少层超表面声波调控机理及其在紧致型声隐身技术中的应用研究

Due to the features of small energy loss, broadband efficiency and small size, the acoustic metasurfaces may open a new avenue for the miniaturization and easy realization of many acoustic wave manipulation devices. However, current researches about the acoustic metasurfaces are limited to the single-layer planar profile and restricted to the manipulation of acoustic reflection wavefront. This project focuses on the new construction schemes and parameters characterization methods of few-layer metasurfaces based on the resonant unit cells and nonresonant unit cells , and on the ultrathin cloak design method based on these few-layer metasurfaces. In this project, the relationship between the equivalent characteristics of the nonresonant coiling-up unit cells with the constituent material and bending distance and impedance gradient will be investigated, and a novel type of acoustic metasurface unit cells, which have the characteristics of isotropy, high refractive index, low loss and impedance matching, will be proposed; the parametric studies of symmetry-broken metamaterial will be performed and the double negative metamaterials based on only one type of single Helmholtz resonant unit cells will be proposed and used to construct the metasurfaces; the interferometric mechanism and coupling mechanism between the layers of the few-layered metasurfaces will be studied and the functionality of the layered metasurfaces will be optimized in order to provide more degrees of freedom to manipulate the propagation and phase amplitude of acoustic wave; an integrated design approach of ultrathin metasurface-based cloaking devices that can combine technical advantages of current major cloaking strategies (include the optimization method and scattering cancellation method and coordinate transformation method) in a unified manner was studied. This project will provide the technical supports for enhancing metasurfaces functionalities and extending its applications, and offer theoretical guidance for ultrathin cloaking devices to achieve.

新型声波超表面因具有损耗小、频带宽、尺寸小的特点而被视为解决声波控制器件“小型化、实用化”问题的利器，但当前超表面研究多为单层平面构型且多局限于对反射波的调控。本项目重点研究基于非共振单元与共振单元的少层超表面构建与表征方法，以及基于超表面的紧致隐身覆盖层设计问题。项目研究盘绕型非共振单元中材料组成、弯折距离、阻抗渐变等对于等效特性的影响，提出适用于超表面的各向同性、高折射率、低损耗、阻抗匹配的单元新构型；研究对称性对共振单元间动力耦合效应的影响，提出基于单一Helmholtz共振单元的双负材料设计方法并用于构造超表面；研究层状超表面内声波的干涉与耦合效应，优化少层超表面构造，实现对声波相位与幅值的灵活调控；研究反向设计方法与散射相消方法、坐标变换方法综合运用问题，提出基于少层超表面的超薄隐身杂交设计思路。本项目的完成将为提升超表面效能、扩展其应用提供技术支撑，为超薄隐身结构实现提供指导。

新型声波超表面因具有损耗小、频带宽、尺寸小的特点而被视为解决声波控制器件“小型化、实用化”问题的利器，但当前超表面研究多为单层平面构型且多局限于对反射波的调控。本项目重点研究基于非共振单元与共振单元的少层超表面构建与表征方法，以及基于超表面的多功能设计问题。研究主要工作包括，通过调节迷宫结构的几何构型来调节微结构等效声学属性，获得了一系列具有与背景介质匹配的等效阻抗且具有高达7的可调折射率的迷宫结构单元；在空气通道宽度连续变化的锥形迷宫单元中实现了3.76kHz至4.83kHz频带内的近似全透射；提出了一种非对称三层单元。单元中芯层用于调整单元相位相应，芯层两侧利用四分之一波长阻抗变化层实现单元的法向声阻抗与声波匹配，这种少层非对称单元具有双各向异性响应。本项目的完成将为提升超表面效能、扩展其应用提供技术支撑，为超薄隐身结构实现提供指导。

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