Methane Sensor Research Articles

Transformer oil-dissolved methane detection based on non-adiabatic tapered fiber using polyacrylate and cryptophane-A overlay deposition

Transformer overheating faults can lead to an increase in the transformer oil-dissolved methane content, therefore, the high-precision in-situ detection of oil-dissolved methane is significant for early-stage transformer fault diagnosis. However, traditional methods can not achieve in-situ monitoring, and there is a shortage of methane-sensitive materials. To enable high-sensitivity in-situ detection of transformer oil-dissolved methane, this paper proposed a methane sensor based on the evanescent field of the non-adiabatic tapered optical fiber (NATOF), utilizing the specific adsorption of cryptophane-A to methane. A NATOF with a waist diameter of 8.17 µm and length of 8 mm was fabricated using the melt-drawn tapering method, and a polyacrylate/cryptophane-A film was deposited on the surface of the NATOF by drip-coating method. The sensor's response to transformer oil-dissolved methane was experimentally investigated. The results showed that the sensor exhibited a detection sensitivity of 9.8 pm/ppm for transformer oil-dissolved methane, with a detection limit of 2.35 ppm. Furthermore, the sensor's excellent reversibility was validated through cyclic experiments. The sensor proposed in this paper can realize the in-situ detection of transformer oil-dissolved methane.

Tailoring the gas sensing parameters of pure ZnO sensor with addition of Ni

Methane (CH4) is a widely used gas in daily life for domestic and industrial purposes, but its inherent danger stems from a low explosive limit of 4.9 %. Without knowledge of its concentration, working with methane in confined spaces is dangerous. However, creating a methane sensor with a low detection limit is challenging due to its tetrahedral structure and limited chemical reactivity. To address this, we have synthesized pure and Ni-doped ZnO sensors using co-precipitation. These sensors are energy-efficient, operating within a voltage range of −5V to 5 V, with a rapid 16-second response time that demonstrated a maximum 39 % response for CH4. Our study introduces efficient methane sensors with significant potential in sensing technology, primed for future optimization.

Application of Semiconductor Metal Oxide in Chemiresistive Methane Gas Sensor: Recent Developments and Future Perspectives.

The application of semiconductor metal oxides in chemiresistive methane gas sensors has seen significant progress in recent years, driven by their promising sensitivity, miniaturization potential, and cost-effectiveness. This paper presents a comprehensive review of recent developments and future perspectives in this field. The main findings highlight the advancements in material science, sensor fabrication techniques, and integration methods that have led to enhanced methane-sensing capabilities. Notably, the incorporation of noble metal dopants, nanostructuring, and hybrid materials has significantly improved sensitivity and selectivity. Furthermore, innovative sensor fabrication techniques, such as thin-film deposition and screen printing, have enabled cost-effective and scalable production. The challenges and limitations facing metal oxide-based methane sensors were identified, including issues with sensitivity, selectivity, operating temperature, long-term stability, and response times. To address these challenges, advanced material science techniques were explored, leading to novel metal oxide materials with unique properties. Design improvements, such as integrated heating elements for precise temperature control, were investigated to enhance sensor stability. Additionally, data processing algorithms and machine learning methods were employed to improve selectivity and mitigate baseline drift. The recent developments in semiconductor metal oxide-based chemiresistive methane gas sensors show promising potential for practical applications. The improvements in sensitivity, selectivity, and stability achieved through material innovations and design modifications pave the way for real-world deployment. The integration of machine learning and data processing techniques further enhances the reliability and accuracy of methane detection. However, challenges remain, and future research should focus on overcoming the limitations to fully unlock the capabilities of these sensors. Green manufacturing practices should also be explored to align with increasing environmental consciousness. Overall, the advances in this field open up new opportunities for efficient methane monitoring, leak prevention, and environmental protection.

Surface-Catalyzed Zinc Oxide Nanorods and Interconnected Tetrapods as Efficient Methane Gas Sensing Platforms

