Research On Vibration Demodulation System Of Eccentric Core Fiber

In recent years, with the continuous frequent of earthquakes and the progress technology of the bridge building vibration monitoring, vibration sensor quickly become a hot topic worldwide. Among them, optical fiber vibration sensor with a simple structure has the advantages of immunity to electromagnetic interference and can achieve high precision and sensitivity has been widely used. Eccentric core optical fiber has a stronger evanescent field and thus has more unique advantages in terms of sensing. In this paper, a vibration detection system based on eccentric core optical fiber combined optical fiber sensing technology, dual optical path difference technique and vibration signal detection technology is designed.Firstly, the structure and characteristics of the eccentric core optical fiber is introduced. Optical transmission theory study and eccentric core fiber bending loss are researched, and eccentric core fiber bending loss is simulated through Rsoft. The mathematical model of a eccentric core optical fiber vibration sensor is established.Secondly, design of the vibration detector is completed, Resonance frequency and the acceleration sensitivity dynamic characteristics of vibration detector are analyzed. According to the frequency characteristics of the measured signal and ground vibration and the degree of difficulty, the size of the cantilever is optimized. The natural frequency of the cantilever design is simulated to verify the theoretical calculation of the natural frequency of the cantilever through ABAQUS simulation software.Finally, Eccentric core optical fiber vibration detector demodulation scheme is designed by dual optical differential detection technology. The light source, connectors, couplers are analyzed and compared. Circuits are designed such as the preamplifier circuit integrated with I/V conversion, filtering and amplification differential function. Lab VIEW Signal Express module provides real-time monitoring of vibration signals.By comparing with wavelet denoising method, the validity of EMD method to deal with vibration signal noise is verified. Simulation result shows that the signal which is dealed with EMD method has a distinct advantage. Several experiments are implemented to verify the sensitivity and accuracy of the detection system measuring the frequency of a vibration wave.