Wang Zheng-fang, Wang Jing, Sui Qing-mei
Guang Pu Xue Yu Guang Pu Fen Xi. 2016 Dec;36(12):4113-9.
Fiber optic sensing technology has been widely used for acoustic emission (AE) measurement in aerospace and geotechnical engineering due to the advantages of immunity to electro-magnetic interference, high accuracy, and multiplexing capacity. As for the fiber Bragg grating based on AE measurement system, traditional efforts have been made to study the spectra of Fiber Bragg Grating under AE signal. While this paper focused on phase-shifted fiber Bragg grating (PS-FBG) which is a new type fiber Bragg grating, and investigated the spectra of under dynamic strain field generating with an AE signal. A dynamic strain sensing model of PS-FBG was built based on the transfer matrix theory, and a cosine exponential attenuation function was utilized to simulate the dynamic strain field. Then the effects of amplitude, sampling time, exponential attenuation coefficient, frequency and wavelength of AE signal on the spectra of PS-FBG were studied in detail using numerical simulation. The result demonstrate that the spectra of PS-FBG changes periodically with frequency and different sampling time, especially the peak wavelength of the transmission window in the PS-FBG spectrum shifts periodically; and the increase of amplitude mainly contribute to more harmonic peaks in the reflected spectrum. The attenuation coefficient affects the spectrum of PS-FBG within certain range. And the AE wavelength affect the spectrum of PS-FBG when it is between 0.1 to 2 L, beyond the range, the spectrum of PS-FBG has minor variation with the AE wavelength. Finally, dynamic strain experiments were conducted, and the spectrum of PS-FBG under continuously vibration signal with different amplitude and frequency were logged for analysis. The experimental results agree well with simulation, which indicate that under different dynamic strain fields generated by AE signal, the spectra of PS-FBG are different, while the variation of spectra follows certain laws. This paper provides theoretical support for the AE measurement system on the basis of PS-FBG.
由于具有抗电磁干扰、高精度和复用能力等优点，光纤传感技术已在航空航天和岩土工程中的声发射（AE）测量中得到广泛应用。对于基于光纤布拉格光栅的声发射测量系统，传统上一直在研究声发射信号作用下光纤布拉格光栅的光谱。而本文聚焦于新型光纤布拉格光栅——相移光纤布拉格光栅（PS - FBG），并研究了由声发射信号产生的动态应变场作用下的光谱。基于传输矩阵理论建立了PS - FBG的动态应变传感模型，并利用余弦指数衰减函数模拟动态应变场。然后通过数值模拟详细研究了声发射信号的幅度、采样时间、指数衰减系数、频率和波长对PS - FBG光谱的影响。结果表明，PS - FBG的光谱随频率和不同采样时间呈周期性变化，特别是PS - FBG光谱中透射窗口的峰值波长会周期性移动；幅度的增加主要导致反射光谱中出现更多谐波峰值。衰减系数在一定范围内影响PS - FBG的光谱。当声发射波长在0.1至2L之间时，其会影响PS - FBG的光谱，超出该范围，PS - FBG的光谱随声发射波长的变化较小。最后进行了动态应变实验，记录了PS - FBG在不同幅度和频率的连续振动信号作用下的光谱用于分析。实验结果与模拟结果吻合良好，这表明在声发射信号产生的不同动态应变场下，PS - FBG的光谱不同，但其光谱变化遵循一定规律。本文为基于PS - FBG的声发射测量系统提供了理论支持。
