Metamaterial Waveguide Research Articles

Beam Scanning Leaky-Wave Slot Antenna Using Balanced CRLH Waveguide Operating Above the Cutoff Frequency

In this paper, a composite right-left-handed (CRLH) rectangular waveguide satisfying a balanced condition above the cutoff frequency and a beam scanning leaky-wave slot antenna are presented. The proposed metamaterial waveguide consists of one shorted stub and two H-plane irises, which produce a negative permittivity and negative permeability, respectively. To design a balanced CRLH transmission line, the H -plane irises are materialized by twisted shapes that present a minimized coupling with the shorted stub. The independent controls of the LH and RH regions above the cutoff frequency make it relatively easy to obtain a balanced condition due to the minimized coupling effects. Additionally, using the CRLH waveguide, a beam scanning leaky-wave antenna (LWA) is designed. The LWA achieves good leakage radiation and high gain performance through insertion of the slot, which is set as close as possible to the operating frequency band. The design results show that the LWA supports the backward to forward beam scanning property, including a broadside radiation pattern by changing the frequencies without a band gap. The antenna consisting of 20 unit-cells has a beam steering angle from -31° or +52° and a high gains performance of more than 11.5 dBi in a frequency band from 9.5 GHz to 12.4 GHz.

Acoustic total transmission and total reflection in zero-index metamaterials with defects

The acoustic wave propagation is investigated in the zero-index metamaterial (ZIM) waveguide embedded with defects. Two types of ZIMs, the index-near-zero metamaterials with matched impedance and the density-near-zero metamaterials with mismatched impedance, are examined. Theoretical derivations and numerical simulations show that the total transmission or total reflection can be achieved by properly tailoring the parameters of the defects even in deep-subwavelength scale. Moreover, the transmission is sensitive to the parameters of the defects, suggesting the active control of acoustic transmission by using particular defects with tunable parameters such as porous materials.

Abruptly terminated planar left-handed material waveguide

The problem of guided mode reflection from an abruptly terminated planar metamaterial waveguide is studied by the variational technique. The theory is illustrated by examples of abruptly terminated three-layer waveguides with step permittivity and permeability profiles. Differences in the scattering characteristics for systems with metamaterials and usual media are discussed.

Leaky and bound modes in terahertz metasurfaces made of transmission-line metamaterials

Prism coupling and reflection spectroscopy are used to characterize bound modes within composite right/left handed terahertz metamaterial waveguides. The cavity antenna model is used to understand the polarization dependence of the radiative coupling to TM00 and TM01 waveguide modes. Furthermore, the cavity model along with transmission-line theory is used to derive a surface impedance model for a waveguide array metasurface. Qualitative agreement with the experiment is observed, including a mode splitting for p-polarized surface waves at the light line and the existence of s-polarized magnetic spoof surface plasmons.

Active terahertz quantum-cascade composite right/left-handed metamaterial

We report the demonstration of a composite right/left-handed (CRLH) metamaterial waveguide for terahertz quantum-cascade (QC) lasers. By incorporating gap capacitors (∼250 nm) in the top metallization of a metal-metal waveguide operating in a higher order lateral mode, we have realized a CRLH transmission line that supports traveling modes with negative effective phase indices (i.e., left-handed or backward-wave propagation). The CRLH metamaterial waveguide is employed as an active leaky-wave antenna for a terahertz QC-laser. Directional single-lobed beams launched in the backwards direction at angles of −4° and −63° were experimentally observed at excitation frequencies 2.59 and 2.48 THz, respectively.

MM-Wave Metamaterial Adjustable Antenna on Magnetically Biased Ferritic Substrate

The paper presents a mm-wave metamaterial coplanar waveguide (CPW) zeroth-order resonating (ZOR) antenna on magnetically biased ferrite substrate. The measurements demonstrate tuning of the resonant frequency and steering of the radiation characteristic depending on the strength of biasing magnetic field. The resonant frequency shifts about 1.1 GHz for magnetic biasing field strength variation between 0 T and 0.265 T. The return loss is reduced as result of elimination of ferrite low field loss. The radiation characteristic in transversal plane steers between approximately −15° and +14° depending on the magnetic field strength. In the magnetically unbiased state the antenna gain is 4.16 dBi and increases slightly to 4.22 dBi due to small field loss reduction following the magnetic polarization application.

Experimental study of EIT-Like phenomenon in a metamaterial plasma waveguide

This paper demonstrates the realization of the electromagnetically induced transparency (EIT)-like transmission in a metamaterial plasma waveguide with double side defects based on transmission lines. The waveguide with a single side defect works as a plasma resonator and the resonance wavelength is determined by the Fabry-Perot resonance of surface plasma. While in a waveguide with double side defects, a transmission peak appears between the two resonators frequencies because of the destructive interference between the resonance modes of the two resonators, which indicates a pronounced EIT phenomenon. The experiment results agree well with simulations in microwave frequencies.

