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Special Issue "Gas Sensors - 2013"

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Chemical Sensors".

Deadline for manuscript submissions: closed (30 November 2013)

Special Issue Editor

Guest Editor
Prof. Dr. Michael Tiemann

Department of Chemistry, Faculty of Science, University of Paderborn, Warburger Str. 100, D-33098 Paderborn, Germany
Website | E-Mail
Interests: porous materials; semiconducting; gas sensors; nanoparticles; in-situ studies; chemical synthesis; functional materials

Special Issue Information

Dear Colleagues,

Gas sensors continue to be a dynamic and fast-emerging field of research for both scientists and developers. Modern advances in the synthesis of functional materials and in the fabrication of smart devices open up new opportunities to create novel sensors with enhanced properties. Fundamental research, at the same time, allows us to understand the underlying principles and sensing mechanisms in greater detail. This special issue on ‘gas sensors' aims to cover all various aspects, such as (but not limited to) the preparation of functional materials and micro-fabricated systems for gas sensing, new insights in gas-sensing mechanisms, and the large number of different types of gas-sensing principles (resistive, mechanical, capacitive, etc.).

Prof. Dr. Michael Tiemann
Guest Editor

Submission

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Keywords

  • functional sensor materials
  • sensing mechanisms
  • metal oxide gas sensors
  • thin films
  • porous materials / nanostructures
  • resistive gas sensors
  • electrochemical gas sensors
  • optical gas sensors
  • thermometric gas sensors / pellistors
  • acoustic wave / crystal microbalance gas sensors
  • cantilever gas sensors
  • capacitive humidity sensors
  • field-effect gas sensors
  • microfabrication / MEMS

Published Papers (32 papers)

