Dual Gas Sensor Research Articles

UV-triggered and temperature-control carrier transport regulation of ZnO/Ti3C2Tx MXene heterostructures for dual selective HCHO and triethylamine detection

Food safety is crucial to the health and life of every individual. Triethylamine and formaldehyde, as key indicators for assessing the freshness of seafood, are increasingly important for food safety. Consequently, this study has developed a dual-gas sensor that is easy to operate and can rapidly detect both formaldehyde and triethylamine. The ZnO-MXene based gas sensors were prepared by a two-step electrostatic adsorption method. Under irradiation with 450 nm LED light, the sensors can detect formaldehyde gas at room temperature. By adjusting the temperature, it is possible to detect 100 ppm triethylamine in the dark at 160 ℃, with a response value of 28.2, which is 5.2 times that of the pure ZnO based sensors. Additionally, it exhibits good selectivity, excellent stability, and reproducibility. This paper also provides a detailed discussion of the sensing mechanism for detecting dual gases. It is significant for the development of dual-gas or multi-gas sensors and has potential applications in food safety testing and addressing complex changes in air environments.

Near-infrared dual-gas sensor for simultaneous detection of CO and CH4 using a double spot-ring plane-concave multipass cell and a digital laser frequency stabilization system

A novel double spot-ring plane-concave multipass cell (DSPC-MPC) gas sensor was proposed for simultaneous detection of trace gases, which has lower cost and higher mirror utilization than the traditional multipass cell with 129 m, 107 m, 85 m, 63 m and 40 m effective optical path lengths adjustable. The performance of the DSPC-MPC gas sensor was evaluated by measuring CO and CH4 using two narrow linewidth distributed feedback lasers with center wavelengths of 1567 nm and 1653 nm, respectively. An adjustable digital PID laser frequency stabilization system based on LabVIEW platform was developed to continuously stabilize the laser frequency within ∼±30.3 MHz. The Allan deviation results showed that the minimum detection limits for CO and CH4 were 0.07 ppmv and 0.008 ppmv at integration times of 711 s and 245 s, respectively. The proposed concept of DSPC-MPC provides more ideas for the realization of gas detection under different absorption path lengths and the development of multi-component gas sensing systems.

A baseline correction and noise suppression method based on fitting neural network for CH4/C2H6 dual gas sensing system

We designed a methane/ethane (CH4/C2H6) dual-gas sensor on the basis of direct absorption spectroscopy (DAS) technology and explored the potential for low power consumption and miniaturization of the detection system using the effective optical range is only 25 cm for absorption cell and an uncooled photodetector. The problem of baseline drift introduced by uncooled photodetectors has been improved by using of a fitting neural network approach, and absorbance spectrum denoising has been realized. We established the mathematical relationship between absorbance and concentration for each gas of CH4/C2H6 through experimental detection, which shows strong linearity. And the correlation coefficients (R2) reached 0.99995 and 0.99998, demonstrating the robustness of the sensor. Through 3 h of measured and evaluated system, we obtained the minimum detectable column densities of 0.588 ppm⋅m and 0.128 ppm⋅m for CH4 and C2H6, respectively, which proved that the sensor has high sensitivity, strong stability, and has broad application prospects.

Dual gas sensor based on anti-resonant hollow-core fiber for detection of CO2 and CH4 with different absorption lines

