Methane Sensor Research Articles

The Designed MEMS Methane Sensor Based on Pulse Power Supply

As the power too high, the traditional catalytic methane sensor has high wiring cost and quantitative restriction in single circuit. In this paper, a new intelligent methane sensor aimed at low power consumption is designed by using low power MEMS catalytic methane cell, pulse supply mechanism and low power waste circuit. It is observed from the test that the new sensor has low power consumption and well performance.

Room temperature methane sensor based on single wall CNTs/SnO 2 nanoparticles

Fabrication and characterisation of a new methane sensor based on carbon nanotubes (CNTs) is proposed. The sensor uses low-cost SnO 2 nanoparticles and it can detect 0.5% of methane at room temperature. SnO 2 nanoparticles were deposited by electron beam deposition. The crystallography of CNT and SnO 2 was investigated by X-ray diffraction analysis. The presence of SnO 2 nanoparticles on CNTs was confirmed by scanning electron microscope images. The study's room temperature sensor is applicable in explosive environments like refineries. Furthermore, it is easily reversible (i.e. it can return to its initial state) in air at room temperature. Low power consumption and high sensitivity are also the other advantages of this sensor. Finally, a charge transfer mechanism is proposed to describe the sensing behaviour.

Highly Sensitive to Methane Sensor Materials Based on Nano-Pd/SnO2

Catalytic activities of nanomaterials based on tin dioxide with various palladium contents in the oxidation of CH4 and sensitivities of adsorption semiconductor sensors to methane based on them were studied. It was shown that responses of the sensors to methane are determined by the catalytic activites of the materials of their gas sensitive layers in the oxidation of CH4 by oxygen chemisorbed on active sites localized at the Pd–SnO2 interface.

Silicon microheater based low-power full-range methane sensing device

For many industrial applications of the methane sensor in a wireless node, the primary requirements are low power consumption and wide detection range. These requirements are considerably challenging as compared to the requirements related with conventional methane sensors. To meet such requirements of Internet of Things (IoT) development for methane monitoring in underground coal mines, we propose a full concentration range methane detector using a micro silicon device with low power consumption. The microheaters are fabricated with a CMOS-compatible SOI (silicon-on-insulator) MEMS (microelectromechanical system) process. Joule heating is utilized to enable micro-local high temperature for methane sensing. To obtain signals with high sensitivity and low heating power under an appropriate supplied current, a working point is determined by means of the maximum voltage variations from the voltage-current characteristics of the microheater. In general, the methane sensitivity of the micro heater increases and the power consumption decreases, as the length of the heater increases. The device has an exponential-decay response in the entire methane concentration range. A typically low power consumption around 27 mW yields an average sensitivity of approximately 20 mV/% CH4 for the methane concentration ranging from 0 to 17%.

IAMES: An inexpensive, Automated Methane Ebullition Sensor.

Atmospheric concentrations of methane have increased ∼2.4 fold since the industrial revolution with wetlands and inland waters representing the largest source of methane to the atmosphere. Substantial uncertainties remain in global methane budgets, due in part to the lack of adequate techniques and detailed measurements to assess ebullition in aquatic environments. Here, we present details of a low cost (∼$120 US per unit) ebullition sensor that autonomously logs both volumetric ebullition rate and methane concentrations. The sensor combines a traditional funnel bubble trap with an Arduino logger, a pressure sensor, thermal conductivity methane sensor, and a solenoid valve. Powered by three AA batteries, the sensor can measure autonomously for three months when programmed for a sampling frequency of 30 min. For field testing, four sensors were deployed for six weeks in a small lake. While ebullition was spatially and temporally variable, a distinct diurnal trend was observed with the highest rates from mid-morning to early afternoon. Ebullition rates were similar for all four sensors when integrated over the sampling period. The widespread deployment of low cost automated ebullition sensors such as the iAMES described here will help constrain one of the largest uncertainties in the global methane budget.

