Pulse reference-based compensation technique for intensity-modulated optical fiber sensors

We propose a compensation technique based on pulse reference for intensity-modulated optical fiber sensors that can compensate the power fluctuation of the light source, the change of optical components transmission loss, and the coupler splitting ratio. The theoretical principle of this compensation technique is analyzed and a temperature sensor based on fiber coating-covered optical microfiber is carried out to demonstrate the compensation effect. The system noise is measured to be 0.0005 dB with the temperature sensitivity reaching -0.063 dB/℃, and the output drift is 0.006 dB in 2 h at room temperature. The output shows a slight variation （0.0061 dB） when the light source and the common liKht path suffer a 3 dB attenuation fluctuation.

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 tatigue 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.

A new demodulation technique for optical fiber interferometric sensors with[3×3]directional couplers

Optical fiber interferometric sensors based on [3×3] couplers have been used in many fields. A new technique is proposed to demodulate output signals of this kind of sensors. The technique recovers the signal of interest by fitting coefficients of elliptic （Lissajous） curves between each fiber pair. Different from other approaches, this technique eliminates the dependence on the idealization of [3×3] coupler, provides enhanced tolerance to the variance of photoelectric converters, and is anti-polarization in a certain extent. The main algorithm has been successfully demonstrated both by numerical simulation and experimental result.

Recent advances in optical fiber high-temperature sensors and encapsulation technique[Invited]

In the aerospace field,for aerospace engines and other high-end manufacturing equipment working in extreme environments,like ultrahigh temperatures,high pressure,and high-speed airflow,in situ temperature measurement is of great importance for improving the structure design and achieving the health monitoring and the fault diagnosis of critical parts.Optical fiber sensors have the advantages of small size,easy design,corrosion resistance,anti-electromagnetic interference,and the ability to achieve distributed or quasi-distributed sensing and have broad application prospects for temperature sensing in extreme environments.In this review,first,we introduce the current research status of fiber Bragg grating-type and Fabry–Perot interferometer-type high-temperature sensors.Then we review the optical fiber hightemperature sensor encapsulation techniques,including tubular encapsulation,substrate encapsulation,and metalembedded encapsulation,and discuss the extreme environmental adaptability of different encapsulation structures.Finally,the critical technological issues that need to be solved for the application of optical fiber sensors in extreme environments are discussed.

Fiber optic strain twin-sensor-array for smart structural health monitoring

A multiplexed white light interferometric fiber optic twin-sensor-array was designed to monitor the structural health of large buildings.In this sensing system,based on a Michelson interferometer,an optical path matching technique is used to demodulate each twin-sensor.Each twin-sensor-array consists of a 2×N sensing element linked by a 3 dB coupler.When one of the twin-sensor is used to measure strain,variations caused by temperature can be compensated for by referencing the other twin-sensor.The multiplexing capacity of the sensing scheme has been analyzed and experimental results with a 2×3 twin-sensor-array are given.

Modeling, Simulation and Experimental Studies of Refractometric Fiber Optic Sensor

Refractometric fiber optic sensors have a number of applications in industry due to advantages like remote sensing ability, compact size, easy to fit, etc. A refractometric sensor contains a pair of parallel fibers and a gap between the sensor probe and reflector, wherein the liquid whose refractive index is to be measured is filled. This paper describes the importance of mathematical modeling of this sensor. Ray tracing approach is used to model the sensor mathematically. This mathematical model is generalized for any scenario which is useful to avoid tedious trial and error techniques to design the sensor prototype. Mathematical modelling is a useful tool to optimize the gap distance for a detection of refractive index of liquid. The model is developed and analyzed rigorously considering adulteration of diesel by kerosene where refractive index varies from 1.44 to 1.46. Simulation experiments are carried out to optimize the gap distance which is found to be 6.8 mm using both models. Experiments are carried out where sensor probe is fabricated and results are analyzed. It is observed that for suggested gap distance sensor output varies almost linear over the entire range.

Reflective Ladder Topology Network Based on White Light Fiber-Optic Mach-Zehnder Interferometer

In order to improve the multiplexing capability of the optical sensors based on the lower interferential optic fiber sensing technology and the white light fiber-optic Mach-Zehnder interferometer,reflective ladder topology network ( RLT) with tailored formula was proposed. The topology network consists of 6 rungs sensing elements linked by 5 couplers. Two cases with different choices of couplers were contrasted: one is equal coupling ratio,and the other is tailored coupling ratio. Through the simulation of these two cases,the detailed multiplexing capability was analyzed,and accordingly the experiments were also carried out. The simulation results showed that,the tailored formula enhances the multiplexing capability of the structure. In the first case, the maximum number of sensors which can be multiplexed is 8,and in the other case is 12 fiber optic sensors. The experimental results have a good agreement with numerical simulation results. Thus,it is considered expedient to incorporate RLT into large-scale building,grounds,bridges,dams,tunnels,highways and perimeter security.

