." International Journal of Chemical Engineering 2021 (March 12, 2021): 1–18. http://dx.doi.org/10.1155/2021/5551259.

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A numerically solvable engineering model has been proposed that predicts the sensitivity of metal oxide- (MOX-) based potentiometric pH sensors. The proposed model takes into account the microstructure and crystalline structure of the MOX material. The predicted pH sensitivities are consistent with experimental results with the difference below 6% across three MOX (RuO2, TiO2, and Ta2O5) analysed. The model distinguishes the performance of different MOX phases by the appropriate choice of surface hydroxyl site densities and dielectric constants, making it possible to estimate the performance of MOX electrodes fabricated through different high-temperature and low-temperature annealing methods. It further addresses the problem, cited by theoreticians, of independently determining the C1 inner Helmholtz capacitance parameter while applying the triple-layer model to pH sensors. This is done by varying the C1 capacitance parameter until an invariant pH sensitivity across different electrolyte ionic strengths is obtained. This invariance point identifies the C1 capacitance. The corresponding pH sensitivity is the characteristic sensitivity of MOX. The model has been applied across different types of metal oxides, namely, expensive platinum group oxides (RuO2) and cheaper nonplatinum group MOX (TiO2 and Ta2O5). High temperature annealed, RuO2 produced a high pH sensitivity of 59.1082 mV/pH, while TiO2 and Ta2O5 produced sub-Nernstian sensitivities of 30.0011 and 34.6144 mV/pH, respectively. Low temperature annealed, TiO2 and Ta2O5 produced Nernstian sensitivities of 59.1050 and 59.1081 mV/pH, respectively, illustrating the potential of using cheaper nonplatinum group MOx as alternative sensor electrode materials. Separately, the usefulness of relatively less investigated, cheap, and readily available MOX, viz. Al2O3, as the electrode material was analysed. Low-temperature-annealed Al2O3 with a Nernstian sensitivity of 59.1050 mV/pH can be considered as a potential electrode material. The proposed engineering model can be used as a preliminary prediction mechanism for choosing potentially cheaper alternative sensor electrode materials.

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Jaeschke, Carsten, Oriol Gonzalez, Marta Padilla, Kaylen Richardson, Johannes Glöckler, Jan Mitrovics, and Boris Mizaikoff. "A Novel Modular System for Breath Analysis Using Temperature Modulated MOX Sensors." Proceedings 14, no. 1 (June 19, 2019): 49. http://dx.doi.org/10.3390/proceedings2019014049.

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In this work, a new generation of gas sensing systems specially designed for breath analysis is presented. The developed system comprises a compact modular, low volume, temperature-controlled sensing chamber with three compartments that can host different sensor types. In the presented system, one compartment contains an array of 8 analog MOX sensors and the other two 10 digital MOX sensors each. Here, we test the system for the detection of low concentrations of several compounds.

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Hammer, Christof, Johannes Warmer, Stephan Maurer, Peter Kaul, Ronald Thoelen, and Norbert Jung. "A Compact 16 Channel Embedded System with High Dynamic Range Readout and Heater Management for Semiconducting Metal Oxide Gas Sensors." Electronics 9, no. 11 (November 5, 2020): 1855. http://dx.doi.org/10.3390/electronics9111855.

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The simultaneous operation of multiple different semiconducting metal oxide (MOX) gas sensors is demanding for the readout circuitry. The challenge results from the strongly varying signal intensities of the various sensor types to the target gas. While some sensors change their resistance only slightly, other types can react with a resistive change over a range of several decades. Therefore, a suitable readout circuit has to be able to capture all these resistive variations, requiring it to have a very large dynamic range. This work presents a compact embedded system that provides a full, high range input interface (readout and heater management) for MOX sensor operation. The system is modular and consists of a central mainboard that holds up to eight sensor-modules, each capable of supporting up to two MOX sensors, therefore supporting a total maximum of 16 different sensors. Its wide input range is archived using the resistance-to-time measurement method. The system is solely built with commercial off-the-shelf components and tested over a range spanning from 100 Ω to 5 GΩ (9.7 decades) with an average measurement error of 0.27% and a maximum error of 2.11%. The heater management uses a well-tested power-circuit and supports multiple modes of operation, hence enabling the system to be used in highly automated measurement applications. The experimental part of this work presents the results of an exemplary screening of 16 sensors, which was performed to evaluate the system’s performance.

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Alvarado, M., A. Romero, J. L. Ramírez, S. De la Flor, and E. Llobet. "Testing the Reliability of Flexible MOX Gas Sensors under Strain." Proceedings 14, no. 1 (June 19, 2019): 20. http://dx.doi.org/10.3390/proceedings2019014020.

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We present flexible chemo-resistive sensors based on AACVD grown tungsten trioxide (WO3) nanowires. The sensor response to gases, before and after a 50-cycle bending test, is reported. Thus, proving that reliable gas sensors, able to withstand repeated bending, have been achieved. Moreover, their integrity and durability have been tested under harsh bending conditions until break down.

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Moumen, Abderrahim, Gayan C. W. Kumarage, and Elisabetta Comini. "P-Type Metal Oxide Semiconductor Thin Films: Synthesis and Chemical Sensor Applications." Sensors 22, no. 4 (February 10, 2022): 1359. http://dx.doi.org/10.3390/s22041359.

