Differential strain measurement using multiplexed fiber Bragg grating sensors

We investigate differential measurement of strain using fiber Bragg gratings and spatial demultiplexing methods. Differential measurement is shown to improve strain resolution in the presence of noise by an average of 34% compared to absolute measurements of the Bragg wavelengths. Spatial demultiplexing of the gratings provides potentially high-resolution sensing without calculating the sensor wavelengths. The differential method is still temperature dependent. We apply the differential technique to the problem of oil-water boundary detection in production columns, with promising preliminary results.     

高精度弓型光纤光栅微位移传感器

为了测量控机床结构件、微加工工作台的微小变形量,设计了一种高精度弓型光纤布拉格光栅(FBG)微位移传感器。将光纤布拉格光栅的栅区部分粘贴在弓型上下壁处,当弓形件发生变形时,可测出上下壁的应变值,从而测得位移值并进行温度解耦。实验结果表明,在量程为1mm时,传感器的灵敏度为2.02pm/μm,线性相关系数为0.998 3,实验的迟滞误差为4.08%,重复性误差为4.08%。在温度补偿实验中可以看出,当温度上升1℃,波长漂移量不到1pm。类似于弓型结构衍生出一种半弓型结构的位移传感器。两类传感器相比,弓型传感器的温度灵敏度比半弓型传感器小0.001 5pm/μm,温度补偿效果更好;但半弓型传感器的线性度为0.4%,线性度比弓型传感器好。两种传感器均满足测量值稳定可靠、精度高、抗电磁干扰能力强,温度不敏感等要求。     

A diaphragm-type fiber Bragg grating pressure sensor with temperature compensation

A diaphragm-type fiber Bragg grating (FBG) pressure sensor with two bare FBGs directly bonded on a circular diaphragm along the radial direction has been proposed and studied. Measurement principle and simulation analysis of the pressure sensor are introduced. Using the wavelength shift difference of the two FBGs which respectively measure the positive and negative strain as sensing signal, the pressure sensitivity is increased and the temperature cross-sensitivity is compensated. Experimental results indicate that the measurement sensitivity is 1.57 pm/kPa in a range from 0 to 1 MPa, the correlative coefficient reaches 99.996%, and the temperature compensation performance is distinct. This kind of pressure sensor could be used to measure and monitor the static/dynamic pressure of gas or liquid.     

两种封装的光纤光栅温度传感器的低温特性

介绍了光纤光栅(FBG,Fiber Bragg Gratings)温度传感器的两种封装形式。推导了两种FBG温度传感器的温度敏感因素并进行了实验验证。实验研究了两种FBG温度传感器在-70~0 ℃的中心波长低温变化特性,比较了相同条件下两种FBG温度传感器的实验结果。结果表明:细不锈钢管封装的FBG温度传感器的中心波长在-60 ℃时发生了突变,急剧下降;而镀金FBG温度传感器的中心波长在-70~0 ℃随温度线性变化,重复性较好并且几乎没有迟滞现象。两种传感器在线性变化区间的温度灵敏系数KT 分别为28.2 pm/ ℃和21.3 pm/ ℃,分别是裸光纤布拉格光栅的3倍和2.3倍,它们的线性拟合度都超过0.999。     

Application of Fabry-Pérot and fiber Bragg grating pressure sensors to simultaneous measurement of liquid level and specific gravity

An approach is proposed for obtaining simultaneous measurements of the level and specific gravity of a liquid using a dual-pressure-sensor system comprising a fiber Bragg grating (FBG) pressure sensor and a Fabry-Pérot (FP) pressure sensor. In the FBG sensor, the pressure is derived from the FBG wavelength shift induced when the sensor is immersed in the liquid. Meanwhile, in the FP sensor, the pressure is calculated from the change in cavity length which takes place when the sensor is immersed. The advantageous concept of the dual-pressure-sensor system is atmospheric pressure compensation. The experimental results show that the FBG and FP pressure sensors have sensitivities of 0.1495 nm/kPa and 0.1569 μm/kPa, respectively. Analytical formulae are derived for the level and specific gravity of the liquid in terms of the FBG wavelength shift, the change in cavity length, and the vertical separation distance between the two sensors.     

