Study On Modulation Of Acoustic Wavefront Based On Artificial Metasurfaces

Acoustics is an important branch of modern scientific research.This discipline is closely related to real life,but also closely related to medical,aerospace and national defense fields.For the purpose of acoustic research,the most important thing is to achieve easy,flexible and efficient sound wave control.However,it is not easy to fully control sound waves in fact.Due to the existence of natural materials,its acoustic properties can no longer meet the needs of more complex sound field control,because there are often limitations,for example,it's difficult to use small-sized structures to control sound waves in the low frequency range and manipulate sound waves in a wide frequency range.Therefore,people urgently need some artificial materials that can effectively and efficiently manipulate the propagation of sound waves.Researchers have discovered that by artificially designing the materials called metamaterials according to the requirements,more complex properties can be obtained to achieve more richer and special functions.Acoustic metasurfaces are one of the frontiers in the design of such materials.The main core is the use of artificially designed acoustic materials to achieve flexible modulation of the acoustic wavefront.Firstly,this article gives a brief overview of the basic concepts of acoustic metamaterials,acoustic metasurfaces,research status and development of metasurfaces.Secondly,the basic properties and equations of acoustics,the calculation method of metasurface and the simulation software are introduced,respectively.Then,the main research contents of this paper are described in detail.We propose an impedance-matched acoustic metasurface.Based on this idea,the designed metasurface is used to realize a variety of control mode for the acoustic wave front.The vortex effect obtained from the point source is discussed according to the distributions of refractive index and its effectiveness is verified by simulation,such as the conversion of point source into vortex waves and vortex sound fields with different topological charges,and the conversion in multiple frequency ranges reflecting its broadband effect.At the same time,based on the designed single-layer curved metasurface,a double-layer curved metasurface is also designed,which realizes the control of the vortex sound field again,and explains the physical mechanism of phase superposition principle theoretically.In addition,we have designed a variety of acoustic wave collimation effects through another impedance-matched metasurface,which can convert cylindrical waves emitted by point sound sources into plane waves.Then,by arranging the metasurfaces,the collimating effect of directional radiation can be achieved.Finally,we designed a reflected metasurface based on Helmholtz resonators.By controlling one parameter,the arbitrary manipulation of the structural unit phase can be achieved.And eight units discretized in the 2? phase were selected to achieve the acoustic wave reflection and acoustic focusing effects,respectively.The above research results have certain practical significance and reference value for the designing acoustic metasurface and acoustic devices.Acoustic metasurface is based on subwavelength thickness.Due to its small size,and the flexible and simple structure design,it is often easier to be industrialized and integrated on this basis.The main core is to achieve arbitrary control of sound wave and produce many strange phenomena by precisely arranging phase distributions of the acoustic wavefront.