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This review focuses on the synthesis of p-type metal-oxide (p-type MOX) semiconductor thin films, such as CuO, NiO, Co3O4, and Cr2O3, used for chemical-sensing applications. P-type MOX thin films exhibit several advantages over n-type MOX, including a higher catalytic effect, low humidity dependence, and improved recovery speed. However, the sensing performance of CuO, NiO, Co3O4, and Cr2O3 thin films is strongly related to the intrinsic physicochemical properties of the material and the thickness of these MOX thin films. The latter is heavily dependent on synthesis techniques. Many techniques used for growing p-MOX thin films are reviewed herein. Physical vapor-deposition techniques (PVD), such as magnetron sputtering, thermal evaporation, thermal oxidation, and molecular-beam epitaxial (MBE) growth were investigated, along with chemical vapor deposition (CVD). Liquid-phase routes, including sol–gel-assisted dip-and-spin coating, spray pyrolysis, and electrodeposition, are also discussed. A review of each technique, as well as factors that affect the physicochemical properties of p-type MOX thin films, such as morphology, crystallinity, defects, and grain size, is presented. The sensing mechanism describing the surface reaction of gases with MOX is also discussed. The sensing characteristics of CuO, NiO, Co3O4, and Cr2O3 thin films, including their response, sensor kinetics, stability, selectivity, and repeatability are reviewed. Different chemical compounds, including reducing gases (such as volatile organic compounds (VOCs), H2, and NH3) and oxidizing gases, such as CO2, NO2, and O3, were analyzed. Bulk doping, surface decoration, and heterostructures are some of the strategies for improving the sensing capabilities of the suggested pristine p-type MOX thin films. Future trends to overcome the challenges of p-type MOX thin-film chemical sensors are also presented.

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Samotaev, Nikolay, Konstantin Oblov, Denis Veselov, Boris Podlepetsky, Maya Etrekova, Nikolay Volkov, and Nazar Zibilyuk. "Technology of SMD MOX Gas Sensors Rapid Prototyping." Materials Science Forum 977 (February 2020): 231–37. http://dx.doi.org/10.4028/www.scientific.net/msf.977.231.

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This work discusses the design of flexible laser micromilling technology for fast prototyping of metal oxide based (MOX) gas sensors in SMD packages as an alternative to traditional silicon clean room technologies. By laser micromilling technology it is possible to fabricate custom Micro Electro Mechanical System (MEMS) microhotplate platform and also packages for MOX sensor, that gives complete solution for its integration in devices using IoT conception. The tests described in the work show the attainability of the stated results for the fabrication of microhotplates.

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Samotaev, Nikolay. "Rapid Prototyping of MOX Gas Sensors in Form-Factor of SMD Packages." Proceedings 14, no. 1 (June 19, 2019): 52. http://dx.doi.org/10.3390/proceedings2019014052.

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By laser micromilling technology it is possible to fabricate custom MEMS microhotplate platform and also SMD package for MOX sensor, that gives complete solution for integration in mobile devices-smart phones, tablets and etc. The 3D design and fabrication of MEMS microhotplates and packages products occurs simultaneously that give opportunity for ultra-fast time making unique solutions for MOX sensors (number of microhotplates, hot spot size on microhotplates, diameter holes in package cap and etc.) without looking at standard solutions (primarily the package type).

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Kim, Taejung, Seungwook Lee, Wootaek Cho, Yeong Min Kwon, Jeong Min Baik, and Heungjoo Shin. "Development of a Novel Gas-Sensing Platform Based on a Network of Metal Oxide Nanowire Junctions Formed on a Suspended Carbon Nanomesh Backbone." Sensors 21, no. 13 (July 1, 2021): 4525. http://dx.doi.org/10.3390/s21134525.

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Junction networks made of longitudinally connected metal oxide nanowires (MOx NWs) have been widely utilized in resistive-type gas sensors because the potential barrier at the NW junctions leads to improved gas sensing performances. However, conventional MOx–NW-based gas sensors exhibit limited gas access to the sensing sites and reduced utilization of the entire NW surfaces because the NW networks are grown on the substrate. This study presents a novel gas sensor platform facilitating the formation of ZnO NW junction networks in a suspended architecture by growing ZnO NWs radially on a suspended carbon mesh backbone consisting of sub-micrometer-sized wires. NW networks were densely formed in the lateral and longitudinal directions of the ZnO NWs, forming additional longitudinally connected junctions in the voids of the carbon mesh. Therefore, target gases could efficiently access the sensing sites, including the junctions and the entire surface of the ZnO NWs. Thus, the present sensor, based on a suspended network of longitudinally connected NW junctions, exhibited enhanced gas response, sensitivity, and lower limit of detection compared to sensors consisting of only laterally connected NWs. In addition, complete sensor structures consisting of a suspended carbon mesh backbone and ZnO NWs could be prepared using only batch fabrication processes such as carbon microelectromechanical systems and hydrothermal synthesis, allowing cost-effective sensor fabrication.

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Kumar, Navjot, and Rahul Prajesh. "Selectivity enhancement for metal oxide (MOX) based gas sensor using thermally modulated datasets coupled with golden section optimization and chemometric techniques." Review of Scientific Instruments 93, no. 6 (June 1, 2022): 064702. http://dx.doi.org/10.1063/5.0083061.

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The ever-increasing demand for smart sensors for internet of things applications drove the change in outlook toward smart sensor system design. This paper focuses on using low-cost gas sensors [Metal Oxide (MOX)] for detection of more than one gas, which is otherwise complex due to poor selectivity of MOX sensors. In this work, detection of two gases, namely, ammonia (NH3) and carbon monoxide (CO), using a single metal oxide (pristine tin oxide) sensor is demonstrated. Furthermore, chemometric based algorithms have been used to classify and quantify both gases. The present investigation uses the temperature modulated gas sensor response obtained at different concentrations for the mentioned gases. The golden section based optimization technique has been employed to obtain two different ranges of temperatures for both gases. After applying certain pre-processing techniques, the acquired data from the sensors were fed to various classification techniques, such as partial least squares (PLS) discriminant analysis, k-means, and soft independent modeling by class analogy, and 100% classification results were obtained. Furthermore, PLS regression (PLS-R) was used to perform quantitative analysis on the data using the optimized temperature ranges for both gases, and R2 regression coefficients, 0.999 25 for NH3 and 0.9399 for CO, were obtained. The results obtained from both the qualitative and quantitative analyses make our approach low-cost and smart to mitigate the cross-selectivity of metal oxide semiconductor based smart sensor design.

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Kočí, Michal, Alexander Kromka, Adam Bouřa, Ondrej Szabó, and Miroslav Husák. "Hydrogen-Terminated Diamond Surface as a Gas Sensor: A Comparative Study of Its Sensitivities." Sensors 21, no. 16 (August 10, 2021): 5390. http://dx.doi.org/10.3390/s21165390.

