Research On Optical Fiber Acoustic Sensing Technology Of Localized Mie Resonance Composite Structure

The sound field has become one of the important media for information transmission due to its ability to carry information.The sound field attenuates significantly as the distance from the sound source increases.Under the interactive influence of a complex environment,the sound field information far away from the sound source will be annihilated in the environmental noise.Therefore,improving the sensitivity of the acoustic sensor and realizing the detection of weak sound field information have become the research focus in the field of acoustic sensing.The emerging acoustic metamaterials have sound field modulation capabilities that are unmatched by natural materials.They have shown extremely high technical application value in achieving acoustic stealth,perfect sound absorption,and construction of acoustic lenses.It can achieve directional localization of sound fields.Resonance amplification.In this paper,the local dipole Mie resonance structure is introduced into the sound field detection,combined with a small Fabry-Perot optical fiber acoustic sensor,to achieve all-photoacoustic detection in the sound field.Through this composite structure,the sound field detection capability is improved,and at the same time,the defect that the traditional piezoelectric transducer is susceptible to electromagnetic interference is compensated.First,the paper introduces the research background and application requirements of sound field sensing,outlines the research progress of acoustic metamaterials and Mie resonance structures,and analyzes the research status of optical fiber acoustic sensors in recent years.Based on the analysis of the basic principle of sound field control of acoustic metamaterial Mie resonance structure,based on the method of modal expansion and mode matching,the resonance conditions of different Mie resonance structures are deduced.In the thesis,a local Mie resonance structure model is constructed,and the local Mie resonance structure in this thesis is simulated by multi-physics using finite element analysis.The dipole resonance of the structure is excited by the incident sound field,which realizes the energy concentration and directivity of the sound field,and improves the sensitivity and signal-to-noise ratio of the sound field.Through parameterized scanning,the different influences of structural parameters on frequency are studied,the optimal conditions of Mie resonance structure are obtained,and the selection of frequency is realized.In addition,the influence of the embedded optical fiber sensor on the internal sound field of the Mie resonant structure is analyzed,and the built-in method of the optical fiber sensor that has the least influence on the sound field measurement is designed.Secondly,the paper describes the basic principle and demodulation method of the thin-film Fabry-Perot optical fiber acoustic sensor.Through the performance analysis of different diaphragm materials,the type and parameters of the diaphragm were screened and determined,and the production of the thin-film Fabry-Perot optical fiber acoustic sensor was completed.Through the acoustic experimental system built,the acoustic sensing performance of the optical fiber acoustic field sensor is tested.Finally,combining the respective advantages of the Fabry-Perot optical fiber sensor and the Mie resonant structure,the Mie resonant structure-Optical fiber acoustic sensor was made,and a composite sensor acoustic sensing system was established.Test and analyze the acoustic performance of the system such as linearity,sound field response,directivity,signal-to-noise ratio,and sensitivity response.Experimental results show that under the action of the Mie resonance structure,the optical fiber sensor achieves a pressure gain of 23 times at a single frequency point,an increase in sensitivity and a certain directivity.Therefore,the acoustic sensing system achieves signal amplification and pickup at sub-wavelength scales,has narrow-band filtering and spatial directivity gain,and provides new technical methods for future acoustic positioning measurement and acoustic camera research.