Broadband Negative Refractive Index Research Articles

Realization of Broadband Negative Refractive Index in Terahertz Band by Multilayer Fishnet Metamaterial Approach

Realization of Broadband Negative Refractive Index in Terahertz Band by Multilayer Fishnet Metamaterial Approach

Realization of broadband polarization-insensitive negative refraction using water-based metamaterial

We propose a water-based metamaterial to realize the broadband polarization insensitive negative refraction. The designed metamaterial exhibits the multiple resonances in broadband region and displays negative permittivity and permeability simultaneously with a broadband negative refractive index. Simulated result shows that two separated wide bandwidths of negative refractive index are formed at 12.5–22.7 GHz, and 26.2–28.0 GHz, and the relative bandwidths of which are 58.0%, and 6.7%, respectively. In addition, beam shifting simulation is carried out to verify the retrieved effective refractive index from the scatter parameters, and the calculated results based on beam shifting simulation are agreed well with the retrieved effective refractive indices. Finally, the microwave measurement is performed to exam the simulated and calculated results, and three results of simulation, calculation, and measurement are consistent with each other. The design using water-based metamaterial provides an alternative approach to realize a broadband negative refraction.

Active control of the hybridization effect of near-field coupled resonators in metamaterial for a tunable negative refractive index at terahertz frequencies

To achieve broadband negative refraction, which is useful for many practical applications, recent studies have shown that the use of hybridization is one of the most effective methods. Nevertheless, reported studies often propose changing structural parameters rather than external factors. In this article, a method to control actively the bandwidth of negative refractive index (NRI) metamaterials based on second-order hybridization operating in the terahertz regime is proposed numerically by use of a simple disk-grid dimer. By use of the semiconductor InSb as the metallic component, the conductivity is tunable according to temperature, which changes the separation of magnetic resonant frequencies in second-order hybridization scheme and the plasma frequency of metamaterial. Consequently, the fractional bandwidth of the double-NRI region is extended. The mechanism of the phenomenon is explained clearly by both calculations and simulation. Finally, the fractional bandwidth of the NRI region was optimized by variation of the dielectric thickness of the disk-grid monomer and the thickness of the interlayer between the two monomers. The optimal fractional bandwidth is 10.4%, with a high transmitted power of 94% and a high figure of merit of 52.9 at 1.68 THz. Our results pave the way for the implementation of diverse semiconductors in tunable broadband NRI metamaterials at terahertz frequencies.

Synthesis and Simulation of Nano-Composite Metamaterial for Broadband Negative Refractive Index in Visible Spectral Regime

In this paper, a nano-metamaterial with the structure of Ag-SiO2-PbTe is proposed that has a random arrangement in the host medium of expanded polystyrene (foam) for the realization of a broadband negative refractive index at the visible spectrum. The negative refractive index for the purposed meta-material was obtained from the plasmonic resonance in the core and outer layer for both electric and magnetic components of light. Here, we use different radii for the outer layer of nanoparticles to create the broadband negative permeability. In this way, the doped semiconductor nanoparticles are included in the host medium to create the broadband negative permittivity. The overlap between the spectrum of the negative permittivity and permeability introduces the broadband negative refractive index at the visible band. The novel introduced structure creates the broadband negative refractive index and it is simple and practical for fabrication. For the realization of the proposed material, synthesis and characterization of the designed nanocomposite structure are investigated. To this end, the absorption and the transmission coefficients of the synthesized material are measured and compared with theoretical results. The obtained results indicate that the numerical simulations using Mie theory have good agreement with the experimental results.

Plasmonic hybridization in symmetric metamaterial for broadband negative refractive index: simulation, experiment and characterization

This work demonstrates a broad-band negative refractive index (NRI) by using the hybridization effect of dish-net dimer metamaterials (MMs), in the GHz frequency regime. Two symmetric layers of dishnet structure are expected to realize a wideband of negative refractive index with a high transmitted power of 88%, a high figure of merit of 26 at 15.2 GHz and to make the MM insensitive for polarization/wide-incident angle of electromagnetic wave. By adjusting the distance between these layers and their dielectric thickness, the NRI bandwidth are flexibly controlled. Further study indicates that the refractive index strongly depends on tangent loss of the dielectric substrate and number of hybridized modes. Also, we numerically investigate the hybridization characteristic in various operational frequency ranges. The performance of the proposed metamaterial is numerically, theoretically and experimentally demonstrated. This paper strengthens the novelty and computation of NRI metamaterials.