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A nanocrystalline diamond (NCD) layer is used as an active (sensing) part of a conductivity gas sensor. The properties of the sensor with an NCD with H-termination (response and time characteristic of resistance change) are measured by the same equipment with a similar setup and compared with commercial sensors, a conductivity sensor with a metal oxide (MOX) active material (resistance change), and an infrared pyroelectric sensor (output voltage change) in this study. The deposited layer structure is characterized and analyzed by Scanning Electron Microscopy (SEM) and Raman spectroscopy. Electrical properties (resistance change for conductivity sensors and output voltage change for the IR pyroelectric sensor) are examined for two types of gases, oxidizing (NO2) and reducing (NH3). The parameters of the tested sensors are compared and critically evaluated. Subsequently, differences in the gas sensing principles of these conductivity sensors, namely H-terminated NCD and SnO2, are described.

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Voss, Andreas, Rico Schroeder, Steffen Schulz, Jens Haueisen, Stefanie Vogler, Paul Horn, Andreas Stallmach, and Philipp Reuken. "Detection of Liver Dysfunction Using a Wearable Electronic Nose System Based on Semiconductor Metal Oxide Sensors." Biosensors 12, no. 2 (January 26, 2022): 70. http://dx.doi.org/10.3390/bios12020070.

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The purpose of this exploratory study was to determine whether liver dysfunction can be generally classified using a wearable electronic nose based on semiconductor metal oxide (MOx) gas sensors, and whether the extent of this dysfunction can be quantified. MOx gas sensors are attractive because of their simplicity, high sensitivity, low cost, and stability. A total of 30 participants were enrolled, 10 of them being healthy controls, 10 with compensated cirrhosis, and 10 with decompensated cirrhosis. We used three sensor modules with a total of nine different MOx layers to detect reducible, easily oxidizable, and highly oxidizable gases. The complex data analysis in the time and non-linear dynamics domains is based on the extraction of 10 features from the sensor time series of the extracted breathing gas measurement cycles. The sensitivity, specificity, and accuracy for distinguishing compensated and decompensated cirrhosis patients from healthy controls was 1.00. Patients with compensated and decompensated cirrhosis could be separated with a sensitivity of 0.90 (correctly classified decompensated cirrhosis), a specificity of 1.00 (correctly classified compensated cirrhosis), and an accuracy of 0.95. Our wearable, non-invasive system provides a promising tool to detect liver dysfunctions on a functional basis. Therefore, it could provide valuable support in preoperative examinations or for initial diagnosis by the general practitioner, as it provides non-invasive, rapid, and cost-effective analysis results.

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Shaposhnik, Aleksei, Pavel Moskalev, Alexey Zviagin, Kristina Chegereva, Stanislav Ryabtsev, Alexey Vasiliev, and Polina Shaposhnik. "Selective Gas Detection by a Single MOX-Sensor." Proceedings 1, no. 4 (August 25, 2017): 594. http://dx.doi.org/10.3390/proceedings1040594.

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Fioravanti, Ambra, Pietro Marani, Giorgio Paolo Massarotti, Stefano Lettieri, Sara Morandi, and Maria Cristina Carotta. "(Ti,Sn) Solid Solution Based Gas Sensors for New Monitoring of Hydraulic Oil Degradation." Materials 14, no. 3 (January 28, 2021): 605. http://dx.doi.org/10.3390/ma14030605.

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The proper operation of a fluid power system in terms of efficiency and reliability is directly related to the fluid state; therefore, the monitoring of fluid ageing in real time is fundamental to prevent machine failures. For this aim, an innovative methodology based on fluid vapor analysis through metal oxide (shortened: MOX) gas sensors has been developed. Two apparatuses were designed and realized: (i) a dedicated test bench to fast-age the fluid under controlled conditions; (ii) a laboratory MOX sensor system to test the headspace of the aged fluid samples. To prepare the set of MOX gas sensors suitable to detect the analytes’ concentrations in the fluid headspace, different functional materials were synthesized in the form of nanopowders, characterizing them by electron microscopy and X-ray diffraction. The powders were deposited through screen-printing technology, realizing thick-film gas sensors on which dynamical responses in the presence of the fluid headspace were obtained. It resulted that gas sensors based on solid solution TixSn1–xO2 with x = 0.9 and 0.5 offered the best responses toward the fluid headspace with lower response and recovery times. Furthermore, a decrease in the responses (for all sensors) with fluid ageing was observed.

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Gomri, S., T. Contaret, J. Seguin, K. Aguir, and M. Masmoudi. "Noise Modeling in MOX Gas Sensors." Fluctuation and Noise Letters 16, no. 02 (March 15, 2017): 1750013. http://dx.doi.org/10.1142/s0219477517500134.

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In this paper, we propose a new model of adsorption–desorption (AD) noise in chemoresistive gas sensors by taking into account the polycrystalline structure of the sensing layer and the effect of the adsorbed molecule’s density fluctuation on the grain boundary barrier height. Using Wolkenstein’s isotherm, in the case of dissociative and non-dissociative chemisorption, combined with the electroneutrality, we derive an exact expression for power density spectrum (PDS) of the AD noise generated around one grain. We show that the AD noise generated in the overall sensing layer is a combination of multi-Lorentzian components. The parameters of each Lorentzian depend on the nature of the detected gas, the grain size, and the gas concentration. Moreover, we show that, according to the sensing layer microstructure (distribution of grain sizes in the sensing layer), this combination can lead to a [Formula: see text] spectrum, and in this case the noise level of the [Formula: see text] spectrum depends on the nature of the detected gas. The noise modeling presented in this paper confirms that noise spectroscopy is a useful tool for improving the gas sensor selectivity.

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Krivetskiy, Valeriy, Matvey Andreev, and Alexander Efitorov. "Selective Detection of Hydrocarbons in Real Atmospheric Conditions by Single MOX Sensor in Temperature Modulation Mode." Proceedings 14, no. 1 (June 19, 2019): 47. http://dx.doi.org/10.3390/proceedings2019014047.

