arXiv subjects

Sergei Tretyakov

Publications and source records attributed to Sergei Tretyakov.

80 records · Page 5Linked to original sources

arXiv2005

Near-field enhancement and imaging in double cylindrical polariton-resonant structures: Enlarging perfect lens

We experimentally demonstrate a prototype of a cylindrical enlarging lens capable of enhancing and restoring evanescent fields. The enabling phenomenon is the resonant excitation of coupled surface modes in a system of two cylindrical arrays of small resonant particles. As was shown in [J. Appl. Phys. 96, 1293 (2004)], this phenomenon in planar arrays can be used in electromagnetic near-field imaging. Here, we use a similar structure in a cylindrically symmetric configuration, which gives us a possibility to obtain an enlarged near-field image.

physics.optics↗

arXiv2005

On Artificial Magneto-Dielectric Loading for Improving the Impedance Bandwidth Properties of Microstrip Antennas

In the present paper we discuss the effect of artificial magneto-dielectric substrates on the impedance bandwidth properties of microstrip antennas. The results found in the literature for antenna miniaturization using magnetic or magneto-dielectric substrates are revised, and discussion is addressed to the practically realizable artificial magnetic media operating in the microwave regime. Using a transmission-line model we, first, reproduce the known results for antenna miniaturization with non-dispersive material fillings. Next, a realistic dispersive behavior of a practically realizable artificial substrate is embedded into the model, and we show that frequency dispersion of the substrate plays a very important role in the impedance bandwidth characteristics of the loaded antenna. The impedance bandwidths of reduced size patch antennas loaded with dispersive magneto-dielectric substrates and high-permittivity substrates are compared. It is shown that unlike substrates with dispersion-free permeability, practically realizable artificial substrates with dispersive magnetic permeability are not advantageous in antenna miniaturization. This conclusion is experimentally validated.

physics.class-ph↗

arXiv2005

Improving antenna near-field pattern by use of artificial impedance screens

An antenna prototype utilizing artificial impedance surfaces to control the near field distribution is described. The antenna is a folded dipole placed above a finite-size artificial impedance surface. We have found that the field screening is most effective if the surface is a metal conductor. However, to achieve a reasonable value of the radiation resistance the dipole should be located far off the screen. If the surface is a magnetic wall, the antenna design is more compact, but the field behind the screen is large. Here we realize a compromise solution using an inductive surface of a moderate surface impedance, which allows realization of an effective near-field screen with still a reasonably low-profile design.

physics.class-ph↗

arXiv2005

Light-Weight Base Station Antenna with Artificial Wire Medium Lens

In this paper we study the possibility of utilizing a loaded wire medium as an artificial material for beam shaping element in base station antenna applications. The wires in the lattice are loaded with a proper capacitive impedance to come up with a structure effectively operating as a dielectric lens at the UMTS (Universal Mobile Telecommunications System) frequency range. It is proven with full-wave simulations that the interpretation of a finite size wire lattice as a dielectric lens is physically sound even with a moderate number of lattice periods. A prototype having a mechanically reconfigurable beam width is constructed and measured. It is shown that very promising performance can be achieved with a rather simple structure and a cheap manufacturing process.

physics.class-ph↗

arXiv2004

Electromagnetic field energy density in artificial microwave materials with negative parameters

General relations for the stored reactive field energy density in passive linear artificial microwave materials are established. These relations account for dispersion and absorption effects in these materials, and they are valid also in the regions where the real parts of the material parameters are negative. These relations always give physically sound positive values for the energy density in passive metamaterials. The energy density and field solutions in active metamaterials with non-dispersive negative parameters are also considered. Basic physical limitations on the frequency dispersion of material parameters of artificial passive materials with negative real parts of the effective parameters are discussed. It is shown that field solutions in hypothetical materials with negative and non-dispersive parameters are unstable.

cond-mat.mtrl-sci↗

arXiv2003

Near-field enhancement and imaging in double planar polariton-resonant structures

It is shown that a system of two coupled planar material sheets possessing surface mode (polariton) resonances can be used for the purpose of evanescent field restoration and, thus, for the sub-wavelength near-field imaging. The sheets are placed in free space so that they are parallel and separated by a certain distance. Due to interaction of the resonating surface modes (polaritons) of the sheets an exponential growth in the amplitude of an evanescent plane wave coming through the system can be achieved. This effect was predicted earlier for backward-wave (double-negative or Veselago) slab lenses. The alternative system considered here is proved to be realizable at microwaves by grids or arrays of resonant particles. The necessary electromagnetic properties of the resonating grids and the particles are investigated and established. Theoretical results are supported by microwave experiments that demonstrate amplification of evanescent modes.

physics.optics↗

arXiv2003

The planar perfect lens: physical requirements and possible alternative realizations

Several alternative possibilities of how to create an electromagnetic device being able to reconstruct near-field distribution of a source with sub-wavelength resolution (so-called perfect lens) are considered. It is shown that there is a variety of such means not involving double-negative (left-handed, or Veselago) materials or periodical backward-wave structures. It is demonstrated that devices working in a similar manner can be constructed using planar grids or material sheets imposing necessary boundary conditions at two parallel planes in air.

cond-mat.mtrl-sci↗

arXiv2002

Waves and energy in chiral nihility

A model for a chiral material in which both the permittivity and permeability are equal to zero is discussed. Such a material is referred by us as a ``chiral nihility". It is shown that this exotic material can be realized as a mixture of small helical inclusions. Wave solutions and energy in such a medium are analyzed. It is shown that an extraordinary wave in chiral nihility is a backward wave. Wave reflection and refraction on a chiral nihility interface is also considered. It is shown that a linearly polarized wave normally incident onto this interface produces the wave of "standing phase" and the same wave in the case of oblique incidence causes two refracted waves, one of them with an anomalous refraction.

cond-mat↗