High-speed Four-channel Optical Fiber FP Cavity Sensor Signal Demodulation System Research And Software Implementation

In the field of ultrasonic detection applications such as discharge detection of highvoltage substation equipment and non-destructive testing of aero-engine structures,ultrasonic sensors are often required to have the characteristics of small size,light weight,front passive,anti-electromagnetic interference,and high temperature and high pressure resistance.In this paper,aiming at the signal demodulation requirements of optical fiber MOEMS(Micro-Opto-Electro-Mechanical Systems)ultrasonic sensors,a high-speed four-channel optical fiber FP cavity sensor signal demodulation based on optical fiber EFPI(Extrinsic Fabry-Perot Interferomter)sensor is studied.System,completed the design and development of system hardware and software,and conducted experimental research and analysis on the demodulation performance of the system.The high-speed multi-channel demodulation system of optical fiber EFPI sensor studied in this paper combines FPGA and virtual instrument technology to realize a four-channel ultrasonic detection scheme with large response bandwidth,good linearity and high signal-to-noise ratio.The system can achieve effective signal acquisition and demodulation for two optical fiber EFPI ultrasonic sensors that adopt air coupling and contact coupling,and the system can be adapted to a variety of ultrasonic detection application requirements.The main research contents of this paper are as follows:(1)The paper explored the structure and working principle of the diaphragm optical fiber EFPI sensor.This subject is based on the principle of optical fiber FP(Fabry-Perot)double-beam interference,using micron-thickness MEMS silicon-based film to form a Fabry-Perot interference cavity with the end face of the fiber,and using the cavity length of the fiber Fabry-Perot interference cavity to achieve the effect of the external ultrasonic signal Sensing.The design cavity length of the sensor in the research of this thesis is,when the free spectral range of the interference spectrum is 4.8nm,the interference fringe contrast can reach more than 38 d B.(2)Aiming at the optical fiber EFPI sensor based on MEMS film,this paper uses a three-wavelength adaptive demodulation algorithm.The algorithm uses the phase difference relationship between the three wavelength signals to adaptively select the signal light wavelength in the linear working area as the demodulation working wavelength of the sensor.It effectively solves the problem of demodulation operating point drift caused by environmental temperature changes and low-frequency disturbances in actual use of the sensor.(3)Designed and constructed a high-speed four-channel optical fiber FP cavity sensor signal demodulation hardware system based on optical fiber EFPI sensor.Including the design of demodulation optical system,the selection of key optical components such as light source,detector,and wavelength division multiplexer,and the design and development of high-speed four-channel data acquisition card.Successfully built a stable high-speed four-channel optical fiber FP cavity sensor signal demodulation hardware system,and realized a practical four-channel ultrasonic detection engineering prototype.(4)Based on the LabVIEW(Laboratory Virtual Instrument Engineering)platform,the upper computer software that matches the high-speed four-channel optical fiber FP cavity sensor signal demodulation hardware system is designed and realized.Completed the development of software acquisition control,waveform display,data storage,data format conversion,test report generation and other functional modules,and realized the software interface of the optical fiber ultrasonic sensor signal demodulation system that can be operated by man-machine interaction.(5)Based on the experimentally built high-speed four-channel optical fiber FP cavity sensor signal demodulation hardware and software system,this topic has performed performance tests for the detection of optical fiber ultrasonic sensors with two coupling modes: air coupling and contact coupling.Among them,in the contact coupling ultrasonic sensor test,under the excitation of the piezoelectric ultrasonic driver,the system signalto-noise ratio reached 61 d B or more,and the output signal has a good linear response and channel consistency.The subject also used aluminum alloy sheet samples to conduct an experimental exploration on the ultrasonic Lamb wave detection in the metal sheet.The system effectively detects the ultrasonic Lamb wave signal with a clear envelope.The experimental results also preliminarily verify the application of the system to metal Or the feasibility of non-destructive testing of other composite material structures.