Nanostructured metal oxide semiconductors have proven to be promising for the gas sensing domain. However, there are challenges associated with the fabrication of high-performance, low-to-room-temperature operation sensors for methane and other gases, including hydrogen sulfide, carbon dioxide, and ammonia. The functional properties of these semiconducting oxides can be improved by altering the morphology, crystal size, shape, and topology. Zinc oxide (ZnO) is an attractive option for gas sensing, but the need for elevated operating temperatures has limited its practical use as a commercial gas sensor. In this work, we prepared ZnO nanorod (ZnO-NR) arrays and interconnected tetrapod ZnO (T-ZnO) network sensing platforms as chemiresistive methane sensors on silicon substrates with platinum interdigitated electrodes and systematically characterized their methane sensing response in addition to their structural and physical properties. We also conducted surface modification by photochemical-catalyzed palladium, Pd, and Pd-Ag alloy nanoparticles and compared the uniformly distributed Pd decoration versus arrayed dots. The sensing performance was assessed in terms of target gas response magnitude (RM) and response percentage (R) recorded by changes in electrical resistance upon exposure to varying methane concentration (100–10,000 ppm) under thermal (operating temperatures = 175, 200, 230 °C) and optical (UV A, 365 nm illumination) excitations alongside response/recovery times, and limit of detection quantification. Thin film sensing platforms based on T-ZnO exhibited the highest response at 200 °C (RM = 2.98; R = 66.4%) compared to ZnO-NR thin films at 230 °C (RM = 1.34; R = 25.5%), attributed to the interconnected network and effective bandgap and barrier height reduction of the T-ZnO. The Pd-Ag-catalyzed and Pd dot-catalyzed T-ZnO films had the fastest response and recovery rates at 200 °C and room temperature under UV excitation, due to the localized Pd nanoparticles dots resulting in nano Schottky barrier formation, as opposed to the films coated with uniformly distributed Pd nanoparticles. The experimental findings present morphological differences, identify various mechanistic aspects, and discern chemical pathways for methane sensing.

Annealing effect on the methane sensing performance of Pt–SnO2/ZnO double layer sensor

Low power consumption is a new emerged requirement for methane sensors long-term working in a gas supervisorycontrolsystem. Great challenges remain in development of heat free methane sensors based on metal oxide semiconductors (MOS). In this work, Pt-doped SnO2 (Pt-SnO2) grow on well aligned ZnO nanorod-array to form an inter-staggered double-layer structure on AZO glass by a two-step hydrothermal method, with the annealing temperature being systematically studied. The optimized processing parameters are 1 at% Pt doping content and 700 °C annealing temperature, offering the best sensing response of 3.36 to 800 ppm CH4 at room temperature. SnO2/ZnO without Pt doping shows linear I-V relationship, while the Pt-SnO2/ZnO shows a Schottky-like I-V curve with the Schottky barrier height decreases as increasing the CH4 concentration. The activation energy (ΔEa) for CH4 dissociation decreases with increasing the annealing temperature, and the ΔEa of the optimized Pt-SnO2/ZnO sample is only one-third of that in the SnO2/ZnO. In addition to the piezoelectric polarization electric field in ZnO, the build up Schottky-like barrier and the reduced activation energy via Pt doping and annealing are demonstrated to be efficient for enhancing the methane sensing performance at low operation temperature.

Methane Sensor Based on High-Q Microsphere Whispering Gallery Mode

In this paper, the principle of the methane gas enhanced the laser absorption by the WGM of high-Q microsphere was studied. A taper optical fiber was used as a coupler to couple 1653.72 nm laser into a microsphere with a optical fiber handle to form whispering gallery mode(WGM). The resonant wavelength of the microsphere cavity was changed to 1653.72 nm by injecting heating light along the handle, so that one resonant wavelength of the microsphere is just 1653.72 nm. The 1653.72 nm laser forms WGM continuously to surround the microsphere, and the effective optical path is greatly increased, which increases the interaction distance with methane, and thus the sensitivity of methane detection is improved. The results show that the microsphere with WGM can be used as a gas sensor.

Laser photo-acoustic methane sensor (7.7 µm) for use at unmanned aerial vehicles

A compact laser photo-acoustic (PA) methane sensor based on a quantum-cascade laser (∼7.7 μm; 1750 Hz; 25 mW), a resonant differential photo-acoustic detector (PAD), and a sealed-off gas-filled PA Ref-cell has been developed. Normalization of the absorption signals in the PAD is carried out according to the absorption signals in the gas-filled PA Ref-cell, which significantly reduces the measurement errors of the methane concentration in the case of instability of the laser emission wavelength. The minimum measured background signal of the PA sensor (using high purity nitrogen) is nmin≈(26.6 ± 8.4) ppb CH4 (at a bandwidth of 20 Hz), the value of normalized noise equivalent absorption (NNEA) = 8.22 × 10–10 cm−1·W/Hz1/2. A comparison of various research groups results with mid-IR PA gas analyzers is carried out. The developed PA methane sensor is adapted for placement on the UAV’s board. Device has dimensions of 315 × 165 × 110 mm, weight ∼3.1 kg, power supply from an external source (9…60 VDC), power consumption ∼20 VA.

