Cloaking and transparency for collections of particles with metamaterial and plasmonic covers

Optics Express

Volumn 15, Issue 12, 2007, Pages 7578-7590

  Alù, Andrea ^a   Engheta, Nader ^a  

^a UNIVERSITY OF PENNSYLVANIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

COMPUTER SIMULATION; CONDUCTIVE MATERIALS; INSULATING MATERIALS; LIGHT SCATTERING;

CLOAKING; INSULATING SPHERE; METAMATERIAL;

PLASMONS;

EID: 34250174199     PISSN: None     EISSN: 10944087     Source Type: Journal    
DOI: 10.1364/OE.15.007578     Document Type: Article

References (19)

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18. We understand that a material like the one considered here, with combined plasmonic properties and magnetic permeability higher than that of free space, may not be readily available in nature. However, here and in [2] we are mainly concerned in showing the fundamental theoretical possibilities of this cloaking technique. In the present simulations, therefore, we have employed a sample cover that may simultaneously cancel two multipolar orders (i.e., electric dipole and magnetic dipole moments), requiring electric and magnetic parameters different from those of the background. In different cases, or for different purposes, however, as shown in [1], [3], it may be enough to rely just on plasmonic materials with required permittivity (with no magnetic response, i.e., with relative permeability of unity), which may be available in different ranges of frequencies. Moreover, the material suggested here may be fabricated in some frequency range, in order to have required values of permittivity and permeability. Distinctly from other proposed techniques for metamaterial cloaking, the examples reported here rely on isotropic and homogeneous materials or metamaterials.
19. Heuristically, we may justify this down-shift in the cloaking frequency for the horizontal polarization, when the objects touch or are merged together, with the following considerations: in the horizontal polarization the electrical contact and the resulting current flow between the two objects may generate an electric dipole moment somehow larger than those of two separate objects. Therefore, for the same cover geometry and material, a slightly lower frequency provides a closer-to-zero permittivity for the material cover, or effectively a larger induced "opposite" dipole moment that may cancel the increase in the dipole moment scattered by the merged object. In reality, the dynamics is more complex than this simple picture, due to contributions from higher-order multipoles and interactions between the object and the cover, but the results in Fig. 1-2 appears to be consistent with this explanation. The cloaking frequency may be easily retuned to the desired value by slightly increasing the cover thickness or changing the plasma frequency of the cloaking material.