Uniaxial Metamaterials Research Articles

Magnetically tunable Brewster angle in uniaxial magneto-optical metamaterials for advanced integration of high-resolution sensing devices.

In this Letter, we introduce a concept to produce high-resolution, highly integrable biosensing devices. Our idea exploits the highly absorbing modes in multilayered metamaterials to maximize the transverse magneto-optical Kerr effect (TMOKE). Results are discussed in the context of dielectric uniaxial (ε eff,∥ ε eff,⊥>0) and hyperbolic metamaterial (ε eff,∥ ε eff,⊥<0) regimes. For applications in gas sensing, we obtained sensitivities of S = 46.02 deg/RIU and S = 73.91 deg/RIU when considering the system working in the uniaxial and hyperbolic regimes, respectively, with figures of merit (resolution) in the order of 310 or higher. On the contrary, when considering the system for biosensing applications (incidence from an aqueous medium), we observed that the proposed mechanism can only be successfully used in the uniaxial regime, where a sensitivity of 56.87 deg/RIU was obtained.

Mechanical response of a novel square dome shell with bistable behavior: Improved analytical method and empirical model

In this study, a novel square dome-shaped shell with a fascinating bistable behavior is proposed, which is able to quickly switch to a new stable configuration within its elastic range under a certain load, due to its elastic instability. Compared to most circular shells currently studied, it is easier to arrange multiple structures in three-dimensional space to obtain multistable responses. Numerical and experimental methods were adopted for the study of the mechanical response of the square shell, and main influence parameters were also investigated. In addition, an improved piecewise fitting method is introduced to establish an empirical formula for predicting the mechanical response of bistable shells, which can be used to guide the design of bistable shells. Finally, two types of metamaterials, uniaxial compressible metamaterials and triaxial compressible metamaterials, are successfully designed according to the above theory, the typical behaviors of which are studied via simulations. This novel structure presented in this paper has broad application prospects in the fields of energy absorption and programmable deformation structures.

Analysis of a Strip Antenna Located at a Plane Interface of Uniaxial Metamaterials

A rigorous solution is found to the problem of determining the current distribution and input impedance of a straight strip antenna located at a plane interface of two uniaxial metamaterials. The anisotropy axes of the metamaterials are parallel to each other and to the medium interface. The antenna is oriented perpendicular to these axes and excited by a given time-harmonic voltage. Using the Fourier transform technique, singular integral equations for the antenna current are derived and solved for all possible combinations of the metamaterial parameters. Closed-form representations for the current distribution and input impedance of an infinitely long strip are obtained and their generalization to the case of a finite-length antenna is discussed.

General Analysis of a Loop Antenna Located on a Uniaxial Metamaterial Cylinder

The general problem of determining the electrodynamic characteristics of a circular loop antenna located coaxially on the surface of a metamaterial cylinder is studied using the integral equation method. The antenna has the form of a perfectly conducting, infinitesimally thin, narrow strip coiled into a ring and is excited by a given time-harmonic voltage. The cylinder is assumed to be filled with a uniaxial metamaterial and surrounded by an isotropic magnetodielectric. Integral equations for azimuthal harmonics of the antenna current are derived and solved in the cases where the normal waves of the metamaterial inside the cylinder have either hyperbolic or nonhyperbolic dispersion. Based on the solutions of these equations, the current distribution and input impedance of the antenna are found in closed form. The behavior of the antenna characteristics as functions of the metamaterial parameters is discussed.