Phase constant peculiarities of cylindrical zero-index anisotropic metamaterial waveguide

Here, we present the phase constant dependencies of propagating eigenmodes of an open cylindrical anisotropic metamaterial waveguide when the metamaterial permittivity and permeability tensor components may accept values close or equal to zero. Dispersion characteristics of rod and hollow-core waveguides with the radii 0.5, 2.5, and 5 mm at the left-handed polarization of the microwave are shown here. There are unusual shapes of eigenmode dispersion characteristics and anomalous sectors of the characteristics at certain frequencies. The first eigenmode of the rod waveguide with the lowest cutoff frequency is a particularly important mode because it is a single one in the frequency range 1.0–1.9 GHz, and some small variations on the frequency produce large changes in the phase constant. We can observe packages of dispersion characteristic branches when their cutoff frequencies closed to the metamaterial electric and magnetic plasma frequencies between 1.9 and 3.5 GHz. There are only three modes in the hollow core anisotropic metamaterial waveguide at the frequency range 1.4–2.8 GHz.

Giant transverse optical forces in nanoscale slot waveguides of hyperbolic metamaterials

Here we demonstrate that giant transverse optical forces can be generated in nanoscale slot waveguides of hyperbolic metamaterials, with more than two orders of magnitude stronger compared to the force created in conventional silicon slot waveguides, due to the nanoscale optical field enhancement and the extreme optical energy compression within the air slot region. Both numerical simulation and analytical treatment are carried out to study the dependence of the optical forces on the waveguide geometries and the metamaterial permittivity tensors, including the attractive optical forces for the symmetric modes and the repulsive optical forces for the anti-symmetric modes. The significantly enhanced transverse optical forces result from the strong optical mode coupling strength between two metamaterial waveguides, which can be explained with an explicit relation derived from the coupled mode theory. Moreover, the calculation on realistic metal-dielectric multilayer structures indicates that the predicted giant optical forces are achievable in experiments, which will open the door for various optomechanical applications in nanoscale, such as optical nanoelectromechanical systems, optical sensors and actuators.

Ultra-small single-negative electric metamaterials for electromagnetic coupling reduction of microstrip antenna array

We report initially the design, fabrication and measurement of using waveguided electric metamaterials (MTM) in the design of closely-spaced microtrip antenna arrays with mutual coupling reduction. The complementary spiral ring resonators (CSRs) which exhibit single negative resonant permittivity around 3.5GHz are used as the basic electric MTM element. For verification, two CSRs with two and three concentric rings are considered, respectively. By properly arranging these well engineered waveguided MTMs between two H-plane coupled patch antennas, both numerical and measured results indicate that more than 8.4 dB mutual coupling reduction is obtained. The mechanism has been studied from a physical insight. The electric MTM element is electrically small, enabling the resultant antenna array to exhibit a small separation (λo/8 at the operating wavelength) and thus a high directivity. The proposed strategy opens an avenue to new types of antenna with super performances and can be generalized for other electric resonators.

The dispersion characteristics of metamaterial waveguide modes

The eigenmodes and noneigenmodes of a planar metamaterial dielectric waveguide are investigated. The dispersion dependences and field distributions of the modes are calculated for structures with step and parabolic profiles of the permittivity and permeability. It is shown that the magnetic field can exhibit an anomalously large increase in a waveguide with variable permittivity and permeability profiles. The effect of the nonlinearities of media on the mode propagation coefficients is studied.

Nanoscale metamaterial optical waveguides with ultrahigh refractive indices

We propose deep-subwavelength optical waveguides based on metal-dielectric multilayer indefinite metamaterials with ultrahigh effective refractive indices. Waveguide modes with different mode orders are systematically analyzed with numerical simulations based on both metal-dielectric multilayer structures and the effective medium approach. The dependences of waveguide mode indices, propagation lengths and mode areas on different mode orders, free space wavelengths and sizes of waveguide cross sections are studied. Furthermore, waveguide modes are also illustrated with iso-frequency contours in the wave vector space in order to investigate the mechanism of waveguide mode cutoff for high order modes. The deep-subwavelength optical waveguide with a size smaller than {\lambda}0/50 and a mode area in the order of 10-4 {\lambda}02 is realized, and an ultrahigh effective refractive index up to 62.0 is achieved at the telecommunication wavelength. This new type of metamaterial optical waveguide opens up opportunities for various applications in enhanced light-matter interactions.

Macroscopic electromagnetic response of arbitrarily shaped spatially dispersive bodies formed by metallic wires

In media with strong spatial dispersion the electric displacement vector and the electric field are typically linked by a partial differential equation in the bulk region. The objective of this work is to highlight that in the vicinity of an interface the relation between the macroscopic fields cannot be univocally determined from the bulk response of the involved materials, but requires instead the knowledge of internal degrees of freedom of the materials. We derive such relation for the particular case of "wire media", and describe a numerical formalism that enables characterizing the electromagnetic response of arbitrarily shaped spatially dispersive bodies formed by arrays of crossed wires. The possibility of concentrating the electromagnetic field in a narrow spot by tapering a metamaterial waveguide is discussed.

