Lossless Dielectrics Research Articles

Optimum Design of Millimeter-Wave Double-Dielectric Fresnel Zone-Plate Lens and Antenna

The microwave/millimeter-wave Fresnel-zone plate (FZP) lenses differ substantially in construction, technology and applications from their optical analogs and require specific design equations and methods of electromagnetic analysis. In this paper, optimum design equations for double-dielectric lossless FZP lens are derived. The best and worst choices of the permittivity ratio for lossless dielectrics are discussed in detail. In addition, the influence of dielectric losses on the lens thickness for given wavelength and permittivities is examined.

Domain-product technique solution for the problem of electromagnetic scattering from multiangular composite cylinders

The paper presents a domain-product technique solution for the problem of electromagnetic scattering from a two-dimensional structure composed of multiple perfect conductors and lossless dielectrics with arbitrarily polyhedral boundaries. The configuration is assumed to be excited by a plane wave polarized transverse magnetic or transverse electric to the axis of the cylinders. For both the interior and exterior subregions, efficient field representations are attained in the forms of Mathieu function expansions. A system of infinite matrix equations with respect to the expansion coefficients results from the boundary conditions. A solution to the system is found using a truncation procedure. Numerical examples are presented that demonstrate the validity, flexibility, and capability of the technique. In the middle frequency range, the approach proposed enables accurate numerical analysis of fairly complicated structures with low computational cost.

A robust and efficient method for obtaining the complex modes in inhomogeneously filled waveguides

AbstractIn this paper, we present a computational simulation of the complex wave propagation in inhomogeneously filled waveguides with lossless and lossy dielectrics. We use a biorthonormal‐basis method as a numerical technique. The behavior of complex modes in different waveguides whose characterization with other methods involves some difficulties is analyzed. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 218–222, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10875

Extraction of the surface waves and waveguide modes of the Green's function in layered anisotropic dielectrics between two ground planes

In layered lossless dielectrics between two ground planes there exist the complicated waveguide modes as well as the surface waves in the electromagnetic field induced by a horizontal electric dipole. All these modes can be characterized by the rational parts with the real poles of the spectral domain vector and scalar potentials. The accurate extraction of these modes plays an important role in the evaluation of the Green's function in spatial domain. In our previous work [Song and Hong, 2002] a new algorithm based on rational approximation is presented for the extraction of surface waves and waveguide modes of the Green's function for layered isotropic dielectrics. In this paper, we extend the algorithm to the more complex case of layered anisotropic dielectrics; this algorithm can accurately extract all the real poles and their residues simultaneously. Thus we can get all the surface waves and waveguide modes, which can greatly help in the calculation of the spatial domain Green's function. The numerical results demonstrate the accuracy and efficiency of the proposed method.

A new technique to calculate the electrostatic Coulomb force on a conductor coated with a lossless dielectric

In this article, the authors apply a new technique based on expressing the Coulomb force in terms of a special singularity integral to calculate the electrostatic force exerted on a conductor coated with a lossless dielectric. Specifically, the example of the calculation of the electrostatic Coulomb force on a lossless dielectric slab attached to the lower plate of a parallel-plate capacitor is considered.

Radiative transfer over small distances from a heated metal

Published works have predicted that the radiative transfer from a heated metal to a lossless dielectric a short distance away is many orders of magnitude times the free-space Planck density. It is shown analytically that the radiative transfer from a heated metal to a lossless dielectric of index n(3) is n(3)(2)e(13) times the free-space Planck density, where e(13) is the emissivity of the metal radiating into the lossless dielectric. This radiative transfer is never larger than n(3)(2) (approximately one order of magnitude for semiconductors in the infrared) times the free=space Planck density. The expressions presented show that the maximum radiative transfer from a lossy metallic heat source with a dielectric function of imaginary part ?(I) must be proportional to n(3)(3)/ radical?(I), of which a factor of n(3)(2) arises from the power density within a dielectric and a factor of n(3)/ radical?(I) arises from the emissivity of a metal radiating directly into a dielectric.

