Remote structural health monitoring with serially multiplexed fiber optic acoustic emission sensors

Development and testing of a serially multiplexed fiber optic sensor system is described.The sensor differs from conventional fiber optic acoustic systems,as it is capable of sensing AE emissions at several points along the length of a single fiber.Multiplexing provides for single channel detection of cracks and their locations in large structural systems. An algorithm was developed for signal recognition and tagging of the AE waveforms for detection of' crack locations,Labora- tory experiments on plain concrete beams and post-tensioned FRP tendons were pcrlormed to evaluate the crack detection capability of the sensor system.The acoustic emission sensor was able to detect initiation,growth and location of the cracks in concrete as well as in the FRP tendons.The AE system is potentially suitable lot applications involving health monitoring of structures following an earthquake.

Absolute Measurement Fiber-optic Sensors inLarge Structural Monitoring

The security of civil engineering is an important task due to the economic, social and environmental significance. Compared with conventional sensors, the optical fiber sensors have their unique characteristics.Being durable, stable and insensitive to external perturbations,they are particular interesting for the long-term monitoring of civil structures.Focus is on absolute measurement optical fiber sensors, which are emerging from the monitoring large structural, including SOFO system, F-P optical fiber sensors, and fiber Bragg grating sensors. The principle, characteristic and application of these three kinds of optical fiber sensors are described together with their future prospects.

Loading Localization by Small-Diameter Optical Fiber Sensors

Structural health monitoring(SHM)in service has attracted increasing attention for years.Load localization on a structure is studied hereby.Two algorithms,i.e.,support vector machine(SVM)method and back propagation neural network(BPNN)algorithm,are proposed to identify the loading positions individually.The feasibility of the suggested methods is evaluated through an experimental program on a carbon fiber reinforced plastic laminate.The experimental tests involve in application of four optical fiber-based sensors for strain measurement at discrete points.The sensors are specially designed fiber Bragg grating(FBG)in small diameter.The small-diameter FBG sensors are arrayed in 2-D on the laminate surface.The testing results indicate that the loading position could be detected by the proposed method.Using SVM method,the 2-D FBG sensors can approximate the loading location with maximum error less than 14 mm.However,the maximum localization error could be limited to about 1 mm by applying the BPNN algorithm.It is mainly because the convergence conditions(mean square error)can be set in advance,while SVM cannot.

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.

Novel Fiberoptic Sensing Array and Fundamental Experiments

A suitable fiberoptic sensing array embedded in the smart structure to monitor quasi-distributed forces on the structure is presented in this paper.Artificial nearal networks are used in processing of fiberoptic sensing array signals.Fundamental experiments have been done and the results are also given.

Feasibility and Application Study of Optical Voltage/Current Sensors Using FBG

This paper concludes the case study work on the optical sensor, which is a new method for voltage and current measurement. Fiber Bragg gratings (FBG) have been developed and used for decades in the telecommunication industry. In recent years, FBG sensors have found wide applications in monitoring strain, temperature, voltage and current across all industries. As the process of constructing a robust smart grid, thousands of miles of optical-fibers have been deployed along the power transmission lines for the purpose of power production communication. This paper focuses on using the power optical fiber as voltage/current sensors instead of those copper wired traditional current transformers. By using piezoelectric layers, the optical sensor is able to transform voltage/current magnitude into optical signal, as well as transmit the signal through the optical fiber. The application of using optical fiber will significantly reduce the cost of deploying traditional current transformers all around the power grid. Moreover, the optical sensor is more stable, more accurate and faster, with such characteristics, the smart grid monitoring system could be much better. The application of combining the optical composite low-voltage cable (OPLC) and the optical current sensor in the distribution network for smart distribution monitoring has been analyzed.

A novel smart steel strand based on optical-electrical co-sensing for full-process and full-scale monitoring of prestressing concrete structures

As the main load bearing component,the steel strand has a significant impact on the safety of civil infrastructure.Real-time monitoring of steel strand stress distribution throughout the damage process is an impor-tant aspect of civil infrastructure health assessment.Hence,this study proposes an optical-electrical co-sensing(OECS)smart steel strand with the DOFS and CCFPI embedded in.It can simultaneously measure small strains in the initial damage phase with high accuracy and obtain information in the large deformation phase with relatively low precision.Several experiments were carried out to test its sensing performance.It shows both DOFS and CCFPI have good linearity,repeatability and hysteresis.In comparison to DOFS,CCFPI has a relatively lower accuracy and resolution,but a large enough measurement range to tolerate the large strain in the event of a steel strand failure.To verify the reliability of the proposed smart steel strand in real structures,the strand strain distribution in the full damage process of bonded prestressed beams under four-point bending loading was monitored using the smart steel strand as a prestressing tendon.The strain measured by the OECS steel strand is shown to reflect the deformation and stiffness variation of prestressed beams under different load.

