Abstract
This paper presents the design, fabrication, and characterization of a middle-infrared (MIR) linear variable optical filter (LVOF) and thermopile detectors that will be used in a miniaturized mixed gas detector for CH4/CO2/CO measurement. The LVOF was designed as a tapered-cavity Fabry-Pérot optical filter, which can transform the MIR continuous spectrum into multiple narrow band-pass spectra with peak wavelength in linear variation. Multi-layer dielectric structures were used to fabricate the Bragg reflectors on the both sides of tapered cavity as well as the antireflective film combined with the function of out-of-band rejection. The uncooled thermopile detectors were designed and fabricated as a multiple-thermocouple suspension structure using micro-electro-mechanical system technology. Experimentally, the LVOF exhibits a mean full-width-at-half-maximum of 400 nm and mean peak transmittance of 70% at the wavelength range of 2.3~5 μm. The thermopile detectors exhibit a responsivity of 146 μV/°C at the condition of room temperature. It is demonstrated that the detectors can achieve the quantification and identification of CH4/CO2/CO mixed gas.
Highlights
Taking natural gas for example, it contains a mixture of a large amount of methane (CH4) and small amount of various hydrocarbon gas (e.g., CxHy), which has emerged as a major energy source
It produces a great deal of water vapor and a mixture of compounds, e.g., nitrogen oxides (N2O), carbon dioxide (CO2), and even carbon monoxide (CO) and fumes caused by the incompletecombustion of natural gas [2]
We focus on MIR band of 2.3~5.0 μm to design the linear variable optical filter (LVOF) configuration where most of characteristic gas absorption peaks (e.g., Carbon dioxide (CO2), CO, Nitrogen oxides (N2O), and CxHy) related to indoor air quality and general industrial environment are centralized
Summary
Gas sensors have a great demand in many industrial and real-life applications. In many of these applications, multiple gases must be monitored simultaneously over a long period of time with minimal maintenance and in different locations [1]. When natural gas burns openly, the use of natural gas has been found to increase the risk of human health and environment. It produces a great deal of water vapor and a mixture of compounds, e.g., nitrogen oxides (N2O), carbon dioxide (CO2), and even carbon monoxide (CO) and fumes caused by the incompletecombustion of natural gas [2].
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