| The Phase Sensitive Optical Time Domain Reflectometer(φ-OTDR)can use a single optical fiber to realize the omnidirectional and continuous distributed detection of small disturbances in space,and has become an important means to obtain information in the era of the Internet of Things because of its simple structure,high sensing accuracy,multi-point disturbance detection and other advantages.In addition to identifying and locating vibration signals,optical fiber sensing technology can also identify and locate sound signals in space.The spatial location technology based on the combination of φ-OTDR sensor system and sound source location algorithm has been widely used in radar,sonar,geological survey,oil pipeline safety monitoring,video conference,border security,intrusion alarm and other fields.In this paper,the phase extraction and phase demodulation of φ-OTDR system are analyzed and studied in detail,which effectively avoids the error increase of phase jump contained in phase itself caused by differential processing,which affects the result of phase demodulation.By combining the proposed optical fiber sensitization structure with antenna uniform array,the low sensitivity of ordinary bare optical fiber to sound in space is solved,and the location of 2D/3D sound source signals in space is also achieved.The specific research contents of this paper are as follows:(1)The sensing mode and theory of optical fiber sensor system are studied,deduce the advantages of φ-OTDR system with coherent detection structure compared with other sensor systems;Three spatial sound source localization algorithms are studied and analyzed,and the localization advantages of multiple signal classification(MUSIC)algorithm in sensing system are deduced.(2)The selection of experimental instruments and the influence of system performance parameters on the φ-OTDR sensor system is analyzed.The phase of the backscattered Rayleigh light signal extracted by the φ-OTDR sensing system is demodulated by IQ phase demodulation experiments of difference unwinding phase(DUP)and unwinding difference phase(UDP).Through the comparison of DUP and UDP,the advantages of DUP IQ phase demodulation method in the sensing system are analyzed.(3)The antenna sensor array model is studied,and the uniform linear array with different number and spacing of array elements is simulated and analyzed.A sensitizing structure is proposed to increase the sensitivity of bare optical fiber to space acoustic waves,which solves the problem that bare optical fiber has limited ability to detect signals.(4)A design of sensitized uniform linear array based on φ-OTDR system is proposed.The 2D location of single sound source can be realized by using MUSIC algorithm,and the location error is less than 0.5m.However,MUSIC algorithm can only locate the sounds with known number of sound source signals.To overcome this problem,the minimum description length(MDL)criterion is used to estimate the number of spatial sound source signals.(5)Based on the sensitized uniform linear array,the forward and backward space smoothing method is used to decoherent the multi sound source signals of the same frequency.The simulation results show that the proposed method can effectively improve the estimation of the azimuth of the sound source signal,and the signal-to-noise ratio can be increased by 18 d B.A parallel uniform surface array is designed for 3D space sound source location,and the MUSIC algorithm is used to realize the 3D location of a single sound source. |
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