Metamaterial Slab Research Articles

Waveguide Method for Electromagnetic Parameter Extraction of Weakly Coupled Metamaterials

A retrieval method is proposed for electromagnetic parameter extraction of metamaterial (MM) slabs having electric coupling to magnetic resonance (weak coupling) from waveguide measurements. Underlying expressions of electromagnetic properties in the retrieval process are derived. The method is validated by the simulated and measured waveguide scattering parameters of an MM slab constructed by split-ring-resonators.

Conical Refraction of Elastic Waves by Anisotropic Metamaterials and Application for Parallel Translation of Elastic Waves

Conical refraction, which is quite well-known in electromagnetic waves, has not been explored well in elastic waves due to the lack of proper natural elastic media. Here, we propose and design a unique anisotropic elastic metamaterial slab that realizes conical refraction for horizontally incident longitudinal or transverse waves; the single-mode wave is split into two oblique coupled longitudinal-shear waves. As an interesting application, we carried out an experiment of parallel translation of an incident elastic wave system through the anisotropic metamaterial slab. The parallel translation can be useful for ultrasonic non-destructive testing of a system hidden by obstacles. While the parallel translation resembles light refraction through a parallel plate without angle deviation between entry and exit beams, this wave behavior cannot be achieved without the engineered metamaterial because an elastic wave incident upon a dissimilar medium is always split at different refraction angles into two different modes, longitudinal and shear.

Giant spin splitting induced by orbital angular momentum in an epsilon-near-zero metamaterial slab.

An orbital angular momentum (OAM)-induced spin splitting is theoretically predicted when a higher-order Laguerre-Gaussian beam is transmitted through a metamaterial slab. The upper bound of this spin splitting is found to be |ℓ|w0/(|ℓ|+1)1/2, where ℓ and w0 are the incident OAM and beam waist, respectively. By optimizing the structure parameter of the metamaterial, as well as the incident angle, the OAM-induced spin splitting can reach more than 0.99 of the upper bound in the cases of both the horizontal and vertical incident polarization states, and the transmitted light fields turn out to be full Poincaré beams. These findings provide a deeper insight into the spin-orbit interaction, and, thereby, facilitate the development of spin-based applications.

Spin Hall Effect Enhancement of Transmitted Light Through an Anisotropic Metamaterial Slab

We study the spin Hall effect (SHE) enhancement of transmitted light through an anisotropic metamaterial slab. Physical mechanism of large transverse shift is explained based on the coupling between spin angular momentum and orbit angular momentum. Theoretical analysis predicts large transverse shift of transmitted light can be realized by four possible combinations of real or imaginary z component of the wave vectors, which is verified by simulation results. The anisotropy of metamaterial brings greatly enhanced SHE of transmitted light but the metamaterial loss and dispersion will reduce the transverse shift significantly. A maximum transverse shift of 15.24 μ m (12λ) can be achieved in an anisotropic metamaterial of ZnGaO/ZnO multilayer without any amplification method.

Geometry Defines Ultrafast Hot‐Carrier Dynamics and Kerr Nonlinearity in Plasmonic Metamaterial Waveguides and Cavities

Hot carrier dynamics in plasmonic nanorod metamaterials and its influence on the metamaterial's optical Kerr nonlinearity is studied. The electron temperature distribution induced by an optical pump in the metallic component of the plasmonic metamaterial leads to geometry‐dependent variations of the optical response and its dynamics as observed in both the transmission and reflection properties of the metamaterial slab. Thus, the ultrafast dynamics of a metamaterial's optical response can be controlled via modal engineering. Both the transient response relaxation time and magnitude of the nonlinearity are shown to depend on the modal‐induced spatial profile of the electron temperature distribution and the hot‐electron diffusion in nanorods. The nonlocal effects, depending on the excitation‐induced losses in the metal, are shown to dictate the modal structure of the metamaterial slab and the associated dynamics of its nonlinear response. The opportunity of controlling the electron temperature profile induced in the plasmonic nanorods by changing the metamaterial's geometry and/or excitation conditions paves the way to achieve controllable dynamics of the nonlinear optical response for free‐space as well as integrated nanophotonic applications involving nonequilibrium electrons.

