Bragg光纤传感技术应用研究

分析了光纤光栅传感器的工作原理,介绍了成栅技术及应用前景,提出了在应用光纤光栅传感技术时解决温度、应力交叉敏感等问题的新方法.研究结果对Bragg 光纤传感器在工程技术领域具有一定的应用价值.     

Small diameter fiber Bragg gratings and applications

Small diameter optical fibers are preferred in sensing systems as they have less influence on mechanical performance of smart composite. The static and dynamic monitoring capabilities of the small-diameter fiber Bragg gratings (FBG) are experimentally studied in this paper. Firstly, a small-diameter FBG is used as a strain sensor. Secondly, a temperature sensor is fabricated using a specific FBG. Thirdly, a simple sensing system is proposed in order to discriminate temperature at sensing point. Finally, utilization of these small diameter FBGs for vibration monitoring is discussed. The experiments revealed that the central wavelengths of the small-diameter fiber Bragg gratings shift linearly with strain or temperature. The FBG is more sensitive than a thermocouple inside the thermostat. Acquisition and analysis of the dynamic signal indicates that the designed FBG can be used for dynamic signal monitoring.     

采用光纤光栅传感器测量模型材料应变的原理和应用

应变是材料与结构的重要物理特性,最能反映结构局部特性,是材料和工程结构健康监测最为重要的参数。对材料应变测量,可以预知局部荷载的状态。光纤传感器具有灵敏度高、响应速度快、电磁兼容性强、无零漂、可靠性高、使用寿命长等特点。光纤光栅应变传感器是一种极具发展潜力和应用价值的应变传感器。研究了光纤光栅应变传感器的传感原理、应变传递规律及其在模型试验相似材料应变测量中的应用,测量得到的应变历程与实际物理过程相一致。     

光纤光栅压力传感器的研究进展与趋势

由于在灵敏度、绝缘性、抗腐蚀和分布式测量等方面具有优势,光纤光栅压力传感器在能源化工、航空航天和土木工程等领域中逐渐地受到人们关注,并成为研究热点。通过综述近年来迅速发展的光纤光栅压力传感器的研究进展,介绍了利用光纤布拉格光栅(FBG)轴向应变构建压力传感器的工作原理、结构和特点,并按照光纤光栅安装方式对此类压力传感器进行了分类,同时概述了光纤光栅横向压力传感的实验研究,并对光纤光栅压力传感器的发展趋势进行了述评。     

基于桥梁结构的FBG传感器温度与应变交叉敏感问题的研究

对光纤布拉格光栅(FBG)传感器在桥梁结构健康监测中产生的温度与应变交叉敏感问题进行了研究。采用参考光纤光栅法在应变传感光纤光栅附近额外加入一个温度测量光纤光栅,对应变光栅实现温度补偿功能。设计了基于参考光纤光栅法的FBG传感器及FBG传感器封装的机械结构,并通过实验来验证FBG传感器的性能。实验数据表明,温度传感光纤光栅几乎不受应变的影响,应变传感光栅的中心波长变化与温度变化呈一阶线性关系,修正后的测量结果更加精确,达到了双参数同时测量的目的,应变与布拉格波长的线性关系非常好,相关系数达到0.99以上。参考光纤光栅法能够很好地解决FBG传感器温度与应变交叉敏感的问题。     

基于光纤布拉格光栅的载荷定位与检测方法

针对传统定位系统存在的结构复杂、实时性低、需要建立训练集等问题,提出利用光纤Bragg光栅结合直角应变花结构的方法对冲击源进行定位。在平面应变下,建立横向效应补偿因子模型和应变解耦模型,证明了光纤布拉格光栅(Fiber Bragg grating,FBG)直角应变花结构用于定位时不受横向效应的影响。同时针对四边简支薄板结构,提出一种判定冲击载荷大小的新方法。通过不同位置两组FBG应变花分别测得的主应变方向,其交点来确定冲击源坐标;通过FBG传感器测得的轴向应变经横向效应补偿,并结合四边简支板扰度曲线和定位坐标,来对冲击载荷大小进行测量。试验表明其定位精度达到2.9 cm以内,定位实时性1 ms左右,冲击载荷大小判定误差在3 N以内。为冲击平台载荷检测提供了一种实用可行的方法。     