基于光纤光栅的高速气流总温测量方法

针对航空发动机高速气流总温测量的需求,结合光纤光栅尺寸小、无需回路的结构特点,本文提出一种采用光纤光栅作为感温元的滞止罩式微型总温探针设计与测量方法。通过数值模拟方法对光纤光栅总温探针进行了气动结构设计,分析了探针结构参数对总温测量结果的影响;在此基础上,制作了光纤光栅总温探针,搭建了总温测量数据处理系统,并通过亚音速风洞试验测试了光纤光栅总温探针的工作性能。结果表明,在马赫数为0.3～0.8亚音速气流冲击下,光纤光栅总温探针具有良好的滞止效果和稳定性,马赫数大于0.5时其复温系数达到0.8以上,在马赫数为0.8时达0.99。所制作的微型光纤光栅总温探针直径低至0.8 mm,结构尺寸远低于热电偶探针,在满足总温精准测量的同时,可有效降低对流场的干扰。     

Optical fiber sensors for static and dynamic health monitoring of civil engineering infrastructures: Abode wall case study

Nowadays, structural health monitoring is a fundamental tool to control the civil infrastructures lifetime. Raw earth masonry structures (as adobe, rammed earth, among other techniques) were very common in many regions of the World. With the introduction of reinforced concrete structures in the construction industry, the adoption of traditional masonry systems, and adobe in particular, rapidly declined. However, an important number of the adobe buildings in the world are of cultural, historical and architectural recognized value, presently, about 30% of the World population lives in raw earth buildings.     

Characterization of a differential fiber Bragg grating sensor for oil-water boundary detection

We investigate the operating characteristics of an oil-water boundary detector utilizing differential interrogation of fiber Bragg grating sensors. The system resolution is shown to be stable with respect to the choice of strain actuator and long-term temperature changes and changes in the initial strain on the fiber string. Fluid flow, particularly turbulent flow, is found to reduce system resolution significantly for the current system design. Improvements in the system design are required to minimize the effects of fluid flow and to accurately detect the presence of oil-water emulsions.     

Optimization of the frequency-modulated continuous wave technique for referencing and multiplexing intensity-based fiber optic sensors

In this paper, we demonstrate the interrogation of fiber optic intensity sensors by using the combination of the frequency-modulated continuous wave concept with the spectral selective reflectivity of fiber Bragg gratings. Thus, we multiplex these kinds of sensors with this technique having simultaneously a referenced system. The basis of this dual functionality is described and results are presented for the case of interrogation of two multiplexed intensity sensors. Their evaluation permits to establish the conditions to address a sensor network of this type. Also, it is proposed a strategy to implement this sensing approach without the requirement of using optical fiber delay lines in the sensor heads.     

Monitoring corrosion of reinforcement in concrete structures via fiber Bragg grating sensors

Corrosion of steel and rebar in concrete structures is one of the most frequent reasons for civil infrastructure failures. Thus, improving the effective corrosion sensor technology can greatly reduce cost and provide safe structures with long service lives. However, assessing the corrosion condition of rebars is not simple because they are buried in concrete. In this paper, using fiber Bragg grating (FBG), a corrosion sensor for monitoring steel rebars embedded in a concrete structure is developed and validated by experiments. Based on the fact that the volume and diameter of a rebar embedded in concrete will enlarge due to corrosion, an FBG packaged with fiber-reinforced plastics (FRP) is wrapped on the steel bar. During corrosion, the increase in the bar diameter leads to the increase in fiber strain, which can be measured by the shift of the wavelength of FBG. Performances of the corrosion sensor are validated by accelerating corrosion in lab experiments. The corrosion sensor is embedded in a concrete specimen put in a 5% sodium chloride solution with a constant current. Experimental results show that the corrosion sensor can monitor the concurrence of corrosion of rebars in concrete. The corrosion extent can be quantitatively evaluated through the change in the wavelength of FBG. Therefore, the corrosion sensor developed in this paper is feasible for monitoring the early corrosion of rebars in concrete.     