Optimization of the quality factor and sensitivity of one-dimensional photonic crystal methane sensor with cryptophane A cavity

In this work, we introduce a sensor for measuring different methane concentration levels. The model is based on a defective one-dimensional photonic crystal composed of alternating layers of air and Silicon with a cryptophane A cavity. We assume that the refractive index of silicon depends on temperature. The transmittance spectrum was calculated using the transfer matrix method. This work also assessed the effects of temperature and methane concentration on the wavelength shift of a localized mode within the photonic band gap. The results show the shift of this localized mode toward longer wavelengths as temperature increases, with the quality factor reaching its maximum value at around 8994.35. When maintaining a constant temperature, we observed a blue-shift when the methane concentration is in a range of 0.0–3.5%, and the quality factor decreases to 6358.26, with a maximum sensitivity of 144.485 nm by RIU. Due to its excellent performance to store energy within the cavity, this sensor can be used to detect different gas concentrations.

Applicability of Semiconductor Methane Sensors for Measuring Methane Emission from the Surface of a Water Body

Applicability of Semiconductor Methane Sensors for Measuring Methane Emission from the Surface of a Water Body

Selective methane chemiresistive detection using MWCNTs array decorated by metal organic framework layer

Methane as a main component of natural gas, but simultaneously an explosive compound with pronounced negative environmental impact. Therefore, methane should be detected with high precision and reliability. However, the inertness and non-polar nature of methane is limiting its simple detection (e.g., by a chemiresistive approach) living a gap in sensing solution. In this paper, we propose a selective chemiresistive methane sensor consisting of abundant carbon materials (multi-walled carbon nanotubes - MWCNTs) with a metal-organic framework (PCN-14). The sensor is based on decorating a non-ordered array of MWCNTs with PCN-14, which is known to have high selectivity towards methane. The methane molecules are selectively entrapped by PCN-14 pores, which significantly affect the resistance of created hybrid materials. As a result, we could detect methane under air pressure and at room temperature, with a negligible false response from other interfering gases or moisture (except hydrogen or ethane). Despite its extreme simplicity, our chemiresistive sensor does not require chemical reaction or material-destructive binding/oxidation of methane. Therefore, long operation time and sensor stability were expected and experimentally confirmed. Finally, the initial resistance of MWCNTs-PСN-14 hybrid materials was adjusted to be measurable by a portative multimeter range, which makes our approach very simple and technically undemanding.

Calibration-free near-infrared methane sensor system based on BF-QEPAS

Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) is a sensitive and selective analytical technique widely used for gas sensing. To improve the response time of the methane sensing system based on QEPAS, a Beat Frequency Quartz-Enhanced Photoacoustic Spectroscopy (BF-QEPAS) system was developed. Theoretical model based on the classical spring-mass oscillator model to explain the generation of beat-frequency signal in the quartz tuning fork (QTF) was established. The BF-QEPAS system parameters were optimized and evaluated using the developed system. The performance of the system was analyzed through Allan variance and gas calibration. Experimental results showed that the BF-QEPAS system achieved a minimum detectable limit of 28.35 ppm for methane with an integration time of 114 s. The corresponding minimum detectable normalized noise equivalent absorption (NNEA) coefficient was 1.93 × 10-9 cm-1WHz1/2, which demonstrates the excellent sensitivity of the BF-QEPAS system for methane detection.

Numerical Simulation of Catalytic Methane Combustion in Al2O3 Directional Nanotubes Modified by Pt and Pd Catalyst

“Blind holes” are the main reasons for the reduced performance of microgas sensor carriers. To improve the “blind hole” of catalytic combustion methane sensors and therefore, their thermal stability, this study presents a numerical simulation of the catalytic combustion in an Al2O3− oriented ceramic array involving porous microthermal plates. A three-visualization model of the sensor is established using the FLUENT software, and the simulation results are systematically analyzed based on the dynamics and thermodynamic mechanism of the microgas sensor. The results show that the regularity of the surface reaction presents a circular distribution, with the center line of the channel serving as the axis symmetry. The total reaction velocity in the array hole increases gradually from the inlet to the outlet. The flow velocity at the inlet should be controlled at more than 1 × 10−8 m/s, which is more accurate compared with the concept of “uniform velocity” in previous studies. The optimum pore size at the inlet should be 150 nm, and the inner pore size of the wall should be slightly higher than 300 nm, which is a more careful division compared with previous pore-size studies. The efficient reaction position is from the inlet to the quarter of the hole. The simulation results make up for the deficiencies in the analysis of the process parameters of the methane sensor carrier array hole and the internal reaction change process, as well as provide innovative comments on the sensor structure design. Through digital simulations, the limitations associated with the experiments can be avoided, the theoretical study can be improved, theoretical support can be provided for experiments related to the improvement of thermal stability, the predictability of experiments can be improved, and the feasibility of the research proposal can be verified. These steps are important for the improvement of the “blind hole” problem of catalytic combustion methane sensors.

