Negative Refractive Index Materials Research Articles

Evanescent wave in multiple slit diffraction and n-array antennas in metamaterial using Cesàro convergence

In this paper, we study Multiple slit diffraction and n- array linear antennae in negative refractive index material. We show that the evanescent wave plays a vital role in the near-field term. The evanescent wave grows significantly, unlike in conventional materials, and satisfies a novel kind of convergence known as Cesàro convergence. We calculate the intensity of multiple slits and the antenna’s amplification factor (AF) in terms of the Riemann zeta function. We further demonstrate that the Riemann zeta function gives rise to additional nulls. We deduce that all the diffraction scenarios in which the traveling wave satisfies the geometric series in the medium of the positive refractive index will enhance the evanescent wave, which satisfies Cesàro convergence in the medium of the negative refractive index.

The Influence of Nonlocal Metal-Dielectric Environments on Physical and Chemical Processes.

ConspectusPlasmonic nanolayers and laminar metallic/dielectric multilayers were originally developed for optical cloaking applications and lensing applications that could potentially image objects whose size was below the diffraction limit. These assemblies were initially formed from gold or silver nanorods grown within an alumina mesh. However, more recently, assemblies with similar properties have also been prepared by sequential thin-layer deposition of alternating layers of gold and magnesium fluoride (MgF2). These metal/dielectric composite materials enable control of the dielectric constant in the directions perpendicular to the layers and balance the real and imaginary dielectric constants of the assembly such that the speed and the amplitude of the waves traveling through the assembly are not attenuated.In this Account, we will also focus on a few of the applications ranging from surface wetting to fluorescence quenching to enhancement of photochemical reactions. First, we will share an introduction to processes used to create these materials, which are combinations of low refractive index metals and transparent higher index materials arranged in a scalable repeating fashion. Two fabrication methods were employed: an electrochemical deposition of Ag nanorods into an anodized alumina matrix which produced materials with an anisotropic negative refractive index material within the plane of the film and lamellar metal/dielectric layers in which the negative index perpendicular to the growth direction. These alternating layers of plasmonic metals and dielectric materials were ultimately chosen to prepare films for further testing, because of their relative ease of fabrication. We will continue with a discussion of a few of the applications of both of these nonlocal dielectric composite materials including more specialized plasmonic, composite, and hyperbolic metamaterials including fluorescence quenching, photochemical reactions, and surface wetting. In each of these applications, the unique response caused by the enhancement of the electric field and the interface between hyperbolic materials and plasmonic materials as they interact photophysically with their near neighbors is presented. In each of the applications, the enhanced electric field extends from the composite substrate layer to interact with its near neighbors and beyond. The presence of this extended interaction can be observed in the form of decreased emission lifetime, enhancement of photochemical reaction rates, and changes in the surface energies measured by contact angle goniometry. In this Account, all of these situations will be addressed. Finally, we will conclude with a summary and vision for the future as well as a discussion of the unique challenges and opportunities available as research active faculty at an HBCU.

Engineered photonic spin Hall effect of Gaussian beam in antisymmetric parity-time metamaterials

A model of the photonic spin Hall effect (PSHE) in antisymmetric parity-time (APT) metamaterials with incidence of Gaussian beams is proposed here. We derive the displacement expression of the PSHE in APT metamaterials based on the transport properties of Gaussian beams in positive and negative refractive index materials. Furthermore, detailed discussions are provided on the APT scattering matrix, eigenstate ratio, and response near exceptional points in the case of loss or gain. In contrast to the unidirectional non-reflection in parity-time (PT) symmetric systems, the transverse shift that arises from both sides of the APT structure is consistent. By effectively adjusting the parameters of APT materials, we achieve giant displacements of the transverse shift. Finally, we present a multi-layer APT structure consisting of alternating left-handed and right-handed materials. By increasing the number of layers, Bragg oscillations can be generated, leading to an increase in resonant peaks in transverse shift. This study presents a new approach to achieving giant transverse shifts in the APT structure. This lays a theoretical foundation for the fabrication of related nano-optical devices.

