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Novel Electromagnetic Metamaterials

Negative Index Metamaterials


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1-) Theoretical Formulation for an Electrically Small Microstrip Patch Antenna Loaded with Negative Index Materials
by J. S. Petko and D. H. Werner
2005 IEEE Antenna and Propagation Society International Symposium, Vol. 3B, pp. 343 - 346, 3-8 July 2005

ABSTRACT: There has been a considerable amount of recent interest in the class of composite metamaterials that possess simultaneously negative permeability and permittivity, causing them to exhibit a negative index of refraction [1,2]. This type of metamaterial is known as a Negative Index Material (NIM). An application of NIMs to increasing the power radiated from electrically small antennas has been suggested by Ziolkowski and Kipple [3]. Moreover, Engheta recently proposed in [4] the use of NIMs to design thin sub-wavelength cavity resonators. It was found that a miniature resonator could be created by filling the cavity with a region of NIM and a region of conventional Positive Index Material (PIM), leading to a “resonance condition” dependent upon the permeabilities of the two embedded materials. In this paper we expand on this principle by introducing a method to miniaturize a circular microstrip patch antenna that uses NIM loading. This is accomplished by including two distinct regions inside the cavity of a microstrip patch antenna, one consisting of a NIM and one consisting of a conventional PIM. By applying the boundary conditions commonly associated with the cavity model of a patch antenna, a “resonance condition” is found that is dependent only on the permittivities of the two embedded substrate materials.

2-) Nanosphere dispersed liquid crystals for tunable negative–zero–positive index of refraction in the optical and terahertz regimes
by I. C. Khoo, D. H. Werner, X. Liang, A. Diaz and B. Weiner

ABSTRACT: An analysis of aligned nematic liquid crystal cells containing core-shell nanospheres shows that it is possible to devise a new type of metamaterial whose index of refraction is tunable from negative, through zero, to positive values. The design parameters for the constituents can be scaled for application in the optical as well as very long wavelength (e.g., terahertz and microwave) regions.

3-) Near-infrared metamaterials with dual-band negative-index characteristics
by Do-Hoon Kwon, Douglas H.Werner, Alexander V. Kildishev and Vladimir M. Shalaev
Optics Express, Vol. 15, No. 4, 19 February 2007.

ABSTRACT: Dual-band negative-index metamaterial designs in the near-infrared frequency range are presented and their performance is analyzed using a full-wave numerical electromagnetic scattering method. Negative effective permittivity is provided by a thin layer of metallic film. Negative effective permeabilities are supplied in two distinct frequency bands by magnetic resonators of different dimensions.

4-) Liquid crystal clad near-infrared metamaterials with tunable negative-zero-positive refractive indices
by Douglas H. Werner, Do-Hoon Kwon, Iam-Choon Khoo, Alexander V. Kildishev and Vladimir M. Shalaev
Optics Express, Vol. 15, No. 6 , 19 March 2007.

ABSTRACT: Near-infrared metamaterials that possess a reconfigurable index of refraction from negative through zero to positive values are presented. Reconfigurability is achieved by cladding thin layers of liquid crystal both as a superstrate and a substrate on an established negative-index metamaterial, and adjusting the permittivity of the liquid crystal. Numerical results show that the index of refraction for the proposed structure can be changed over the range from -1 to +1.8 by tuning the liquid crystal permittivity from 2 to 6 at a wavelength of 1.4 µm.

5-) Tunable optical negative-index metamaterials employing anisotropic liquid crystals
by Xiande Wang, Do-Hoon Kwon, Douglas H. Werner, Iam-Choon Khoo, Alexander V. Kildishev and Vladimir M. Shalaev
Applied Physics Letters, 91, 143122 (2007).

ABSTRACT: A full-wave analysis technique based on the finite element-boundary integral method is developed and used to rigorously treat the scattering from periodically structured metamaterials incorporating anisotropic liquid crystals (LCs) and dispersive materials. Reconfiguration of the negative-index metamaterials is achieved by controlling the magnetic resonance via tuning permittivity of the embedded anisotropic LCs. Numerical results show that the refractive index of the metamaterials can be reconfigured by tuning the director orientation of anisotropic LCs or by using temperature-dependent LCs. The design configurations and their characteristics in the near- and the mid-infrared ranges are presented.

