Structural Deformation Monitoring of Flight Vehicles Based on Optical Fiber Sensing Technology:A Review and Future Perspectives

Structural deformation monitoring of flight vehicles based on optical fiber sensing(OFS)technology has been a focus of research in the field of aerospace.After nearly 30 years of research and development,Chinese and international researchers have made significant advances in the areas of theory and methods,technology and systems,and ground experiments and flight tests.These advances have led to the development of OFS technology from the laboratory research stage to the engineering application stage.However,a few problems encountered in practical applications limit the wider application and further development of this technology,and thus urgently require solutions.This paper reviews the history of research on the deformation monitoring of flight vehicles.It examines various aspects of OFS-based deformation monitoring including the main varieties of OFS technology,technical advantages and disadvantages,suitability in aerospace applications,deformation reconstruction algorithms,and typical applications.This paper points out the key unresolved problems and the main evolution paradigms of engineering applications.It further discusses future development directions from the perspectives of an evolution paradigm,standardization,new materials,intelligentization,and collaboration.

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.

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.

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.

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.

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.

基于物联网和弱反射光栅阵列的地质灾害监测系统设计与应用

我国是世界上地质灾害类型最多、地质灾害最严重的国家之一,而雨量监测和形变监测在地质灾害监测中发挥着越来越重要的作用,因此确保地质灾害监测系统的长期运行以及在降雨期间的稳定运行尤为重要。文中基于STM32微控制器、LORA模块、4G模块设计了一款物联网数据采集控制板,并结合压电式雨量传感器、拉绳位移传感器研制了雨量智能监测仪、裂缝位移智能监测仪;结合物联网数据采集控制板和弱反射光栅阵列传感技术构建了基于物联网的弱反射光栅地质灾害监测系统,实现了对地质灾害体的定时监测和降雨期间的自动监测;最后将雨量智能监测仪、裂缝位移智能监测仪和弱反射光栅地质灾害监测系统应用于桐梓县大河镇新场火车站新场滑坡、崩塌的监测实验中。监测数据表明,弱反射光栅监测系统测得传感光缆41#弱反射光栅传感段的位移变化达5 mm,在其附近的位移监测仪也测到有位移变化,可有效实现对地质灾害的定时监测和降雨期间的自动监测。

Towards a fast and stable tachypnea monitor:a C_(60)-Lys enabled optical fiber sensor for humidity tracking in breath progress

The pandemic of respiratory diseases enlightened people that monitoring respiration has promising prospects in averting many fatalities by tracking the development of diseases.However,the response speed of current optical fiber sensors is still insufficient to meet the requirements of high-frequency respiratory detection during respiratory failure.Here,a scheme for a fast and stable tachypnea monitor is proposed utilizing a water-soluble C_(60)-Lys ion compound as functional material for the tracking of humidity change in the progression of breath.The polarization of C_(60)-Lys can be tuned by the ambient relative humidity change,and an apparent refractive index alteration can be detected due to the small size effect.In our experiments,C_(60)-Lys is conformally and uniformly deposited on the surface of a tilted fiber Bragg grating(TFBG)to fabricate an ultra-fast-response,high-sensitivity,and long-term stable optical fiber humidity sensor.A relative humidity(RH)detecting sensitivity of 0.080 dB/%RH and the equilibrium response time and recovery time of 1.85 s and 1.58 s are observed,respectively.Also,a linear relation is detected between the resonance intensity of the TFBG and the environment RH.In a practical breath monitoring experiment,the instantaneous response time and recovery time are measured as 40 ms and 41 ms,respectively,during a 1.5 Hz fast breath process.Furthermore,an excellent time stability and high repeatability are exhibited in experiments conducted over a range of 7 days.

Temperature-and Strain-Compensated Directional Curvature Sensor Based on Bragg Gratings in Three-Core Fiber with Bridged Waveguides

Fiber-based curvature sensors,especially those capable of discerning the direction of curvature,have attracted more and more interest due to their promising applications in structural health monitoring,high-precision measurement,medical and biological diagnosis-treat instruments,and so on.Here,we propose and demonstrate a compact directional curvature sensor that comprises two bridged waveguides and three Bragg gratings in a section of three-core fiber(TCF).Both the waveguides and gratings are integrated by femtosecond laser micromachining method.The waveguides,connecting the TCF outer cores to the lead-in single-mode fiber core,function as beam couplers to realize simultaneous interrogation of all three gratings without any separate fan-in/out component.Owing to the spatial specificity,the outer-core gratings exhibit high and direction-dependent sensitivity to curvature,whereas the central-core grating is nearly insensitive to curvature but shows similar sensitivities to ambient temperature and axial strain as the outer-core gratings.It can be used to compensate the cross impact of temperature and strain when the outer-core gratings are applied for curvature detection.Moreover,the wavelength interval between two outer-core gratings is also proposed as an indicator for curvature sensing.It features with a much higher sensitivity to curvature and reduced sensitivities to temperature and axial strain.The corresponding maximum sensitivity to curvature is as high as 191.89 pm/m-1,while the sensitivities to temperature and strain are only 0.3 pm/℃and 0.0218 pm/με,respectively.Therefore,our proposed device provides a compact and robust all-infiber solution for directional curvature sensing.It not only offers high sensitivity and accuracy but also immunity to temperature and axial strain fluctuations,making it a promising tool for a wide range of applications.