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Research

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Open AccessArticle Improved Algorithms for the Classification of Rough Rice Using a Bionic Electronic Nose Based on PCA and the Wilks Distribution
Sensors 2014, 14(3), 5486-5501; doi:10.3390/s140305486
Received: 11 January 2014 / Revised: 22 February 2014 / Accepted: 11 March 2014 / Published: 19 March 2014
Cited by 3 | PDF Full-text (880 KB) | HTML Full-text | XML Full-text
Abstract
Principal Component Analysis (PCA) is one of the main methods used for electronic nose pattern recognition. However, poor classification performance is common in classification and recognition when using regular PCA. This paper aims to improve the classification performance of regular PCA based on
[...] Read more.
Principal Component Analysis (PCA) is one of the main methods used for electronic nose pattern recognition. However, poor classification performance is common in classification and recognition when using regular PCA. This paper aims to improve the classification performance of regular PCA based on the existing Wilks ?-statistic (i.e., combined PCA with the Wilks distribution). The improved algorithms, which combine regular PCA with the Wilks ?-statistic, were developed after analysing the functionality and defects of PCA. Verification tests were conducted using a PEN3 electronic nose. The collected samples consisted of the volatiles of six varieties of rough rice (Zhongxiang1, Xiangwan13, Yaopingxiang, WufengyouT025, Pin 36, and Youyou122), grown in same area and season. The first two principal components used as analysis vectors cannot perform the rough rice varieties classification task based on a regular PCA. Using the improved algorithms, which combine the regular PCA with the Wilks ?-statistic, many different principal components were selected as analysis vectors. The set of data points of the Mahalanobis distance between each of the varieties of rough rice was selected to estimate the performance of the classification. The result illustrates that the rough rice varieties classification task is achieved well using the improved algorithm. A Probabilistic Neural Networks (PNN) was also established to test the effectiveness of the improved algorithms. The first two principal components (namely PC1 and PC2) and the first and fifth principal component (namely PC1 and PC5) were selected as the inputs of PNN for the classification of the six rough rice varieties. The results indicate that the classification accuracy based on the improved algorithm was improved by 6.67% compared to the results of the regular method. These results prove the effectiveness of using the Wilks ?-statistic to improve the classification accuracy of the regular PCA approach. The results also indicate that the electronic nose provides a non-destructive and rapid classification method for rough rice. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Design and Experimentation with Sandwich Microstructure for Catalytic Combustion-Type Gas Sensors
Sensors 2014, 14(3), 5183-5197; doi:10.3390/s140305183
Received: 7 November 2013 / Revised: 16 February 2014 / Accepted: 25 February 2014 / Published: 12 March 2014
Cited by 1 | PDF Full-text (517 KB) | HTML Full-text | XML Full-text
Abstract
The traditional handmade catalytic combustion gas sensor has some problems such as a pairing difficulty, poor consistency, high power consumption, and not being interchangeable. To address these issues, integrated double catalytic combustion of alcohol gas sensor was designed and manufactured using silicon micro-electro-mechanical
[...] Read more.
The traditional handmade catalytic combustion gas sensor has some problems such as a pairing difficulty, poor consistency, high power consumption, and not being interchangeable. To address these issues, integrated double catalytic combustion of alcohol gas sensor was designed and manufactured using silicon micro-electro-mechanical systems (MEMS) technology. The temperature field of the sensor is analyzed using the ANSYS finite element analysis method. In this work, the silicon oxide-PECVD-oxidation technique is used to manufacture a SiO2-Si3N2-SiO2 microstructure carrier with a sandwich structure, while wet etching silicon is used to form a beam structure to reduce the heat consumption. Thin-film technology is adopted to manufacture the platinum-film sensitive resistance. Nano Al2O3-ZrO-ThO is coated to format the sensor carrier, and the sensitive unit is dipped in a Pt-Pd catalyst solution to form the catalytic sensitive bridge arm. Meanwhile the uncoated catalyst carrier is considered as the reference unit, realizing an integrated chip based on a micro double bridge and forming sensors. The lines of the Pt thin-film resistance have been observed with an electronic microscope. The compensation of the sensitive material carriers and compensation materials have been analyzed using an energy spectrum. The results show that the alcohol sensor can detect a volume fraction between 0 and 4,500 × 10−6 and has good linear output characteristic. The temperature ranges from −20 to +40 °C. The humidity ranges from 30% to 85% RH. The zero output of the sensor is less than ±2.0% FS. The power consumption is ≤0.2 W, and both the response and recovery time are approximately 20 s. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Membrane-Based Characterization of a Gas Component — A Transient Sensor Theory
Sensors 2014, 14(3), 4599-4617; doi:10.3390/s140304599
Received: 23 December 2013 / Revised: 22 February 2014 / Accepted: 28 February 2014 / Published: 7 March 2014
Cited by 1 | PDF Full-text (1519 KB) | HTML Full-text | XML Full-text
Abstract
Based on a multi-gas solution-diffusion problem for a dense symmetrical membrane this paper presents a transient theory of a planar, membrane-based sensor cell for measuring gas from both initial conditions: dynamic and thermodynamic equilibrium. Using this theory, the ranges for which previously developed,
[...] Read more.
Based on a multi-gas solution-diffusion problem for a dense symmetrical membrane this paper presents a transient theory of a planar, membrane-based sensor cell for measuring gas from both initial conditions: dynamic and thermodynamic equilibrium. Using this theory, the ranges for which previously developed, simpler approaches are valid will be discussed; these approaches are of vital interest for membrane-based gas sensor applications. Finally, a new theoretical approach is introduced to identify varying gas components by arranging sensor cell pairs resulting in a concentration independent gas-specific critical time. Literature data for the N2, O2, Ar, CH4, CO2, H2 and C4H10 diffusion coefficients and solubilities for a polydimethylsiloxane membrane were used to simulate gas specific sensor responses. The results demonstrate the influence of (i) the operational mode; (ii) sensor geometry and (iii) gas matrices (air, Ar) on that critical time. Based on the developed theory the case-specific suitable membrane materials can be determined and both operation and design options for these sensors can be optimized for individual applications. The results of mixing experiments for different gases (O2, CO2) in a gas matrix of air confirmed the theoretical predictions. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Challenges in the Design and Fabrication of a Lab-on-a-Chip Photoacoustic Gas Sensor
Sensors 2014, 14(1), 957-974; doi:10.3390/s140100957
Received: 15 November 2013 / Revised: 18 December 2013 / Accepted: 18 December 2013 / Published: 8 January 2014
Cited by 9 | PDF Full-text (577 KB) | HTML Full-text | XML Full-text
Abstract
