We have developed an approach to building superluminal medium for transformation opticsbased devices, including invisibility cloaks, from photonic crystals. Analysis of dispersion diagrams of 2D arrays composed from dielectric rods has shown that at frequencies corresponding to the second bands formed due to bandgap opening at increase of rod permittivity, the medium formed by arrays exhibits refractive indices providing for superluminal phase velocities of propagating waves. It is further demonstrated that rod arrays with various lattice constants could be used for realizing a range of superluminal index values prescribed by transformation optics for cylindrical cloaks at arbitrary chosen operating frequency. The performed studies allowed for solving a row of problems with employment rod arrays in the cloak medium: in particular, formulating transformation optics-based prescriptions for refractive index dispersion in the cloaking shell, defining the dimensions of array fragments capable of responding similar to infinite arrays, finding optimal distribution of linear arrays sets at their coiling to form concentric material layers in the cloaking shell, and employing interaction between neighboring array sets with various lattice constants to assist the realization of prescribed index dispersion. The performance of the superluminal medium formed by rod array sets was demonstrated on an example of a cloaking shell developed for microwave frequency range. In contrast to metamaterial-based cloak media, the developed media requires neither material homogenization, nor obtaining the effective parameters with peculiar values and Lorentz's type resonances in rods. Combination of these advantages and low losses makes photonic crystals perspective materials for invisibility cloaks operating in THz and optical ranges.

No abstract

Abstract-We present the design, characterization, and experimental verification of a dual-band metamaterial absorber (MA) in the microwave frequencies. The proposed MA consists of a metallic gammadion-shaped structure and a complete metal layer, separated by a dielectric spacer. The results show that the proposed MA has two absorption peaks at nearly 5.6 GHz and 6 GHz with absorption rates of 97% and 99%, respectively. The interference theory is used to investigate the physical mechanism of the proposed MA. The experimental results are in good agreement with the theoretical predictions. Furthermore, it is verified by simulations that the absorption of the proposed MA is almost insensitive to the incident wave polarization and oblique incident angle for the both TM and TE modes. This MA has broad prospect of potential applications.

A negative-refractive-index transmission-line (NRI-TL) metamaterial-loaded dipole antenna is proposed, which has a fully-printed configuration and exhibits multiband performance. The antenna consists of a conventional dipole antenna loaded with two unequal parallel NRI-TL metamaterial unit cells which have the same electrical length, but each is loaded with a thin inductive strip that has a different length and therefore a different effective shunt inductance. An equivalent circuit is extracted to investigate the performance of the proposed metamaterial-loaded dipole antenna by modeling each of the dipole arms as a transmission line. This circuit is then used to verify that the resonant behavior of the proposed antenna can be altered by simply adjusting the lengths of the thin inductive strips. A fabricated prototype has compact dimensions of 40 mm × 10 mm × 1.6 mm, and exhibits good agreement between the measured and simulated results. Index Terms-Compact, CRLH, dipole antenna, metamaterial, multiband, negative-refractive-index transmission-line (NRI-TL).0018-926X (c)

Metasurfaces composed of cylindrical dielectric resonators, responding either in optical or microwave ranges, are investigated with the goal of clarifying common features of their electromagnetic responses and their transformations at variations of array lattice constants and resonator heights. It is found that occurrence of dipolar electric resonances in dense metasurfaces is accompanied by full transmission without relation to overlapping of two dipolar resonances. Since electric resonances in dense metasurfaces experience strong coupling, these structures could not be considered as homogenized media of identical meta-atoms. We demonstrate the possibility of scaling metasurfaces, in order to substitute challenging optical experiments by experiments at microwaves.