Homogeneous Dielectric Material Research Articles

Surface electromagnetic waves supported by the interface of two semi-infinite rugate filters with sinusoidal refractive-index profiles

The canonical problem of surface-wave propagation guided by the interface of two semi-infinite rugate filters made of isotropic dielectric materials was formulated and solved. Numerical studies showed that multiple Tamm waves—with different phase speeds, polarization states, and degrees of localization—can be guided by the interface of a homogeneous dielectric material and a rugate filter. Multiple Tamm waves and optical Tamm states are supported by a phase-defect interface in a rugate filter. A sudden change of either the mean refractive index or the amplitude of the sinusoidal variation of the refractive index also creates an interface that can guide multiple Tamm waves, as can the interface of two distinct rugate filters. Whereas the Tamm waves can be either p or s polarized, all optical Tamm states were found to be p polarized.

Partial discharge behavior within a spherical cavity in a solid dielectric material as a function of frequency and amplitude of the applied voltage

Modeling of the partial discharge (PD) process allows a better understanding of the phenomena. In this paper, a simulation model for spherical cavities within a homogeneous dielectric material has been developed. The model is implemented using Finite Element Analysis (FEA) software in parallel with a mathematical package. This method provides many advantages over previous PD models because discharge events can be simulated dynamically and the electric field in the cavity can be calculated numerically. The model has been used to study the effect of different amplitudes and frequencies of the applied voltage and simulation results have been compared with experimental measurement results. It is found that certain model parameters are dependent on the applied stress and parameters that clearly affect PD activity can be readily identified, these parameters include; the electron detrapping time constant, the cavity surface conductivity, the initial electron generation rate and the extinction voltage. The influence of surface charge decay through conduction along the cavity wall on PD activity has also been studied.

Modeling of partial discharge activity in spherical cavities within a dielectric material

In this paper, a model for a spherical cavity within a homogeneous dielectric material was developed using finite element analysis (FEA) software. The model was used to study the influence of different cavity conditions on local electric field distribution and consequent PD activity. The study involved variation of cavity diameter and cavity location within the dielectric material. In addition, experimental measurements were undertaken using epoxy samples containing single spherical cavities of different diameters.

TE MODE PROPAGATION THROUGH TAPERED CORE LIQUID CRYSTAL OPTICAL FIBERS

An analysis is presented of a three-layer tapered core liquid crystal optical flber (TLCF) having the outermost clad section made of radially anisotropic liquid crystal. TE mode propagation through TLCF is demonstrated with maximum distribution of power in the liquid crystal section under the situation that the TLCF core and the inner clad regions are constructed of homogeneous and isotropic dielectric materials. Such a propagation feature is attributed to the radial anisotropy of the liquid crystal outer region, and attracts useful applications of TLCFs in evanescent fleld optical sensing and other coupling devices primarily used in integrated optics.

Infrared carpet cloak designed with uniform silicon grating structure

Through a particularly chosen coordinate transformation, we propose an optical carpet cloak that only requires homogeneous anisotropic dielectric material. The proposed cloak could be easily imitated and realized by alternative layers of isotropic dielectrics. To demonstrate the cloaking performance, we have designed a two-dimensional version that a uniform silicon grating structure fabricated on a silicon-on-insulator wafer could work as an infrared carpet cloak. The cloak has been validated through full wave electromagnetic simulations, and the nonresonance feature also enables a broadband cloaking for wavelengths ranging from 1372 to 2000 nm.