High-precision measurements of nitrous oxide and methane in air with cavity ring-down spectroscopy at 7.6 µm

Abstract. A high-sensitivity methane (CH4) and nitrous oxide (N2O) sensor based on mid-infrared continuous-wave (CW) cavity ring-down spectroscopy (CRDS) techniques was developed for environmental and biomedical trace-gas measurements. A tunable external-cavity mode-hop-free (EC-MHF) quantum cascade laser (QCL) operating at 7.4 to 7.8 µm was used as the light source. The effect of temperature fluctuation on the measurement sensitivity of the CRDS experimental setup was analyzed and corrected, and a sensitivity limit of absorption coefficient measurement of 7.2×10-10 cm−1 was achieved at 1330.50 cm−1 with an average of 139 measurements or 21 s averaging time and further improved to 2.3×10-10 cm−1 with an average of 3460 measurements, or 519 s averaging time. For the targeted CH4 and N2O, absorption lines located at 1298.60 and 1327.07 cm−1 with temperature effect correction detection limits of 13 and 11 pptv were experimentally achieved with 10.4 and 10.2 s averaging times and could be further improved to 5 and 9 pptv with 482.5 and 311 s averaging times, respectively. Four spectral bands (1298.4 to 1298.9 cm−1, 1310.1 to 1312.3 cm−1, 1326.5 to 1328 cm−1, and 1331.5 to 1333 cm−1) in the spectral range from 1295 to 1335 cm−1 were selected for the separate and simultaneous measurements of CH4 and N2O under normal atmospheric pressure, and all were in good agreements. The concentrations of CH4 and N2O of atmospheric air collected at different locations and of exhaled breath were measured and analyzed. Continuous measurements of CH4 and N2O concentrations of indoor laboratory air over 45 h were also taken. It was found that anaerobic bacteria in the water and soil of wetlands might significantly increase the CH4 concentration in the air. The measured N2O concentration in the central city area was somewhat lower than the reported normal level in open air. Our results demonstrated the temporal and spatial variations of CH4 and N2O in the air.

Low-cost quartz tuning fork based methane sensor for coal mine safety applications

This paper reports a simple but effective methane sensor based on off-the-shelf quartz tuning forks (QTFs). The operation of the sensor is based on the fact that the presence of methane will increase QTF’s resonant frequency since methane is lighter and less viscous than air. Unlike other resonant gas sensors based on the gravimetric principle, this new QTF sensor is not coated with any sensitive layer to absorb methane molecules, thus minimizing the hysteresis, reducing response and recovery time, and potentially improving long-term stability. It has been experimentally demonstrated that the presence of methane increases the resonant frequency of QTF with a sensitivity of 0.0063 Hz/1% or 0.19 ppm/1% and a detection limit of 0.025% at 0.5 Hz sampling rate. An excellent selectivity to carbon dioxide, which causes a decrease of the resonant frequency, has been illustrated. Temperature, pressure and humidity responses have been characterized. This new methane sensor is expected to meet the requirements of cost, power, size, reliability and explosion permissibility for coal mine safety applications.

Study on thermal field coupling simulation of methane sensor based on ceramic micro-hot plate

In view of the lack of high concentration online gas detection sensors in the current mine safety monitoring system to cope with gas emission and gas outburst, a design method of full-range gas sensor based on ceramic micro-hot plate is presented in this paper. COMSOL finite element simulation is used to study the thermal field coupling of sensor array units. Based on the electro-thermal coupling model, the thermal field was est ablished, and the influence of isolation groove, base material, working temperature and platinum film thickness on the thermal interference between the sensor units was studied. The results show that the heat loss is reduced by 2.57 times and the heating efficiency is improved. Compared with AlN and SiC ceramic substrates, Al2O3 has the least thermal disturbance and the best thermal performance. The average working temperature at 1.3v reaches 587.77k. The temperature difference between the units is directly proportional to the unit operating temperature. Increasing the thickness of platinum film can improve the working temperature and heating efficiency. The research provides a t heoretical basis for the design of the integrated MEMS array gas sensor.

