Anisotropic Slab Research Articles

Design of a one-dimensional electromagnetic transparent wall

For a one-dimensional (1D) anisotropic slab, if its electromagnetic parameters satisfy certain conditions, an incident wave can be totally transmitted without any reflections. In this work, a classical method based on analytical results and a transformation optics method using an arbitrary piecewise continuous transformation function are applied to design a 1D electromagnetic transparent wall, whose presence does not disturb the field distribution in the ambient environment. Material parameters and the geometrical requirement of the layered structure using these two different methods are derived, and they agree well with each other. Full-wave simulations validate the transparency of the proposed wall. Because of the simple constitutive parameters and geometry, a transparent structure could be realized using anisotropic and homogeneous materials. The proposed structure has potential applications in radomes, anti-reflection films, and various sensor sectors.

Approximate Green’s function for a uniaxially anisotropic metamaterial slab, and its application in analyzing a spectrometer

An analytic solution for a magnetic line source imaged through a uniaxially anisotropic slab is derived for electric fields, and example results are supported by finite element simulations. The analytical result provides a convenient means to evaluate the effect of material parameters in applications. We introduce a spectrometer that can be realized by illuminating a slab composed of a Ag/ZnO multilayer stack through a small aperture, and we use this example to evaluate the performance of the analytic model.

Goos-Hänchen shift from an anisotropic metamaterial slab

Abstract We have theoretically and numerically investigated the Goos-Hänchen shift (the lateral shift) from the anisotropic metamaterial slab. The sign and degree of the shift can be determined by the choices of the electromagnetic parameters and thicknesses of slab, which is different from the case of the isotropic media. We also find that the weak lossy may produce large positive or negative lateral shift.

Spectral Collocation Method for Transient Combined Radiation and Conduction in an Anisotropic Scattering Slab With Graded Index

The spectral collocation method for transient combined radiation and conduction heat transfer in a planar participating medium with spatially variable refractive index is introduced and formulated. The angular dependence of the problem is discretized by discrete ordinates method and the space dependence is expressed by Chebyshev polynomial and discretized by spectral collocation method. Due to the exponential convergence of spectral methods, very high accuracy can be obtained even using a small resolution for present problem. Numerical results in one-dimensional planar slab by Chebyshev collocation spectral-discrete ordinates method (SP-DOM) are compared with those available data in references. Effects of various parameters such as the variable thermal conductivity, the scattering albedo, the emissivity of boundary, the conduction-radiation parameter, the optical thickness, and the graded index are studied for absorbing, emitting, and anisotropic scattering medium. The SP-DOM has been found to successfully and efficiently deal with transient combined radiation and conduction heat transfer problem in graded index medium.

Creation of large band gap with anisotropic annular photonic crystal slab structure

A two-dimensional anisotropic annular photonic crystal slab structure composed of circular air holes and dielectric rods with finite thickness in a triangular lattice is presented to achieve an absolute photonic band gap. Positive uniaxial crystal Tellurium is introduced to the structure with the extraordinary axis parallel to the extension direction of rods. The role of each geometric parameter is investigated by employing the conjugate-gradient method. A large mid-gap ratio is realized by the parameter optimization. A flat band called as anomalous group velocity within two large gaps is discovered and can be widely applied in many fields. A hybrid structure with GaAs slab and Te rods is designed to achieve a large gap and demonstrates that the annular structure can improve the gap effectively.

Focusing properties of the uniaxially anisotropic metamaterial slab lens

We studied the focusing properties of an anisotropic metamaterial slab lens by means of the angular spectrum representation of the vectorial electromagnetic field. The analytical expressions for vectorial fields in all the propagation regions are obtained，and the quantitative relationship between the focusing characteristics of the vectorial electromagnetic field and the anisotropic parameters of the anisotropic metamaterial slab lens is disclosed. The polarization state of the focusing beam is found to be changed due to the effect of anisotropy. As an application of the vectorial theory，we have analyzed the focusing property of an anisotropic metamaterial slab for which the permeability along longitudinal axis is -1. It is demonstrated that this slab lens can redirect a beam initially polarized along a transverse axis to a partial focus and give a clear polarization rotation of the beam.

TE Volume Modes in Anisotropic Single-Negative Slab with Negative Component in Permeability Tensor

Existence of backward TE volume modes which are to be identified as Magnetostatic Wave (MSW) in anisotropic single-negative slab with partly negative permeability tensor component have already been revealed by present authors. In this paper, detailed modal analysis has been carried out for this kind of TE volume modes to find out their novel and peculiar properties. From these numerical results, it has been clarified that dispersion curve of the lowest order mode for thicker slab has a frequency of turning point below which both forward and backward waves can be simultaneously observed and also there is a critical slab thickness for each order of TE volume modes to exist.

