Strain-Insensitive Fiber Bragg Grating Composite Structure for Wide-Range Temperature Sensing

This paper reports on the design,fabrication,and temperature strain sensing performance of a fiber Bragg grating composite structure for surface mounted temperature measurements over a wide temperature range,with highly reduced strain cross-sensitivity.The fiber Bragg grating sensor is encapsulated in a polyimide tube filled with epoxy resin,forming an arc-shaped cavity.This assembly is then placed between two layers of glass fiber prepreg with a flexible pad in between and cured into shape.Experimental results,supported by finite element simulations,demonstrate an enhanced temperature sensitivity is 26.3 pm/°C over a wide temperature range of–30°C to 70°C,and high strain transfer isolation of about 99.65%.

Novel Apodized Fiber Bragg GratingApplied for Medical Sensors:Performance Investigation

Sensors play an important role in shaping and monitoring human health.Exploration of methods to use Fiber Bragg Grating(FBG)with enhanced sensitivity has attracted great interest in the field of medical research.In this paper,a novel apodization function is proposed and performance evaluation and optimization of the same have been made.A comparison was conducted between various existing apodization functions and the proposed one based on optical characteristics and sensor parameters.The results evince the implementation of the proposed apodization function for vital sign measurement.The optical characteristics considered for evaluation are Peak Resonance Reflectivity level,Side Lobes Reflectivity level and FullWidth HalfMaximum(FWHM).The proposed novel apodization novel function has better FWHM,which is narrower than the FWHM of uniform FBG.Sensor characteristics like a quality parameter,detection accuracy and sensitivity also show improvement.The proposed novel apodization function is demonstrated to have a better shift in wavelength in terms of temperature and pulse measurement than the existing functions.The sensitivity of the proposed apodized function is enhanced with a Poly-dimethylsiloxane coating of varying thickness,which is 6 times and 5.14 times greater than uniform Fiber Bragg grating and FBG with the proposed novel apodization function,respectively,enhancing its utilization in the field of medicine.

Modified simulated annealing evolutionary algorithm for fully distributed fiber Bragg grating temperature sensing

In this paper, we present a simple and fast spectra inversion method to reconstruct the temperature distribution along single fiber Bragg grating （FBC） temperature sensor. This is a fully distributed sensing method based on the simulated annealing evolutionary （SAE） algorithm. Several modifications are made to improve the algorithm efficiency, including choosing the most superior chromosome, setting up the boundary of every gene according to the density of resonance peaks of the reflection spectrum, and dynamically modifying the boundary with the algorithm running. Numerical simulation results show that both the convergence rate and the fluctuation are significantly improved. A high spat-ial temperature resolution of 0.25 mm has been achieved at the time cost of 86 s.

Fiber Bragg Grating Strain Sensing Detecting Multi-Crack Damages under Vibrating Status

The multi-crack damages modal of simple supported beam has been build, at the vibrating status, the multi-damage detecting method of simple supported beam measured by fiber Bragg grating strain sensing array has been studied. From 0 hz to 200 hz, using exciter vibrating simple supported beam, with different damages, resonant frequency of simple supported beam has changed. So, when the damage appears in simple supported beam, the local rigidity will decrease, the resonant frequency of simple supported beam will be affected, the damage status of simple supported beam have been determined by this. The experimental result indicates that the resonant frequency of simple supported beam has changed when there is no damage, one damage, two damages, three damages on simple supported beam. According to this, the fiber Bragg grating strain sensing array can detect multi-crack damage of simple supported beam under vibrating status.

A Novel Temperature-Compensated, Intensity-Modulated Fiber Bragg Grating Sensor System

An intensity-modulated, fiber Bragg grating （FBG） sensor system based on radio-frequency （RF） signal measurement is presented. The RF signal is generated at a photodetector by two modulated optical signals reflected from the sensing FBG and a reference one. Bragg wavelength shift of the sensing FBG changes intensity of the RF signal by changing phase difference between the two optical signals, with temperature effect being compensated automatically by the reference FBG, Strain measurement with a maximum sensitivity of -0.34 μV/με has been achieved.

