Cut-wire Structure Research Articles

Analogue of Electromagnetically Induced Transparency Based on Bright–Bright Mode Coupling Between Spoof Electric Localized Surface Plasmon and Electric Dipole

We report a novel type of electromagnetically induced transparency (EIT) analogue based on metamaterials (MMs) with hybrid structures, in which spiral and cut-wire structures serve as bright-mode resonators with the spoof electric localized surface plasmons and electric dipole resonance. With the simulations and experiments, the EIT analogue generated by the frequency detuning and hybridization between the resonators is verified. The simulated surface charge density and electric and magnetic field distributions, together with the theoretical analysis based on the Lorentz oscillator model, reveal the principle of the EIT analogue. Moreover, the transmission window of the MM demonstrates linear dependence on the refractive index’s change of surrounding media, showing the potential as a tool for environmental detection.

Fano-Resonant Hybrid Metamaterial for Enhanced Nonlinear Tunability and Hysteresis Behavior.

Artificial resonant metamaterial with subwavelength localized filed is promising for advanced nonlinear photonic applications. In this article, we demonstrate enhanced nonlinear frequency-agile response and hysteresis tunability in a Fano-resonant hybrid metamaterial. A ceramic cuboid is electromagnetically coupled with metal cut-wire structure to excite the high-Q Fano-resonant mode in the dielectric/metal hybrid metamaterial. It is found that the significant nonlinear response of the ceramic cuboid can be employed for realization of tunable metamaterials by exciting its magnetic mode, and the trapped mode with an asymmetric Fano-like resonance is beneficial to achieve notable nonlinear modulation on the scattering spectrum. The nonlinear tunability of both the ceramic structure and the ceramic/metal hybrid metamaterial is promising to extend the operation band of metamaterials, providing possibility in practical applications with enhanced light-matter interactions.

Tunable Electromagnetically Induced Transparency in Asymmetric Graphene-Based Metamaterial at Terahertz Region

We theoretically investigate the active control of electromagnetic induced transparency (EIT) in a terahertz graphene-based metamaterial, whose unit cell structure is composed two perpendicularly connected graphene cut-wires. The theoretical investigations and field distributions reveal that the EIT window arises from the destructive interference caused by asymmetric coupling between two cut-wire structures. Moreover, the strength and frequency of the EIT peak, the associated group delay and delay bandwidth product can be actively controlled. Therefore, the work presents a novel modulation strategy for controlling EIT behavior and exhibits potential applications for switching, modulation, and slow-light devices.

Actively modulated propagation of electromagnetic wave in hybrid metasurfaces containing graphene

Here we present the actively modulated transportation of electromagnetic wave through hybrid metasurfaces containing graphene. The hybrid metasurfaces are composed of patterned metallic layers of extraordinary transmission and backed with graphene-sandwich layers. With the designed metallic layer with perforated structure, we demonstrated effective modulation on the on-resonance transmission amplitude by increasing the bias voltage from 0 to 4 V to electrically tune the Fermi level as well as the sheet resistance of the graphene-sandwich structure. We also found that the modulation depth can be further improved by properly designing the perforated metallic structure. By change the geometry from cut-wire structure to the “butterfly”-like pattern we preliminarily achieved 19.2% improvement on the on-resonance transmission modulation. The measured transmittances of the active metasurfaces show good agreement with the numerical simulations with fitted graphene sheet resistances. The hybrid metasurfaces presented in this work may be deployed in a wide range of applications based on active electromagnetic or optical modulations.

Broadband Polarization Conversion Metasurface Based on Metal Cut-Wire Structure for Radar Cross Section Reduction.

A class of linear polarization conversion coding metasurfaces (MSs) based on a metal cut-wire structure is proposed, which can be applied to the reduction properties of radar cross section (RCS). We firstly present a hypothesis based on the principle of planar array theory, and then verify the RCS reduction characteristics using linear polarization conversion coding MSs by simulations and experiments. The simulated results show that in the frequency range of 6–14 GHz, the linear polarization conversion ratio reaches a maximum value of 90%, which is in good agreement with the theoretical predictions. For normal incident x- and y-polarized waves, RCS reduction of designed coding MSs 01/01 and 01/10 is essentially more than 10 dB in the above-mentioned frequency range. We prepare and measure the 01/10 coding MS sample, and find that the experimental results in terms of reflectance and RCS reduction are in good agreement with the simulated ones under normal incidence. In addition, under oblique incidence, RCS reduction is suppressed as the angle of incidence increases, but still exhibits RCS reduction effects in a certain frequency range. The designed MS is expected to have valuable potential in applications for stealth field technology.

