Acoustic Wave Regulation Based On New Type Of Acoustic Artificial Structure

Acoustic artificial materials have become a hot research field in acoustics because of their significant applications in the fields of noise reduction,holographic acoustics,particle manipulation,national defense,and military affairs.Designing artificial materials with special structures can result in various novel acoustic effects,such as negative refraction,self-bending beam,vortex beam,non-diffraction beam,diffuse reflection and acoustic focusing.Compared with the traditional acoustic materials,the new acoustic artificial structure has the advantages of sub-wavelength size,flexible regulation and intelligence,thus,it has more extensive application prospects in practical fields.Based on the artificial structure of acoustics,a variety of new acoustic devices have been designed.The first chapter is the introduction,and the eighth chapter involves the summary and the outlook.The main research contents are from second chapter to sixth chapter:(1)Theory and calculation methods of acoustic artificial structures;(2)Broadband acoustic logic gates in a circular waveguide with multiple ports;(3)Modulating sound with acoustic metafiber bundles;(4)Multi-band asymmetric acoustic transmission in a bended waveguide with multiple mechanisms;(5)Broadband tunable acoustic asymmetric focusing lens from dual-layer metasurfaces;(6)Programmable coding acoustic topological insulator.In the second chapter,we introduce the common theories and research methods in acoustic artificial structures field.It includes generalized Snell's law,equivalent parameter inversion method based on transfer matrix,and calculation method of reciprocal lattice basis vector of phononic crystals.In the third chapter,we report a broadband acoustic logic gate realized by multiport circular waveguides both experimentally and numerically.The logic functions OR,NOT,AND,XOR,and XNOR are realized by the three-port and four-port circular waveguides with a uniform threshold in the range of 3640–8920 Hz,which arises from the linear interference mechanism by adjusting the phase difference and propagation path between two input signals.Besides,the complex logic NOR and NAND functions are obtained by the cascading of two basic logic gates,and interesting applications of the logic calculus C+A×B by the four-port circular waveguide are discussed in detail.Compared with other acoustic logic devices,the proposed acoustic logic gate has the advantages of wide frequency band,same threshold value,simple structure and convenient for connection,providing theoretical solutions and design ideas for new type of acoustic communication and logic computing devices.In the fourth chapter,a design and realization of a broadband multifunctional acoustic metafiber bundle are presented.Based on the eigenmodes of acoustic metafiber unit structure,the ratio of operating bandwidth to center frequency could reach about 0.25.By changing the geometrical parameters of the super-fiber element,the metafiber can steer a local phase shift that spans 0 to 2? range.Based on different phase distributions,acoustic metafiber bundles can achieve a variety of novel acoustic effects,such as single negative acoustic refraction,double negative acoustic refractions,and acoustic focusing,respectively.In addition,based on the simple structure and the flexibility of the acoustic metafiber bundles,the manipulation of the focal position and the acoustic cloak are realized.Acoustic metafiber bundles have significant applications in the fields of acoustic communication and national defense.In the fifth chapter,we report the realization of a multi-band device of the oneway acoustic transmission by placing a phononic crystal inside a bended waveguide immersed in water both experimentally and numerically.The one-way acoustic transmission exists in three frequency bands below 500 kHz induced by multiple mechanisms.Except for the band gap of the phononic crystal,we introduce the deaf mode and interaction between the phononic crystal and waveguide.More importantly,this one-way transmission can be systematically controlled by mechanically rotating the square rods of the phononic crystal.In the sixth chapter,we designe a broadband acoustic lens with asymmetric focusing by dual-layer metasurfaces in air.For left incidence,the acoustic waves are focused on the other side with 0.4 wavelength resolution focusing characteristic,but cannot transmit through the lens in a large range of incident angles on the right side,as the acoustic waves are transformed into surface wave along the right side metasurface.This exotic phenomenon exists in the range of 2910–3610 Hz,which arises from the asymmetric phase manipulation induced from the dual-layer metasurfaces.More importantly,without changing the structure of both metasurfaces,the positions of the focus can be systematically manipulated by mechanically changing the distance between both metasurfaces.This acoustic asymmetric focusing lens has the advantages of sub-wavelength focusing,planar structure,adjustable focal length and so on,and has important application in the fields of focused ultrasound therapy and medical ultrasound imaging.In the seventh chapter,we theoretically and experimentally propose a programmable acoustic topological insulator based on two digital elements “0” or “1”,which consist of honeycomb-lattice sonic crystals made of cylindrical rods with different diameters.The acoustic propagation paths in the topological insulators can be controlled automatically by programming different coding sequences,which arises from efficient transformation of pseudospin-dependent edge modes on both interfaces of the digital elements.More importantly,we experimentally fabricated a unique unit hat has either a “0” or “1” response automatically manipulated by an air cylinder,and design topological insulators with programmable functionality to realize digital acoustic devices,such as a single-pole double-throw switch and a tunable logic gate.The proposed programmable topological insulators may enable future intelligent acoustic devices with exciting reconfigurable and programmable functionalities,which may lead to important advances in various applications,such as integrated acoustics,acoustic security,and information processing.