Design of Self-collimating Fiber FP Cavity and Localization of Sound Source Based on Silver Film
Sound source localization is a pivotal research area within the field of acoustics,finding extensive applications in domains such as Unmanned Aerial Vehicle(UAV)navigation,intelligent traffic systems,medical imaging,and structural health monitoring.Traditional sound source localization methods typically rely on arrays of multiple microphones or sensor networks.Nevertheless,these conventional approaches are beset by challenges related to complex installation,intricate data processing,and poor resistance to interference.In recent years,there has been considerable attention directed towards the emerging field of optical fiber-based acoustic localization,within which most optical fiber-based detection systems have employed Fiber Bragg Grating(FBG)sensor arrays due to their wavelength-based multiplexing capabilities.However,FBG sensors exhibit limitations in sensitivity.In contrast,optical fiber Extrinsic Fabry-Perot Interferometer(EFPI)sensors,with their probe-like structure and advantages in terms of high sensitivity and structural simplicity,are better suited for sound source localization.In this research endeavor,we have introduced optical fiber collimators within EFPI sensor arrays to develop a self-collimating optical fiber-based EFPI acoustic sensor array.The primary objective is to augment the sound pressure sensitivity and detection range of the sensor array.The designed sensor array exhibits elevated acoustic sensitivity and an expanded spatial detection range,thus holding immense potential for applications in sound source localization and the detection of partial discharge phenomena.Firstly,the optical field distribution of a quarter-pitch-length gradient multimode optical fiber was verified using Rsoft software.Subsequently,an EFPI(Extrinsic Fabry-Perot Interferometer)acoustic sensor with a self-collimating optical fiber was designed.To assess whether the proposed sensor exhibits enhanced sensitivity to sound pressure,it was compared to an EFPI acoustic sensor without the self-collimating feature.Next,three EFPI acoustic sensors with identical structures and self-collimating optical fibers were fabricated for sound source localization experiments.Prior to conducting the localization experiments,the consistency of sound pressure sensitivity and sound source directionality among the three sensors with self-collimating optical fibers was verified.Subsequent to these preparations,time-delay signals were acquired using an intensity demodulation technique and recorded on an oscilloscope.The time-delay signals were processed using conventional cross-correlation algorithms to calculate the time delays between pairs of sensors.Finally,based on the geometric positions of the sensor array,an estimation of the approximate sound source location was determined.The experimental results show that the interference spectrum FSR of EFPI sensor with collimator is 5.25 nm,and the maximum fringe visibility is 14.96 dB.The EFPI sensor without a collimator has a FSR of 5.18 nm and a maximum fringe visibility of 9 dB.The FSR of them is almost the same,but the interference spectral intensity of the former is increased by about 6 dB.In addition,the EFPI spectral slopes were 6.5 dB/nm and 10.2 dB/nm,respectively,without and with collimators,and the spectral slope of the latter increased nearly twice as much as the former.In the response characteristic experiment for the single sensor,EFPI acoustic sensor with collimator is superior to EFPI acoustic sensor without collimator in sound pressure response waveform and sound pressure sensitivity test.EFPI acoustic sensor with collimator has sound pressure sensitivity of 185 mV/Pa.The minimum detectable sound pressure is 52.7 µPa/Hz1/2@500 Hz,and the signal-to-noise ratio reaches 62 dB.In the experiment of sound source directionality,the designed sensor showed good performance under different sound pressure directionality.When the sound source was placed directly in front of the sensor,its sound pressure sensitivity reached 185 mV/Pa.When the sound source was set on the side of the sensor(90°,270°),its sound pressure sensitivity could still reach 177 mV/Pa.This indicates the ability of the sensor array to achieve sound source localization within a wide-angle range.In the two-dimensional plane sound source location experiment,the signal delay in the time domain signal is extracted by the correlation algorithm,and the two-dimensional plane sound source location within the range of 200 cm×200 cm is finally realized.The theoretical spatial resolution is 0.71 cm,and the maximum positioning error of the system is no more than 2.8 cm.Finally,the performance comparison with other EFPI acoustic arrays shows that the system has the advantages of high sensitivity,low production cost,simple demodulation system and large detection range.
Fiber acoustic sensorFabry-Perot cavityAutocollimatorSound localizationTime difference of arrival
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