Metamaterial Layer Research Articles

Band structure and broadband compensation of absorption by amplification in layered optical metamaterials

The frequency dependence of the gain required to compensate for absorption is determined for a layered structure consisting of alternating absorbing and amplifying layers. It is shown that the fulfillment of the same conditions is required for the existence of a band structure consisting of alternating bands allowed and forbidden for optical radiation propagation in the frequency-wave vector parametric region. Conditions are found under which the gain required for compensation is smaller than thresholds for absolute (parasitic lasing) and convective (waveguide amplification of radiation) instabilities.

Negative-index metamaterial at visible frequencies based on high order plasmon resonance

A type of negative-index metamaterial composed of periodic arrays of SRRs is proposed and numerically investigated in the visible frequencies. Employing the high order magnetic resonance to induce negative permeability, negative refractive index is obtained between 395 THz and 430 THz with the maximum FOM=4.59. The effective permeability exhibits a rapid convergence with increasing number of metamaterial layers. Different responses from the electric and magnetic resonances to the changing geometric parameters are compared and analyzed in terms of the field distribution. Simulation results show that the high order magnetic resonance can be greatly enhanced at visible frequencies as well as effectively tuned over a wide spectral range without notably altering the coupling between unit cells.

Microdisk sensor based on double negative metamaterials

In this article, a microdisk sensor coated with a double negative metamaterial (DNM) layer is studied. The dispersion relation of the cylindrical dielectric waveguide coated with a DNM layer is derived. The electric field distributions and resonant frequencies of the corresponding whispering gallery mode are computed and simulated, and its quality factors are obtained using finite element method. Numerical results of resonant frequency and electric field distribution are in good agreement with the analytical results. We show that the sensitivity of the DNM microdisk sensor is about 12 times higher than the one of the microdisk resonator sensor in both homogeneous sensing and surface sensing, and the increasing thickness of the DNM leads to a further improvement of sensitivity. Moreover, the Q factor of the DNM microdisk resonator can be tailored by tuning the coupling distance between the straight waveguide and microdisk. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22:512–521, 2012. © 2012 Wiley Periodicals, Inc.

Transformation-based metamaterials to eliminate the staircasing error in the finite difference time domain method

A coordinate transformation technique is introduced for the finite difference time domain method to alleviate the effects of errors introduced by the staircasing approximation of curved geometries that do not conform to a Cartesian grid. An anisotropic metamaterial region, which is adapted to the Cartesian grid and designed by the coordinate transformation technique, is constructed around the curved boundary of the object, and the region occupied between the curved boundary and the inner boundary of the anisotropic metamaterial layer is discarded. The technique is validated via several numerical simulations. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22:530–540, 2012. © 2012 Wiley Periodicals, Inc.

Metamaterials with a network structure

This paper is a review of the literature data on metamaterials with a network structure, which are currently the most promising type of metamaterials for obtaining a negative refractive index in the optical region. “Monomolecular” layers of metamaterials of this type with a negative refractive index in the IR and visible regions are presented. For a bulk metamaterial with a network structure, a negative refractive index in the 1.54–1.775-µm wavelength region has been demonstrated on the basis of Snell’s law.

Optical properties of metamaterials: Influence of electric multipoles, magnetoelectric coupling, and spatial dispersion

We present a study on the optical properties of metamaterial layers containing U-shaped resonators with resonances in the near infrared. We show that the description of the optical properties requires taking into account permittivity, permeability, and chirality tensors. The elements of these tensors were tentatively attributed to surface plasmon resonances of the arms, magnetoelectric coupling, and spatial dispersion. We show that measurements of the Mueller matrix of the sample in appropriately chosen conditions allow unambiguous discrimination of the contribution of the different elements of the tensors to the optical properties of the metamaterial. Emphasis is put on the description of transfers of polarization and symmetries among the Mueller matrix elements. The findings of the theoretical part are confirmed by spectroscopic ellipsometric measurements made on this sample. The spectral dispersion of the different elements of permittivity, permeability, and chirality, modeled using oscillators with Lorentzian line shape, allows correct adjustment of measurements.