Remarkably Enhanced Methane Sensing Performance at Room Temperature via Constructing a Self‐Assembled Mulberry‐Like ZnO/SnO2 Hierarchical Structure

Development of metal oxide semiconductors‐based methane sensors with good response and low power consumption is one of the major challenges to realize the real‐time monitoring of methane leakage. In this work, a self‐assembled mulberry‐like ZnO/SnO2 hierarchical structure is constructed by a two‐step hydrothermal method. The resultant sensor works at room temperature with excellent response of ~56.1% to 2000 ppm CH4 at 55% relative humidity. It is found that the strain induced at the ZnO/SnO2 interface greatly enhances the piezoelectric polarization on the ZnO surface and that the band bending results in the accumulation of chemically adsorbed ions close to the interface, leading to significant improvement in the sensing performance of the methane gas sensor at room temperature.

High-sensitivity photonic crystal fiber methane sensor with a ring core based on surface plasmon resonance and orbital angular momentum theory

ObjectiveWith the advent of optical fiber sensing technology, photonic crystal fiber (PCF) sensors based on surface plasmon resonance (SPR) have become a research hotspot. Herein, a PCF-SPR methane sensor with a ring-core structure is designed based on the orbital angular momentum (OAM) theory. To our best knowledge, this type of sensor has not been reported yet. MethodsThrough the finite element method, the PCF structure is designed and the appropriate filling material is selected. ResultsThe sensor consists of a three-layer clad air hole and an extra-large central gas channel, forming a ring core for beam transmission. By adding high refractive index material Amethyst and methane sensitive material to the central gas channel, the mode field is improved and the methane concentration is detected efficiently. Numerical results show that the sensor can stably transmit OAM modes and excite SPR with the OAM2,1 mode, namely the HE3,1 eigenmode. With the help of methane sensitive film, changes in methane concentration can greatly affect the refractive index distribution in PCF and alter the excitation characteristics of SPR. In the methane concentration range of 0–3.5 %, the resonance wavelength shifts from 4.52 µm to 4.58 µm. The average wavelength sensitivity reaches 17.07 nm/%, and the corresponding detection limit is 117 ppm. The results reveal that the designed PCF-SPR methane concentration sensor has excellent performance, which can stably transmit OAM mode while achieving SPR effect. It has great innovation and commercial potential in the petroleum, biomedical, chemical, and other industry.

A Flexible, Low-Cost, Miniature Methane Sensor Based on PEDOT:PSS

The development of methane sensors with high sensitivity is vital for the safe application of methane. In this work, we developed a new flexible, low cost, miniature methane sensor based on PEDOT:PSS coated screen-printed electrochemical electrodes as a resistive sensor. PEDOT:PSS is used as a sensing electrode, and the presence of methane causes a change in the resistance of the PEDOT:PSS layer. The sensor demonstrates a fast detection time of 10 s, excellent sensitivity of 0.5 pA/ppm, and a wide linear detection range of 600 to 0.8x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> ppm. The sensor shows excellent stability and reliability. The detection error is within 2.8% for a single sample, 7.1% for different samples from the same batch, 16% for different batches and different samples, 3.4% for storage for 4 days, and 14% for temperature increase to 70°C. The sensor is simple to prepare, low cost and highly flexible. We anticipate that this work could open up exciting opportunities for the development and application of methane sensors, such as natural gas exploration and identification of methane leaks in mining and kitchens.

Introduction of Level Sensor Assembly in Korea Space Launch Vehicles II

Level sensors are widely used in the aerospace field to measure the quantity of propellant. Especially, measuring the quantity of the propellant is very important in launch vehicles because the performance of launch vehicles strongly depends on the weight of the propellant. Many launch vehicles use cryogenic propellants, such as oxygen, hydrogen, and methane, and level sensors for cryogenic propellants are needed in these applications. In this study, the development process for the newly designed level sensor assembly based on a magnetostrictive level transmitter is introduced. Based on the thermal analysis, a level sensor assembly using a magnetostrictive level transmitter for cryogenic propellants was proposed. Several experimental studies have been conducted for the assembly level and the complete integrated system level to confirm the performance of the level sensor assembly. Finally, this newly designed level sensor assembly is successfully validated by flight tests of Test Launch Vehicle and Korea Space Launch Vehicle II.