The simultaneous detection of a mixture of two gases with the aid of unique and excellent capabilities of anti-resonance hollow-core fibers (AR-HCF), is numerically investigated in this article. Low-loss transmission bands in near and mid-infrared, which correspond to the transition of methane (CH[Formula: see text] and carbon dioxide (CO[Formula: see text], are considered in this work. Reasonable consideration of structural parameters has caused the low-loss transmission band covering 1.57 [Formula: see text]m and 3.33 [Formula: see text]m wavelengths. The second harmonics caused by the interaction of the laser beam and the gas sample inside the hollow core of the fiber were analyzed utilizing the fast Fourier transform (FFT) method. The maximum amplitude for the corresponding frequency at the determined concentration has reached 3002 [Formula: see text] for CH4 and 6381 [Formula: see text] for CO2. Enhancement of the inhibited coupling between the fundamental mode and some of the cladding modes and leakage loss reduction, extra capillary tubes nested inside the silica tubes forming the fiber cladding. The simulation results confirm the suitability of the proposed structure for efficient utilization in gas sensing applications for two different spectral ranges in the near and mid-infrared. Benefiting from a large hollow core, very low background noise and anti-resonance properties, high sensitivity of about 99.6% and confinement loss of 0.127 dB/m were obtained.

Dual-Gas Sensor Based on the Pt NPs/AlGaN/GaN High Electron Mobility Transistor for H and NH Gases Detection

Dual-Gas Sensor Based on the Pt NPs/AlGaN/GaN High Electron Mobility Transistor for H and NH Gases Detection<sub /> <sub />

Near-infrared wide-range dual-gas sensor system for simultaneous detection of methane and carbon monoxide in coal mine environment

To effectively monitor gas explosion and coal spontaneous combustion in coal mine, an intrinsically safe and explosion-proof dual-gas sensor system was developed for methane (CH4) and carbon monoxide (CO) measurement. A distributed feedback (DFB) laser was used to scan two adjacent absorption lines (CH4: 4284.51 cm−1, CO: 4285.01 cm−1). Two measurement ranges of 0–500 parts per million by volume (ppmv) and 0–300,000 ppmv for CH4 and 0–100 ppmv and 0–4000 ppmv for CO were realized using a ∼25 cm single-pass gas cell (SPGC) and a ∼25 m multi-pass gas cell (MPGC), respectively. A gas pre-treatment module was used to remove moisture and aerosols from gas samples. A temperature compensation algorithm was adopted to deal with ambient temperature change. Based on the Allan deviation analysis, the limit of detection (LoD) of CH4 is 0.19 ppmv and the LoD of CO is 0.12 ppmv, respectively, at an averaging time of 0.5 s. A continuous two-day CH4 measurement was performed to demonstrate the long-term stability and environmental monitoring capability. The sensor system was successfully deployed in coal mine gas analysis at Longjiapu, Changchun City, China.

Optical Dual Gas Sensor for Simultaneous Detection of Nitric Oxide and Oxygen

This work presents a new optical dual sensor based on PtTFPP-containing electrospun fibers and CsPbBr3 perovskite quantum dots (PQDs) for simultaneous detection of oxygen (O2) and nitric oxide (NO) gases, wherein PtTFPP-containing electrospun fibers for O2 sensing was based on electrospinning process fabricated by platinum(II) meso-tetrakis (pentafluorophenyl) porphyrin (PtTFPP) complex immobilized in cellulose acetate (CA) matrix. CsPbBr3 PQDs were used as NO-sensitive material and coated on the surface of PtTFPP-containing electrospun fibers. Both materials were excited by a UV LED with a central wavelength of 380 nm, and the fluorescence intensities of sensing materials were recorded and analyzed with a spectrometer. The experiment results show that the optical NO and O2 sensors have linear Stern–Volmer plots, and the sensitivities are around 2.7 and 10.7, respectively. The response and recovery times of the optical NO sensor are 71 and 109 s, respectively. For optical O2, response and recovery times are 60 and 65 s, respectively. The optical dual sensor with a new method based on fluorescent dye containing electrospun fibers and coated with CsPbBr3 PQDs has been successfully developed to detect NO and O2 gases simultaneously. The optical dual gas sensor provides great potential for practical applications with low cost and ease of fabrication.