The favorable downscaling behavior of photoacoustic spectroscopy has provoked in recent years a growing interest in the miniaturization of photoacoustic sensors. The individual components of the sensor, namely widely tunable quantum cascade lasers, low loss mid infrared (mid-IR) waveguides, and efficient microelectromechanical systems
[...] Read more.
The favorable downscaling behavior of photoacoustic spectroscopy has provoked in recent years a growing interest in the miniaturization of photoacoustic sensors. The individual components of the sensor, namely widely tunable quantum cascade lasers, low loss mid infrared (mid-IR) waveguides, and efficient microelectromechanical systems (MEMS) microphones are becoming available in complementary metal–oxide–semiconductor (CMOS) compatible technologies. This paves the way for the joint processes of miniaturization and full integration. Recently, a prototype microsensor has been designed by the means of a specifically designed coupled optical-acoustic model. This paper discusses the new, or more intense, challenges faced if downscaling is continued. The first limitation in miniaturization is physical: the light source modulation, which matches the increasing cell acoustic resonance frequency, must be kept much slower than the collisional relaxation process. Secondly, from the acoustic modeling point of view, one faces the limit of validity of the continuum hypothesis. Namely, at some point, velocity slip and temperature jump boundary conditions must be used, instead of the continuous boundary conditions, which are valid at the macro-scale. Finally, on the technological side, solutions exist to realize a complete lab-on-a-chip, even if it remains a demanding integration problem. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Effect of Embedded Pd Microstructures on the Flat-Band-Voltage Operation of Room Temperature ZnO-Based Liquid Petroleum Gas Sensors
Sensors 2013, 13(12), 16801-16815; doi:10.3390/s131216801
Received: 15 October 2013 / Revised: 19 November 2013 / Accepted: 25 November 2013 / Published: 5 December 2013
Cited by 7 | PDF Full-text (3098 KB) | HTML Full-text | XML Full-text
Abstract
Three methods were used to fabricate ZnO-based room temperature liquid petroleum gas (LPG) sensors having interdigitated metal-semiconductor-metal (MSM) structures. Specifically, devices with Pd Schottky contacts were fabricated with: (1) un-doped ZnO active layers; (2) Pd-doped ZnO active layers; and (3) un-doped ZnO layers
[...] Read more.
Three methods were used to fabricate ZnO-based room temperature liquid petroleum gas (LPG) sensors having interdigitated metal-semiconductor-metal (MSM) structures. Specifically, devices with Pd Schottky contacts were fabricated with: (1) un-doped ZnO active layers; (2) Pd-doped ZnO active layers; and (3) un-doped ZnO layers on top of Pd microstructure arrays. All ZnO films were grown on p-type Si(111) substrates by the sol-gel method. For devices incorporating a microstructure array, Pd islands were first grown on the substrate by thermal evaporation using a 100 μm mesh shadow mask. We have estimated the sensitivity of the sensors for applied voltage from Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle NO Detection by Pulsed Polarization of Lambda Probes–Influence of the Reference Atmosphere
Sensors 2013, 13(12), 16051-16064; doi:10.3390/s131216051
Received: 30 September 2013 / Revised: 15 November 2013 / Accepted: 15 November 2013 / Published: 26 November 2013
Cited by 1 | PDF Full-text (808 KB) | HTML Full-text | XML Full-text
Abstract
The pulsed polarization measurement technique using conventional thimble type lambda probes is suitable for low ppm NOx detection in exhaust gas applications. To evaluate the underlying sensor mechanism, the unknown influence of the reference atmosphere on the NO sensing behavior is investigated
[...] Read more.
The pulsed polarization measurement technique using conventional thimble type lambda probes is suitable for low ppm NOx detection in exhaust gas applications. To evaluate the underlying sensor mechanism, the unknown influence of the reference atmosphere on the NO sensing behavior is investigated in this study. Besides answering questions with respect to the underlying principle, this investigation can resolve the main question of whether a simplified sensor element without reference may be also suitable for NO sensing using the pulsed polarization measurement technique. With an adequate sensor setup, the reference atmosphere of the thimble type lambda probe is changed completely after a certain diffusion time. Thus, the sensor response regarding NO is compared with and without different gas atmospheres on both electrodes. It is shown that there is still a very good NO sensitivity even without reference air, although the NO response is reduced due to non-existing overlying mixed potential type voltage, which is otherwise caused by different atmospheres on both electrodes. Considering these results, we see an opportunity to simplify the standard NOx sensor design by omitting the reference electrode. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Theoretical Calculation of the Gas-Sensing Properties of Pt-Decorated Carbon Nanotubes
Sensors 2013, 13(11), 15159-15171; doi:10.3390/s131115159
Received: 11 August 2013 / Revised: 10 October 2013 / Accepted: 24 October 2013 / Published: 6 November 2013
Cited by 13 | PDF Full-text (890 KB) | HTML Full-text | XML Full-text
Abstract
The gas-sensing properties of Pt-decorated carbon nanotubes (CNTs), which provide a foundation for the fabrication of sensors, have been evaluated. In this study, we calculated the gas adsorption of Pt-decorated (8,0) single-wall CNTs (Pt-SWCNTs) with SO2, H2S, and CO
[...] Read more.
The gas-sensing properties of Pt-decorated carbon nanotubes (CNTs), which provide a foundation for the fabrication of sensors, have been evaluated. In this study, we calculated the gas adsorption of Pt-decorated (8,0) single-wall CNTs (Pt-SWCNTs) with SO2, H2S, and CO using GGA/PW91 method based on density functional theory. The adsorption energies and the changes in geometric and electronic structures after absorption were comprehensively analyzed to estimate the responses of Pt-SWCNTs. Results indicated that Pt-SWCNTs can respond to the three gases. The electrical characteristics of Pt-SWCNTs show different changes after adsorption. Pt-SWCNTs donate electrons and increase the number of hole carriers after adsorbing SO2, thereby enhancing its conductivity. When H2S is adsorbed on CNTs, electrons are transferred from H2S to Pt-SWCNTs, converting Pt-SWCNTs from p-type to n-type sensors with improved conductivity. However, Pt-SWCNTs obtain electrons and show decreased conductivity when reacted with CO gas. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Harmful Gas Recognition Exploiting a CTL Sensor Array
Sensors 2013, 13(10), 13509-13520; doi:10.3390/s131013509
Received: 23 July 2013 / Revised: 4 September 2013 / Accepted: 18 September 2013 / Published: 9 October 2013
Cited by 5 | PDF Full-text (537 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a novel cataluminescence (CTL)-based sensor array consisting of nine types of catalytic materials is developed for the recognition of several harmful gases, namely carbon monoxide, acetone, chloroform and toluene. First, the experimental setup is constructed by using sensing nanomaterials, a
[...] Read more.
In this paper, a novel cataluminescence (CTL)-based sensor array consisting of nine types of catalytic materials is developed for the recognition of several harmful gases, namely carbon monoxide, acetone, chloroform and toluene. First, the experimental setup is constructed by using sensing nanomaterials, a heating plate, a pneumatic pump, a gas flow meter, a digital temperature device, a camera and a BPCL Ultra Weak Chemiluminescence Analyzer. Then, unique CTL patterns for the four types of harmful gas are obtained from the sensor array. The harmful gases are successful recognized by the PCA method. The optimal conditions are also investigated. Finally, experimental results show high sensitivity, long-term stability and good linearity of the sensor array, which combined with simplicity, make our system a promising application in this field. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Silicon Carbide-Based Hydrogen Gas Sensors for High-Temperature Applications
