弹性波主动开放式的隐身现象的研究

In recent years, the cloaking of classical waves is a hot research topic in the domain of artificial microstructure. Since the coupling of transverse mode and longitudinal mode, the gerenal elastic waves can't be cloaked by using the conventional coordinate transformation method, unless some special conditions have been satisfied. In this project, we investigate a new cloaking mode: active exterior cloaking. In this cloaking pattern, some active sources have been set in the medium. They can produce a cloak region by means of the interference between active sources and incident waves. The advantage of this cloaking mode is that it can cloak the general elastic waves. The cloaking only depends on the properties of active sources. Then we can design the structures more freely. We apply boundary integral equation method to simulation the active exterior cloaking of elastic waves in two dimensional and three dimensional system. We foucs on the design of a simple and practical cloaking structures. And we investigate how the incident direction and polarization mode of incident waves can affect the cloak quality. Further more, by considering the scattering of incident waves on the boundary of active sources materials, we update the results to agree with the experimental situation. At last, we expand the special cloaking phenomenon to the general illusion phenomenon. Based on the results of numerical simulation, we can design some structure to practice cloaking in experiment.

经典波的隐身现象是近年来人工微结构领域中的一个热门研究课题。由于弹性波的波动方程中横波模式和纵波模式的耦合，使得一般化的弹性波无法使用传统的坐标变换法产生隐身，利用坐标变换产生弹性波的隐身只在某些特殊条件下才能实现。在本项目中，我们研究一种新型的隐身模式：主动开放式隐身。它是在空间中设置一些外部波源，通过与入射波的干涉，在空间中主动产生一个隐身区域。这种隐身模式的优点是可以对一般的弹性波进行隐身，其隐身现象的产生仅依赖于外部源的性质，在结构设计上，具有更大的自由度。本项目采取边界积分方程法，研究弹性波在二维和三维体系中的主动开放式隐身现象，设计简洁实用的产生隐身的结构，研究结构对入射波隐身的方向选择性、模式选择性等物理性质，并考虑外部源本身对入射波的散射，对结果进行修正，使之更接近真实的实验。最后将特殊的隐身现象扩展到更一般的幻象现象。根据理论模拟结果，设计结构，指导实验。

本项目主要通过设计声学人工结构，比如声子晶体和声学超材料，调节与操控声波或弹性波在结构中的传播，从而产生新奇的物理现象。本项目是一个以理论研究为主的项目，主要内容包括声学隐身以及相关问题，同时依据国内外研究现状，开展关于声学负反射、声波囚禁、声学宇称-时间对称结构、声学拓扑态等热门方向的研究。截止到项目结题，在国际知名物理学期刊上一共发表文章八篇，培养学生两名。其研究结果在声学新奇状态的研究、声波的操控、新型声学器件的设计等方面有重要的指导作用，研究内容在水下声学、空气声学、超声医学、声学探测等方面有重要的应用价值和科学意义。