Affiliated with the
Communication & Space
Sciences Laboratory

Novel Electromagnetic Metamaterials

Electromagnetic Cloaking

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..: References :..

1-) Two-dimensional eccentric elliptic electromagnetic cloaks
by Do-Hoon Kwon and Douglas H. Werner
Applied Physics Letters, 92, 013505, January 4, 2008.

ABSTRACT: A spatial transformation technique is applied to an important class of two-dimensional electromagnetic cloaks that do not possess rotational symmetry around the longitudinal axis. These cloaks are based on an eccentric elliptic annular geometry, which represents a generalization of previously published cloaking configurations. The required material properties of the cloak are derived in terms of the geometrical parameters and the coordinates in the transformed system. The validity of the cloak parameters is verified by a full-wave finite-element simulation of plane wave scattering from uncloaked and cloaked perfectly conducting cylinders with elliptic cross section. Go

2-) Near-infrared metamaterial films with reconfigurable transmissive/reflective properties
by Do-Hoon Kwon, Xiande Wang, Zikri Bayraktar, Brian Weiner and Douglas H. Werner
Optics Letters, Vol. 33, No. 6, pp. 545 - 547, March 15, 2008.

ABSTRACT: A near-infrared metamaterial design that is reconfigurable between almost completely transmissive and reflective states is presented. The reconfiguration is enabled by tuning the anisotropic nematic liquid crystals used as a spacer layer between two silver nanoplates in a planar doubly periodic metamaterial. The design is optimized for maximum difference in transmittance between the two states by using a genetic algorithm. For a linearly polarized illumination at normal incidence, full-wave electromagnetic analysis predicts that the optimized metamaterial film can change the transmittance between 98.7% and 0.1% at a wavelength of 1.1 µm. Go

3-) Two-dimensional electromagnetic cloak having a uniform thickness for elliptic cylindrical regions
by Do-Hoon Kwon and Douglas H. Werner
Applied Physics Letters, 92, 113502 (2008).

ABSTRACT:A two-dimensional electromagnetic cloak recipe having a uniform thickness is presented for cloaked regions of elliptic cylindrical shape. The cloak material parameters are obtained from the spatial transformation approach. The effectiveness of the cloak design is verified by full-wave simulations of plane wave scattering from uncloaked and cloaked conducting elliptic cylinders. The proposed design provides a more practical cloak geometry when compared to previous designs that have the outer boundary limited only to a scaled version of the inner boundary. Go

4-) Restoration of antenna parameters in scattering environments using electromagnetic cloaking
by Do-Hoon Kwon and Douglas H. Werner
Applied Physics Letters, 92, 113507 (2008).

ABSTRACT: It is proposed that electromagnetic cloaks be used as effective shielding devices which enable improved antenna performance in highly scattering, multiple-antenna environments. In multiple frequency, multiple-antenna environments, each antenna is enclosed in a dispersive cloak that is designed to operate at the transmitting frequencies of the neighboring antennas. The loading effect of large objects in close proximity to a radiating antenna can be removed by enclosing the scatterer with a cloak. Application of cloaks to microwave antenna shielding only requires narrow band performance, which can be realized using currently available metamaterials technology. Go

5-) Genetic Algorithm Synthesis of Planar Zero Index Metamaterials for the Infrared with Application to Electromagnetic Cloaking
Jeremy A. Bossard, Yan Tang, Douglas H. Werner, and Theresa S. Mayer
2007 IEEE Antennas and Propagation International Symposium, pp. 5555 - 5558, 9-15 June 2007.

ABSTRACT: A planar metamaterial structure using a single Ag FSS screen sandwiched between layers of polyimide was proposed that is straightforward to fabricate. This structure was optimized by a GA to have a low/zero index of refraction with high transmission in the far-IR. Measured dielectric and metallic properties incorporation into the model provide confidence that the PMM predictions are accurate. Fabrication constraints in the GA ensured that the design result can be fabricated. Experimental efforts are currently underway to characterize this design for the predicted ZIM properties.

6-) An infrared invisibility cloak composed of glass
by Elena Semouchkina, Douglas H. Werner, George B. Semouchkin, and Carlo Pantano
Applied Physics Letters, 96, 233503 (2010).

ABSTRACT: We propose to implement a nonmetallic low-loss cloak for the infrared range from identical chalcogenide glass resonators. Based on transformation optics for cylindrical objects, our approach does not require metamaterial response to be homogeneous and accounts for the discrete nature of elementary responses governed by resonator shape, illumination angle, and inter-resonator coupling. Air fractions are employed to obtain the desired distribution of the cloak effective parameters. The effect of cloaking is verified by full-wave simulations of the true multiresonator structure. The feasibility of cloak fabrication is demonstrated by prototyping glass grating structures with the dimensions characteristic for the cloak resonators. Go

7-) Exploiting Metasurface Anisotropy for Achieving Near-perfect Low-profile Cloaks Beyond The Quasi-static Limit
by Zhi Hao Jiang and Douglas H. Werner
Journal of Physics D: Applied Physics, 46, 505306 (2013).

ABSTRACT: In this paper, we report an approach for achieving near-perfect low-profile electromagnetic cloaking beyond the quasi-static limit. In contrast to previous works on metasurface cloaks where only the Leontovich surface impedance boundary condition has been considered, we employ a second-order surface impedance boundary condition to account for the radial response of the proposed anisotropic metasurfaces. This radial surface polarizability tensor parameter can be tailored to eliminate the higher order scattering modes. It is shown from analytical expressions that for a moderate-sized perfect electric conducting or dielectric cylinder (~0.4λ0 in width), near-perfect scattering reduction, i.e. >98%, can be achieved by a single anisotropic metasurface with non-vanishing radial response, which is far superior to the conventional scalar impedance surface. A practical design of the metasurface is also presented and further validated by full-wave simulations. The physical mechanism of the metasurface cloaks is investigated in detail, revealing that the radiation cancellation of the induced surface currents is responsible for the scattering reduction. Importantly, it is shown that in addition to a 'low-visibility coating', the metasurface also functions to provide induced current enhancement which would be beneficial for the operation of a 'cloaked sensor'. These findings will broaden the usage of metasurfaces to applications ranging from scattering reduction to noninvasive probing for objects beyond the quasi-static limit. Go

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