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.

Multiwavelength Actively Mode-locked Fiber Laser with a Double-ring Configuration and Integrated Cascaded Sampled Fiber Bragg Gratings

A modified multiwavelength actively mode-locked fiber ring laser is proposed and experimentally demonstrated. In this kind of laser, stable multiwavelengths lasing is achieved by integrating cascaded sampled fiber Bragg gratings(SFBGs) into the laser cavity. To implement actively mode-locking technique, a double-ring cavity configuration is used to assure that the cavity lengths for all wavelengths lasing are identical. Thus, simultaneous mode locking of all wavelengths has been successfully achieved by using the same mode-locking signal.

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FBG传感器阵列反演结构振动位移的监测方法

针对现有振动位移监测方法易受环境影响且精度不高的问题,提出了一种基于光纤布喇格光栅(FBG)传感器阵列反演结构振动位移的监测方法。该方法使用FBG传感器阵列获取结构振动过程中的多点应变和单点加速度数据,先利用基于正交曲率的曲线重构算法和获得的应变数据重构结构各点的动态位移,然后运用卡尔曼滤波算法将曲线重构算法导出的位移数据与同位置处的单点加速度数据相融合,获得更为准确的位移数据。实验结果表明:该方法可成功重构出监测结构任意时刻的振动形态,悬臂铝板和简支管道的振动位移重构相对均方根误差分别小于5.5%和7%。

基于FBG的微小型三轴振动传感器研究

为了研制一种微小型、三轴测量的高灵敏度振动传感器,提出一种分立元件交错组合的超紧凑光纤光栅三轴振动传感器设计方法。采用分立元件组合设计方法降低了设计加工难度,与一体化设计对比,分立元件组合结构的零件结构简单、易于加工、结构设计也更为灵活,缩短了传感器结构的优化迭代周期。通过理论模型分析和有限元仿真,优化传感器结构参数,最终封装完成的尺寸为15 mm×15 mm×15 mm,质量约为24.26 g。最后进行实验测试和传感器性能分析。实验结果表明:该传感器的工作频段为0~1 200 Hz,在X、Y、Z轴方向的固有频率分别为1 850 Hz、1 770 Hz和1 860 Hz,三个轴向的灵敏度分别达到77.37 pm/g、80.73 pm/g和75.04 pm/g,横向抗干扰小于5%。该传感器满足航天振动测量轻量化、工作范围和灵敏度的应用需求,在遥感卫星微振动测量等领域具有重要应用前景。

Irradiation effect on strain sensitivity coefficient of strain sensing fiber Bragg gratings

The effect of irradiation on the strain sensitivity coefficient of strain sensing fiber Bragg gratings(FBGs) has been investigated through experiments. FBGs were fabricated in single mode fibers with 3 mol% Ge-concentration in the core and with a H2-loading treatment. In experiments, the FBGs were subjected to γ-radiation exposures using a Co60 source at a dose-rate of 25 Gy/min up to a total dose of 10.5 kGy. The GeO defect in fiber absorbs photons to form a GeE' defect; the interaction with H2 is a probable reason for the γ-radiation sensitivity of gratings written in hydrogen loaded fibres. The effect mechanism of radiation on the strain sensitivity coefficient is similar to that of radiation on the temperature sensitivity coefficient. Radiation affects the effective index neff, which results in the change of the thermo-optic coefficient and the strain-optic coefficient. Irradiation can change the strain sensitivity coefficient of FBGs by 1.48%–2.71%, as well as changing the Bragg wavelength shift(BWS) by 22 pm–25 pm under a total dose of 10.5 kGy. Our research demonstrates that the effect of irradiation on the strain sensitivity coefficient of FBG is small and that strain sensing FBGs can work well in the radiation environment.

基于空间耦合传输方法的FBG传感器转子涡动测温误差及其影响因素研究

针对电机转子涡动对光纤光栅温度监测系统精度产生的影响,采用光纤光栅(FBG)的传输矩阵理论和自聚集透镜的耦合损耗理论,建立了涡动条件下FBG扫描光谱模型,结合相关试验,研究了扫描光谱的畸变规律及系统测温误差的影响因素。结果表明:涡动导致扫描光谱反射峰发生偏移、3 dB带宽减小,通过协调涡动频率和解调仪扫描频率,使准直器间耦合损耗周期达到FBG光谱扫描时间的10倍以上(q>10)是保证较低测温误差的关键;同时,质心法对剧烈涡动条件下扫描光谱的寻峰效果明显优于高斯曲线拟合法。随着转子端面处的径向位移幅值或轴线偏角幅值的增大,系统的测温误差先缓慢地增大、后剧烈地增大;随着椭圆形轴心运动轨迹轴比的增大,测温误差先剧烈地增大、后缓慢地增大至稳定。当转子径向位移幅值小于200μm、轴线偏角幅值小于0.167°时,在轴比等于3、q值等于10条件下,15次采样试验反映出质心法和高斯曲线拟合法分别令系统的测温误差从2.9℃降低至0.6℃和1.1℃,为监测系统的应用与测温精度的预估提供了依据。

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.