Analysis and experiments on Fano interference using a 2D metamaterial cavity for field localized wireless power transfer

To meet both safety and efficiency demands of future wireless power transfer (WPT) systems, field leakage to the nearby environment should be controlled below a certain level. Therefore, field localization is one of the key issues in advanced WPT systems. Recently, metamaterials have shown great potential for enhanced control of electromagnetic propagation in various environments. In this work, we investigate a locally modified metamaterial to create a two-dimensional (2D) cavity for field localization at a sub-wavelength scale. We also show that the field localization in the cavity can be explained using Fano-type interference. We believe that this is one of the first works demonstrating that Fano-type interference can be applied for resonance-coupled mid-range WPT. Using the proposed approach, we achieve a localized WPT in a region that is eight times smaller than that of a transmit coil. At a distance of 0.6 meters, the measured efficiency is 56.5%, which represents a six-fold and two-fold enhancement compared to free space and uniform metamaterial slabs, respectively.

Investigation of a metamaterial slab lens and an imaging system based on an ellipsoidal cavity.

A slab metamaterial lens with a refractive index of -1 is capable of producing a perfect image, since it transfers all the plane waves from the object plane to the image plane without creating any distortion in their amplitudes and phases. However, its practical implementation encounters several challenges. In this paper, a lossless slab metamaterial lens is investigated using the ray-tracing technique. We also discuss propagating waves and evanescent waves and investigate an imaging system based on an ellipsoidal cavity. It is shown that since an ellipsoidal cavity transfers the beams from one of its foci to the other with the same amplitude and phase, it acts similarly to a metamaterial slab lens of n=-1. Therefore, this structure can be used as a subwavelength resolution imaging system. Also, it does not suffer from chromatic aberration, since all the rays transmitted from one focus pass through the other independent of the wavelength. Another important advantage of this system, compared to metamaterial-based superlenses, is that it can operate at any frequency as long as the dimensions of the cavity are much larger than the wavelength.

A Broadband Ultrathin Nonlinear Switching Metamaterial

In this paper, an ultrathin planar nonlinear metamaterial slab is designed and simulated. Nonlinearity is provided through placing diodes in each metamaterial unit cell. The diodes are auto-biased and activated by an incident wave. The proposed structure represents a broadband switching property between two transmission and reflection states depending on the intensity of the incident wave. High permittivity values are presented creating a near zero effective impedance at low power states, around the second resonant mode of the structure unit cell; as the result, the incident wave is reflected. Increasing the incident power to the level which can activate the loaded diodes in the structure results in elimination of the resonance and consequently a drop in the permittivity values near the permeability one as well as a switch to the transmission state. A full wave as well as a nonlinear simulations are performed. An optimization method based on weed colonization is applied to the unit cell of the metamaterial slab to achieve the maximum switching bandwidth. The structure represents a 24% switching bandwidth of a 10 dB reduction in the reflection coefficient.

Gain Enhancement of Microstrip Patch Antenna Loaded with Split Ring Resonator Based Relative Permeability Near Zero as Superstrate

In this presented work, Split Ring Resonator (SRR) is arranged in 7X7X4 form to create a metamaterial superstrate which is incorporate on patch antenna. The SRR based metamaterial slab is analysed with Nicolson–Ross–Wier approach to extract the effective parameters of the medium. The Extracted parameters Shows that the relative permeability of the slab is near zero in the vicinity of the resonant frequency of the designed antenna. The experimental results clearly reflect that the gain of the superstrate loaded patch improves by 7.6 dB with variation less than 1 dB in the vicinity of resonant frequency. Structures are simulated on Ansoft HFSS v14 and experimentally verified.

Effective Constitutive Parameters Retrieval Method for Bianisotropic Metamaterials Using Waveguide Measurements

An effective method for extraction of electromagnetic properties of bianisotropic biaxial omega-type metamaterial (MM) slabs from waveguide measurements is presented. The method relies on measurements of S-parameters of two MM slab configurations (transverse and longitudinal) to extract electromagnetic properties endowed with strong bianisotropic coupling. An uncertainty analysis is performed for examining the effect of geometrical parameters of the longitudinal configuration on its resonance characteristic. For verification of the proposed method, constitutive parameters of a polyethylene sample are extracted at the $X$ -band (8.2–12.4 GHz). Then, the method is applied for extraction of electromagnetic properties of an MM slab (square split-ring resonators over FR4 substrate) using simulated and measured S-parameters for the two configurations at the $X$ -band. It is noted that extracted electromagnetic properties obtained from measured S-parameters are in good agreement with those obtained from simulated S-parameters except for a small frequency shift and magnitude change, which could arise from fabrication tolerances, air gaps present between MM cells, and local irregular surface of the longitudinal configuration. For completeness, it is analyzed whether extracted properties satisfy the locality conditions.

