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

学院早期职业发展(Career)计划补助金的目标是能够设计用于声波和弹性波控制的创新的非线性超材料，并在预先设计的几组互补功能之间进行可逆切换。通过使用内部材料非线性作为工具，使波浪控制策略能够将材料系统的定性动态响应与入射波的特征相耦合。该方法将产生第一个全面和通用的平台，以设计广泛的可编程超材料架构系列，这些架构可以重新配置其对不同外部调谐参数的响应，或自主调整其性能以适应不断变化的操作和环境条件。这种功能切换是在材料系统中没有宏观形状或尺寸变化的情况下实现的，从而允许将它们用作集成的结构元件。该方法非常适合于重要的工程应用，包括振动控制、防爆、声音操纵以及水下机器人和结构的隐身。该项目将促进激光测振技术用于复杂几何结构的动态测试，并将开发基于可视化的新教学工具，以简化结构动力学和声学领域的学习经验。研究战略围绕非线性诱导模式混合的思想。通过高次谐波的产生，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，即使在受到低频激励的情况下，系统也会经历多种模式的混合，并显示出通常与高频制度相关的行为。非线性的可逆激活和去激活是通过外部参数调节或作为对激励幅度变化的自发响应来获得的。研究小组将对广泛的候选超材料结构进行建模，包括颗粒状晶体和柔软的多孔材料，同时识别最佳配置和提供对观察到的现象的机械洞察。将使用3D激光测振仪进行实验测试，以验证理论结果，并评估诱导波操纵效应的可测量性和幅度。

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.