Poiana Dragos A, Garcia-Souto Jose A, Bao Xiaoyi
Physics Department, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
Sensors and Instrumentation Techniques Research Group, Electronics Technology Department, University Carlos III de Madrid, Leganes, 28911 Madrid, Spain.
Sensors (Basel). 2021 Jun 8;21(12):3967. doi: 10.3390/s21123967.
The broad-frequency response and nanometer-range displacements of ultrasound detection are essential for the characterization of small cracks, structural health monitoring and non-destructive evaluation. Those perturbations are generated at sub-nano-strain to nano-strain levels. This corresponds to the sub-nm level and, therefore, to about 0.1% of wavelength change at 1550 nm, making it difficult to detect them by conventional interferometric techniques. In this paper, we propose a demodulation system to read the random fiber grating spectrum using a self-heterodyne acousto-optic frequency comb. The system uses a self-heterodyne approach to extract phase and amplitude modulated signals to detect surface acoustic waves with sub-nanometer amplitudes in the frequency domain. The method can detect acoustic frequencies of 1 MHz and the associated displacement. The system is calibrated via phase detection with a heterodyne interferometer, which has a limited frequency response of up to 200 kHz. The goal is to achieve sub-nanometer strain detection at MHz frequency with random fiber gratings.
超声检测的宽频响应和纳米级位移对于小裂纹表征、结构健康监测和无损评估至关重要。这些扰动是在亚纳米应变到纳米应变水平产生的。这对应于亚纳米级水平，因此在1550nm波长处约为波长变化的0.1%，使得用传统干涉技术难以检测到它们。在本文中，我们提出了一种解调系统，使用自外差声光频率梳来读取随机光纤光栅光谱。该系统采用自外差方法提取相位和幅度调制信号，以在频域中检测具有亚纳米幅度的表面声波。该方法可以检测1MHz的声频及相关位移。该系统通过外差干涉仪进行相位检测校准，其频率响应上限为200kHz。目标是利用随机光纤光栅在MHz频率下实现亚纳米应变检测。