Ultrafast and low power all-optical switching in the mid-infrared region based on nonlinear highly doped semiconductor hyperbolic metamaterials

Guided wave modes in the uniaxial anisotropic hyperbolic metamaterials (HMMs) based on highly doped semiconductor instead of metal in the mid-infrared region are investigated theoretically. The heavily doped semiconductor is used to overcome the restrictions of the conventional metal-based structures caused by the lake of tunability and high metal loss at mid-infrared wavelengths. The unit cells of our proposed metamaterial are composed of alternating layers of undoped InAs as a dielectric layer and highly doped InAs as a metal layer. We numerically study the linear and nonlinear behavior of such multilayer metamaterials, for different arrangements of layers in the parallel (vertical HMM) and perpendicular (horizontal HMM) to the input wave vector. The effect of doping concentration, metal to dielectric thickness ratio in the unit cell (fill-fraction), and the total thickness of structure on the guided modes and transmission/reflection spectra of the metamaterials are studied. Moreover, the charge redistribution due to band-bending in the alternating doped and undoped layers of InAs is considered in our simulations. We demonstrate that the guided modes of the proposed hyperbolic metamaterial can change by increasing the intensity of the incident lightwave and entering the nonlinear regime. Therefore, the transition from linear to the nonlinear region leads to high-performance optical bistability. Furthermore, the switching performance in the vertical and horizontal HMMs are inspected and an ultrafast, low power, and high extinction ratio all-optical switch is presented based on a vertical structure of nonlinear highly doped semiconductor hyperbolic metamaterials.

Near-field radiative heat transfer between nanowire-based dual uniaxial magneto-dielectric metamaterials

Over past several years, much attention has been paid on near-field radiation with super-Planckian heat flux due to resonant coupling of surface polaritons and non-resonant hyperbolic modes but mainly with non-magnetic materials. With nanowire-based magneto-dielectric metamaterials, this work theoretically investigates the near-field radiative heat transfer associated with both uniaxial magnetic and electric responses. Maxwell–Garnett effective medium theory is used to obtain the dual uniaxial effective permeability and permittivity of the magneto-dielectric metamaterials. With the fluctuational electrodynamics, multiple resonant and non-resonant modes associated with both magnetic and electric responses that spectrally enhance the radiative heat transfer, such as magnetic and electric hyperbolic modes, magnetic and electric surface polaritons, mu- and epsilon-near-pole modes, are identified and elucidated at different wave polarizations. Effects of filling ratio, magnetic and electric scattering rates, and vacuum gap distance are also studied, and it is found that the spectral and total heat fluxes of s-polarized waves, which are usually neglected for non-magnetic materials, are much enhanced and comparable with that of p-polarized waves. The results here will deepen the fundamental understanding in magneto-dielectric metamaterials and facilitate their applications in the area of near-field thermal radiation.

Berreman effect in bimetallic nanolayered metamaterials

The visible and ultraviolet responses of a binary regular stack, composed of alternating Al and Ag nano-thin layers, are both experimentally and theoretically studied. It is found that the s- and p-polarization reflectivity spectra (Rs and Rp, respectively) of the inherently anisotropic bimetallic system are noticeably different due to the appearance of a prominent dip near the zero of the Ag permittivity. Such an effect is similar to the Berreman one, which is observed in thin polar-crystals films near the longitudinal-optical phonon frequency, as well as in thin metal films near plasma frequency. Using both the effective medium approach and a nonlocal homogenization formalism, being valid even beyond the long wavelength limit, it is demonstrated that the bimetallic multi-layer stack behaves as a uniaxial anisotropic metamaterial. As it is shown, the appearance of the dip in the p-polarization spectrum is associated to the zero of the longitudinal component of the effective permittivity (ϵz). The calculation of 45-degree reflectometry spectrum, namely the difference Rp−Rs2, from experimental and theoretical reflectivity data confirmed that the observed dip in Rp is connected to a plasma resonance of the energy-loss function ℑ(−1∕ϵz).

