Lossy Metamaterials Research Articles

Origin of large lateral shift in a prism⿿waveguide coupling system with metamaterial

We study the lateral shifts of reflected light beams in a prism⿿waveguide system with lossless or lossy metamaterial, four sufficient conditions for the appearance of large lateral shift is concluded when the metamaterial is lossless, and the influence of lossy metamaterial on the properties of lateral shift is also analyzed by simulation results.

The refractive index sign chosen for amplifying and lossy metamaterials

Three definitions of a refractive index that differ in the meaning of its real part are considered for a homogeneous isotropic medium. The signs of wave characteristics (a refractive index and an impedance) are determined for sixteen possible combinations of the signs of the real and imaginary parts of the permittivity and permeability of a medium.

ARBITRARY LOSS FACTORS IN THE WAVE PROPAGATION BETWEEN RHM AND LHM MEDIA WITH CONSTANT IMPEDANCE THROUGHOUT THE STRUCTURE

We investigate the wave propagation properties in lossy structures with graded permittivity and permeability involving left- handed metamaterials. An exact analytic solution to Helmholtz' equation for a lossy case with both real and imaginary parts of permittivity and permeability proflle, changing according to a hyperbolic tangent function along the direction of propagation, is obtained. It allows for difierent loss factors in RHM and LHM media. Thereafter, the corresponding numerical solution for the fleld intensity along the composite structure is obtained by means of a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms. We present the expressions and graphical results for the fleld intensity along the composite structure and compare the analytic and numerical solutions, showing that there is an excellent agreement between them.

Near-field radiative heat transfer between chiral metamaterials

We investigate the near-field radiative heat transfer between two dispersive and lossy chiral metamaterials. Our theory takes into account the magnetoelectric coupling effect compared with the existing theories. It is shown that the contribution of surface modes to heat transfer is strongly modulated by the magnetoelectric coupling effect. We predict that in the presence of strong coupling effect, the resonant tunneling modes with small parallel wavenumbers activate a novel energy transfer channel. We also find that the dissipation effect in material, which is characterized by the scattering rate, significantly influences the effect of magnetoelectric coupling on near-field heat transfer. We finally discuss the applications of these results in thermophotovoltaic energy conversion and the experimental realization of near-field heat transfer.

Nonlinear absorption due to linear loss and magnetic permeability in metamaterials

We predict theoretically that linear magnetic permeability induces nonlinear absorption (NA) of an electric field in lossy metamaterials (MMs) with Kerr-type nonlinear polarization even when the imaginary part of the nonlinear polarization is absent. The nonlinear magnetic susceptibility, if it exists and although it may be real, enhances or reduces the NA of the electric field, depending on the relative values of the electric and magnetic losses. In particular, it is shown that the NA effect can be tuned by the figure of merit (FOM) of the MM: generally, MMs with a better FOM have a weaker NA effect. Moreover, the nonlinear coefficient can also be enhanced greatly due to the combined effect of the linear losses and the nonlinear magnetization of MMs. The control of the tunable NA and nonlinear coefficients by the structural parameters of MMs is also discussed.

Lossy gradient index transmission optics with arbitrary periodic permittivity and permeability and constant impedance throughout the structure

A remarkably simple exact analytical solution is obtained for the electromagnetic field distribution across infinite metamaterial-containing composites with any arbitrary periodic variation of complex effective permittivity and permeability for the case of constant impedance across the structure. Arbitrary temporal dispersion and losses are allowed and the model is generally applicable to different inhomogeneous and anisotropic media simultaneously containing positive and negative refractive index constituents, as long as the effective medium approximation remains valid. The analytical solution is validated by a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms, where a close agreement between the analytic and numerical results is obtained.

Experimental investigation on transmission properties of lossy single-negative metamaterials

The properties of the wave transmission in the lossy single-negative (SNG) metamaterials are experimentally investigated. The model structure of lossy epsilon-negative (ENG) monolayer and SNG bilayer consisting of a lossy ENG material and a mu-negative (MNG) are considered in this work. Simulation and experimental results show that the transmittance of the lossy SNG materials can be enhanced by two approaches, increasing dissipation coefficient and increasing the thickness of the lossy SNG. The lossy ENG material is physically fabricated by using composite right- and left-handed transmission lines grafted with radiation unit cell. The experimental results are in very good agreement with the previous theoretical analysis.

A Cloak Scheme Insusceptible to the Change of Material Properties

An electromagnetic cloak based on a coordinate transformation approach is always inhomogeneous and anisotropic. In this paper, we investigate the sensitiveness of different cloaking schemes, when EM parameters are limited to a range more plausible to realize. Numerical experiments show that the imperfect cloak under moderate compression presents low anisotropy and is a candidate scheme more insusceptible to changes in EM parameters. When devising the cloak using dispersive lossy metamaterials, the unavoidable deviation in material parameters favors a lower anisotropic model such as the imperfect cloaking model.