一步超声法金属化封装FBG的传感特性

为解决传统胶封传感器普遍存在的蠕变、老化问题,本文提出基于一步超声法的光纤光栅表面金属化封装方法。在相同条件下分别对有聚酰亚胺涂覆层和无涂层的两种FBG进行金属化封装,研究了封装后FBG传感器的光谱、热学和力学特性,并利用扫描电子显微镜对其横截面的微观形貌进行了表征。结果表明:封装后有涂覆层FBG的反射光谱无明显畸变、边模抑制比大于10 dB,温度灵敏系数达34.63 pm/℃,应变灵敏系数为1.18 pm/με,应变传递效率达98.5%,线性度达0.999,均优于无涂层的FBG传感器。当温度从14.2℃突变到80℃经过多次冲击试验,发现金属化封装无涂层的FBG的温度增敏结构被破坏,而有涂层的FBG传感器仍保持优异的温度响应特性。SEM图显示,金属合金与有无涂覆层的光纤和金属基底都结合致密。该方法无需对光纤进行表面金属化预处理,操作简单易行,在恶劣环境、超长服役时间的光纤传感应用领域中具有重要的价值。     

用于复合材料蒙皮的FBG正交传感网络研究

为了实现对复合材料蒙皮的结构健康监测与损伤识别,本文在对光纤布拉格光栅(FBG)应变传感器理论分析的基础上,结合CFRP材料特性和波分复用技术设计了一种由16个FBG传感器构成的光纤光栅正交传感网络布局,对碳纤维复合材料(CFRP)蒙皮进行相关准分布式传感网络研究。通过对复合材料中心位置进行逐级加载实验,并提取中心波长漂移量做相关性分析,证明了正交对称FBG传感网络对CFRP蒙皮进行结构健康监测的可行性,同时对称布局位置处的FBG传感器信号具有高度相关性质,相关系数可高达0.9996。实验结果为进一步研究准分布式FBG网络的位置布局优化以及传感网络的可靠性冗余设计提供了依据。     

Monitoring and analysis of PHC pipe piles under hydraulic jacking using FBG sensing technology

Pretensioned high-strength concrete (PHC) pipe piles have been widely used for geotechnical engineering such as foundation engineering, slope engineering, highway engineering. To study the performance of a PHC pipe pile under hydraulic jacking, the monitoring of the strain profile along the PHC pipe pile under hydraulic jacking was carried out using FBG sensing technology. In this study, a PHC pipe pile was instrumented with two series of fiber Bragg grating (FBG) sensors along pile axial direction and was then installed in the field using a hydraulic jacking method. To monitor the variation of strains along a PHC pile, two series of eight FBG strain sensors with different peak wavelengths were mounted on opposite sides of the pile with one meter spacing. In addition, based on the pile theory, both the axial force of the pile and average shear stress on the pile surface are calculated using the measured axial strains. It is found that there were significant residual strains in the piles after installation when hydraulic force was removed. This study confirms that the fiber Bragg grating (FBG) sensors are suitable for monitoring strain distribution along a pile under hydraulic jacking.     

Design and development of Fiber Bragg Grating sensing plate for plantar strain measurement and postural stability analysis

This paper describes an ab initio design and development of a novel Fiber Bragg Grating (FBG) sensor based strain sensing plate for the measurement of plantar strain distribution in human foot. The primary aim of this work is to study the feasibility of usage of FBG sensors in the measurement of plantar strain in the foot; in particular, to spatially resolve the strain distribution in the foot at different regions such as fore-foot, mid-foot and hind-foot. This study also provides a method to quantify and compare relative postural stability of different subjects under test; in addition, traditional accelerometers have been used to record the movements of center of gravity (second lumbar vertebra) of the subject and the results obtained have been compared against the outcome of the postural stability studies undertaken using the developed FBG plantar strain sensing plate.     

