Affiliated with the
Communication & Space
Sciences Laboratory

Novel Electromagnetic Metamaterials

Zero Index Metamaterials


..: References :..

1-) Synthesis of low / zero index of refraction metamaterials from frequency selective surfaces using genetic algorithms
by M.A. Gingrich and D.H. Werner
IEE Electronics Letters,
Vol. 41, No. 23, November 10, 2005.

ABSTRACT: Presented is a new means of synthesising thin, planar low or zero index metamaterials (LIM / ZIM) via frequency selective surfaces (FSS), the parameters of which are optimised using a genetic algorithm. FSS-based LIM / ZIM possess advantages such as light weight, ease of fabrication, low loss, and are readily scalable in frequency.

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
Optics Letters, Vol. 31, No. 17, pp. 2592 - 2594, September 1, 2006.

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-) Zero index metamaterials with checkerboard structure
D.-H. Kwon, L. Li, J.A. Bossard, M.G. Bray and D.H. Werner
IEE Electronics Letters,
Volume 43, Issue 6, pp. 9-10, March 15, 2007. .

ABSTRACT: A metamaterial design is presented with an effectively zero index of refraction, which utilises Drude-type material blocks arranged in a checkerboard pattern within a nondispersive dielectric host. An averaging effect over constituent materials of the checkerboard structure yields an effective permittivity that approaches zero. This results in a metamaterial with a zero index of refraction and a high intrinsic impedance. A design example and the associated effective medium parameters are provided.

4-) Low-index metamaterial designs in the visible spectrum
D.-H. Kwon, and D.H. Werner
Optics Express,
Vol. 15, Iss. 15, pp. 9267-9272, July 23, 2007. .

ABSTRACT: Low-index metamaterial designs in the visible spectrum that are impedance matched to free space are presented. The unit cell of the periodic metamaterial design incorporates a magnetic resonator and silver meshes for respective control of the effective permeability and permittivity. A genetic algorithm is employed to optimize the metamaterial design to achieve a desired set of values for the index of refraction and the intrinsic impedance. Two example GA optimized designs are provided which target the important special cases of a zero and unity index of refraction. Go/

5-) 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/

6-) 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.

7-) 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.

8-) Synthesizing metamaterials with angularly independent effective medium properties based on an anisotropic parameter retrieval technique coupled with a genetic algorithm
by Zhi Hao Jiang, Jeremy A. Bossard, Xiande Wang, and Douglas H. Werner
Journal of Applied Physics, Vol. 109, pp. 013515/1-11, January, 2011.

ABSTRACT: In this paper, we present a method to retrieve the effective electromagnetic parameters of a slab of anisotropic metamaterial from reflection and transmission coefficients (or scattering parameters). In this retrieval method, calculated or measured scattering parameters are employed for plane waves incident obliquely on a metamaterial slab at different angles. Useful analytical expressions are derived for extracting the homogeneous anisotropic medium parameters of a metamaterial. To validate the method, the effective permittivity and permeability tensor parameters for a composite split-ring resonator-wire array are retrieved and shown to be consistent with observations previously reported in the literature. This retrieval method is further incorporated into a genetic algorithm (GA) to synthesize an infrared zero-index-metamaterial with a wide field-of-view, demonstrating the utility of the new design approach. The anisotropic parameter retrieval algorithm, when combined with a robust optimizer such as GA, can provide a powerful design tool for exploiting the anisotropic properties in metamaterials to achieve specific angle dependant or independent responses.


9-) Low-Loss Impedance-Matched Optical Metamaterials with Zero-Phase Delay
by Seokho Yun, Zhi Hao Jiang, Qian Xu, Zhiwen Liu, Douglas H. Werner, and Theresa S. Mayer
ACS Nano, 6 (5), pp. 4475-4482, 2012.

ABSTRACT: Metamaterials have dramatically expanded the range of available optical properties, enabling an array of new devices such as superlenses, perfect absorbers, and ultrafast switches. Most research has focused on demonstrating negative- and high-index metamaterials at terahertz and optical wavelengths. However, far less emphasis has been placed on low-loss near-zero-index metamaterials that exhibit unique properties including quasi-infinite phase velocity and infinite wavelength. Here, we experimentally demonstrate a free-standing metallodielectric fishnet nanostructure that has polarization-insensitive, zero-index properties with nearly ideal transmission at 1.55 um. This goal was achieved by optimizing the metamaterial geometry to allow both its effective permittivity and permeability to approach zero together, which simultaneously produces a zero index and matched impedance to free space. The ability to design and fabricate low-loss, near-zero-index optical metamaterials is essential for new devices such as beam collimators, zero-phase delay lines, and transformation optics lenses.


10-) Near-Zero-Index Metamaterial Lens Combined With AMC Metasurface for High-Directivity Low-Profile Antennas
by Jeremiah P. Turpin, Qi Wu, Douglas H. Werner, Bonnie Martin, Matt Bray, and Erik Lier
IEEE Transactions on Antennas and Propagation, Vol. 62, No. 4, pp. 1928 - 1936, April, 2014.

ABSTRACT: A high-gain reduced-profile antenna is designed by combining the effects of a near-zero-index volumetric metamaterial lens and an artificial magnetic conducting (AMC) ground plane. The AMC/metalens antenna design presented here has 20% reduced height over an equivalent metalens antenna with conventional metallic ground plane at the cost of reduced peak directivity and pattern bandwidth. Both the metamaterial unit cells and the mushroom-type AMC structure are designed independently and retuned in the presence of the other for optimal performance. The lens collimates the electromagnetic radiation of a dipole feed by refraction as well as via a Fabry-Perot cavity effect, with resulting gain and patterns that are better than either mechanism can achieve individually. Full wave simulations of the entire metamaterial and AMC structure with a feed dipole agree well with measurements of the fabricated design.


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