Simple structure THz metamaterial with broadband double-negative refraction

A broadband negative-refractive index metamaterial, composited of two square-shaped aluminum apertures with different title angles etched on both sides of polyimide substrate, has been proposed. The calculated results indicate that the coupling between the titled and untitled square-shaped apertures is more conducive to the high-pass and broadband transmission than the combination of two untitled structure. The high-pass band of metamaterial increases from 0.43 to 0.76 THz with the increasing aperture width from 30.0 to 35.0 μm, meanwhile, the maximum bandwidths of double-negative refraction and negative-refractive index can reach up to 0.58 and 0.78 THz, respectively. The highpass transmission mainly locates at the double-negative refraction region. Furthermore, the negative refraction of the NIMs has been verified by the classical method of the wedge, and the results show many unique properties of the symmetric slab waveguide based on the proposed NIM.

A broadband negative refractive index meta‐atom for quad‐band and sensor applications

AbstractA new modified hexagonal design structure with broadband‐negative refractive index metamaterial was proposed in this manuscript. The proposed structure was composed of two symmetrical metallic layers which had same thickness and an FR4 dielectric layer that was sandwiched between these metallic layers. Frequency domain solver of CST microwave studio, which is commercially available was utilized to observe the results of the design structure. The design structure was analyzed by two orientations with respect to the incident plane wave. For normal wave incidence, the suggested structure displays broadband negative refractive index (3.18 GHz) and (0.9 GHz) with a higher effective medium ratio (17.26) that was indicated small electrical size of the structure, whereas for parallel wave incidence, broadband negative refractive index (2.45 GHz), (1.22 GHz), and (1.93 GHz) bandwidth with a higher effective medium ratio (28.01) was obtained. The negative refractive index was verified by simulation and measurement for quad‐band applications. Furthermore, the effective medium ratio (λ/a) of the proposed broadband negative refractive index metamaterial was considerably improved compared to previous suggested multiband metamaterials. In addition, the design structure can also be utilized as a pressure sensor.

A broadband tunable terahertz negative refractive index metamaterial

A strategy to greatly broaden negative refractive index (NRI) band, reduce loss and ease bi-anisotropy of NRI metamaterials (MMs) has been proposed at terahertz frequencies. Due to the symmetric structure of the MM, the transmission and refractive index are independent to polarizations of incident radiations, and a broadband NRI is obtainable for the range of the incident angle from 0° to 26°. In addition, THz MMs’ properties such as transmission, phase and negative refraction exhibit a real-time response by controlling the temperature. The results indicate that the maximum bands of the negative and double-negative refraction are 1.66 THz and 1.37 THz for the temperature of 40 °C and 63 °C, respectively. The figure of merit of the MMs exceeds 10 (that is, low loss) as the frequency increases from 2.44 THz to 2.56 THz in the working temperature range, and the maximum figure of merit is 83.77 at 2.01 THz where the refractive index is −2.81 for a given temperature of 40 °C. Furthermore, the negative refraction of the MMs at the low loss band is verified by the classical method of the wedge, and the symmetric slab waveguide based on the proposed MM has many unique properties.

Hybrid three-dimensional dual- and broadband optically tunable terahertz metamaterials

The optically tunable properties of the hybrid three-dimensional (3D) metamaterials with dual- and broadband response frequencies are theoretically investigated in the terahertz spectrum. The planar double-split-ring resonators (DSRRs) and the standup double-split-ring resonators are fabricated on a sapphire substrate, forming a 3D array structures. The bi-anisotropy of the hybrid 3D metamaterials is considered because the stand-up DSRRs are not symmetrical with respect to the electric field vector. Due to the electric and magnetic response realized by the planar and the standup double-split-ring resonators respectively, the dual-band resonance response and the negative refractive index can be achieved. The potential of the phase modulation under photoexcitation is also demonstrated. Further analysis indicates that, photoexcitation of free carriers in the silicon within the capacitive region of the standup DSRRs results in a broad resonance response bandwidth (about 0.47 THz), and also functions as a broadband negative refractive index that roughly lies between 0.80 and 2.01 THz. This tunable metamaterials is proposed for the potential application of electromagnetic wave propagation in terahertz area.

Broadband negative refractive index obtained by plasmonic hybridization in metamaterials

We experimentally demonstrate a broadband negative refractive index (NRI) behavior in combined dimer and fishnet dimer metamaterials operating in the GHz frequency range. The observations can be well explained by a hybridization model and are in agreement with numerical modelling results. Hybridization of the magnetic resonances is obtained by reducing the distance between the layers in the dimer structures. A ratio of the double negative refractive index bandwidth to operational frequency of approximately 10% was achieved in the fishnet dimer. The applicable frequency range of the broadband NRI was shown to scale with the size of the structures from the microwave to the far infrared.

