Monitoring shear deformation of sliding zone via fiber Bragg grating and particle image velocimetry

Monitoring shear deformation of sliding zones is of great significance for understanding the landslide evolution mechanism,in which fiber optic strain sensing has shown great potential.However,the cor-relation between strain measurements of quasi-distributed fiber Bragg grating(FBG)sensing arrays and shear displacements of surrounding soil remains elusive.In this study,a direct shear model test was conducted to simulate the shear deformation of sliding zones,in which the soil internal deformation was captured using FBG strain sensors and the soil surface deformation was measured by particle image velocimetry(PIV).The test results show that there were two main slip surfaces and two secondary ones,developing a spindle-shaped shear band in the soil.The formation of the shear band was successfully captured by FBG sensors.A sinusoidal model was proposed to describe the fiber optic cable deformation behavior.On this basis,the shear displacements and shear band widths were calculated by using strain measurements.This work provides important insight into the deduction of soil shear deformation using soil-embedded FBG strain sensors.

基于正弦式波纹膜片的压差式FBG静力水准仪

为解决建筑物不均匀沉降长期、可靠监测的问题,基于连通器原理,推导了膜片半径r、刚度K、光纤自由段长度l、波长变化量Δλ_(B)等参数和沉降量的线性关系式。以此设计了带有正弦式波纹膜片的压差式光纤布拉格光栅(FBG)静力水准仪,并通过标定试验验证压差式FBG静力水准仪的传感性能。结果表明:此静力水准仪灵敏度不小于13.2 pm/mm,综合误差不大于3.26%,相关性系数均在0.99以上。该型静力水准仪传感性能满足工程结构沉降测量的要求,丰富了FBG静力水准仪的研究,具有理论和现实意义。

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。

FBG反射谱数据滑动相关滤波算法设计与实现

针对光纤光栅解调系统中现有滤波算法计算速度与滤波效果难以兼顾的问题,提出了一种基于滑动相关滤波的光纤布拉格光栅(Fiber Bragg Grating,FBG)反射谱滤波方法并在现场可编程门阵列(Field Programmable Gate Array,FPGA)上实现算法加速设计。该算法根据FBG半峰全宽确定高斯函数二阶导数的标准差,用函数的负数作为滤波模板权重,通过滑动数据窗口进行反射谱数据与滤波模板的相关计算,从而实现滤波操作。使用该算法处理含高斯噪声、坏点和基线的仿真数据,验证了该方法对多种异常反射谱数据处理的有效性,并与其他下位机滤波算法进行对比分析,该算法能较好地保留原始数据特征,有较好的鲁棒性,信噪比最高提升28.23dB,中心波长平均偏差和偏差标准差最小,分别为1.712 pm和2.996pm。同时在FPGA片上平台实现了该算法,采用循环队列策略设计存储器,提高了存储器使用率,降低了资源消耗。实验表明,该算法可以有效校正多种异常FBG反射谱,在100MHz系统时钟下处理一个反射谱数据所需时间仅5.09μs,易于实现工程化应用,克服了下位机现有滤波算法对FBG反射谱中坏点、基线抑制作用较差和滤波后信号变形的问题,实现了FBG反射谱滑动相关滤波算法的加速设计。

Study on rock deformation monitoring using fiber Bragg grating in simulation experiment

Presented the fiber Bragg grating （FBG） sensors for rock strain monitoring in the 1.2 m long plane stress model of the simulation experiment. In the past, for the lack of appropriate technique to measure the deformation of rock structures, the measurement of deflection was restricted to just a few discrete points along rock, and the measuring points were limited to the location installed with displacement transducers. We developed a method to monitor the deformation of rock structures using fiber optical Bragg grating strain sensors. The sensors were embedded in rock layers of simulation experiment before the materials were put in. These sensors were then used to monitor the experienced strain with different face advancing distance. The test results indicate that, if properly installed, FBG sensors can survive under severe conditions associated with embedment process and yield accurate measurements of strains response. At the same time, we make comparisons of the data obtained by FBG sensors with those by centesimal gauge. The interest in FBG sensors was motivated by the potential advantages that they can offer more than existing sensing technologies.