Highly sensitive near-infrared gas sensor system using a novel H-type resonance-enhanced multi-pass photoacoustic cell

A dual-gas sensor system was developed using a H-type resonance-enhanced multi-pass photoacoustic (PA) cell. The sensitivity was improved by the double enhancement of optical path length extension and acoustic resonance. Two silver-coated concave mirrors with a reflectivity of > 95% were fabricated to form a multi-pass PA cell. The laser beam was reflected 24 times to obtain an optical path length of ∼ 3.6 m. The sensor performance was evaluated using a 1572.34 nm laser for CO2 measurement and a 1653.73 nm laser for CH4 measurement. The PA signal amplitude is enhanced by a factor of > 10. The limits of detection of CO2 and CH4 are respectively 20.83 parts per million by volume (ppmv) and 0.43 ppmv. The normalized noise equivalent absorption (NNEA) coefficients are 3.02 × 10−9 cm−1‧W‧Hz−1/2 for CO2 and 9.75 × 10−9 cm−1‧W‧Hz−1/2 for CH4. Online in-situ gas analysis in a coal mine verifies the practicability of the sensor system.

Tunable diode laser absorption spectroscopy for open-path monitoring gas markers in fire combustion products

This paper presents an open-path gas sensing technique based on tunable diode laser absorption spectroscopy (TDLAS) for simultaneously detecting multiple gas markers in fire combustion products for the purpose of early warning of fires. To demonstrate this detection method, a dual-gas sensing system was developed by combing calibration-free direct absorption spectroscopy (DAS) and a homemade three-mirror multi-pass optical system. A near-infrared (NIR) distributed feedback (DFB) diode laser emitting near 1579 nm was used as an excitation light source for simultaneously measuring dual-gas fingerprint absorption spectra of CO and CO2 in combustion products. Details of laser tuning characteristics, the cross-talk effect of CO and CO2 absorption spectra, and concentration response characteristics are initially investigated both theoretically and experimentally. Finally, various coal samples (anthracites) are used for evaluating the developed dual-gas sensor’s real-time response and combustion characteristics. The experimental results are in good agreement with the theoretical expectation, which proves its great potential for early diagnosis and warning research of fires and practical engineering applications.

Dual-Comb Gas Sensor Integrated with a Neural Network-Based Spectral Decoupling Algorithm of Overlapped Spectra for Gas Mixture Sensing.

Cross-interference among absorptions severely affects the ability to achieve accurate gas concentration retrieval through gas molecular specificity. In this study, a novel dual gas sensor was proposed to separate methane and water absorbance from the blended spectra of their mixture in the mid-infrared (MIR) band by employing a neural network algorithm. To address the scarcity of experimental data, the neural network was trained over a simulated data set constructed with the same distribution as the experimental ones. The system takes advantages of the broadband spectra to provide high-quality comb data and allows the neural network to establish an accurate spectral decoupling function. In addition, a feature absorption peak screening mechanism was proposed to achieve more accurate concentration retrieval, which avoids the prediction error introduced by interrogating the only peak of the separated spectra. The promising results of the systematic evaluation have demonstrated the feasibility of our methods in practical detections.

Photoacoustic dual-gas sensor for simultaneous detection of hydrogen and water vapor

Hydrogen (H2) is an important energy carrier, however, it can be hazardous owing to the risks involved with boring and explosion with colorless flames. By detecting the concentrations of H2 and vapor water (H2O) in real time, such risks can be prevented in advanced. In this study, a sensor system is developed based on photoacoustic spectroscopy using an H-type photoacoustic cell (PAC). Further, the time division multiplexing technique is used in a specific scanning period to realize dual-gas simultaneous detection. The dimensions of the PAC are optimized (inner volume: 1.8 cm3) and N-th characteristic frequencies are simulated through multiphysics simulation in COMSOL software. The optimized PAC is applied in the system and experiments of simultaneous dual gases detection are performed. The detection results show that the sensor's response time is 0.51 s and the recovery time is 0.38 s, and the minimal detection limit of H2 is 138.69 ppm and H2O can reach 3.70 ppm.

