| The Fiber Bragg Grating(FBG)can be applied in structural health monitoring in aerospace,precision equipment and ships,with its advantages of light weight,electromagnetic interference resistance,easy multiplexing,high sensitivity and corrosion resistance.However,there are few researches on acoustic emission positioning system based on fiber Bragg grating in the market at present.Therefore,this paper proposes an acoustic emission acquisition system based on FBG sensor to process and locate acoustic emission source information.The main content of the article is as follows:(1)A reflection Fabry-Perot interferometer with free spectral range of 25 GHz,50 GHz and 80 GHz was developed for the demodulation experiment of FBG sensor.A single FBG sensor was attached to the buzzer plate,and a function generator was used to control the buzzer plate to generate a stable sine wave as an acoustic emission source.The demodulation experiment was carried out with a reflection Fabry-Perot interferometer of different free spectral ranges.The results show that the 50 GHz reflector interferometer had better demodulation stability,demodulation frequency(up to 200 k Hz)and signal-to-noise ratio.Finally,the demodulation experiment was carried out by using the 50 GHz Fabry-Perot etalon(transmission type).The demodulation frequency was up to 278 k Hz.Compared with the reflection Fabry-Perot interferometer,it could be seen that the Fabry-Perot etalon had better demodulation effect on the FBG sensor.(2)The sensing part of the semiconductor optical amplifier ring laser system was optimized.Three FBG sensors with different central wavelengths were used as the acoustic emission signal acquisition system,and the Fabry-Perot etalon was used as the demodulator.Three FBG sensors were pasted on the aluminum plate in the form of equilateral triangle for impact experiment.The experimental results showed that the system has a good demodulation effect on the FBG sensor array.(3)Two acoustic emission signal processing methods and positioning algorithms with different principles were used to process acoustic emission signals and locate acoustic emission sources.The AE signals were processed by direct threshold method and Lamb wave dispersion curve method of wavelet transform respectively,and then the plane triangulation algorithm and elliptic location algorithm were used for location processing.The experimental results showed that the average error of plane triangulation algorithm processed by direct threshold method was 5.58 cm,which was relatively large.The average error of elliptic localization algorithm processed by Lamb wave dispersion curve after wavelet transform was 2.04 cm,which was small and stable.A commercial acoustic emission instrument was used as the positioning comparison experiment,and the positioning error of the acoustic emission instrument was 8.775 cm.The results showed that the elliptic localization algorithm with Lamb wave dispersion curve processing had better positioning accuracy and could meet the requirements of industry.(4)The influence of impact distance on the signal received by FBG sensor was explored,and the FBG sensor array was arranged in a "T" shape to eliminate the influence of angle on FBG sensor signal acquisition.The effective acquisition distance of FBG sensor was tested by using small balls hitting different positions on the aluminum plate,and the results proved that the FBG sensor signal acquisition distance was 20-30 cm.Six FBG sensor arrays were arranged in a "T" shape on the aluminum plate,which eliminates the problem of poor reception of some angle signals by FBG sensors and greatly improves the positioning accuracy. |
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