Giant circular dichroism in extrinsic chiral metamaterials excited by off-normal incident laser beams

Recently it was shown by experiments that circular dichroism (CD) can be observed in the metamaterials of non-chiral structures when they were subjected to obliquely incident light (E. Plum, et al., Physical Review Letters 102, 113902, 2009). By far, external chirality simulation was only done for a particle array embedded in a homogenous medium (V. Yannopapas, Optics Letters 34, 5, 2009); no attempt has been made on simulating and modelling of circular dichroism in layered metamaterials (e.g., thin film on substrate structure). In this paper, we present the simulation of CD effect in layered external chiral metamaterials using CST software, theoretically investigate this intriguing phenomenon through a frequency domain finite integration technique, and optimize the metamaterial unit cell configurations (size, periodicity and film thickness) to maximize the CD phenomenon in near-infrared spectrum range. We show that the CD effect can be enhanced by five times using an optimized unit cell configuration, which is more than three times higher than the existing maximum theoretical results. The CD generation mechanism was elaborated with the help of induced surface current distributions.

Transmission and Anderson localization in dispersive metamaterials

Comprehensive theoretical and numerical studies of the effects of dispersion and absorption on the Anderson localization of classical waves in weakly disordered, one-dimensional stacks composed of dispersive metamaterials and normal materials are presented. An asymptotic analysis for studying the effects of dispersion and absorption is developed. It is shown that the localization of waves in random stacks composed entirely of either metamaterial or normal dielectric layers is completely suppressed at frequencies where the magnetic permeability or the dielectric permittivity is zero. In mixed stacks of alternating layers of normal and metamaterials with disorder present in either the dielectric permittivity or the magnetic permeability, localization is substantially suppressed not only at these frequencies but in essentially wider frequency ranges. When both the permittivity and the permeability are random, the localization behavior is similar to that in monotype stacks. At the transition from a double negative metamaterial to a single negative metamaterial, the transmission length drops dramatically in a manner that might be useful in optical switching. Polarization effects are also considered and it is shown that localization is suppressed at the Brewster angle, in a manner dependent on both the polarization and the nature of the disorder. Theoretical predictions are in excellent agreement with numerical calculations.

Miniaturized coaxial cavity resonator based on anisotropic negative permeability metamaterial loading

AbstractIn this letter, a miniaturized coaxial cylindrical cavity resonator was presented, in which a combination of an ordinary dielectric material and a metamaterial layer has been inserted. First, the general dispersion relation was formulated for such a resonator in three different cases in which the metamaterial layer is: (i) an isotropic μ and ε negative (double negative or DNG) medium; (ii) an isotropic μ negative (MNG) medium; or (iii) an anisotropic MNG (AMNG) medium. Extracting the approximate dispersion relation in the subwavelength scenario, it is shown that this configuration may in principal exhibit an arbitrary low resonant frequency for a fixed dimension, not only in the case of isotropic DNG or isotropic MNG layers but also in the case of a much less complex AMNG layer, which is of importance from the practical realization point of view. In comparison with miniaturized rectangular cavities and also miniaturized one‐dimensional resonators, the aforementioned resonator provides the possibility of selecting a distinct mode and also provides a further degree of freedom in the approximate dispersion relation, which brings more flexibility in designing miniaturized resonators. As an example, design and simulation of a miniaturized coaxial cavity resonator together with the complete design of the AMNG layer are presented. The resultant cavity diameter is shortened by ∼ 60% in comparison with theoretical minimum dimensions of a cylindrical cavity resonator of the same height. Finally, the designed cavity has been fabricated and tested. The measured and simulated responses are in close agreement with each other. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:595–599, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26600

Terahertz bandpass filters using double-stacked metamaterial layers

Bandpass filters are reported based on double-stacked metamaterial layers separated by an air gap for operation at terahertz frequencies. Several stacking configurations were investigated designed for a ~0.5 THz center frequency. The filters exhibited improved spectral transmission properties when compared with conventional ones based on single metamaterial layers. 3 dB bandwidth of ~78 GHz and sidelobe suppression ratio >16 dB were determined when symmetric or asymmetric double layers were stacked. We demonstrate that superior frequency selectivity can be achieved when metamaterial layers with different unit cells are used. Good agreement was found between measured and simulated transmission response.

