Left-handed Media Research Articles

Bragg resonances in left-handed bigyrotropic media based on periodic ferromagnetic semiconductor

In this work, a theoretical model for a periodic bigyrotropic left-handed medium, which is a ferromagnetic semiconductor, is developed. The presence of periodicity in such a structure leads to the formation of Bragg band gaps in the spectrum of propagating waves, both in the microwave and terahertz ranges. Band gaps in the microwave range are formed in the frequency region with double negative effective parameters of the medium. The band gaps density decreases with increasing frequency in the microwave range and increases in the terahertz range.

Development and possible applications of tunable elements based on composite materials

This work is devoted to the synthesis of nano-sized weakly agglomerated magnetic particles with different crystal structures, which were used in the development of nonlinear composite structures, in particular, nonlinear resonant microwave elements, left-handed media, and nonlinear magnetoelectric systems.

Simulation of Wave Propagation in Plasma-Metamaterial Composites Based on Plasma Parameters and Metamaterial Structures

Metamaterial is a left-handed medium used in antenna design to overcome the typical design's larger size and untunable nature. Because of its design with a high permittivity dielectric substrate and some deformation, the wireless sector may be able to solve this difficulty. Metamaterial antennas have a five-fold reduction in size, a higher bandwidth, a wider scanning angle, good beam performance, and electronically controlled targeting. Metamaterials antennas also improve antenna parameters such as frequency generation, gain, and bandwidth. This research aims to suggest the best metamaterials structure for improving antenna performance using plasma as a base. This study used 12 types of plasma with varying plasma frequencies and collision frequencies with four metamaterials structures: 1D-split ring structure, Symmetrical structure, Omega structure, and S structure. Computer Simulation Technology (CST) Studio Suite was used to design and simulate each structure with a sequence of plasma. At frequencies ranging from 1 GHz to 20 GHz, parameters including return loss, gain, radiation pattern, and Voltage Standing Wave Ratio (VSWR) are used to assess an antenna's performance. Due to its electromagnetic qualities, the 1D-split ring construction has a better omnidirectional figure and VSWR value of 1.0039 dB. When all criteria were considered, the best results were obtained when using a 1D-split ring structure of the Plasma 9 (plasma frequency of 3.58528 x1011 rad/s and collision frequency of 1.3349 x109 1/s) produces an efficient return loss, high gain, better VSWR and a better omnidirectional figure among the four structures evaluated.

Magnetic bias field driven ferro- and antiferromagnetic semiconductors as double negative media for microwave and terahertz ranges

In this work, a theoretical study of the backward electromagnetic waves (BEMWs) existing in the bigyrotropic left-handed media controlled by a magnetic bias field is presented. The bigyrotropic media are both longitudinally and transversely magnetized ferromagnetic (FM) or antiferromagnetic (AFM) semiconductors (SCs) with electric and magnetic loss. It is shown that the BEMWs are observed both in the microwave and terahertz frequency ranges, in which the effective material parameters of the FM or AFM SCs are double negative. We demonstrate the control of the BEMW dispersion characteristics not only by changing the magnetic bias field direction and strength, but also by variation a material magnetization and thickness, an electron concentration in a solid-state plasma, as well as the electric and magnetic loss.

Super-resolution imaging method assisted by a left-handed medium slab based on a neural network.

In this study, a super-resolution imaging method is proposed that combines the physical properties of a left-handed medium (LHM) slab and the mathematical methods of a neural network. Firstly, for the problem of super-resolution information loss in the received scattering field in general scenes, the LHM slab is used to construct a perfect lens to recover the evanescent wave component that carries super-resolution information. Secondly, the compressed sensing (CS) method is applied to image the sparse targets under the LHM environment. However, the perfect focus only occurs in spot or line positions. Therefore, the imaging width of conventional methods is limited and a more powerful mathematical method is needed. Finally, the neural network method is introduced to relax the limitations of target imaging width due to its strong non-linear fitting capability. The simulation results demonstrate that the imaging resolution can reach λ/10 with the assistance of LHM, while the CS method can realize super-resolution imaging of λ/20 based on prior information of spatially sparse targets. In addition, the neural network method proposed in this paper relaxes the limitation of targets, realizing super-resolution imaging of λ/20 for general targets.

