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Acoustic metamaterials that allow low-frequency band gaps are interesting for many practical engineering applications, where vibration control and sound insulation are necessary. In most prior studies, the mechanical response of these structures has been described using linear continuum approximations. In this work, we experimentally and theoretically address the formation of low-frequency band gaps in locally resonant granular crystals, where the dynamics of the system is governed by discrete equations. We investigate the quasi-linear behavior of such structures. The analysis shows that a stopband can be introduced at about one octave lower frequency than in materials without local resonances. Broadband and multi-frequency stopband characteristics can also be achieved by strategically tailoring the non-uniform local resonance parameters. V C 2013 AIP Publishing LLC. [http://dx

Collective plasmonic modes in two- and three-dimensional periodic assemblies of metallic nanoshells are studied by means of full electrodynamic calculations using the layer-multiple-scattering method. We consider structures made of a single type of nanoshell as well as binary heterostructures made of two different types of nanoshells. The complex photonic band structure of such three-dimensional photonic crystals is analyzed in conjunction with relevant transmission diagrams of corresponding finite slabs and the physical origin of the different optical modes is elucidated. Moreover, we discuss associated absorption spectra and provide a consistent interpretation of the underlying physics. In the case of the binary systems, the plasmonic modes of the two building components coexist, leading to a rich structure of resonances over an extended frequency range and to broadband absorption.

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Plasmonic excitations in two-and three-dimensional ordered assemblies of metal-dielectric-metal nanosandwiches are studied by means of full-electrodynamic calculations using the layer-multiple-scattering method. Plasmon hybridization results in collective electric-dipole-like and magnetic-dipole-like resonant modes, which are directly controlled by the lattice constant and the geometrical characteristics of the building units. It is shown that, in planar arrays of such composite nanoparticles on a dielectric substrate, the magnetic resonance induces a negative effective permeability, as large as −2, which can be tuned within the range of near-infrared and visible frequencies. However, as successive layers are stacked together to build a three-dimensional crystal, the region of negative effective permeability shrinks and disappears for relatively thick slabs. Our analysis demonstrates that the complex photonic band structure is a valuable tool in the study of threedimensional metamaterials and their effective-medium description.