Effects of visco-thermal losses in metamaterials slabs based on rigid building units

Potential applications of negative-index acoustic metamaterials are strongly limited by absorptive effects of different origin. In this context, we present an investigation of the visco-thermal effects on the acoustic properties of double-negative metamaterials based on specifically designed rigid units with subwavelength dimensions. It is shown that visco-thermal losses dissipate about 70% of the acoustic energy associated to the excitation of monopolar and dipolar resonances, leading to the suppression of negative refractive index. Our numerical simulations based on the Boundary Element Method (BEM) are in excellent agreement with recent experimental data showing the quenching of the double-negative transmission peak. The BEM numerical model, which has been specifically adapted to this purpose, has also been validated against an equivalent Finite Element Method model. We also present the results and discuss the differences of visco-thermal effects on monopolar resonances leading to negative bulk modulus metamaterials, and Fabry-Perot resonances in metamaterial slabs.

Hyperbolic Carbon Nanoforest for Phase Matching of Ordinary and Backward Electromagnetic Waves: Second Harmonic Generation

We show that a deliberately engineered dispersive metamaterial slab can enable the coexistence and phase matching of ordinary fundamental and contra-propagating backward second harmonic electromagnetic waves. Energy flux and phase velocity are contra-directed in the backward waves, which is the extraordinary phenomenon that gives rise to unique nonlinear optical propagation processes. We demonstrate that frequencies, phase, and group velocities, as well as the losses inherent to the guided electromagnetic modes supported by such metamaterial, can be tailored to maximize the conversion of frequencies and to reverse the propagation direction of the generated second harmonic wave. Such a possibility, which is of paramount importance for nonlinear photonics, is proven using a numerical model describing the hyperbolic metamaterial made of carbon nanotubes standing on the metal surface. Extraordinary properties of the backward-wave second harmonic generation in the reflection direction and of the corresponding frequency doubling metareflector in the THz are investigated with a focus on the pulsed regime.

Tunable lateral shifts of the reflected wave on the surface of an anisotropic chiral metamaterial

The lateral shifts (i.e., the spatial GH shifts) of reflected wave from a uniaxial anisotropic chiral metamaterial slab are predicted based on the stationary-phase method. The two cases of the uniaxial chiral slab are investigated in detail. It is found that the negative uniaxial chiral slab can be realized for both the two cases as the group refraction of the left circularly polarized (LCP) wave is negative. The GH shifts of the perpendicular component (Δsp) are similar for both of the cases, which are enhanced at close-to-grazing incidence. However, the GH shifts of the parallel component (Δpp) can be enhanced near the Brewster angle. For case (I), by introducing a different chirality parameter and the thickness of the chiral slab, the transition between the positively and negatively enhanced GH shifts of the parallel component (Δpp) can be realized. For case (II), the magnitude and the position of the enhancement of the positively enhanced GH shifts (Δpp) can be tunable by adjusting the chirality and the thickness of the chiral slab.

Perfect Nonreciprocal Absorption Based on Metamaterial Slab

In order to achieve nonreciprocal absorption, we design a metamaterial slab made of arrays of tilted metal layers. Through studying the extraordinary material dispersion, we derive the transfer matrix to calculate its transmittance and absorption. Given specific conditions and two opposite incidence directions, the slab can achieve total absorption for one direction and total transmittance for the other direction. The designed structure is demonstrated to be a perfect nonreciprocal absorber.

Ultra-broadband and high-efficiency reflective linear polarization convertor based on planar anisotropic metamaterial in microwave region

A simple design of an ultra-broadband and high-efficiency reflective linear polarization convertor with 90° rotation is presented in the microwave region. This convertor is formed from the planar anisotropic metamaterial (MM) using cut-wire (CW) structure. Three resonance modes are generated by electric and magnetic fields of incident wave, which lead to bandwidth expansion extremely of cross-polarization reflection. The simulation result shows that a linearly polarized wave can be converted into its orthogonal polarization after reflection, the polarization conversion ratio is above 90% in the frequency range of 5.1–12.1GHz and the relative bandwidth is up to 78.6%, which agree well with the experimental results. Both simulation and experiment results demonstrate the capability of linear polarization conversion by 90° with high polarization purity after reflection in the above frequency range, which can be confirmed by ellipticity η and the polarization rotation azimuth angle θ. The designed structure that utilized to build the thin MM slab is about λ0/8.72 evaluated at operating center frequency. It has application values in polarization control with high performances.

Loss enhanced spin Hall effect of transmitted light through anisotropic epsilon- and mu-near-zero metamaterial slab.