Single-layer terahertz metamaterials with bulk optical constants

We investigate the conditions under which single layer metamaterials may be described by bulk optical constants. Terahertz time domain spectroscopy is utilized to investigate two types of geometries, both with two different sizes of embedding dielectric---cubic and tetragonal unit cells. The tetragonal metamaterials are shown to yield layer dependent optical constants, whereas the cubic metamaterials yielded layer independent optical constants. We establish guidelines for when $\ensuremath{\epsilon}$ and $\ensuremath{\mu}$ can be used as material parameters for single layer metamaterials. Experimental results at terahertz frequencies are presented and supported by full wave three-dimensional electromagnetic simulations.

Research on a cylindrical cloak with active acoustic metamaterial layers

Enlightened by the tunable properties of effective density of the active acoustic metamaterial, we design an active infinite cylinder acoustic cloak according to the idea of the multilayer structured acoustic cloak with homogeneous isotropic materials. Utilizing the electrical analog, the dynamical equation of the acoustic cavity with Piezo-Diaphragm is presented. By analyzing the circuit diagram, the control strategy of achieving various effective densities which are used for constructing the acoustic cloak is given. Based on the necessary parameters such as the wide range values of the relative densities gained by active control, and the acoustic speed of each composite layer, the acoustic pressure field of the plane wave incident on the cloak is calculated, via the FEM model. Also the pressure map of a rigid cylinder scatterer with surrounded fluid is performed for comparison. Results show that outside the cloaking shell, the plane wave field is almost undisturbed. However inside the shell, the plane wavefronts are gradually deflected, and guided around the cloaked domain, returning to the original plane shape with small perturbation. This phenomenon making the cloak acoustically invisible in some frequency ranges has useful values in engineering applications. Finally, the total scattering cross section of the cloak is calculated to investigate the invisible effect according to the frequency domain. The total number of the composite active metamaterial layers is 15, which is much easier to realize in experiment.

Simulation and analysis of single negative metamaterial sensor based on microring resonator

A novel microring resonator sensor coated with a single negative metamaterial (SNM) layer is proposed. The dispersion relation of hollow cylindrical dielectric waveguide covered with a SNM layer is derived, and resonant frequencies of the corresponding whispering gallery mode are computed. We find that there is a good agreement between the theoretical results and numerical results of resonant frequencies and electric field distributions. Compared with traditional resonator sensor, the sensitivity and resolution are significantly enhanced by SNM, and the Q factor can be tailored by adjusting the distance between the waveguide and the microring.

Tunneling and filtering characteristics of cascaded ɛ-negative metamaterial layers sandwiched by double-positive layers

In this paper, we examine the electromagnetic (EM) wave tunneling and filtering characteristics of multi-layer structures composed of an arbitrary number of ɛ-negative (Epsilon-negative or ENG) metamaterial layers sandwiched by very thin double-positive (DPS) layers with high dielectric constant values. We explain the phenomenon of EM wave tunneling through this propagation barrier by drawing an analogy between this problem and a generalized coupled resonator system. Using this analogy, we demonstrate that a multi-layer structure composed of N DPS layers (N ≥ 2 is an integer number) that sandwich N-1 ENG layers can not only be made transparent in a frequency range where the ENG layers are normally opaque but also be designed to provide a desired spectral filtering characteristics. Furthermore, we present an analytical method for synthesizing such multi-layer spectral filters from the characteristics of their desired responses. The proposed synthesis procedure can be used to develop spatial filters operating throughout the microwave and mm-wave frequency bands as well as multi-layer metallo-dielectric filters at optical wavelengths. We demonstrate the validity of the proposed analytical synthesis method using full-wave numerical electromagnetic simulations. Finally, using the duality principle, we expand these analytical results to the problem of EM wave tunneling through multiple μ-negative layers surrounded by thin DPS layers with high relative permeability values.