Utilizing the plasmonic resonance to enhance three wave mixing effects in nano-scale cut-wire

In this paper, quantitative study of the enhanced three wave mixing effects from periodic array of nano-scale golden cut-wires embedded in nonlinear dielectric is performed. Geometrical parameters of the considered structure are chosen so that the plasmonic resonance occurs in the wavelength 1.5 μm. Plasmonic resonance of this structure gives rise to the localization factor significantly larger than that of the cut-wire structures with no plasmonic resonance. Considering the surrounding medium of the cut-wire a typical second-order nonlinear optical medium, enhancement of the nonlinearity of this nonlinear medium is illustrated. Since the mentioned structure can be considered a homogeneous nonlinear medium with the effective nonlinear susceptibility, nonlinear retrieval method is used to determine the effective nonlinear susceptibility for all four frequency combinations. Maximum enhancement of the effective susceptibility is obtained for the second harmonic generation of the applied wave with the frequency corresponding to the plasmonic resonance, with the enhancement up to two orders of magnitude. Efficiency of the second harmonic generation in this resonant structure surrounded with nonlinear dielectric is calculated to be 30 times more than that of the nonlinear dielectric with the same dimensions.

Realization of low-scattering metamaterial shell based on cylindrical wave expanding theory

In this paper, we demonstrate the design of a low-scattering metamaterial shell with strong backward scattering reduction and a wide bandwidth at microwave frequencies. Low echo is achieved through cylindrical wave expanding theory, and such shell only contains one metamaterial layer with simultaneous low permittivity and permeability. Cut-wire structure is selected to realize the low electromagnetic (EM) parameters and low loss on the resonance brim region. The full-model simulations show good agreement with theoretical calculations, and illustrate that near -20dB reduction is achieved and the -10 dB bandwidth can reach up to 0.6 GHz. Compared with the cloak based on transformation electromagnetics, the design possesses advantage of simpler requirement of EM parameters and is much easier to be implemented when only backward scattering field is cared.

Enhanced second order nonlinearity using plasmonic resonance of nano-scale metallic cut-wires

In this paper, we study quantitatively the enhanced second harmonic generation from periodic array of nano-scale golden cut-wires embedded in nonlinear dielectric. Geometrical parameters of this structure are varied so that the plasmonic resonance occurs in the wavelength of Nd:YAG laser (1064 nm), which its second-harmonic (with the wavelength 532 nm) is usually used in optical devices. Plasmonic resonance of these structures gives rise to the localization factor more than two times larger than that of the cut-wire structures with no plasmonic resonance. After then, surrounding medium of the cut-wire is considered a typical second-order nonlinear optical medium. In order to show the enhancement of the nonlinearity, unit cell of the cut-wires embedded in nonlinear medium is considered a homogeneous nonlinear medium with the effective nonlinear susceptibility. Nonlinear retrieval method, which is based on the transfer matrix approach, is used to determine the effective nonlinear susceptibility. The obtained results show the enhancement of the effective nonlinear susceptibility two orders of magnitude larger compared to the susceptibility of the embedding nonlinear dielectric. Efficiency of the second harmonic generation in these resonant structures surrounded with nonlinear dielectric is calculated to be 20 times more than that of the nonlinear dielectric with the same dimensions.

Experimental verification of the bending of electromagnetic waves using metamaterials

In this study, the bending of electromagnetic waves using metamaterials in free space was demonstrated. The optical transformation approach was utilized to design the bend, and the required metamaterials are inhomogeneous and anisotropic. The corresponding parameter-reduced metamaterials were realized using nonresonant cut-wire structures, which worked over an ultrabroad bandwidth with uniform permittivities and permeabilities. A microwave horn antenna focused the electromagnetic wave into the bend. The radiation patterns of the horn with and without bend were compared. The experimental and full-wave simulation results showed that the electromagnetic waves were bent in the desired direction.

Investigation on the role of the dielectric loss in metamaterial absorber

The authors report a metamaterial (MM) consisting of cut-wire structures which shows near-perfect absorption at microwave frequencies. Experimental results show slight lower performance than simulation. The analysis of the spectra and retrieved electromagnetic parameters demonstrate that the mismatch is attributed to the considerable influence of the dielectric loss on the strength of the electric and magnetic resonances, which largely determines the ability of the MM absorber. Such dependence on dielectric loss provides an important clue for the design of MM absorber aiming at specific applications where high efficiency energy collection in dielectric is needed.

Left-handed transmission in a simple cut-wire pair structure

It is well known that, together with the plasma behavior of continuous wires, the use of cut-wire pair as a metamagnetic component is to drive the negative permeability in the left-handed combined structure. In this study, we have investigated a strange left-handed transmission in a metamaterial consisting of only conventional cut-wire pair structure without additional adjustment. It is shown that the observed left-handed behavior, which occurs at a frequency three times higher than that for the combined structure, originates from the fundamental negative permittivity provided by the symmetric resonant mode and a negative permeability by the third-order asymmetric resonance. Our results would simplify extremely the fabricating procedure, especially, for terahertz regime as well as reveal many possibilities to design optical devices based on the electromagnetic responses of cut-wire structure.