光学低相干反射技术实现光纤光栅分布式传感测量的研究

Research on non-uniform distributed strain measurement of fiber Bragg grating (FBG) is still focusing on the theoretical research in China. For the study, a set of FBG-OLCR measurement system based on optical low coherence reflectometry and lay-peeling algorithm is proposed and designed, aiming to achieve the distributed non-uniform strain detection in FBG's effective length. The genetic algorithm is employed within lay-peeling algorithm to solve the problem of reconstruction of high- reflectivity fiber grating. As while, the genetic algorithm is combined with chaos operator to enhance the optimal search strategy of the population, improve the algorithm accuracy and speed. Based on a Michelson optical low-coherence reflectometry joined together with a tunable laser source, piezoelectric ceramics,and balanced photodetectors etc., a new measurement system for FBG is planned to build up. The analysis of choice of system parameters and system performance assessment are needed to complete. Use the LabVIEW software to code the software procedures of the measurement system, for completing the function of controlling and testing. MATLAB functions are called in the LabVIEW software to run the lay-peeling algorithm. A variety of cantilever structures are designed for the FBG's non-uniform strain tuning. The results from the ANSYS simulation and the FBG-OLCR measurement system are compared to verify the FBG-OLCR measurement system. Error source analysis of the FBG-OLCR system is planned and the evaluation of uncertainty of the measurement result is needed.

国内对光纤光栅的分布式非均匀应变研究尚处于理论研究阶段，项目以光纤Bragg光栅（FBG）为研究对象，拟采用光学低相干反射技术（OLCR），通过剥层算法，构建一套FBG-OLCR测量系统，实现FBG工作长度上分布式非均匀应变的检测。遗传算法引入剥层算法中，解决剥层算法在重构高反射率光栅参数上的不足，遗传算法结合了混沌算子，以增强最优种群的搜索策略，提高算法精度和速度。在Michelson光学低相干反射仪基础上，增加可调激光光源、压电陶瓷驱动、平衡检测机构等，构建适用于FBG的测量系统，需要完成系统参数的分析选择、系统性能的评定，利用LabVIEW软件编写系统的控制测量程序，并调用MATLAB函数实现剥层算法。设计多种悬臂梁结构实现FBG的非均匀应变调谐，ANSYS仿真结果与FBG-OLCR测量系统结果比对验证，对FBG-OLCR测量系统的误差源进行分析，对测量结果的不确定度进行评定。

光纤光栅（FBG）点式和多点准分布式传感应用日益广泛，与此同时，FBG分布式传感应用虽然在局部结构健康检测中的优势显而易见，但因解调技术的限制而得不到有效发展。项目对基于光学低相干反射技术（OLCR）在FBG分布式应变检测中的原理和技术进行研究。研究了FBG的重构方法，提出并设计实现了基于复耦合系数常幅值的改进剥层算法（QAC-LP），相比经典剥层算法（LP），QAC-LP算法获得的应变在解调范围内的最大应变误差和均方根误差都得到了较大改善；提出了基于多项式函数初始化（PFI）思想的遗传算法，用于FBG分布式应变重构的优化，在收敛精度、收敛效率方面得到改善；针对高反射率FBG末端重构精度差的问题，提出了从反射率入手选用FBG一系列参数的原则和方法。搭建了一套基于动态扫描OLCR的FBG检测系统，完成了硬件控制系统的软件编程和FBG解调算法的软件实现；重点研究了光源特性、平移台特性、平衡探测结构、光路偏振态对测试信号的影响，结果表明当前配置已能基本解调出FBG信号，初步完成所需解调功能。对FBG的应变传递特性及应用做了有益探索，研究结果直接用于表贴式FBG悬臂梁调谐结构中；利用ANSYS有限元分析了不同类型悬臂梁的表面应变分布规律，选取了等腰悬臂梁和矩形截面悬臂梁实现分布式均匀应变和分布式非均匀应变；系统测试结果表明FBG-OLCR系统能解调出FBG轴向分布式应变。所搭建的检测系统尚需进一步改善，且由于检测验条件仍限制于实验室，离商用化距离较远，但研究结果给FBG分布式应变解调技术提供了很好的指导作用，有利于FBG分布式传感的应用。