FBG-based ultrasonic wave detection and acoustic emission linear location system

The ultrasonic (US) wave detection and an acoustic emission (AE) linear location system are proposed, which employ fiber Bragg gratings (FBGs) as US wave sensors. In the theoretical analysis, the FBG sensor response to longitudinal US wave is investigated. The result indicates that the FBG wavelength can be modulated as static case when the grating length is much shorter than US wavelength. The experimental results of standard sinusoidal and spindle wave test agree well with the generated signal. Further research using two FBGs for realizing linear location is also achieved. The maximum linear location error is obtained as less than 5 mm. FBG-based US wave sensor and AE linear location provide useful tools for specific requirements.     

基于布里渊光时域分析分布式光纤漏油传感器

研究了一种新型基于布里渊光时域分析(BOTDA )的光纤漏油传感器,可在min量级发现小规模 漏油事件,主要用于长距离输油管线、油库等场所的实时漏油监测。通过模拟监测输油管道 输运状态,将 光纤埋敷于特种油敏材料中沿输油管线铺设,用BOTDA仪实时监测光纤布 里渊频移,可快速发 现并定位漏油事件。实验证明了本文技术的可行性,能够在10min内 准确定位小规 模漏油事 件,采用DiTeStSTA-R系列BOTDA仪,在1.7km的传感光纤上实现了 0.1 m的定位 精度。     

基于空间域差分的φ-OTDR光纤分布式扰动传感器定位方法研究

针对-OTDR光纤分布式扰动传感器偏振衰落导致漏报的问题,提出了一种基于空间域差分的定位方法。在不增加光路器件的情况下,在空间域对探测光强进行差分处理,与现有时域定位方法相结合,通过在时域和空间域分别设置报警阈值,可以有效抑制偏振衰落导致的漏报。对提出的定位方法进行了实验验证,在空间分辨率为50 m、光纤长度为25.05 km的条件下进行多次实验测试,与现有单一时域定位方法相比,漏报率从18.5%降低到2%,报警准确率从76%提高至89%。该研究工作可以为优化和提高-OTDR光纤分布式扰动传感器在实际应用中的技术性能提供理论指导和技术参考。     

Theoretical model of a fiber optic remote sensor based on surface plasmon resonance for temperature detection

This paper reports on a novel design of a remote sensor for temperature detection based on surface plasmon resonance and optical fiber technology. We theoretically analyze the performance of proposed sensor under different conditions related to its constituents, i.e., optical fiber, metallic layer, sensing region, and launched light. The effect of the related parameters such as numerical aperture, fiber length, core diameter, FWHM of the Gaussian input on sensor is analyzed along with its physical explanation. The numerical results presented in this paper leads to a significant optimization of the important design parameters to achieve a high temperature detection accuracy and sensitivity of a fiber optic remote sensor.     

Planar location of the simulative acoustic source based on fiber optic sensor array

A fiber optic sensor array which is structured by four Sagnac fiber optic sensors is proposed to detect and locate a simulative source of acoustic emission (AE). The sensing loops of Sagnac interferometer (SI) are regarded as point sensors as their small size. Based on the derived output light intensity expression of SI, the optimum work condition of the Sagnac fiber optic sensor is discussed through the simulation of MATLAB. Four sensors are respectively placed on a steel plate to structure the sensor array and the location algorithms are expatiated. When an impact is generated by an artificial AE source at any position of the plate, the AE signal will be detected by four sensors at different times. With the help of a single chip microcomputer (SCM) which can calculate the position of the AE source and display it on LED, we have implemented an intelligent detection and location.     

基于BP算法和FBG传感的复合材料冲击定位检测技术

复合材料在服役过程中易受到外部的低能量冲击,造成不可见损伤,为了监测复合材料健康状况,将光纤布喇格光栅(FBG)传感网络粘贴布置于碳纤维复合材料表面,采用基于反向传播(BP)神经网络系统的智能复合材料冲击定位识别技术,获取FBG传感的时域信号响应值,从而进行了复合材料冲击位置的预判.结果表明,BP神经网络算法具有非线性...     