Sensors 2013, 13(10), 13575-13583; doi:10.3390/s131013575
Received: 1 August 2013 / Revised: 10 September 2013 / Accepted: 30 September 2013 / Published: 9 October 2013
Cited by 7 | PDF Full-text (350 KB) | HTML Full-text | XML Full-text
Abstract
We investigated SiC-based hydrogen gas sensors with metal-insulator-semiconductor (MIS) structure for high temperature process monitoring and leak detection applications in fields such as the automotive, chemical and petroleum industries. In this work, a thin tantalum oxide (Ta2O5) layer was
[...] Read more.
We investigated SiC-based hydrogen gas sensors with metal-insulator-semiconductor (MIS) structure for high temperature process monitoring and leak detection applications in fields such as the automotive, chemical and petroleum industries. In this work, a thin tantalum oxide (Ta2O5) layer was exploited with the purpose of sensitivity improvement, because tantalum oxide has good stability at high temperature with high permeability for hydrogen gas. Silicon carbide (SiC) was used as a substrate for high-temperature applications. We fabricated Pd/Ta2O5/SiC-based hydrogen gas sensors, and the dependence of their I-V characteristics and capacitance response properties on hydrogen concentrations were analyzed in the temperature range from room temperature to 500 °C. According to the results, our sensor shows promising performance for hydrogen gas detection at high temperatures. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Micro Ethanol Sensors with a Heater Fabricated Using the Commercial 0.18 μm CMOS Process
Sensors 2013, 13(10), 12760-12770; doi:10.3390/s131012760
Received: 6 August 2013 / Revised: 11 September 2013 / Accepted: 17 September 2013 / Published: 25 September 2013
Cited by 4 | PDF Full-text (981 KB) | HTML Full-text | XML Full-text
Abstract
The study investigates the fabrication and characterization of an ethanol microsensor equipped with a heater. The ethanol sensor is manufactured using the commercial 0.18 µm complementary metal oxide semiconductor (CMOS) process. The sensor consists of a sensitive film, a heater and interdigitated electrodes.
[...] Read more.
The study investigates the fabrication and characterization of an ethanol microsensor equipped with a heater. The ethanol sensor is manufactured using the commercial 0.18 µm complementary metal oxide semiconductor (CMOS) process. The sensor consists of a sensitive film, a heater and interdigitated electrodes. The sensitive film is zinc oxide prepared by the sol-gel method, and it is coated on the interdigitated electrodes. The heater is located under the interdigitated electrodes, and it is used to supply a working temperature to the sensitive film. The sensor needs a post-processing step to remove the sacrificial oxide layer, and to coat zinc oxide on the interdigitated electrodes. When the sensitive film senses ethanol gas, the resistance of the sensor generates a change. An inverting amplifier circuit is utilized to convert the resistance variation of the sensor into the output voltage. Experiments show that the sensitivity of the ethanol sensor is 0.35 mV/ppm. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Real-Time N2O Gas Detection System for Agricultural Production Using a 4.6-µm-Band Laser Source Based on a Periodically Poled LiNbO3 Ridge Waveguide
Sensors 2013, 13(8), 9999-10013; doi:10.3390/s130809999
Received: 17 June 2013 / Revised: 12 July 2013 / Accepted: 1 August 2013 / Published: 5 August 2013
Cited by 2 | PDF Full-text (595 KB) | HTML Full-text | XML Full-text
Abstract
This article describes a gas monitoring system for detecting nitrous oxide (N2O) gas using a compact mid-infrared laser source based on difference-frequency generation in a quasi-phase-matched LiNbO3 waveguide. We obtained a stable output power of 0.62 mW from a 4.6-μm-band
[...] Read more.
This article describes a gas monitoring system for detecting nitrous oxide (N2O) gas using a compact mid-infrared laser source based on difference-frequency generation in a quasi-phase-matched LiNbO3 waveguide. We obtained a stable output power of 0.62 mW from a 4.6-μm-band continuous-wave laser source operating at room temperature. This laser source enabled us to detect atmospheric N2O gas at a concentration as low as 35 parts per billion. Using this laser source, we constructed a new real-time in-situ monitoring system for detecting N2O gas emitted from potted plants. A few weeks of monitoring with the developed detection system revealed a strong relationship between nitrogen fertilization and N2O emission. This system is promising for the in-situ long-term monitoring of N2O in agricultural production, and it is also applicable to the detection of other greenhouse gases. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Metal Oxide Gas Sensor Drift Compensation Using a Dynamic Classifier Ensemble Based on Fitting
Sensors 2013, 13(7), 9160-9173; doi:10.3390/s130709160
Received: 18 April 2013 / Revised: 11 July 2013 / Accepted: 15 July 2013 / Published: 17 July 2013
Cited by 2 | PDF Full-text (242 KB) | HTML Full-text | XML Full-text
Abstract
Sensor drift is currently the most challenging problem in gas sensing. We propose a novel ensemble method with dynamic weights based on fitting (DWF) to solve the gas discrimination problem, regardless of the gas concentration, with high accuracy over extended periods of time.
[...] Read more.
Sensor drift is currently the most challenging problem in gas sensing. We propose a novel ensemble method with dynamic weights based on fitting (DWF) to solve the gas discrimination problem, regardless of the gas concentration, with high accuracy over extended periods of time. The DWF method uses a dynamic weighted combination of support vector machine (SVM) classifiers trained by the datasets that are collected at different time periods. In the testing of future datasets, the classifier weights are predicted by fitting functions, which are obtained by the proper fitting of the optimal weights during training. We compare the performance of the DWF method with that of competing methods in an experiment based on a public dataset that was compiled over a period of three years. The experimental results demonstrate that the DWF method outperforms the other methods considered. Furthermore, the DWF method can be further optimized by applying a fitting function that more closely matches the variation of the optimal weight over time. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle A Remote Sensor for Detecting Methane Based on Palladium-Decorated Single Walled Carbon Nanotubes
Sensors 2013, 13(7), 8814-8826; doi:10.3390/s130708814
Received: 27 May 2013 / Revised: 24 June 2013 / Accepted: 27 June 2013 / Published: 10 July 2013
Cited by 5 | PDF Full-text (523 KB) | HTML Full-text | XML Full-text
Abstract
The remote detection of the concentration of methane at room temperature is performed by a sensor that is configured by the combination of radio frequency identification (RFID), and functionalized carbon nanotubes (CNTs). The proposed sensor is schemed as a thin film RFID tag
[...] Read more.