Spin Hall effect of light (SHEL) is prosperous in precision metrology and quantum information processing. In normal situations, the inevitable loss of material will greatly weaken SHEL, which is a major constraint to its potential applications. We first report the loss enhanced SHEL through epsilon and mu-near-zero (EMNZ) metamaterial slab by anisotropic configuration of epsilon and mu tensors. It is verified that the loss of EMNZ metamaterial can effectively enlarge the splitting between right-circularly polarized (RCP) and left-circularly polarized light (LCP) components of linear polarized light even when the incident angle is much larger than critical angle. Calculation results show that when the imaginary part of permeability's vertical component is equal to 0.1, a flat-top transverse shift peak can be observed which remains unchanged for different vertical component of permeability and thickness of EMNZ metamaterial. In this case the maximum transverse shift of left-circularly polarized light can be increased to 24.676 micrometers by EMNZ metamaterial loss without any amplification method. Meanwhile, the transverse shifts of RCP (LCP) light can be modulated flexibly by EMNZ metamaterial loss. Therefore the loss enhanced SHEL makes quantum devices applicable which paves the way towards on-chip and inter-chip optical circuitry.

Collective dynamics and entanglement of two distant atoms embedded into single-negative index material.

We study the dynamics of two two-level atoms embedded near to the interface of paired meta-material slabs, one of negative permeability and the other of negative permittivity. This combination generates a strong surface plasmon field at the interface between the meta-materials. It is found that the symmetric and antisymmetric modes of the two-atom system couple to the plasmonic field with different Rabi frequencies. Including the Ohmic losses of the materials we find that the Rabi frequencies exhibit threshold behaviour which distinguish between the non-Markovian (memory preserving) and Markovian (memoryless) regimes of the evolution. Moreover, it is found that significantly different dynamics occur for the resonant and an off-resonant couplings of the plasmon field to the atoms. In the case of the resonant coupling, the field does not appear as a dissipative reservoir to the atoms. We adopt the image method and show that the dynamics of the two atoms coupled to the plasmon field are analogous to the dynamics of a four-atom system in a rectangular configuration. A large and long living entanglement mediated by the plasmonic field in both Markovian and non-Markovian regimes of the evolution is predicted. We also show that a simultaneous Markovian and non-Markovian regime of the evolution may occur in which the memory effects exist over a finite evolution time. In the case of an off-resonant coupling of the atoms to the plasmon field, the atoms interact with each other by exchanging virtual photons which results in the dynamics corresponding to those of two atoms coupled to a common reservoir. In addition, the entanglement is significantly enhanced.

Tunable polarization sensitive absorber made of graphene-based hyperbolic metamaterials

Theoretically, the absorption properties of a hyperbolic metamaterial (HMM) slab constructed from graphene-dielectric multilayers are investigated using the transfer matrix method. The effective medium approximation reveals that the graphene-based HMM slab is an anisotropic and homogeneous medium. It is shown that the absorption of the slab depend on the polarization and incidence angle due to the strong anisotropy of the HMMs. The results revealed that the complete absorption is only possible for the TM-polarized waves in a broad region of wavelength. It is found that the region of total absorption can be controlled and tuned using some controlling parameters such as incidence angle, the orientation of the optical axis of the HMM medium and the chemical potential of the graphene monolayers. Finally, the intensity distribution of a TM-polarized Gaussian beam is simulated which verifies the strong absorption of the waves inside the HMM slab. This absorber may have potential applications in the design of tunable filters, polarizers, detectors, photovoltaic devices and so on.

High-efficiency wireless power transfer by optimal load and metamaterial slab

High-efficiency wireless power transfer by optimal load and metamaterial slab

A Low-Profile High-Gain Substrate-Integrated Waveguide-Slot Antenna With Suppressed Cross Polarization Using Metamaterial

This letter presents a novel low-profile high-gain antenna with cross-polarization (x-pol) suppression using cross circular loop resonator (CCLR) metamaterial (MTM) slab in substrate-integrated waveguide-fed-slot antenna (SIW-SA). The SIW-SA antenna, which is the reference antenna, operates at 9.73 GHz. The CCLR MTM slab acts as a low-impedance slab, which is placed in the superstrate of the reference antenna at the height of only λ0 /10, where λ0 is the free-space wavelength at the resonance frequency of the antenna. At the broadside direction, the proposed antenna obtains 5.8 dB higher gain, 10 dB lower x-pol level (in both radiation planes), and 9.1 dB higher front-to-back ratio than the reference antenna, due to the presence of low-impedance slab. The simulated results are verified with fabrication and measurement.