Low-noise and highly stable optical fiber temperature sensor using modified pulse-reference-based compensation technique

We modify the pulse-reference-based compensation technique and propose a low-noise and highly stable optical fiber temperature sensor based on a zinc telluride film-coated fiber tip. The system noise is measured to be 0.0005 dB, which makes it possible for the detection of the minor reflectivity change of the film at different temperatures. The temperature sensitivity is 0.0034 d B/℃, so the resolution can achieve 0.2℃. The maximum difference of the temperature output values of the sensor at 20℃ at different points in time is 0.39℃. The low cost, ultra-small size, high stability, and good repeatability of the sensor make it a promising temperature sensing device for practical application.

光纤光栅传感器研发及其在土木工程中的应用进展

从传感器类型出发介绍了表贴式、纤维增强聚合物式、管式和内嵌式封装光纤布拉格光栅传感器的结构型式、实施方式和关键技术,简述了各种封装方式传感器的工作原理、技术研发及工程应用进展,总结了不同封装方式传感器的优势和不足。然后,简要介绍了光纤布拉格光栅传感器在桥梁结构状态监测或检测中的典型工程应用案例。最后,指出了光纤布拉格光栅传感器在土木工程领域中的工艺工法、耐久性和分布式测量以及未来推广应用有待解决的关键问题等,为光纤布拉格光栅传感器技术优化及其在土木工程中的推广应用提供参考。

基于光纤复合测量技术的涡轮叶片气膜孔检测

为了解决航空发动机涡轮叶片气膜孔几何特征参数有效检测手段缺乏、测量结果一致性差的问题,设计并搭建了基于光纤复合测量技术的涡轮叶片气膜孔检测系统,提出了利用该系统对涡轮叶片气膜孔进行测量的方法,通过试验进行了方法验证。搭建的系统为多传感器测量系统,具备叶片接触与非接触测量、空间姿态定位及3D投影能力,实现了涡轮叶片全范围气模孔的测量。在试验中,选取高压涡轮叶片作为被测物体,应用该测量系统对叶片上的气膜孔进行了测量,计算得到了气膜孔直径、轴线角度及位置度的准确信息。结果表明:通过测量不确定度的分析评定可知,该系统对气膜孔直径、位置度的测量不确定度均小于0.01 mm,完全满足设计公差对测量仪器的精度要求,可以用于涡轮叶片气膜孔工程化测量。

基于光纤位移传感器的桥梁基坑沉降监测的试验研究

文中以某大型桥梁深基坑工程为例,利用光纤位移传感器对基坑施工过程中冠梁和行车道的水平位移、地表沉降、锚索轴力、地下水位等进行动态监测和分析,以研究深基坑的开挖变形规律。结果表明,随着基坑的开挖,基坑的冠梁和行车道向基坑方向倾斜,最终趋于稳定,且随着开挖深度的增加,第一层的预应力锚杆轴向力随深度的增加而增加。两个开挖面的地下水有不同的发展规律,但均在短期之内逐渐趋于平稳。基坑各个部位的累积沉降均处于控制之中,但由于其北部和邻近一栋建筑的地面沉陷还没有得到控制,因此,需对该地区进行进一步的沉降监控。

分布式光纤管道泄漏检测和定位技术

提出了一种基于Mach-Zehnder光纤干涉仪原理的新型分布式光纤管道泄漏测试技术。该检测技术利用在管道沿线附近敷设的一条光缆中的3条单膜光纤构成分布式微振动测试传感器,通过检测管道沿途所发生的泄漏噪声,可以实时地监测管道沿线所发生的泄漏情况。利用广义相关时延估计算法,通过确定2个测试信号的时延可以获得泄漏点的位置。阐述了该检测技术的测试原理和泄漏点定位方法,并对现场试验数据进行了分析。理论分析和试验结果表明,该测试技术可以有效地提高管道泄漏测试的灵敏度和定位精度。

单索面斜拉桥模型钢索载荷应变的光纤传感测量方法

采用光纤应变测量仪对桥梁钢索的应力应变在载荷情况下的变化进行了实验研究 .采用有机玻璃和0 .8mm钢丝 ,设计并制作了单索面斜拉桥模型 .在该桥梁模型上进行了模拟活载的线性加载实验 ,为斜拉桥索力及应力应变的检测提供了一种新测式方法 .

