Research On Acoustic Devices Based On Mie Resonance

Acoustic metamaterials are artificial structures with responses beyond their natural constitutive materials.The acoustic metamaterials offer great opportunity to the manipulation of sound fields and have made great progress in the past decade,such as acoustic cloaking,holography,negative refraction of sound waves and acoustic absorbing.Recently,sub-wavelength high-refractive-index particles have been proposed as ideal candidates for multifunctional elements in acoustic devices for the flexibly tunable frequency,highly stable shape and a controllably regular arrangement.Using the interaction between the Mie resonance modes of the particles and the sound waves,modulation of the sound emission,transmission and reception can be realized.Under this background,this paper focuses on the study of acoustic devices based on the Mie resonance.The contents are as follows.Firstly,this thesis introduces the origin and classification of acoustic metamaterials,as well as their application.In addition,the research progress of the Mie resonance in recent years is introduced to demonstrate the application prospect of acoustic devices based on Mie resonance in the modulation of sound waves.The realization of underwater acoustic forward scattering phenomenon has provided a technical basis for underwater target detection.However,how to achieve forward scattering in the air in a problem.This paper realizes acoustic unidirectional forward scattering in air based on the unique scattering properties of Mie resonators in the case of plane wave incidence.The scattering of characteristics of the resonators are theoretically analyzed by multiple scattering theory and the forward scattering phenomenon is verified by the simulation based on a finite element method.We also demonstrate that the forward scattering can be achieved in a wider frequency range by the combination structure of several resonators with different parameter.It is a challenge to modulate the emission mode of a classic acoustic source with a sub-wavelength scale structure.In this paper,based on the intensive coupling between classic acoustic source and Mie resonators,a tunable directional subwavelength acoustic antenna is designed.We demonstrate theoretically and experimentally that the antenna can realize a 2.33-fold enhancement of the radiated power and a 7.81-fold enhancement of the sound intensity in the main lobe direction.In addition,the unidirectional performance of the antenna can be further improved by constructing array antenna.Benefitting from the subwavelength scale and the simple structure of the Mie resonators,the directivity of sound radiation can be easily adjusted by rotating the antenna around the point source.In the fourth chapter,a tunable acoustic impedance metasurface based on coupled Mie resonators is designed to realize extraordinary acoustic transmission in the lowfrequency regime.The extraordinary transmission is attributed to the strong coupling between the proposed Mie resonator dimer.According to the acoustic equivalent circuit theory,the system can be divided into over-coupled,critical coupled and under coupled states depending on different strength of the coupling.When the system works in the over-coupled region,the frequency splitting phenomenon appears and the maximum transmission is obtained at each peak.As the coupling between the resonators decreases,the two modes converge at a single frequency.If the coupling strength continues to decrease,the system will be under-coupled and the delivered power begins fall of precipitously.We demonstrate theoretically and experimentally that the coupling strength is affected by the distance between the resonators of the dimer.As a result,a widely tunable impedance modulation of the proposed metasurface can be achieved by tuning the distance of the resonators.The proposed metasurface also shows good robustness so as to promise a better application prospect.In order to break through the limitations of traditional radiative transceiving system,this paper put forward a remote whispering acoustic transceiving(RWAT)system enabling weak sound at audible frequencies to reach unprecedented signal enhancement without altering the detected ambient soundscape and enabling unintended disclosure.Theoretical model based on the multiple scattering theory shows that a pair of elements with higher relative refractive index can acquire a significantly improved sound signal at a target position.Despite the influence of the dissipation,the RWAT system remains to display more than 40 d B enhancement of the detected signals.The simulation and experimental results are in good agreement with the theoretical predictions.Comparing with the traditional radiative transceiving system in free space,the proposed system exhibits an average of-20 d B in reduction of the ambient sound leakage.The RWAT system can also recover weak sound signals completely overwhelmed by strong noise with enhanced signal-to-noise ratio form-3 d B below the detection limit of 0 d B in free space to 17.7 d B.The proposed transceiving system demonstrates a number of key advantages,including good robustness,subwavelength scale and the ability to transfer the weak sound signals to different locations.In the last chapter,the paper is summarized and the future development is prospected.