Resistance Spot Welding Method for Metal-Based Fiber Bragg Grating Sensors

Aiming at the requirements of installation and work environment of metal-based fiber Bragg grating(FBG)sensor,a resistance spot welding method is presented.Firstly,the effect of welding parameters on welding quality is discussed theoretically,and a suitable resistance spot welding method for the metal-based FBG sensor is proposed for the first time.Then through serial resistance spot welding tests,the feasibility and practicability of the method are verified,and optimal welding parameters for two different tested metals are obtained.Fatigue performance test validates FBG sensors installed by the proposed method with good fatigue properties and long-term stable measurement performance.The research results can provide technical guidance for engineering structure long-term safety monitoring.

An active temperature compensated fiber Bragg grating vibration sensor for high-temperature application

An active temperature compensated fiber Bragg grating(FBG)vibration sensor with a constant section cantilever beam is proposed for the simultaneous measurement of temperature and vibration,and the sensor is verified by a temperature compensation feedback system.The high-temperature vibration sensor is composed of a quartz cantilever beam and a femtosecond Bragg grating.The feedback control demodulation system of active temperature compensation can adjust the laser wavelength to stabilize the grating offset point and realize simultaneous measurement of temperature and vibration.On this basis,the performance of the sensor is tested and analyzed within the range of 20-400℃by setting up a high-temperature vibration test system.The experimental results show that the sensitivity of the sensor is about 132.33 mV/g,and the nonlinearity is about 3.33%.The sensitivity between the laser wavelength and temperature is about 0.01307 nm/℃.In addition,the active temperature compensated fiber Bragg grating vibration sensor has the advantages of a simple structure,stable performance,easy demodulation and high sensitivity.Moreover,the sensor can achieve high temperature vibration signal monitoring and has good practical application value.

表贴式矿用FBG传感器应力传感特性分析研究

本文重点对表贴式矿用光纤布拉格光栅(FBG)传感器应力传感特性进行了分析研究,针对表贴式FBG传感器应力传感特性受基体剪切模量进行系统性的分析,建立表贴式FBG应变三层结构理论分析模型,推导表贴式FBG的应变传递数学表达式,从基体的剪切模量角度分析矿用FBG传感器应力传感特性。通过试验分析总结,得出铜基体材料应变和波长线性关系最佳,可达99.89%,表贴式FBG基体剪切模量越大,应力与波长线性度越好,为矿用FBG传感器结构设计和灵敏度优化提供理论研究基础。

Fiber Bragg Grating Based Sensing'Platform for Foot Plantar Pressure Measurement

presented an application of using 3 D printing technique for the design and fabrication of a novel fiber Bragg grating( FBG)based sensing platform for foot planar pressure measurement.Pressure sensing unit was fabricated using 3 D printing technique by layering of extruded polylactic acid( PLA) material and mounting FBG sensor at the center of each sensing unit for pressure measurement. Performance of the sensing system was validated by applying load step by step as well as cyclic load on FBG pressure sensors. A simulation study was carried out using the sensing platform to assess foot plantar pressure distribution arises from weight gaining and losing processes of pregnant woman. The monitored four different foot positions such as first metatarsus,second metatarsus,mid-foot and heel exhibited obvious differences during testing process. Foot plantar pressure of heel was 1. 7 times of the pressure occurred at the first and second metatarsus( fore-foot),while there was limited pressure occurred at the mid-foot position during weight gaining process of a female subject. The occurred pressures at the two metatarsus areas were around 90%( pressure ratio) of heel and decreased continuously as the increase of subject weight,but weight losing process had very limited influence on this pressure ratio. Center of gravity of pregnant woman was found to shift backward substantially during the weighting gaining process,leading to a significant rise of the heel pressure. Hence, the protection of the heel position for female is highly important during both pregnancy and after baby delivery.