Broadband negative refractive index at visible range with composite materials

In this research work, composite media based on metamaterials including random distribution of spherical nanoparticles in a polymeric foam host are suggested to achieve negative effective refractive index in the visible spectrum. For this purpose structures including single, two and three layer spherical particles are investigated. Based on simulation results, media including single layer spheres (metallic and dielectric particles) and two layer nanospheres (core–shell particles consist of metallic core and dielectric shell) based on superposition of nanoparticles with different sizes and fill fractions are proposed for desired result. In this work, to obtain optimized band with negative RI media, superposition of three layer nanoparticles and doped semiconductor are designed.

Nanocomposite Multilayer Structure for Broadband MIR Negative Refractive Index

The main purpose of this study is designing a structure with the broadband negative refractive index (NRI) in the wavelengths range of 3–5 μm using multilayer structures. In the proposed structure, actually nanocomposite thin films are used to make multilayer waveguide to show effective NRI. In the composite structure, core-shell nanoparticles including metallic core and a dielectric shell with high refractive index are used. Here, it is shown that by increasing the number of composite layers, the bandwidth for NRI can be increased. Therefore, based on simulation results, in eight-layer waveguide, NRI is available in complete 3- to 5-μm MIR band. In this regard, also, the effect of filling factor (in each thin-film layer) on NRI is studied.

Design of fishnet metamaterials with broadband negative refractive index in the visible spectrum.

We propose a technique capable of designing fishnet metamaterials that have a negative refractive index (NRI) over a broad range in the visible and infrared. The technique relies on optimizing the shape and scale of the fishnet apertures as well as the depth of different layers of the composite. A metamaterial is obtained that exhibits an unbroken 552nm bandwidth of NRI, covering the entire red and infrared regions. Moreover, two fishnet structures perforated with star-like holes are found to render refractive index negative in the yellow and green spectra.

Measurement of a Broadband Negative Index with Space-Coiling Acoustic Metamaterials

We report the experimental demonstration of a broadband negative refractive index obtained in a labyrinthine acoustic metamaterial structure. Two different approaches were employed to prove the metamaterial negative index nature: one-dimensional extractions of effective parameters from reflection and transmission measurements and two-dimensional prism-based measurements that convincingly show the transmission angle corresponding to negative refraction. The transmission angles observed in the latter case also agree very well with the refractive index obtained in the one-dimensional measurements and numerical simulations. We expect this labyrinthine metamaterial to become the unit cell of choice for practical acoustic metamaterial devices that require broadband and significantly negative indices of refraction.

Dual-band metamaterial with a windmill-like structure

A broadband negative refractive index metamaterial based on a windmill-like structure is proposed, and investigated numerically and experimentally at the microwave frequency range. From the numerical and experimental results, effect media parameters are retrieved, which clearly show that two broad frequency bands exist in which the permittivity and permeability are negative. The two negative bands are from 9.1 GHz to 10.5 GHz and from 12.05 GHz to 14.65 GHz respectively, and the negative bandwidth is 4 GHz. Due to the good bandwidth performance, the metallic cell with double negative property obtained in this paper is suitable for use in the design of multiband or broadband microwave devices.

A novel structure for a broadband left-handed metamaterial

A low absorptivity broadband negative refractive index metamaterial with a multi-gap split-ring and metallic cross (MSMC) structure is proposed and investigated numerically and experimentally in the microwave frequency range. The effective media parameters were retrieved from the numerical and experimental results, which clearly show that there exists a very wide frequency band where the permittivity and permeability are negative. The influence of the structure parameters on the magnetic response and the cut-off frequency of the negative permittivity are studied in detail. This metamaterial would have potential application in designing broadband microwave devices.

A Broadband Three-Dimensionally Isotropic Negative-Refractive-Index Medium

When designing negative-refractive-index (NRI) metamaterials, scientists have struggled to overcome three primary obstacles: polarization dependence, narrow bandwidth, and fabrication challenges. Here, we address these issues with the design of a three-dimensional, fully isotropic, broadband NRI medium that can be produced on a large scale. The simulated structure exhibits a NRI bandwidth of 24.1%, more than twice that achievable using a typical split-ring resonator/wire medium. A four-hundred-unit-cell slab measuring 15 cm×15 cm×6 cm is fabricated and used as a flat NRI lens. The lens produces a super- resolved focus independent of the type of source or its polarization.

Three-dimensional surface current loops in broadband responsive negative refractive metamaterial with isotropy

We propose a bulk negative refractive index (NRI) metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed on the six sides of a cube for applications of superlenses. The structural characteristics of the three-dimensional (3D) metamaterial consist in the high symmetry and the superposition of metallic cross-pairs, which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI. The proposed 3D structure is simulated using the CST Microwave Studio 2006 to verify the design validity. The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic (EM) wave, but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%. In addition, the NRI band is insensitive to the polarization and the incident angle of the incident EM wave. Therefore, the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.