EFRI NewLAW: Dynamic Elastic media: Passive and Active non-Reciprocal Theory, Experiment and Design

波传播和信号传输中最基本的两个概念是密切相关的互易性原理和时间反转对称性原理。互易性要求沿一个方向传播的波也可以沿着相反的方向传播，而时间反转对称性在时间反转时提供了同样的关系。工程上的最新进展表明，在特殊条件下，例如在流动的流体和固体元素存在的情况下，可能会违反其中之一或两个原则。该奖项支持基础研究，以展示通过设计不同种类的声学、弹性和机电系统来实现非互易性的新方法。违反这些基本规则的技术可能会改变测量和利用声波和弹性波的标准操作程序。这项工作将这些新概念与强大的材料设计方法和添加剂制造专业知识相结合，以帮助国家重新引导S在声学、结构振动、超声波检测、地震防护和生物医学成像方面的技术进步。该奖项支持的研究工作特别为未被充分代表的本科生提供机会，通过在合作机构并行进行的多学科项目参与知识获取和探索。要考虑打破线性系统中的时间反转对称性的一种方法是基于对具有空间不对称微观结构的声学和弹性介质在快、慢时间尺度上使用激励来动态耦合动量和应变。由泵浦激励产生的振荡提供了准静态动量偏置，使得非互易信号传播成为可能。实现非互易响应的其他途径包括从驱动频率到高次谐波的弹性非线性上转换。利用例外点与阻尼之间的一种未知的强大关系，我们将研究弹性波导中的最优阻尼和吸收。其他有待研究的领域包括通过分流压电元件和混合时变电路进行主动控制。材料设计是离开项目的中心，以期有效地探索设计空间，并采用最先进的添加剂制造技术来开发这些结构的最佳微结构拓扑。

Two of the most fundamental concepts in wave propagation and signal transmission are the closely related principles of reciprocity and time-reversal symmetry. Reciprocity requires that a wave traveling in one direction can just as well travel in the opposite direction, while time-reversal symmetry provides the same relationship when time is reversed. Recent advances in engineering have shown that either or both principles can be violated under special conditions, for instance in the presence of moving fluid and solid elements. This award supports fundamental research to demonstrate novel methods for realizing non-reciprocal behavior through the design of heterogeneous acoustic, elastic, and electro-mechanical systems. Technology that violates these fundamental rules opens the possibility of changing the standard operating procedures for measuring and utilizing acoustic and elastic waves. The work pairs these new concepts with robust materials design methodologies and additive manufacturing expertise to help redirect the nation?s technological advances in acoustics, structural vibration, ultrasonic inspection, seismic protection, and biomedical imaging. Research efforts supported in this award specifically provide opportunities for underrepresented undergraduate students to participate in knowledge acquisition and exploration via multidisciplinary projects conducted in parallel at the collaborating institutions.One approach to breaking time-reversal symmetry in linear systems to be considered is based on the dynamic coupling of momentum and strain using excitation on fast and slow time scales for acoustic and elastic media with spatially asymmetric microstructure. Oscillations from a pump excitation provide a quasi-static momentum bias that enables non-reciprocal signal propagation. Other routes to achieving non-reciprocal response include elastically nonlinear up-conversion from the drive frequency to higher harmonics. Optimal damping and absorption in elastic waveguides, using an unexplored powerful relation between exceptional points and damping, will be examined. Other areas to be investigated include active control via shunted piezoelectric elements and hybrid time-varying circuits. Materials design is at the center of the DEPARTED project with a view towards efficient design space exploration and employing state-of-the art additive manufacturing techniques to develop optimal microstructural topology of these structures.