Enhanced CH4 sensing performances of g-C3N4 modified ZnO nanospheres sensors under visible-light irradiation

High operating temperature, low response as well as insufficient stability are still enormous challenges faced by MOS methane sensors in practical application. An effective strategy to address these drawbacks is to use light irradiation, but the activation response of sensors operating at room temperature is unsatisfactory. Therefore, we developed an artful precipitation-calcination strategy to fabricate a series of g-C3N4 modified ZnO composites and investigated light-activated methane-sensing performance at room temperature. The material characterization results indicated that ZnO nanospheres with porous nanosheet structures were attached to the tulle-like g-C3N4 surface and the modification of g-C3N4 enhanced the light absorption ability of ZnO in the visible region, with the wavelength range of 400–520 nm. Noticeably, ZnO/g-C3N4–5 wt% (ZC-5 wt%) sensor exhibited superior sensing performance to 1000 ppm CH4 under visible light irradiation, with a response value of 6.891. The improved methane-sensing properties are most likely due to visible light irradiation and the heterojunction interface formed between the composites. Last but not least, the sensor presented excellent repeatability and stability, which will hold broad application prospects in the detection of methane.

Room-temperature methane sensors based on ZnO with different exposed facets: A combined experimental and first-principle study

Methane is a flammable and explosive gas, which is difficult to detect at room temperature. In this work, the photo-activation route was explored to realize the monitoring of methane at room temperature, and the strategy of surface morphology engineering was used to boost excellent methane gas-sensing performance. Three types of ZnO structures: rods, plates, and spheres with exposed (001) and (100) crystal facets in different ratios, were obtained using solvothermal methods. Such characteristics of samples were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption analyzer. The gas-sensing performances of sensors based on as-prepared materials were tested under UV light and in the dark. The results indicate that sensors exhibit excellent gas-sensing performances toward methane under UV light at room temperature. ZnO spheres showed a much better response of 20.577 toward 5000 ppm methane and a faster response time of 6 s compared to ZnO plates and rods. The enhanced gas sensing properties were ascribed to high-energy exposed facets and unique hollow structures. In addition, density functional theory (DFT) was investigated to support the effect of crystal facets

Study on SAW Methane Sensor Based on Cryptophane-A Composite Film

Surface Acoustic Wave (SAW) methane-sensing technology is a new way to detect methane at room temperature. However, the material and structure of the sensitive film are the important factors affecting the detection performance of the sensor. In this paper-with a SAW methane sensor using graphene-nickel cavitation-a composite film is proposed, which can work at room temperature. A delay linear dual-channel differential oscillator with center frequency of 204.3 MHz and insertion loss of -5.658 dB was designed; Cryptophane-A material was prepared by the "three-step method". The composite sensitive film was synthesized by a drop coating method, electrochemical deposition method and electroplating method. The composite film was characterized by SEM. The sensor performance test system and gas sensitivity test system were constructed to determine the response performance of the sensor at concentrations of 0~5% CH4. The results showed that the sensor had a good response recovery performance in the test concentration range, and the frequency offset was positively correlated with methane concentration. The 90% average response time and recovery times were 41.2 s and 57 s, respectively. The sensor sensitivity was 809.4 ± 6.93 Hz/(1% CH4). This study provides a good theoretical basis for the development of surface acoustic-wave methane sensors.

Highly sensitive methane detection using a mid-infrared interband cascade laser and an anti-resonant hollow-core fiber.

For over a decade hollow-core fibers have been used in optical gas sensors in the role of gas cells. However, very few examples of actual real-life applications of those sensors have been demonstrated so far. In this paper, we present a highly-sensitive hollow-core fiber based methane sensor. Mid-infrared distributed feedback interband cascade laser operating near 3.27 µm is used to detect gas inside anti-resonant hollow-core fiber. R(3) line near 3057.71 cm-1 located in ν3 band of methane is targeted. Compact, lens-free optical setup with an all-silica negative curvature hollow-core fiber as the gas cell is demonstrated. Using wavelength modulation spectroscopy and 7.5-m-long fiber the detection limit as low as 1.54 ppbv (at 20 s) is obtained. The demonstrated system is applied for a week-long continuous monitoring of ambient methane and water vapor in atmospheric air at ground level. Diurnal cycles in methane concentrations are observed, what proves the sensor's usability in environmental monitoring.