The remote detection of the concentration of methane at room temperature is performed by a sensor that is configured by the combination of radio frequency identification (RFID), and functionalized carbon nanotubes (CNTs). The proposed sensor is schemed as a thin film RFID tag in a polyethylene substrate, on which a metal trace dipole, a metal trace T impedance matching networks, a 0.5 µm-CMOS RF/DC rectifier chipset and a sensor head of palladium-decorated single walled carbon nanotubes (Pd-SWCNTs) are surface mounted in cascade. The performances of the sensor are examined and described by the defined parameters of the received signal strength index (RSSI) and the comparative analog identifier (∆AID). Results validate the sensor’s ability to detect molecules of methane at room temperature, showing that the RSSI can increase 4 dB and the ∆AID can increase 3% in response to methane concentrations ranging from zero to 100 ppm. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Self-Assembled 3D ZnO Porous Structures with Exposed Reactive {0001} Facets and Their Enhanced Gas Sensitivity
Sensors 2013, 13(7), 8445-8460; doi:10.3390/s130708445
Received: 10 April 2013 / Revised: 21 May 2013 / Accepted: 19 June 2013 / Published: 2 July 2013
Cited by 21 | PDF Full-text (1315 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Complex three-dimensional structures comprised of porous ZnO plates were synthesized in a controlled fashion by hydrothermal methods. Through subtle changes to reaction conditions, the ZnO structures could be self-assembled from 20 nm thick nanosheets into grass-like and flower-like structures which led to the
[...] Read more.
Complex three-dimensional structures comprised of porous ZnO plates were synthesized in a controlled fashion by hydrothermal methods. Through subtle changes to reaction conditions, the ZnO structures could be self-assembled from 20 nm thick nanosheets into grass-like and flower-like structures which led to the exposure of high proportions of ZnO {0001} crystal facets for both these materials. The measured surface area of the flower-like and the grass, or platelet-like ZnO samples were 72.8 and 52.4 m2∙g−1, respectively. Gas sensing results demonstrated that the porous, flower-like ZnO structures exhibited enhanced sensing performance towards NO2 gas compared with either grass-like ZnO or commercially sourced ZnO nanoparticle samples. The porous, flower-like ZnO structures provided a high surface area which enhanced the ZnO gas sensor response. X-ray photoelectron spectroscopy characterization revealed that flower-like ZnO samples possessed a higher percentage of oxygen vacancies than the other ZnO sample-types, which also contributed to their excellent gas sensing performance. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
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Open AccessArticle Hydrogen Sensing with Ni-Doped TiO2 Nanotubes
Sensors 2013, 13(7), 8393-8402; doi:10.3390/s130708393
Received: 2 May 2013 / Revised: 19 June 2013 / Accepted: 24 June 2013 / Published: 1 July 2013
Cited by 18 | PDF Full-text (611 KB) | HTML Full-text | XML Full-text
Abstract
Doping with other elements is one of the efficient ways to modify the physical and chemical properties of TiO2 nanomaterials. In the present work, Ni-doped TiO2 nanotubes were fabricated through anodic oxidation of NiTi alloy and further annealing treatment. The hydrogen
[...] Read more.
Doping with other elements is one of the efficient ways to modify the physical and chemical properties of TiO2 nanomaterials. In the present work, Ni-doped TiO2 nanotubes were fabricated through anodic oxidation of NiTi alloy and further annealing treatment. The hydrogen sensing properties of the nanotube sensor were investigated. It was found that the Ni-doped TiO2 nanotubes were sensitive to an atmosphere of 1,000 ppm hydrogen, showing a good response at both room temperature and elevated temperatures. A First-Principle simulation revealed that, in comparison with pure anatase TiO2 oxide, Ni doping in the TiO2 oxide could result in a decreased bandgap. When the oxide sensor adsorbed a certain amount of hydrogen the bandgap increased and the acceptor impurity levels was generated, which resulted in a change of the sensor resistance. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle TREFEX: Trend Estimation and Change Detection in the Response of MOX Gas Sensors
Sensors 2013, 13(6), 7323-7344; doi:10.3390/s130607323
Received: 2 May 2013 / Revised: 27 May 2013 / Accepted: 30 May 2013 / Published: 4 June 2013
Cited by 6 | PDF Full-text (6516 KB) | HTML Full-text | XML Full-text
Abstract
Many applications of metal oxide gas sensors can benefit from reliable algorithms to detect significant changes in the sensor response. Significant changes indicate a change in the emission modality of a distant gas source and occur due to a sudden change of concentration
[...] Read more.
Many applications of metal oxide gas sensors can benefit from reliable algorithms to detect significant changes in the sensor response. Significant changes indicate a change in the emission modality of a distant gas source and occur due to a sudden change of concentration or exposure to a different compound. As a consequence of turbulent gas transport and the relatively slow response and recovery times of metal oxide sensors, their response in open sampling configuration exhibits strong fluctuations that interfere with the changes of interest. In this paper we introduce TREFEX, a novel change point detection algorithm, especially designed for metal oxide gas sensors in an open sampling system. TREFEX models the response of MOX sensors as a piecewise exponential signal and considers the junctions between consecutive exponentials as change points. We formulate non-linear trend filtering and change point detection as a parameter-free convex optimization problem for single sensors and sensor arrays. We evaluate the performance of the TREFEX algorithm experimentally for different metal oxide sensors and several gas emission profiles. A comparison with the previously proposed GLR method shows a clearly superior performance of the TREFEX algorithm both in detection performance and in estimating the change time. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Distributed Fiber Optical Sensing of Oxygen with Optical Time Domain Reflectometry
Sensors 2013, 13(6), 7170-7183; doi:10.3390/s130607170
Received: 19 February 2013 / Revised: 27 May 2013 / Accepted: 28 May 2013 / Published: 31 May 2013
Cited by 5 | PDF Full-text (662 KB) | HTML Full-text | XML Full-text
Abstract
In many biological and environmental applications spatially resolved sensing of molecular oxygen is desirable. A powerful tool for distributed measurements is optical time domain reflectometry (OTDR) which is often used in the field of telecommunications. We combine this technique with a novel optical
[...] Read more.
In many biological and environmental applications spatially resolved sensing of molecular oxygen is desirable. A powerful tool for distributed measurements is optical time domain reflectometry (OTDR) which is often used in the field of telecommunications. We combine this technique with a novel optical oxygen sensor dye, triangular-[4] phenylene (TP), immobilized in a polymer matrix. The TP luminescence decay time is 86 ns. The short decay time of the sensor dye is suitable to achieve a spatial resolution of some meters. In this paper we present the development and characterization of a reflectometer in the UV range of the electromagnetic spectrum as well as optical oxygen sensing with different fiber arrangements. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle A Compact and Low Cost Electronic Nose for Aroma Detection
Sensors 2013, 13(5), 5528-5541; doi:10.3390/s130505528
Received: 31 January 2013 / Revised: 18 April 2013 / Accepted: 19 April 2013 / Published: 25 April 2013
Cited by 14 | PDF Full-text (573 KB) | HTML Full-text | XML Full-text
Abstract
