Research On Acoustic Manipulations And Functional Devices Based On Acoustic Artificial Structures

Acoustic manipulations based on acoustic artificial structures have significant applications in the fields of medical ultrasound,acoustic communication and architectural acoustics.Therefore,the research of acoustic artificial structures has become a hot spot.Various novel acoustic effects and functional devices have be realized by using acoustic artificial structures,such as acoustic focusing,Bessel beam,anomalous refraction and reflection,negative refraction and so on.Compared with the traditional acoustic materials,the acoustic manipulation based on artificial structures has the advantages of high efficiency,flexible regulation and broad bandwidth,which has more extensive application prospects.In this paper,based on the artificial structure of acoustics,acoustic manipulations have been discussed and a variety of novel acoustic functional devices have been designed.In addition to the first chapter and the sixth chapter,which are the introduction and the summary and prospect,respectively,the main research contents are divided into four parts:（1）Basic theories and methods of acoustic artificial structures;（2）Multifunctional reflected lenses based on aperiodic acoustic metagratings;（3）Multifunctional acoustic logic gates by valley sonic crystals;（4）Floquet higher-order topological insulator based on a two-dimensional acoustic lattice.In the second chapter,we introduce the related theories and research methods of acoustic artificial structures.It includes acoustic linear interference mechanisms,generalized Snell’s law（GSL）and its extension,and calculation method of reciprocal vector of sonic crystal,which offers the theoretical basis for realizing acoustic manipulation based on acoustic artificial structures and designing acoustic functional devices.In the third chapter,we theoretically design and experimentally demonstrate a class of reflected aperiodic AMs and related multifunctional acoustic lenses.By using the extension of the GSL,we can overcome the limitations of the GSL（such as the phase gradient and the incident critical angle）and experimentally demonstrate theoretical predictions of sound reflections created by the aperiodic AMs with arbitrary phase gradients under a full-angle incidence.Additionally,we experimentally design a multifunctional reflected lens composed of two selected aperiodic AMs.Interestingly,by simply adjusting the incident angle of sound,we can realize the transformation between the beam splitting and the Bessel-like beam,and the transformation between the beam splitting and the single beam.Our work paves a new way for modulating sound reflections and designing reflected multifunctional devices with promising applications.In the fourth chapter,we numerically design and experimentally demonstrate a multifunctional logic gate based on valley sonic crystals（VSCs）.In a designed waveguide composed of VSC-I and VSC-II,a pair of valley edge states can be obtained in the domain wall.Additionally,we experimentally design a multifunctional logic gate composed of four VSCs.The logic functions OR and XOR with the fractional bandwidths of 0.24 and 0.19 can be realized at two output ports,which arises from both valley conservation and linear interference mechanisms.More importantly,we experimentally demonstrate the robustness of the logic gate by introducing a V-shaped defect,and the corresponding logic functions and their bandwidths created by the valley transport of edge states are almost immune to backscattering from the V-shaped defect.The proposed logic gate has the advantages of multifunctionality,broad bandwidth,and high robustness,which may have practical applications in advanced acoustic devices for computing and information processing.In the fifth chapter,we realize the Floquet higher-order topological insulator（HOTI）based on a 2D acoustic lattice consisting of square-ring waveguides and coupling channels,which is equivalent to the Floquet states of periodically driven lattices.By changing the number of the coupling channels,we can get various topological phases.In our designed Floquet topological insulators with n₁=12,n₂=12,n₁=12,n₂=8 and n₁=10,n₂=4,corner states can be observed.Besides,we also exhibit the Floquet corner states and Floquet chiral edge states in the same Floquet HOTI at different frequency experimentally.The proposed acoustic Floquet HOTI paves a new way for designing acoustic functional devices,which may have practical applications in acoustic communication and information processing.