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Selective detection of hydrocarbons – methane and propane – in urban air for industrial safety properties by single metal oxide semiconductor gas sensor has been demonstrated. As sensors were fabricated on the basis of nanocrystalline SnO2 and alumina micro-hotplates. Sensor working temperature modulation has been applied during raw sensor data collection. Pre-processing of acquired data – scaling, baseline extraction and exclusion of non-valid data points has been demonstrated to be critical procedures before application of machine learning algorithms. The achieved accuracy of 86% for correct gas identification in 40-200 ppm range has been demonstrated.

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Núñez-Carmona, Estefanía, Marco Abbatangelo, and Veronica Sberveglieri. "Innovative Sensor Approach to Follow Campylobacter jejuni Development." Biosensors 9, no. 1 (January 7, 2019): 8. http://dx.doi.org/10.3390/bios9010008.

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Campylobacter spp infection affects more than 200,000 people every year in Europe and in the last four years a trend shows an increase in campylobacteriosis. The main vehicle for transmission of the bacterium is contaminated food like meat, milk, fruit and vegetables. In this study, the aim was to find characteristic volatile organic compounds (VOCs) of C. jejuni in order to detect its presence with an array of metal oxide (MOX) gas sensors. Using a starting concentration of 103 CFU/mL, VOCs were analyzed using Gas-Chromatography Mass-Spectrometry (GC-MS) with a Solid-Phase Micro Extraction (SPME) technique at the initial time (T0) and after 20 h (T20). It has been found that a Campylobacter sample at T20 is characterized by a higher number of alcohol compounds that the one at T0 and this is due to sugar fermentation. Sensor results showed the ability of the system to follow bacteria curve growth from T0 to T20 using Principal Component Analysis (PCA). In particular, this results in a decrease of ΔR/R0 value over time. For this reason, MOX sensors are a promising technology for the development of a rapid and sensitive system for C. jejuni.

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Collier-Oxandale, Ashley M., Jacob Thorson, Hannah Halliday, Jana Milford, and Michael Hannigan. "Understanding the ability of low-cost MOx sensors to quantify ambient VOCs." Atmospheric Measurement Techniques 12, no. 3 (March 5, 2019): 1441–60. http://dx.doi.org/10.5194/amt-12-1441-2019.

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Abstract. Volatile organic compounds (VOCs) present a unique challenge in air quality research given their importance to human and environmental health, and their complexity to monitor resulting from the number of possible sources and mixtures. New technologies, such as low-cost air quality sensors, have the potential to support existing air quality measurement methods by providing data in high time and spatial resolution. These higher-resolution data could provide greater insight into specific events, sources, and local variability. Furthermore, given the potential for differences in selectivities for sensors, leveraging multiple sensors in an array format may even be able to provide insight into which VOCs or types of VOCs are present. During the FRAPPE and DISCOVER-AQ monitoring campaigns, our team was able to co-locate two sensor systems, using metal oxide (MOx) VOC sensors, with a proton-transfer-reaction quadrupole mass spectrometer (PTR-QMS) providing speciated VOC data. This dataset provided the opportunity to explore the ability of sensors to estimate specific VOCs and groups of VOCs in real-world conditions, e.g., dynamic temperature and humidity. Moreover, we were able to explore the impact of changing VOC compositions on sensor performance as well as the difference in selectivities of sensors in order to consider how this could be utilized. From this analysis, it seems that systems using multiple VOC sensors are able to provide VOC estimates at ambient levels for specific VOCs or groups of VOCs. It also seems that this performance is fairly robust in changing VOC mixtures, and it was confirmed that there are consistent and useful differences in selectivities between the two MOx sensors studied. While this study was fairly limited in scope, the results suggest that there is the potential for low-cost VOC sensors to support highly resolved ambient hydrocarbon measurements. The availability of this technology could enhance research and monitoring for public health and communities impacted by air toxics, which in turn could support a better understanding of exposure and actions to reduce harmful exposure.

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Álvarez Simón, Luis Carlos, and Emmanuel Gómez Ramirez. "Circuito CMOS para el control de temperatura de sensores de gas MOX." Ingeniería Investigación y Tecnología 20, no. 3 (July 1, 2019): 1–10. http://dx.doi.org/10.22201/fi.25940732e.2019.20n3.036.

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En los últimos años, la contaminación del aire y la detección de gases nocivos se han convertido en una vertiente en la investigación. Por ello, hoy en día se han desarrollado diversos sensores capaces de detectar diferentes gases, por ejemplo, los sensores químico-resistivos y los de tipo metal-óxido-semiconductor (sensores MOX), los cuales se destacan entre otras tecnologías. Los sensores de gas MOX permiten detectar múltiples gases con una alta sensibilidad y además son compatibles con tecnologías de integración CMOS. Los sensores MOX combinan un elemento de sensado de gas y un elemento de calentamiento para la selectividad de gases. Actualmente, la modulación de la temperatura de operación es una de las técnicas más usadas para mejorar la selectividad y estabilidad de los sensores de gas MOX. En este trabajo se propone un circuito de control on/off para la modulación de la temperatura de operación de sensores MOX utilizando la resistencia del calentador para monitorear su temperatura. Este circuito permite aplicar diferentes técnicas de modulación de temperatura tales como la técnica de modulación por pulsos, la técnica de modulación por ondas periódicas y el control a diferentes niveles de la temperatura de operación para la generación de matrices virtuales de sensores mediante un solo sensor. El circuito se diseñó en una tecnología CMOS de 180nm y se simuló usando un modelo simple del sensor comercial AS-MLC de AppliedSensor. El circuito propuesto permite alcanzar exactitudes de 0.2 Ω en el valor de la resistencia del calentador, el cual, corresponde aproximadamente a un error de 1 °C en la temperatura de operación del sensor.

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Xing, Yuxin, Timothy Vincent, Marina Cole, and Julian Gardner. "Real-Time Thermal Modulation of High Bandwidth MOX Gas Sensors for Mobile Robot Applications." Sensors 19, no. 5 (March 8, 2019): 1180. http://dx.doi.org/10.3390/s19051180.