Envelope Dyadic Green\u2019s Function for Uniaxial Metamaterials

We introduce the concept of the envelope dyadic Green’s function (EDGF) and present a formalism to study the propagation of electromagnetic fields with slowly varying amplitude (EMFSVA) in dispersive anisotropic media with two dyadic constitutive parameters: the dielectric permittivity and the magnetic permeability. We find the matrix elements of the EDGFs by applying the formalism for uniaxial anisotropic metamaterials. We present the relations for the velocity of the EMFSVA envelopes which agree with the known definition of the group velocity in dispersive media. We consider examples of propagation of the EMFSVA passing through active and passive media with the Lorentz and the Drude type dispersions, demonstrating beam focusing in hyperbolic media and superluminal propagation in media with inverted population. The results of this paper are applicable to the propagation of modulated electromagnetic fields and slowly varying amplitude fluctuations of such fields through frequency dispersive and dissipative (or active) anisotropic metamaterials. The developed approach can be also used for the analysis of metamaterial-based waveguides, filters, and delay lines.

Theory of a Strip Antenna Located at a Plane Interface of a Uniaxial Metamaterial and an Isotropic Magnetodielectric

Electrodynamic characteristics of a straight strip antenna located at a plane interface of a uniaxial metamaterial and an isotropic magnetodielectric are studied using the integral equation method. The antenna is perpendicular to the anisotropy axis of the metamaterial filling the half-space on one side of the interface and is excited by a given voltage. The cases of metamaterials with hyperbolic and nonhyperbolic dispersion are considered. A closed-form solution for the current distribution of an infinitely long strip is obtained and the input impedance of such an antenna is found. Based on this solution, the limits of applicability of the transmission line theory for determining the characteristics of the antenna are established and a generalization to the case of a finite-length strip antenna is discussed.

Reflection of Light by a Hyperbolic Metamaterial Layer in a Case of Propagation of Special Inhomogeneous Waves in It

The boundary problem of reflection of electromagnetic waves by a hyperbolic metamaterial layer under conditions of total reflection from the boundary with this layer in the absence of birefringence has been solved. In this case, so-called “special inhomogeneous electromagnetic waves” may propagate in the layer. Analytical expressions are obtained for the vector amplitudes of the waves reflected by the layer and transmitted through it and for the special inhomogeneous electromagnetic waves propagating in this layer. These expressions allows calculating the energy characteristics of reflected and transmitted light for an optically uniaxial metamaterial.

Отражение света слоем гиперболического метаматериала в случае распространения в нем особых неоднородных волн

AbstractThe boundary problem of reflection of electromagnetic waves by a hyperbolic metamaterial layer under conditions of total reflection from the boundary with this layer in the absence of birefringence has been solved. In this case, so-called “special inhomogeneous electromagnetic waves” may propagate in the layer. Analytical expressions are obtained for the vector amplitudes of the waves reflected by the layer and transmitted through it and for the special inhomogeneous electromagnetic waves propagating in this layer. These expressions allows calculating the energy characteristics of reflected and transmitted light for an optically uniaxial metamaterial.

Magnetoelectric uniaxial metamaterials as wide-angle polarization-insensitive matching layers

Antireflection or impedance matching is a topic that has been extensively researched by the optical and microwave communities over the past century and until today. However, due to the diverging wave impedances of TE (s) and TM (p) polarizations with increasing incident angle, it is impossible to achieve perfect matching simultaneously for both polarizations at an oblique incident angle with a single conventional matching layer. In this paper, we show that simultaneous perfecting matching of an arbitrary substrate at an arbitrary incident angle from air is possible with a single uniaxial metamaterial matching layer (UMML) that possesses specific permittivity and permeability tensors. We demonstrate this concept by synthesizing a physical UMML to match a high-index ({\epsilon}r= 10.2) substrate at 45{\deg}. The required permittivity and permittivity tensors of the UMML are achieved through the judicious control of the tangential and longitudinal electric and magnetic responses. Around -30 dB reflections are observed for both polarizations at the design angle. Building on the UMML concept, we design a novel radome in microwave regime with a near omni-directional matching performance. For incident angles from 0{\deg}-85{\deg}, reflections remain below -14 dB for both polarizations. To our best knowledge, this is the widest angular range that has been achieved while maintaining less than 5% power reflection for both polarizations. The proposed UMML concept offers a new paradigm for designing high-performance microwave, terahertz, and optical devices.

