【作者】 张伟；

【导师】 陈伟民；

【作者基本信息】 重庆大学 ， 仪器科学与技术， 2016， 博士

【摘要】 光纤布拉格光栅(Fiber Bragg Grating,FBG)应变传感系统因其独特的优势,已在各行各业获得了广泛的应用。但在实际应用中,传感系统会出现不同程度的性能退化、进而产生各种类型的故障,严重影响其推广效果。这使得系统的可靠性成为了用户最关注并亟待解决的共性难题。但因其牵涉面广、技术难度高,且耗时费力、极难在理论上取得突破,因而难以受到研究人员足够的重视,是光纤传感研究领域最薄弱的环节。要在FBG应变传感系统可靠性研究上取得突破,就必须从传感器和解调仪这两个关键环节入手,从传感器与信号解调的基本原理出发,深入研究FBG传感元件在各种恶劣环境中的性能变化规律,研究传感器封装与安装的应变传递特性,研究解调方法的鲁棒性、评估解调结果的可信性。这既能为FBG传感器的制造企业提供指导,也可以为FBG传感器的用户提供使用帮助,对促进FBG传感技术、国民经济和国防事业的发展都具有重大的意义。为此,本文从FBG传感元件、应变传递和传感解调三大方面开展了深入研究,主要的研究内容如下:(1)为了提供研究FBG可靠性基本的理论与方法,总结分析了FBG结构的形成机理,提出了从光化学反应角度理解FBG折射率变化的思想;基于耦合模理论和传输矩阵法,推导了FBG光谱的仿真方法;总结分析了FBG光谱特征指标。(2)全面探索了FBG传感元件在力学、温度、和辐照环境中的性能变化规律。针对轴向、横向作用力对FBG传感特性影响研究归纳不全面的问题,分别推导了轴向、横向受力对FBG光谱的影响模型,仿真了分析轴向、横向作用力对FBG光谱影响的规律,并提出了确保FBG可靠传感的许用条件。针对弯曲对FBG传感特性影响机理不明确的问题,建立了弯曲对FBG光谱的影响模型,并结合此模型给出了确保FBG可靠传感的弯曲条件。针对长期作用力下FBG光谱恶化机理与规律不明确的问题,通过理论分析和实验得出了长期作用力下FBG光谱的恶化机理及恶化规律。针对温度使用寿命不明确的问题,建立了FBG温度寿命预测模型,并结合高温加速老化实验,低温持续实验和高低温冲击实验预测了FBG在常规应用温度环境(-40~80℃)下的寿命。针对辐照影响机理不明确的问题,建立了辐照对FBG光谱的影响模型,利用该模型揭示了辐照实验中出现Bragg波长漂移差异性的机理。(3)为了全面探讨FBG应变传感器的应变传递特性,建立了广义的应变传递模型,统一了目前形式各异的应变传递模型。针对目前应变传递特性研究存在的局限性,全面分析了粘接层对平均应变传递效率和FBG光谱的影响。在平均应变传递效率方面,基于FBG应变传递简化模型推导了四种FBG应变传递形式的平均应变传递效率,然后具体分析了粘接层材料特性和几何特征对FBG平均应变传递效率的稳定性和一致性的影响,并给出了解决稳定性和一致性的方法。在FBG光谱受粘接层的影响方面,建立了粘接层横向应力对FBG光谱的影响模型,通过仿真及实验探究了其影响规律,并给出避免FBG光谱因其发生畸变的方法。另外,从理论和实验上探讨了粘接层恶化对光谱信号的影响机理与规律。(4)为了优化FBG解调软件的解调算法、提升其鲁棒性,从传感系统的实际情况出发,建立了FBG测量光谱的恶化模型,更加全面地刻画了由FBG传感器恶化形成的光谱畸变、FBG传感系统引入的干涉噪声、基线噪声和高斯噪声。在此基础上,分析了光谱噪声对目前有代表性的解调算法的影响,并相应地提出了提高解调算法鲁棒性的改进方案。最后通过分析光谱畸变对解调算法的影响,发现了利用光谱的黄金边模抑制比进行解调结果可信性评估的方法,并通过实验证实了方法的有效性,这解决了目前在实际应用中无法得知解调结果是否可信的难题;同时也发现鲁棒性相对较高的是改进的相关算法和改进的直接寻峰解法,为用户提供了解调算法选用的参考。更多还原

