Hybrid elastic solids.
ABSTRACT Metamaterials can exhibit electromagnetic and elastic characteristics beyond those found in nature. In this work, we present a design of elastic metamaterial that exhibits multiple resonances in its building blocks. Band structure calculations show two negative dispersion bands, of which one supports only compressional waves and thereby blurs the distinction between a fluid and a solid over a finite frequency regime, whereas the other displays 'super anisotropy' in which compressional waves and shear waves can propagate only along different directions. Such unusual characteristics, well explained by the effective medium theory, have no comparable analogue in conventional solids and may lead to novel applications.
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ABSTRACT: We theoretically investigate the unusual transmission property of in-plane elastic waves through systems of isotropic elastic zero-index-metamaterials (ZIM) slab embedded with solid defects. Both double-zero-index-metamaterials (DZIM) and single-zero-index-metamaterials (SZIM) are examined. Particularly, mode conversion does not occur when either longitudinal (P) wave or transverse (S) wave is scattered by the defects in a specific type of DZIM possessing near zero reciprocal of shear modulus and near zero mass density . Thus, P wave and S wave can be controlled independently by simply adjusting the parameters of the defects to achieve high transmission (cloaking) and total reflection (blocking). And an analytic model is proposed to explain the mechanisms of the total reflection. On the other hand, enhanced transmission is observed for the SZIM systems. Our analysis shows that the enhanced transmission is due to resonant modes arisen in the defects. In addition, we suggest a two-dimensional (2D) phononic crystal (PC), which has effective double-zero-index, to provide the possibility of achieving the intriguing transmission properties experimentally.
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ABSTRACT: In this paper, we introduce an alternative model of elastic metamaterial by following the conceptual design of hybrid elastic solid reported by Lai and colleges . The proposed model is comprised of build-in resonant microstructures which are made of three kinds of conventional materials. Under specific incident frequencies, it behaves seemingly as a medium with negative mass density and elastic modulus so that a few novel wave propagation properties can be observed. We utilize finite element simulation to analyze the effective material parameters as well as the wave transmission properties. Comparing to the literatures, the proposed model appears larger band of practical application, and furthermore the required material is reduced which may be more easy to fabricate.Procedia Engineering 12/2014; 79. DOI:10.1016/j.proeng.2014.06.389
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ABSTRACT: We have investigated the Lamb wave propagation in cellular metamaterial plates constructed by bending-dominated and stretch-dominated unit-cells with the stiffness differed by orders of magnitude at an ultralow density. The simulation results show that ultralight metamaterial plates with textured stubs deposited on the surface can support strong local resonances for both symmetric and anti-symmetric modes at low frequencies, where Lamb waves at the resonance frequencies are highly localized in the vibrating stubs. The resonance frequency is very sensitive to the geometry of textured stubs. By reasonable design of the geometry of resonant elements, we establish a simple loaded-bar model with the array of oscillators having a gradient relative density (or weight) that can support multiple local resonances, which permits the feasibility of a broadband Lamb wave trapping. Our study could be potentially significant in designing ingenious weight-efficient acoustic devices for practical applications, such as shock absorption, cushioning, and vibrations traffic, etc.Scientific Reports 03/2015; 5:9376. DOI:10.1038/srep09376 · 5.08 Impact Factor