Very large radiative transfer over small distances from a black body for thermophotovoltaic applications

The maximum amount of radiated heat intensity which can be transferred from a black body of refractive index D/sub BB/ to an object of refractive index D/sub OBJ/ located a short distance away is shown to be n/sub smaller//sup 2/ times the free space Planck distribution where n/sub smaller/ is the smaller of n/sub BB/ and n/sub OBJ/, and where n/sub BB/ and n/sub OBJ/ are assumed greater than unity. The implication is that the radiative power spectral density within a thermophotovoltaic cell could be designed to be much greater than the free space Planck distribution. The maximum radiative intensity transferred occurs when the index of the black body matches that of the object at wavelengths where the Planck distribution is sizeable. A simple expression is found for the transferred radiative intensity as a function of the refractive indices of and the distance separating, the black body and the object. This expression is interpreted in terms of the specific black body modes which are evanescent in the space between the black body and the object and which make the largest contribution to the transmission of radiation. The black body, the object, and the region are all modeled as lossless dielectrics.

The optical theorem for light scattering from a dielectric rough surface

The problem of a plane electromagnetic wave scattering from an infinite plane interface of two lossless dielectrics with a one-dimensional localized roughness of arbitrary shape is considered. The generalized optical theorem for the scattering amplitude is obtained. This theorem is supposed to be used as a necessary condition against which any theoretical approach for solving the scattering problem under consideration can be verified.

Localization of light in lossless inhomogeneous dielectrics

The localization of electromagnetic waves in lossless inhomogeneous dielectric media is studied. We consider a three-dimensional lossless periodic medium (photonic crystal) having a gap in the frequency spectrum (photonic bandgap). If such a medium is perturbed by either a single defect or a random array of defects, exponentially localized electromagnetic waves arise with frequencies in the gap. For a single defect, we derive equations for these midgap frequencies and estimate their number. For a random medium, we show the occurrence of Anderson localization for electromagnetic waves.

Uniqueness of the solution of electromagnetic boundary-value problems in the presence of lossy and piecewise homogeneous lossless dielectrics

In this paper, the uniqueness of the solution of electromagnetic boundary-value problems is investigated and, in some cases, proven. The boundary-value problems considered are always defined in limited regions containing linear dielectric materials that are neither lossy nor lossless everywhere. The boundary conditions are given by specifying over the closed boundaries either the tangential components of the electric field or the tangential components of the magnetic field (or possibly by specifying the tangential components of the electric field over part of the boundaries and the tangential components of the magnetic field over the rest of the boundaries). In particular, the solution is proven to be unique in the case of linear dielectric materials which are piecewise homogeneous and lossless, except for some linear and lossy subregions that may be inhomogeneous. As a byproduct of this analysis, one can conclude that a cavity resonator, loaded with linear and lossy dielectrics together with linear piecewise homogeneous and lossless dielectric materials, does not admit undamped resonances.

Decomposition of the electromagnetic field in lossless inhomogeneous dispersive dielectrics.

The interaction of the electromagnetic field with lossless Lorentz oscillators modeling the inhomogeneous dielectrics is diagonalized in a closed Fabry-P\'erot resonator using the generalized polariton transformation. Resulting dispersion relations coincide with the classical ones obtained by the solution of the wave equation. The corresponding decomposition is, however, orthogonal and complete in the enlarged Hilbert space. \textcopyright{} 1996 The American Physical Society.

Radial-line to coaxial-line junction to a dielectrically sheathed post

An analysis of a coaxial line/radial line junction is presented for the case where the center conductor of the coaxial line extends the full width across the radial line and is completely sheathed in a lossless dielectric. The problem is analyzed by the Fourier transform method using a realistic model for the coaxial excitation. Expressions for the current distribution on the post and the admittance of the junction are deduced. Comparison of theoretical and experimental results show the theory to be very accurate. >

Angular Momentum Balance on Light Reflection

Abstract It was pointed out by Holbourn in 1936 that there is an apparent breakdown of angular momentum conservation on reflection of circularly polarized light at the plane interface between two lossless dielectrics. The analysis presented in this paper shows that this discrepancy does not arise provided that: (a) the intensities of the incident, reflected, and transmitted beams vanish at large distances from their axes, and (b) the angular momentum of each beam is calculated from first principles.