Light drag in an optically dense left-handed atomic medium

In this paper, we investigate the light drag in an optically dense negative refractive index medium. Our model is a four-level atomic system in which we demonstrate an enhancement of the light drag while keeping the negative refraction condition. Furthermore, we control the shift in the light drag by tuning both the strong coupling field and the detuning. Hence, we observe that the light drag in the negative refractive index material can be controlled to switch from subluminal to superluminal at various ranges of the detuning. Our system suggests a straightforward technique for realizing and controlling light dragging in materials with negative refractive indices, or ‘NRI,’ which might open the way for more efficient use of left-handedness in atomic systems.

Electronic and optical properties of boron nitride nanoribbons exploiting DFT

We have used density functional theory and the SIESTA code to investigate the electronic bandgap and optical spectra of zigzag boron nitride nanoribbons n-ZBNNRs (n = 18, 22, 26, 30). The electronic structure of the simulated nanoribbons reveals that they are semiconductors with a bandgap of 4.87–4.95 eV. For energies greater than 5 eV, the real part of the dielectric function suggests that ZBNNRs are negative refractive index materials. n-ZBNNRs also have a lower static refractive index than armchair graphene nanoribbons. The fundamental reason is that the boron nitride nanoribbons have more localized electrons. The optical absorption of n-ZBNNRs (n = 18, 22, 26, 30) is anisotropic for the x, y, and z polarizations as well. Moreover, Eoptical gap18-BNNRs = 4.95 eV, Eoptical gap22-BNNRs = 4.94 eV, Eoptical gap26-BNNRs = 4.92 eV, and E optical gap30-BNNRs = 4.87 eV. The maximum optical extinction occurs at E ≈ 6–7 eV for the y polarization and E ≈ 5–6 eV for the z-direction. Besides, by around 6 eV for the y polarization (and 5 eV for the z polarization), σ is almost 1500 Ω−1 cm−1 (and 860–1500 Ω−1 cm−1). The imaginary part of the optical conductivity indicates that for the low energy range, n-ZBNNRs (n = 18, 22, 26, 30) supply the conditions of the transverse-electric mode existence. In addition, for $$E_{y} \, > \,6$$ eV and $$E_{x} \, > \,5$$ , n-ZBNNRs (n = 18, 22, 26, 30) support the transverse-magnetic plasmons.

Modulation instability solitons in oppositely double-doped directed couplers with two negative refractive index material channel and non-Kerr nonlinearity

In a three-core nonlinear contrarily directed coupler with two negative-index material channels, we theoretically explore the instability in the presence of a non-Kerr-like nonlinear refractive-index shift. Through the use of linear stability analysis, we determine an expression for the instability gain. It is discovered that the septic saturation, the ratio of the forward- to backward-propagating wave power, pump power, and nonlinearity all have a substantial impact on the MI in the nonlinear three-core contrarily directed coupler. The septic and saturation nonlinearity is found to improve the MI in the case of forward-to-backward ratio power (f) by boosting the width and gain of the instability profile in both normal and abnormal dispersion regimes. However, septic nonlinearity improves the MI in the case of pumps by boosting both its width gain and in the abnormal dispersion regime alone. Using 2D pictures, we could investigate the MI's dynamic behaviour during an anomalous dispersion regime. We discovered from the contour images that the gain of the instability profile grows as septic and saturation nonlinearity increases in both normal and abnormal dispersion regimes. So, with a focus on a negative refractive material channel in the existence of contamination and saturation nonlinearity, we report new techniques for producing and controlling MI and soliton in three-core contrarily directed couplers.

Propagation characteristics of adjustable abnormal hollow beams in gradient negative refractive index material

In this paper, the propagation characteristics of adjustable abnormal hollow (AAH) beams in gradient negative refractive index material are investigated theoretically and numerically. We focus on analyzing and discussing the intensity pattern, beam width and axial intensity of AAH beam, and give the mathematical expressions of these physical quantities. The results show that the AAH beams can have many different evolution forms. In general, the intensity pattern of AAH beam changes periodically during the propagation, but solitons can be formed under special parameters. Through parameter control, the beam width of AAH beam can be widened or compressed in one or two transverse directions, or even constant in one transverse direction and periodically changed in the other transverse direction. The evolution of axial light intensity of AAH beam can also show different transmission types such as concave type, flat-top type and convex type.

