Thin Dielectric Slab Research Articles

Transverse shift of the transmitted beam of a non-uniformly polarized paraxial light beam at dielectric interfaces

This paper reports that the central position of the reflected and transmitted beams of a nonlinear polarized light beam at the interface between two media undergoes transverse shifts. It presents a solution to the problem of transverse shift of a non-uniformly polarized paraxial light beam transmitting through interfaces between two homogeneous media by using a two-form amplitude and an extension matrix to represent the vector angular spectrum of a three-dimensional (3D) light beam. It derives general formula for the transverse shift of the transmitted beam, and discusses the shift of a well-collimated beam transmitting through an interface between two homogeneous media and a thin dielectric slab.

Simulation of photonic crystal nanocavity using the FETI‐DPEM method

AbstractThe dual‐primal finite element tearing and interconnecting (FETI‐DPEM) method, as an application of a nonoverlapping domain decomposition method to the finite element analysis of electromagnetic problems, is applied to the three‐dimensional (3D) full‐wave simulation of a high quality (Q) factor photonic crystal (PhC) nanocavity in an optically thin dielectric slab. Curvilinear tetrahedral elements and higher‐order vector basis functions are employed in the FEM to accurately represent the field in the PhC nanocavity. Geometrical repetitions associated with PhCs nanocavities are fully exploited, which significantly reduces the computational complexity and memory requirement. Moreover, due to its domain decomposition nature, the FETI‐DPEM method is highly parallelizable, which further accelerates the computation using parallel computing techniques. As a result, such a method is ideally suited for the fullwave analysis of PhC nanocavities. Simulations of a high Q PhC nanocavity using the FETI‐DPEM method are carried out to demonstrate the efficiency of the method. The calculated Q factors are compared with previously published data. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2083–2086, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23580

Non-geometrical effects on Gaussian beams transmitting through a thin dielectric slab

It is shown that a Gaussian light beam transmitting through a planar thin dielectric slab in the air undergoes four different effects, i.e. lateral Goos-Hänchen-like (GHL) displacement, angular deflection, width modification and longitudinal focal shift as compared with the results predicted by geometrical optics. According to the Taylor expansion of the exponent of transmission coefficient when expressed as an exponential form, the lateral GHL displacement and the angular deflection are the first-order effects and can be negative or positive. The width modification and the longitudinal focal shift are the second-order effects and can also be positive or negative. Owing to the waist-width dependent term, the non-geometrical effects of transmitted beam are not identical with the non-specular effects of reflected beam. The conditions for the validity of those effects are suggested and numerical simulations are also given.

Characteristics Estimation for Jerusalem Cross-Based Artificial Magnetic Conductors

This letter proposes a circuit model capable of predicting the bandwidth and resonance frequency of a well-known artificial magnetic conductor (AMC). The AMC is composed of an array of Jerusalem cross-shaped frequency selective surfaces (FSSs) (JC-FSS) deployed on a thin PEC-backed dielectric slab. The model benefits from the static (Quasi-TEM) closed-form equations, available in literature for the characteristic impedance of microstrip transmission lines. These equations enable the model to incorporate the influences of the slab thickness on the FSS impedance, a feature that the available models have not been able to offer exactly. In order to check the competence of the model, some sample AMCs are designed by the model, and their properties are verified by numerical analysis.

A Low-Profile Dual-Band Surface Wave Antenna With a Monopole-Like Pattern

A dual-band surface wave antenna (DBSWA) that realizes a monopole-like radiation pattern with a low-profile configuration is designed and measured. The antenna consists of two parts: a center-fed modified crosspatch to excite surface waves at two frequency bands, and a thin dielectric slab loaded with periodic patches to support the propagation of the surface waves. The surface wave property and radiation mechanism of the DBSWA are described, and parametric studies are performed to understand the dual-band characteristics of the antenna. The proposed antenna with only 3 mm thickness (< 0.05 lambda) is fabricated and tested, which resonates at 4.2 and 4.9 GHz. The corresponding impedance bandwidths and gains are 1.10% and 4.9 dBi for the low frequency band and 3.94% and 5.4 dBi for the high frequency band.

Enhanced microwave transmission through quasicrystal hole arrays

The authors report on the observation of enhanced microwave transmission through quasiperiodic hole arrays in metal films. The fraction of transmitted light reaches 50% in a self-standing metal film and approaches 90% when the film is sandwiched between thin dielectric slabs, while the holes occupy only 10% of the sample area. The maximum transmission exhibits a Breit-Wigner resonance behavior, accompanied by zero phase change and rendering the film almost invisible over a wide frequency range. The extraordinary transmission phenomenon is interpreted in terms of resonances in the self-consistent interaction between holes, which are represented by effective electric and magnetic dipoles.

