【作者】 杨先辉；

【导师】 孙圣和；

【作者基本信息】 哈尔滨工业大学 ， 仪器科学与技术， 2007， 博士

【摘要】 应变和温度的传感技术研究在智能材料与结构领域以及结构健康监测领域中占据着十分重要的位置。光纤光栅传感器由于其自身所具有的独特优点,已经逐渐发展成为各种场合中对应变、温度等多种参量进行传感、监测的首选元件,其制作技术、信号解调技术的研究以及应用领域的拓展都达到了前所未有的高度。然而,光纤光栅传感器在应用中还存在着一些限制,其中比较突出的有光纤光栅传感器的温度-应变交叉敏感以及传感信号解调装置结构复杂、价格昂贵等问题,对这些问题的妥善解决是保证光纤光栅传感器性能、促使其进一步走向工程实用化的关键,具有重要的理论价值和工程意义。本文在大量查阅国内外相关文献的基础上,对光纤光栅的传输理论、传感机理及其信号解调技术进行了深入研究,提出了一种可用于解决温度-应变交叉敏感的光纤光栅应变传感器设计方案,并通过实验对该应变传感器的性能及其传感信号解调装置进行了深入研究,取得了满意的效果。论文的主要创造性研究工作如下:在分析已有的锥形光纤光栅传感器机理和优缺点的基础上,提出了一种锥形光纤光栅应变传感器设计方案。该方案基于对锥形光纤光栅反射光的带宽解调,具有传感信号为波长调制的特点;结构简单,容易实现。实验结果表明,所设计的锥形光纤光栅应变传感器在宽范围内对温度不敏感,对应变/应力具有线性敏感特性,提高了应变测量的准确度;易组成分布式传感网络,对智能结构应变检测和结构健康监测有重要意义。在分析锥形光纤光栅反射光带宽特性的基础上,提出了锥形光纤光栅传感器反射光带宽调制与解调方法。将待测应变转换成锥形光纤光栅反射光的带宽变化,故避免了温度影响。将反射光中心波长与带宽调制相结合,可实现应变和温度的同时测量。这一方法较双波长移位传感方法具有结构简单、容易实现、成本较低等优点。在反射光带宽解调时,为了提高准确性,提出了“阈值限制”的预处理方法。即通过设定阈值来对传感信号进行筛选,只对满足要求的信号进行下一步的处理。实验表明这种方法有效避免了反射光中的旁瓣信号对测量结果的影响,提高了测量的精度;同时减少了数据处理量,提高了解调速度,对锥形光纤光栅的分布式应用有较大意义。在研究光纤光栅的综合问题时,分别提出了基于模拟退火和遗传机理的光纤光栅参数重构方法。这两种方法基于同一种思想,即在设定光纤光栅各物理参数的离散化取值范围的基础上,通过不同的参数组合来使计算反射谱符合或逼近目标反射谱,从而将光纤光栅的参数重构问题转化成为组合优化问题,通过模拟退火算法和遗传算法来进行求解。仿真实验验证了这两种方法的有效性,可用于解决针对给定反射谱的光纤光栅综合问题。更多还原

【Abstract】 The study of the strain and temperature sensing technology is the most important part of the fields of smart material and structure and health monitoring of large civil infrastructure. Because of their special characters, optical fiber grating sensors have been considered the critical sensing components in these two fields. With the development of the optical communication technology in past ten years, optical fiber Bragg grating (FBG) sensors have progressed very rapidly, many research works, such as the fiber grating fabricating technology, signal demodulating technology, have been made a great progress, and the application fields of the optical fiber grating sensor have grown wider and wider.However, there are many problems which still limit the practice application of optical fiber grating sensing technology, such as the problem which is called cross sensitivity of strain and temperature of FBG, the wavelength demodulating equipments for FBG sensors are usually complex and expensive, and so on. How to solve these problems has been the key to ensure the sensing properties and make FBG sensors advancing in practical applications. It must show great academic value and practical importance.Through collecting and studying of many documents about FBG sensing technology, this thesis makes studies of the transmitting theory, the sensing principle, and the interrogation technology of FBG sensors. Then, a novel optical fiber grating strain sensor which can be used to solve the problem of cross sensitivity is proposed, the sensing property of this kind of strain sensor and its signal demodulation system are studied by experiment. The main innovative contributions of this thesis are as follows:On the basis of the studies of tapered fiber grating sensing principle and its characters, a strain sensor which is based on the measurement of reflected bandwidth of tapered fiber grating is proposed. This strain sensor still retains the wavelength modulation characteristic of the optical fiber grating, and it possesses characteristics as simple structure, easy to achieve. The results of the experiment have shown that, the reflected bandwidth of this strain sensor has a strict linear relationship with the stress and strain, but it is insensitive to the temperature in a wide changing range. It has also been demonstrated that this kind of strain sensor can be used in distributed sensing applications. So it must have great value to strain sensing in fields of smart structure and health monitoring of large civil infrastructure.On the basis of analysis of the characteristics of the reflected bandwidth, several methods to demodulate the reflected bandwidth of the tapered fiber grating are proposed. Because the bandwidth of the reflected light will be modulated only by strain, it is insensitive to the change of temperature. By demodulating both reflected bandwidth and the center reflected wavelength, this tapered fiber grating sensor could be used for simultaneous measurement of the strain and temperature. Compared with the method which is based on the principle of dual-wavelength shifted by two optical fiber gratings, this sensing method has so many advantages, such as simpler system structure, lower cost, easy to achieve, and so on.During the course of interrogation of the sensing system, a signal pre-procession method called threshold limiting method is used to promote the demodulation accuracy. That is, only the data which are higher than a certain value will be transmitted into the demodulation system to be processed, and the others which are lower will be eliminated, this certain value is called threshold value. By adopting this method in data processing, the experimental result shows that the influence of the side pulses in reflected light on measurement result is eliminated, and the processing amount of sensing data is greatly decreased. So, the demodulating speed and the measurement precision of this sensing system would be approved simultaneously. All of these advantages are very important to the tapered fiber grating sensors when they are used in distributed sensing applications.The algorithm to solve the synthesis problem of the optical fiber grating has also been studied, and two methods to reconstruct the physical parameters of FBG from the target reflected spectrum are proposed. These two methods are based on the same principle to transform the synthesis problem of FBG into a global optimization problem, and then solve this optimization problem by simulated annealing algorithm and modified genetic algorithm respectively. The presented numerical examples show that these two methods all can give results that are comparable or better than other design methods.更多还原