用于光纤光栅传感的低成本高分辨率多通道波长解调仪

本文报道一种用于光纤光栅传感的低成本高分辨率多通道波长解调仪。基于薄膜滤波技术的密集波分复用模块已被广泛用于光纤通信系统中，在本文中，采用已商品化的薄膜密集波分复用模块同时完成了以波分复用方式连接的多个光纤光栅传感器的信号分离与波长解调功能，研究了一种结构简单、低成本、高分辨率的光纤光栅传感系统。该传感系统的特点是可用于多通道动态测量。本文将具体介绍一种旧通道传感系统，该系统在3kHz频率下的动态应变的分辨率优于1nε√Hz。     

粘贴于薄板表面的光纤布拉格光栅应变传感器误差修正

考虑现有光纤布拉格光栅(FBG)传感器的应变传递理论均未考虑传感器对基体应变的影响,本文针对FBG传感器粘贴于薄板的情况研究了薄板的应变传递理论。由于光纤应变与薄板应变并不相等,故研究了光纤应变与薄板应变之间的关系以提高FBG传感器的测量精度。建立了粘贴于薄板表面的FBG传感器应变传递理论,分析了FBG传感器与薄板之间的相互作用;利用有限元法(FEM)和实验法验证了理论的正确性。最后,分析了薄板参数对应变传递率的影响。结果显示:FEM解与理论解的误差在4%以内,实验值和理论解误差在5%以内,应变传递率随着薄板厚度和弹性模量的增加而逐渐增大。该理论模型完全满足FBG传感器精度要求,对其实际应用具有一定的指导意义。     

A new flexible FBG sensing beam for measuring dynamic lateral displacements of soil in a shaking table test

In this paper, the design, validation, and application of a new flexible fiber Bragg grating (FBG) sensing beam are presented for effectively measuring dynamic lateral displacements inside soil mass in a shaking table test. The special flexible FBG sensing beam has been fabricated by employing a series of FBG sensors along with design of temperature compensation. Based on this design, equations of converting strains to lateral displacements are derived by using both differential and integral methods. Subsequently, the effectiveness of the FBG sensing beam has been verified in a shaking table test with non-contact laser displacement sensors (LDSs). The dynamic lateral displacements at different depths of the soil mass in the shaking table box throughout time history are calculated by differential and integral methods and compared with the results of LDSs. The comparison validates the measurement accuracy of the FBG sensing beam. Additionally, the Fast Fourier Transform (FFT) analysis result demonstrates that frequency measured by the sensing beam fits well with the results of traditional accelerometers and LDSs. Therefore, it can be concluded that the flexible FBG sensing beam is compatible with the stiffness of the soil and is capable of measuring dynamic lateral displacements with good accuracy in a shaking table test.     

Evaluation of bending strain measurements in a composite sailboat bowsprit with embedded fibre Bragg gratings

Acrylate-coated Fibre Bragg Gratings (FBGs) were embedded in a sailing boat bowsprit tubular section manufactured using the vacuum bagging process in autoclave with the aim of measuring strains under realistic loading conditions. In order to establish an effective procedure for sensor integration, flat tensile specimens with embedded sensors were firstly produced under different processing conditions, using advanced composite material employed in the marine industry. Information obtained in this way was used to manufacture a sailboat bowsprit with an array of gratings embedded between the last inner plies. In order to assess the sensitivity and accuracy of the embedded sensors, the bowsprit was subjected to bending tests and the results were compared to analytical values and to data obtained from electrical strain gages. Results are very encouraging but reveal that great attention must be paid both to the integration process and to the in situ calibration of the embedded sensors.     

光纤布拉格光栅传感分析仪

提出了一种基于FPGA与DSP平台的光纤布拉格光栅传感分析仪,将外界参量的变化转化为光纤布拉格光栅波长的偏移,通过数据采集、过滤杂波、信号波峰检测、高斯曲线拟合以及加权波长计算等关键步骤来实现波长解调技术,进而完成温度、应变、压力或位移等对象的在线测量,并且可以实现光纤线路故障分析与定位的功能.实验结果表明:该系统功耗低、线性度好、波长解调精度与分辨率较高.经过长期测试,系统软硬件运行稳定可靠.     

