基于光纤布拉格光栅传感器的光纤光栅智能夹层试验研究

传感元件与复合材料的一体化是智能结构研究的最终目标之一。设计一种具有自诊断功能的标准化、模块化光纤智能夹层系统,正是实现这种一体化最有潜力的技术途径。采用聚酰亚胺薄膜制作了基于光纤布拉格光栅（FBG）传感器的光纤光栅智能夹层,对智能夹层中光纤布拉格光栅传感器的应变、温度特性进行了标定试验,并建立了基于光纤布拉格光栅传感器光纤光栅智能夹层的应变、温度测量模型。试验表明,智能夹层内布拉格光栅波长偏移与应变、温度之间具有良好的线性关系。不过在温度测量时,必须考虑被埋人结构的热膨胀效应。利用光纤光栅智能夹层内光纤布拉格光栅传感器网络和先进信息处理技术,可以建立结构损伤主动、在线和实时监测系统。     

一种监测钢筋腐蚀的光纤光栅传感器的研究

钢筋腐蚀是导致钢筋混凝土结构耐久性劣化的最重要因素之一。钢筋腐蚀将导致钢筋体积大大增加,混凝土保护层开裂、剥落,结构承载力下降,甚至倒塌。基于光纤布拉格光栅应变传感器的原理,根据钢筋腐蚀体积膨胀,提出了一种新的钢筋腐蚀光纤光栅传感器及温度补偿方法。传感器构造是在两根紧靠的钢筋中心附近粘贴光纤光栅,由于钢筋腐蚀体积膨胀,钢筋直径增加将转变成布拉格光纤光栅的应变,从而实现对钢筋腐蚀程度及速率的监测。传感器的监测原理是设置一个钢筋腐蚀光纤光栅传感器来监测由于钢筋腐蚀和温度变化引起的光栅应变,同时单独设置一个不锈钢光纤光栅传感器来测量温度引起的光栅应变。这两个光纤光栅传感器的应变监测,可分离出钢筋由于腐蚀所引起的体积变化。在混凝土结构中埋入封装的传感器,通过监测光纤光栅波长的漂移可以直接测量钢筋腐蚀程度,而且不受腐蚀因素的影响,可用于混凝土结构中钢筋腐蚀的早期监测。最后通过实验标定了钢筋腐蚀率与光栅波长位移的关系。     

可分离温度影响的FBG应变测量方法

光纤布拉格光栅在通信和传感领域具有广泛的应用。利用光纤布拉格光栅中心波长的偏移，可以测量温度和应变等多种物理量，但必须解决光栅对温度和应变的交叉敏感问题。该文简要分析了光纤光栅作为传感器的基本原理及其优点，设计了利用参考光栅法分离温度影响以及利用掺铒光纤的自发发射放大特性分离温度影响的2种应变测量方法。最后，介绍了一种利用倾斜光纤光栅的主模和边模对布拉格光栅中心波长的偏移进行解调的方法，该方法成功地分离了温度对应变测量的影响。     

动态激励下的FBG应变传感器原位校准方法

针对光纤光栅应变传感器测量桥梁结构动态应变值的准确性问题,提出了一种动态激励下的光纤光栅应变传感器的校准方法。采用等强度悬臂梁模拟桥梁结构,在等强度悬臂梁末端瞬间悬挂不同重量的砝码来模拟桥梁上汽车产生的动态激励。以电阻应变片作为参考传感器,光纤光栅应变传感器作为待校准传感器,将这两个传感器的测量数据序列进行比对。针对传感器的测量数据序列出现的时间错位问题,采用互相关算法对参考传感器和待校准传感器的测量数据进行数据匹配。在光纤光栅应变传感器有初始值的情况下进行测量值校准的研究。实验结果表明,该方法有效解决了测量数据序列的时间错位问题,实现了光纤光栅应变传感器的动态校准,采用不同重量的砝码作为激励源对校准结果没有影响,1529 nm和1547 nm波长的光纤光栅应变传感器灵敏度校准系数与静态标定结果基本一致。     