Encrypted optical fiber tag based on encoded fiber Bragg grating array

Optical fibers are typically used in telecommunications services for data transmission,where the use of fiber tags is essential to distinguish between the different transmission fibers or channels and thus ensure the working functionality of the communication system.Traditional physical entity marking methods for fiber labeling are bulky,easily confused,and,most importantly,the label information can be accessed easily by all potential users.This work proposes an encrypted optical fiber tag based on an encoded fiber Bragg grating(FBG)array that is fabricated using a point-by-point femtosecond laser pulse chain inscription method.Gratings with different resonant wavelengths and reflectivities are realized by adjusting the grating period and the refractive index modulations.It is demonstrated that a binary data sequence carried by a fiber tag can be inscribed into the fiber core in the form of an FBG array,and the tag data can be encrypted through appropriate design of the spatial distributions of the FBGs with various reflection wavelengths and reflectivities.The proposed fiber tag technology can be used for applications in port identification,encrypted data storage,and transmission in fiber networks.

Critical dispersion of chirped fiber Bragg grating for eliminating time delay signature of distributed feedback laser chaos

Optical chaos has attracted widespread attention owing to its complex dynamic behaviors.However,the time delay signature(TDS)caused by the external cavity mode reduces the complexity of optical chaos.We propose and numerically demonstrate the critical dispersion of chirped fiber Bragg grating(CFBG)for eliminating the TDS of laser chaos in this work.The critical dispersion,as a function of relaxation frequency and bandwidth of the optical spectrum,is found through extensive dynamics simulations.It is shown that the TDS can be eliminated when the dispersion of CFBG is above this critical dispersion.In addition,the influence of dispersive feedback light and output light from a laser is investigated.These results provide important quantitative guidance for designing chaotic semiconductor lasers without TDS.

Determination of the Postmortem Interval Using Fiber Bragg Grating Sensors

Fiber Bragg grating(FBG)sensors are often used in monitoring activities and to ensure that environmental parameters satisfy industrial requirements.They offer crucial safety measures in the early detection of hazards due to their greatly reduced size,low weight,flexibility,and immunity to electromagnetic interference.These characteristics make FBGs suitable also for use in relation to the human body for in vivo measurements and long-term monitoring.In this study,recent developments are presented with regard to the utilization of these sensors to measure the so-called post-mortem interval(PMI).Such developments rely on numerical simulations based on the Matlab software and monitoring of the rectal temperature,which is one of the main parameters for estimating the PMI.First,the Matlab software is used to solve the Henssge equation for different ambient temperatures and for different body masses;then a Bragg grating sensors is used for post-mortem dating.The results and their accuracy are discussed.

Advances in femtosecond laser direct writing of fiber Bragg gratings in multicore fibers:technology,sensor and laser applications

In this article,we review recent advances in the technology of writing fiber Bragg gratings(FBGs)in selected cores of multicore fibers(MCFs)by using femtosecond laser pulses.The writing technology of such a key element as the FBG opens up wide opportunities for the creation of next generation fiber lasers and sensors based on MCFs.The advantages of the technology are shown by using the examples of 3D shape sensors,acoustic emission sensors with spatially multiplexed channels,as well as multicore fiber Raman lasers.

结合FBG-FP的变压器局部放电光纤全方向传感研究

为实现变压器局部放电的灵敏检测,避免漏检局部放电信号,基于光纤布拉格光栅(FBG)与法布里珀罗腔(Fabry-Perot cavity)传感原理提出了一种结合FBG-FP的变压器油中局部放电光纤全方向传感方法。介绍了FBG与FP腔的局部放电传感原理,局部放电产生的超声波会引起FBG反射光谱与FP腔干涉光谱的偏移,通过光谱边缘解调法进行光强解调可实现局放信号的检测。研制了局部放电光纤全方向传感器,通过3D打印技术制作了尺寸为25 mm×25 mm×25mm的长方体探头,探头中空结构用于插入单模光纤形成FP腔,四个侧面用于形成膜片式FBG传感结构,可接收不同方向的超声信号。基于变压器油中局部放电的频谱特性与液相环境中膜片的振动模型设计了超声传感膜片,选用镀有高反介质膜的康宁玻璃作为FP腔传感膜片,膜片半径为1.7 mm,厚度为0.165 mm,理论谐振频率为82 kHz;选用单晶硅作为FBG传感膜片,膜片半径为2.5 mm,厚度为0.1 mm,理论谐振频率为25.6 kHz。搭建了光纤局部放电传感系统并进行了局部放电光纤全方向传感器性能测试。通过断铅实验测得变压器油中传感器FBG传感膜片实际谐振频率约为23 kHz,FP腔传感膜片实际谐振频率为71.4 kHz。将光纤全方向传感器与压电传感器(PZT)对同一局部放电信号进行对比检测,光纤全方向传感器FBG传感部分可检测到83.8 pC的金属尖端放电,FP腔传感部分可检测到27.1 pC的金属尖端放电,其局部放电检测灵敏度高于PZT。测试了传感器的方向响应,普通的FP传感器高灵敏检测范围有限,存在检测盲区,所研制的光纤全方向传感器FP腔传感部分与FBG传感部分高灵敏检测范围互补,可实现局部放电全方向灵敏检测,具有良好的方向响应性能。

