EFRI NewLAW: Reconfigurable pathways and directionality for sound using time-varying engineered materials

传播波（电磁波、光波、声波）是广泛应用于通信、计算、信号处理和传感系统的基本现象。然而，自然获得的材料基本上不允许波（尤其是声音）的单向传播，同时阻止反向传播。该奖项支持在工程材料中控制声波传播方向性的基础研究。该项目的成果将在多个领域产生巨大的社会影响——设计声波的方向性可以更好地降低环境噪声，改善医疗保健中的超声成像，基于无损声音的材料测试，甚至是通信系统的信号处理。这个研究项目结合了电气工程、物理和机械工程，为学生提供了一个独特的跨学科训练机会。这项努力还将有助于扩大妇女和少数民族学生对研究的参与，并将导致发展创新的教育和科学推广活动，本科生将大量参与。互易性是静止介质中声音传播的基本特征，其中时间反转的输出正好映射回输入。然而，对于信号保护和路由，以及信号屏蔽和隐形应用，构建隔离器和环行器需要非互易行为。因此，操纵材料表现出非互易性是一项重大的工程挑战，涉及从光学、电子到声学的各个物理领域。研究小组提出了一种新的概念，通过材料的时空调制与模式的色散工程相结合，实现非互反的声音传播。拟议的研究将在从纳米尺度到宏观尺度的三种不同的多物理平台上实验发展这一概念；包括结构化机电系统中声子与电磁波和声波的耦合，以及金刚石中氮空位中心等缺陷态。该团队最终将展示非互易单元细胞的1D/2D工程阵列如何创建新颖的、可重构的、单向的声音通路。这种方法的通用性使其在未来有可能直接扩展到光学和电磁领域。

Propagating waves (electromagnetic, light, sound) are the fundamental phenomena that are used in a very wide range of communication, computation, signal processing, and sensing systems. However, naturally obtained materials fundamentally do not allow one-way propagation of waves (especially sound) while blocking the reverse path. This award supports fundamental research for developing techniques to control the directionality of sound wave propagation in engineered materials. Results from this project will have large social impact in multiple areas -- engineering the directionality of sound waves can enable better environmental noise reduction, improvements in ultrasound imaging in healthcare, nondestructive sound-based testing of materials, and even signal processing for communication systems. This research project combines electrical engineering, physics, and mechanical engineering, offering students a unique interdisciplinary training opportunity. The effort will also help broaden participation of women and minority students in research, and will lead to development of innovative educational and scientific outreach activities, with significant involvement of undergraduate students.Reciprocity is a fundamental characteristic of sound propagation in stationary media, wherein time-reversed outputs map exactly back to the input. However, non-reciprocal behavior is required for building isolators and circulators for signal protection and routing, and for signal shielding and cloaking applications. Manipulating materials to exhibit non-reciprocity is thus a significant engineering challenge that extends across physical domains from optics, to electronics, to acoustics. The research team proposes a new concept for achieving non-reciprocal sound propagation, through spatio-temporal modulation of the material in conjunction with dispersion engineering of modes. The proposed research will experimentally develop the concept in three distinct multiphysical platforms spanning from nano-scale to macro-scale; including the coupling of phonons to electromagnetic and acoustic waves in structured electromechanical systems, and with defect states such as nitrogen vacancy centers in diamond. The team will ultimately demonstrate how 1D/2D engineered arrays of non-reciprocal unit cells can create novel, reconfigurable, unidirectional pathways for sound. The general nature of this approach potentially makes it directly extensible into optical and electromagnetic domains in the future.