Advances in the development of methane sensors with gas-sensing materials

The development of fast response, highly accurate methane sensor becoming an important target for their indispensable role in the detection of methane during the coal mine and natural gas transportation, supply and use. In this cut-edge review, we summarized the development of gas sensors in these years in both technology and materials aspects. We believe this review could inspire scientists, inventors, researchers and engineers in this field. The methane sensors can be divided into semiconductor resistive-type gas sensors, optical fiber gas sensors and mass-sensitive gas sensors according to their functions. For example, the typical methane gas-sensing materials can be divided into semiconductor metal oxides, nanocomposites, organic polymer composites, cryptophane-A, carbon nanotubes and their doping materials etc. Semiconductor metal oxide nanomaterials such as SnO2, ZnO, In2O3, Fe2O3, Co3O4 are the most used methane gas-sensing materials. In a certain temperature range, the resistance of the gas sensor can be changed by the adsorption and desorption of methane molecules with the surface of semiconductor metal oxide film. In order to promote the sensitivity and lower the working temperature of methane sensors with semiconductor metal oxides, noble metal nanoparticles, carbon nanotubes or graphene were doped into metal oxides to form nanocomposites. The methane sensor prepared by doped polymer composites could work at room temperature which made it more applicable in closed, flammable and explosive places. Cryptophane-A has an amazing affinity for methane. When cryptophane-A was exposed to the methane gas, the methane molecules would enter the cavity of the cryptophane-A. Furthermore, some studies have shown that CNTs doped with noble metals were sensitive to methane but remain controversial. The future challenges and opportunities in this field are also discussed in the perspective section. The exploitation of high-response, high sensitivity and selectivity methane-sensing materials which can work at room temperature remains a major challenge. The properties of methane sensors can be improved from grain size, porosity and thickness of gas-sensing materials. With the development of preparation process of gas-sensing materials and intelligent control technology, the intelligent gas sensors which could monitor many kinds of gas would be one trend in development of methane gas sensor.

High Sensitive Methane Sensor With Temperature Compensation Based on Selectively Liquid-Infiltrated Photonic Crystal Fibers

A highly sensitive and temperature-compensated methane sensor based on a liquid-infiltrated photonic crystal fiber (PCF) is proposed. Two bigger holes near the core area are coated with a methane-sensitive compound film, and specific cladding air holes are infiltrated into the liquid material to form new defective channels. The proposed sensor can achieve accurate measurement of methane concentration through temperature compensation. The sensitivity can reach to 20.07 nm/% with a high linearity as the methane concentration is within the range of 0%–3.5% by volume. The proposed methane sensor can not only improve the measurement accuracy, but also reduce the metrical difficulty and simplify the process.

Towards determining spatial methane distribution on Arctic permafrost bluffs with an unmanned aerial system

Arctic permafrost stores vast amounts of methane (CH4) in subsurface reservoirs. Thawing permafrost creates areas for this potent greenhouse gas to be released to the atmosphere. Identifying ‘hot spots’ of methane flux on a local scale has been limited by the spatial scales of traditional ground-based or satellite-based methane-sampling methods. Here we present a reliable and an easily replicable design using only off-the-shelf, cost-effective methane sensor components and an Unmanned Aerial System (UAS). Our results demonstrate the high efficiency of the design and the advantages of this methodology for environmental methane studies that are subjected to the high spatial variability of methane levels. On Barter Island, NE Alaska, we noted spikes in CH4 concentrations coincident with topographic features or anomalies. Such spikes may be attributed to enhanced land/air transfer and may reveal zones of high methane production and/or minimal oxidation in areas of thermoerosional gullies along thawing coastal zones. Thermoerosional gullies represent hotspots that release significantly higher levels of methane than the surrounding areas, thus suggesting that point sampling is inadequate in characterizing methane releases and that increasing rates of permafrost thaw may result in increasing point sources of high CH4 emissions.

An open source algorithm to detect natural gas leaks from mobile methane survey data.

The data collected by mobile methane (CH4) sensors can be used to find natural gas (NG) leaks in urban distribution systems. Extracting actionable insights from the large volumes of data collected by these sensors requires several data processing steps. While these survey platforms are commercially available, the associated data processing software largely constitute a black box due to their proprietary nature. In this paper we describe a step-by-step algorithm for developing leak indications using data from mobile CH4 surveys, providing an under-the-hood look at the choices and challenges associated with data analysis. We also describe how our algorithm has evolved over time, and the data-driven insights that have prompted these changes. Applying our algorithm to data collected in 15 cities produced more than 6100 leak indications and estimates of the leaks’ size. We use these results to characterize the distribution of leak sizes in local NG distribution systems. Mobile surveys are already an effective and necessary tool for managing NG distribution systems, but improvements in the technology and software will continue to increase its value.

