Metamaterial with Independently Tunable Mass, Damping and Stiffness

Abstract: Over the past decades, metamaterials – whose engineered internal architecture grants unusual or extraordinary macroscopic response – have garnered increasing attention from researchers as the desire to shape material behavior beyond natural limitations (e.g., chemistry) arises within several areas of materials science and engineering. For acoustic metamaterials, the clever design of the small-scale architecture – which regulates the propagation of supported mechanical waves – has elicited such exotic properties as negative effective mass, stiffness, and refractive index, and made plausible such fantastic applications as sub-wavelength imaging, cloaking, and topological insulation in addition to wave focusing, filtering, and guiding. The bulk of reported acoustic metamaterial architectures are passive such that their properties and functions are fixed at fabrication. Nevertheless, a tuning capacity is desirable, not only to allow for adaptation in the face of potentially changing service requirements, but also to expand the range of response, in general. Several strategies have been proposed to tune acoustic metamaterials post-fabrication: piezoelectric controllers, precompression, hydration, geometric instability and multi-stability, etc. Nevertheless, despite the diversity of approach and the significance of inertial and dissipative effects in elastodynamics, most studies realize tuning via modifications to the stiffness parameter alone, often requiring significant metamaterial distortion. Moreover, the use of special, stimuli responsive constituents necessarily restrict metamaterial architectures to specific compositions. In this presentation, we present a novel implementation of unit cell (geometric) bi-stability and kinematic amplification to independently tune the value and distribution of the effective mass, stiffness, and viscous damping within metamaterial architectures by purely geometric means (and without distortion) which impacts the dynamic response. We demonstrate the effectiveness of our strategy through analytical and numerical investigations of the dynamics of a 1D system (readily extended to 2D/3D). We show that the frequency band structure depends on the specific configurations of the bi-stable elements: opening, sifting, and closing band gaps. As the number of bi-stable elements per unit cell increase, so to do the number of unique dynamic responses from which to choose. The proposed strategy significantly expands the property set available for tuning acoustic metamaterial performance post-fabrication.

Citation: V. Ramakrishnan and M.J.Frazier, “Metamaterial with Independently Tunable Mass, Damping and Stiffness”, at EMI 2022, Baltimore, MD, May 31 - June 3, 2022.