风力发电中全光纤风速传感器及制作工艺研究

为了实现风力发电场多点、远程风速检测,便于测量和风场风速物联网的构建,采用风杯来调制光纤布喇格光栅的方式,设计了一种全光纤风速传感器,通过光纤光栅波长的变化频率可以求出对应风速值,并对传感器设计结构进行了说明,介绍了传感器的制作封装工艺以及相关的设备和实验数据。结果表明,传感器运行稳定可靠,测量误差不超过0.16m/s,适合于风电场的多点大容量风速监测,对风力发电实际应用具有重大意义。

基于光纤传感的边坡工程监测技术

传统的边坡监测技术存在着精度低、耐久性差、难以实现集成等缺陷。针对边坡工程特点,探讨了光纤光栅、布里渊光时域分析和低相干干涉等光纤传感技术在现场监测的应用。根据不同的工程需要,结合这三种技术建立边坡监测系统,可用于对边坡位移和边坡支护结构的应力、应变进行自动化监测。在详细论述了光纤传感技术的基本原理、适用场合和系统架构的基础上,以香港一个公路边坡加固工程为例,简述了光纤传感技术现场应用时的仪器安装、数据采集与分析等工作。

一种温度补偿式光纤氢气检测技术

基于非本征法布里-珀罗光纤传感检测技术,分析研究了氢敏薄膜特性,实现了氢气传感单元设计及制作,简要介绍了传感器结构、制作方法、镀膜工艺及设备。通过分析氢气浓度与法布里-珀罗腔长变化间的关系,建立了光纤法布里-珀罗氢气传感理论模型。为增强系统工程实用性,着重研究了传感器温度与氢气浓度交叉敏感问题,并利用温度补偿技术消除环境温度干扰。介绍了温度补偿原理并构建实验设备,最后通过氢气浓度响应实验及温度特性实验,证明理论公式推导结果与实验数据吻合较好,且氢气传感器温度敏感性降低。此设计具有一定工程实用价值。

双弹簧管光纤差压传感器

设计了一种利用对称反转连接的双弹簧管作为差动压力传感元件 ,进行差动压力测量的光纤传感器 这种光纤传感器是在通用光纤传感设计实验系统的基础上 ,利用三光纤反射调制技术 ,实现光源强度的变化和光纤中光功率损耗的变化以及反射率的变化自动补偿的 理论上 ,分析了这种反转对称差压传感弹性元件在使用过程的优点 ,给出了三光纤补偿理论分析方法 实验上 。

基于法拉第效应双偏振光纤激光磁场传感器的纵向空间响应

利用法拉第效应,正交双偏振光纤激光器已被证明可用来实现灵活小巧的磁场传感器.为了发展适宜的封装结构以优化对磁场的传感灵敏度,有必要研究双偏振光纤激光磁场传感器在磁场中的空间响应特性。对长度为21 mm的光纤激光器在磁场宽度为3 mm、5 mm、7 mm以及磁场强度为0.5 T、0.75 T和1 T时的纵向空间响应进行了实验研究。研究表明,沿着双偏振光纤激光磁场传感器的纵向,其各个部分对磁场的空间响应是不均匀的。空间响应的峰值出现在激光腔的中间并沿激光器纵向呈对称的高斯分布。这种空间响应的分布特性与光纤光栅的分布式布拉格反射有关。

基于光纤传感的富士苹果糖度检测试验研究

利用傅立叶光谱仪的智能光纤传感器 ,探讨了近红外光无损检测水果糖度的方法。通过主成分回归、偏最小二乘法和逐步回归法三种多元校正算法对水果光谱数据的分析 ,得出PLS模式水果糖度预测值和真实值的相关系数为 0 86 ,标准校正误差为 0 14 ,标准预测误差为 0 97,PCA模式水果糖度预测值和真实值相关系数为 0 85 ,标准校正误差为 0 4 7,标准预测误差为 1 2 7,而SMLR模式的水果糖度预测值和真实值相关系数为 0 72 ,标准校正误差为 0 72 ,标准预测误差为 2 10 ,研究结果表明 ,在 12 5 0 0～ 380 0cm- 1

干涉型光纤传感器及阵列的分集消偏振衰落技术的研究与改进

对干涉型光纤传感器的分集检测消偏振衰落技术进行了新的理论分析 ,提出了将各路信号平方后相加的信号处理方式 ,使之能实现单元及阵列的实时消偏振衰落信号检测 .通过理论计算 ,可以使干涉信号幅度波动小于 9.5d B,并得出三路检偏是分集检测的最简取值的结论 ,通过自动增益控制电路 ,能够在信噪比有所降低的情况下消除偏振衰落的影响 ,实现干涉型光纤传感器的消偏振衰落 。