Effectiveness of Fiber Bragg Grating monitoring in the centrifugal model test of soil slope under rainfall conditions

Centrifugal model testsare playing an increasingly importantrolein investigating slope characteristics under rainfall conditions. However, conventional electronic transducers usually fail during centrifugal model tests because of the impacts of limitedtest space, high centrifugal force, and presence of water, with the result that limited valid data is obtained. In this study, Fiber Bragg Grating(FBG) sensing technology is employed in the design and development of displacement gauge, an anchor force gauge and an anti-slide pile moment gauge for use on centrifugal model slopes with and without a retaining structure. The two model slopes were installed and monitored at a centrifugal acceleration of 100 g. The test results show that the sensors developed succeed in capturing the deformation and retaining structure mechanical response of the model slopes during and after rainfall. The deformation curvefor the slope without retaining structure shows a steepresponse that turns gradualfor the slope with retaining structure. Importantly, for the slope with the retaining structure, results suggest that more attention be paid to increase of anchor force and antislide pile moment during rainfall. This study verifies the effectiveness of FBG sensing technology in centrifuge research and presents a new and innovative method for slope model testing under rainfall conditions.

Development of a monitoring and warning system based on optical fiber sensing technology for masonry retaining walls and trees

Hong Kong has a long history of applying masonry retaining walls to provide horizontal platforms and stabilize man-made slopes.Due to the sub-tropical climate,some masonry retaining walls are colonized by trees.Extreme weather,such as typhoons and heavy rains,may cause rupture or root failure of those trees,thus resulting in instability of the retaining walls.A monitoring and warning system for the movement of masonry retaining walls and sway of trees has been designed with the application of fiber Bragg grating(FBG)sensing technology.The monitoring system is also equipped with a solar power system and 4G data transmission devices.The key functions of the proposed monitoring system include remote sensing and data access,early warning,and real-time data visualization.The setups and working principles of the monitoring systems and related transducers are introduced.The feasibility,accuracy,serviceability and reliability of this monitoring system have been checked by in-site calibration tests and four-month monitoring.Besides,a two-level interface has been developed for data visualization.The monitoring results show that the monitored masonry retaining wall had a reversible movement up to 2.5 mm during the monitoring period.Besides,it is found that the locations of the maximum strain on trees depend on the crown spread of trees.

The Sensing Principle of FBG and Its Experimental Application in Structure Strengthening Detection

Based on the basic theory of the fiber Bragg grating sensor,a kind of stickup FBG sensor is developed,which is applied in the structure strengthening.With the experiment of the FBG senor and the common electricity sensor stuck on the reinforced structure,the result shows that the FBG sensor not only has a high performance,but also can realize the control on the spot and on the line.

Pure Bending Characteristic of Tilted Fiber Bragg Grating

a novel structure of the pure macro- bending sensor based on the tilted fiber Bragg grating （TFBG） is proposed. The TFBG located in the half circle with the different diameters is bent at a constant angle with respect to the tilted grating planes. With the variations of the curvature, the core-mode resonance is unchanged and the transmission power of cladding modes detected by the photodiodes varies linearly with curvature, while the ghost mode changes by the form of two-order polynomial. So we can use the transmission power of ghost mode or other cladding modes to detect bending curvature as shape sensor. From a practical point of view, the sensor proposed here is simple, low cost and easy to implement. Moreover, it is possible to make a temperature-insensitive shape sensor due to the same temperature characteristic between the core mode and the cladding modes.

一种光纤布喇格光栅涡街流量传感器

在流量计量领域中,利用光纤传感技术对涡街流量计量的研究较少,故具有重要的研究意义。该文设计了一种悬臂梁式的光纤布喇格光栅涡街流量传感器,其利用悬臂梁自由端振动使光纤布喇格光栅中心波长发生周期性移位,从而测量涡街频率,得到流体流量信息。温度传感测试实验与流量传感测试实验结果表明,该传感器温度灵敏度为17 pm/℃,涡街流量灵敏度为0.01895 Hz/(L·h^(-1)),非线性误差为2.23%。实验验证了该传感器可应用于液体涡街流量计量。