Dual trace gas detection using a compact two-channel multipass cell with dense and line spot patterns

A highly sensitive dual-gas sensor based on a two-channel multipass cell (MPC) was designed and developed for simultaneous detection of atmospheric methane (CH4) and carbon dioxide (CO2) by using two distributed feedback lasers emitting at 1653 nm and 2004 nm. The nondominated sorting genetic algorithm was applied to intelligently optimize the MPC configuration and accelerate the dual-gas sensor design process. A compact and novel two-channel MPC was used to achieve two optical path lengths of 27.6 m and 2.1 m in a small volume of 233 cm3. Simultaneous measurements of CH4 and CO2 in the atmosphere were performed to demonstrate the stability and robustness of the gas sensor. According to the Allan deviation analysis, the optimal detection precision for CH4 and CO2 was 4.4 ppb at an integration time of 76 s and 437.8 ppb at an integration time of 271 s, respectively. The newly developed dual-gas sensor exhibits superior characteristics of high sensitivity and stability, cost-effectiveness and simple structure, which make it well-suited for multiple trace gas sensing in various applications, including environmental monitoring, safety inspections and clinical diagnosis.

CH4/C2H6 dual gas sensing system using a single mid-infrared laser

Methane (CH4) and ethane (C2H6) dual gas sensor with low system complexity and strong stability is proposed. The correction method based on absorbance spectrum is applied, and the cross-interference of C2H6 to CH4 is eliminated. In the single gas concentration measurement, linear fitting is performed between the absorbance and concentration of CH4 and C2H6, and the correlation coefficients of R2 = 0.99959 and R2 = 0.99994 are obtained respectively, which proves that the accuracy of the dual gas sensor is robust. In the dual gas concentration measurement, we carry out continuous measurement of five mixed gases and a long-term measurement of a mixture of gases, which verifies that our sensor has the fast response speed and strong stability. The minimum detectable column densities of 0.62 ppm·m for CH4 and 0.1 ppm·m for C2H6 are achieved, respectively. The CH4/C2H6 dual gas sensor assisted by the correction method has high sensitivity and strong robustness to cross-interference, and has great potential for application in various scenarios.

Smoldering peat fire detection by time-resolved measurements of transient CO2 and CH4 emissions using a novel dual-gas optical sensor

A compact and sensitive dual-gas laser absorption sensor was developed for smoldering peat fire detection by real-time monitoring of transient CO2 and CH4 emissions from peat combustion exhaust. The sensor combines two infrared lasers to exploit CH4 and CO2 absorption lines centered at 6057.09 cm−1 and 6359.96 cm−1, respectively. Scanned-wavelength modulation spectroscopy with the second-harmonic detection (WMS-2f) and a custom-designed Herriot multipass gas cell (10.3 m path length in a 40.5 mL volume) were employed to improve detection sensitivity. The simultaneous real-time transient emissions (CH4 and CO2) were measured at an interval of 0.1 s under various smoldering peat combustion conditions in a top open cylindrical reactor. An increasing trend of CH4/CO2 ratio from 0.053 to 0.075 and the greenhouse gas (GHG) flux from 1.5 g/m2 s to 3.4 g/m2 s was observed with increasing oxygen supplies from 10 mm/s to 24 mm/s. However, a decreasing trend of CH4/CO2 ratio from 0.06 to 0.043 and GHG flux from 2.6 g/m2 s to 0.4 g/m2 s was noticed with increasing peat moisture content from 8% (dry peat) to 100%. The measurement results agree well with commercial non-dispersive infrared CO2 and CH4 analyzers which are not fast enough to capture transient emissions due to their low time response. The developed dual-gas sensor has the potential to be applied for detecting underground peatland fires and evaluating the overall GHGs emissions from smoldering wildfires due to its excellent temporal resolution, hardware simplicity, and compactness.

