Design Of Distributed Optical Fiber Strain Detector

Distributed optical fiber strain detection technology based on Brillouin Optical Time Domain Reflector(BOTDR)has the advantages of single-ended input,long measuring distance,measurable breakpoint,and fully distributed detection.It can be effectively applied to structural health monitoring of large-scale basic projects.In view of the difficulty in the health monitoring of long-distance large-scale infrastructure projects,design a distributed optical fiber strain detector.The strain detector combines the coherent detection method and the microwave heterodyne sweep method to realize the Brillouin scattering signal detection.Meanwhile,it utilizes the advantages of the high-speed operation of the FPGA to realize the Brillouin scattering signal denoising and the Brillouin gain spectrum demodulation to increase its measurement speed.The human-computer interaction interface is written based on MFC to realize visual strain measurement.We can analyze the stress distribution of the mearsured structure intuitively and judge its structural health state to prevent the happening of accidents.The major research works in this paper includes the following aspects:Design a strain detection scheme based on BOTDR technology and build a detection system.In-depth analysis of Brillouin frequency shift and strain relationship,clarify the principle of strain detection;compare different detection methods of Brillouin scattering signals,design a Brillouin scattering signal demodulation scheme based on coherent detection combined with microwave frequency sweep,according to the designed scheme and the technical objectives of the project research,comprehensive consideration of the parameter indicators of each key module,select the appropriate hardware to build the detection system.Brillouin scattering signal denoising and Brillouin gain spectrum demodulation are implemented on the integrated circuit.Using the advantages of FPGA high-speed operation,the Brillouin scattering signal is denoised on the FPGA by the cumulative averaging algorithm.At the same time,the Brillouin gain spectrum demodulation scheme based on L-M algorithm is designed and implemented on the FPGA.Quickly demodulate the strain information along the fiber to improve the real-time performance of the system.Considering the functional requirements of the distributed optical fiber strain detector,the host computer interface based on MFC software is designed to realize functions such as hardware monitoring,signal acquisition and processing,data storage and display.Integrate the inspection system and experimentally test the strain detector parameters.The SolidWorks is used to complete the hardware structure design of the measurement system,and the prototype integration is completed.The test results show that the system detection distance can reach 10 km,maximum measurable strain is 8500??,the strain measurement error is ±46??,the repeatability measurement deviation is ±36??,the spatial resolution is 1m,and the positioning error is ±2m.