Minimum Detectable Gas Concentration Research Articles

Highly sensitive ethanol sensor based on Ag NP-modified SnO2–In2Sn2O7-x ternary composite enhanced by synergistic catalysis

In this paper, the noble metal Ag-modified SnO2–In2Sn2O7-x ternary nanocomposites were designed to detect ethanol efficiently. Firstly, the SnO2–In2Sn2O7-x nanocomposites were synthesized by a simple hydrothermal method, and the microstructure of the SnO2 nanomaterials were adjusted by controlling the content of In2Sn2O7-x. With the increase of In2Sn2O7-x content, the morphology of the synthesized SnO2–In2Sn2O7-x composites gradually tends to be regular with porous spherical morphology. In the same synthesis conditions, the porous spherical morphology of SnO2–In2Sn2O7-x composites was more uniform at 0.5 at% of In element content, and the distribution in the material was more homogeneous and dispersed, which was conducive to the diffusion and adsorption of gases on the surface of the material, as well as to the loading of Ag nanoparticles. On this basis, the Ag nanoparticles were successfully modified through the chemical reduction route, and the Ag nanoparticles modified SnO2–In2Sn2O7-x with 0.5 at% In elemental content ternary nanocomposites were prepared. X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Energy Dispersive Spectrometer (EDS) were used to characterize the structure and morphology of the prepared gas-sensitive materials. The gas-sensing performance of SnO2, In2Sn2O7-x, SnO2–In2Sn2O7-x, and Ag-modified SnO2–In2Sn2O7-x sensors were tested systematically. The results showed that the 1.5 wt% Ag-modified SnO2–In2Sn2O7-x nanocomposites with 0.5 at% In elemental content have good gas-sensing properties. The response of the sensor to 100 ppm ethanol vapor can reach 666 at the optimal operating temperature of 250 °C, and the response time is shortened to 45 s. It has good sensitivity for ethanol gas, and the minimum detectable gas concentration is reduced to 500 ppb. The improved performance of the sensor is primarily due to the construction of the heterogeneous interface of the SnO2 and In2Sn2O7-x and the catalytic synergism of the noble metal Ag.

InGaAs Membrane Waveguide: A Promising Platform for Monolithic Integrated Mid-Infrared Optical Gas Sensor.

Mid-infrared (mid-IR) absorption spectroscopy based on integrated photonic circuits has shown great promise in trace-gas sensing applications in which the mid-IR radiation directly interacts with the targeted analyte. In this paper, considering monolithic integrated circuits with quantum cascade lasers (QCLs) and quantum cascade detectors (QCDs), the InGaAs-InP platform is chosen to fabricate passive waveguide gas sensing devices. Fully suspended InGaAs waveguide devices with holey photonic crystal waveguides (HPCWs) and subwavelength grating cladding waveguides (SWWs) are designed and fabricated for mid-infrared sensing at λ = 6.15 μm in the low-index contrast InGaAs-InP platform. We experimentally detect 5 ppm ammonia with a 1 mm long suspended HPCW and separately with a 3 mm long suspended SWW, with propagation losses of 39.1 and 4.1 dB/cm, respectively. Furthermore, based on the Beer-Lambert infrared absorption law and the experimental results of discrete components, we estimated the minimum detectable gas concentration of 84 ppb from a QCL/QCD integrated SWW sensor. To the best of our knowledge, this is the first demonstration of suspended InGaAs membrane waveguides in the InGaAs-InP platform at such a long wavelength with gas sensing results. Also, this result emphasizes the advantage of SWWs to reduce the total transmission loss and the size of the fully integrated device's footprint by virtue of its low propagation loss and TM mode compatibility in comparison to HPCWs. This study enables the possibility of monolithic integration of quantum cascade devices with TM polarized characteristics and passive waveguide sensing devices for on-chip mid-IR absorption spectroscopy.

Minimum detectable gas concentration performance evaluation method for gas leak infrared imaging detection systems.

Thermal imaging technology is an effective means of detecting hazardous gas leaks. Much attention has been paid to evaluation of the performance of gas leak infrared imaging detection systems due to several potential applications. The minimum resolvable temperature difference (MRTD) and the minimum detectable temperature difference (MDTD) are commonly used as the main indicators of thermal imaging system performance. This paper establishes a minimum detectable gas concentration (MDGC) performance evaluation model based on the definition and derivation of MDTD. We proposed the direct calculation and equivalent calculation method of MDGC based on the MDTD measurement system. We build an experimental MDGC measurement system, which indicates the MDGC model can describe the detection performance of a thermal imaging system to typical gases. The direct calculation, equivalent calculation, and direct measurement results are consistent. The MDGC and the minimum resolvable gas concentration (MRGC) model can effectively describe the performance of "detection" and "spatial detail resolution" of thermal imaging systems to gas leak, respectively, and constitute the main performance indicators of gas leak detection systems.