Spectral analysis of scattering resonances with application on high-contrast nanospheres

In this paper, we provide further spectral analysis of the general asymptotic scattering resonances formula of small 3D dielectrics of arbitrary shape with high contrast, already derived in other works to a first-order approximation. To investigate the components of a full expansion of such resonances, a breakdown is presented for the case of high-contrast nanospheres, in terms of its radius h in the interval [0, 1]. We also derive, for radially symmetric fields, an exact resonance formula for a spherical scatterer in terms of its radius, not necessarily small, and dielectric susceptibility coefficient, not necessarily high. This formula is further developed and simplified in the case of high contrast nanospheres. Such formulas are useful in imaging applications to identify objects’ properties from frequency measurements. Another application is the study of negative refractive index materials, such as metamaterials, and the anomalous localized resonance phenomenon (ALR) that is associated with cloaking and superlensing.

Dielectric-Metamaterial Reflectors for Effective Absorption of Light in Solar Cells

Recent designs of dielectric-metamaterial composites have some advantages in improving the coupling effect of light in the visible region. The refractive index of the designed metal mesh or fishnet metamaterial structure consists of metals such as Ag, Cu and Al with MgF2 dielectric material as the substrate which is calculated theoretically using Bruggeman equation. It has been established recently that the dielectric-metamaterial reflector coating (DMMRC) produces outstanding results. It drastically increases the internal reflection and enhances absorption in the visible region. DMMRC is designed by two slabs with exclusive thickness and contrary refractive indices. One is dielectric material and the other is negative refractive index material (NIM). This theoretical model can be treated as a photonic crystal and hence novel light trapping mechanism can be revealed. The transmission spectrum is analyzed using the transverse matrix method (TMM). This system may also be analyzed for various incident angles and for various substrates which are used to improve the efficiency of the solar cell.

Overview of Planar Antenna Loading Metamaterials for Gain Performance Enhancement: The Two Decades of Progress

Metamaterials (MTMs) are artificially engineered materials with unique electromagnetic properties not occurring in natural materials. MTMs have gained considerable attention owing to their exotic electromagnetic characteristics such as negative permittivity and permeability, thereby a negative refraction index. These extraordinary properties enable many practical applications such as super-lenses, and cloaking technology, and are used to design different electromagnetic devices like filters, polarization converters, sensors, and absorbers. Advances in MTMs have made new application fields to emerge in communication subsystems, especially in the field of antennas. MTMs are usually arranged in front or above the radiating element, or incorporated in the same substrate to improve the performance of planar antennas, in terms of improving directivity, gain, bandwidth, and efficiency, reducing the size and mutual coupling, and deflecting the radiation characteristics. High gain antennas are demanded in modern wireless communication systems. Their importance is in improving the signal strength by reducing the interference and alleviating the free space path loss. This review paper provides a brief introduction to MTMs, with the focus on their operating principles. Furthermore, a detailed study of antenna gain enhancement based on the various properties of MTMs is carried out. MTMs with low values of constitutive parameters; zero-index material (ZIM), low-index material (LIM), epsilon-near-zero (ENZ), and mu-near-zero (MNZ) are discussed in detail in the context of their capability to enhance the gain of a broad class of planar antennas. The low impedance property and lensing property, which is achieved by three different characteristics: high refractive index (HRI), gradient refractive index (GRIN), and negative refractive index (NRI) materials, are loaded to planar antennas for gain enhancement. The scope of this review has been limited to antennas that were experimentally validated in the respective source papers.

Optical Properties of Nano-circuits for Metallic and Non-Metallic Nanoparticles

Optical properties of the nanoparticles can be studied theoretically by using the lumped electronic components. The particles having >0 behaved as capacitor whereas for <0 had inductor properties on the other hand the electric field perpendicular to the components then the properties of series combinations dominates and vice versa. A first principles electronic structure based method is presented to determine the equivalent circuit representations of nanostructured physical systems at optical frequencies, via a mapping of the effective permittivity calculated for a lattice of physical nano-elements using density functional theory to that calculated for a lattice of impedances using circuit theory. Specifically, it is shown that silicon nanowires and carbon nanotubes can be represented as series combinations of inductance, capacitance and resistance. It is anticipated that the generality of this approach will allow for an alternate description of physical systems at optical frequencies, and in the realization of novel opto and nanoelectronic devices, including negative refractive index materials.

