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

波传播和信号传输中的两个最基本的概念是相互作用和时间反演对称性的密切相关的原则。 互易性要求波在一个方向上传播也可以在相反的方向上传播，而时间反演对称性在时间反转时提供了相同的关系。 工程学的最新进展表明，在特殊条件下，例如在存在运动的流体和固体元素的情况下，可以违反其中一个或两个原则。 该奖项支持基础研究，以展示通过设计异质声学，弹性和机电系统实现非互易行为的新方法。 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增材制造专业知识相结合，以帮助重新引导国家？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代表性不足的本科生提供了机会，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。要考虑的线性系统中的反向对称性是基于动量和应变的动态耦合，使用声学和弹性介质的快和慢时间尺度上的激励，空间不对称微结构。 来自泵浦激励的振荡提供准静态动量偏置，其使得能够进行非互易信号传播。 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变频。 最佳阻尼和吸收弹性波导，使用未探索的强大的例外点和阻尼之间的关系，将被检查。其他有待研究的领域包括通过并联压电元件和混合时变电路的主动控制。 材料设计是DEPARTED项目的中心，旨在实现有效的设计空间探索，并采用最先进的增材制造技术来开发这些结构的最佳微观结构拓扑。

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.