Miniature fiber-tip photoacoustic spectrometer for trace gas detection

We demonstrate a fiber-tip photoacoustic spectrometric sensor for trace gas detection. The sensor head is a miniature fiber-tip hollow-cavity with a deflectable polymer diaphragm. Periodic light absorption of gas molecules within the cavity generates an acoustic pressure wave, which causes deflection of the diaphragm. The hollow cavity also is a Fabry-Perot interferometer with which the diaphragm deflection is detected with high sensitivity. Experimental test around the P(9) absorption line of C(2)H(2) achieved a minimum detectable gas concentration of 4.3 ppm with an excitation laser power of 8 mW. The miniature sensor head and fiber optic detection system make this type of spectrometers ideally suited for remote and space-limited applications as well as for multipoint detection in a multiplexed fiber optic sensor network.

수동형 퓨리에변환 적외선 분광기의 잡음등가온도지수

The passive open-path Fourier-Transform-Infrared system was implemented for the toxic gas monitoring. Noise Equivalent Differential Temperature(NEDT) was investigated as a system performance evaluation figure and analyzed numerically with the designed parameters. Calculated NEDT was compared with the experimental value in the wavelength region of <TEX>$700{\sim}1400cm^{-1}^$</TEX>. The minimum detectable gas concentration was estimated from the obtained NEDT at the absorption wavelength of <TEX>$SF_6$</TEX>.

Capability of Raman lidar for monitoring the variation of atmospheric CO2 profile

Lidar (Light detection and ranging) has special capabilities for remote sensing of many different behaviours of the atmosphere. One of the techniques which show a great deal of promise for several applications is Raman scattering. The detecting capability, including maximum operation range and minimum detectable gas concentration is one of the most significant parameters for lidar remote sensing of pollutants. In this paper, based on the new method for evaluating the capabilities of a Raman lidar system, we present an evaluation of detecting capability of Raman lidar for monitoring atmospheric CO2 in Hefei. Numerical simulations about the influence of atmospheric conditions on lidar detecting capability were carried out, and a conclusion can be drawn that the maximum difference of the operation ranges caused by the weather conditions alone can reach about 0.4 to 0.5km with a measuring precision within 30ppmv. The range of minimum detectable concentration caused by the weather conditions alone can reach about 20 to 35 ppmv in vertical direction for 20000 shots at a distance of 1 km on the assumption that other parameters are kept constant. The other corresponding parameters under different conditions are also given. The capability of Raman lidar operated in vertical direction was found to be superior to that operated in horizontal direction. During practical measurement with the Raman lidar whose hardware components were fixed, aerosol scattering extinction effect would be a significant factor that influenced the capability of Raman lidar. This work may be a valuable reference for lidar system designing, measurement accuracy improving and data processing.

Development of a SNR parameterization scheme for general lidar assessment

We present a general methodology for evaluating the capabilities of a general lidar system encompassing both backscatter (elastic and Raman lidar) and topographic targets. By introducing a well-defined atmospheric reference medium and by individually examining and decomposing the contributions of lidar system parameters including lidar transmitter power, field of view, receiver noise, atmospheric conditions, and sky background on the signal-to-noise ratio, we obtain a simple dimensionless parameterization of the lidar system. Using this parameterization, numerical simulations are carried out to determine achievable lidar performance including operation range, minimum detectable gas concentration, and so on.

Application of the method of decomposition of lidar signal-to-noise ratio to the assessment of laser instruments for gaseous pollution detection

A general methodology for rating both performance and potential of lidar systems used for detection of atmospheric trace constituents including pollutants and gas leaks is developed. By individually examining and decomposing the contribution of both lidar system parameters and atmospheric operating conditions on signal-to-noise-ratio, a generalized figure of merit, V, for lidar quality is introduced and evolved. Computer simulations based on V and atmospheric parameters are carried out to determine achievable lidar performance. A simple design procedure is outlined for determination of lidar instrumentation parameters to ensure the best monitoring efficiency for a given set of initial parameters/requirements, including operation range, minimum detectable gas concentration, and so on.

An opto-thermal gas concentration detector

A new gas concentration detector is proposed in this paper. By measuring the amplitude of the temperature variations caused by a chopped laser beam in a sample cell using a piece of pyroelectric material, the number of molecules which can absorb radiation of the laser frequency chosen may be determined. At present the minimum detectable gas concentration is estimated as 0.01 ppm for typical parameter values of available tunable lasers and pyroelectric materials and for typical molecular gases.

A new theoretical model of the opto-acoustic gas concentration detector

A new theoretical model, describing the pressure variations caused by a chopped laser beam in an opto-acoustic gas concentration detector, is introduced in this paper. Expressions are derived for the minimum detectable gas concentration and the laser beam power needed to reach this sensitivity. The theoretical model is applied to experimental data given by Kreuzer: this gives improved interpretation of the experiments. The minimum detectable gas concentration for typical detector parameter values is about 10 −4 ppm.