Counterposition and negative phase velocity in uniformly moving dissipative materials

We considered the phenomena of counterposition and negative phase velocity, which are relevant to certain metamaterials and certain astrophysical scenarios. The Lorentz transformations of electric and magnetic fields were implemented to study (i) the refraction of linearly polarized plane waves into a half-space occupied by a uniformly moving material and (ii) the traversal of linearly polarized Gaussian beams through a uniformly moving slab. Motion was taken to occur tangentially to the interface(s) and in the plane of incidence. The moving materials were assumed to be isotropic, homogeneous and dissipative dielectric materials from the perspective of a co-moving observer. Two different moving materials were considered: from the perspective of a co-moving observer, material A supports planewave propagation with only positive phase velocity, whereas material B supports planewave propagation with both positive and negative phase velocity, depending on the polarization state. For both materials A and B, the sense of the phase velocity and whether or not counterposition occurred, as perceived by a non-co-moving observer, could be altered by varying the observer's velocity. Furthermore, the lateral position of a beam upon propagating through a uniformly moving slab made of material A, as perceived by a non-co-moving observer, could be controlled by varying the observer's velocity. In particular, at certain velocities, the transmitted beam emerged from the slab laterally displaced in the direction opposite to the direction of incident beam. The transmittances of a uniformly moving slab made of material B were very small and the energy density of the transmitted beam was largely concentrated in the direction normal to the slab, regardless of the observer's velocity.

A Study of Properties of the Photonic Band Gap of Unmagnetized Plasma Photonic Crystal

In this study, the propagation of electromagnetic waves in one-dimensional plasma photonic crystals (PPCs), namely, superlattice structures consisting alternately of a homogeneous unmagnetized plasma and dielectric material, is simulated numerically using the finite-difference time-domain (FDTD) algorithm. A perfectly matched layer (PML) absorbing technique is used in this simulation. The reflection and transmission coefficients of electromagnetic (EM) waves through PPCs are calculated. The characteristics of the photonic band gap (PBG) are discussed in terms of plasma density, dielectric constant ratios, number of periods, and introduced layer defect. These may provide some useful information for designing plasma photonic crystal devices.

MEASUREMENT OF DIELECTRIC CONSTANT AND LOSS FACTOR OF THE DIELECTRIC MATERIAL AT MICROWAVE FREQUENCIES

A new technique to evaluate the dielectric constant and loss factor of a homogeneous dielectric material using rectangular shaped perturb cavity has been developed. The values of S-parameters are measured experimentally by placing the sample in the center of the cavity resonator. Sample under test is fabricated in the form of a cylinder. The real and imaginary part of the permittivity can be then calculated from the shift in the resonance frequency and Q-factor. The results of a Teflon sample are also tabulated.

A Quasi-Optical Free-Space Measurement Setup Without Time-Domain Gating for Material Characterization in the $W$-Band

In this paper, a new free-space measurement setup at millimeter waves for material characterization is presented. Using specific Gaussian optics lens antennas and a thru, reflect, and line calibration, the setup provides the free-space four S-parameters over the W-band of planar dielectric slabs without time-domain gating. An efficient optimization procedure is implemented to extract complex permittivity from the four S-parameters of homogeneous dielectric materials. Nonhomogeneous materials can also be tested, and measurements are presented. Very good agreement is observed between simulated and measured four S-parameters of various dielectric plates. Thanks to this new specific calibration and measurement procedure, automation of the test bench is easily achieved

Various Shapes of 3 D Resonators Pass-Band Filters

The integral equations technique based on a three dimensional finite element method is applied as a quick and accurate analysis tool for the design of microwave passband filters. A three resonator H-plane bandpass filters with the various shapes of cavities and the irises are analyzed with this method in a single step and for only one mode, take into account all the electromagnetic effects. Consequently, it consumes less memory and CPU time. We propose also to study the same filters filled by homogeneous high dielectric material (eτ = 9.6) for Both resonator and coupling section. All these numerical results have been validated through a comparison with the results available in the scientific literature.

