Research On High Frequency Acoustic Sensor Based On Optical Fiber F-P Interferometry

Partial discharge of transformer in large power system often brings huge hidden danger of power safety and may cause incalculable economic loss.Partial discharge often produces ultrasonic waves and other physical phenomena.The detection of ultrasonic signals can effectively monitor the operation state of the power system,so that the transformer can be repaired in time to avoid the occurrence of catastrophic accidents.Scholars at home and abroad have proposed many sound detection methods,but these detection methods are limited by electromagnetic environmental interference,vulnerability to corrosion,signal demodulation dynamic range is small,demodulation speed is slow and other factors,it is difficult to achieve real-time accurate monitoring.Optical fiber sensing technology has been widely used in power grid health assessment and monitoring due to its ability to resist electromagnetic interference and tolerance to harsh environment.Based on the advantages of optical fiber sensing technology,a high frequency acoustic sensor of optical fiber fabry-perot(F-P)interferometry is proposed in this paper to improve the signal detection accuracy.Based on the sensing characteristics of the non-intrinsic(EFPI)structure of the sensor and the fast white light interference demodulation algorithm,a demodulation system of the fiber-optic f-p high-frequency acoustic sensor was designed,with a demodulation rate of 35 kHz and a demodulation resolution of 0.089 nm.Based on the vision acquisition module NI MAX and NI-IMAQ driver,the high-speed acquisition software of spectral data was developed.After software testing,the acquisition function of the upper computer,real-time display and operation calculation function were verified.To design high performance fiber F-P high frequency sound wave sensor sensing probe,respectively using ANSYS Workbench platform of circular diaphragm structure and sensitive diaphragm on the structure of the cantilever beam simulation,to verify the two kinds of structure geometry parameters on the natural frequency and the influence of the sensitivity of diaphragm,and the final optimal design 50 microns thick,1.0 mm long cantilever beam sensing probe and 90 microns thick,radius of 2.6 mm diaphragm sensing probe.To test the two kinds of structure of partial discharge ultrasonic sensor detection performance,the design of the ultrasonic source uses the signal generator to drive the PZT experiment system and simulation based on ANSYS simulation,cantilever beam structure is verified by ANSYS simulation theory ofoptical fiber F-P sensor within the frequency range of 20 kHz-35 kHz response sensitivity is greater than 0.03nm/Pa,circular diaphragm structure of the fiber optic F-P sensors within the frequency range of 20kHz-35 kHz response sensitivity is greater than 0.06nm/Pa.The low-frequency experiment verifies that the fiber-optic f-p high-frequency acoustic sensor can accurately detect the acoustic signal,and the SNR reaches 514.04.Finally,according to the simulation results,the sound pressure resolutions of the two structures were calculated to be1.04 Pa and 0.18 Pa,respectively.