基于FBG的农业大棚土壤温度测量与研究

研究农业大棚土壤温度,对农业生产具有重要意义。针对传统热电偶等传感器测量土壤温度场存在效率低、误差大等问题,该文采用一种基于光纤布拉格光栅(FBG)的温度传感器来监测农业大棚内的土壤温度变化。该方法将封装了FBG串的不锈钢管垂直埋入被测土壤中,采用可调谐激光器法和寻峰算法解调FBG串各传感器波长,在大棚环境下进行了土壤多层温度场测量实验。实验结果表明,土壤内部温度呈余弦函数模型周期性变化。随着土壤深度增加,温度变化逐渐减小,在一定的湿度范围内,土壤湿度越大,浅层土壤温度越低。土壤湿度对深层土壤温度影响较小,太阳辐射对浅层土壤温度影响较大。

Interrogating a Fiber Bragg Grating Vibration Sensor by Narrow Line Width Light

A method to interrogate fiber Bragg grating vibration sensor by narrow line width light is demonstrated. The interrogation scheme takes advantage of the intensity modulation of narrow spectral bandwidth light, such as distributed feedback laser, when a reflection or transmission spectrum curve of an fiber Bragg grating （FBG） moves due to the strain which is applied on the sensor. The sensor＇s response to accelerating frequency and amplitude is measured by experiment. The factors which have impacts on the sensitivity of the interrogation system are also discussed.

Fiber Bragg Grating Sensor Array System Based on Digital Phase Generated Carrier Demodulation and Reference Compensation Method

A novel fiber Bragg grating （FBG） sensor array system based on digital phase generated carrier （PGC） demodulation and reference compensation method is proposed and set up. Experimental results confirm that the digital PGC demodulation can be used for wavelength-division-multiplexed FBG sensor array and the reference compensation method can reduce the environmental interference by approximately 40 dB in the frequency range from 20 Hz to 2 kHz. The minimum detectable wavelength-shift of the sensor system is 1 × 10^-3 pm/Hz^1/2.

Hollow and filled fiber bragg gratings in nano-bore optical fibers

To combine the technical functions and advantages of solid-core fiber Bragg gratings(FBGs) and hollow-core optical fibers(HCFs), the hollow and filled FBGs in nano-bore optical fibers(NBFs) with nano-bore in the GeO2-doped core are proposed.The fundamental mode field, effective mode index, and confinement loss of NBF with 50 nm–7 μm-diameter hollow and filled nano-bore are numerically investigated by the finite element method.The reflected spectra of FBGs in NBFs are obtained by the transmission matrix method.The hollow FBGs in NBFs can be acheived with ~5% power fraction in the bore and the ~0.9 reflectivity when bore diameter is less than 3 μm.The filled FBGs can be realized with^1% power fraction and 0.98 reflectivity with different fillings including o-xylene, trichloroethylene, and chloroform for 800-nm bore diameter.The feasibility of the index sensing by our proposed NBF FBG is also analyzed and discussed.The experimental fabrication of hollow and filled FBGs are discussed and can be achieved by current techniques.The aim of this work is to establish a principle prototype for investigating the HCFs and solid-core FBGs-based fiber-optic platforms,which are useful for applications such as the simultaneous chemical and physical sensing at the same position.

FBG技术监测分析机场跑道沥青加铺层反射裂缝扩展过程

反射裂缝是导致机场跑道加铺层失效的主要病害之一。为分析机场水泥跑道沥青加铺层反射裂缝扩展过程,本文基于光纤布拉格光栅(FBG,fiber Bragg grating)传感技术,提出了可用于实时监测机场水泥跑道沥青加铺层反射裂缝扩展过程的柔性FBG传感器封装方法,并对研发的FBG传感器进行了标定。基于室内组合梁试验,分析了机场水泥跑道沥青加铺层复合结构反射裂缝扩展过程,包括微裂纹萌生与积累、反射裂缝扩展、反射裂缝贯通3个阶段。在反射裂缝扩展初期,FBG传感器中心波长增长速率相对较小;随着反射裂缝逐渐扩展,FBG传感器中心波长迅速增大。结果表明,柔性FBG传感器全部存活且性能完整,验证了其在实时监测机场水泥跑道沥青加铺层反射裂缝扩展过程中的可行性。

