Multi-component Trace Gas Detection System Based On MEMS-FPI On-chip Spectroscopy Chi

Multi-component trace gas detection is of great value in medical,environmental,industrial,defense,and military fields.Nowadays,multi-component gas detection methods are mainly divided into non-optical and optical detection,among which spectral detection technology has attracted widespread attention because of its high sensitivity,good selectivity,and long service life.Due to the limitation of laser light source bandwidth,the gas spectrum detection technology marked by tunable Diode laser absorption spectroscopy(TDLAS)is challenging to balance the needs of wideband and high-precision detection when performing multi-component gas detection.Therefore,multi-component trace gas detection technology with high integration,speed,stability,and the wide band has always been a hot spot in scientific research.Based on TDLAS technology,this paper designs and builds a multicomponent trace gas detection system,which is as follows:(1)Based on the absorption spectroscopy theory of gas molecules and Beer-Lambert’s law,TDLAS-WMS(wavelength modulation)technology is analyzed to determine the spectral absorption lines of each target component gas.For the time-division multiplexing(TDM)method in a multi-component gas detection system,the time consumption is too long,and the system structure of the frequency division multiplexing(FDM)method is complicated.The microelectromechanical Fabery interference(MEMS-FPI)on-chip spectroscopic chip with tunable filtering function is introduced,and the addressing filtering function of the MEMS-FPI spectroscopy chip realizes high-speed and high-precision detection of absorption spectral line signals in different bands.(2)Design of multi-component gas trace detection system based on TDLAS-WMS technology.According to the gas absorption spectral line,a tunable DFB laser corresponding to the center band is selected to form a multispectral laser light source.Utilizing the advantages of MEMS-FPI on-chip spectral chip with narrow detection bandwidth(5 nm),precise adjustment of working wavelength,and high filtering efficiency,it realizes synchronous detection with multi-spectral laser light sources and effectively suppresses the mutual interference of cross gases.Combined with WMS technology,a single lock-in amplifier demodulates the second harmonic signal of different component gas absorption lines and is digitally sampled and analyzed.Rapid trace detection of seven gases,methane,carbon dioxide,and acetone,was completed(recognition speed within 2 s).(3)Through multi-component gas detection experiments,the lower detection limit and stability of the system are tested.The experiments show that the lower detection limit of methane in the system reaches 0.2 ppm,and the lower detection limit of the other target component gases is: carbon dioxide(10 ppm),acetone(2 ppm),ethylene(1 ppm),hydrogen sulfide(1 ppm),ammonia(5 ppm),hydrogen chloride(4 ppm).The lower detection limit is reduced by 1,000 compared to traditional broad-spectrum direct measurement methods(0.02 %).At the same time,the long-term measurement error is less than ±3.1 %.It meets the application requirements of a series of trace-level multi-component gas detection such as low-concentration greenhouse gas monitoring under the background of dual carbon and human exhaled gas detection in the medical field.