Microwave imaging of inhomogeneous objects made of a finite number of dielectric and conductive materials from experimental data

We deal with an electromagnetic inverse scattering problem where the goal is to characterize unknown objects from measurements of the scattered fields that result from their interaction with a known interrogating wave in the microwave frequency range. This nonlinear and ill-posed inverse problem is tackled from experimental data collected in a laboratory-controlled experiment led at the Institut Fresnel (Marseille, France), which consist of the time-harmonic scattered electric field values measured at several discrete frequencies. The modelling of the wave–object interaction is carried out through a domain integral representation of the fields in a 2D-TM configuration. The inverse scattering problem is solved by means of an iterative algorithm tailored for objects made of a finite number of different homogeneous dielectric and/or conductive materials. The latter a priori information is introduced via a Gauss–Markov field for the distribution of the contrast with a hidden Potts–Markov field for the class of materials in the Bayesian estimation framework. In this framework, we first derive the posterior distributions of all the unknowns and, then, an appropriate Gibbs sampling algorithm is used to generate samples and estimate them. The proposed Bayesian inversion method is applied to both a linear case derived from diffraction tomography and the full nonlinear problem.

Analyse multi-modale de filtres en guide d’ondes rectangulaire à iris multi-sections Optimisation génétique et réalisation de filtres à faibles dimensions possédant des zéros de transmission

We present the design and the development of a research method for new microwave waveguide filtering structures with low dimensions and tranmission zeros. An electromagnetic analysis technique is exposed. It permits to characterize all structures composed of rectilinear pieces of rectangular waveguide whose opened areas at the extremities partially overlap. Non shared areas are supposed perfectly conductive and every piece of waveguide is filled with homogeneous isotropic dielectric material. Basic elements are size discontinuities and dielectric discontinuities. We determine the generalized scattering matrix using multimode analysis. Using a lot of modes leads also to reduce dimensions. Coupling of two modes leads to the realization of a zero transmission and improves the selectivity of the filters. Optimization is made using genetic algorithm. In addition to theory, the measured response of a filter is presented and valids the proposed filter concept.

Measurement of the relativistic potential difference across a rotating magnetic dielectric cylinder

According to the Special Theory of Relativity, a rotating magnetic dielectric cylinder in an axial magnetic field should exhibit a contribution to the radial electric potential that is associated with the motion of the material’s magnetic dipoles. In 1913 Wilson and Wilson reported a measurement of the potential difference across a magnetic dielectric constructed from wax and steel balls. Their measurement has long been regarded as a verification of this prediction. In 1995 Pelligrini and Swift questioned the theoretical basis of the experiment. In particular, they pointed out that it is not obvious that a rotating medium may be treated as if each point in the medium is locally inertial. They calculated the effect in the rotating frame and predicted a potential different from both the Wilsons’ theory and experiment. Subsequent analysis of the experiment suggests that the Wilsons’ experiment does not distinguish between the two predictions due to the fact that their composite steel–wax cylinder is conductive in the regions of magnetization. We report measurements of the radial voltage difference across various rotating dielectric cylinders, including a homogeneous magnetic dielectric material (YIG), to unambiguously test the competing calculations. Our results are compatible with the traditional treatment of the effect using a co-moving locally inertial reference frame, and are incompatible with predictions based on the model of Pelligrini and Swift.

An inverse technique to evaluate permittivity of material in a cavity

A numerical technique to estimate the dielectric constant and loss factor of a homogeneous dielectric material placed in an arbitrary shaped cavity has been developed. The values of S-parameters are measured experimentally by placing the sample in the cavity. Starting with a trial set of permittivity values, the computation is carried out using the finite-element method (FEM) to match the S-parameters around the fundamental resonance frequency. The FEM routine is run several times while optimizing the values of dielectric constant and conductivity of the sample. During the process of optimization, eight different measures of error between computed and experimental values of complex S-parameters are examined. It is found that there is no single measure of error, which can be minimized to estimate two parameters (dielectric constant and the loss factor), but the combination of errors has to be minimized to get the exact solution. The computer program can generate the solution with an accuracy of less than 0.01% in a few hours on a Pentium-based personal computer.

