Study On Acoustic Manipulation Performance And Topological Properties Of Acoustic Artificial Materials

In the past two decades,acoustic artificial materials have become an important research area and have received widespread attention from researchers.This area mainly includes phononic crystals and acoustic metamaterials.Acoustic artificial materials are artificially constructed unit structures to produce novel physical properties not found in traditional natural materials,e.g.,negative mass density,negative elastic modulus,near-zero parameters,anisotropic parameters,and so on.Acoustic artificial materials can realize diverse control of acoustic waves.Among them,one-way acoustic control and acoustic beam control are usually implemented based on different types of devices.Acoustic metasurfaces with sub-wavelength thickness,as an important class of acoustic metamaterials,can be used for simple and accurate manipulation of spatial acoustic fields,such as abnormal refraction,focused acoustic beams,and self-bending acoustic beams.However,the active acoustic metasurface with adjustable parameter response is usually not convenient for real-time adjustment of structural parameters,thus limiting its prospects in practical applications.In addition,with the development of the theory of topological energy bands,related concepts in topology are also introduced into the study of acoustic artificial materials.By analogizing the quantum Hall effect and the quantum spin Hall effect,the researchers have realized topologically protected unidirectional boundary states in acoustic systems.Recently,the Valley Hall effect can achieve topological phase transitions by breaking the symmetry of the structure.The topological transport with valley vortex state will provide people with a new way of sound wave manipulation.Considering the complexity of problems in fields such as medical imaging and acoustic communication,it is of great significance to implement topological valley states to transport at different frequencies along the required trajectory.In this paper,the research on the acoustic manipulation characteristics and topological properties of artificial acoustic structures is carried out.Based on the above problems,we have made important research results in three main directions: acoustic unidirectional beam splitters,thin film active acoustic metasurfaces and topological phononic crystals with adjustable interface states.These acoustic devices may have significant value in a variety of applications,opening up new ways for the design and application of new acoustic devices.The main contents include:In Chapter ?,we review the development of phononic crystals,acoustic metamaterials and topological properties in acoustic systems,and briefly introduce the related theories of metamaterials such as wave equations and equivalent media in acoustic metamaterials.In Chapter ?,we propose the concept of one-way acoustic beam splitter.Firstly,the background of acoustic beam splitter and acoustic diode are reviewed.Then we pointed out that the previous beam splitter designs support only symmetric acoustic transmission.By combining the functions of acoustic beam splitter and acoustic diode,one-way acoustic beam splitter is designed.We elucidate the underlying mechanism that controls the transmission of asymmetric cavity defect to achieve the one-way acoustic beam splitter.Our design can split acoustic beam incident from the input port into multiple beams while effectively reduce the backward transmission from any of the output ports.Furthermore,our design enables flexibly adjusting the number and angle of output beams by blocking the unused line defects.The numerical results verify the theoretical predictions and demonstrate the phenomenon of one-way acoustic beam splitter at the predesigned frequency.In Chapter ?,an ultrathin membrane-type active acoustic metamaterial with deep-subwavelength thickness is studied.Firstly,the background of acoustic metasurfaces was reviewed,and we point out that the real-time adjustment of structural parameters by traditional active hypersurfaces is not easy.Then,we proposed an active acoustic metamaterial based on two composite membrane structures and effectively simplified and reduced the previous device.The underlying mechanism is that the change of tension on the middle membrane by the stresses introduced by the voltage exerted on the piezoelectric layers modulates the surface phase profile.Therefore,by modulating the static voltage exerted on each metamaterial unit cell,the whole active metasurface device can be tuned to produce different phase profiles needed for realizing distinctive wave-steering phenomena.In Chapter ?,a topological phononic crystal structure with tunable interface states based on local resonance element is studied.Firstly,the background of topological properties of acoustic metamaterials is reviewed.Then we propose the possibility of topological phononic crystals with adjustable interface states in practical applications.The underlying mechanism is that the modulation of edge modes change the interface state by controlling local resonance elements and breaking mirror symmetry.The performance of the resulting device is numerically demonstrated via production of robust topological valley transport along the straight and sharp bends interfaces for incident waves of different frequencies.In Chapter ?,the conclusions of the paper and the future work are summarized.The innovation of this paper is as follows:1.We present the scheme of acoustic beam splitting based on phononic crystal.The resulting device can split the acoustic waves incident from the input port into multiple beams,while effectively reducing the back incident from any output port.Our design with functionality and flexibility bridges the gap between acoustic diodes and BSs and may enable novel multi-functional devices with great application prospects in diverse fields.2.A design based on composite membrane structure for active acoustic supersurface is proposed.By adjusting the static voltage distribution,the transmitted acoustic wavefront can be manipulated in real time without changing the geometry of the structure.The active acoustic metasurface can conveniently adjust the structural parameters in real time,which has great significance for the practical application of the new active acoustic metasurface.3.A scheme for achieving tunable interface states of topological phononic crystal structure with is proposed based on local resonance element.Considering the complexity of real-world problems such as medical imaging or acoustic communication that may need the topological valley states to transport along desired trajectory or emerge at different frequencies,it would be the fundamental interest and practical significance to realize topological phononic crystal structure with tunable interface states.We can change topological interface state by reconfiguring the structural parameters,and the robust topological valley transport at different frequencies along the straight and sharp bending interfaces is demonstrated.The resulting device helps to improve the design of tunable topological phononic crystals and provides new ideas for the design and application of tunable acoustic devices.