This article explains the development of a prototype of a portable and a very low-cost electronic nose based on an mbed microcontroller. Mbeds are a series of ARM microcontroller development boards designed for fast, flexible and rapid prototyping. The electronic nose is comprised
[...] Read more.
This article explains the development of a prototype of a portable and a very low-cost electronic nose based on an mbed microcontroller. Mbeds are a series of ARM microcontroller development boards designed for fast, flexible and rapid prototyping. The electronic nose is comprised of an mbed, an LCD display, two small pumps, two electro-valves and a sensor chamber with four TGS Figaro gas sensors. The performance of the electronic nose has been tested by measuring the ethanol content of wine synthetic matrices and special attention has been paid to the reproducibility and repeatability of the measurements taken on different days. Results show that the electronic nose with a neural network classifier is able to discriminate wine samples with 10, 12 and 14% V/V alcohol content with a classification error of less than 1%. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Half-Cell Potential Analysis of an Ammonia Sensor with the Electrochemical Cell Au | YSZ | Au, V2O5-WO3-TiO2
Sensors 2013, 13(4), 4760-4780; doi:10.3390/s130404760
Received: 19 March 2013 / Revised: 1 April 2013 / Accepted: 8 April 2013 / Published: 10 April 2013
Cited by 12 | PDF Full-text (753 KB) | HTML Full-text | XML Full-text
Abstract
Half-cell potentials of the electrochemical cell Au, VWT | YSZ | Au are analyzed in dependence on oxygen and ammonia concentration at 550 °C. One of the gold electrodes is covered with a porous SCR catalyst, vanadia-tungstenia-titania (VWT). The cell is utilized as a potentiometric ammonia gas sensor
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Half-cell potentials of the electrochemical cell Au, VWT | YSZ | Au are analyzed in dependence on oxygen and ammonia concentration at 550 °C. One of the gold electrodes is covered with a porous SCR catalyst, vanadia-tungstenia-titania (VWT). The cell is utilized as a potentiometric ammonia gas sensor and provides a semi-logarithmic characteristic curve with a high NH3 sensitivity and selectivity. The analyses of the Au | YSZ and Au, VWT | YSZ half-cells are conducted to describe the non-equilibrium behavior of the sensor device in light of mixed potential theory. Both electrode potentials provide a dependency on the NH3 concentration, whereby VWT, Au | YSZ shows a stronger effect which increases with increasing VWT coverage. The potential shifts in the anodic direction confirm the formation of mixed potentials at both electrodes resulting from electrochemical reactions of O2 and NH3 at the three-phase boundary. Polarization curves indicate Butler-Volmer-type kinetics. Modified polarization curves of the VWT covered electrode show an enhanced anodic reaction and an almost unaltered cathodic reaction. The NH3 dependency is dominated by the VWT coverage and it turns out that the catalytic properties of the VWT thick film are responsible for the electrode potential shift Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Improvement of H2S Sensing Properties of SnO2-Based Thick Film Gas Sensors Promoted with MoO3 and NiO
Sensors 2013, 13(3), 3889-3901; doi:10.3390/s130303889
Received: 29 January 2013 / Revised: 4 March 2013 / Accepted: 15 March 2013 / Published: 19 March 2013
Cited by 18 | PDF Full-text (837 KB) | HTML Full-text | XML Full-text
Abstract
The effects of the SnO2 pore size and metal oxide promoters on the sensing properties of SnO2-based thick film gas sensors were investigated to improve the detection of very low H2S concentrations (<1 ppm). SnO2 sensors and
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The effects of the SnO2 pore size and metal oxide promoters on the sensing properties of SnO2-based thick film gas sensors were investigated to improve the detection of very low H2S concentrations (<1 ppm). SnO2 sensors and SnO2-based thick-film gas sensors promoted with NiO, ZnO, MoO3, CuO or Fe2O3 were prepared, and their sensing properties were examined in a flow system. The SnO2 materials were prepared by calcining SnO2 at 600, 800, 1,000 and 1,200 °C to give materials identified as SnO2(600), SnO2(800), SnO2(1000), and SnO2(1200), respectively. The Sn(12)Mo5Ni3 sensor, which was prepared by physically mixing 5 wt% MoO3 (Mo5), 3 wt% NiO (Ni3) and SnO2(1200) with a large pore size of 312 nm, exhibited a high sensor response of approximately 75% for the detection of 1 ppm H2S at 350 °C with excellent recovery properties. Unlike the SnO2 sensors, its response was maintained during multiple cycles without deactivation. This was attributed to the promoter effect of MoO3. In particular, the Sn(12)Mo5Ni3 sensor developed in this study showed twice the response of the Sn(6)Mo5Ni3 sensor, which was prepared by SnO2(600) with the smaller pore size than SnO2(1200). The excellent sensor response and recovery properties of Sn(12)Mo5Ni3 are believed to be due to the combined promoter effects of MoO3 and NiO and the diffusion effect of H2S as a result of the large pore size of SnO2. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle A Zirconium Dioxide Ammonia Microsensor Integrated with a Readout Circuit Manufactured Using the 0.18 μm CMOS Process
Sensors 2013, 13(3), 3664-3674; doi:10.3390/s130303664
Received: 19 December 2012 / Revised: 19 February 2013 / Accepted: 13 March 2013 / Published: 15 March 2013
PDF Full-text (1070 KB) | HTML Full-text | XML Full-text
Abstract
The study presents an ammonia microsensor integrated with a readout circuit on-a-chip fabricated using the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process. The integrated sensor chip consists of a heater, an ammonia sensor and a readout circuit. The ammonia sensor is
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The study presents an ammonia microsensor integrated with a readout circuit on-a-chip fabricated using the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process. The integrated sensor chip consists of a heater, an ammonia sensor and a readout circuit. The ammonia sensor is constructed by a sensitive film and the interdigitated electrodes. The sensitive film is zirconium dioxide that is coated on the interdigitated electrodes. The heater is used to provide a working temperature to the sensitive film. A post-process is employed to remove the sacrificial layer and to coat zirconium dioxide on the sensor. When the sensitive film adsorbs or desorbs ammonia gas, the sensor produces a change in resistance. The readout circuit converts the resistance variation of the sensor into the output voltage. The experiments show that the integrated ammonia sensor has a sensitivity of 4.1 mV/ppm. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle CO Responses of Sensors Based on Cerium Oxide Thick Films Prepared from Clustered Spherical Nanoparticles
Sensors 2013, 13(3), 3252-3261; doi:10.3390/s130303252
Received: 24 January 2013 / Revised: 25 February 2013 / Accepted: 28 February 2013 / Published: 8 March 2013
Cited by 7 | PDF Full-text (641 KB) | HTML Full-text | XML Full-text
Abstract
Various types of CO sensors based on cerium oxide (ceria) have been reported recently. It has also been reported that the response speed of CO sensors fabricated from porous ceria thick films comprising nanoparticles is extremely high. However, the response value of such