Validation of thermal and electrical model for induction motors using fiber Bragg gratings

This works presents the simulation and validation of the thermal, electrical and mechanical models of a three-phase induction motor (TIM). Fiber Bragg grating (FBG) sensors are used to measure stator temperature and validate the thermal model. The knowledge of the relationship between losses and temperature variation in the TIM makes a simulation of the motor possible. To determine losses in the TIM an equivalent electrical circuit in arbitrary reference frame is used, which combines a traditional model with the more usual modeling of losses in the stator iron. The thermal study of the motor is performed using an equivalent thermal circuit formed by thermal capacitances and thermal conductivities that are separately considered for the stator and rotor. The losses calculated with the electrical and mechanical models are the input parameters for the thermal model. The simulation of the electrical model produces an error of approximately 4.2% when determining the Joule effect losses in the motor when compared to the experimentally obtained results. The simulation of the mechanical model presents an error of 0.2% for the losses due to friction and ventilation. The stator and rotor temperature, obtained with the thermal model, presented a high correlation with the measured values. The thermal model presents a maximum error of 0.75 °C when one compares them to the average experimental values of temperature in the stator during the temperature transient behavior. When the temperature in the stator reaches steady state, the experimental and simulated results converge to the same values. The use of FBGs to measure temperature in the machine allowed a thermal model to be developed, which also uses the mechanical losses of the machine and is the main contribution of this work.     

Influence of lamination process on optical fiber sensors embedded in composite material

In the paper we present the results of our research on optical fiber sensors embedded into composite material samples. We investigate the influence of the lamination process, axial orientation of an optical fiber sensor and coating of a fiber on stress monitoring of a composite material. In the paper we present two approaches to the case of composite condition monitoring, using a polarimetric fiber optic sensor as well as fiber Bragg gratings. We also present experimental evidence that interaction between a composite material and fiber optic sensors is very significant and depends on many factors such as fiber optic axial orientation and the coating layer surrounding an optical fiber.     

埋入式光纤布拉格光栅传感器封装结构对测量应变的影响

考虑在实际应变测量中传感器封装形式会影响光纤Bragg光栅测得的应变响应,本文研究了测量应变与实际应变之间的关系。针对埋入式光纤Bragg光栅传感器,建立了应变传递函数,并对传递函数的正确性和各个参数对测量应变的影响进行了研究。首先,根据埋入式光纤Bragg光栅传感器的受力特点,提出了多项式形式的剪应力分布,进一步建立了应变传递函数。然后,利用数值方法和实验对该应变传递函数进行验证。最后,分析了传感器长度、胶结层弹性模量、胶结层厚度对测量应变的影响。计算结果表明:该应变传递函数正确;胶结层厚度越薄,弹性模量越大,越有利于应变传递。该应变传递函数计算误差控制在5%以内,完全满足埋入式光纤Bragg光栅测量精度要求,对其实际应用具有指导意义。     

镍金属保护光纤布拉格光栅的热处理及高温传感

为了改善镍保护后光纤布拉格光栅(FBG)的高温传感性能,即降低其回程误差,减少其升温与降温灵敏度的差异,本文研究了产生这些现象的原因,认为其主要源于化学镀结合电镀镍过程中的残余应力.讨论了残余应力产生的机理,提出了适用于镍金属保护FBG的热处理方法.三次将金属镍保护后的FBG放置在120℃恒温炉中保温8h后随炉冷却,对...     

Digital monitoring and health diagnosis for mechanical equipment operation safety based on fiber Bragg grating sensor

This paper introduces fiber Bragg grating (FBG) based on a fiber optic grating sensor developed to be embedded on mechanical equipment for digital monitoring and health diagnosis. The theoretical and experimental researches on the new-style FBG sensor (FBGS) technology, high-speed demodulation, and data transmission are discussed. The transmission characteristics between the FBG and the detection interface, modeling and compensation method for online distributed multi-parameter digital monitoring and methods for data processing, synchronous sampling, and long-term dynamic digital monitoring using embedded technology are also presented. The acquired information by an FBGS can be used for the optimization of maintenance schedules and refinement of mechanical equipment design. It is a challenge to gather real-time data from components working at high speed and in a severe environment of high temperature, high pressure, and high rotation speed. Currently, there are no sensors or technologies available for digital monitoring and health diagnosis under this rigorous situation for use in mechanical engineering operation safety. As a result, this paper introduces an online distributed and integrated digital monitoring system and health diagnosis. The new principle and new method will contribute to modern measurements in science and technology, mechanical engineering, and large mechanical equipment operation safety.     