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A new signal processing technique has been developed for resistive metal oxide (MOX) gas sensors to enable high-bandwidth measurements and enhanced selectivity at PPM levels (<5 PPM VOCs). An embedded micro-heater is thermally pulsed from a temperature of 225 to 350 °C, which enables the chemical reaction kinetics of the sensing film to be extracted using a fast Fourier transform. Signal processing is performed in real-time using a low-cost microcontroller integrated into a sensor module. Three sensors, coated with SnO2, WO3 and NiO respectively, were operated and processed at the same time. This approach enables the removal of long-term baseline drift and is more resilient to changes in ambient temperature. It also greatly reduced the measurement time from ~10 s to 2 s or less. Bench-top experimental results are presented for 0 to 200 ppm of acetone, and 0 ppm to 500 ppm of ethanol. Our results demonstrate our sensor system can be used on a mobile robot for real-time gas sensing.

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Danesh, Ehsan, Richard Dudeney, Jone-Him Tsang, Chris Blackman, James Covington, Peter Smith, and John Saffell. "A Multi-MOx Sensor Approach to Measure Oxidizing and Reducing Gases." Proceedings 14, no. 1 (June 19, 2019): 50. http://dx.doi.org/10.3390/proceedings2019014050.

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Vincent, Timothy A., Yuxin Xing, Marina Cole, and Julian W. Gardner. "Thermal Modulation of a High-Bandwidth Gas Sensor Array in Real-Time for Application on a Mobile Robot." Proceedings 2, no. 13 (November 20, 2018): 858. http://dx.doi.org/10.3390/proceedings2130858.

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A new signal processing technique has been developed for resistive metal oxide (MOX) gas sensors to enable high-bandwidth measurements and enhanced selectivity at PPM levels (<50 PPM VOCs). An embedded micro-heater is thermally pulsed from 225 to 350 °C, which enables the chemical reactions in the sensor film (e.g., SnO2, WO3, NiO) to be extracted using a fast Fourier transform. Signal processing is performed in real-time using a low-cost microcontroller integrated into a sensor module. The approach enables the remove of baseline drift and is resilient to environmental temperature changes. Bench-top experimental results are presented for 50 to 200 ppm of ethanol and CO, which demonstrate our sensor system can be used within a mobile robot.

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Sun, Jianhai, Jinhua Liu, Chunxiu Liu, Wen Wang, Junhong Li, Yanni Zhang, Xiaofeng Zhu, Zhanwu Ning, and Ning Xue. "Microfabricated metal oxide array sensor based on nanosized SnO–SnO2 sensitive material." Modern Physics Letters B 32, no. 18 (June 27, 2018): 1850199. http://dx.doi.org/10.1142/s0217984918501993.

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In this work, a microfabricated metal oxide (MOX) array sensor based on nanosized SnO–SnO2 sensitive material was proposed. To maximize detection response and reduce power consumption, sensitive units supported by a multi-layer beam were suspended in center of micro reaction cell which could greatly improve thermal isolation. The sensitive units were fabricated with nanosized SnO–SnO2 sensitive material, and Au-doped sensitive material was proposed which was able to greatly increase selectivity and sensitivity of sensitive film. The results demonstrate that the sensitive unit has good specificity of benzene, and the MOX array sensor was able to detect benzene with an extremely low concentration, in which the lowest detectable concentration was less than 5 ppb.

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Graunke, Thorsten, Katrin Schmitt, and Jürgen Wöllenstein. "Organic Membranes for Selectivity Enhancement of Metal Oxide Gas Sensors." Journal of Sensors 2016 (2016): 1–22. http://dx.doi.org/10.1155/2016/2435945.

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We present the characterization of organic polyolefin and thermoplastic membranes for the enhancement of the selectivity of metal oxide (MOX) gas sensors. The experimental study is done based on theoretical considerations of the membrane characteristics. Through a broad screening of dense symmetric homo- and copolymers with different functional groups, the intrinsic properties such as the mobility or the transport of gases through the matrix were examined in detail. A subset of application-relevant gases was chosen for the experimental part of the study: H2, CH4, CO, CO2, NO2, ethanol, acetone, acetaldehyde, and water vapor. The gases have similar kinetic diameters and are therefore difficult to separate but have different functional groups and polarity. The concentration of the gases was based on the international indicative limit values (TWA, STEL). From the results, a simple relationship was to be found to estimate the permeability of various polar and nonpolar gases through gas permeation (GP) membranes. We used a broadband metal oxide gas sensor with a sensitive layer made of tin oxide with palladium catalyst (SnO2:Pd). Our aim was to develop a low-cost symmetrical dense polymer membrane to selectively detect gases with a MOX sensor.

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Qomaruddin, Cristian Fàbrega, Andreas Waag, Andris Šutka, Olga Casals, Hutomo Suryo Wasisto, and Joan Daniel Prades. "Visible Light Activated Room Temperature Gas Sensors Based on CaFe2O4 Nanopowders." Proceedings 2, no. 13 (December 4, 2018): 834. http://dx.doi.org/10.3390/proceedings2130834.

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Gas sensors based on CaFe2O4 nanopowders, which are p–type metal oxide semiconductor (MOX), have been fabricated and assessed for ethanol gas monitoring under visible light activation at room temperature. Regardless of their inferior sensitivity compared to thermally activated counterparts, the developed sensors have shown responsive sensing behavior towards ethanol vapors confirming the ability of using visible light for sensor activation. LEDs with different wavelengths (i.e., 465–590 nm) were employed. The highest sensitivity (3.7%) was reached using green LED activation that corresponds to the band gap of CaFe2O4.

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Shaposhnik, A., A. Zviagin, E. Sizask, S. Ryabtsev, A. Vasiliev, and D. Shaposhnik. "Acetone and Ethanol Selective Detection by a Single MOX-sensor." Procedia Engineering 87 (2014): 1051–54. http://dx.doi.org/10.1016/j.proeng.2014.11.343.