布里渊光时域光纤传感中的快速测量技术

布里渊光时域光纤传感是一种连续分布式光纤传感技术,可广泛用于获取沿传感光纤的温度和应变等物理量分布。如何提高布里渊散射信号的测量和处理速度,以满足工程应用中的快速测量需求,是布里渊光纤传感领域研究者的主要关注点之一。文章通过分析传统布里渊光时域光纤传感系统的耗时来源,综述了近年来基于频率调制、功率谱测量、图像处理去噪和布里渊谱拟合方法改进等布里渊光时域传感中的快速测量技术研究进展。     

基于Sagnac型的双光路平衡探测光纤声传感器

为解决传统声电传声器易腐蚀、易受电磁干扰等问题,提出了一种用光纤提取声音的声光换能器结构。该传感器以Sagnac干涉仪为原型,利用声压作用于感应光纤产生的光弹效应实现光波相位的调制,采用3 × 3耦合器构建双光路平衡探测系统,通过干涉实现语音信号的解调,将光电转换后得到的幅值相等的两路信号进行差分处理,消除共模干扰信号和降低光源噪声。实验测试表明,系统性能稳定,波形失真小,在300~3 400 Hz范围内实现声音信号的提取与还原。     

基于33耦合器Fox-Smith型光纤周界系统的定位技术

为了对长距离周界入侵进行定位,提出一种使用33耦合器作为基本元件的Fox-Smith干涉仪光纤入侵探测系统。对此结构及其定位方法进行了理论分析和实验验证。当有冲击作用在传感光纤上时,光纤中的光波受到相位调制,利用两束光波受到调制的时间不同从而产生相位差;通过对解调出的相位信号进行傅里叶变换,获取了一系列的陷波点。结果表明,在长度为34.793km传感光纤上,获得平均定位误差为83m,可见该种结构在长距离周界系统定位是可行的。这一结果在长距离周界入侵定位上具有一定的帮助。     

复合光纤对φ-OTDR振动传感远程敏感

为了避免在高功率脉冲下产生光纤非线性效应和前端振动不敏感,采用了一种复合光纤的新型光纤传感结构方法,进行了理论分析和实验验证。使用多模光纤与单模光纤的混合作为传感光纤的方法,通过处理不同功率脉冲下的传感信号,取得了光纤传感的距离数据,并针对多模光纤在喇曼系统的传感作用,对其传感特性进行了讨论。结果表明,该新型复合光纤传感结构可探测30km处的振动信号。此研究为多模光纤在相位敏感光时域传感领域的科学研究和工程应用提供了参考。     

Coherence addressing of quasi-distributed absorption sensors by theFMCW method

We report a new addressing mechanism for quasi-distributed absorption sensors based on the frequency modulated continuous wave (FMCW) method. The sensor units consist of open-path microoptic cells constructed from gradient index (GRIN) lenses, each of differing lengths. Coherence addressing of the cells using FMCW is achieved by the interferometric mixing of two signals originating from each cell (from the glass/air interfaces). The time delay between the two reflections, along with the linear frequency ramp of the source, gives rise to beat frequencies in the mixed output which are different for each cell. The connecting fiber length between two successive sensor cells is chosen to be much greater than the coherence length of the source so that the reflections from different cells do not interfere. The interference patterns of all sensor cells add up at the detector whereby each individual sensing cell is identified, by its power spectrum in the frequency domain. We show theoretically and experimentally how individual cells can be addressed and the measured signals obtained by suitable choice of cell length, proper modulation of the source and appropriate signal processing     

Optical time domain reflectometry on optical amplifier systems

The use of optical time-domain reflectometry (OTDR) on long-span fiber transmission systems containing in-line optical amplifiers is discussed. Having identified the specific requirements for OTDR equipment, measurements were carried out on systems of up to 300 km in length, containing three semiconductor laser amplifiers. The results demonstrate that OTDR can be used not only for fault location on fiber links several hundred kilometers in length but also as an alternative to standard system supervisory techniques, thus providing the potential for minimizing the hardware in the optical amplifier stages of future long-span fiber optic transmission systems     

基于菱形光纤布拉格光栅传感阵列的声发射定位技术

声发射技术是结构损伤检测的重要手段,声发射源定位是损伤检测的首要环节。时差定位技术具有快速、高效、精确的特点,以此设计了由菱形阵列光纤布拉格光栅（FBG）传感器构成的声发射定位系统。采用小波变换和传统阈值法提取特征信号,结合互相关法获得传感器间的信号到达时差,然后根据几何定位模型求解非线性方程组得到声源可能存在的位置,最后根据时差的正负特性进一步确定声源的准确位置,有效避免了伪声源的情况。在铝合金板上,以对角线为48 cm48 cm的监测区域进行了10组测试实验验证,平均误差为1.29 cm。     

Doppler effect-based fiber-optic sensor and its application in ultrasonic detection

Based on the Doppler effect of light wave transmission in optical fiber, Doppler effect-based fiber-optic (FOD) sensor possesses outstanding advantages in acquiring vibration/acoustic waves with high sensitivity. Furthermore, when shape of the FOD sensor was properly selected, its sensitivity was bonding direction-independent, namely non-directionality. In this paper, characteristics of the FOD sensor were investigated for the purpose of ultrasonic detection. A piezoelectric wafer was applied as an actuator to excite Lamb waves, a kind of ultrasonic wave, in an aluminum-alloy plate. Features of the ultrasonic wave signals, collected using a number of spiral FOD sensors with various inner diameters and outer diameters, were compared to investigate characteristics of FOD sensor. Amplitude curves of the FOD sensors were hereby obtained for the future applications in ultrasonic acquisition. The results demonstrated that sensitivity of the spiral FOD sensor with longer optical fiber length was higher than that with shorter fiber length.     