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。

桥梁缆索智能监测多参量光纤传感器及其封装保护技术

本文介绍了一种可直接植入缆索结构内部,实现缆索温度、湿度和应变多参量同步监测的新型光纤传感器。采用飞秒光纤光栅无损刻写技术制作缆索监测传感光纤,大幅提升了传感器耐久性。研发了基于聚酰亚胺套管的增敏型湿度传感器,大幅提升传感器测量灵敏度。提出了基于螺旋铠装+不锈钢套管的双层光纤传感器封装保护方案。研究了传感光纤从缆索锚头区域引出工艺,并开展了缆索试验研究,验证了本文研发的缆索监测多参量光纤传感器在实际缆索样品应用中的效果。

Etched Optical Fiber Vibration Sensor to Monitor Health Condition of Beam Like Structures

Using a center etched single mode optical fiber, a simple vibration senor is designed to monitor the vibrations of a simply supported beam. The sensor has high linear response to the axial displacement of about 0.8mm with a sensitivity of 32mV/10p, m strain. The sensor is tested for periodic and suddenly released forces, and the results are found to coincide with the theoretical values. This simple design, small in size and low cost sensor may find applications in industry and civil engineering to monitor the vibrations of the beam structures and bridges.

用于光纤振动传感的盘片式振动增敏研究

目前光纤传感器增敏的研究方向主要从改变光纤自身结构和成分的角度出发或者借助外部封装工艺来实现增敏效果,导致传感器研发制作的成本和时间都会大幅提升。为满足地震勘探和结构安全监测中分布式光纤传感系统对振动测量的实际需要,设计了一种基于马赫—曾德尔干涉仪(MZI)光纤干涉的盘片式振动增敏结构,结合弹性力学与光纤弹光效应对其灵敏度进行了推导;使用有限元方法分析了盘片参数对灵敏度的影响,通过对增敏结构的合理设计及优化确定了盘片的尺寸。基于此结构设计的振动传感器有效工作频率范围为0.1~2.5kHz,灵敏度可达6988.2 rad/gn,对于60 m外的震源可以采集到有效振动信号,能够满足振动监测领域的实际需要以及系统运行的经济性。

Structural Health Monitoring of Different Geometry Structures With Optical Fiber Sensors

In this paper, we describe the structural health monitoring of several structures, with different geometry, materials and behaviors, using optical fiber sensors. Those studies aimed to demonstrate the feasibility of such technologies in structural health monitoring, with all the advantages inherent to the optical fiber technology.

基于分布式光纤传感与U-Net网络的复合材料分层损伤定量识别方法

结构健康监测(SHM)是确保飞行器复合材料结构安全性和完整性的重要手段。基于背向瑞利散射的分布式光纤传感器可以通过测量高密度的应变分布为复合材料损伤监测提供数据支持。然而,结构应变分布特征和损伤的映射关系较为复杂,无法直接根据应变分布准确判定损伤的定量信息。另外,分布式光纤传感器数据量大,通过人为分析应变数据识别损伤较为耗时且准确性偏低。为了应对这一挑战,提出了一种基于分布式光纤传感数据与U-Net神经网络的智能损伤识别方法,旨在自动精确识别复合材料中常见的分层损伤。首先,通过有限元仿真构建U-Net神经网络的训练集与验证集;随后进行含分层损伤复合材料板的悬臂加载试验,通过分布式光纤传感器采集结构应变分布数据作为测试集。损伤识别结果表明,U-Net神经网络可以对分层损伤的位置、尺寸与形状进行较为精确的定量识别。

埋入式光纤传感原理及实验研究——航天Smart结构

对Ｓｍａｒｔ材料／结构中的光纤传感原理进行了探讨，并进行了实验研究。首先介绍了Ｓｍａｒｔ结构中常见的埋入式光纤传感器的特点及其工作原理，然后提出了应用多模光纤在编织复合材料Ｓｍａｒｔ结构中进行应变场测量的方案，建立了实验装置，给出了实验结果并进行了讨论。

Case studies of high-sensitivity monitoring of natural and engineered slopes

High-sensitivity monitoring solutions are crucial for early warning systems of earth structures. In this paper, we discuss the design and implementation of such systems for natural and engineered slopes using two case studies. At the Gradenbach Observatory, one key element of the monitoring system is a large fiber optic strain rosette embedded in the slope. We demonstrate that the strain rosette can depict landslide deformations much earlier than geodetic sensors like GPS or total stations and is therefore well suitable for an early warning system. In a second application we report the construction of a reinforced earth structure using geogrids. A distributed fiber optic measurement system was installed to measure the current operating grade of the geogrids within the earth structure. About 2 km of Brillouin sensing cables were installed in the project area. It is demonstrated that the developed monitoring system is well suited for assessing the current state of health of reinforced earth structures.