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Rastrello, F., P. Placidi, L. Abbati, A. Scorzoni, E. Cozzani, I. Elmi, S. Zampolli, and G. C. Cardinali. "Thermal Transient Measurements of an Ultra-Low-Power MOX Sensor." Journal of Sensors 2010 (2010): 1–8. http://dx.doi.org/10.1155/2010/493765.

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This paper describes a system for the simultaneous dynamic control and thermal characterization of the heating of an Ultra Low Power (ULP) micromachined sensor. A Pulse Width Modulated (PWM) powering system has been realized using a microcontroller to characterize the thermal behavior of a device. Objectives of the research were to analyze the relation between the time period and duty cycle of the PWM signal and the operating temperature of such ULP micromachined systems, to observe the thermal time constants of the device during the heating phase and to measure the total thermal conductance. Constant target heater resistance experiments highlighted that an approximately constant heater temperature at regime can only be obtained if the time period of the heating signal is smaller than 50 s. Constant power experiments show quantitatively a thermal time constant that decreases during heating in a range from 2.3 ms to 2 ms as a function of an increasing temperature rise between the ambient and the operating temperature. Moreover, we calculated the total thermal conductance. Finally, repeatability of experimental results was assessed by guaranteeing the standard deviation of the controlled temperature which was within C in worst case conditions.

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Piedrahita, R., Y. Xiang, N. Masson, J. Ortega, A. Collier, Y. Jiang, K. Li, et al. "The next generation of low-cost personal air quality sensors for quantitative exposure monitoring." Atmospheric Measurement Techniques 7, no. 10 (October 7, 2014): 3325–36. http://dx.doi.org/10.5194/amt-7-3325-2014.

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Abstract. Advances in embedded systems and low-cost gas sensors are enabling a new wave of low-cost air quality monitoring tools. Our team has been engaged in the development of low-cost, wearable, air quality monitors (M-Pods) using the Arduino platform. These M-Pods house two types of sensors – commercially available metal oxide semiconductor (MOx) sensors used to measure CO, O3, NO2, and total VOCs, and NDIR sensors used to measure CO2. The MOx sensors are low in cost and show high sensitivity near ambient levels; however they display non-linear output signals and have cross-sensitivity effects. Thus, a quantification system was developed to convert the MOx sensor signals into concentrations. We conducted two types of validation studies – first, deployments at a regulatory monitoring station in Denver, Colorado, and second, a user study. In the two deployments (at the regulatory monitoring station), M-Pod concentrations were determined using collocation calibrations and laboratory calibration techniques. M-Pods were placed near regulatory monitors to derive calibration function coefficients using the regulatory monitors as the standard. The form of the calibration function was derived based on laboratory experiments. We discuss various techniques used to estimate measurement uncertainties. The deployments revealed that collocation calibrations provide more accurate concentration estimates than laboratory calibrations. During collocation calibrations, median standard errors ranged between 4.0–6.1 ppb for O3, 6.4–8.4 ppb for NO2, 0.28–0.44 ppm for CO, and 16.8 ppm for CO2. Median signal to noise (S / N) ratios for the M-Pod sensors were higher than the regulatory instruments: for NO2, 3.6 compared to 23.4; for O3, 1.4 compared to 1.6; for CO, 1.1 compared to 10.0; and for CO2, 42.2 compared to 300–500. By contrast, lab calibrations added bias and made it difficult to cover the necessary range of environmental conditions to obtain a good calibration. A separate user study was also conducted to assess uncertainty estimates and sensor variability. In this study, 9 M-Pods were calibrated via collocation multiple times over 4 weeks, and sensor drift was analyzed, with the result being a calibration function that included baseline drift. Three pairs of M-Pods were deployed, while users individually carried the other three. The user study suggested that inter-M-Pod variability between paired units was on the same order as calibration uncertainty; however, it is difficult to make conclusions about the actual personal exposure levels due to the level of user engagement. The user study provided real-world sensor drift data, showing limited CO drift (under −0.05 ppm day−1), and higher for O3 (−2.6 to 2.0 ppb day−1), NO2 (−1.56 to 0.51 ppb day−1), and CO2 (−4.2 to 3.1 ppm day−1). Overall, the user study confirmed the utility of the M-Pod as a low-cost tool to assess personal exposure.

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Wimmer-Teubenbacher, Robert, Florentyna Sosada-Ludwikowska, Bernat Travieso, Stefan Defregger, Oeznur Tokmak, Jan Niehaus, Marco Deluca, and Anton Köck. "CuO Thin Films Functionalized with Gold Nanoparticles for Conductometric Carbon Dioxide Gas Sensing." Chemosensors 6, no. 4 (November 22, 2018): 56. http://dx.doi.org/10.3390/chemosensors6040056.

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Metal oxides (MOx) are a well-established material for gas sensing. MOx-based gas sensors are sensitive to a wide variety of gases. Furthermore, these materials can be applied for the fabrication of low-cost and -power consumption devices in mass production. The market of carbon dioxide (CO 2 ) gas sensors is mainly dominated by infra-red (IR)-based gas sensors. Only a few MOx materials show a sensitivity to CO 2 and so far, none of these materials have been integrated on CMOS platforms suitable for mass production. In this work, we report a cupric oxide (CuO) thin film-based gas sensor functionalized with gold (Au) nanoparticles, which exhibits exceptional sensitivity to CO 2 . The CuO-based gas sensors are fabricated by electron beam lithography, thermal evaporation and lift-off process to form patterned copper (Cu) structures. These structures are thermally oxidized to form a continuous CuO film. Gold nanoparticles are drop-coated on the CuO thin films to enhance their sensitivity towards CO 2 . The CuO thin films fabricated by this method are already sensitive to CO 2 ; however, the functionalization of the CuO film strongly increases the sensitivity of the base material. Compared to the pristine CuO thin film the Au functionalized CuO film shows at equal operation temperatures (300 ∘ C) an increase of sensitivity towards the same gas concentration (e.g., 2000 ppm CO 2 ) by a factor of 13. The process flow used to fabricate Au functionalized CuO gas sensors can be applied on CMOS platforms in specific post processing steps.

