Abstract
Elastic waves exhibit rich polarization characteristics absent in acoustic and electromagnetic waves. By designing a solid elastic metamaterial based on three-dimensional anisotropic locally resonant units, here we experimentally demonstrate polarization bandgaps together with exotic properties such as ‘fluid-like' elasticity. We construct elastic rods with unusual vibrational properties, which we denote as ‘meta-rods'. By measuring the vibrational responses under flexural, longitudinal and torsional excitations, we find that each vibration mode can be selectively suppressed. In particular, we observe in a finite frequency regime that all flexural vibrations are forbidden, whereas longitudinal vibration is allowed—a unique property of fluids. In another case, the torsional vibration can be suppressed significantly. The experimental results are well interpreted by band structure analysis, as well as effective media with indefinite mass density and negative moment of inertia. Our work opens an approach to efficiently separate and control elastic waves of different polarizations in fully solid structures.
Highlights
Elastic waves exhibit rich polarization characteristics absent in acoustic and electromagnetic waves
The elastic properties of our meta-rods are vastly different from rods made of traditional solid materials. They all arise through a simple mechanism: the anti-crossing between local resonances in metamaterial units and a certain vibration branch of the rod
For translational modes (TMs), the structure is quite similar to the design first reported by Liu et al.[26], that is, a spherical metal core evenly coated with a layer of silicone rubber, and embedded in an epoxy cube
Summary
Elastic waves exhibit rich polarization characteristics absent in acoustic and electromagnetic waves. We present the design and experimental realization of a type of three-dimensional locally resonant elastic metamaterial, which exhibits polarization bandgaps and ‘fluid-like’ elasticity Based on such metamaterials, we construct unique rod-shape structures, which we denote as ‘meta-rods’. We construct unique rod-shape structures, which we denote as ‘meta-rods’ By measuring their response functions for flexural, longitudinal and torsional vibrations, we demonstrate the selective suppression of these vibrations by polarization bandgaps and unprecedented elastic rod properties. Whereas in another configuration of the same metamaterial units, the meta-rod can significantly suppress the torsional vibration in a certain frequency regime These unusual characteristics revealed by experiments are well interpreted by band structures as well as effective medium theory that exhibits negative moment of inertia and indefinite mass densities
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