【作者】 王彦；

【导师】 梁大开；

【作者基本信息】 南京航空航天大学 ， 仪器科学与技术， 2008， 博士

【摘要】 长周期光纤光栅是一种周期在数百微米的光纤光栅,具有插入损耗低、无后向反射、制作简单以及成本低、许多方面灵敏度高于FBG等独特优点,在光纤传感和光纤通讯领域具有良好的应用前景,成为近年来的研究热点。但是,目前对长周期光纤光栅的研究主要还停留在理论与实验的探索阶段,实用化程度不高。本课题致力于将长周期光纤光栅应用到实际的工程结构当中,包括结构的振动监测以及民用的土木工程结构,实现结构的健康监测。全文研究工作内容包括如下几个方面:(1)对长周期光纤光栅进行理论分析,介绍了长周期光纤光栅的写入技术及形成机理。以耦合模理论为基础,基于三层光纤模型,对阶跃单模光纤中写入的非倾斜均匀长周期光纤光栅的传输特性进行了分析,给出了基于此理论的长周期光纤光栅的有效折射率、耦合系数、透射率以及谐振波长的表达式,为光栅的制作及其传感特性提供了理论基础;(2)长周期光纤光栅的基本传感特性是其进行实际工程应用的基础。从理论分析和实验研究的角度出发,讨论长周期光纤光栅的基本传感特性,包括温度、轴向应变、弯曲、折射率和横向负载特性,分别讨论了各个情况下长周期光纤光栅透射光谱的变化,并给出相应的特性曲线和灵敏度系数;(3)基于长周期光纤光栅的弯曲特性研究,发现其透射光中某固定波长处的光功率与LPFG的弯曲度近似成线性,提出利用这一特点,将长周期光纤光栅粘贴在待测板结构上,实现对板结构动态信号的监测;(4)利用布拉格光栅的窄带特性解调长周期光纤光栅,始终监测LPFG某固定波长处的光功率,建立了基于长周期光纤光栅微弯特性的动态信号监测系统,该系统用于对待测板结构振动信号的监测,初步实现了分布式振动信号的采集;(5)基于长周期光纤光栅动态信号监测系统,对待测结构各种损伤状况下采集到的动态信号进行分析,提取小波包能量谱变化率为结构的损伤指标,实现结构的损伤识别;(6)基于混凝土结构中钢筋的锈蚀机理,利用长周期光纤光栅对折射率的传感特性,设计了相关方案,在实验室环境下实现了对钢筋锈蚀的监测;(7)基于长周期光纤光栅对微弯的传感特性,设计了混凝土结构的钢筋锈蚀传感器,在实验室环境下可行的基础上,将其埋入钢筋混凝土结构,对结构内部的钢筋锈蚀情况进行了监测。更多还原

【Abstract】 A long-period fiber grating(LPFG) is a periodic refractive index structure on the fiber core whose periodicity is in the range of several hundred micrometers. The transmission spectrum of a typical LPFG consists of a number of rejection bands that arise from light coupling from the fundamental mode to the cladding modes of the fiber. LPFG has many remarkable advantages, such as low insertion loss, low back reflection, easy to fabricate, polarization independence and etc., The LPFG also offers a series of interesting properties for sensing applications, compared with FBG, they are also sensitive to measurands such as strain, curvature, temperature or the external refractive index, so it becomes a most important part of fiber sensors. Meanwhile, most research on it are in the laboratory while a little in application. This dissertation aims to research on the application of LPFG in structural health monitoring, including the vibration monitoring and the civil engineering structure. All these work provide theoretical and practical preparation for promoting the availability of LPFG detection technology. The main achievements are described as follows:(1)The theory analyse of LPFG has been studied, the written technology and the formation mechanism were introduced. Based on the coupling theory and the three-layer fiber model, the transmission speciality of long period fiber grating is analyzed, and the transmission spectrum function, resonance wavelength, effective refractive index of LPFG were deduced, which offer the theoretical foundation of the manufacture and the sensor characteristic of LPFG.(2)The sensing characteristic of LPFG is the precondition to apply in practice. The basical characters of long-period fiber gratting are studied. It includes the temperature, axial strain, bending, refractive index and transverse-load characteristic. The simple theories and experiments related were concerned.(3)Based on the study of micro-bending characteristic of LPFG, it is found that the loss amplitude of one wavelength is linear to the curvature of LPFG. A new scheme to monitor the structure vibration by gluing the LPFG onto the experimental laminate is proposed and realized. (4)The narrow band reflection light characteristic of Bragg grating was used to demodulate LPFG, by detecting the power of certain fixed wavelength transmission light of LPFG, the dynamic signal monoring system is realized based on the micro-bending characteristic of LPFG, and the acquisition of distributed vibration signal was realized preliminary.(5)Based on the vibration monitor of optical fiber grating smart structure, different damage situation are studied through an analysis of an experimental laminate, the variation of wavelet packet energy spectrum used as the damage character is picked up to identify the structual damage status. And the damage diagnosis of the optical fiber grating smart structure were realized.(6)Base on the mechanism of steel corrosion in reinforced concrete, a scheme was proposed to measure the steel corrosion using the refractive index characteristic, and the experimental results was effective.(7)A new technique to measure the corrosion of steel in concrete structures was proposed, it is based on the microbending characteristic of LPFG, and the corrosion sensor designed was produced to monitor the corrosion of steel in concrete.更多还原