通过光纤频移干涉技术测量了超声在光纤中产生的多普勒频移, 提出一种光纤超声传感方法.将缠绕在压电陶瓷上的光纤环接入到频移干涉萨格拉克干涉仪中, 以压电陶瓷作为超声波信号源, 调节声光调制器使得干涉信号偏置在零点, 达到系统灵敏度最高, 通过干涉信号的频率和幅值测量到了超声引起光纤环中发生的多普勒频移, 进而获得了作用在光纤环上的超声波信号.实验结果表明, 用该方法测量超声频率的相对误差为0.001%, 频响在所测量的20~200 kHz范围内具有良好的线性.该方法在管道健康监测、固体内部裂缝监测、大型机械装备结构损伤监测等方面具有应用前景.

Doppler frequency shift in optical fiber is measured by fiber frequency shift interferometry, and a method of optical fiber ultrasonic sensing is obtained. The optical fiber loop wound on the piezoelectric ceramic is inserted into the frequencyshift interference Sagnac interferometer, where the piezoelectric ceramic is taken as the ultrasonic signal source, the acoustooptic modulator is adjusted so that the interference signal is biased at the zero point to reach the highest sensitivity of the system. Through the frequency and amplitude of the interference signal, the Doppler frequency shift in the fiber loop caused by ultrasound is measured, and the ultrasonic signal acting on the fiber loop is obtained. The experimental results show that, the relative error of the sensing method is 0.001% for the ultrasonic frequency measurement, and the frequency response has a good linearity in the measured range of 20 kHz to 200 kHz. There are some application prospects of the proposed method in the aspects of pipeline health monitoring, solid internal crack monitoring and structural damage monitoring of large machinery and equipment.