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Gongora, Andres, Javier Monroy, and Javier Gonzalez-Jimenez. "An Electronic Architecture for Multipurpose Artificial Noses." Journal of Sensors 2018 (2018): 1–9. http://dx.doi.org/10.1155/2018/5427693.

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This paper deals with the design of an electronic device aimed at the detection and characterization of volatile chemical substances, that is, an electronic nose (e-nose). We pursue the development of a versatile, multipurpose e-nose that can be employed for a wide variety of applications, can integrate heterogeneous sensing technologies, and can offer a mechanism to be customized for different requirements. To that end, we contribute with a fully configurable and decentralized e-nose architecture based on self-contained and intelligent sensor boards (i.e., modules). This design allows for the integration not only of heterogeneous gas sensor technologies, like MOX and AEC sensors, but also of other components, such as GPS or Bluetooth, for a total of up to 127 individual modules. We describe an implementation of a fully operative prototype as an illustrative example of its potential for sensor networks, mobile robotics, and wearable technologies, each using different combinations of sensors.

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Piedrahita, R., Y. Xiang, N. Masson, J. Ortega, A. Collier, Y. Jiang, K. Li, et al. "The next generation of low-cost personal air quality sensors for quantitative exposure monitoring." Atmospheric Measurement Techniques Discussions 7, no. 3 (March 12, 2014): 2425–57. http://dx.doi.org/10.5194/amtd-7-2425-2014.

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Abstract. Advances in embedded systems and low-cost gas sensors are enabling a new wave of low cost air quality monitoring tools. Our team has been engaged in the development of low-cost wearable air quality monitors (M-Pods) using the Arduino platform. The M-Pods use commercially available metal oxide semiconductor (MOx) sensors to measure CO, O3, NO2, and total VOCs, and NDIR sensors to measure CO2. MOx sensors are low in cost and show high sensitivity near ambient levels; however they display non-linear output signals and have cross sensitivity effects. Thus, a quantification system was developed to convert the MOx sensor signals into concentrations. Two deployments were conducted at a regulatory monitoring station in Denver, Colorado. M-Pod concentrations were determined using laboratory calibration techniques and co-location calibrations, in which we place the M-Pods near regulatory monitors to then derive calibration function coefficients using the regulatory monitors as the standard. The form of the calibration function was derived based on laboratory experiments. We discuss various techniques used to estimate measurement uncertainties. A separate user study was also conducted to assess personal exposure and M-Pod reliability. In this study, 10 M-Pods were calibrated via co-location multiple times over 4 weeks and sensor drift was analyzed with the result being a calibration function that included drift. We found that co-location calibrations perform better than laboratory calibrations. Lab calibrations suffer from bias and difficulty in covering the necessary parameter space. During co-location calibrations, median standard errors ranged between 4.0–6.1 ppb for O3, 6.4–8.4 ppb for NO2, 0.28–0.44 ppm for CO, and 16.8 ppm for CO2. Median signal to noise (S/N) ratios for the M-Pod sensors were higher for M-Pods than the regulatory instruments: for NO2, 3.6 compared to 23.4; for O3, 1.4 compared to 1.6; for CO, 1.1 compared to 10.0; and for CO2, 42.2 compared to 300–500. The user study provided trends and location-specific information on pollutants, and affected change in user behavior. The study demonstrated the utility of the M-Pod as a tool to assess personal exposure.

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Burgués, Javier, Victor Hernández, Achim Lilienthal, and Santiago Marco. "Smelling Nano Aerial Vehicle for Gas Source Localization and Mapping." Sensors 19, no. 3 (January 24, 2019): 478. http://dx.doi.org/10.3390/s19030478.

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This paper describes the development and validation of the currently smallest aerial platform with olfaction capabilities. The developed Smelling Nano Aerial Vehicle (SNAV) is based on a lightweight commercial nano-quadcopter (27 g) equipped with a custom gas sensing board that can host up to two in situ metal oxide semiconductor (MOX) gas sensors. Due to its small form-factor, the SNAV is not a hazard for humans, enabling its use in public areas or inside buildings. It can autonomously carry out gas sensing missions of hazardous environments inaccessible to terrestrial robots and bigger drones, for example searching for victims and hazardous gas leaks inside pockets that form within the wreckage of collapsed buildings in the aftermath of an earthquake or explosion. The first contribution of this work is assessing the impact of the nano-propellers on the MOX sensor signals at different distances to a gas source. A second contribution is adapting the ‘bout’ detection algorithm, proposed by Schmuker et al. (2016) to extract specific features from the derivative of the MOX sensor response, for real-time operation. The third and main contribution is the experimental validation of the SNAV for gas source localization (GSL) and mapping in a large indoor environment (160 m2) with a gas source placed in challenging positions for the drone, for example hidden in the ceiling of the room or inside a power outlet box. Two GSL strategies are compared, one based on the instantaneous gas sensor response and the other one based on the bout frequency. From the measurements collected (in motion) along a predefined sweeping path we built (in less than 3 min) a 3D map of the gas distribution and identified the most likely source location. Using the bout frequency yielded on average a higher localization accuracy than using the instantaneous gas sensor response (1.38 m versus 2.05 m error), however accurate tuning of an additional parameter (the noise threshold) is required in the former case. The main conclusion of this paper is that a nano-drone has the potential to perform gas sensing tasks in complex environments.

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Gomri, S., J. Seguin, T. Contaret, T. Fiorido, and K. Aguir. "A Noise Spectroscopy-Based Selective Gas Sensing with MOX Gas Sensors." Fluctuation and Noise Letters 17, no. 02 (May 2, 2018): 1850016. http://dx.doi.org/10.1142/s0219477518500165.

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We propose a new method for obtaining a fluctuation-enhanced sensing (FES) signature of a gas using a single metal oxide (MOX) gas micro sensor. Starting from our model of adsorption–desorption (A–D) noise previously developed, we show theoretically that the product of frequency by the power spectrum density (PSD) of the gas sensing layer resistance fluctuations often has a maximum which is characteristic of the gas. This property was experimentally confirmed in the case of the detection of NO2 and O3 using a WO3 sensing layer. This method could be useful for classifying gases. Furthermore, our noise measurements confirm our previous model showing that PSD of the A–Dnoise in MOX gas sensor is a combination of Lorentzians having a low frequency magnitude and a cut-off frequency which depends on the nature of the detected gas.

