Theodosios D. Karamanos

Compact Double-Negative Metamaterials Based on Electric and Magnetic Resonators

The efficient design of a double-negative (DNG) medium by combining electric and magnetic resonators on the opposite sides of a dielectric substrate is introduced in this letter. The effective parameters of the structure are extracted from numerical data via the Nicolson-Ross-Weir homogenization technique. Two different approaches are implemented to mitigate the well-known branching problem in the determination of Re{n}, both revealing the negative-refractive properties of the configuration. Moreover, the negative refraction phenomenon is observed by simulating the wave propagation via a wedge-shaped sample of the material. Finally, a dual-band DNG metamaterial is presented as a direct extension of the proposed method toward the design of devices with enhanced attributes for real-world applications.

Radiation Efficiency Enhancement of Graphene THz Antennas Utilizing Metamaterial Substrates

The radiation efficiency improvement of graphene plasmonic antennas via synthesized substrates with metamaterial resonators is introduced in this letter. Graphene, represented as an ultrathin layer, can support highly confined surface waves of significantly decreased wavelength compared to the vacuum one. Although this concept yields more compact devices, its applicability to graphene antennas is limited, due to the degradation of radiation efficiency. Thus, the effect of a substrate material on the surface-wave wavelength is thoroughly examined, while radiators of larger dimensions and enhanced efficiency are designed for an epsilon-negative medium. Also, a novel realistic metamaterial substrate is developed for graphene terahertz (THz) antennas, successfully verifying all theoretical estimations. Numerical results are extracted via an accurate finite-difference time-domain algorithm that treats graphene as an efficient surface boundary condition.

Surface plasmon polariton waves onto graphene's surface over an anisotropic metamaterial substrate

The present work investigates the propagation properties of the surface plasmon polariton wave supported on graphene surface over an anisotropic substrate at far-infrared frequencies. Initially, the surface wave’s propagation on isotropic media substrate is studied and verified with the theoretical estimation, including the noteworthy epsilon-near-zero case. Moreover, after utilizing theoretical substrate media and examining anisotropy relative to the normal to graphene’s surface, direction, the anisotropy is enforced to the tangential direction revealing the significant influence of the substrate on the surface wave that is propagating on graphene. Additionally, the more realistic implementation with graphene’s substrate consisting of metamaterial resonators is thoroughly investigated. Numerical results are extracted through a reliable finite-difference time-domain (FDTD) algorithm, focalising, mainly, on the wavelength of graphene’s surface wave.

Miniaturization of metamaterial electrical resonators at the terahertz spectrum

An efficient methodology for the modification of electrical resonators in order to be readily applicable at the terahertz regime is developed in this paper. To this aim, the proposed miniaturization technique starts from the conventional resonator which, without any change, exhibits the lowest possible electrical resonance for minimum dimensions. Subsequently, a set of interdigital capacitors is embedded in the original structure to increase capaci- tance, while their impact on the main resonance is investigated through computational simulations. Furthermore, to augment the inductance of the initial resonator, and, hence reduce the resonance frequency, the concept of spiral inductor elements is introduced. Again, results for the featured configuration with the additional elements are numerically obtained and all effects due to their presence are carefully examined. Finally, the new alterations are combined together and their in influence on the resonance position and quality is thoroughly studied.

Effective parameter calculation of 3D bianisotropic scatterer arrays through extracted polarizabilities

In this paper, an efficient technique for computing the bulk parameters of infinite, normally-illuminated 3D arrays is developed. Initially, the dispersion equation of the array is derived and, then, the complex wavenumber for the TEM case is obtained through a rigorous algorithm. The retrieved polarizabilities of a single scatterer and the wavenumber are, finally, incorporated in first-principles homogenization formulas to evaluate the effective parameters. The proposed method is applied to popular bianisotropic scatterers and the validity of the results is successfully certified via numerical simulations.

Effective-surface modeling of infinite periodic metascreens exhibiting the extraordinary transmission phenomenon

The consistent analysis of metallic screens perforated with subwavelength apertures of diverse geometrical patterns (metascreens) by means of a systematic methodology is presented in this paper. The principal concept of the new technique stems from the efficient characterization—via the use of effective surface parameters—of the metascreen’s complementary array of scatterers (i.e., a metafilm) and the proper utilization of the Babinet duality principle. To this end, a previously developed model for metafilms is carefully extended (for normal plane wave incidence) in order to apply to frequencies where the extraordinary transmission phenomenon typically occurs. General-purpose analytical formulas for the reflection and transmission coefficients of an arbitrary metascreen are also derived as part of this generalized framework. Finally, the predictions for the extraordinary transmission spectra through various metascreens operating in the microwave regime, as obtained via two distinct realizations of the proposed formulation, are compared with the results of a commercial computational package in order to verify the precision of the developed technique and provide instructive physical insights.