Research on the Surface Subsidence Monitoring Technology Based on Fiber Bragg Grating Sensing

In order to monitor the process of surface subsidence caused by mining in real time, we reported two types of fiber Bragg grating （FBG） based sensors. The principles of the FBG-based displacement sensor and the FBG-based micro-seismic sensor were described. The surface subsidence monitoring system based on the FBG sensing technology was designed. Some factual application of using these FBG-based sensors for subsidence monitoring in iron mines was presented.

Simulation Tools for a Fiber-Optic Based Structural Health Monitoring System

Probability of detection(POD)graphics allow for a change from qualitative to quantitative assessment for every damage detection system,and as such it is a main request for conventional non-destructive testing(NDT)techniques.Its availability can greatly help towards the industrialization of the corresponding Structural health monitoring(SHM)system.But having in mind that for SHM systems the sensors are at fixed positions,and the location of a potential damage would change its detectability.Consequently robust simulation tools are required to obtain the model assisted probability of detection(MAPOD)which is needed to validate the SHM system.This tool may also help for the optimization of the sensor distribution,and finally will allow a probabilistic risk management.INDEUS,simulation of ultrasonic waves SHM system,was a main milestone in this direction.This article deals with the simulation tools for a strain based SHM system,using fiber optic sensors(FOS).FOS are essentially strain/temperature sensors,either with multi-point or with distributed sensing.The simulation tool includes the finite element model(FEM)for the original and damaged structure,and algorithms to compare the strain data at the pre-established sensors locations,and from this comparison to extract information about damage occurrence and location.The study has been applied to the structure of an all-composite unmanned aircraft vehicle(UAV)now under construction,designed at Universidad Politecnica de Madrid for the inspection of electrical utilities networks.Distributed sensing optical fibers were internally bonded at the fuselage and wing.Routine inspection is planned to be done with the aircraft at the test bench by imposing known loads.From the acquired strain data,damage occurrence may be calculated as slight deviations from the baselines.This is a fast inspection procedure without requiring trained specialists,and it would allow for detection of hidden damages.Simulation indicates that stringer partial debondings are detected before they become critical,while small delaminations as those produced by barely visible impact damages would require a prohibited number of sensing lines.These simulation tools may easily be applied to any other complex structure,just by changing the FEM models.From these results it is shown how a fiber optic based SHM system may be used as a reliable damage detection procedure.

Long Period Grating Imprinted on a Flat-Shaped Plastic Optical Fiber for Refractive Index Sensing

A corrugated surface long period grating(LPG)was fabricated on a flat-shaped plastic optical fiber(POF)as a refractive index(RI)sensor by a simple pressing with the heat pressure and mechanical die press print method.The light propagation characteristics of an LPG imprinted on a multi-mode POF were analyzed by the method of geometrical optics.Theoretical and experimental results showed that the structural parameters of the sensor affected the RI sensing performance,and the sensor with a thinner flat thickness,a deeper groove depth of the corrugated surface LPG,and a longer LPG exhibited better RI sensing performance.When the POF with a diameter of 1 mm was pressed with the heat pressure to a flat shape with a thickness of 600μm,an LPG with a period of 300μm,a groove depth of 200μm,and a length of 6 cm was fabricated on it,and the RI sensitivity of 1447%/RIU was obtained with a resolution of 5.494×10^(−6) RIU.In addition,the influences of the POF cladding,tilting of LPG,and bending of the sensing structure were investigated.The results demonstrated that after removing the cladding and tilting or bending the LPG,the RI sensing performance was improved.When the LPG imprinted on the flat-shaped POF was bent with a curvature radius of 6/πcm,the highest sensitivity of 6563%/RIU was achieved with a resolution of 2.487×10^(−9) RIU in the RI range of 1.3330–1.4230.The proposed sensor is a low-cost solution for RI measurement with the features of easy fabrication,high sensitivity,and intensity modulation at the visible wavelengths.