A novel finite-difference time-domain scheme for electromagnetic scattering by stratified anisotropic plasma under oblique incidence condition

A novel finite-difference time-domain(FDTD) implementation, by which electromagnetic(EM) wave scattering characteristic can be analyzed for oblique incidence on stratified anisotropic plasma, is proposed. This method transforms two-dimensional electromagnetic wave scattering question to one-dimensional question, and avoids two-dimensional scattering problem by 2D FDTD method, by which the computational efficiency can be greatly improved. FDTD iterative formula of EM scattering by layered anisotropic plasma are deduced in the TEz and TMz wave oblique incidence situations, and the connection boundary(CB) and the absorbing boundary condition (ABC) in the oblique incidence situation are carried out the revision. The EM wave reflection coeffientes of the anisotropic plasma slab are calculated in the oblique incidence situation by the method. The computed results and the analytic solutions are in good agreement. The results show the accuracy and validity of the method. Finally, the algorithm is applied to calculate the reflection coefficients of the metal plate coated with the stratified anisotropic plasma under different incidence angles. The numerical results show the incidence angle have a great impact on the reflection coefficients.

Compact planar far-field superlens based on anisotropic left-handed metamaterials

Pendry's perfect lens has spurred intense interest for its practical realization at visible frequencies. However, fabrication of low-loss isotropic left-handed metamaterials is a current challenge. In this work, we theoretically show that under specific conditions anisotropic metamaterial slabs can emulate Pendry's perfect-lens phenomenon on a plane. Geometric optics leads to a new lens formula for this special anisotropic metamaterial superlens, which allows significant shrinkage of the metamaterial slab thickness for a certain range of far-field operation. Conversely, such anisotropic metamaterial superlens with the same thickness as its isotropic analog can operate for much larger distances between object and lens. We present numerical simulations which confirm our theoretical calculations. In particular, we find subdiffraction focusing that rivals the perfect isotropic negative-index metamaterial lens performance and obeys the new lens formula as predicted. In addition, we demonstrate that it is possible to attain far-field superfocusing with a metamaterial slab as thin as half the free-space wavelength. We believe this work will inspire new anisotropic metamaterial designs and opens a promising route for the realization of compact far-field superlenses in the visible regime.

Rainbow-like radiation from an omni-directional source placed in a uniaxial metamaterial slab

In this paper, the radiation of an omni-directional line source placed in a uniaxial metamaterial slab is experimentally presented. The anisotropic slab made of metallic symmetrical rings with dispersive permeability is investigated both theoretically and experimentally. For low value of the permeability, a directive radiation at the broadside of the slab can be obtained. Due to the excitation of the leaky wave mode supported by this structure, the emitted electromagnetic wave transmits at a greater angle from the normal of the slab as the value of permeability increases along with the frequency. Thus a rainbow-like radiation will be formed since waves of different frequencies will deflect into different directions.

Optical circuits from anisotropic films

The theory for inductive and capacitive elements realized from anisotropic slabs is developed. These elements are shown to have low sensitivity to angle of incidence and nondispersive performance. It is therefore possible to realize optical circuits that perform more effectively than would be possible with isotropic materials. Low-pass filtering and antireflection examples are given. Desirable anisotropy can be achieved using a metal-insulator stack operating in the effective-medium metamaterial regime. The approach allows circuit synthesis at optical wavelengths.

Optical imaging superresolution by a negative refraction anisotropic photonic crystal

Abstract Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the focusing of electromagnetic wave propagation inside an anisotropic PC slab by means of finite-difference time-domain simulations. The PC structure composed of air cylinders in the anisotropic–dielectric medium is studied by solving Maxwell's equations using the plane wave expansion method. Numerical simulations show that the optical imaging resolution can be improved greatly in the square lattices consisting of anisotropic–dielectric background. Such a mechanism of negative refraction PCs should open up a new application for designing components in optical imaging systems.

Large Positive and Negative Lateral Shifts from an Anisotropic Metamaterial Slab Backed by a Metal

The lateral shift of a light beam at the surface of an anisotropic metamaterial (AMM) slab backed by a metal is investigated. Analytical expressions of the lateral shifts are derived using the stationary-phase method, in the case that total refection does and does not occur at the first interface. The sign of the lateral shift in two situations is discussed, and the necessary conditions for the lateral shift to be positive or negative are given. It is shown that the thickness and physical parameters of the AMM slab and the incident angle of the light beam strongly affect the properties of the lateral shift. Numerical results validate these conclusions. The lossy effect of the metamaterial on the lateral shift is also investigated.

