光纤激光声学传感器的换能原理和解调技术研究

Fiber acoustic sensors have attracted great interests in recent years for their samll size,immunity to electromagetic interference,chemical corrosion and high precision. Fiber acoustic sensor becomes more and more important in some measurement fields, such as flaw detection, acoustic communication and flaut locating，especially in harsh and strong electrmagnetic interference environment. However, up to now, there are few theoretical analysis and experimental reports for the fiber acoustic flaw detection and flaut locating techonology. This project aims on designing a superior perfomance and good consistency of fiber acoustic sensor for flaw detection and flaut locating. The fiber multi-longitudinal mode laser sensor is used as acoustic sensor in this roject. Based on reconstruction-equivalent-chirp (REC) technique, a novel method for fabricating the multi-longitudinal fiber laser sensor with high coupling coefficient is proposed and initially studied. In addition, we also simulate and analyze acoustics-optics transducers, and the detailed study on demodulation mechanisms between aoustics field and multi-longitudinal laser mode is also given. These studies can provide some guidance for designing the improved structure of sensor to increase sensitvity of acoustic-optics sensor. The acoustic singal can be demodulated by the eletrcal shift-phase and orthogonal FM demodulation techniques. These demodulation techniques offer a integrated, highly speed and all-electrical demodulation method. The project will attempt to carry out a frequency-division multipelex technology for the fiber laser acoustic array sensor. In summary,under the support of this project, we want to design a high cost-effectiv and high-precision fiber acoustic sensor for acoustics measurement in some harsh field, such as strong electrmagnetic fields, lutra-small space and extreme environments.

光纤声传感器以其体积小、精度高、抗电磁干扰等优点受到研究人员的青睐，特别在复杂和高电磁干扰环境下探伤、故障定位等方面发挥不可替代的作用。目前，光纤声学探伤和定位领域还处于起步阶段，实用报道比较少。本课题旨在探索发展一种性能优越且具有良好一致性的光纤声传感器。拟采用多纵模光纤激光传感器作为声传感节点，研究声波和光纤换能原理以及对多纵模激光的调制机制，利用光纤光栅等效重构技术，改善激光拍频信号与声场交互作用的效率，提高单节点声传感精度。通过模拟和理论优化传感器结构，来提高光-声耦合系数。采用电子移相正交信号解调技术，通过对多纵模之间的拍频信号的解调来还原待测声信号。它避免了激光强度、相位等噪声影响，且提供一种高度集成、全电子的高速声信号解调手段。尝试发展频分复用技术实现多光纤声传感器阵列检测。通过项目支持，努力为强电磁场、超小空间和极端恶劣环境等声测量领域提供了一种低值、高精度的声传感器。

光纤激光传感器因为有超窄的激光带宽和很高的信噪比，在水声测量、加速度测量、声麦克等领域得到了广泛的应用。在国家自然基金的支持下，本项目完成了多纵模光纤激光声学传感器的研制。利用弹性波理论分析了在平面声波作用下，光纤光栅激光器输出波长与声压变化的线性关系。提出了一种简单的动态拍频解调方案。通过一个光电探测器和一个移相乘法鉴频器就把施加在传感器上的动态信号无失真的解调出来。它提供了一种全电子、高度集成化的解调方案。利用硅胶空心顺变柱体结构，实现了声学信号的拾取。传感器的信噪比和灵敏度分别高达55dB和-137dB。该顺变柱体光纤多纵模激光传感器同时具有良好的垂直和水平指向性，传感器在10-5KHz的频率范围内具有良好的响应。灵敏度起伏低于±1.5dB。研制了FBG激光传感器，高频检测范围可以到达4 MHz，大大提高了其检测带宽范围。将传感器应用于304不锈钢板Lamb波的非线性检测，可以检测钢板的基波和二次谐波，甚至可检测到微弱的三、四次谐波，表明光纤激光传感器在检测Lamb波非线性上是有很大潜力的。 研究多纵模传感器大规模复用技术，提出基于频分复用技术和频分、波分混合式复用技术，成功实现了16只传感器温度和应力的监测。利用光纤多纵模传感器对变压器的压紧力松动等故障进行检测，初步完成了健结构康监测应用研究。为了提高声学探测的效率，设计一种具有较宽带宽、低损耗单向负折射超流体棱镜，减小了反射声场对测量的影响。同时，基于光纤激光耦合原理，提出一种基于层叠结构的微结构耦合器，实现高于98%的耦合效率。提出零色散弯曲声场控制器件，利用这种螺旋型空间折叠结构，构建一种声学超透镜，在理论和实验上实现了自弯曲的声学艾里波束。本项目提出的传感器技术可广泛应用于医疗诊断和工业监测等领域。项目执行期间，在Nature Communications,Applied Physics Letters等国家和国内期刊发表学术论文26篇，其中SCI收录25篇。授权专利11项。培养博士2人，硕士4人。