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Various types of CO sensors based on cerium oxide (ceria) have been reported recently. It has also been reported that the response speed of CO sensors fabricated from porous ceria thick films comprising nanoparticles is extremely high. However, the response value of such sensors is not suitably high. In this study, we investigated methods of improving the response values of CO sensors based on ceria and prepared gas sensors from core-shell ceria polymer hybrid nanoparticles. These hybrid nanoparticles have been reported to have a unique structure: The core consists of a cluster of ceria crystallites several nanometers in size. We compared the characteristics of the sensors based on thick films prepared from core-shell nanoparticles with those of sensors based on thick films prepared from conventionally used precipitated nanoparticles. The sensors prepared from the core-shell nanoparticles exhibited a resistance that was ten times greater than that of the sensors prepared from the precipitated nanoparticles. The response values of the gas sensors based on the core-shell nanoparticles also was higher than that of the sensors based on the precipitated nanoparticles. Finally, improvements in sensor response were also noticed after the addition of Au nanoparticles to the thick films used to fabricate the two types of sensors. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Gas Sensors Characterization and Multilayer Perceptron (MLP) Hardware Implementation for Gas Identification Using a Field Programmable Gate Array (FPGA)
Sensors 2013, 13(3), 2967-2985; doi:10.3390/s130302967
Received: 7 January 2013 / Revised: 31 January 2013 / Accepted: 21 February 2013 / Published: 1 March 2013
Cited by 4 | PDF Full-text (1281 KB) | HTML Full-text | XML Full-text
Abstract
This paper develops a primitive gas recognition system for discriminating between industrial gas species. The system under investigation consists of an array of eight micro-hotplate-based SnO2 thin film gas sensors with different selectivity patterns. The output signals are processed through a signal
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This paper develops a primitive gas recognition system for discriminating between industrial gas species. The system under investigation consists of an array of eight micro-hotplate-based SnO2 thin film gas sensors with different selectivity patterns. The output signals are processed through a signal conditioning and analyzing system. These signals feed a decision-making classifier, which is obtained via a Field Programmable Gate Array (FPGA) with Very High-Speed Integrated Circuit Hardware Description Language. The classifier relies on a multilayer neural network based on a back propagation algorithm with one hidden layer of four neurons and eight neurons at the input and five neurons at the output. The neural network designed after implementation consists of twenty thousand gates. The achieved experimental results seem to show the effectiveness of the proposed classifier, which can discriminate between five industrial gases. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Sensing Performance of Precisely Ordered TiO2 Nanowire Gas Sensors Fabricated by Electron-Beam Lithography
Sensors 2013, 13(1), 865-874; doi:10.3390/s130100865
Received: 7 November 2012 / Revised: 5 January 2013 / Accepted: 9 January 2013 / Published: 11 January 2013
Cited by 44 | PDF Full-text (658 KB) | HTML Full-text | XML Full-text
Abstract
In this study, electron beam lithography, rather than the most popular method, chemical synthesis, is used to construct periodical TiO2 nanowires for a gas sensor with both robust and rapid performance. The effects of temperature on the sensing response and reaction time
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In this study, electron beam lithography, rather than the most popular method, chemical synthesis, is used to construct periodical TiO2 nanowires for a gas sensor with both robust and rapid performance. The effects of temperature on the sensing response and reaction time are analyzed at various operation temperatures ranging from 200 to 350 °C. At the optimized temperature of 300 °C, the proposed sensor repeatedly obtained a rise/recovery time (ΔR: 0.9 R0 to 0.1 R0) of 3.2/17.5 s and a corresponding sensor response (ΔR/R0) of 21.7% at an ethanol injection mass quantity of 0.2 μg. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle Overcoming the Slow Recovery of MOX Gas Sensors through a System Modeling Approach
Sensors 2012, 12(10), 13664-13680; doi:10.3390/s121013664
Received: 2 August 2012 / Revised: 2 October 2012 / Accepted: 5 October 2012 / Published: 11 October 2012
Cited by 18 | PDF Full-text (2676 KB) | HTML Full-text | XML Full-text
Abstract
Metal Oxide Semiconductor (MOX) gas transducers are one of the preferable technologies to build electronic noses because of their high sensitivity and low price. In this paper we present an approach to overcome to a certain extent one of their major disadvantages: their
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Metal Oxide Semiconductor (MOX) gas transducers are one of the preferable technologies to build electronic noses because of their high sensitivity and low price. In this paper we present an approach to overcome to a certain extent one of their major disadvantages: their slow recovery time (tens of seconds), which limits their suitability to applications where the sensor is exposed to rapid changes of the gas concentration. Our proposal consists of exploiting a double first-order model of the MOX-based sensor from which a steady-state output is anticipated in real time given measurements of the transient state signal. This approach assumes that the nature of the volatile is known and requires a precalibration of the system time constants for each substance, an issue that is also described in the paper. The applicability of the proposed approach is validated with several experiments in real, uncontrolled scenarios with a mobile robot bearing an e-nose. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessArticle The Effect of the Thickness of the Sensitive Layer on the Performance of the Accumulating NOx Sensor
Sensors 2012, 12(9), 12329-12346; doi:10.3390/s120912329
Received: 2 August 2012 / Revised: 28 August 2012 / Accepted: 31 August 2012 / Published: 10 September 2012
Cited by 6 | PDF Full-text (584 KB) | HTML Full-text | XML Full-text
Abstract
A novel and promising method to measure low levels of NOx utilizes the accumulating sensor principle. During an integration cycle, incoming NOx molecules are stored in a sensitive layer based on an automotive lean NOx trap (LNT) material that changes
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A novel and promising method to measure low levels of NOx utilizes the accumulating sensor principle. During an integration cycle, incoming NOx molecules are stored in a sensitive layer based on an automotive lean NOx trap (LNT) material that changes its electrical resistivity proportional to the amount of stored NOx, making the sensor suitable for long-term detection of low levels of NOx. In this study, the influence of the thickness of the sensitive layer, prepared by multiple screen-printing, is investigated. All samples show good accumulating sensing properties for both NO and NO2. In accordance to a simplified model, the base resistance of the sensitive layer and the sensitivity to NOx decrease with increasing thickness. Contrarily, the sensor response time increases. The linear measurement range of all samples ends at a sensor response of about 30% resulting in an increase of the linearly detectable amount with the thickness. Hence, the variation of the thickness of the sensitive layer is a powerful tool to adapt the linear measurement range (proportional to the thickness) as well as the sensitivity (proportional to the inverse thickness) to the application requirements. Calculations combining the sensor model with the measurement results indicate that for operation in the linear range, about 3% of the LNT material is converted to nitrate. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)