基于布里渊光时域峰值边沿分析的变压器绕组局部热点检测

变压器绕组的温度分布一直是电网运行人员重点关注的对象。与传统传感器相比,分布式光纤传感具有抗电磁干扰能力强、可实现分布式测量等优势,其中布里渊光时域分析技术(BOTDA)的性能稳定,适用于大多数场景,但BOTDA的空间分辨率为m级,难以分辨绕组运行中的局部热点。该文从布里渊散射增益谱的机理入手,利用双峰拟合算法,并结合对异常峰值曲线的边沿分析,提出了一种在不增加系统硬件复杂度的基础上提升BOTDA空间分辨率的方法,以满足局部热点检测要求。通过对光纤沿线不同位置、不同热点长度及不同热点温度下的模拟试验验证了该方法的有效性,在实验室条件下可将准确传感的热点长度提升至原空间分辨率的一半以内。基于变压器实际绕组的局部升温试验,实现了绕组异常热点的精确定位和长度感知,并准确解调了绕组局部热点的温度,进一步验证了该方法的实际可行性和检测优越性,温度相对误差控制在5%以内,为提高变压器绕组温度在线监测的经济性和可行性提供新的思考,同时也为变压器绕组局部故障的提前感知和预警提供了新的思路。

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。

基于布里渊动态光栅的高灵敏度保偏光纤多参量同时解调

为了实现基于保偏光纤在布里渊动态光栅的温度、快轴压力和慢轴压力同时解调,并克服传统压力传感灵敏度不足的缺点,提出了一种边孔型高灵敏度光子晶体光纤。利用有限元方法,研究了温度、快轴压力和慢轴压力与双折射频移、布里渊频移和布里渊线宽之间的关系,据此可实现多参量的同时解调。结果表明,该光子晶体光纤可以实现三参量的同时解调,且解调误差在1 MPa和1℃以内。快轴压力、慢轴压力和温度的误差均值分别为0.21 MPa、0.31 MPa和0.30℃,误差的标准差分别为0.15 MPa、0.21 MPa和0.21℃。在施加0~30 MPa的横向压力和0~100℃的温度时,该光子晶体光纤快轴方向上的压力灵敏度为-1.961 GHz/MPa,光纤慢轴方向上的压力灵敏度为1.356 GHz/MPa,其温度灵敏度为0.105MHz/℃。相较于目前最优结构的光子晶体光纤压力灵敏度提升了-957MHz/MPa。该传感器及解调方法适用于土木结构和大型机械在建造和使用过程中监测其内部所受温度和不同方向压力的变化。

基于光纤传感技术的工程监测应用研究

光纤传感技术作为当前热门技术之一,在工程监测领域有着许多重要应用。通过探讨光纤传感技术在工程形变监测中的应用案例,展示了其在工程监测领域的重要性。光纤传感技术利用光纤作为传感元件,可以实现对形变的连续、实时监测,并提供高精度的监测数据。通过布设应变光缆和温度补偿光缆,在合璧津高速公路K134段高架桥上进行了监测实验。结果表明,光纤传感技术能够准确评估结构的变形情况,并通过温度补偿算法消除了温度变化对数据的影响。通过几何方法计算沉降位移,可以实现对沉降位移的估算。

光纤激光传感器结构发展综述

光纤激光传感技术是光纤传感技术中的重要组成部分。首先介绍了光纤激光传感技术的原理,然后分析了基于单一结构和双结构的10种光纤激光传感器的原理和特性,并对比了2种传感结构的应用情况和温度灵敏度,最后从解调方式、多参量测量以及提升检测范围等3个方面对光纤激光传感技术进行了总结和展望。

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。

分布式光纤传感技术在水力压裂中的研究进展

分布式光纤传感技术作为最新的水力压裂监测技术,应用于各大油田的水力压裂过程中,并且能够实现实时监测,已取得了显著的应用效果。为使业界进一步了解不同类型传感技术的基本原理、理论模型研究进展、现场应用情况,从分布式光纤温度传感技术和声波传感技术在水力压裂过程中的监测基本原理出发,系统总结了各类传感技术的理论模型研究进展和在产液剖面、裂缝扩展形态监测等方面的应用现状,最后提出了未来分布式光纤传感技术的发展方向。研究结果表明:①分布式光纤传感技术可以利用温度或者声波信号转换得到周围环境温度或应变的变化情况,从而实现水力压裂过程中的实时监测;②与分布式光纤声波传感技术相比,温度传感技术的相关理论模型相对较为成熟,能够实现产液剖面及裂缝形态的相关计算;③分布式光纤传感技术主要用于水力压裂过程中压裂液的注入、裂缝扩展等方面的监测。结论认为:分布式光纤传感技术可以有效地推动中国非常规储层的勘探和开发,同时提高水力压裂效果评价技术水平,这对中国油气行业的可持续发展具有重要推动作用。