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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 12 — Jun. 11, 2007
  • pp: 7578–7590

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

Andrea Alù and Nader Engheta  »View Author Affiliations

Optics Express, Vol. 15, Issue 12, pp. 7578-7590 (2007)

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Following our recently developed idea of employing plasmonic covers to cloak an isolated conducting, plasmonic or insulating sphere through scattering cancellation, here we extend this concept by investigating the possibility of cloaking multiple objects placed in close proximity of each other, or even joined together to form a single object of large electrical size. We show how the coupling among the single particles, even when placed in the very near zone of each other, is drastically lowered by the presence of suitably designed covers, thus providing the possibility of making collections of objects transparent and “cloaked” to the impinging radiation even when the total physical size of the system is sensibly larger than the wavelength. Numerical simulations and animations validate these results and give further insights into the anomalous phenomenon of transparency and cloaking induced by plasmonic materials and metamaterials.

© 2007 Optical Society of America

OCIS Codes
(160.3900) Materials : Metals
(160.4670) Materials : Optical materials
(290.5850) Scattering : Scattering, particles

ToC Category:

Original Manuscript: April 20, 2007
Revised Manuscript: May 28, 2007
Manuscript Accepted: May 28, 2007
Published: June 5, 2007

Andrea Alu and Nader Engheta, "Cloaking and transparency for collections of particles with metamaterial and plasmonic covers," Opt. Express 15, 7578-7590 (2007)

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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 re-tuned to the desired value by slightly increasing the cover thickness or changing the plasma frequency of the cloaking material.

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