Near-infrared methane sensor based on a distributed feedback laser

In this article, a near-infrared methane detection system using tunable diode laser absorption spectroscopy technology was designed and implemented. The distributed feedback laser was driven by a self-developed temperature and current controller to allow scanning the selected absorption wavelength at 1654 nm. Laser temperature fluctuation was lower than 0.01%, and the output emission wavelength was linear and stable. The emitted beam passed a reflective gas chamber and was received by the Indium Gallium Arsenide photodiode detector. Through a data acquisition card, a digital lock-in amplifier was developed to extract the second harmonics with real-time monitoring and adjustment. Based on Allan deviation analysis, the limit of detection was about 48 ppm with a path length of 30 cm, at an integration time of 6 s. The experimental results revealed a maximum detection error of less than 3% at a gas concentration higher than 100 ppm. The fluctuations rates in long-term (9 hr) stability measurements for 1 × 103 ppm and 1 × 104 ppm methane samples were 0.8% and 0.48%, respectively, indicating good stability for the sensor. In the control module design, compared with previous reports on methane detection systems, the current system uses a self-developed temperature controller, a current driver and a signal processor, to allow real-time display and adjustments. The potential for adjustable wavelength scanning is available for multi-gas detection based on a single detection system.

An improved tin oxide core mismatch optical fiber sensor and its preparation method

Abstract A sensor was fabricated based on optical gas sensing, the sensitivity of tin oxide to methane via surface adsorption and electromagnetic theory. A 62.5/125 μm standard multimode fibre (MMF) and a 9/125 μm standard single-mode fibre (SMF) were spliced to fabricate a core diameter mismatch-based optical fibre methane sensor with an MM-SM-MM structure. The exposed fibre core areas were coated with graphene-doped tin oxide such that a novel graphene-based optical fibre methane sensor was fabricated. The experimental results show that the sensor exhibited a better linear fitting for greater reproducibility in the detection of low concentrations of methane than did the D-type gas sensor reported previously by the same authors.

Low-cost, Arduino-based, portable device for measurement of methane composition in biogas

An inexpensive, portable device to measure methane content of biogas samples was constructed. The central component of the device was an MQ-4 methane sensor. This sensor, along with humidity, temperature and pressure sensors, was enclosed in an airtight glass jar and interfaced with a programmable Arduino Uno clone for data logging and operation. The sensor was able to detect methane within the jar to as low as 400 ppm, but responded linearly to concentrations ranging from about 4000 to 110,000 ppm. Measurements made by the sensor were compared to analysis by a gas chromatograph equipped with a thermal conductivity detector. Analysis of biogas samples from an anaerobic digester using the device produced an average absolute error of 0.69 ± 0.55% when compared to GC measurements. Using 10 ml biogas sample size, methane content as low as 18% by volume could be reliably measured by the device. By increasing sample to 90 ml, methane content as low as 2.4% could be analyzed. This device was assembled for a cost of US$37. A field version that includes an LED display and power pack could be assembled for under US$50.

Ultrasensitive Electrochemical Methane Sensors Based on Solid Polymer Electrolyte-Infused Laser-Induced Graphene.

Methane is a potent greenhouse gas, with large emissions occurring across gas distribution networks and mining/extraction infrastructure. The development of inexpensive, low-power electrochemical sensors could provide a cost-effective means to carry out distributed sensing to identify leaks for rapid mitigation. In this work, we demonstrate a simple and cost-effective strategy to rapidly prototype ultrasensitive electrochemical gas sensors. A room-temperature methane sensor is evaluated which demonstrates the highest reported sensitivity (0.55 μA/ppm/cm2) with a rapid response time (40 s) enabling sub-ppm detection. Porous, laser-induced graphene (LIG) electrodes are patterned directly into commercial polymer films and imbibed with a palladium nanoparticle dispersion to distribute the electrocatalyst within the high surface area support. A pseudo-solid-state ionic liquid/polyvinylidene fluoride electrolyte was painted onto the flexible cell yielding a porous electrolyte, within the porous LIG electrode, simultaneously facilitating rapid gas transport and enabling the room temperature electro-oxidation pathway for methane. The performance of the amperometric sensor is evaluated as a function of methane concentration, relative humidity, and tested against interfering gases.