6-) Stochastic optimization of low-loss optical negative-index metamaterial
by Alexander V. Kildishev, Uday K. Chettiar, Zhengtong Liu, Vladimir M. Shalaev, Do-Hoon Kwon, Zikri Bayraktar, and Douglas H. Werner
JOSA B, Vol. 24, Issue 10, pp. A34-A39, published in Feature Issue on Photonic Metamaterials (2007).

ABSTRACT: Optical metamaterial consisting of metal-dielectric composites creates a complicated system that is not amenable to analytical solutions. This presents a challenge in optimizing these intricate systems. We present the application of three nature-inspired stochastic optimization techniques in conjunction with fast numerical electromagnetic solvers to yield a metamaterial that satisfies a required design criterion. In particular, three stochastic optimization tools (genetic algorithm, particle swarm optimization, and simulated annealing) are used for designing a low-loss optical negative index metamaterial. A negative refractive index around -0.8+0.2i is obtained at a wavelength of 770 nm. The particle swarm optimization algorithm is found to be the most efficient in this case.

7-) Low Loss Planar Negative Index Metamaterials for the Mid-Infrared Based on Frequency Selective Surfaces
by Jeremy A. Bossard, Do-Hoon Kwon, Yan Tang, Douglas H. Werner, and Theresa S. Mayer
2007 IEEE Antennas and Propagation International Symposium, pp. 2873 - 2876, 9-15 June 2007.

8-) Tunable Frequency Selective Surfaces and Negative-Zero-Positive Index Metamaterials Based on Liquid Crystals
by Jeremy A. Bossard, Xiaotao Liang, Ling Li, Seokho Yun, Douglas H. Werner, Brian Weiner, Theresa S. Mayer, Paul F. Christman, Andres Diaz, and I. C. Khoo
IEEE Transactions on Antennas and Propagation, Vol. 56, No. 5, pp. 1308 - 1320, May, 2008.

ABSTRACT: We utilize the properties of aligned nematic liquid crystal (LC) cells in the design of: (i) a new type of metamaterial whose index of refraction is tunable from negative, through zero, to positive values and (ii) micron-scale metallodielectric and all-dielectric tunable frequency selective surfaces (FSSs). The metamaterial is constructed by randomly doping a liquid crystal substrate with coated dielectric (non-magnetic) spheres and can be utilized over a large spectral range. FSSs with a liquid crystal superstrate are synthesized using conventional and genetic algorithm methods to exhibit broadband tunable filter characteristics at mid-infrared (mid-IR) wavelengths. These LC tunable FSS structures can be used to develop a new class of infrared/optical switches for terahertz applications.

9 -) Material parameter retrieval procedure for general bi-isotropic metamaterials and its application to optical chiral negative-index metamaterial design
Do-Hoon Kwon, Douglas H. Werner, Alexander V. Kildishev, and Vladimir M. Shalaev
Optics Express, Vol. 16, Issue 16, pp. 11822-11829, July 23, 2008.

ABSTRACT: A chiral optical negative-index metamaterial design of doubly periodic construction for the near-infrared spectrum is presented. The chirality is realized by incorporating sub-wavelength planar silver-aluminasilver resonators and arranging them in a left-handed helical (i.e., stair-step) configuration as a wave propagates through the metamaterial. An effective material parameter retrieval procedure is developed for general bi-isotropic metamaterials. A numerical design example is presented and the retrieved effective material parameters exhibiting a negative index of refraction are provided.

10-) Synthesizing low loss negative index metamaterial stacks for the mid-infrared using genetic algorithms
Jeremy A. Bossard, Seokho Yun, Douglas H. Werner, and Theresa S. Mayer
Optics Express, Vol. 17, Issue 17, pp. 14771-14779, 17 August 2009.

ABSTRACT: Negative index metamaterial designs for the mid-infrared with low absorption and impedance mismatch losses are presented. A robust genetic algorithm is employed to optimize the flexible metamaterial structure for targeted refractive index and impedance values. A new figure of merit is introduced to evaluate the impedance match of the metamaterial to free space. Two designs are presented demonstrating low-loss characteristics for a thin metamaterial with two metal screens and a thick metamaterial stack with five screens. The device performance is analyzed when adding more screens to the structure, revealing that optimizing a thick stack produces a metamaterial with properties approaching those of a bulk material.

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