Revealing the truth about ‘trapped rainbow’ storage of light in metamaterials

It was claimed that the incident light can be gradually slowed down and finally trapped in a tapered metamaterial waveguide. Here we show that the energy incident from the input port of the tapered metamaterial waveguide will be totally reflected (instead of being trapped) due to the strong intermodal coupling between the forward and backward modes. The underlying physical mechanism for this strong intermodal-coupling is given. The occurrence of energy reflection is unambiguously proved using several independent methods, (1) the semi-analytical mode matching technique, (2) the numerical finite element simulation, (3) the requirement of energy and momentum conservation, and (4) an experimental verification at microwave frequency. The dream of ‘trapped rainbow’ for storage of light might still be possible if this intermodal coupling could be blocked, and our study provides a useful guidance for such an endeavor.

Optical field enhancement in nanoscale slot waveguides of hyperbolic metamaterials

Nanoscale slot waveguides of hyperbolic metamaterials are proposed and demonstrated for achieving large optical field enhancement. The dependence of the enhanced electric field within the air slot on waveguide mode coupling and permittivity tensors of hyperbolic metamaterials is analyzed both numerically and analytically. Optical intensity in the metamaterial slot waveguide can be more than 25 times stronger than that in a conventional silicon slot waveguide, due to tight optical mode confinement enabled by the ultrahigh refractive indices supported in hyperbolic metamaterials. The electric field enhancement effects are also verified with the realistic metal-dielectric multilayer waveguide structure.

Group velocity reduction in multilayer metamaterial waveguide

Stopping light using metamaterial optical waveguide is one of recent research outlines to realize optical memory. Complete stopping is impossible because of nonzero optical loss in metamaterial waveguides. The group velocity will be much higher than zero in real metamaterial waveguides having considerable optical loss. There are a huge try to compensate observed optical loss in metamaterial using active waveguides. In this paper, we study the possibility of more reduction of group velocity in real metamaterial waveguides using multilayer structure with dielectric and single negative (SNG) layers as cladding. Our obtained results show that more group velocity reduction is possible without using active waveguide and optical amplifier.

Low-loss surface modes and lossy hybrid modes in metamaterial waveguides

We show that waveguides with a dielectric core and a lossy metamaterial cladding (metamaterial-dielectric guides) can support hybrid ordinary-surface modes previously only known for metal-dielectric waveguides. These hybrid modes are potentially useful for frequency filtering applications as sharp changes in field attenuation occur at tailorable frequencies. Our results also show that the surface modes of a metamaterial-dielectric waveguide with comparable electric and magnetic losses can be less lossy than the surface modes of an analogous metal-dielectric waveguide with electric losses alone. Through a characterization of both slab and cylindrical metamaterial-dielectric guides, we find that the surface modes of the cylindrical guides show promise as candidates for all-optical control of low-intensity pulses.

Realizing almost perfect bending waveguides with anisotropic epsilon-near-zero metamaterials

We study metamaterials with an anisotropic permittivity tensor in which one component is near zero. We find that such an anisotropic metamaterial can be used to control wave propagation and construct almost perfect bending waveguides with a high transmission rate (>95%). This interesting effect originates in the power flow redistribution by the surface waves on the input and output interfaces, which smoothly matches with the propagating modes inside the metamaterial waveguide. We also find that waves in such anisotropic epsilon-near-zero materials can be reflected by small-sized perfect magnetic conductor defects. Numerical calculations have been performed to confirm the above effects.

Excitation of an electrically thick metamaterial waveguide of a finite length

The problem of diffraction of a cylindrical wave by a plate whose medium has a negative refractive index (a metamaterial) is numerically solved. The near and far fields are investigated for the case when a cylindrical wave source is located near the narrow butt-end of a long plate and when the metamaterial of the plate has various values of the permittivity and permeability. The results obtained are interpreted in terms of the geometric optics. It is shown that a plate made from such a metamaterial can be applied for fabricating antennas with multi- and single-lobe patterns.

Promising Future of Metamaterials

This article summarized and reviewed the realization and applications of the waveguide-based metamaterial structures. In particular, an overview of the existing metamaterial elements was presented. We discussed the possible solutions to enable wave propagation below the waveguide cutoff frequency by loading these elements. Then a detailed analysis on those waveguide unit-cells loaded with different metamaterial elements was provided based on HFSS simulation. Various guided and radiated microwave applications based on these novel metamaterial-based waveguide structures were presented. Those obtained simulation and experimental results were found to be in good agreement with the theoretical prediction. These applications also demonstrate that the combination of waveguide structure and metamaterials offers an excellent alternative approach to the design of miniaturized and high-performance microwave components. Waveguide has high-power handling capability and high Q-factor. It also provides a uniform and lossless ε-negative (μ-negative) environment when operated based on the TE modes (TM modes) below the cutoff frequency. This is a promising and potentially rewarding research topic. We are looking forward to achieving more truly high-performance metamaterial devices by taking advantages of these features in the near future.