Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.

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.

Practical Pattern Recognition System for Distributed Optical Fiber Intrusion Monitoring Based on Ф-COTDR

At present, the demand for perimeter security system is in-creasing greatly, especially for such system based on distribut-ed optical fiber sensing. This paper proposes a perimeter se-curity monitoring system based on phase-sensitive coherentoptical time domain reflectometry(Ф-COTDR) with the practi-cal pattern recognition function. We use fast Fourier trans-form(FFT) to exact features from intrusion events and a multi-class classification algorithm derived from support vector ma-chine(SVM) to work as a pattern recognition technique. Fivedifferent types of events are classified by using a classifica-tion algorithm based on SVM through a three-dimensional fea-ture vector. Moreover, the identification results of the patternrecognition system show that an identification accurate rate of92.62% on average can be achieved.

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.

Optical Fiber Sensor's Applied in Vibration Measurement of Turbine Blade

A new type optical fiber sensor--Tip timing Sensor is introduced in this paper. It is mostly used in vibration measurement of turbine blade, which can realize real-time and non-contact measurement.

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。

基于光纤F-P传感器变压器铁心在线监测研究

利用变压器振动测试原理,运用光纤Fabry-Perot(F-P)振动传感器对变压器铁心的振动信号进行了在线监测研究。将光纤F-P传感器粘贴在变压器铁心上,直接提取变压器铁心的振动信号,这将避免传统的间接测量方法所带来的误差。分析了光纤F-P的测量原理,并建立了光纤F-P腔的数学模型。实验验证了空载状况下铁心的磁致伸缩率与输入电压呈很好的线性关系。

光纤F-P腔反射面的形变与传感应用研究

建立了反射端面为弧形形变的光纤F-P传感腔数学模型.将弧形形变的F-P腔等效为阶梯分布的、环状、平行端面F-P腔体的组合,结合多光束干涉理论,利用光强叠加处理方法对弧形腔输出光强进行数学建模.依所建模型仿真,提出弧形端面曲率大于300μm时,利用弧形形变特性进行传感测量的可行性.选取腔长变动大、形变弧度小,平衡状态稳定性高的形变端面保证传感腔的高灵敏度和稳定的工作点.

高速铁路箱梁伸缩缝位移传感器研究

高速铁路箱梁状态对轨道平顺性和行车安全具有决定性作用。由于箱梁滑移变化缓慢且微小,同时需克服电力牵引产生的强电磁干扰,实现自动化监测面临较大挑战。该问题的难点在于箱梁伸缩缝的起始缝宽不同,只有实现等精度测量,才能使不同箱梁伸缩缝的变化具备可比性。本文设计了一种光学低相干高速铁路箱梁伸缩缝位移传感器,在实验室条件下进行了抗振动性能测试,验证了传感器在常见低频振动工况下的性能,并在京津城际高速铁路简支箱梁伸缩缝的监测中应用。结果表明:受日照和温度的影响,箱梁伸缩缝上下表面的位移差异可达150μm,传感器的实测长期监测精度可达50μm。研究成果为实现高速铁路箱梁伸缩缝自动化监测提供了参考借鉴。

Research on stress characteristics of Fabry-Perot sensor with center microbubble structure

The optical fiber based on silicon materials has a smaller thermal expansion coefficient, therefore it can be used for the preparation of sensor devices which are insensitive to temperature but sensitive to refractive index, strain, stress, etc. For example, we can use optical fiber Fabry-Perot （F-P） sensor to achieve high sensitivity stress sensing. In this paper, we design an optical fiber F-P sensor with low cost and high sensitivity based on chemical etching method and analyze the stress sensing properties. Hydrofluoric acid is used to prepare the end face concave hole of the optical fiber first, and then the hollow struc-ture of the fiber F-P sensor is obtained by melting and discharge. This preparation method contributes greatly to enhancing the stress sensing properties and temperature insensitivity of the optical fiber device. The experimental results show that interference spectrum peak change is proportional to the stress change of optical fiber F-P sensor, stress sensitivity can reach 5. 2, and the cost is relatively low. Based on this,it has a certain application value in the stress sensing field.

光机材料与光纤振动传感器连接力学可靠性研究

针对不同的典型空间相机光机结构材料,研制典型空间相机用光机材料试块,能够有效代表现有相机主要光机结构组成和光纤振动传感器安装对象。设计相关试验工装,通过工装连接进行拉伸强度和剪切强度试验,获得其强度破坏参数。从而进行连接工艺强度研究,验证连接力学工艺可靠性。以确保实现传感器与空间相机结构的有效连接,完成极限力学环境试验考核,为传感器在后续型号中的应用提供参考。

Distributed Vibration Sensor With Laser Phase-Noise Immunity by Phase-Extraction φ-OTDR

We have demonstrated a distributed vibration sensor based on phase-sensitive optical time-domain reflectometer (φ-OTDR) system exhibiting immunity to the laser phase noise. Two laser sources with different linewidth and phase noise levels are used in the φ-OTDR system, respectively. Based on the phase noise power spectrum density of both lasers, the laser phase is almost unchanged during an extremely short period of time, hence, the impact of phase noise can be suppressed effectively through phase difference between the Rayleigh scattered light from two adjacent sections of the fiber which define the gauge length. Based on the phase difference method, the external vibration can be located accurately at 41.01 km by the(φ-OTDR system incorporating these two lasers. Meanwhile, the average signal-to-noise ratio (SNR) of the retrieved vibration signal by using Laser I is found to be -37.7 dB, which is comparable to that of -37.5 dB by using Laser II although the linewidth and the phase noise level of the two lasers are distinct. The obtained results indicate that the phase difference method can enhance the performance of(φ-OTDR system with laser phase-noise immunity for distributed vibration sensing, showing potential application in oil-gas pipeline monitoring, perimeter security, and other fields.

