基于相干光时域反射型的光纤分布式声增敏传感研究

Research on improving detection sensitivity to acoustic based on coherent-OTDR distributed fiber-sensing system

开展了基于相干光时域反射型的光纤分布式声增敏传感研究,提出了单端固定开口波纹薄筒光纤声增敏方法,建立了光纤声增敏装置波节间距、单波节轴向刚度、光纤长度等参数对光纤相位灵敏度的影响理论模型.制作了3种规格的光纤声增敏传感装置进行声传感实验.实验结果表明,声增敏传感装置相位灵敏度达到2.975 rad/Pa,最小声探测信号达到60.1 dB,3种规格的声增敏传感装置的灵敏度测试值与理论分析基本一致.研究结果为高灵敏度的光纤分布式声传感的进一步发展提供了理论和实验基础.

Coherent-OTDR technology is one of acoustic distributed fiber-sensing systems. Because of the advantages of antielectric magnetic field interference, anti-corrosion and flexibility, it has been attracting more and more interest. Because the sound pressure is weak, the strain generated on the fiber is tiny and the sensitivity of the sensing system is low.Although many research has been made on expanding measuring distance and improving response frequency, the acoustic signals in the experiments are always replaced by PZT＇s mechanical stretching. In this work, a device for increasing sensitivity for acoustic in the passive acoustic detection system based on coherent optical time domain reflection（COTDR） is promoted. A way of improving sensitivity partly based on a thin-walled corrugated tube was promoted. The thin-walled corrugated tube was used as the element to transmit the energy of acoustic into the vibration of fiber.In section 2, a mathematical model of sensing based on corrugated tube was established. Theoretical result shows that the vibration of fiber is mainly caused by the tube movement along the axis direction. And it also shows the linear relationship between the vibration and the sound pressure. The sensitivity of the improved sensing devices is calculated and a computational formula for sensitivity calculating are also given.In section 3, the C-OTDR acoustic distributed fiber-sensing systems are set up. Fiberring and three types of thinwalled corrugated tubes are used for acoustic sensing. The minimum detection sound pressure level reaches 60.1 dB and the phase sensitivity reaches 2.975 rad/Pa. The experimental phase sensitivity of different sensing devices with different parameters change similarly to the theory results. The experimental results show that the way of improving sensitivity and the mechanical model for calculating sensitivity are effective. This research provides theoretical and experimental basis for further development of distributed optical fiber sensing.