Research On Optical Fiber Acoustic Sensing And Recognition System Based On Sagnac Principle

While low-altitude small drones bring convenience to all walks of life,they also lead to frequent occurrences of "black flying" incidents,posing threats to traffic order,citizens' personal and privacy safety,etc.Low-altitude security,with the prevention of "black flight" as the primary issue,has become a hot social issue.Therefore,the development of an intelligent system for real-time detection and early warning of low-altitude drone activities has become the key to purifying the low-altitude urban environment and maintaining low-altitude safety.Due to the dense population,huge buildings and complex electromagnetic environment in the downtown area,and the drone has the characteristics of extremely low flying height,slow speed,and loud noise.The low-altitude drone detection and early warning technology needs to meet the requirements of adapting to complex geographic building environments,all weather operations,anti-electromagnetic interference,intelligent identification etc.The characteristics of acoustic detection technology are highly consistent with these requirements,and the optical fiber acoustic sensing technology has the advantages of simple structure,high precision,anti-electromagnetic interference,anti-humidity,corrosion resistance,etc.It has advantages over traditional electro-acoustic sensing technology in low-altitude drone detection and early warning.Therefore,this subject proposed the research of optical fiber acoustic sensing and recognition system based on Sagnac principle to achieve the detection,identification and early warning of low-altitude small drones.In this thesis,the coupling model of sound pressure and light wave phase was established by analyzing the phase modulation mechanism of sound on the light wave in the optical fiber.The sound pickup structure was introduced to enhance the sensitivity of the optical fiber to the sound signal response,the pick-up material selection and structure design were completed with the aid of finite element simulation analysis method,and the physical model of the optical fiber pickup structure was established.Combined with low-altitude drone application environment,the physical model of the linear optical fiber acoustic sensor system was designed based on the Sagnac principle,and the characteristic parameters were simulated and analyzed.According to the theoretical design and simulation analysis results,the selection of system optical components and the construction of optical path system were completed.The pickup design and manufacturing process were improved based on a large number of test results.The FPGA-based data acquisition circuit system was designed.The dual-thread high-speed data storage program was designed.The feature extraction algorithm based on MFCC and BP neural network voice recognition algorithm were designed.Based on independent unit research and testing,the system hardware debugging and installation work were completed,and the main characteristic parameters of the system were tested.According to the test results,the sensing system can maintain good stability in allweather operations.The sound detection frequency range of the system is 20?8000Hz,The minimum sound detection intensity that meets the identification requirements of the system is 60 d B(0.02Pa).The detection sensitivity of the system within the detection range is 38.13 m V/Pa.The sensing system could recognize and classify a variety of sound signals,and the recognition accuracy rate more than 95%.The system characteristic indicators meet the low-altitude drone detection and early warning requirements.The system has a good application prospect in the field of low-altitude drone detection and early warning.