Lossy metamaterials: No effective medium properties without noise

Lossy metamaterial elements act as sources of Johnson noise, making such materials inherently noisy. A coupled transmission line model capable of describing the effective medium properties, propagation and internal reflections, the internal noise distribution, and the noise factor is developed. Two analyses are provided, a numerical solution with limited physical insight and an approximation based on physical principles, and excellent agreement is obtained. It is shown that the internal noise spectrum is modified as it couples to the electromagnetic wave, and that there can be no change in permeability without an increase in the noise factor. This result implies that metamaterials will require careful evaluation of their noise performance before use in practical devices.

Surface wave propagation at the interface between lossy metamaterials medium and nonlinear media with arbitrary nonlinearity

The dispersion relation in a system that consists of a lossy metamaterials (MTMs) film surrounded by a linear substrate and a nonlinear cladding with an arbitrary nonlinearity is derived. The surface plasmonic (SP) wave at the interfaces between metamaterials (MTMs) and the nonlinear cover is recovered by taking certain limits. Lossy MTMs have simultaneously complex-negative permeability μ and complex-negative permittivity ε. Results are presented by plotting the SP frequency as a function of the nonlinearity at chosen damping factors. Both the real and imaginary parts are studied. Results also display the wave frequency as a function of plasma frequency. For comparison, the imaginary part is set to zero and curves are reproduced.

Large positive and negative lateral shifts near pseudo-Brewster dip on reflection from a chiral metamaterial slab

The lateral shifts from a slab of lossy chiral metamaterial are predicted for both perpendicular and parallel components of the reflected field, when the transverse electric (TE)-polarized incident wave is applied. By introducing different chirality parameter, the lateral shifts can be large positive or negative near the pseudo-Brewster angle. It is found that the lateral shifts from the negative chiral slab are affected by the angle of incidence and the chirality parameter. In the presence of inevitable loss of the chiral slab, the enhanced lateral shifts will be decreased, and the pseudo-Brewster angle will disappear correspondingly. For the negative chiral slab with loss which is invisible for the right circularly polarized (RCP) wave, we find that the loss of the chiral slab will lead to the fluctuation of the lateral shift with respect to the thickness of the chiral slab.The validity of the stationary-phase analysis is demonstrated by numerical simulations of a Gaussian-shaped beam.

Input Impedance of Horizontal Dipole Located Above Lossy Metamaterial Half-Space

In this letter, accurate analytical expressions for the impedance of horizontal electric and magnetic dipoles located above half-space materials of arbitrary permittivity and permeability are derived. In this regard, the Fresnel reflection coefficients are approximated by series of exponential functions, and the impedance integrals are analytically solved. The results are compared to the case of natural materials (positive permittivity and permeability), and the key differences are explained. It is shown that for horizontal dipoles above materials of high and/or low conductivities, both results are coincident. For dipoles in the vicinity of low-loss materials, the results are somewhat identical. However, a better agreement could be obtained using higher-order approximations for the integrand.

A new material classification of lossy metamaterials

The propagation constant is extended and derived for lossy metamaterials in which e 0 (ENG), e > 0 and μ < 0 (MNG), and e < 0 and μ < 0 (DNG).Regardless of the magnitudes of e and μ, DPS materials are a RH medium and DNG materials are a LH medium. However, SNG materials become a RH medium when the sign of (e × μ + e × μ) is positive and a LH medium when the sign is negative. A new diagram is proposed to classify any lossy metamaterial into either RH or LH medium. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:445–447, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25687

Spectral response and far-field pattern of a dipole nano-antenna on metamaterial substrates having near-zero and negative indices of refraction

In this work the resonance, frequency response, and far-field patterns of an optical nano-antenna placed on an interface between air and a metamaterial substrate is obtained through finite element calculations. The metamaterial is characterized by an effective, macroscopic index of refraction which can take negative and near-zero values, or by published values of the effective permittivity and permeability for metamaterials. The results show that the resonant wavelength and response can be fitted to analytical functions that are even functions of the index of refraction, this is consistent with the knowledge that negative indices of refraction allows for wave propagation in the same magnitude but opposite direction observed with positive indices of refraction. The simulations also show that substrates with near-zero index of refraction will enhance the antenna response by 62% compared to substrates with n>1. Lossy metamaterials are also considered in the simulations. The far-field pattern of the antenna, obtained through a near-field to far-field transformation, behaves the same independently of the sign of the index of refraction, also the far-field pattern for the emission towards near-zero substrates is nearly constant and independent of the angle for the evaluated angular range.