基于无芯光纤与光栅级联的反射式大量 程高分辨力海水温度传感器

针对海洋环境探测中海水温度的大量程高分辨力测量需求,本文提出并验证了一种基于无芯光纤(NCF)与光纤布拉格光栅(FBG)级联的反射式传感器。传感器的制作过程包括将刻有FBG的单模光纤与带有涂覆层的NCF熔接,之后在NCF的端面上镀金膜形成反射镜,最后将光纤结构封装于毛细管中。其中,无涂覆层的NCF是多模波导,而有涂覆层的NCF可以看作反谐振反射波导,理论分析可知多模干涉和反谐振效应叠加得到输出光谱。由于聚合物涂覆层的热光系数较高,干涉波长的位置随着温度变化发生明显偏移。根据FBG中心波长和干涉波长所在位置,通过对应的拟合曲线可以计算出准确的温度值。实验结果表明,在-6℃～54℃温度范围内,最小可探测温度分辨力为0.000 1℃。该反射式光纤传感器具有加工方便、结构紧凑、灵敏度高等优点,在大范围高分辨力海水温度测量中具有很大的应用潜力。     

基于光纤布拉格光栅的压力蒸汽灭菌器气体质量监测

基于光纤布拉格光栅(Fiber Bragg Grating,FBG)的灭菌全过程物理参数实时动态监测系统,提出基于聚酰亚胺涂覆的FBG(Polyimide-Coated FBG,PI-FBG)对灭菌器气体的质量进行监测,研究其可行性和监测方法.评估PI-FBG的温度稳定性及温度灵敏度,通过考查合格灭菌器排气期和干燥期传...     

Structural health monitoring with fiber optic sensors

Optical fiber sensors have been successfully implemented in aeronautics, mechanical systems, and medical applications. Civil structures pose further challenges in monitoring mainly due to their large dimensions, diversity and heterogeneity of materials involved, and hostile construction environment. This article provides a summary of basic principles pertaining to practical health monitoring of civil engineering structures with optical fiber sensors. The issues discussed include basic sensor principles, strain transfer mechanism, sensor packaging, sensor placement in construction environment, and reliability and survivability of the sensors.     

In situ monitoring of photostriction in chalcogenide glass film using fiber Bragg grating sensors

The reversible photostriction (photomechanical strain) in Ge₃₅S₆₅ chalcogenide thin film deposited by a solvent casting method has been monitored using a fiber Bragg grating (FBG) sensor. The shift in Bragg wavelength is used as a probing parameter to quantitatively measure the photoinduced strain arising because of structural modifications in these films under illumination. Exposure to band gap light (405?nm) and above band gap light (302 and 254?nm) leads to a reversible photostriction effect of the order of 100?µε. The present study shows that FBG sensors can be used to effectively measure the optomechanical actuation in chalcogenide films caused by the reversible photostriction effect in the visible and ultraviolet wavelength region.     

植入光纤光栅的软体驱动器形状传感研究

软体机器人由于具有柔顺性和适应性等特点,在外科手术和狭窄空间等方面具有无可比拟的优势,为了实现微创手术等狭小空间中软体驱动器的姿态传感监测,提出基于植入式光纤光栅的柔性传感方法,首先将光纤布拉格光栅（FBG）植入在软体驱动器中;然后在软体驱动器的不同弯曲状态下,通过实验测试分析FBG点的光谱、波长漂移量和曲率等信息,利用3次样条插值等算法实现软体驱动器的三维形状拟合重构。实验结果表明,驱动器实际弯曲角度和重构算法之间的误差不足45%,传感器重复性的偏差指数不足7%。所提出的基于植入式光纤光栅的柔性传感方法可以实现软体机器人的姿态传感监测,在医疗外科手术领域具有广阔的应用前景。