Hybrid elastic solids

Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Nature Material (Impact Factor: 36.5). 06/2011; 10(8):620-4. DOI: 10.1038/nmat3043
Source: PubMed


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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Available from: Pai Peng, Jun 12, 2014
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    • "To obtain low frequency band gaps, the insertion in the microstructure of local resonators generally made of a hand core surrounded by a soft coating has been proved effective. In fact, the locally resonant material may exhibit the emergence of stop bands at frequencies around the natural frequency of the resonator with overall negative mass density and bulk modulus (see for instance Liu et al., 2000, Huang et al., 2009a, b, Lai et al., 2011, Raghavan and Srikantha Phani, 2013, Krushynska et al., 2014). Chiral periodic metamaterials with internal locally resonant structures supporting tunable low-frequency stop bands have been recently proposed by Liu et al., 2011a, Bigoni et al., 2013, and Zhu et al., 2014. "
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    ABSTRACT: A simplified model of periodic chiral beam-lattices containing local resonators has been formulated to obtain a better understanding of the influence of the chirality and of the dynamic characteristics of the local resonators on the acoustic behavior. The simplified beam-lattices is made up of a periodic array of rigid heavy rings, each one connected to the others through elastic slender massless ligaments and containing an internal resonator made of a rigid disk in a soft elastic annulus. The band structure and the occurrence of low frequency band-gaps are analysed through a discrete Lagrangian model. For both the hexa- and the tetrachiral lattice, two acoustic modes and four optical modes are identified and the influence of the dynamic characteristics of the resonator on those branches is analyzed together with some properties of the band structure. By approximating the generalized displacements of the rings of the discrete Lagrangian model as a continuum field and through an application of the generalized macro-homogeneity condition, a generalized micropolar equivalent continuum has been derived, together with the overall equation of motion and the constitutive equation given in closed form. The validity limits of the micropolar model with respect to the dispersion functions are assessed by comparing the dispersion curves of this model in the irreducible Brillouin domain with those obtained by the discrete model, which are exact within the assumptions of the proposed simplified model.
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    • "Meanwhile, the concept of metamaterials has been extended to acoustic and elastic media. Much effort has been focused on negative index of refraction [15] [16] [17] [18] [19], sub-wavelength imaging [20] [21], and transformation acoustic [22] [23] [24] [25] [26] [27] [28]. Recently, acoustic ZIM have also drawn intense attention and various schemes have been proposed to realize them, such as acoustic waveguides loaded with membranes and/or Helmholtz resonator [29] [30] [31], coiling up space with curled channels [32] [33], and 2D acoustic crystals with Dirac-like cones [34] [35] [36] [37]. "
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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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    • "This model provided richer applications than other model reported so far but the microstructure is more complex due to the lack of symmetry. In this letter, we follow the same concept [17] to propose an alternative design of anisotropic elastic metamaterials with simpler constituents but better functionality. Numerical method is performed to analyze the effective parameters and wave propagation characteristics through the text. "
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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 [17]. 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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