Magnetic metasurfaces with metallic inclusions

Purpose of this paper is the development and creation of the magnetic metasurfaces with metallic inclusions operating both in the microwave and terahertz frequency ranges. Methods. The Maxwell’s equations and the expressions for the effective medium parameters are used to build the analytical models of the magnetic metasurfaces based on either a ferromagnetic (FM) or antiferromagnetic (AFM) dielectric matrix, containing a two-dimensional periodic structure of thin metal (non-magnetic) wires surrounded by insulators. Numerical simulation of such structures operating in the microwave range is carried out using the MaxLLG software package. The magnetron sputtering, liquid etching, optical lithography, and lift-off photolithography are used to create bicomponent magnetic metasurfaces, consisting of two magnetic materials with very different values of magnetization. The study of linear and nonlinear characteristics of the bicomponent magnetic metasurfaces is carried out using the methods of microwave and Brillouin spectroscopy. Results. Based on the developed analytical model of the magnetic metasurface with metallic (nonmagnetic) inclusions it is shown that the FM metasurface possesses properties of a left-handed medium in a microwave range and the AFM metasurface possesses similar properties in a terahertz range. In the last case, the material parameters of the AFM metasurface are twice negative in two frequency bands. For the magnetic metasurfaces with metallic magnetic inclusions, the formation of absorption bands in the spectrum of a traveling magnetostatic surface spin wave due to the resonant properties of the inclusions has been established. In the nonlinear regime, the effect of nonreciprocal parametric three-wave resonance was obtained. Conclusion. The results presented in the paper demonstrate a number of physical phenomena that are observed only in the magnetic metasurfaces with metallic (nonmagnetic and magnetic) inclusions.

Propagation of adjustable anomalous hollow Gaussian beams in the cascade of left-handed and right-handed media

In this paper, the propagation characteristics of adjustable anomalous hollow Gaussian beams are investigated in different cascaded systems composed of left-handed medium and right-handed medium. The propagation expressions of adjustable anomalous hollow Gaussian beams through different cascaded systems are derived, and the effects of negative refractive index and beam parameters on the propagation characteristics are analyzed in detail. It is found that when the negative refractive index changes, the position of the maximum axial intensity is different for different cascades. But the magnitude of the maximum axial intensity is not affected by the negative refractive index. The effects of negative refractive index and beam parameters on the beam width and intensity pattern evolution are also analyzed in detail. Although the propagation characteristics in this paper are obtained under certain parameters, it is very convenient to study the evolution characteristics under various conditions through the analytical formula obtained in this paper.

Slow Electromagnetic Waves in Double-Layer Cylindrical Waveguide Filled With Right- and Left-handed Media

Slow Electromagnetic Waves in Double-Layer Cylindrical Waveguide Filled With Right- and Left-handed Media

Double negative media based on antiferromagnetic metamaterials

The paper presents the theoretical study results of the dispersion characteristics of electromagnetic waves existing in antiferromagnetic (AFM) metamaterial. The AFM metamaterial consists of a transversely magnetized antiferromagnet, inside of which a two-dimensional periodic structure of thin conducting wires surrounded by insulators is placed. It has been established that the AFM metamaterial has two frequency ranges, in which there are backward waves, and the material pa-rameters of the medium are twice negative. The indicated areas are located in the terahertz range. Keywords: metamaterials, left-handed medium, antiferromagnetics, spin waves.

Double negative media based on antiferromagnetic semiconductors for the terahertz frequency range

The paper presents the results of a theoretical study of the dispersion characteristics of electromagnetic waves (EMW) existing in a transversely magnetized antiferromagnetic (AFM) semiconductor with loss. An AFM semiconductor is an infinite bi-gyrotropic medium, the effective material parameters of which are twice negative in several frequency ranges. It was found that these frequency bands are in the terahertz range, and there are four backward EMEs in them, two of which are TE waves, and the other two are TM waves. Keywords: left-handed media, antiferromagnets, semiconductors, spin waves.