Equivalence between positive and negative refractive index materials in electrostatic cloaks

We investigate, both theoretically and numerically, the equivalence relationship between the positive and negative refraction index dielectric materials in electrostatic invisibility cloak. We have derived an analytical formula that enables fast calculate the corresponding positive dielectric constant from the negative refraction index material. The numerical results show that the negative refraction index material can be replaced by the positive refractive index materials in the static field cloak. This offers some new viewpoints for designing new sensing systems and devices in physics, colloid science, and engineering applications.

Designing “Metamolecules” for Photonic Function: Reduced Backscattering

Metamaterials, subwavelength nanostructured materials, can exhibit novel optical properties such as a negative index of refraction. Dielectric core–nanoparticle satellite clusters, termed “metamolecules,” can have strong optical magnetic resonances in the visible wavelength range—a requirement to achieve negative refractive index materials. However, achieving the desired photonic properties is challenging due to limited control in forming the metamolecule structures. Here, polystyrene (PS) core–gold nanoparticle (AuNP) satellite metamolecules with highly ordered single layers (monolayers) of AuNPs are fabricated and single particle spectroscopy, electron tomography structural measurements, and electrodynamics simulations are conducted to study the photonic properties of metamolecules constituted of ≈100 AuNPs. The simulated and experimental spectra of the many metamolecules studied, including excitation with azimuthally and radially polarized light, are in excellent agreement. It is shown that the scattering properties of the metamolecules are dominated by the AuNPs near the “equator” of the cluster, and that backscattering is strongly suppressed when different multipolar modes (e.g., dipolar and quadrupolar) of electric or optical magnetic character have comparable intensity due to the π‐phase shift of their scattering. Both the optical excitation fields and the ordering of the nanoparticles within metamolecules affect their optical excitation and scattering properties, providing new insights into designing novel photonic metamaterials.

Transmission Characteristics of Ultrasonic Longitudinal Wave Signals in Negative Refractive Index Materials

Longitudinal waves have important applications in modern scientific research and production; as a special acoustic wave, longitudinal waves have a sound transmission performance in negative refractive index materials. This paper has designed a new structure for negative refractive index materials by virtue of COMSOL software and conducted related simulation analysis. Experimental results illustrated that the structure designed had good acoustic longitudinal wave transmission performance. Besides, the effect of sound wave focusing could be achieved by a combination of existing test methods. The design proposed could break the limitation of previous structures on acoustic longitudinal wave transmission. This study is expected to have important implications for the development of solid metamaterial structures.

Tuning band structures of photonic multilayers with positive and negative refractive index materials according to generalized Fibonacci and Thue–Morse sequences

We investigate the photonic band structure, using the transfer-matrix method, in one-dimensional structures composed of a dispersive metamaterial A juxtaposed with a non-dispersive dielectric B according to the generalized Fibonacci and Thue–Morse sequences, which are ruled and characterized by two positive integer numbers, p and q. We present the band structures of different generations of these sequences for both TE and TM modes and discuss how they are affected by the p and q parameters and the ratio between the thicknesses of the building blocks. We obtain a new and very important analytical expression for the frequency in which the average refraction index vanishes, i.e. when the gap condition is satisfied, and we investigate, in detail, the behavior of this emergent scale insensitive gap, as a function of the thicknesses ratio, for all structures considered. For the metamaterial considered, we show that the reduced frequency for converges faster or slower to 0.41 depending on the sequence. By adjusting the p and q parameters, we can obtain a higher concentration of the pass bands inside (outside) the nA < 0 region when there are more (less) blocks A than B in the unit cell. Our results also show the presence of omnidirectional and complete band gaps, which have various practical and technological applications.