Phase shifts in transmission line models of thin periodic metal grids

This paper describes simple formulas for the phase shifts associated with reflection and transmission of electromagnetic waves by a thin periodic metal grid on a plane boundary between two lossless dielectrics, for the case where the wavelengths on both sides of the boundary are greater than the grid period. The phase shifts are expressed in terms of the zero-order intensity reflectance and transmittance of the grid and are correct even when the grid has loss. They correspond exactly to the phase shifts that can be calculated using the well-known equivalent-circuit models for thin metallic grids but are applicable for any thin nondiffracting layer on a dielectric boundary, for normal incidence.

Equivalent-circuit formulas for metal grid reflectors at a dielectric boundary

This paper points out a number of errors that have appeared in the literature concerning transmission-line models for metal grid reflectors (strip gratings and meshes) especially in regard to the design of laser mirrors and filter elements for use at submillimeter wavelengths. General formulas are given for the transmittance of lossy grids and for the equivalent circuit impedances to be used in these formulas for strip gratings and meshes at a plane boundary between two lossless dielectrics. The results apply for normal incidence and for wavelengths in both dielectrics greater than the grid period. Limitations of the transmission-line models for meshes at dielectric boundaries are discussed.

Loop antennas for directive transmission into a material half space

The horizontal circular loop and the coaxial array of loops above a material half space are studied as antennas for directive transmission into the half space. In a practical situation the loops might be located in air with the directive transmission into the earth. In determining the optimum geometry for the single loop and the array, the far‐zone field patterns and directivities of these antennas when placed over lossless dielectrics are considered first. The directive properties for the lossless dielectric are found to be indicative of those for the same antenna over a medium with low loss when proper account is taken of the exponential attenuation experienced in the lossy medium. Parametric studies are used to obtain the maximum directivities for these antennas. For the single loop of resonant size, the optimum height over the interface is determined, and for the two‐element array consisting of a driven loop of resonant size with a single parasite, the optimum size and spacing of the parasitic reflector are found. Measured electric field patterns and gains of model antennas above an interface between air and fresh water are in good agreement with the theoretical results.

Electric Dipole Radiation in the Presence of a Moving, Dispersive Dielectric Half‐Space

The problem of a point electric dipole moving over a dispersive dielectric half‐space is studied. The dipole is located in the free space above the dielectric and is assumed to be time harmonic in its rest frame, oriented perpendicular to the interface, and moving parallel to it. Solutions for this problem are obtained by using integral transform techniques. Expressions for the electric and magnetic fields in the free space region are formulated for the reflected radiation field for the case of an arbitrary, dispersive dielectric and for the lateral wave and surface wave fields for the case of a lossless plasma dielectric. In the rest frame of the source, it is found that all three waves exhibit the frequency of the source and that the field patterns are distorted by the relative motion. In the rest frame of the dielectric, it is found that each of the waves exhibits some form of Doppler shift (different from the primary wave) and that their field patterns are also distorted. It is also found that the criterion for existence of the lateral wave is not modified by the relative motion of the source and dielectric but that the criterion for existence of the surface waves is greatly modified by the relative motion. In addition, for velocities greater than some critical velocity, it is found that a new type of surface wave comes into existence.

DIFFRACTION OF 3.2 CM. ELECTROMAGNETIC WAVES BY DIELECTRIC RODS: I. LUCITE AND TENITE 1 IN. DIAMETER CYLINDERS

Diffraction patterns of lucite and tenite cylindrical rods of approximately one inch diameter, in a nearly plane beam of square-wave modulated 3.2 cm. waves with electric vector parallel to the cylinder axis, have been measured in several planes transverse to the incident beam direction. Patterns are compared with theoretical ones (Froese and Wait 1954) and with ones obtained earlier, under similar experimental conditions, for brass and hard rubber cylinders (Wiles and McLay 1954). Some general marked trends in the patterns of the four rods, comprising a conductor, two nearly lossless dielectrics with different dielectric constants, and a lossier dielectric, are related to the effects of transmission and/or surface reflection expected from geometrical optics considerations.

RADIATION RESISTANCE OF DIPOLES IN AN INTERFACE BETWEEN TWO DIELECTRICS

Exact expressions are derived for the radiation resistance of electric and magnetic dipoles located in the plane interface between two semi-infinite lossless dielectrics.