Research On The Dynamic Signal Monitoring Of Smart Structure Using Fiber Bragg Grating

Fiber Bragg grating (FBG) sensors have been expected to candidates for distributed sensoring system by arrangement many sensors in a single fiber because of their transmission and Sensing property. Besides these advantages, FBG sensors are Suitable for manufacturing network of structural health monitoring, FBG sensors have extensive potential applications in smart structure and materials health monitoring field. FBG sensors are applied for the dynamic signal monitoring of smart structure in the paper. In order to built a impact loading self-diagnosing system, Acquisition methods of dynamic signal, feature extraction and loading location algorithm are researched. Meanwhile, a preliminary study of vehicle frame health monitoring based on Fiber Bragg grating sensors is proposed in the paper.The main achievements are described as follows:(1) Spectrum numerical simulationof FBG is studied in the paper. In order to study sensing properties of FBG, reflectivity and transmission spectrum of FBG is analyzed under the condition of grating length and refractive index change. Because the wavelength change of FBG and strain is linear, structural strain is monitored by wavelength change of FBG monitoring.(2) High speed demodulation system based on double long period grating is studied in order to research dynamic signal monitored by FBG sensor. Double LPFG is consisted of two LPFGS whose center wavelengths are same. Reflection light of FBG modulated by double LPFG is obtained and studied by use of band-hider filter characteristics for double LPFG, and wavelength change of FBG is deduced by light intensity achieved by photodetector.Demodulation system using total fiber technology has the property sunch as compact structure, high precision,linear output.(3) Vibration and impact monitoring method based on FBG network is proposed. Many FBG sensors are used to set up sensing network, which is nervous system of optical fiber smart structure. Impact response signal monitoring is achieved by detecting wavelength change of FBG. Impact different location of structure, impact response signal monitored by FBG is studied.(4)Impact loading localization algorithm is proposed. Feature extraction of acquisition impact response signal is realized with signal energy of different frequency segment using wavelet packet analysis used as characteristic index. Energy corresponding to modal frequency reguarded as sample is imput to Support Vector Machine to set up regression model and impact loading localization of composite speciment is realizated.(5)FBG sensors are applied for health monitoring field of vehicle frame to detect dynamic load states under different conditions. Vibration Conditions of vehicle frame are analysed by experiments of vibration, transient impact and pavement.