基于光纤传感稳态热容平衡模型的架空线路导线温度监测

架空线路温度监测过程中,受环境温度、日照等因素的影响,导致其监测数据失真,降低监测准确度。提出基于光纤传感器的架空线路导线温度监测方法。建立架空线路导线的稳态热容平衡模型,分析影响导线温度相关因素。通过光纤温度传感器得到热膨胀的反应系数,计算求得光纤布拉格光栅对温度变化的灵敏度系数,构建传感稳态热平衡方程。结合环境温度、风速和日照辐射等参数,利用导线温升公式计算出传感导线各部位热阻值,获得相对应温度监测数据,实现架空线路导线温度监测。实验结果表明,所提方法在不影响线路正常运行情况下,实验测得导线上表面、侧方位和下表面的温度分别为27.8℃、26.6℃和23.4℃,温度监测准确,误差小。

基于光学传感技术的呼吸监测智能服装研究

呼吸监测智能服装是生理体征监测类智能服装中的一类,可以通过对呼吸信号的监测来反映穿着者的健康状况。文章针对消费者对日常呼吸监测的需求,利用缺口光纤开发压力传感器,并进行不同结构传感器的性能对比,制作出具有呼吸监测功能的智能服装。试验表明:所设计制作的基于光学传感技术的呼吸监测智能服装与商业呼吸监测传感器监测结果一致,呼吸监测准确率达到了95%,能够为消费者在不同姿势下的呼吸监测提供保障。

Optimization of monitoring the stability of surrounding rock in a metal mine

Through analyzing the failure mechanics of rock under blasting effect, the optical fiber sensing system was used to monitor the strain of surrounding rock under blasting effect. Combined with practical exploration, the stability of surrounding rock was computed by numerical simulation using the blasting wave obtained from the site. According to the change regularities of displacement, stress, acceleration, and velocity of tunnels before and after explosion, the layout of key monitoring points was optimized. When disposed the monitoring position of sensors, the regular points should be considered to use as key points and the periodical monitor should be a part of the long-term monitor. In practical application, considering the geology condition in site, monitor points should be added on the area with joints and faults to assure the integrity of monitor data and the preciseness of decision.

Study on the spectral response of fiber Bragg grating sensor under non-uniform strain distribution in structural health monitoring

Many theoretical studies have been developed to study the spectral response of a fiber Bragg grating (FBG) under non-uniform strain distribution along the length of FBG in recent years. However, almost no experiments were designed to obtain the evolution of the spectrum when a FBG is subjected to non-uniform strain. In this paper, the spectral responses of a FBG under non-uniform strain distributions are given and a numerical simulation based on the Runge-Kutta method is introduced to investigate the responses of the FBG under some typical non-uniform transverse strain fields, including both linear strain gradient and quadratic strain field. Experiment is carried out by using loads applied at different locations near the FBG. Good agreements between experimental results and numerical simulations are obtained.

Multi-Channel Monolithic Integrated Optic Fiber Bragg Grating Sensor Interrogator

Fiber Bragg grating （FBG） is a mature sensing technology for the measurement of strain, vibration, acoustics, acceleration, pressure, temperature, moisture, and corrosion. It has gained rapid acceptance in civil, aerospace, chemical and petrochemical, medicine, aviation and automotive industries. The most prominent advantages of FBG are： small size and light weight, distributed array of FBG transducers on a single fiber, and immunity to radio frequency interference. However, a major disadvantage of FBG technology is that conventional state-of-the-art FBG interrogation system is typically bulky, heavy, and costly bench top instruments that are typically assembled from off-the-shelf fiber optic and optical components integrated with a signal electronics board into an instrument console. Based on the industrial need for a compact FBG interrogation system, this paper describes recent progress towards the development of miniature fiber Bragg grating sensor interrogator （FBG-TransceiverTM） system based on multi-channel monolithic integrated optic sensor microchip technology. The integrated optic microchip technology enables monolithic integration of all functionalities, both passive and active, of conventional bench top FBG sensor interrogator system, packaged in a miniaturized, low power operation, 2 cmx5 cm small form factor （SFF） package suitable for long-term structural health monitoring in applications where size, weight, and power are critical for operation.