基于应变增敏的双层十字型FBG触觉感知单元

触觉感知是仿生智能感知的重要内容,为了提高光纤布拉格光栅(Fiber Bragg Grating, FBG)触觉感知灵敏度,结合机器手指尖触觉感知需求,提出了一种应变增敏的FBG触觉感知单元。基于应变增敏机理和触觉感知机理分析,设计了一种基于应变增敏的双层十字型FBG触觉感知单元,采用刚性球型多点增压结构进行应变增敏。利用仿真分析方法优化了FBG空间分布,并对感知单元进行了静力学和热力学仿真。最后搭建了触觉感知实验平台,结合机器手完成了温度-力触觉协同感知实验。仿真和实验结果表明,FBG1和FBG2的力触觉感知灵敏度分别为18.069 nm/MPa和1.065 nm/MPa,温度感知灵敏度为11.256 pm/℃和11.153 pm/℃。该触觉感知单元有效提高了触觉感知灵敏度,具有良好的线性度和重复性。

基于多FBG组合传感的机械臂外部干扰应力监测系统

为了解决机械臂工作过程中外部应力干扰导致装配位置偏差的问题,设计了一种基于多光纤光栅传感器组合传感的监测系统。根据机械臂运动角度范围,仿真分析了在两个特征位置上不同方向外加应力后外机械臂与内机械臂的应力场分布特征。依据应力场分布特性,设计了多FBG的传感阵列,并计算了不同FBG响应与外部干扰应力的对应关系。实验采用16个FBG对FS-MP1C型小型机械的抓取过程进行在线监测,随机外部干扰应力设置为2~20 N。16个FBG的响应线性度均在0.99以上,正向和负向波长响应最大值分别为1354 pm和-984 pm。在100次分层干扰测试中,X与Y轴向干扰应力检出率优于80.0%,Z轴向干扰应力检出率优于97.5%。系统平均误检率低于4.0%。可见,本设计可以在线完成外部干扰应力的实时监测,具有一定的实用价值。

基于FBG和F-P的温度和折射率双参量传感器

提出了一种由单模布拉格光栅和多模Fabry-Perot腔级联而成的温度和折射率双参量传感器。对多模光纤的末端采用氢氟酸进行腐蚀,在腐蚀后形成的凹陷处填充紫外胶,从而形成Fabry-Perot腔。Fabry-Perot腔和单模光纤布拉格光栅级联后,构成最终的传感结构。Fabry-Perot腔对温度和折射率敏感,而光纤布拉格光栅对温度敏感而对折射率不敏感。利用上述特性,采用灵敏度矩阵法可实现对温度和折射率的同时测量。实验结果表明,传感器的温度和折射率灵敏度分别为-0.4832nm/℃和-508.64pm/RIU。该传感器具有制作工艺简单、结构紧凑、成本低、灵敏度高的优点,有很好的应用前景。

钢-连续纤维复合筋珊瑚混凝土梁式拉拔粘结应力分布研究

为探究钢-连续纤维复合筋(SFCB)在珊瑚混凝土中的粘结应力分布,使用梁式拉拔试验方法,对碳纤维增强复合材料(CFRP)筋和不同直径SFCB珊瑚混凝土进行拉拔,并采用光纤Bragg光栅(FBG)传感技术对筋材应力分布变化动态监测。研究结果表明:SFCB直径和钢芯直径均会影响荷载-滑移曲线形状;箍筋对筋材初始粘结刚度和SFCB纤维层加载端应变有明显提升;箍筋一定程度可以增强螺纹钢芯的粘结,对光圆钢芯粘结影响不大;SFCB屈服后的粘结应力分布与屈服前有明显差异,钢芯屈服后应力传递现象更明显;由于钢芯具有较高的弹性模量,在相同荷载下SFCB纤维层粘结段各处粘结应力均要大于CFRP筋。

