【作者】 吴希军；

【导师】 王玉田；

【作者基本信息】 燕山大学 ， 仪器科学与技术， 2010， 博士

【摘要】 甲烷易燃易爆,是巷道瓦斯和天然气的主要成分,当其泄漏到环境中时,利用可靠传感器对其进行及时检测对于化工设备、煤气厂、矿山及住宅区具有重要意义。气体光谱是评估气体物质浓度的高选择性、高灵敏度方法。利用近红外谱带和光纤光学器件可实现气体光谱的遥测。井下基于光纤的甲烷遥测方法不会产生任何电信号,与采用电子气体传感器和传输导线的传统方法相比优势明显(全光学,无危险,易校正,不易受扰动气体及电磁干扰等)。从分子光谱与分子结构入手,分析了甲烷分子振动、转动及振转光谱理论。阐述了孤立吸收线的不同展宽机理及其线型函数,为实际测量中吸收线型的选取提供了理论依据。针对波长调制吸收谱分析中的光源频率与幅度调制问题、标准具条纹产生与抑制问题、系统检测能力与信噪比等问题进行了详尽的理论分析,揭示了锁相放大器谐波输出与气体吸收线型及光电探测器输出信号傅里叶分解的关系,给出了一次、二次谐波检测与比值处理技术的相关理论。发展了梳状光源等效吸收系数的理论,设计了低噪声光电预放大电路及LabVIEW数据采集系统。提出由其它气体浓度的测量间接推知甲烷浓度的方案。实测了SO2吸收与荧光光谱,设计了吸收荧光式多气体检测系统。探讨了空芯光子晶体光纤(HC-PCF)作为吸收荧光探头的可行性,并设计了相应吸收与荧光检测系统。分析了光纤分束器组网及锁模光纤激光器多点传感的相关理论。运用棱镜气室与谐波检测技术,由步进电机调节棱镜中线间的距离,进而改变气室内有效吸收光程,构建了适用于宽广浓度范围内的光纤甲烷检测系统;应用取样光纤光栅、级联F-P干涉仪滤波和改进的差分吸收检测技术,实现了对甲烷气体等距分布的多条近红外吸收线的同时测量,完善了差分吸收技术应用于弱气体检测的理论,提高了气体测量的抗串扰能力;HC-PCF的空芯区域可实现很长的光与气体作用距离,适于对甲烷的微弱吸收波段进行检测。以多段级联的空芯光子带隙光纤作为气体传感探头,分析了甲烷在空芯内的扩散特性,构建了新型全光纤甲烷监测系统;泄漏到光纤外部的泵浦光能被附着在光纤光栅外部的金属涂敷层吸收,影响了光栅的谐振波长。当有气流通过光纤光栅时,由于热量被带走,导致光纤光栅温度变化,通过监测谐振波长的改变测量了气体的泄漏速度。更多还原

【Abstract】 Methane is the dominant ingredient of coal mine tuunel gas and natural gas, which is flammabel and explosive. Therefore, in the event of spill in our enviroment its early and accurate detection by means of reliable sensor is vital for chemical facilities, gas plants, mines and residential areas.Gas spectrosclpy is a selective and sensitive technque for evaluating the concentrations of gaseous species. Fiber optics enable gas spectroscopy to be performed remotely using the near infrared band of spectrum. The fiber-based remote sensing method for methane detection in coal mine tunnel has advantages over the conventional pellistor sensors employ a catalyst head, such as fully optical, non-hazardous, easy calibration, little disturbance owing to interference gases and electromagnetic noise.The dissatation starts with molecular structure and spectrum, and gave a detailed theretical analysis on the subject of vibration, rotation and vibration-rotation spectra. Different broadening mechanisms and lineshapes on isolate absorption line were illustrated.Key issues, such as frequency and amplitude modulation, fringe generation and supression, system detectability, have been explained in detail. The relation between phase-locked amplifier harmonic output and Fourier decomposition on lineshape and electric signal form photodevice has also been interpreted.The equivalent absorption coefficient theory was improved on comb-shaped light source, and photo-electric pre-amplifier and LabVIEW data acquisition system were proposed. Methane concentration information can be deduced from that of other gas ingredient. Absorption and fluorescence spectra of SO2 have been measured in experiment. Multi-component gas detection system employing absorption and fluorescence measurement has been designed. The feasibility of hollow-core photonic crystal fiber(HC-PCF) used as absorption-fluorescence measurement sensor was disscussed. Sensor network based on fiber splitter and fiber laser was analysed.A novel fiber methane detection system was constructed based on integration of prism gas cell and harmonic detection technique. The system can be applied to broad-range concentration detection and its sensitivity can be adjusted by changing the prism distance using step motor; A novel fibre-optic methane detection system was proposed based on sampled fiber bragg grating (SFBG) , tandem Fabry-Perot filtering technique. By means of SFBG and tandem F-P, Near-infrared equal-spaced multi methane absorption lines were detected simultaneously and difference absorption detection theory was developed; In hollow-core photonic bandgap fibres, long interaction pathlengths between light and the gas confined in the core are achieved, which enables sensitive detection of methane even at its weak absorption bands. It is proposed a novel optical fiber gas sensor based on cascade of HC-PCFs. The diffusion of gas inside of the hollow core is also analysed; A novel gas leakage detection sensor based on self-heated effect of fibre optic is presented. The optical energy leaking out from the fibre is absorbed by the metallic coating, which alter the grating pitch of the fibre Bragg grating. When gas leaking out from the pipeline blow on the fibre grating, its temperature changes accordingly. The gas leaking velocity can be determined by monitoring the change of resonance wavelength.更多还原