Carbon Monoxide Trace Gas Detection Based On Quartz Enhanced Photoacoustic Spectroscopy

Carbon monoxide?CO?,an important component of environmental pollutants,is a colorless,odorless and highly toxic gas which is produced in power generation,petrochemical refining,fossil fuels and other carbon-containing fuel combustion activities.In the environment,CO can react with hydroxyl groups which contributes to global warming indirectly.In medical treatment,CO can be used as an indicator of judge asthma,diabetes and other diseases.Therefore,high sensitivity detection of CO is of great significance in various fields.Quartz enhanced photoacoustic spectroscopy?QEPAS?is a new gas detection technology based on the photoacoustic effect,which has the advantages of low cost,high sensitivity,fast response time and so on.At present,it is a common means to detect flammable,explosive or toxic gases.In this paper,the gas absorption line at2330.19 nm(4291.5 cm^-1)of CO is chosen as the target spectral line and the gas sensor is optimized with the customized quartz tuning fork?QTF?,3D printing miniaturization unit and customized gradient index lens?Grin lens?to improve the sensor's detection ability and practicability.The theory of molecular absorption of gas is introduced briefly.The technical principle of photoacoustic spectroscopy is described in detail.The piezoelectric effect and physical parameters of QTF are discussed.The principle of resonance cavity enhancement is analyzed.In the simulation part,vibration amplitude of QTF is calculated based on finite element method and COMSOL software.Taking the standard QTF and customized small gap QTF as simulation targets,the vibration amplitudes under the condition of different beam positions and resonant tube length are calculated.The optimal parameters of these two QTFs are obtained by theoretical simulation results.Under the optimal conditions,the vibration amplitude of the small gap QTF is larger than that of the standard QTF.CO was detected by standard QTF and small gap QTF respectively and the simulation results are verified experimentally.Firstly,a QEPAS sensor based on collimating focusing lens group to realize spatial light transmission is built to detect CO.The experimental parameters are optimized.Subsequently,because of the poor structural stability of lens group in traditional QEPAS system and the difficulty in miniaturization of lens size,3D printing technology and Grin lens are adopted to reduce the system volume to 3.5 cm³ and realize the miniaturization of CO-QEPAS sensor.Then,gas detection based on small-gap QTF is carried out for the first time.Finally,trace gas detection with high sensitivity and small volume is realized and the experimental results are in good agreement with the simulation results.In this project,the high-sensitivity and miniaturized CO-QEPAS sensor based on standard QTF and customized small-gap QTF is proposed.The characteristics of small volume make the sensor meet higher requirements of the detection environment,such as gas mine,medical diagnosis and other fields,and improving the practicability of the sensor to some extent.