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

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

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.