单光纤光栅波谱展宽温度压力同时区分测量

报道了利用单光纤布拉格光栅反射波带宽展宽技术实现温度与压力同时区分测量的新方案。通过聚合物材料将光栅粘接于双孔悬臂梁非均匀应变区 ,在压力作用下悬臂梁带动光栅发生非均匀应变 ,使布拉格反射波波长漂移的同时带宽展宽 ,而温度变化仅引起反射波波长漂移。在 2 0～ 10 0℃和 0～ 7.8N的温度和压力测量范围内 ,温度测量精度± 1.1℃ ,压力测量精度± 0 .18N ,布拉格反射波中心波长漂移量和带宽展宽量随温度和压力的变化呈良好的线性关系 ,线性度均高于 99.6 %。多次测量表明 ,此方案的展宽波形稳定 ,重复性好。     

用光纤光栅传感器测量外压力的动态调制方法

为了提高光纤布拉格光栅压力传感器的精度和降低系统成本，提出一种使用光纤双布拉格光栅测定压力的测量方法，即在外界压力作用下，传感光纤布拉格光栅反射波长的飘移被转变成在交变力策动下发生弯曲的等强度悬臂梁调制的扫描光栅的反射光脉冲间隔的变化。实验结果表明：光纤布拉格光栅反射波长漂移的测量范围为0～3nm，波长测量的不确定度为1pm；压力传感器的量程为0～6MPa时，压力的测量不确定度为0.005MPa。     

光纤布拉格光栅传感器应变传递双向耦合分析

粘贴于受弯基体表面的光纤布拉格光栅传感器测量应变与基体真实应变之间存在误差,因此研究光纤布拉格光栅传感器的变形机理、分析测量应变与真实应变之间的关系是目前的研究热点.首先研究光纤布拉格光栅传感器与基体之间的相互作用机理,然后,利用有限元解、实验值和理论解进行对比验证,并分析产生误差的原因.最后,通过参数分析研究弹性模量、厚度、粘结长度等参数对光纤布拉格光栅传感器测量效果的影响.结果表明有限元解、实验值和理论解具有相同的变化趋势,有限元解与理论解的误差在2%以内,测量值与理论解的误差在7%以内.平均应变传递率随着基体弹性模量的增大、粘结长度的增长而逐渐增大,随粘结层弹性模量的减小、粘结层厚度的增大而逐渐减小.该理论对应用于受弯基体应变测量的光纤布拉格光栅传感器的设计具有一定的指导意义.     

光纤光栅压力传感器中应力迟滞的消除方法

提出了一种利用双光纤光栅消除光纤光栅压力传感器中应力迟滞的方法.将两个相同波长的光纤布拉格光栅分别对称粘贴于悬臂梁的上下表面并串接在一起,外压力作用下可实现调谐双光栅布拉格波长差.研究结果表明,该方法可消除弹性元件材料所引起光纤光栅压力传感器的应力迟滞,改善传感器的线性响应特性和重复性,在0~40 MPa的压力范围内,双峰波长差的调谐范围为5.12 nm,是单峰波长调谐范围的2倍,压力调谐双峰波长差的灵敏度可达0.128 nm/MPa,是压力调谐单峰波长灵敏度的2倍.     

基于阵列波导光栅的智能服装人体测温解调系统研究

研究并实现了一种应用于智能服装中人体温度测量的阵列波导光栅解调系统。分析了系统的解调原理,搭建了光纤布拉格光栅解调实验平台,采用了强度法解调出光纤光栅的布拉格波长,完成了光纤光栅传感器串联前后解调的实验。结果表明,系统对光纤布拉格光栅的布拉格波长的解调具有高线性度,波长测量精度可达0.001 nm,光纤布拉格光栅传感器间串扰所造成的解调误差为0.000 5 nm,人体温度的测量误差为±0.16 ℃。该解调系统精度高、串扰低,可适用于智能服装中人体温度的测量。     

非本征型法布里-珀罗干涉仪光纤布拉格光栅应变温度传感器及其应用

介绍了光纤布拉格光栅非本征型法布里珀罗干涉仪集成复用传感器的结构、应变和温度同时监测的原理 ;观察到光纤布拉格光栅反射谱和非本征型法布里珀罗干涉仪干涉谱间的串扰 ,用 3dB带宽平均波长法减小了该串扰 ,提高了测量精度 ;将该传感器应用于三维编织复合材料的应变及温度同时监测。实验结果表明温度精度为± 1℃ ,应变精度为± 2 0 μ ,可满足实际应用的要求     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.