Dual gas sensor with innovative signal analysis based on neural network

Carbon monoxide and methane dual gas sensor with low system complexity and high stability is proposed in this study. A neural separator based on deep learning is developed to solve the cross-interference problem from the ultra-high spectral overlap between CO and CH4 molecules. A large amount of simulated overlapping spectra of different concentrations CO and CH4 are used to construct, train, tune and test the neural separator, instead of collecting data from onerous experiments. The linear fitting is performed between the predicted concentrations and preset concentrations of CH4 and CO, determination coefficients of R2 = 0.99960 and R2 = 0.99301 are achieved respectively which proves the accuracy of the dual gas sensor is robust and greatly enhanced by the neural separator. In addition, the minimum detection limits of 120.86 ppm (CH4) and 0.5 ppm (CO) are achieved in real-time simultaneous detection of CO and CH4 overlapping environment. This is a successful attempt to apply deep learning method to tunable diode laser absorption spectroscopy (TDLAS) gas sensors to solve the problem of spectral cross-interference, which provides an alternative direction for the realization of simultaneous measurement of multi-component gases.

Multi-component gas measurement aliasing spectral demodulation method for interference separation in laser absorption spectroscopy

The interference between overlapping gas absorption lines often occurs in the measurement of multi-component gas mixture with using laser absorption spectroscopy. It has become a “bottleneck” problem in many application areas. Therefore, in this paper, we take the measurement of CH4 and CO gas mixture as an example to develop a dual-gas sensor using tunable diode laser absorption spectroscopy with a novel multi-component gas measurement aliasing spectral demodulation method for interference separation. With the assistance of the above methods, the concentrations of CO and CH4 are inverted by analyzing the severely aliased second harmonic signal (2f) in the coexistence of trace CO and CH4 with high concentration. Experiments have verified that precise measurement results can be obtained, whether it is to measure individual CO or CH4, or to measure the gas mixture. Even in the presence of 1.6 × 104 ppm CH4, the measurement error of 10 ppm CO is no more than 0.9 ppm. And, the response time of this sensor for CO and CH4 detection are both ~17 s. Finally, the repeatability of this sensor is validated by continuous detection analysis, which indicates that measurement precision is 0.10 ppm for 20 ppm CO and 1.02 ppm for 200 ppm CH4, respectively. Therefore, this novel processing method avoids the shortage of low-pressure control without adding any hardware, which is more universal and convenient.

Vehicle-Deployed Off-Axis Integrated Cavity Output Spectroscopic CH4/C2H6 Sensor System for Mobile Inspection of Natural Gas Leakage.

A vehicle-deployed parts-per-billion in volume (ppbv)-level off-axis integrated cavity output spectroscopic (OA-ICOS) CH4/C2H6 sensor system was experimentally presented for mobile inspection of natural gas leakage in urban areas. For the time-division-multiplexing-based dual-gas sensor system, an antivibration 35-cm-long optical cavity with an effective path length of ∼2510 m was fabricated with a high-stability temperature and pressure control design. An Allan deviation analysis yielded a minimum detection limit of 0.2 ppbv for CH4 detection and 10 ppbv for C2H6 detection for a 1 s averaging time. A natural gas leakage source location algorithm was proposed using an improved hybrid Nelder-Mead simplex search method and a particle swarm optimization (NM-PSO) algorithm. For field industrial application, the accuracy of the sensor system and leakage source location algorithm was confirmed through a CH4/C2H6 cylinder leakage experiment on the campus. Furthermore, through natural gas pipeline network inspection measurements in urban areas, three types of leakage sources, including natural gas, biogas, and possible leakage source were respectively located and confirmed using the global positioning system and wind speed and direction measurement system, verifying the reliability and potential application of the vehicle-deployed inspection system for future natural gas pipeline leakage monitoring.