High-Sensitivity Detection of Hazardous Chemical by Special Featured Grating-Assisted Surface Plasmon Resonance Sensor Based on Bimetallic Layer

In this article, we present the analysis of a special featured grating-assisted surface plasmon resonance (SPR) phenomena by multiple stacked metamaterial and silver layers as one grating structure. The bimetallic layer of gold (Au) and silver (Ag) has been used with stacked multiple negative refractive index (NRI) metamaterial layers to explore the special featured sensing capability. NRI grating with Ag layer supports better coupling to excite the multimode for the proposed structure at the same excitation condition. Hence, the alternating layer of NRI material along with Ag is used as a grating structure that is an excellent combination of the grating layer through which the proposed structure supports better coupling to the adjacent sensing region. The grating parameters have been optimized in such a way to enhance the number of resonance modes in the sensing region. It is found that SPR sensor sensitivity using negative diffraction order has a larger dip, while the resonant angle became wider for positive diffraction order. The transfer matrix method is used for the calculation of various parameters. The special featured structure with corresponding response graphs is described along with discussing what happens when the metamaterial layer thickness varies (and vice versa). Sensitivity tunability is demonstrated with variable metamaterial layer thickness. A sensitivity study is a significant parameter in the design of any high-sensitive sensor to enhance the performance. Hence, the sensitivity slope property has been explored further for each case.

A graphene‐based tunable negative refractive index metamaterial and its application in dynamic beam‐tilting terahertz antenna

AbstractGraphene is emerging as a kind of promising 2D material in designing reconfigurable terahertz (THz) devices owning to its tunability of the surface conductivity, which can be tuned by changing the chemical potential. In this work, we demonstrated a graphene‐based THz tunable negative refractive index metamaterial. The proposed metamaterial unit consists of a metallic resonant structure and embedded graphene, which presents a dynamic negative refractive index in the corresponding bands by modulating the chemical potential of the embedded graphene. In addition, a dynamic beam‐tilting antenna loaded with the metamaterial‐based stacked configuration has been designed. Through changing the refractive index of the metamaterial or the number of layers in the stacked configuration, the steering angle can be adjusted from 0° to −27°. This work demonstrates the great potential of graphene in THz tunable negative refractive index materials, provides a classic case about the practical application of controllable negative refractive index, and also gives an effective way to design dynamic beam‐tilting antenna.

含负折射率材料光量子阱透射谱对比研究

含负折射率材料光量子阱透射谱对比研究

Left-handed lens tomography and holography

ABSTRACTPossibilities of the coherent scanning tomography with negative-index metamaterial lens are studied. Such lens (a slab of negative refractive index material) has the power to focus the source field into a sounded media with dielectric inhomogeneities. The proposed solution of the corresponding inverse scattering problem, i.e. the retrieval of 3D distributions of the complex permittivity in the inhomogeneous region, is based on the 3D integral equation for the scattered field that is reduced to the one-dimensional Fredholm integral equation of the 1-st kind relative to the depth profile of lateral spectrum of inhomogeneities. After the solution of this equation for each pair of spectral components, the inverse Fourier transform leads to the desired solution. For solid targets, it appeared possible to retrieve the shape of their surface with the computing holography algorithm. This approach can be very suitable for diagnostics of media with a plane or flexible surface, in particular, in the biomedical diagnostics. The feasibility of this tomography for low-contrast targets is demonstrated in numerical simulation.

Modeling the Chiral Imprinting Response of Oriented Dipole Moments on Metal Nanostructures

Chiral plasmonics is a growing field because of its potential to produce high-performance biomolecule sensors and negative refractive index materials. Understanding and controlling molecular properties and their effect on the chiroptical coupling between chiral molecular films and metal nanostructures is thus vital for the future design of devices. Here we develop and apply a theoretical method to study that coupling. We first extend the three-dimensional finite-difference time-domain method to include chiral molecular layers with arbitrarily oriented induced dipole moments relative to the nanostructure’s surface. We then use the methodology to investigate the chiral imprinting response from molecularly coated nanospheres as a test of the method. Finally we study a gold nanocross array to understand how long- and short-range interactions between the chiral molecular layer and the nanoparticles affect their optical response.