Calculation of the Transmission Through a Rectangular Hole Filled With an Extreme Uniaxial Metamaterial

Of late, wave-guiding structures, filled with uniaxial extreme metamaterials of infinite longitudinal components of permittivity ( $\varepsilon _{{z}}$ ) and permeability ( $\mu _{{z}}$ ), have attracted researchers’ attention because of the potential they hold for applications in massive-capacity communication, super-resolution imaging, and other such areas. However, no efficient method has been found so far to overcome the electromagnetic transmission problem of such structure. The huge number of meshing grids in complex structure makes the problem rather difficult to solve with high efficiency. Against this drawback, here, we devise an efficient computational method in the context of a coupled-mode method. We study the influencing role of some important factors, such as the geometric profiles of the rectangular hole, illumination angles, and the loss of the metamaterial. This method is numerically examined, and the results confirm its effectiveness and accuracy.

Influence of the polarization and optical axis on the transmission behavior in a one dimensional photonic crystal containing uniaxial metamaterial

In this letter, we introduce a one-dimensional photonic crystal (1DPC) structure with a uniaxial metamaterial defect layer. It is proposed to control the transmitted wave of the defect mode by adjusting the orientation of the optical axis and incidence angle for both polarization states. The 4 × 4 transfer matrix method was employed to calculate the transmittance spectrum of the proposed structure. It is shown that the photonic band gaps, the intensity and the peak wavelength of the defect mode depends on the polarization, the orientation of the optical axis and the incidence angle of the wave, due to the strong anisotropy of the metamaterial. The transmittance spectrum curves at different optical axes of the uniaxial metamaterial and the distinct incidence angles are illustrated graphically. It is shown that the defect mode appears as a peak in the transmission spectrum. Pronounced contrasts in the intensity, wavelength positions of the defect mode and photonic band gap were demonstrated depending on the incidence angle and the orientation of the optical axis of the uniaxial metamaterial defect layer for both polarizations. Our structure offers a great variety of possibilities for designing and controlling the transmitted intensity of the defect mode.

Tunable Toughness of Model Fibers With Bio-Inspired Progressive Uncoiling Via Sacrificial Bonds and Hidden Length

Nature has a proven track record of advanced materials with outstanding mechanical properties, which has been the focus of recent research. A well-known trade-off between ultimate strength and toughness is one of the main challenges in materials design. Progress has been made by mimicking tough biological fibers by applying the concepts of (1) sacrificial bond and (2) hidden length, providing a so-called “safety-belt” for biological materials. Prior studies indicate a relatively common behavior across scales, from nano- to macro-, suggesting the potential of a generalized theoretical mechanistic framework. Here, we undertake molecular dynamics (MD) based simulation to investigate the mechanical properties of model nanoscale fibers. We explore representative models of serial looped or coiled fibers with different parameters—specifically number of loops, loop radii, cross-link strength, and fiber stiffness—to objectively compare strength, extensibility, and fiber toughness gain. Observing consistent saw-tooth like behavior, and adapting worm-like chain (WLC) mechanics (i.e., pseudo-entropic elasticity), a theoretical scaling relation which can describe the fiber toughness gain as a function of the structural factors is developed and validated by simulation. The theoretical model fits well with the simulation results, indicating that engineering the mechanical response based on controlled structure is possible. The work lays the foundation for the design of uniaxial metamaterials with tunable and predictable tensile behavior and superior toughness.

Agile Beamwidth Control and Directivity Enhancement for Aperture Radiation With Low-Profile Metasurfaces

Uniaxial anisotropic near-zero metamaterials have been utilized to design 2-D apertures with beamwidth control and directivity enhancement. Theoretical study shows that the two principal plane beamwidth of an aperture can be significantly reduced, both independently and simultaneously. With two proposed simplified loading models as a transitional structure, the 3-D bulk metamaterials are eventually reduced to 2-D metasurfaces with an array of metallic inclusions. In the design procedure, a critical equivalence between 2-D metasurfaces and 3-D metamaterial slabs with a specific thickness is discussed and validated. Measured results of the fabricated prototypes have demonstrated that a final aperture design loaded with low-profile electric LC and split-ring resonator metasurfaces has a substantial beamwidth reduction on both principal planes and a 4.32 dBi gain enhancement around the operating frequency.