Controllable refractive index in a four-level left-handed medium using pulse shaping

In this paper we control the negative refractive index of a four-level left-handed medium by applying different waveforms to excite the atomic system. The control field is a few-cycle strong pulse described by a double exponential function, and its modified forms, a Gaussian field, and a tan-hyperbolic pulse. The considered four-level system was fully analyzed in terms of the density matrix formalism under the rotating wave approximation, and the refractive index for various control fields was obtained. Hence, under specific conditions, the tunneling, and the modulation of the negative refractive index are achieved for various shaped waveforms. Such strong-shaped laser pulses open the way to fully control the system.

Graphene-loaded left-handed media for tunable electromagnetic surface waves

Theoretical investigation has been carried out on the tunable electromagnetic surface waves propagating along the Graphene loaded semi-infinite left-handed media (LHM) interface. The analytical modeling of the graphene has been done in the frame work of Kubo's formulation. The split ring resonators (SRRs) model and Kramers-Kronig relations-based causality principle have been used to simulate the GHz-LHMs and THz-LHMs respectively. To realize the graphene loaded LHM interface, the impedance boundary conditions (IBCs) have been employed. The dispersion curves, effective mode index, propagation length, penetration depth, phase velocity and fields profiles of surface waves supported by graphene loaded GHz-LHM and THz-LHM have been computed numerically. It has been concluded that the graphene parameters can be used to tune the characteristics of surface waves in GHz and THz range. The proposed study may have potential applications in designing the near field imaging platforms, communication devices and tunable surface wave guides.

Slow Electromagnetic Waves in a Left-Handed Medium Based on Magnetoactive Plasma Metamaterial

The spectrum of slow electromagnetic waves (EMWs) existing in a left-handed medium based on a magnetoactive plasma metamaterial has been theoretically studied. The metamaterial under study is a strip waveguide completely filled with longitudinally magnetized cold electron plasma containing a periodic structure made from ideally conducting split-ring resonators. It is shown that there exists either one (ordinary) or two (ordinary and extraordinary) slow EMWs in a left-handed medium based on anisotropic plasma, depending on the chosen values of the split-ring resonator eigenfrequency and magnetic induction. It is found that the extraordinary EMW has a negative dispersion, while the dispersion characteristic of the ordinary EMW contains portions of both negative and positive dispersion.

Reversed Cherenkov-transition radiation in a waveguide partly filled with an anisotropic dispersive medium

We analyze the electromagnetic field of a bunch that moves uniformly in a circular metal waveguide and crosses a boundary between a vacuum area and an area filled with an anisotropic dispersive nonmagnetic medium. The medium is characterized by the diagonal dielectric permittivity tensor with components possessing frequency dispersion of plasma types. The investigation of the waveguide mode components is performed with the methods of the complex variable function theory. It is shown that in compliance with the parameters of the medium, Cherenkov radiation (CR) generated in the filled area of the waveguide can have reversed direction in relation to the bunch motion. CR can penetrate into the vacuum area of the waveguide, that is, the intensive reversed Cherenkov-transition radiation (RCTR) can be generated. The main properties of this radiation are described, and essential differences from the RCTR in the case of isotropic left-handed medium are revealed.

Interaction of plane waves with the edge discontinuity of a half-sheet at the interface of two different media

The present work considers the interaction of plane waves with a conductive half-sheet at the boundary of left- and right-handed media. The shadow boundary shifts toward the lower surface of the half-plane because of the anomalous refraction property of left-handed medium. For this reason, the diffracted fields are modified slightly by dividing into its subfields in order to satisfy the boundary conditions. The uniform version of fields is obtained and the results are plotted and discussed for different sets of parameters.

