基于声学超材料的声波非对称传输、聚焦和调控新机制及其应用研究

The problem of the direction divergence (two beam or multiple beam) of the positive transmitted acoustic waves exists in the acoustic asymmetric transmission generating in the current linear systems. This project focuses on the acoustic metamaterials. At first, the new mechanism of the acoustic asymmetric transmission in the linear systems is investigated in details. And then, the new acoustic metamaterials with more simple structure and higher negative refractive index are explored, and the metamaterial composite structures with the distribution of the refractive index are studied. In addition, the relationships between the parameters of the composite structures and the refractive index distribution and the acoustic impedance mismatch are analysed, and the distribution functions of the refractive index for focusing the multi-direction acoustic waves are obtained. Therefore, the broadband omnidirectional acoustic focusing effect is realized. Based on those results, a special acoustic focusing composite structure is introduced into the model of the acoustic asymmetric transmission. The new mechanism of broadband focusing of the acoustic asymmetric one-way transmission is studied, and the energy of the positive transmitted acoustic waves focuses on the same direction. Therefore, the effect in the focusing of the acoustic asymmetric one-way transmission is realized. Besides, the factors which influence the efficiency of the focusing of the acoustic asymmetric one-way transmission and the methods which increase the efficiency are also analysed. The project provides the theoretical basis and the prototype device to help develop a perfect and efficient acoustic device with focusing asymmetric one-way transmission, which is of great scientific significance and application value.

现有的线性系统产生的声波非对称传输存在正向透射声波方向发散（两束或多束）的问题。本项目以声学超材料为研究对象，深入研究线性系统中声波非对称传输的新机制；探索结构更简单、负折射率更高的新型声学超材料，研究并设计具有一定折射率分布的超材料复合结构，分析复合结构的参数与折射率分布及阻抗匹配之间的关系，探索多方向的声波聚焦所需的折射率分布函数，实现宽频带全方位入射声波的聚焦效应；在此基础上，在声波非对称传输模型中引入特殊设计的声波聚焦超材料复合结构，研究宽频带聚焦超声非对称单向传输的新机理；使得正向透射声能量聚焦在同一方向，实现聚焦超声非对称单向传输效应，并分析影响聚焦超声非对称单向传输效率的因素及提高效率的方法，从而为研制更完善、更高效的聚焦超声非对称单向传输器件提供理论依据及器件原型，具有重要的科学意义和应用价值。

本项目基于课题组声学超材料与声非对称单向传输等方面的研究基础，在声单向传输与声聚焦两个领域开展深入的理论与实验研究。系统研究复杂声学结构中声非对称单向传输与声聚焦效应，发展了多种新型声单向传输与声聚焦器件的设计原理与制备技术，使两种类型器件的性能得到了显著提高。同时，结合声非对称单向传输与声聚焦两种反常声学效应，深入探索声单向聚焦的物理机制，研制同时具有声单向传输与声聚焦性能的声学原理性器件。主要研究创新点包括：(1) 提出了基于金属平板与周期性栅格的多频带声单向器件、基于声子晶体的多频带多机制声单向波导、基于两组对称三角形腔的声单向隧道、基于金属平板与三角形散射体的超宽带声单向器件等多种新型声单向传输器件的设计原理，并制备了原理性器件。上述工作使得声单向传输器件的工作频带数量与带宽及单向特性得到显著的增强，为此类器件带宽受限、正向透射率低及路径阻塞等问题提供了解决方案。(2) 提出了基于金属柱状结构的多焦点声聚焦器件、基于声超纤维簇的宽频带声聚焦器件、基于不同个数腔结构相控阵列的宽频带声聚焦效应、基于近零折射率材料的声聚焦透镜等多种新型声聚焦器件的设计原理，制备了部分原理性器件，极大拓展了现有的声聚焦的物理机制，并提高声聚焦器件的工作带宽。在此基础上，基于热声耦合机制，研究了不同位置与数量的恒温热源与热声相控阵列对声传播路径的影响，实现了多种类型的宽频带声聚焦与声单向传输器件。(3) 基于具有两种不同类型狭缝(斜缝和竖缝)的金属平板，首次制备了声单向聚焦的原理性器件，该器件同时具有声单向传输与声聚焦两种性能，可用于优化和提高聚焦超声治疗和超声成像等医学设备的性能。本项目共发表学术论文38篇，其中SCI30篇 (中科院SCI二区11篇)，申请发明专利4项。项目成果不仅在声学超材料研究领域中富含基础性的学术意义，更有望应用于国防安全及经济建设等重要领域，蕴含着潜在的经济价值。