双膜结构FBG土压力传感器优化设计及灵敏度分析

为实现桩基础结构安全及其服役状态的监测和有效评估,提出一种双膜结构土压力传感器,以光纤布拉格光栅(fiber Bragg grating,FBG)为传感元件,通过保护结构中增加的温度补偿膜,实现温度作用与外部荷载作用的彻底分离。基于双膜结构土压力传感器的工作原理,讨论了传感器压力灵敏度系数特性。结合有限元分析和实验研究,对灵敏度系数的影响参数展开了系统分析。数值分析结果表明,膜片厚度对压力敏感度系数的影响最大,结构半径和膜片厚度可选取为20 mm和1.8 mm;实验结果表明,在0-2 MPa范围内,压力灵敏度系数达3.32 pm/kPa。

Time Division Multiplexing Fiber Bragg Grating Sensor System Using Composite Codes

A novel multi-point sensing scheme to improve the signal-to-noise ratio(SNR),temperature measurement range of the fiber Bragg grating(FBG)sensors is proposed.The new sensing scheme adopted a composite coding technique based on Simplex codes and Golay codes and time division multiplexing technique to enhance the performance of the sensing system.Simulation results,in good agreement with the theory,confirmed that the maximum SNR enhancement of the sensor system employing composite coding based on 15-bit Simplex codes and 16-bit Golay codes was approximately 6.01 dB in comparison to the conventional single pulse case.

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.

Adaptive Performance Improvement of Fiber Bragg Grating in Radio over Fiber System

The combination of Radio Frequency and Optical Fiber has resulted high capacity transmission at lower costs components and makes Radio over Fiber as a current trend of large broadband communication. In Fiber optics field, the use of Fiber Bragg Grating (FBG) was been proposed in recent research with different purpose of uses. However, the compensation of dispersion method of Fiber Bragg Grating (FBG) can boost significantly the system performance. This paper investigates the performance capacity improvement of adaptive Radio over Fiber system. The system design was performed using OptiSystem 7.0 software, which 10 Gb/s Non Return to Zero (NRZ) signal was launched into 50 Km Universal Mode Fiber and Fiber Bragg Grating was used as a compensator of dispersion before frequency up conversion. Therefore, the system performances were investigated by comparing the Bit Error Rate (BER) and Q-factors of Positive Intrinsic Negative (PIN) and Ultrafast Avalanche Photodiode (APD) as optical receivers. The Eye diagram analyzer showed acceptable improvement due to use of Fiber Bragg Grating as a compensator of dispersion.

双光纤Bragg光栅用于FBG型传感器的温度补偿

理论分析了FBG型传感器的温度应变交叉敏感机制,利用温度和应变响应相同的光栅对实现了光纤Bragg光栅应力/应变传感器的温度补偿,有效的消除了交叉敏感对FBG型传感器测量精度的影响,有利于光纤Bragg光栅传感器的实用化。

基于FBG-3D打印的土工格栅加筋下伏土洞路基模型试验

光纤布拉格光栅(fiber Bragg grating,FBG)传感技术具有高灵敏度、抗电磁干扰和实时监测等优点,在土木工程领域越来越受到关注,但传统的外部封装方式难以实现传感器与被测物体的完全协调变形,易导致测量误差.基于3D打印技术研发了一种自感知土工格栅,实现了光纤光栅传感器与被测土工格栅的完全协调变形,利用FBG传感技术直接实现对格栅应变的实时、准确测量.并且,将该自感知土工格栅应用于下伏土洞路基的模型试验中,研究在不同加筋层数和加筋间距下路基的极限承载力、顶端沉降及筋材的变形特性.试验结果表明,通过加筋可以大幅提高下伏土洞路基的极限承载力,并可有效减少路基破坏时的沉降;加筋层数的增加和加筋间距的减小均可以提高下伏土洞路基承载力;在垂直方向上,格栅的应变随着格栅的埋深增大而减小;在水平方向上,格栅的应变随着与加载中心之间的距离增大而向两侧递减;顶层格栅的应变随着加筋层数的增加而减小,随着加筋间距的减小而增大.试验结果验证了自感知土工格栅在下伏土洞加筋路基监测中应用的可行性.