GOALI: EFRI NewLaw: Non-reciprocal effects and Anderson localization of acoustic and elastic waves in periodic structures with broken P-symmetry of the unit cell

该奖项将研究周期性介质中由于粘性而产生的非互易超材料，并设计声波通过它的传播。对于光波和声波，自然界理想地遵循互易性规则，即逆转波的传播将使波恢复到原始状态。这种现象类似于电脑或设备上的“撤销”动作，是传统通信和我们对现实的一般感知中使用的波行为的基础。然而，有一类特殊设计的材料违反了这些行为，称为破坏互易对称性的非互易超材料。在这些材料中，“撤消”或反向动作并不能理想地将波恢复到初始状态。对非互易性的深入理解将增强我们对一般声学和影响应用的了解，如建筑、安全通信、隔振、医疗诊断和治疗。主动声子结构包括可调谐透镜，滤波器和声学二极管将被设计。将利用增材制造和微机电技术来实现主动声子结构。本项目将涉及本地物理、机电工程和材料科学专业的高中生、毕业生、博士后和本科生。研究经验和指导（EFRI-REM）将通过该研究项目提供给来自德克萨斯州数学与科学学院的学生。该项目还包括与工业界密切合作，培训学生，并将研究活动的成果商业化。波通过散射体系统的传播遵循互易定理，该定理指出，如果发射器和接收器的位置互换，波的传输保持相同。互易性源于波动方程的基本性质——时间反转对称性。本项目研究了粘性介质中声音非互向或单向传播的新机制。一种常见的观点是，虽然耗散破坏了时间可逆性，但这并不足以引起沿两个相反方向的不同传输。然而，这在粘性流体的情况下是无效的。结果表明，在具有p对称破缺的声子晶体中，声音在粘性介质中的传播不遵循互易定理。更具体地说，我们研究了在不需要动态能量输入的情况下，Navier-Stokes方程中的微分耗散如何导致显著的非倒易效应，并将其扩展到包括非倒易双曲超材料在内的新型非倒易结构。本文还研究了非互易二维无序声子晶体的传输。单个散射体中无序的存在导致声波的定位，这种效应称为安德森定位。这种效应将用于实现加密，可用于开发空气和水中声信号的安全通信。

This award will investigate non-reciprocal metamaterials that arise in periodic media due to viscosity and engineer acoustic wave propagation through it. For light and sound waves, nature ideally follows the reciprocity rule that reversing a wave propagation will return that wave to its original state. This phenomenon is similar to the "undo" action on a computer or device, and is fundamental to the behavior of waves used in conventional communication and our general perception of reality. However, there is a select class of specially designed materials that violate these behaviors called non-reciprocal metamaterials that break reciprocity symmetry. In these materials, the "undo" or reverse action does not ideally return the wave to its initial state. Deeper understanding of non-reciprocity will enhance our knowledge of general acoustics and impact applications like architecture, secure communications, vibration isolation, medical diagnostics and therapeutics. Active phononic structures including tunable lens, filters and acoustic diodes will be designed. Additive manufacturing and micro-electro-mechanical techniques will be utilized to realize active phononic structures. Local high school students, graduates, post-docs, and undergraduates from physics, mechanical and electrical engineering, and material science will be involved in this project. Research experience and mentoring (EFRI-REM) will be offered through this research project to the students from Texas Academy of Math and Sciences. This project also includes close collaboration with the industry for student training and commercialization of the outcome of the research activities.Propagation of waves through a system of scatterers follows the reciprocity theorem which states that the transmission of a wave remains identical if the positions of the emitter and receiver are interchanged. The reciprocity follows from the fundamental property of the wave equation - time reversal symmetry. This project investigates a new mechanism of non-reciprocal or unidirectional propagation of sound in viscous medium. A common viewpoint is that while dissipation breaks time-reversibility, this is not sufficient to induce different transmission along two opposite directions. However, this is not valid in case of a viscous fluid. It will be shown that sound propagating in viscous medium through a phononic crystal with broken P-symmetry does not follow the reciprocity theorem. More specifically, we investigate how differential dissipation arising in the Navier-Stokes equation leads to significant non-reciprocal effects without the requirement of dynamic energy input, and expand that to new classes of non-reciprocal structures including non-reciprocal hyperbolic metamaterials. The transmission through a 2D disordered phononic crystal with non-reciprocity will also be studied. The presence of disorder in an individual scatterer results in localization of sound waves - an effect termed Anderson localization. This effect will be utilized to achieve encryption, which can be used to develop secure communication of acoustic signal both in air and water.