基于NSGA-Ⅱ传感位置优化的曲面重构及误差补偿方法

通过优化光纤布拉格光栅形状传感技术中传感点位置和补偿重构结果来提高薄层合金板三维形状重构精度。通过ANSYS workbench建立合金板仿真模型,提取应变和位移模态振型,根据模态置信准则、转换矩阵稳定性和模态振型相似性分别设计了三个目标函数,采用快速和精英机制的多目标遗传算法优化传感器位置。将镍钛合金板弯曲成不同曲率半径的弧形,利用光纤布拉格光栅中心波长漂移量和线性插值算法计算得出不同形状下的结构应变,重构合金板形状,均方根误差和最大误差相较于单目标优化算法分别减小30%和15%。利用粒子群优化径向基函数神经网络算法拟合误差与位移的关系实现误差补偿,均方根误差和最大误差比无补偿时分别减小了90%和70%,最大相对百分比误差仅为5%,提高了三维形状重构算法精度。

变电设备状态信息光纤/光学传感研究

准确感知输变电设备的运行状态,及时采取有效的运维检修策略,对保证新型电力系统安全高效运行意义重大。光纤/光学传感具有绝缘性能好、抗电磁干扰、可分布式测量、测量精度高等优点,在变电设备领域发展迅速。该文介绍了包括基本电气量(电压、电流)、设备状态量(温度、湿度、压力、振动)、绝缘状态量(分解产物、局放)的光纤/光学感知原理与主要研究进展,对比讨论了不同监测方法的优缺点。并在此基础上,重点分析了现有技术尚未攻克的难点问题与发展趋势,期望对新型电力系统全息感知能力的提升提供参考。

采用WDM技术的光纤Bragg光栅传感网络

采用绝对测量原理的波长调制技术 ,光纤Bragg光栅可组成并行、串行和阵列WDM拓扑结构 分析表明 ,光纤Bragg光栅网络的工作原理类似于一个多宽带平面镜 利用光谱仪可测量上述光纤Bragg光栅网络的反射谱 ,其中 ,光源是宽带为～ 4 0nm的掺饵光纤放大器 当网络中的光纤Bragg光栅受扰动后 ,受扰光栅的反射谱发生相应的变化 ,即Bragg波长发生相应的偏移 结果表明 ,当事先确定了光纤光栅的波长调制范围 ,反射的峰值波长能反应光纤光栅传感网络的信息 值得注意的是～ 3nm的波长调制范围可满足～ 10 0℃和～ 2 0 0 0

光纤Bragg光栅应变传感研究

基于光纤Bragg光栅应变传感模型 ,利用泰勒级数展开法 ,将光纤Bragg光栅反射峰中心波长所满足的Bragg方程展开 ,得到了中心波长相对偏移量与应变增量之间的二次解析关系式 ,进而得到了光纤Bragg光栅一阶、二阶应变灵敏度系数的解析表达式 ,计算了一阶、二阶应变灵敏度系数的理论值 ;并将光纤Bragg光栅粘贴在悬臂梁上进行拉伸和压缩 ,得到了与应变对应的光纤Bragg光栅中心波长偏移量 ,通过线性和二次多项式拟合 ,得到了光纤Bragg光栅一阶、二阶应变灵敏度系数的实验值 ;

光纤Bragg光栅压力传感机理研究

对光纤Bragg光栅的压力传感机理进行了理论研究。分析了引起光纤光栅中心波长偏移的各种物理效应,并对几种不同形式压力下各种物理效应所引起的灵敏度系数进行了计算。计算结果表明,纵向和横向压力灵敏度系数相反,屏蔽一个方向可获得较大的压力传感灵敏度;波导效应所引起的应变灵敏度系数都比弹光效应小几个数量级,因此可以忽略。并首次提出在不同方向的压力作用下,弹光效应对应变灵敏度具有不同的贡献。

双悬臂梁光纤Bragg光栅应力传感器

报道了一种新颖的光纤Bragg光栅应力传感器.理论分析和实验证明了这种传感器Brrag光栅中心波长随应力变化的线性工作区.将光纤Bragg光栅贴于双悬梁的梁端面,在双悬梁的自由端部施加载荷,对光纤Bragg光栅的应力响应特性测试.当所加载荷为300 g时,光纤Bragg光栅中心波长变化了0 .156 nm.从实验上获得了-0 .05 nm/N的应力响应灵敏度.该结构具有应力增敏作用,且应力响应的线性、重复性和迟滞性较好.应力响应灵敏度随着梁的大小以及材料的力学参量的改变而改变.