Thermal radiation and near-field energy density of thin metallic films

We study the properties of thermal radiation emitted by a thin dielectric slab, employing the framework of macroscopic fluctuational electrodynamics. Particular emphasis is given to the analytical construction of the required dyadic Green's functions. Based on these, general expressions are derived for both the system's Poynting vector, describing the intensity of propagating radiation, and its energy density, containing contributions from non-propagating modes which dominate the near-field regime. An extensive discussion is then given for thin metal films. It is shown that the radiative intensity is maximized for a certain film thickness, due to Fabry-Perot-like multiple reflections inside the film. The dependence of the near-field energy density on the distance from the film's surface is governed by an interplay of several length scales, and characterized by different exponents in different regimes. In particular, this energy density remains finite even for arbitrarily thin films. This unexpected feature is associated with the film's low-frequency surface plasmon polariton. Our results also serve as reference for current near-field experiments which search for deviations from the macroscopic approach.

DIELECTRIC CONSTANT MEASUREMENT FOR THIN MATERIAL AT MICROWAVE FREQUENCIES

Apractical problem in the reflection method for dielectric constant measurement is the difficulty to ensure the sample is placed exactly at the waveguide flange. Asmall position offset of the dielectric sample will give rise to some errors in calculating the dielectric constant, especially when a thin sample is used. To circumvent this problem, a method to determine the dielectric constant by measuring the transmission coefficient of the thin slab placed in a waveguide has been developed. Slab position offset from the measurement reference plane has no effect on the measurement accuracy. An explicit expression for the dielectric constant is obtained in terms of the transmission coefficient by simplifying the exact solution for transmission through a thin dielectric slab. The method is verified with measurement on Teflon of 0.5-mm thickness. The measured dielectric constant of Teflon shows excellent agreement of both e � and e �� with published data. Subsequently, the dielectric constant of a vegetation

Microstrip line on an artificial dielectric substrate

This letter presents a new version of an artificial dielectric substrate and a microstrip line built on top of this substrate. The substrate is fabricated as a two-dimensional array of metallic posts separated from the top conductor by a thin dielectric slab. This structure can show a very high effective permittivity and can therefore offer a substantial reduction in the dimensions of microwave circuit elements

A metamaterial surface for compact cavity resonators

We suggest an idea for miniaturization of cavities by utilizing a properly designed metamaterial thin surface inserted inside the cavities. This metamaterial surface is constituted by a thin dielectric slab on both sides of which gangbuster dipoles are printed. Inserting the thin slab inside a parallel-plate one-dimensional (1D) cavity resonator has the effect of decreasing the resonant frequency. Placing the metamaterial slab at the center of a rectangular waveguide lowers the cut-off frequency of the dominant mode of the waveguide also. The corresponding dispersion curve exhibits a smooth transition from a fast-wave to a slow-wave regime and then asymptotically tends to the dispersion curve of the first TE surface-wave mode of the metamaterial slab. This suggests a natural way to conceive a 3D compact cavity resonator by placing two perfectly electrically conducting walls, a half of the wavelength of the slow-wave mode apart, inside the above rectangular waveguide. The analysis, performed by a circuit network theory and validated by a full-wave numerical analysis, provides simple formulas to predict the resonant frequency and the dispersion diagrams of these structures.

Coupling between surface plasma wave and slow waves supported by an anisotropic conductor

A plasma-vacuum interface supports surface plasma wave (SPW) with phase velocity less than the speed of light (v/sub ph/<c). When an anisotropic conductor sheet, separated by a thin dielectric slab is placed on the plasma surface, the SPW couples with the slow wave of the conductor-dielectric structure to give a slow surface plasma wave. The anisotropic conductor is essentially an array of closely spaced thin parallel wires that give electrical conductivity of the structure /spl sigma/=/spl infin/, along the length of the wires and /spl sigma/=0 transverse to it. The field of the slow surface plasma wave decays exponentially in the plasma and in free space above the anisotropic conductor. Inside the dielectric, it can have sinusoidal or exponential variations. The phase velocity of the wave is sensitive to the angle wires make with the direction of wave propagation and to the thickness of the dielectric slab. The slow plasma wave can be excited by a microwave and can sustain large volume plasma, useful for processing of materials.