基于光纤光栅的紧凑型高频振动传感器的设计与应用

设计了一种六边形的紧凑型光纤光栅振动传感器,其结构包括弹性体、质量块、光纤光栅和外壳。首先对六边形弹性体结构进行理论分析和仿真,通过设计发夹弯结构改变灵敏度和频率测量范围,使设计的光纤光栅振动传感器能够满足不同机械设备的振动监测需求。在激振台上测试了传感器的性能,并在真空泵振动监测中应用。实验结果表明,设计的光纤光栅振动传感器具有良好的响应,普通六边形弹性体结构传感器的1阶固有频率高达1481 Hz,在100 Hz振动时的灵敏度为4.93 pm/g;含发夹弯的六边形弹性体结构传感器的1阶固有频率为185 Hz,在100 Hz振动时的灵敏度为105.73 pm/g,两种传感器的横向干扰均小于5%,具有很好的抗横向干扰能力。

高灵敏抗冲击光纤光栅微振动传感器

针对高灵敏度的光纤布拉格光栅(FBG)振动传感器的抗冲击可靠性,设计了一种具有限振结构的双悬臂梁型FBG振动传感器,理论分析了结构参数与灵敏度和振动位移的关系,进行了结构优化,确定了限振幅度。制作了限振幅度约为90μm的传感器样品,对传感器的加速度灵敏、频率响应、抗冲击性能进行了测试,结果表明,传感器的加速度灵敏度达到525 pm/g,谐振频率约为66 Hz,传感器经过50 g反复冲击,频响特性具有良好重复性,表明传感器具有较高的可靠性。

分布式光纤振动传感技术及发展动态

从工程结构安全监测到输油管线的维护以及地震监测,振动传感器发挥着重要作用,可以实现以往需要大量人力物力和时间的监测。而分布式光纤振动传感器具有许多优于传统振动传感器的地方,应用前景广阔,近年来成为光纤传感领域的研究热点。本文主要介绍了分布式光纤振动传感器的实现方法与相关技术,并展望了分布式振动传感技术未来的发展方向和应用领域。

全光纤周界安全防范系统

采用光纤振动传感技术研制了应用于国境线的光纤周界安全防范系统。通过对其进行入侵者翻越周界围栏的入侵探测实验,结果表明,它可有效地敏感由入侵行为产生的振动。通过对振动进行分析表明,翻越围栏的行为会产生非平稳随机信号,该信号存在多个幅度峰值,且频率都集中在500Hz以下的低频,为自动识别算法的开发提供了设计依据。实验环境中风力会产生300Hz以下的低频背景噪声,会增加识别的难度。

基于弓形梁增敏结构的FBG振动传感器研究

利用光纤光栅(FBG)随弓形梁弯曲变形的敏感特性,通过设计特制的增敏结构,研制了一种基于弯曲特性的FBG振动传感器。根据ANSYS数值分析和实验结果表明,在加速度0～5 g、工作频率0～40 Hz范围内,传感器加速度特性曲线呈现良好对应关系,灵敏度可达458.1 pm/g,精度约0.002 g。该传感器系统采用双光栅形式实现了温度补偿,且在所测加速度范围内显示出较好的灵敏度和重复性,频响误差小,能够满足航空结构振动监测与控制需求。

一种基于等强度梁的光纤光栅高频振动传感器

以光纤光栅为敏感元件,设计了一种基于钢制等强度悬臂梁结构的高频振动传感器,该传感器由光纤光栅粘贴于等强度悬臂梁的表面而实现。运用材料力学原理对该等强度悬臂梁的共振频率和应变特性进行了推导。采用匹配滤波法解调光信号,并进行了传感探头优化设计,使该传感器实现了温度补偿。在不同环境温度下对任意频率的振动进行了测量实验,结果表明这种振动传感器可以实现高频振动信号的检测,实际上限频率达6kHz,测量频率误差小于0.5%,能够实现温度补偿,且集成度高,结构轻便,具有广阔的实用前景。

FBG传感器和电阻应变仪的振动监测特性

将光纤布拉格光栅(FBG)传感器和电阻应变片固定在等强度梁上,研究了两种传感器的振动监测性能,总结比较了其优缺点。通过固定在等强度梁末端的电机来产生振动,测试了FBG传感器和电阻应变片监测到随时间变化的振动信号,并分析了振动信号经傅里叶变换(FFT)的频谱图。实验结果表明,FBG传感器和电阻应变片监测到振动信号的时域图基本一致,但是FBG传感器监测到振动信号经FFT变换的频谱图出现较明显的二次谐波和三次谐波,电阻应变仪监测到的频谱图出现的谐波较弱。在实验中还观察到,在有电磁干扰情况下,电阻应变仪监测不到振动信号,而FBG传感器正常工作,不受电磁干扰。

光纤传感振动检测系统及其实验研究

实际工程结构中的振动检测是十分重要的,也是十分复杂的,常用的结构振动检测传感器易受工程现场恶劣环境的影响,而光纤传感器具有小巧、抗电磁干扰、灵敏度高、适合长期监测等优点。本文建立了基于马赫—曾德(Mech-Zehnder)干涉原理的光纤传感振动检测系统,研制了运用先进的数字信号处理技术采集和处理数据的专用软件,并在典型结构件——钢制悬臂梁结构上进行了外加信号作用下的强迫振动检测和冲击载荷作用下的自由衰减振动检测,测量了该结构件的频率及振幅,其结果与同时进行的成熟的电测结果相近,说明光纤传感器用于结构件的振动测量是可靠的。本文为光纤传感器应用于实际工程的振动检测提供了新的技术装置,具有工程应用前景。