Photonic Transmittance in Metallic and Left Handed Superlattices

We study the transmission of electromagnetic waves through layered structures of metallic and left-handed media. Resonant band structures of transmission coefficients are obtained as functions of the incidence angle, the geometric parameters, and the number of unit cells of the superlattices. The theory of finite periodic systems that we use is free of assumptions, the finiteness of the periodic system being an essential condition. We rederive the correct recurrence relation of the Chebyshev polynomials that carry the physical information of the coherent coupling of plasmon modes and interface plasmons and surface plasmons, responsible for the photonic bands and the resonant structure of the surface plasmon polaritons. Unlike the dispersion relations of infinite periodic systems, which at best predict the bandwidths, we show that the dispersion relation of this theory predicts not only the bands, but also the resonant plasmons’ frequencies, above and below the plasma frequency. We show that, besides the strong influence of the incidence angle and the characteristic low transmission of a single conductor slab for frequencies ω below the plasma frequency ω p , the coherent coupling of the bulk plasmon modes and the interface surface plasmon polaritons lead to oscillating transmission coefficients and, depending on the parity of the number of unit cells n of the superlattice, the transmission coefficient vanishes or amplifies as the conductor width increases. Similarly, the well-established transmission coefficient of a single left-handed slab, which exhibits optical antimatter effects, becomes highly resonant with superluminal effects in superlattices. We determine the space-time evolution of a wave packet through the λ / 4 photonic superlattice whose bandwidth becomes negligible, and the transmission coefficient becomes a sequence of isolated and equidistant peaks with negative phase times. We show that the space-time evolution of a Gaussian wave packet, with the centroid at any of these peaks, agrees with the theoretical predictions, and no violation of the causality principle occurs.

Fast and Slow Electromagnetic Waves in a Longitudinally Magnetized Thin-Film Ferromagnetic Metamaterial

We present the results of a theoretical study of the electrodynamic characteristics of fast and slow electromagnetic waves (EMWs) propagating in a metamaterial consisting of a ferromagnetic film inside which there is a periodic lattice of thin metal wires. The ferromagnetic thin-film metamaterial possesses the properties of a left-handed medium at frequencies of slow electromagnetic waves. In a ferromagnetic metamaterial, in comparison with a conventional ferromagnetic film, the cutoff frequencies of fast and slow electromagnetic waves shift to a higher frequency range and the electromagnetic waves themselves become very slow.

An analytical solution for the plane wave diffraction by a resistive half-plane residing at the interface of left and right handed media

The diffraction of waves by a resistive half-plane lying on the interface of left and right handed media is investigated in this study. Because of the anomalous refraction property of left handed media, shadow boundary shifts toward to the lower surface of the half-plane. In order to obtain the shifted boundary, diffracted waves are divided to subfields. Thus, obtained diffracted waves compensates the deficiency of geometrics optics fields at the transition regions. The uniform version of waves is obtained by using the uniform theory of diffraction. The wave behaviors are examined numerically.

Быстрые и медленные электромагнитные волны в продольно намагниченном тонкопленочном ферромагнитном метаматериале

The results of a theoretical study of the electrodynamic characteristics of fast and slow electromagnetic waves (EMWs) propagating in a metamaterial are presented. The metamaterial consists of a ferromagnetic film inside which a periodic lattice of thin metal wires is located. It has been established that the ferromagnetic thin-film metamaterial possesses the properties of a left-handed medium at frequencies of slow electromagnetic waves. It is shown that, in a ferromagnetic metamaterial, compared with a conventional ferromagnetic film, the cutoff frequencies of fast and slow EMWs shift to a higher frequency range, and EMWs themselves become strongly slowed waves.

Surface polaritons in grating composed of left-handed materials

In this work, we developed a unique mathematical model to solve dispersion relation for surface polaritons (SPs) in artificial composite materials grating. Here, we have taken two types of materials for analysis. In the first case, the grating composed of epsilon-negative (ENG) material and air interface. In second case, grating composed of left-handed materials (LHMs) and ENG medium interface is considered. The dispersion curves of both p and s polarized SPs modes are obtained analytically. In the case of ENG grating and air interface, polaritons dispersion curves exist for p-polarization only, whereas for LHM grating and ENG medium interface, the polaritons dispersion curves for both p and s polarization are observed.