NUMERICAL MODELING AND MECHANISM ANALYSIS OF VHF WAVE PROPAGATION IN FORESTED ENVIRONMENTS USING THE EQUIVALENT SLAB MODEL

We study the radio wave propagation at VHF frequencies in a forested environment using a three-layer anisotropic slab model. The analytical solution to the slab model is implemented numerically to generate broadband data. The data are then transformed into the time domain. The various propagation mechanisms including the direct wave, the lateral wave, the multi-reflected slab waves and the multibounce lateral waves are investigated based on their respective timesof-flight. Our results show that the dominant propagation mechanisms are highly dependent on the effective permittivity and conductivity of the forest layer. We then utilize the numerical solution to extract the effective medium parameters of the forest based on the published measurement data of Hicks et al.. Good agreement between the fitted model and the measurement data is achieved. The extracted effective permittivity and conductivity of the forest layer show considerable anisotropy and frequency dependence.

Lateral shifts of an optical beam in an anisotropic metamaterial slab

The lateral shift of a light beam at the surface of an anisotropic metamaterial slab is investigated. Analytical expressions of the lateral shifts are derived using the stationary-phase method, in the case that total reflection does and does not occur at the first interface. The sign of the lateral shift in two situations is discussed, and the necessary conditions for the lateral shift to be positive or negative are given. It is shown that the thickness and physical parameters of the anisotropic metamaterial slab, as well as the incident angle of the light beam, strongly affect the properties of the lateral shift, and numerical results validate these conclusions. The effect of a lossy metamaterial on the lateral shift is also investigated. A restriction on the thickness of the slab is obtained, which is necessary for the stationary-phase method to remain valid.

Subwavelength imaging opportunities with planar uniaxial anisotropic lenses

The imaging properties of a uniaxial anisotropic slab lens, where the dielectric tensor components are of the opposite sign, are studied as a function of the structure parameters. While hypothetical parameters yield various levels of performance, a design principle to achieve good subwavelength resolution is suggested. The anisotropy can be implemented with a metal-insulator stack.

Yield line theory and concrete plasticity

This paper reviews the relationship between yield line theory, developed for reinforced concrete slabs by Johansen in the 1930s and 1940s, and limit analysis, formulated by the Hodge–Hill–Prager school around 1950. Recalling work from the 1970s, it is shown that not only is yield line theory fully compatible with limit analysis, but the Johansen ‘stepped’ yield criterion is in fact the only yield condition for the slab that allows coinciding upper and lower bounds in the sense of limit analysis to be derived by yield line theory. The yield condition for an arbitrarily reinforced slab is reproduced in closed form, obviating the need for coordinate transformations, and allowing the permissibility of stress states to be checked for anisotropic slabs with non-coinciding principal directions of top and bottom reinforcement.

Guided plasmonic modes in nanorod assemblies: strong electromagnetic coupling regime

We demonstrate that the coupling between plasmonic modes of oriented metallic nanorods results in the formation of an extended (guided) plasmonic mode of the nanorod array. The electromagnetic field distribution associated to this mode is found to be concentrated between the nanorods within the assembly and propagates normally to the nanorod long axes, similar to a photonic mode waveguided by an anisotropic slab. This collective plasmonic mode determines the optical properties of nanorod assemblies and can be tuned in a wide spectral range by changing the nanorod array geometry. This geometry represents a unique opportunity for light guiding applications and manipulation at the nanoscale as well as sensing applications and development of molecular plasmonic devices.

Planar EBG on electrically and magnetically anisotropic slab

A full‐wave analysis of planar electromagnetic band‐gap (EBG) on anisotropic slab, which is characterized simultaneously by both nondiagonal second rank [ɛ] and [μ] tensors, is presented. The analytical procedure is based on Galerkin's method applied in the spectral domain, and the spectral dyadic Green's function for the considered structure is formulated based on Maxwell's equations directly. A kind of Uniplanar Compact EBG (UC‐EBG) on anisotropic slab is computed efficiently, and the influence of the principal axes' rotation in the transverse plane on their band structures are studied for several slab materials.

Anisotropy and Interference in Wave Transport: An Analytic Theory

A theory is presented which incorporates the effect of dielectric anisotropy in random multiple scattering media. It predicts anisotropic diffusion, and a deflection of the diffuse energy flow in anisotropic slabs in the direction parallel to the slab. The transmittance integrated over all incoming and outgoing directions scales with the transport mean free path along the surface normal. The escape function in anisotropic dielectrics is no longer bell shaped. In this model anisotropy facilitates Anderson localization.