Application of SnO2 Nanoparticles and Zeolites in Coal Mine Methane Sensors

We evaluated solid-state sensors (MOS) manufactured using nanostructured tin oxide (SnO2) obtained by different synthesis methods for selectivity, response and repeatability at different operating temperatures and methane concentrations. In addition, Zeolite 13X pellets were placed in front of the sensors to improve CH4 selectivity in the presence of CO2. The palladium doped sensor (1.4% w/w) showed the highest sensitivity at 80 oC (83%) and shorter response times (16 s), whereas non-doped sensors exhibited the best sensitivity (78%) and response times (14 s) for those with smaller particle size (8 nm). Zeolite 13X pellets proved to be efficient at making the sensor more selective for CH4 in the presence of CO2.

Transverse-Stress Compensated Methane Sensor Based on Long-Period Grating in Photonic Crystal Fiber

A high-sensitive and transverse-stress compensated methane sensor based on a photonic crystal fiber long-period grating (PCF-LPG) is proposed. The outermost layer of the PCF consists of six large sideholes, five of which are coated with methane-sensitive compound film to achieve methane measurement. Such side-hole structure is helpful for gas sensitive reaction, but not conducive to avoiding external stress interference. Therefore, the last large hole is plated with silver layer to eliminate the cross-sensitivity effect through adding a Surface Plasmon Resonance (SPR) sensing channel with the consideration of photo-elastic effect and material deformation. Results show that the methane gas sensitivity can reach up to 6.39nm/% with the transverse-stress compensation. The sensor is very simple and effective, which provides a new method of gas measurement combined with different actual conditions.

Operational Control of the Feed of the Harvester

Comparison of normative and actual indicators on mining testifies to inefficient work of the excavating equipment. The results of the correlation analysis of the speed of movement of the harvester relative to the section of the support with the readings of methane sensors revealed a significant dependence. When conducting mining operations in complex geological conditions at great depths, a joint step-by-step carrying out of various technological processes is required to ensure the preparation, opening and excavation of reserves and the creation of safe conditions for mining coal seams. At the same time, efforts should be made to minimize time, human and energy resources. In this regard, of particular importance is the right choice of the program of operational management of technological processes of mining, monitoring the implementation of technological operations for the timely detection of deviations from the selected mode, adjustment of the established current modes of operation of technological processes and the development, if necessary, measures aimed at reducing the risks of accidents. A promising direction of solving this problem is the use of modeling methods. The developed models of technological processes of the mining enterprise will allow planning production and supporting decision-making in the implementation of operational management.

A hollow-core photonic band-gap fiber based methane sensor system capable of reduced mode interference noise

The performances of infrared absorption spectroscopic gas sensors using a hollow-core photonic band-gap fiber (HC-PBF) as an absorption cell are usually limited by mode interference of the multimode HC-PBF. To minimize the effect of mode interference, a free space coupling structure was proposed for mode transfer from a single mode fiber (SMF) to a HC-PBF and also from the HC-PBF to a photo-detector. The parameters of the free space coupling structure were optimized based on a detailed theoretical analysis and numerical simulation, and the mode inference reduction was experimentally verified. Wavelength modulation spectroscopy (WMS) combined with the second harmonic (2f) detection was utilized in methane (CH4) measurements by targeting an absorption line at 1653 nm. Using a ∼2 mW laser and a 0.45 m-long HC-PBF for CH4 detection at atmospheric pressure, the optimized sensor demonstrated a 1σ detection limit of ∼4.35 parts per million in volume (ppmv) with a 0.5 s averaging time and a minimum detection limit of ∼360 parts per billion in volume (ppbv) with an averaging time of 75 s. The proposed structure can also be used in a HC-PBF-cell based infrared absorption gas sensor system for the detection of any gas species for suppression of mode interference.