A strain sensor using twisted optical fibers

A sensor using twisted optical fibers to detect the strain distribution along the length of an object is discussed. This sensor is based on the optical loss due to fiber curvature. The distributed strain along the sensor axis is converted into distributed optical loss. The relation between the strain and optical loss is theoretically derived and experimentally confirmed for uniform tensile strain. The dependence of the sensor characteristics on sensor structure and fiber parameter are also shown. Measurement of the strain applied to fibers in an optical cable is also discussed     

光纤法布里珀罗声发射传感系统

实现了一种由多个光纤法布里珀罗传感器构成的声发射传感系统,可用于变压器局部放电的检测与定位.该系统利用光纤法布里珀罗声发射传感器实现信号采集,利用门限检测的方法实现信号检测,并通过计算信号达到不同传感头的时延差实现放电源的空间定位,具有传感头尺寸小、系统结构简单、抗电磁干扰性能强等优势.     

分布式光纤管道安全检测定位技术研究

提出了一种基于Mach-Zehnder光纤干涉仪原理的管道安全检测分布式光纤传感技术,分析了检测系统的组成和工作原理.阐述了检测系统定位结构和方法,采用相关时延估计算法,通过确定两个测试信号的时延可以获得管道沿线所发生事件的位置.理论分析和测试结果表明,该测试技术具有较高的测试灵敏度和定位精度,定位误差小于300 m.     

光纤激光传感技术及其应用

超高灵敏度的信号探测在石油勘探、地震预报和安全监测等领域都具有重要的应用价值.近年来出现了一种以分布反馈(DFB)光纤激光器为传感元件的新一代光纤传感器,它具有尺寸小、输出激光信号极窄的光谱线宽和极低的噪声等优势,与高分辨率波长解调技术结合可以达到极高的探测灵敏度.介绍了在光纤激光传感技术及其应用技术方面的研究进展,包括线宽仅为3 kHz、尺寸仅为3.6 cm的窄线宽低噪声DFB光纤激光器的研制及其测试,波长分辨率达3.5×10~(-7) pm/Hz~(1/2)的超高分辨率波长解调系统,基于密集波分复用的光纤激光传感网络,以及相关技术在水声和地震波探测中的应用研究.     

基于扫描激光器和光放大的100 km光纤布拉格光栅传感系统

提出了对基于扫描激光器的光纤布拉格光栅(FBG)传感系统进行掺铒光纤(EDF)/双波拉曼混合放大的方法,大幅度提高了该光纤布拉格光栅传感系统的传输距离。该方法以高功率扫描激光器作为光源,采用双波长拉曼放大的方法对信号进行低噪声双向放大,再利用系统中间的两段掺铒光纤,将剩余的拉曼抽运功率用来产生自发辐射光和放大传感信号,使得整个系统能在超长的传感距离上获得良好的信噪比(SNR)。实验表明使用一台扫描激光传感分析仪、一只170mW的拉曼抽运和一只2W的拉曼抽运,可以使传感距离达到100km以上,并且传感系统的光纤布拉格光栅反射信号均能获得超过7dB的良好信噪比,从而实现在超长距离上的光纤布拉格光栅传感。     

基于光纤智能夹层的损伤检测系统

介绍了基于光纤智能夹层的损伤检测系统以及该系统的两个关键技术:光纤传感器与材料结构集成以及与静载荷损伤检测算法。标准化、模块化的光纤智能夹层是光纤智能夹层解决了光纤传感器与结构集成的一种实用方法。用聚酰亚胺光制作的纤智能夹层便于存储、运输和埋置,并且可以很方便地埋入或粘贴材料结构,埋入结构对结构的强度和传感器的灵敏度影响不大。为了适应Bragg光栅解调仪的解调速度,本系统采用基于静载荷损伤识别算法。该算法只要求使用结构应变参数,并不需要使用挠度、位移等参数;不需要建立结构的有限元模型;不需要使用优化算法。因此,该算法具有高效、成本低的优点。所设计的软件通用性好,可应用于不同结构和不同类型的损伤。该系统应用于机翼盒段,并成功地实现对盒段上螺钉松动的检测。