基于光纤Bragg光栅超声复合检测金属腐蚀与振动状态方法研究

为了实现钢板腐蚀前后及冲击振动状态复合检测,构建了基于光纤布拉格光栅(FBG)超声检测系统。首先分析了基于可调激光光源的光纤光栅的解调原理。在此基础上,实验研究了钢板腐蚀前后的兰姆波信号变化规律,分析了钢板在不同垂直冲击强度撞击下的时频变化特性以及钢板腐蚀前后冲击振动信号的时频变化规律。研究表明:所搭建的光纤布拉格光栅超声检测系统能够有效地实现钢板腐蚀及冲击振动信号的复合检测,通过兰姆波信号的幅值大小及是否有新的频率分量出现,可以准确识别钢板是否遭受腐蚀。冲击信号的幅值变化与冲击大小存在线性关系,同时通过频域分析证明钢板腐蚀后的频率各分量平均呈现出12 Hz右移。

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。

Engineering approach to in-situ bridge health monitoring with fiber bragg gratings

In this presentation the feasibility and capability of fiber Bragg gratings (FBG) employed in bridge health monitoring are demonstrated on a real bridge. FBG’s wavelength shift depending on strain variance has been tested. The technique of FBG installation on bridges has been developed. 12 FBG strain sensors and 3 temperature sensors have been successfully embedded in the prestressed concrete box girder during the construction of Heilongjiang Hulan River Bridge. The prestressing tension process and quasi-static loading process of the girder were monitored with those sensors before it was installed onto the bridge. After the bridge was completed, the FBG sensors embedded have been utilized to monitor the strain shift of the beam under quasi-static load, traffic load and temperature. The results show that the traffic fluxes, possible fatigue damage and deflection of the bridge can be revealed conveniently through strain measurements with these FBG sensors, which provide key information for structural health diagnosis. The fact that the FBG strain sensors have withstood the ordeal of harsh construction process and lasted for more than one year proves that their durability and stability can satisfy the requirements for bridge health monitoring. It is also shown that the FBG strain sensor is more adaptive to long-term structural health monitoring than the electric resistance strain gauge.

基于TFBG边缘滤波的FBG温度传感器

为了提高系统的温度灵敏度,设计了一种基于倾斜光纤光栅(TFBG)边缘滤波的光纤布喇格光栅(FBG)温度传感器。该系统在常规的TFBG边缘滤波解调系统上引入一个光纤环形镜,将从TFBG透射的光信号反射回来,使其能再次通过TFBG,以增加TFBG透射谱的深度,并对传感光栅进行封装。实验结果表明:封装前和封装后的传感光栅在所测量的温度区间内中心波长的漂移量分别为0.55 nm和7 nm,封装后的漂移量扩大了十多倍;同时,由于TFBG边缘滤波解调传递函数的斜率得到提高,传感器波长解调后的温度灵敏度也得到了改善,是未级联光纤环形镜传感器的1.6~2.4倍。

Thermo-hydro-poro-mechanical responses of a reservoir-induced landslide tracked by high-resolution fiber optic sensing nerves

Thermo-poro-mechanical responses along sliding zone/surface have been extensively studied.However,it has not been recognized that the potential contribution of other crucial engineering geological interfaces beyond the slip surface to progressive failure.Here,we aim to investigate the subsurface multiphysics of reservoir landslides under two extreme hydrologic conditions(i.e.wet and dry),particularly within sliding masses.Based on ultra-weak fiber Bragg grating(UWFBG)technology,we employ specialpurpose fiber optic sensing cables that can be implanted into boreholes as“nerves of the Earth”to collect data on soil temperature,water content,pore water pressure,and strain.The Xinpu landslide in the middle reach of the Three Gorges Reservoir Area in China was selected as a case study to establish a paradigm for in situ thermo-hydro-poro-mechanical monitoring.These UWFBG-based sensing cables were vertically buried in a 31 m-deep borehole at the foot of the landslide,with a resolution of 1 m except for the pressure sensor.We reported field measurements covering the period 2021 and 2022 and produced the spatiotemporal profiles throughout the borehole.Results show that wet years are more likely to motivate landslide motions than dry years.The annual thermally active layer of the landslide has a critical depth of roughly 9 m and might move downward in warmer years.The dynamic groundwater table is located at depths of 9e15 m,where the peaked strain undergoes a periodical response of leap and withdrawal to annual hydrometeorological cycles.These interface behaviors may support the interpretation of the contribution of reservoir regulation to slope stability,allowing us to correlate them to local damage events and potential global destabilization.This paper also offers a natural framework for interpreting thermo-hydro-poro-mechanical signatures from creeping reservoir bank slopes,which may form the basis for a landslide monitoring and early warning system.

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.

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。