冲击定位可为结构冲击损伤提供准确的位置信息。基于光纤布拉格光栅(FBG)传感器存在解调频率低、需要训练样本等缺点,提出了一种利用光纤Sagnac传感技术实现结构冲击定位的方法。基于此方法的传感系统主要由宽带光源、光纤Sagnac干涉仪、光探测器以及数据采集与处理单元构成。当粘贴在结构表面的传感探头受到冲击应力波作用时,Sagnac干涉仪相位受到调制,从而导致输出的光强发生变化,通过光探测器将光信号转换为电压信号输出。首先,对传感系统采样的时域信号进行小波降噪和去直流干扰处理,再利用Db4小波包进行能量特征提取与信号重构,并获取应力波到达2端的传感器的时间,最后利用时差法进行冲击定位。为了验证该冲击载荷定位系统的有效性,对长度为100 cm的钢管结构进行了35次低速冲击实验。结果表明,该方法可以有效地识别冲击位置,最大定位误差和最大均方根误差分别为0.65 cm和0.36 cm。研究结果可为结构冲击定位提供另外一种可靠的方法。

Impact localization can provide accurate location information for structural impact damages. As fiber Bragg grating has low sampling frequency and requires training samples, a method for structural impact localization based on optical fiber Sagnac sensing technique is proposed. The sensing system mainly consists of broadband light source, optical fiber Sagnac interferometers, photo-detectors and data acquisition card. The phase of the interferometer can be modulated when the sensing probe stuck on structure is affected by impact stress waves. Therefore, the output light intensity can be changed and converted to voltage signal by photo-detector. Firstly, the impact response signals are de-noised and direct current interferences are eliminated by wavelet transform. Secondly, the energy characteristics are extracted, time-domain signals are reconstructed by wavelet packet analysis, and the time of wavelet arrival to the two sensors is acquired. Lastly, impact position is calculated by time-difference method. The result shows that 35 impacts on the steel pipe with the length of 100 cm have a maximum error of 0.65 cm, and a maximum root-mean-square error of 0.36 cm, respectively. This research can provide a novel and available method for structural impact localization.