Polarization Maintaining Photonic Crystal Fiber sensor embedded in carbon composite for structural health monitoring

Use of Polarization Maintaining Photonic Crystal Fiber (PMPCF) for structural health monitoring (SHM) of composites has been proposed and demonstrated for accurate strain measurement with very negligible temperature sensitivity. Further, this newly proposed sensor has been compared with the conventional Fiber Bragg Grating (FBG) sensor used for SHM. It is established that the embedded PMPCF in carbon composite is the better choice with enhanced strain sensitivity and less temperature sensitivity compared to the embedded FBG sensor.     

Effect of dispersion compensation on FBG sensing systems’ performance

This paper introduces the use of a fiber-optic communication system for interrogation and transmission of data from fiber Bragg grating (FBG) sensors. Signal coding and dispersion compensation methods, usually used in communication systems, are used to improve the sensing system’s performance. Moreover, communication system parameters are used to assess the improvement in the FBG sensing performance. This is done through the determination of the profiles of Q-factor and eye diagrams. The sensors considered in the simulations are strain sensors subjected to a wide range of strains. The results obtained show a clear improvement of the sensing system with symmetrical compensation. The proposed method is suitable for applications where fiber-optic links are available near both the sensing location and information-collection and-processing unit, even if these two are hundreds of kilometers apart. A good example of where such a system can be applied is the oil industry. The rigs are usually very far from headquarters, but both might be close to a fiber node. Published in Russian in Pribory i Tekhnika Eksperimenta, 2006, No. 3, pp. 115–118. This text was submitted by the authors in English.     

FBG传感器应变标定方法

为了提高光纤光栅应变传感器测量精度,针对光纤光栅传感器工程应用情况,提出了一种光纤布拉格光栅(fiber bragg grating,简称FBG)传感器应变特性标定方法。通过理论分析和实验标定了封装式光纤光栅应变传感器的灵敏度系数,对传感器理论与实验灵敏度系数误差进行了分析。实验结果表明,该方法简单、易行,用于光纤光栅传感器使用前的标定,可以提高基于光栅光栅传感器的测量精度和准确性。同时,该方法为光纤光栅传感器的工程推广应用奠定了基础。     

Concrete beam crack detection using tapered polymer optical fiber sensors

In this paper, a tapered polymer fiber sensor (TPFS) is employed to detect the crack of Concrete Beam (CB). The sensing principle for crack detection is simply described based on V-number theory. The experiments are carried out by cement mixture mixed with high reactive powder to form the CB, in which the TPFSs are embedded and surface glued. Thermocouples and strain gauges are also embedded to calibrate and determine the ambient temperature and applied strain, meanwhile, the Linear Variable Differential Transformer (LVDT) sensors are used to measure the deflection of the CBs. Four points loading test is applied for several samples to evaluate the sensors’ ability for monitoring the beam deflection and crack. Experimental results also indicate that the TPFSs can be used for post-crack detection.     

Extraction and processing of real time strain of embedded FBG sensors using a fixed filter FBG circuit and an artificial neural network

Fibre Bragg Grating (FBG) sensors have been used in the development of structural health monitoring (SHM) and damage detection systems for advanced composite structures over several decades. Unfortunately, to date only a handful of appropriate configurations and algorithm sare available for using in SHM systems have been developed. This paper reveals a novel configuration of FBG sensors to acquire strain reading and an integrated statistical approach to analyse data in real time. The proposed configuration has proven its capability to overcome practical constraints and the engineering challenges associated with FBG-based SHM systems. A fixed filter decoding system and an integrated artificial neural network algorithm for extracting strain from embedded FBG sensor were proposed and experimentally proved. Furthermore, the laboratory level experimental data was used to verify the accuracy of the system and it was found that the error levels were less than 0.3% in predictions. The developed SMH system using this technology has been submitted to US patent office and will be available for use of aerospace applications in due course.