Research On Signal Processing And Hardware Implementation Of Laser Doppler Micro Vibration

Compared with the traditional vibration measurement methods such as mechanical contact and optical fiber contact,laser Doppler detection technology employs the advantages of high precision,no contact and damage detection,little environmental interference,long service life and can obtain higher signal-to-noise ratio.These strength makes laser Doppler technology much more favored by scientists and engineers in the field of weak vibration signal detection.Laser Doppler detection technology is widely used in the fields of target surface roughness measurement,target classification and recognition,MEMS detection,building health detection,biomedical and voice eavesdropping.The detection front-end system has experienced from prism interference structure to half fiber combination structure to all fiber detection system,and its corresponding signal processing technology has also changed from traditional analog demodulation to digital demodulation.In foreign,it has achieved the acquisition of micro vibration caused by sound at a distance of 300 meters.Besides,Germany Polytec company has already had the micro vibration measurement of the order of Picometer for the detection of short-range targets.A series of related researches have been carried out in China.However,due to the big gap between China and foreign countries in terms of laser emission technology,optical matching technology and highfrequency signal processing technology,there is still a lot of room for development in detection accuracy of short-range target detection in China.In this paper,from two aspects of signal processing algorithm and hardware design,theoretical analysis,numerical simulation and experimental research are employed to study the laser Doppler micro vibration detection system.The main contents of this paper are as follows:(1)This paper introduces the background of laser Doppler micro vibration research and the research progress in this field at home and abroad.The characteristics of micro vibration measurement are introduced and the relevant advantages of laser Doppler technology in the field of micro vibration detection are pointed out,especially in the field of sound capture.The bottleneck and deficiency in the field of Doppler micro vibration measurement in China are put forward,which provides guidance for this paper and the follow-up research.(2)The principle of optical Doppler and the expression of the signal collected by the detector in the laser Doppler coherent detection system are introduced and deduced,and the meanings of different components in the detection of optical current are analyzed.The influence of acousto-optic frequency shifter,balance detector and laser linewidth on laser Doppler detection is studied.Several commonly used laser Doppler micro vibration optical detection systems and corresponding signal processing algorithms are analyzed.(3)The disadvantage of IF loop crosstalk existing in the traditional all fiber laser Doppler detection system is studied.Two methods that pulse time domain chopping algorithm and dual acousto-optic transceiver separated laser Doppler detection optical path are proposed eliminate the impact.(4)The structure of FPGA and the development process of hardware circuit based on FPGA is introduced.The design of hardware circuit synthesis of all digital signal processing based on FPGA is designed.The IP cores of CORDIC and FFT are employed to realize arctangent solution and short-time Fourier transform respectively.(5)A laser Doppler detection system based on FPGA full digital hardware circuit is built to acquire the actual mechanical micro vibration signal and voice micro vibration signal.The micro vibration of the macro static target and the macro moving target are measured respectively,and the reliability of the full digital demodulation scheme is verified.(6)The performance of time-frequency analysis of Wigner Ville distribution,smoothed pseudo Wigner Ville distribution,spectrum and extended modified B distribution is analyzed by using the measured data of laser Doppler micro vibration.It is proved that the performance of time-frequency analysis of extended modified B distribution for the measured data of laser Doppler micro vibration is better than that of traditional time-frequency analysis under laboratory conditions.