Empirical equations on electrical parameters of coupled microstrip lines for crosstalk estimation in printed circuit board

Empirical equations for the self and mutual capacitance and inductance (C/sub s/, C/sub m/, L/sub s/, L/sub m/) of coupled microstrip lines in a printed circuit board were derived from the numerical simulation results to reduce the computation time for crosstalk estimation. Comparison of the measured C/sub s/, C/sub m/, L/sub s/ and L/sub m/ values with the derived empirical equations showed good agreements. Also in the near-end and far-end crosstalks, good agreements were obtained between measurements and the derived empirical equations. Microstrip lines embedded in the homogeneous dielectric material as well as those in the inhomogeneous medium with one side exposed to air were considered in this work. Based on the derived empirical equations, a design guide on the spacing between microstrip lines was established.

One-way wave operators for nonstationary dielectrics

Propagation of transverse electric and magnetic (TEM) pulses in nonstationary, linear, homogeneous, and isotropic dielectric and magnetic materials is investigated using an exact wave splitting. Key intrinsic properties are the index of refraction and the relative admittance, which are both temporal integral operators with kernels that depend on two time variables. In addition, the Sommerfeld forerunners in dispersive nonstationary materials are derived. A numerical example — a single-resonance Lorentz model with time-dependent plasma frequency — is presented.

Microstrip patch sensor for measurement of the permittivity of homogeneous dielectric materials

An application of a small air-spaced coaxially fed rectangular microstrip patch antenna as a sensor for permittivity measurement is presented. The models used for the calculation of the permittivity from the shift in the resonant frequency for solid and liquid materials are described. The models are experimentally verified by measurements for several liquid and solid samples. The results are compared with those obtained using standard techniques, namely, coaxial probe and waveguide cell measurements. An error correction technique for the elimination of the systematic error of the measurement is also included.

Characterization of dielectric materials with the finite-element method

A technique to characterize homogeneous and inhomogeneous dielectric materials based on measurements and computations is presented. The first step of the method proposed consists of measuring the resonant frequencies of an arbitrarily shaped cavity containing an arbitrarily shaped sample of the material under test. In the second step, the measured data are used in two different algorithms, both based on the finite-element method, to solve for the dielectric constant.

Near Field Distribution of Hollow Dielectric Wall Diagonal Horn Antennas

Aperture/near-field distributions of hollow dielectric wall diagonal horn antennas have been studied theoretically and experimentally. Solutions of the Helmholtz equation are obtained for TE to x and TE to y modes using separation of variables technique for the horn assumed to be made of an equivalent homogeneous dielectric material of dielectric constant equal to the effective dielectric constant of dielectric slabs and inner free space region bounded by these slabs. Transcendental equations for the transverse components of propagation constants are obtained by applying proper boundary conditions, i.e. the continuity of the electric and magnetic fields at the interfaces each between the dielectric region and outer free space region. These transcendental equations are solved for the transverse propagation constants for the fundamental mode for five horns each of axial length = 12.8 cm and flare angle = 8.5° at 9.418 GHz in the x-band. The dielectric constant of the dielectric slabs used in fabricating the five horns are equal to 2.54, 2.56, 2.56, 2.80 and 3.03 and respective slab thicknesses are equal to 0.15, 0.15, 0.32, 0.32 and 0.32 cm. The theoretical aperture-field distributions obtained for Hx11, and Hy11modes propagating in these antennas are compared with corresponding experimental ones.

Boundary-element calculations of electromagnetic band-structure of photonic crystals

A boundary element method is developed for calculating the photon modes of periodic structures whose unit cells consist of piecewise homogeneous dielectric materials of arbitrary shapes. Green’s function techniques are used to derive integral equations for these structures. These equations involve integrals over the boundaries between the regions, which are discretized and solved numerically. Thus the full set of Maxwell’s equations with boundary conditions in d independent variables is changed into an integral equation in d−1 variables. This allows for the calculation of mode frequencies and field patterns for wave vectors throughout the Brillouin zone, thus allowing the determination of photonic band gaps. An illustrative example is given here for a two-dimensional system.