Elimination of phase singularity to achieve superresolution in lossy metamaterials

The presence of absorption losses softens the singular behavior of transmission resonances and leads to a good image in spite of limited effective spatial frequency range. Nonetheless, we found that the phase singularity does not disappear despite the considerably reduced retardation effects by softening the transmission resonances. Because the phase singularity severely deteriorates the ideal image reconstruction, broad transmission bandwidth in spatial frequency domain is not sufficient enough to achieve superresolution in TiO(2) thin film lens. The present work predicts successful elimination of the phase singularity and the achievement of approximately lambda /12.9 superresolution in TiO(2) thin film lens through the phase correction method.

Sign of the refractive index in lossy metamaterials

One of the criteria for determining the existence of negative index of refraction in artificial electromagnetic structures (metamaterials) is the occurrence of opposite directions of the group and phase velocities. In this work, we study specific examples of metamaterials where we show that the above criterion does not hold when losses are taken into account and dominate the interaction of light with the metamaterial. The structure are three-dimensional superlattices of consisting of plasmonic and polaritonic particles and are studied by a rigorous multiple-scattering theory and effective-medium approximation.

Mathematical formulation for zero reflection from multilayer metamaterial structures and their notable applications

The behaviour of bilayer structures composed of common materials and metamaterials (MTMs) under oblique incidence of plane waves is investigated by exact analytical methods. The TE, TM and elliptical polarisations are analysed. There are several combinations of double positive (DPS), double negative (DNG), epsilon negative (ENG) and mu negative (MNG) media for the bilayer structures, but only DPS-DPS, DPS-DNG and ENG-MNG bilayers with TE, TM and circular polarisations are analysed in detail. For homogeneous and isotropic MTM media, exact mathematical relations are derived for the design of reflectionless bilayer structures as a function of their geometry (thickness) and electric and magnetic parameters. Frequency dispersion is included in the formulations. It is shown that bilayers composed of common materials are not effective for the construction of zero reflection bilayer surfaces, whereas the application of MTMs is required to realise reflectionless phenomena. For the design of zero reflection bilayer structures, their thicknesses and values of epsiv and mu are determined. Finally, the performance of forward and backward notch filters observed by MTM bilayer structures are studied in detail and their designs and applications are investigated. The bandwidth of lossy MTMs increases considerably.

손실 특성의 메타 물질이 포함된 다층 구조 Slab의 특성 분석

본 논문에서는 손실 특성을 갖는 메타 물질로 구성된 다층 구조 slab의 특성을 해석하였다. 기존 메타 물질을 가진 다층 구조 해석은 recursive 방법을 이용했으며, 계산의 복잡성으로 인한 무손실을 가정할 수밖에 없었지만, 본 논문에서는 손실 메타 물질을 갖는 다층 구조를 해석하기 위해 해석 방법이 간단하고, 임의의 다층 구조를 갖는 물질에 대한 전파 특성을 쉽게 얻을 수 있는 ABCD 행렬을 이용하였다. 적용한 ABCD 행렬 방법의 유효함을 검증하기 위해서 유전체-유전체로 구성된 구조와 메타-유전체 물질로 구성된 다층 구조에 적용하여 기존의 recursive 방법과 비교하였다. 본 논문에서 해석한 손실 메타 물질을 갖는 다층 구조는 유전체 다층 구조보다 리플이 없고 광대역 전송 특성을 얻을 수 있다는 장점이 있으며, 안테나의 레이돔이나 전파를 차폐할 수 있는 차폐 물질 등에 다양하게 적용될 수 있다. In this paper, we analyzed the multilayer structure with lossy metamaterials using ABCD Matrix method to get the transmission characteristics. Compared to the recursive method which cannot be used to analyze the lossy characteristics of multilayer structure because of its complexity, we used the ABCD matrix method is easy to apply because of its matrix chain concepts for arbitrary number of multilayer structure and lossy material. To verify the results of this paper, we used both for multilayer dielectric and metamaterial, respectively, and obtained the same results. Multilayer structure with lossy metamaterial showed minimized ripple and broadband transmission compared to dielectric multilayered structure. This can be used in various applications as antenna radome and shielding material, etc.

Phase diagram of lossy negative index metamaterials

For lossy metamaterials, there exist the negative index of refraction regimes that may originate from double negative or single negative of the real parts of complex permittivity and permeability. To represent the regimes of negative index, a material quality factor space is proposed. Within the space the different negative index regimes are found located in the different regions. The contour map of the complex index of refraction in the space show that the negative index can be always possible to realize in three ways, and the loss of single negative metamaterials is greater than that of double negative metamaterials.

Wave scattering by a prism made of a lossy metamaterial

The results of rigorous calculation of the scattering pattern of a Gaussian beam incident onto a finite prism made of a metamaterial are presented for different values of the refractive index nr < 0 and loss factor ν of the medium. It is shown that geometric optics can correctly predict the tilt of the scattering-pattern maximum, while consideration for the medium’s loss factor 0.001 ≤ |ν| ≤ 0.1 affects the amplitudes of the transmitted and reflected fields.