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Fioravanti, Ambra, Antonino Bonanno, Maria Cristina Carotta, Giorgio Paolo Massarotti, Sara Morandi, Nicolò Riboni, and Federica Bianchi. "Novel Methodology Based on Thick Film Gas Sensors to Monitor the Hydraulic Oil Ageing." Proceedings 2, no. 13 (December 10, 2018): 944. http://dx.doi.org/10.3390/proceedings2130944.

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A new methodology for the real time monitoring of hydraulic oil aging based on the vapor analysis using metal oxide semiconductor (MOX) gas sensors has been successfully developed. A dedicated hydraulic test bench was designed and realized to age the oil under controlled condition. Gas chromatographic analyses were performed to detect oil volatile compounds (VOCs) and their concentrations at increasing oil working time. Moreover, a laboratory sensor system have been realized to test the headspace of the same samples. Both measurements highlighted a decrease of the VOCs concentrations.

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Rossi, Maurizio, and Davide Brunelli. "Ultra Low Power MOX Sensor Reading for Natural Gas Wireless Monitoring." IEEE Sensors Journal 14, no. 10 (October 2014): 3433–41. http://dx.doi.org/10.1109/jsen.2014.2339893.

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Thakor, Govind S., Ning Zhang, and Rafael M. Santos. "Sensing and Delineating Mixed-VOC Composition in the Air Using a Single Metal Oxide Sensor." Clean Technologies 3, no. 3 (July 13, 2021): 519–33. http://dx.doi.org/10.3390/cleantechnol3030031.

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Monitoring volatile organic compounds (VOCs) places a crucial role in environmental pollutants control and indoor air quality. In this study, a metal-oxide (MOx) sensor detector (used in a commercially available monitor) was employed to delineate the composition of air containing three common VOCs (ethanol, acetone, and hexane) under various concentrations. Experiments with a single component and double components were conducted to investigate how the solvents interact with the metal oxide sensor. The experimental results revealed that the affinity between VOC and sensor was in the following order: acetone > ethanol > n-hexane. A mathematical model was developed, based on the experimental findings and data analysis, to convert the output resistance value of the sensor into concentration values, which, in turn, can be used to calculate a VOC-based air quality index. Empirical equations were established based on inferences of vapour composition versus resistance trends, and on an approach of using original and diluted air samples to generate two sets of resistance data per sample. The calibration of numerous model parameters allowed matching simulated curves to measured data. Therefore, the predictive mathematical model enabled quantifying the total concentration of sensed VOCs, in addition to estimating the VOC composition. This first attempt to obtain semiquantitative data from a single MOx sensor, despite the remaining selectivity challenges, is aimed at expanding the capability of mobile air pollutants monitoring devices.

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Boiger, Romana, Stefan Defregger, Mirza Grbic, Anton Köck, Manfred Mücke, Robert Wimmer-Teubenbacher, and Bernat Zaragoza Travieso. "Exploring Temperature-Modulated Operation Mode of Metal Oxide Gas Sensors for Robust Signal Processing." Proceedings 2, no. 13 (February 13, 2019): 1058. http://dx.doi.org/10.3390/proceedings2131058.

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Metal oxide (MOx) gas sensor signals are mainly governed by adsorption and desorption processes of oxygen and its reaction with surrounding gas molecules. Different target gases exhibit different reaction rates leading to characteristic sensor responses for specific gas species and their concentrations. In this work, we compare temperature-modulated sensor operation (TMO) with sensor operation at a single temperature. Further, we explore if under specific TMO regimes, a simple signal processing allows for quantification of gas concentrations. We specifically investigate, if the relevant information can be captured in selected discrete wavelet coefficients. In addition, we compare the results received from this wavelet features to reaction rate evaluation features.

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48

Shaposhnik, Alexey, Pavel Moskalev, Elena Sizask, Stanislav Ryabtsev, and Alexey Vasiliev. "Selective Detection of Hydrogen Sulfide and Methane by a Single MOX-Sensor." Sensors 19, no. 5 (March 6, 2019): 1135. http://dx.doi.org/10.3390/s19051135.

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In this paper, we describe a technique for the qualitative and quantitative analysis of such gas mixtures as “hydrogen sulfide in air” and “methane in air” using temperature modulation of a single metal oxide sensor. Using regression analysis in the principal components plane (PC1, PC2), we performed a selective determination of analytes on the minimum set of their concentrations in the training set, which is essential for solving practical problems. An important feature of this work is the difference in test gas concentrations from their concentrations in the training set. For the qualitative analysis of gas mixtures in a wide range of concentrations, we have developed an improved method for processing arrays of multidimensional data. For this improvement, we form a Mahalanobis neighborhood for polynomial regression lines constructed from the projection of training samples for each analyte on the (PC1, PC2) plane. Using the temperature modulation mode for the metal oxide sensor allowed us to increase its response when determining hydrogen sulfide by two to four orders of magnitude compared with the constant temperature mode.

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49

Shaposhnik, Alexey, Stanislav Ryabtsev, Alexey Zviagin, Svetlana Korchagina, Natalia Meshkova, Dmitry Shaposhnik, and Alexey Vasiliev. "Selective detection of ammonia and its derivatives using MOX-sensor and microreactor." Procedia Engineering 25 (2011): 1097–100. http://dx.doi.org/10.1016/j.proeng.2011.12.270.

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50

Sharma, Dharmendra Kumar, Rama Sai Vinay Dwara, B. A. Botre, and S. A. Akbar. "Temperature control and readout circuit interface for Mox based NH3 gas sensor." Microsystem Technologies 23, no. 5 (September 16, 2016): 1575–83. http://dx.doi.org/10.1007/s00542-016-3126-6.

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Journal articles on the topic 'MOx sensor'

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