Hybrid PSTD‐FDTD technique for scattering analysis

AbstractThis paper employs a hybrid method that combines the pseudo‐spectral time‐domain (PSTD) algorithm and the finite‐difference–time‐domain (FDTD) method to analyze the scattering problems involving fine structures. In principle, the PSTD is applied in a direction with low‐density variation of structures but large computation volume, whereas the FDTD is used in other directions with high‐density variation and relatively small computation dimensions. In implementation of this hybrid algorithm, the pure scattered‐field formulation is utilized to introduce the incident wave, and a hybrid near‐to‐far‐zone field transform is developed for calculating the scattering width (SW) of the targets. The hybrid method is illustrated by analyzing two canonical scattering targets: a thin dielectric slab and a conductor‐backed dielectric slab. It is observed that the proposed algorithm is very accurate and efficient compared to the FDTD calculations for the same cases investigated. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 19–24, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10361

Tailoring of the resonant mode properties of optical nanocavities in two-dimensional photonic crystal slab waveguides

Optically thin dielectric slabs, in which a fully etched-through two-dimensional patterning is applied, are used to form high-Q optical cavities with modal volumes approaching the theoretical limit of a cubic half-wavelength. Resonant cavities are formed from local defect regions within the photonic lattice. Simple group theoretical techniques are developed to design cavities which support resonant modes with a particular polarization and radiation pattern. Numerical simulations using the finite-difference time-domain method are then used to study the detailed emission and loss properties of these modes. The cavities are probed spectroscopically through photoluminescence measurements, which when compared with numerical results show the presence of both donor and acceptor type modes. These experimental results show the predictive power of the modest symmetry analysis presented here in describing highly localized defect states within photonic crystals.

Radiation of a vertical electric dipole over a resistive sheet

The radiation of a vertical electric dipole over a thin dielectric slab is analysed. The problem can be decomposed into two simpler ones involving the radiation of the same dipole, first over a perfectly conducting plane, which has a trivial solution, and then over an impedance plane, for which the Green&apos;s function can be directly obtained from the corresponding scalar problem. To demonstrate the effectiveness of the solution for real structures of finite extension, the results are compared with those obtained by resorting to a moment method solution and to a physical optics technique. The proposed Green&apos;s function can be used to analyse the radiation of wire antennas in the presence of planar resistive structures.

Modified spontaneous emission from a two-dimensional photonic bandgap crystal slab

A two-dimensional photonic crystal patterned into a thin dielectric slab waveguide is shown to alter drastically the lifetime of spontaneous emission as well as the radiation pattern. This means that although the light extraction efficiency can be greatly enhanced, inhibited spontaneous emission within the photonic bandgap can result in low power output from such a structure. Strongly inhibited emission is found within the photonic bandgap as well as enhanced emission into the conduction band modes for certain geometries. Coupled with enhanced extraction efficiency in the photonic conduction band, this results in the possibility of a structure with increased total power efficiency.

Ridged waveguides with thin dielectric slabs

The electromagnetic characteristics of ridged waveguides with dielectric slabs in the capacitance gap are analyzed using the numerical solver. Nonconventional filling of the gap is proposed in order to improve the bandwidth properties of the considered waveguiding structures. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 419–423, 2000.

Ridged waveguides with thin dielectric slabs

The electromagnetic characteristics of ridged waveguides with dielectric slabs in the capacitance gap are analyzed using the numerical solver. Nonconventional filling of the gap is proposed in order to improve the bandwidth properties of the considered waveguiding structures. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 419–423, 2000.

Electromagnetic scattering by nonplanar junctions of resistive sheets

Approximate uniform asymptotic expressions are provided to determine the field scattered by a penetrable wedge illuminated at normal incidence. The wedge is formed by two resistive sheets or two thin dielectric slabs definable as resistive sheets having identical geometric and electromagnetic characteristics. The solution is limited to wedge angles and source positions where internal reflections cannot occur. It is obtained by using a geometrical optics (GO) approximation for the field internal to the slabs and by performing a uniform asymptotic evaluation of the physical optics (PO) radiation integral in the hypothesis that a resistive sheet condition is valid. Samples of numerical results so obtained are presented and compared with other methods to demonstrate the effectiveness of the proposed technique.

Broadband planar monopole antenna

A novel kind of planar monopole antenna is experimentally presented for broadband applications. A square planar radiator is electromagnetically coupled with a probe-fed strip. The medium between the radiator and the strip is a thin dielectric slab. The parametrical effects on the bandwidth have also been examined experimentally. The proposed antenna is demonstrated to have an impedance bandwidth of 60% for a VSWR=1.5 and stable radiation patterns across the passband.

High-frequency scattering by the edge of a thin dielectric slab loaded by a metallic strip grating

A heuristic diffraction coefficient is presented that is suitable to describe the scattering from the edge of a thin dielectric half-plane, loaded by a metallic strip grating on one of its faces, when the grating period is much smaller than the free-space wavelength. The most general case of oblique incidence is analysed, with the incident plane wave arbitrarily polarised. The direction of the strips can be arbitrarily oriented with respect to the edge of the half-plane. Extensive numerical tests have been performed to verify the effectiveness of the heuristic solution and to check its accuracy through comparisons with reference data.