CAREER: Adaptive Acoustic Metamaterials with Switchable Functionality: A Design Platform Enabled by Nonlinearity

这项教师早期职业发展（Career）计划的目标是为声学和弹性波控制设计创新的非线性超材料，并在预先设计的互补功能集之间进行可逆切换。采用材料内部非线性作为载体，将材料系统的定性动态响应与识别冲击波的特性相耦合，从而实现了波控制策略。该方法将产生第一个全面和通用的平台，用于设计广泛的可编程超材料体系结构，可以重新配置它们对不同外部调谐参数的响应，或者自主调整它们的性能以适应不断变化的操作和环境条件。这种功能转换在材料系统中没有宏观形状或尺寸变化的情况下实现，从而允许它们作为集成结构元素使用。该方法非常适合于重要的工程应用，包括振动控制，爆炸保护，声音操纵，水下航行器和结构的隐身。该项目将推广使用激光测振仪进行复杂几何结构的动态测试，并将开发新的基于可视化的教学工具，以简化结构动力学和声学领域的学习经验。研究策略围绕非线性诱导模态混合的思想。通过产生高次谐波，非线性晶体的动态响应可以跨越多种可用的波传播模式；因此，即使在低频激励下，系统也会经历各种模态形状的混合，并显示出与高频状态相关的典型行为。非线性的可逆激活和失活可以通过外部参数调谐或作为对激励幅度变化的自发响应来实现。研究团队将建立一个广泛的候选超材料结构模型，包括颗粒晶体和软细胞材料，具有确定最佳配置和提供观察到的现象的机制洞察力的双重范围。将使用3D激光测振仪进行实验测试，以验证理论发现，并评估诱导波操纵效应的可测量性和强度。

The objective of this Faculty Early Career Development (CAREER) Program grant is to enable the design of innovative nonlinear metamaterials for acoustic and elastic wave control with reversible switching between pre-designed sets of complementary functionalities. The wave control strategy is enabled by the use of internal material nonlinearities as a vehicle to couple the qualitative dynamic response of the material system to distinguishing characteristics of the impinging wave. The approach will result in the first comprehensive and versatile platform to design broad families of programmable metamaterial architectures that can reconfigure their response to different external tuning parameters, or autonomously adapt their performance to evolving operational and environmental conditions. This functional switching is achieved without macroscopic shape or size changes in the material systems, thereby allowing their use as integrated structural elements. The approach is well suited for important engineering applications including vibration control, blast protection, sound manipulation, and cloaking of underwater vehicles and structures. The project will promote the use of laser vibrometry for dynamic testing of structures with complex geometries, and will develop new visualization-based teaching tools for simplifying the learning experience in the fields of structural dynamics and acoustics.The research strategy revolves around the idea of nonlinearity-induced modal mixing. Through the generation of higher harmonics, the dynamic response of a nonlinear crystal can undergo jumps across the multiple available wave propagation modes; as a result, the system experiences a blend of mode shapes and displays a behavior that is typically associated with high-frequency regimes even while subjected to low-frequency excitations. The reversible activation and deactivation of nonlinearity is obtained either via external parameter tuning or as a spontaneous response to changes in the amplitude of excitation. The research team will model a broad spectrum of candidate metamaterial architectures, including granular crystals and soft cellular materials, with the double scope of identifying optimal configurations and providing a mechanistic insight in the observed phenomena. Experimental tests using a 3D laser vibrometer will be conducted to validate the theoretical findings and assess the measurability and magnitude of the induced wave manipulation effects.