【Abstract】 Due to its distinguished advantages,Fiber Bragg Grating(FBG)strain sensing system has been widely used in various sensing fields.But in practical applications,the sensing system may degrades and fails,which seriously blocks its promotion.The system’s reliability issue has caught users’ attentions and become an urgent and common problem that needs to be solved.Reliability research involves a wide range of technical difficulties,and it is time-consuming and difficult to make a breakthrough in theory.So,it did not receive enough attention from researchers,making it become the weakest point in the optical fiber sensing research field.In order to achieve a breakthrough in reliability research,the focus must be put on the sensor and the interrogator.Based on basic principles of sensor and signal demodulation,it needs to study FBG sensor’s performance change rules in various harsh environments,strain transfer characteristics of sensor package and installation,the robustness of demodulation method,and the method to evaluate the credibility of demodulation results.Solving these problems can not only provide guidance for FBG sensor manufacturers and help for FBG sensor users,but also is very meaningful to promote FBG sensing market,and national economic and military development.Therefore,this thesis studies reliability problems from FBG,strain transfer and demodulation comprehensively.Main research contents are as follows:(1)In order to provide basic theory and method for studying the FBG,formation mechanism of FBG structure is analyzed and the idea of understanding FBG refractive index change from the photochemical reaction is proposed.Based on coupled-mode theory and transfer matrix method,simulation formulas of FBG spectra are deduced.In addition,FBG spectral characterization indexes are proposed for spectral analysis.(2)FBG’s performance change rules in mechanical,temperature and irradiation environments are investigated comprehensively.Since existing studies on influences of axial and transversal stresses on FBG spectra are imcomplete,FBG’s spectral change rules and reliable sensing conditions under axial and transversal stresses are analyzed based on deduced influencing models respectively.To understand influencing mechanism of bending on the FBG spectrum,a model is established and the bent limiting condition for reliable FBG sensing is given based on this model.Also,degradation mechanism and rule of FBG spectrum under long-term stress are discussed both theoretically and experimentally.To explore FBG’s lifetime in normal temperature application range(-40~80℃),a thermal lifetime prediction model is established and FBG’s lifetime is predicted by combining high-temperature accelerated aging,low-temperature and thermal shock experiments.At last,an irradiation influencing model is established to explain Bragg wavelength drift differences in various irradiation experiments.(3)To disscuss FBG strain sensors’ strain transfer characteristics comprehensively,a generalized strain transfer model is established,which unifies current different strain transfer models.Then,formulas of average strain transfer rates for 4 type FBG strain transfer forms are derived based on a simplified FBG strain transfer model.Based on derived formulas,effects of material and geometrical properties of bonding layers on stability and consistency of average strain transfer rate are analyzed.Correspondingly,solutions are proposed to ensure stability and consistency.An influencing model of transversal stresses of bonding layers on FBG spectra is established.Accordingly,influencing rules are studied by simulation and experiment,and the method to avoid FBG spectral distortion is given.In addition,influencing mechanism and rule of degraded bonding layers on FBG spectra are analyzed theoretically and experimentally.(4)To improve the robustness of algorithm for demodulation software,a degradation model of FBG measuring spectrum is established,and this model can fully depict degradations of FBG sensor,interference noise,baseline noise and Gaussian noise caused by the FBG sensing system.Then,influences of spectral noises on some representative demodulation algorithms are analyzed,and a scheme is proposed to improve the robustness of algorithms.By analyzing effects of spectral distortions on demodulation algorithms,a creditability evaluation method using spectral golden side-mode suppression ratio for demodulation results is found and verified by the experiment.Besides,improved correlation and direct peak detection algorithms are found to be relatively reliable,which provides selection reference for users.更多还原