动态应变场下相移光栅光谱特性及实验研究

光纤传感技术以其抗电磁干扰、高精度、易组网等优势在航空航天及地下工程领域的声发射传感中得到了广泛应用。针对光纤光栅声发射监测系统，目前研究侧重于均匀光纤光栅的动态应变场传感特性，基于相移光纤光栅(phase-shifted fiber Bragg grating, PS-FBG)这一新型光纤光栅器件，重点研究声发射激励产生的动态应变场下相移光纤光栅的光谱特性变化规律。首先利用传输矩阵理论，建立PS-FBG的动态应变传感模型，利用指数衰减的余弦函数模拟声发射激励产生的动态应变场。通过数值仿真，详细研究PS-FBG光谱对动态应变场幅度、采样时刻、衰减系数、声发射频率及波长的响应特性。结果表明，PS-FBG反射谱形状随声发射频率与采样时刻呈现周期性变化，具体表现为透射窗口所对波长产生周期性漂移，而带宽变化不明显;随着动态应变场幅值越大，PS-FBG反射谱的谐振峰向两侧逐渐增多，透射窗口所对波长漂移很小;一定范围内衰减系数对PS-FBG光谱影响较大;而当声发射波长为0.1～2 L时，对PS-FBG光谱产生较大影响，此时光谱畸变较严重，在此范围外，光谱形状不发生明显变化。最后，搭建连续信号激励下的动态应变场实验平台，分析不同幅度a与频率f变化下PS-FBG的光谱特性，实验结果与仿真结果较好吻合。表明PS-FBG光谱对不同声发射激励产生的动态应变场响应不同，呈现一定规律性，该研究为基于相移光纤光栅传感技术的声发射传感提供理论指导。

Research on the Phase-Shifted Fiber Bragg Grating Spectra under Dynamic Strain Fields

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 ca-pacity.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 contrib-ute 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.