【作者】 赵凯；

【导师】 毕云峰；

【作者基本信息】 山东大学 ， 电子信息（专业学位）， 2023， 硕士

【摘要】 在气体检测领域,基于红外吸收光谱原理的检测技术受到广泛的关注。其中,可调谐二极管激光吸收光谱技术(Tunable Diode Laser Absorption Spectroscopy,TDLAS)具有响应速度快、灵敏度高、选择性强的特点,已在很多领域得到了应用。从原理上讲,TDLAS技术优势在于谐波检测方法的应用,而其得以成立的基础是气体弱吸收情况下的线性近似。用于浓度反演的谐波模型对于系统性能具有重要作用。传统2f/1f谐波模型在气体强吸收下会有其适用性问题,且其浓度反演过程中对2f信号的需求限制了激光调制频率的提高,使得低频噪声的抑制受到影响;另外,系统应用中各阶谐波与浓度的相关性会因激光器的老化发生偏移,需要校准以保持长期稳定性。为此,本文提出了一种适用于高光学厚度、高调制频率的新型免校准浓度反演模型。论文首先阐述了气体吸收光谱的基本原理和气体吸收检测的基本方法,对基于激光波长调制技术的谐波浓度反演进行了理论的推导。采用谐波标准化方法实现免校准,利用相敏检波原理修正高光学厚度带来的影响,采用一次谐波构建浓度反演模型解决调制频率的限制,提出了一种新型Y1f/X1f浓度反演模型。其次,搭建了一套TDLAS仿真分析系统,对所提出浓度反演模型进行了理论分析和仿真验证,证明该模型用于反演浓度的可行性。最后,基于一套开放光路的近红外TDLAS系统进行了实验验证和性能测试。在基于波长调制光谱的定峰法实验中,调制频率分别为1kHz、5kHz、10kHz、20kHz的拟合决定系数超过了 0.997,对甲烷的检测限小于4ppm,优于传统的2f/1f模型在同样实验条件下的性能。该模型在扫峰法实验中也有较好的适用性,在1khz、20khz的调制频率下,浓度反演拟合决定系数超过0.997,残差小于3%,同样优于传统2f/1f模型。本文所提出的免校准浓度反演模型为提高TDLAS系统高光学厚度和高调制频率的稳定性提供了新的解决思路。更多还原

【Abstract】 In the field of gas detection,detection technology based on the principle of infrared absorption spectroscopy has received widespread attention.Among them,Tunable Diode Laser Absorption Spectroscopy(TDLAS)has the characteristics of fast response,high sensitivity and strong selectivity,and has been applied in many fields.In principle,the advantage of TDLAS technology lies in the application of harmonic detection methods,which are based on linear approximation under weak gas absorption.Harmonic models for concentration inversion play an important role in system performance.The traditional 2f/1f harmonic model will have its applicability problems under strong gas absorption,and the demand for 2f signal during the concentration inversion process limits the increase of laser modulation frequency,which affects the suppression of low-frequency noise.In addition,the correlation of harmonics and concentration of each order in the system application will be shifted due to the aging of the laser,and calibration is required to maintain long-term stability.Therefore,a new calibration-free concentration inversion model suitable for high optical thickness and high modulation frequency is proposed.Firstly,the basic principles of gas absorption spectroscopy and the basic methods of gas absorption detection are expounded,and the harmonic concentration inversion based on laser wavelength modulation technology is theoretically derived.A new Ylf/Xlf concentration inversion model is proposed by using the harmonic standardization method to achieve calibration-free,the phase-sensitive detection principle is used to correct the influence caused by high optical thickness,and the concentration inversion model is constructed by using a harmonic to solve the limitation of modulation frequency.Secondly,a set of TDLAS simulation and analysis system is built,and the proposed concentration inversion model is theoretically analyzed and simulated to prove the feasibility of the model for inversion concentration.At last,based on a set of open optical path NIR TDLAS system,experimental verification and performance tests were carried out.In the peak-fixing method experiment based on wavelength modulation spectroscopy,the fitting coefficients of the modulation frequencies of 1kHz,5kHz,10kHz and 20kHz respectively exceeded 0.997,and the detection limit of methane was less than 4ppm,which was better than the performance of the traditional 2f/1f model under the same experimental conditions.The model also has good applicability in peak sweeping experiments,and the concentration inversion fitting coefficient exceeds 0.997 and the residual is less than 3%at the modulation frequency of 1kHz and 20kHz,which is also better than the traditional 2f/1f model.The calibration-free concentration inversion model proposed in this thesis provides a new solution for improving the stability of TDLAS system with high optical thickness and high modulation frequency.更多还原