Ultra low-loss super-resolution with extremely anisotropic semiconductor metamaterials

We investigate the mechanisms for the reduction of losses in doped semiconductor multilayers used for the construction of uniaxial metamaterials and show that maximizing the mean scattering time of the doped layers is key to spectrally isolating losses and maximizing anisotropy. By adjusting the layer thickness ratio of the multilayer, we show that the spectral regions of extreme anisotropy can be separated from those of high loss. Using these insights and coupled with realistic semiconductor growth parameters, we demonstrate an InAs-based superlens with an excellent loss factor α ≈ 52mm-1 and maximum perpendicular permittivity, ε⊥ &amp;gt; 250. By tuning the doping concentration, we show that such a system can be designed to operate anywhere in the region λ0 ≈ 5 to 25μm. We find that such a structure is capable of deep sub-wavelength imaging (&amp;lt; λ0/15) at superlens thicknesses up to ∼85μm (∼8λ0).

Effect of small anisotropy and absorption on metamaterial applications: “non-ideal” features of propagation and tunneling of electromagnetic waves

For cases of isotropic, uniaxial, and biaxial electromagnetic metamaterials (MM), a comparative analysis of the effect of small deviations of local material parameters from “ideal” values on the realization of MM applications (“zero” media, the Veselago-Pendry superlens) has been carried out. On the basis of the detailed investigation of the solutions of dispersion equations, it is established that even a very small dielectric and (or) magnetic anisotropy of a general form is the universal “non-ideal” factor determining (to a much greater extent than small losses) the operability of those MM applications where the wave misphasing in the effective medium is undesirable. The characteristics of wave attenuation in the absorbing isotropic and weakly anisotropic MM are mainly comparable for the applications. Limitations of the traditional approaches using the second-order curves (or surfaces) for analytic modeling of the absorbing MM dispersion equations are shown.

Extra-Dimensional “Metamaterials”: A Model of Inflation Due to a Metric Signature Transition

Lattices of topological defects, such as Abrikosov lattices and domain wall lattices often arise as metastable ground states in higher-dimensional field theoretical models. We demonstrate that such lattice states may be described as extra-dimensional metamaterials via higher-dimensional effective medium theory. A 4+1 dimensional extension of Maxwell electrodynamics with a compactified time-like dimension has been considered as an example. It is demonstrated that from the point of view of macroscopic electrodynamics an Abrikosov lattice state in such a 4+1 dimensional spacetime may be described as a uniaxial hyperbolic metamaterial. Extraordinary photons perceive this medium as a 3+1 dimensional Minkowski spacetime in which one of the original spatial dimensions (the optical axis of the metamaterial) plays the role of a new time-like coordinate. Since metric signature of this effective space-time depends on the Abrikosov lattice periodicity, the described model may be useful in studying metric signature transitions. A particular kind of metric signature transition understood as a macroscopic medium effect may emulate cosmological inflation.

Extraordinary optical transmission through a rectangular hole filled with extreme uniaxial metamaterials.

This Letter presents a theory of extraordinary optical transmission (EOT) through a rectangular hole filled with the extreme uniaxial metamaterials with infinite longitudinal components of permittivity (ϵz) and permeability (μz). We demonstrate theoretically and numerically that a number of high-order transverse electromagnetic (TEM) modes can be supported by such a structure, and that, more interestingly, their normalized transmittance can be remarkably enhanced due to the Fabry-Perot resonance effect. A set of illustrative examples has been provided to demonstrate that such an EOT property could be explored for the purpose of subwavelength-resolution imaging.