Simultaneous methane and acetylene detection using frequency-division multiplexed laser absorption spectroscopy

A dual-gas optical sensor was developed using frequency-division multiplexed (FDM) scanned-wavelength modulation spectroscopy for simultaneous detection of methane (CH4) and acetylene (C2H2). Two infrared lasers were combined to exploit C2H2 and CH4 absorption lines centered at 6539.45 cm−1 and 6057.09 cm−1, respectively. Scanned-WMS with the second-harmonic detection (WMS-2f) and a compact astigmatic multipass gas cell (36-m path length in a 0.3 L volume) were employed to improve detection sensitivity. Simultaneous dual-gas detection was realized by modulating each laser at a different frequency (5 kHz for 1529 nm and 13 kHz for 1650 nm) and software lock-in amplifiers were used to obtain the corresponding WMS-2f signals from a single photodetector. The Allan deviation analysis was performed to assess the long-term stability and minimum detection limit (MDL) of the sensor system. The MDL of 0.92 ppm for CH4 and 0.64 ppm for C2H2 was achieved at 0.02-s integration time, which can be further improved to 55 ppb for CH4 and 10 ppb for C2H2 at an optimum integration time of 10-s and 15-s, respectively. Such a dual-gas sensor has a promising potential for detecting dissolved gases (CH4 and C2H2) in transformer oil for fault diagnosis due to its high sensitivity, hardware simplicity, and fast temporal resolution.

Near-Infrared Dual-Gas Sensor System for Methane and Ethane Detection Using a Compact Multipass Cell

In this invited paper, a compact dense-pattern multipass cell-based near-infrared sensor system was demonstrated for detection of parts-per-billion in volume (ppbv)-level methane (CH4) and ethane (C2H6). The dimension size of the fabricated gas cell is 18.5 × 8 × 9 cm3 with an absorption path length of 9.39 m. CH4 measurement was realized within a spectral range of 6,046–6,048 cm−1 and an absorption line of 6,046.95 cm−1. The spectral range for C2H6 detection is 5,951–5,953 cm−1 with an absorption line of 5,951.73 cm−1. Allan deviation analysis was used for evaluating the dual-gas sensing performance, and a detection limit of 78 ppbv for CH4 and 190 ppbv for C2H6 were achieved, respectively, with an averaging time of 0.8 s. Furthermore, CH4 measurement in the indoor and outdoor atmosphere was both performed to verify the field sensing capability of the sensor system. Compared with two separate sensor systems for CH4/C2H6 sensing, the proposed dual-gas sensor system using two near-infrared lasers and one multipass cell has the advantages of low-cost, compact-size without decreasing the selectivity and sensitivity.

Mobile Vehicle Measurement of Urban Atmospheric CH4/C2H6 Using a Midinfrared Dual-Gas Sensor System Based on Interband Cascade Laser Absorption Spectroscopy

A vehicle-mounted mobile mid-infrared dual-gas sensor system for simultaneous detection of methane (CH₄) and ethane (C₂H₆) was developed using two interband cascade lasers (ICLs) for targeting the absorption line of CH₄ at 3038.5 cm^-1 and the line of C₂H₆ at 2996.88 cm^-1, respectively. Two multi-pass gas cells (MPGCs) with an absorption path length of 26.4 m were utilized. The detection limit (1&#x03C3;) of CH₄ using wavelength modulation spectroscopy (WMS) is &#x007E; 4.1 parts-per-billion by volume (ppbv) with a 0.5 s averaging time, and the detection limit (1&#x03C3;) of C₂H₆ is &#x007E; 2.9 ppbv with a 0.5 s averaging time. Vehicle-mounted mobile measurement ability of the dual-gas sensor was enabled by a remote monitoring system based on an embedded Linux processor and a cloud server. Atmospheric CH₄ and C₂H₆ monitoring was performed for 48 hours on the Jilin University campus to evaluate the performance of the sensor system. Vehicle-mounted mobile campaigns were carried out both on the Jilin University campus and in the Changchun Area for dual-gas concentration mapping. The sensor system shows the merits of remote monitoring and mobile gas sensing ability in field applications.