The radiation properties of an axially slotted circular or elliptical antenna coated with metamaterials are investigated. The fields inside and outside the dielectric coating are expressed in terms of Mathieu functions. The boundary conditions at various surfaces are enforced to obtain the unknown field expansion coefficients. Numerical results are presented graphically for the radiation pattern, aperture conductance and antenna gain for the TM case. It was found that slotted antenna coated with metamaterials has more directive beam with lower sidelobes compared to coated with conventional dielectric material.
Using a commercial software, simulations are done on the radiation of a dipole antenna embedded in metamaterial substrates. Metamaterials under consideration are composed of a periodic collection of rods, or of both rods and rings. The S-parameters of these metamaterials in a waveguide are analyzed and compared with their equivalent plasma or resonant structure. Farfield radiation is optimized by analytic method and is simulated numerically. The metamaterial is shown to improve the directivity.
The paper focuses on λ/4 monopole antennas located in a meta-material that exhibits simultaneously negative values of effective permeability and permittivity within a microwave frequency band, as well as our experimental study in an anechoic chamber. The experimental results show that the electromagnetic waves radiated by the monopole are negatively refracted at the interface between the meta-material and the air at certain directions. In addition, the radiation pattern of the monopole in the meta-material is directional while it is non-directional without the meta-material.
Left-handed materials (LHM) are engineered structures that exhibit electromagnetic properties not found in nature. Real applications of LHM need substrates with low loss, wide bandwidth as well as stable mechanical characteristics. In this paper, we summarize some experimental as well as numerical results of left-handed materials with different configurations of rods and split-ring resonators (SRRs). Hot-press technics utilized in PC board manufacture are used to produce solid-state multi-layer left-handed materials. Either mechanical or electromagnetic characteristics of LH samples are notably improved.
We present a theoretical analysis of the radiation of an S-shaped split ring resonator (S-SRR) for the realization of a metamaterial exhibiting left-handed properties. It is shown that the structure is resonant due to its internal capacitances and inductances, which can be adjusted such that the electric plasma frequency and magnetic plasma frequency, both due to the S-SRR only, appear within the same frequency band. Using the same idea, we also present some extended S-shaped split-ring resonator structures with improved performance.
This paper presents a quasi-static analysis of a metamaterial consisting of a three-dimensional array of small tunable stacked split ring resonators (SSRRs). The resonance frequency of the proposed resonator structure can be controlled by adjusting the auxiliary lumped elements which are inserted between the split of each ring. In addition, the size of the ring resonator can be reduced to an order of 0.01λ that is one tenth that of the split ring resonator (SRR) by choosing the proper lumped elements. The analysis is based on the quasi-static Lorentz theory, and the generalized matrix representation of the macroscopic constitutive relations of the composite medium is calculated.
Two-dimensional isotropic metamaterials fabricated from cross split-ring resonators (CSRRs) are characterized and their constitutive relation tensors are studied in this paper. The effective constitutive parameters of the metamaterials are determined utilizing the quasi-static Lorentz theory and numerical method (i.e., the method of moments for solving the electric field integral equation). The induced current distributions of a single CSRR at the resonant frequency are presented. Moreover, the dependence of the resonant frequency on the dimensions of a single CSRR and the space distances of the CSRR array is also discussed. Reflection and transmission coefficients of a metamaterial slab versus frequency are finally discussed.
This paper focuses on the complex guided wave solutions of grounded slab made of metamaterials. Complex solutions of both TE and TM modes have been analyzed. It is found that they are distributed on the proper Riemann sheet. This property differs dramatically from that of a conventional grounded slab. A number of other distribution properties are studied analytically. Some numerical examples are given to verify the analytical results. It is important to take the peculiar complex solutions into account in the problems of microstrip and surface wave excitation.
Guided waves in a wire medium slab are studied. The wire medium is considered as a continuous medium described in terms of uniaxial permittivity dyadic. Nonlocal model of the wire medium, taking into account spatial dispersion, is used in the analysis. Different cases of an arrangement of the wires are considered. Analytic expressions for the fields in unbounded media and numerical solutions for eigenmodes spectrum in wire medium slab are obtained. Comparison of the results given by old (local) and new model of wire medium is presented.