Metamaterial Sensor Based on WGM

Sensor utilizing metamaterials have opened up a new field of considerable interest. We extend here the works of our group about metamaterial sensor based on Whispering Gallery Mode (WGM), which is constructed with a microring resonator sensor coated with metamaterial layer. We demonstrate that our sensor possesses higher sensitivity than the traditional sensor since the amplification and penetration of evanescent wave by metamaterials.

The Field Confinement, Narrow Transmission Resonances, and Green Function of a Multilayered Microsphere with Metamaterial Defects

We numerically investigate the optical transmission through a compound spherical stack with conventional and metamaterial (MM) layers and also embedded MM defect. A formation of extremely narrow resonant peak with nearly complete transmittance in area of a band gap is found. We demonstrate that photon fields of certain frequencies can be strongly confined by a left-handed (LH) defect. The influence of a random deviation in the width of compound spherical layers as well the transit to the whispering gallery mode (WGM) is also discussed.

Interface modes in nanostructured metal-dielectric metamaterials

We study surface modes at an interface separating two different layered metal-dielectric metamaterials. We demonstrate that, in a sharp contrast to the effective-medium approach predicting a single interface mode with the surface-plasmon dispersion, the transfer-matrix method reveals the existence of three types of localized interface modes, including a backward interface mode. These results confirm that metal-dielectric nanostructured metamaterials can demonstrate strong optical nonlocality due to the excitation of surface plasmon polaritons.

Double Negative Metamaterial Sensor Based on Microring Resonator

Metamaterials are artificial media structured on a size scale smaller than the wavelength of external stimuli, and may provide novel tools to significantly enhance the sensitivity and resolution of the sensors. In this paper, we derive the dispersion relation of cylindrical dielectric waveguide loaded on double negative metamaterial (DNM) layer, and compute the resonant frequencies and electric field distribution of the corresponding Whispering-Gallery-Modes (WGM). Theoretical results of resonant frequency and electric field distribution are in good agreement with the simulation results. We show that the DNM sensor based on microring resonator possesses higher sensitivity than the traditional microring sensor since the amplification of evanescent wave, and with the increase of metamaterial layer thickness, the sensitivity will be increased greatly. It might open an avenue for designing perfect sensors.

Octagonal Ring Antenna for a Compact Dual-Polarized Aperture Array

A wideband dual-polarized aperture array design is presented based on elements formed by a triangular configuration of octagonal rings. The octagonal ring elements are linked by capacitors and placed a defined distance from a groundplane. A broader frequency bandwidth has been achieved by placing a further layer of conductive rings above the element rings forming a metamaterial superstrate layer. Low dielectric constant material can be used to fill the space between the array rings and the groundplane, and between the elements and the superstrate layer. A dual-polarized finite ORA array has been fabricated and measured. The octagonal ring antenna array inherently exhibits a broad scan range with a stable cross polarization performance, however in practice the cross polarization depends on the feeding arrangements. Two feeding methods are discussed with a stripline feed showing best performance.

Interaction of a plane electromagnetic wave with a structure consisting of a strip grating, a metamaterial layer, and magnetized plasma: resonance effects and their interpretation

We reduce the boundary-value problem of the diffraction of a plane electromagnetic wave by a structure, which consists of a strip grating, a metamaterial layer, and magnetized plasma, to a system of linear algebraic second-kind equations with the kernel operator. Resonance properties of this structure are studied, and it is found that in the low-frequency range, it has several series of an infinite number of resonance frequencies with condensation points at certain finite frequencies.