Acoustic Modulation Based On Acoustic Gradient Metasurface

Acoustic metamaterials which have a series of abnormal physical properties that natural materials do not possess are a new type of artificial material that emerged at the end of the 20 th century,acoustic waves can be controlled freely by utilizing these exotic properties of metamaterials.The properties of acoustic metamaterials have attracted much attention from researchers,it is expected that acoustic metamaterials can be used to design acoustic devices that are superior to traditional materials in all aspects.However,with the development of acoustic metamaterials,some disadvantages of metamaterials have been exposed,it has the disadvantages of large volume,high cost,large loss and narrow band width.It is difficult to integrate due to its large size,so the design goal of making acoustic metamaterials thinner and lighter has become an urgent need of more and more scientific researchers.After more than a decade of research,a new type of ultra-thin surface has emerged,it is called the “metasurface”.It is a quasi-two-dimensional periodic structure arranged with a size smaller than the wavelength,which makes use of its unique properties to generate phase mutations on the interface so as to realize almost arbitrary manipulation of sound waves.The metasurface breaks the traditional methods manipulation of sound wave such as diffraction and reflection,many phenomena of acoustic manipulation have been realized by using metasurface,such as abnormal refraction or reflection,asymmetric transmission,sound wave focusing,sound wave absorption,etc.The study of acoustic metasurface is not only of great scientific value,but also of great potential value for practical application.According to the previously reported research background of the metasurface,the research content of this paper is divided into two aspects,as follows:(1)The acoustic anomalous refraction is achieved by using gradient metasurface,gradient metasurface matching the impedance of the air is designed,which can achieve high transmission anomalous refraction.In this paper,the finite element method is used to simulate the sound pressure field distribution at different incident angles,when the incident direction is determined which can control the refracted sound wave in a wide range of central frequency.Finally,The theoretical refraction angle is calculated according to the generalized refraction law,The results show that the theoretical analysis is in good agreement with the simulation results.(2)The asymmetric transmission of sound waves is realized by using the monolayer gradient acoustic metasurface,in this paper,Based on the single-layer acoustic gradient-index metasurface,a kind of method realizing acoustic asymmetric transmission was designed and simulated.The asymmetric transmission exhibits the characteristics of wide-angle and high energy contrast.Via proper design of metasurface structure,positive propagation is permitted by negative refraction and negative propagation is prohibited by suppressing high order diffraction.The results of theoretical analysis using the generalized Snell's law agree well with those of simulation based on finite element method.Our design may find many potential applications in various scenarios such as noise control,ultrasound rectifier and therapy.