The increasing interest in electromagnetic effects in double-negative (DNG) materials requires a formulation capable of a full analysis of wave propagation in such materials. We develop a novel technique for discretization of the Drude medium model and adopt multi-domain pseudospectral time-domain (PSTD) algorithm and well-posed PML formulation to analysis the plane wave scattering properties of a single circular cylinder and a periodic array of the circular cylinders fabricated from the Drude medium. The simulation results show accuracy of the proposed constitutive equation-discretization scheme.
nullOptical surface plasmon resonance sensors have been known for a long time. In this paper, we discuss the use of metamaterials to construct a surface plasmon sensor which can be used at microwave frequencies. We review the conditions for the existence of surface plasmon and the use of the forward and backward surface waves. A sharp dip in the reflection coefficient occurs when the propagation constant of the incident wave along the surface is nearly equal to the propagation constant of the plasmon surface wave and may be used to probe bulk material characteristics or to determine metamaterial characteristics. Numerical examples are given to illustrate the basic characteristics.
Characteristics of surface wave modes on a grounded slab of negative permittivity and negative permeability parameters are investigated. It is shown that, unlike a slab with positive parameters, the dominant mode can have evanescent fields on both sides of the interface between the slab and the surrounding air. Detailed characteristics of such mode for various combinations of the slab parameters are given.
This paper presents a new approach to estimate effective constitutive parameters for a cell across an interface between two bianisotropic media. The work is different from those studying effective properties of bi-anisotropic mixtures in that the boundary conditions of field components are taken into consideration. The degenerated cases, including interfaces of two bi-isotropic, anisotropic and isotropic media, are discussed respectively in detail. Simulation for anisotropic media shows significant improvements can be expected from the adoption of the new approach.
We show in this paper that metamaterials in which some components of the permittivity and permeability tensors can have negative real values (thus associated with left-handed metamaterials) call for a reconsideration of the common concepts of critical angle and Brewster angle. By studying the reflection coefficient for isotropic and biaxial half-spaces and slabs, we show that a metamaterial for which the Brewster angle appears beyond the critical angle is realizable. In addition, we also show that the Goos-Hänchen shift induced by left-handed isotropic slabs is not necessarily negative but could be positive when the second interface of the slab supports a surface plasmon. Finally, upon studying a bianisotropic metamaterial, we show that propagation at a negative angle can occur, although it would not if only the permittivity and permeability tensors were considered. All the results have been obtained using an eigenvalue method which we extend to bianisotropic media in this paper.
Depolarization factors of scatterers within anisotropic media are functions of not only the shape of the inclusion but also of the degree of anisotropy of the environment. In this contribution the depolarization factors are studied for anisotropic metamaterials. In such case, qualitatively new phenomena appear because the effective axial ratio of the scatterers, which determines the depolarization factors, may become complex. The negative real part of the depolatization factors is interpreted as "repolarization." The effect of the various parameters on the depolarization factors and effective dielectric parameters are analyzed and discussed for both three- and two-dimensional mixtures, with emphasis on the dissipative character of the homogenized metamaterials.
In this paper, the theoretical justification and the numerical verification of the anomalous scattering from cavities partially filled with metamaterials are presented. A hybrid numerical formulation based on the Finite Element Method (FEM) and on the Boundary Integral (BI) for the analysis of cavity backed structures with complex loading metamaterials is first presented. The proposed approach allows the analysis of cavities filled with materials described by tensorial linear constitutive relations, which may well describe artificial metamaterials synthesized with proper inclusions in a host dielectric. It is found that cavities loaded with pairs of metamaterial layers with "resonant" features possess unusual scattering properties, and with judicious selection of constitutive parameters for these materials the transparency effect or significant enhancement in the backscattering from such cavities are obtained. This may be considered as a first step towards the analysis of the scattering and radiating features of cavity-backed patch antennas and reflect-arrays in presence of multilayered metamaterial loads.
The electromagnetic interactions with left-handed material (LHM) medium postulated by Veselago are examined within the framework of surface integral equations (SIEs) solved by the method of moments (MM). The formulations are given for a general medium and then specialized for cases of LHM media. The scattering, propagation and lensing through such media are investigated. The implications and limitations of using SIE/MM formulations for lossless LHM media are also explored.
We study the energy conservation property and loss condition of a left-handed material (LHM). First we argue by energy conservation that an LHM has to be a backward-wave material (BWM). Then we derive the equivalence of the loss and the Sommerfeld far-field radiation conditions for BWM. Next, we solve the realistic Sommerfeld problem of a point source over an LHM half space and an LHM slab. With this solution, we elucidate the physics of the interaction of a point source with an LHM half space and an LHM slab. We interpret our observation with surface plasmon resonance at the interfaces as well as the resonance tunneling phenomenon. This analysis lends physical insight into the interaction of a point source field with an LHM showing that super-resolution beyond the diffraction limit is possible with a very low loss LHM slab.