Metamaterials With Independently Tunable Acoustic Properties
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Abstract: Waves are a ubiquitous natural phenomenon that transport energy between two points in space. In mechanical systems, wave propagation is the result of the interplay between inertial, elastic and dissipative influences of the supporting medium; changing these properties affects the wave characteristics (e.g., frequency, wavelength, velocity, etc). In recent years, architected metamaterials have emerged as a platform to achieve custom wave propagation via a cleverly designed internal architecture. Metamaterials mimic the atomistic architecture of conventional materials at a more accessible scale, overcoming natural limitations (e.g., chemistry). As a result, fantastic new applications for metamaterials have emerged including wave guiding and filtering, cloaking devices, energy absorption, etc. However, the bulk of available metamaterial designs involve passive elements that fix properties upon fabrication. This limits the functionality of the metamaterial, making it a less suitable choice for applications where dynamic requirements may change, e.g., in unpredictable environments. Consequently, researchers have employed active elements (e.g., piezo-electric) or exploited geometric instability or multi-stability in the metamaterial architecture to enable post-fabrication tuning. The addition of a tuning capability has significantly expanded the range of metamaterial performance, however, most of the available designs achieve change in only a single property, most commonly the stiffness, which may involve significant structural deformation. Since inertia and dissipation also play a significant role in determining the material dynamics, methods to customize these properties post-fabrication in addition to the stiffness are necessary to take full advantage of the relevant properties to further expand and diversify the material functionality. Thus, a holistic approach combining effects of changing multiple material properties simultaneously, independently, and with minimal structural deformation, to control acoustic behavior motivates this project.
In this presentation, we present a novel metamaterial design incorporating (geometric) multi-stability and kinematic amplification to independently tune the effective mass, damping, and stiffness without any residual distortion, impacting the dynamic response. We perform analytical and numerical analysis on a 1D/2D metamaterial (readily extended to 3D) and the dispersion responses reveal the ability of our metamaterial to capture multiple effects such as inertial amplification, metadamping, long-wave speed of sound, previously seen in isolation. These effects translate to a diverse set of acoustic responses allowing us to control the position, width and directionality (2D/3D) of frequency and wavenumber bandgaps. Furthermore, the more multi-stable elements in the unit cell, the deeper the set of acoustically unique configurations to choose from. The proposed strategy broadens the property set available for tuning acoustic metamaterial performance post-fabrication.
Citation: V. Ramakrishnan and M.J.Frazier, “Metamaterials With Independently Tunable Acoustic Properties”, at ASME IMECE 2022, Columbus, OH, October 31 - November 3, 2022.