Review

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Open AccessReview Quartz-Enhanced Photoacoustic Spectroscopy: A Review
Sensors 2014, 14(4), 6165-6206; doi:10.3390/s140406165
Received: 29 November 2013 / Revised: 18 February 2014 / Accepted: 21 March 2014 / Published: 28 March 2014
Cited by 58 | PDF Full-text (1852 KB) | HTML Full-text | XML Full-text
Abstract
A detailed review on the development of quartz-enhanced photoacoustic sensors (QEPAS) for the sensitive and selective quantification of molecular trace gas species with resolved spectroscopic features is reported. The basis of the QEPAS technique, the technology available to support this field in terms
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A detailed review on the development of quartz-enhanced photoacoustic sensors (QEPAS) for the sensitive and selective quantification of molecular trace gas species with resolved spectroscopic features is reported. The basis of the QEPAS technique, the technology available to support this field in terms of key components, such as light sources and quartz-tuning forks and the recent developments in detection methods and performance limitations will be discussed. Furthermore, different experimental QEPAS methods such as: on-beam and off-beam QEPAS, quartz-enhanced evanescent wave photoacoustic detection, modulation-cancellation approach and mid-IR single mode fiber-coupled sensor systems will be reviewed and analysed. A QEPAS sensor operating in the THz range, employing a custom-made quartz-tuning fork and a THz quantum cascade laser will be also described. Finally, we evaluated data reported during the past decade and draw relevant and useful conclusions from this analysis. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
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Open AccessReview Oxygen Sensing for Industrial Safety — Evolution and New Approaches
Sensors 2014, 14(4), 6084-6103; doi:10.3390/s140406084
Received: 20 December 2013 / Revised: 20 March 2014 / Accepted: 21 March 2014 / Published: 27 March 2014
Cited by 4 | PDF Full-text (783 KB) | HTML Full-text | XML Full-text
Abstract
The requirement for the detection of oxygen in industrial safety applications has historically been met by electrochemical technologies based on the consumption of metal anodes. Products using this approach have been technically and commercially successful for more than three decades. However, a combination
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The requirement for the detection of oxygen in industrial safety applications has historically been met by electrochemical technologies based on the consumption of metal anodes. Products using this approach have been technically and commercially successful for more than three decades. However, a combination of new requirements is driving the development of alternative approaches offering fresh opportunities and challenges. This paper reviews some key aspects in the evolution of consumable anode products and highlights recent developments in alternative technologies aimed at meeting current and anticipated future needs in this important application. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessReview Pathlength Determination for Gas in Scattering Media Absorption Spectroscopy
Sensors 2014, 14(3), 3871-3890; doi:10.3390/s140303871
Received: 29 November 2013 / Revised: 19 February 2014 / Accepted: 20 February 2014 / Published: 25 February 2014
Cited by 4 | PDF Full-text (982 KB) | HTML Full-text | XML Full-text
Abstract
Gas in scattering media absorption spectroscopy (GASMAS) has been extensively studied and applied during recent years in, e.g., food packaging, human sinus monitoring, gas diffusion studies, and pharmaceutical tablet characterization. The focus has been on the evaluation of the gas absorption pathlength in
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Gas in scattering media absorption spectroscopy (GASMAS) has been extensively studied and applied during recent years in, e.g., food packaging, human sinus monitoring, gas diffusion studies, and pharmaceutical tablet characterization. The focus has been on the evaluation of the gas absorption pathlength in porous media, which a priori is unknown due to heavy light scattering. In this paper, three different approaches are summarized. One possibility is to simultaneously monitor another gas with known concentration (e.g., water vapor), the pathlength of which can then be obtained and used for the target gas (e.g., oxygen) to retrieve its concentration. The second approach is to measure the mean optical pathlength or physical pathlength with other methods, including time-of-flight spectroscopy, frequency-modulated light scattering interferometry and the frequency domain photon migration method. By utilizing these methods, an average concentration can be obtained and the porosities of the material are studied. The last method retrieves the gas concentration without knowing its pathlength by analyzing the gas absorption line shape, which depends upon the concentration of buffer gases due to intermolecular collisions. The pathlength enhancement effect due to multiple scattering enables also the use of porous media as multipass gas cells for trace gas monitoring. All these efforts open up a multitude of different applications for the GASMAS technique. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessReview Silicon Nanowire‐Based Devices for Gas-Phase Sensing
Sensors 2014, 14(1), 245-271; doi:10.3390/s140100245
Received: 4 October 2013 / Revised: 12 November 2013 / Accepted: 18 November 2013 / Published: 24 December 2013
Cited by 29 | PDF Full-text (1329 KB) | HTML Full-text | XML Full-text
Abstract
Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on
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Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
Open AccessReview TiO2 Nanotubes: Recent Advances in Synthesis and Gas Sensing Properties
Sensors 2013, 13(11), 14813-14838; doi:10.3390/s131114813
Received: 22 August 2013 / Revised: 22 October 2013 / Accepted: 25 October 2013 / Published: 31 October 2013
Cited by 50 | PDF Full-text (782 KB) | HTML Full-text | XML Full-text
Abstract
Synthesis—particularly by electrochemical anodization-, growth mechanism and chemical sensing properties of pure, doped and mixed titania tubular arrays are reviewed. The first part deals on how anodization parameters affect the size, shape and morphology of titania nanotubes. In the second part fabrication of
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Synthesis—particularly by electrochemical anodization-, growth mechanism and chemical sensing properties of pure, doped and mixed titania tubular arrays are reviewed. The first part deals on how anodization parameters affect the size, shape and morphology of titania nanotubes. In the second part fabrication of sensing devices based on titania nanotubes is presented, together with their most notable gas sensing performances. Doping largely improves conductivity and enhances gas sensing performances of TiO2 nanotubes Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
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Open AccessReview Formaldehyde Gas Sensors: A Review
Sensors 2013, 13(4), 4468-4484; doi:10.3390/s130404468
Received: 27 February 2013 / Revised: 25 March 2013 / Accepted: 26 March 2013 / Published: 2 April 2013
Cited by 38 | PDF Full-text (1128 KB) | HTML Full-text | XML Full-text
Abstract
Many methods based on spectrophotometric, fluorometric, piezoresistive, amperometric or conductive measurements have been proposed for detecting the concentration of formaldehyde in air. However, conventional formaldehyde measurement systems are bulky and expensive and require the services of highly-trained operators. Accordingly, the emergence of sophisticated
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Many methods based on spectrophotometric, fluorometric, piezoresistive, amperometric or conductive measurements have been proposed for detecting the concentration of formaldehyde in air. However, conventional formaldehyde measurement systems are bulky and expensive and require the services of highly-trained operators. Accordingly, the emergence of sophisticated technologies in recent years has prompted the development of many microscale gaseous formaldehyde detection systems. Besides their compact size, such devices have many other advantages over their macroscale counterparts, including a real-time response, a more straightforward operation, lower power consumption, and the potential for low-cost batch production. This paper commences by providing a high level overview of the formaldehyde gas sensing field and then describes some of the more significant real-time sensors presented in the literature over the past 10 years or so. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)

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