Equivalent Surface Impedance Research Articles

A general analysis of propagation along multiple-layer superconducting stripline and microstrip transmission lines

A rigorous spectral-domain formulation for a superconducting stripline or microstrip transmission line with a multiple-layer dielectric substrate is presented. The formulation models the strip conductor as a surface current with an equivalent surface impedance, where the surface impedance is approximated in closed form when the strip is either much thinner or much thicker than a penetration depth. In either case the surface impedance is related to the complex conductivity of the material, which is calculated from a two-fluid model. Results are presented to show the slow-wave propagation and attenuation along both microstrip and stripline packages in a realistic multiple-layer configuration, which accounts for the field penetration into the superconducting ground planes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A model for edge scattering from dichroic surfaces

This paper discusses experimental and theoretical results for edge scattering from dichroic (frequency selective) surfaces. Measurements presented for half planes show the nature of the scattering from the edge for both reflection and transmission frequencies. An impedance boundary condition approach is used to calculate the diffraction from dichroic edges. In the analysis the dichroic surface is replaced with an equivalent surface impedance and the total scattered field calculated. Measurements support the theory demonstrating the usefulness of the approach. The method is also useful for calculating diffraction from dielectric edges.

An approximation finite element surface impedance representation for energy absorbing layers

A procedure for determining the scattered pressure field due to a monochromatic harmonic wave that is normally incident upon an energy absorbing submerged structure is treated. The case where the structure is modeled with finite elements and the surrounding fluid is represented with either acoustic finite elements or a boundary integral approach is considered. Finite element modeling problems arise when the details of the submerged structure in the neighborhood of the fluid‐structure interface are not macroscopically homogeneous and in particular when the inhomogeneities are small relative to the acoustic wavelength. An approximate procedure is presented for replacing the detailed microscopic representation of the layered surface configuration with an equivalent simple surface impedance finite element which is specially designed to work at the frequencies of interest.

Statistical theory of scattering and propagation over a random surface

First, a systematic theory is developed for a deterministic surface upon introduction of a surface Green function defined on a reference plane of the rough surface and determined by an equivalent surface impedance. The surface impedance is obtained by an exact transformation of a given boundary equation on the real boundary surface onto the reference plane and is given explicitly in an operator form, in terms of given surface displacement. An exact integral equation is also derived for the reflection coefficient and is applied to a rough surface of large scale, with the aid of an entirely new tangent-plane method. The scattering cross-section per unit area thus obtained is consistent with the power conservation, shadowing and multiple scattering, in contrast with those given in the literature. Governing equations of the statistical-surface Green functions of first and second orders are derived unperturbatively in form of the Dyson and Bethe-Salpeter equations, respectively, by following exactly the procedure established for a random medium. In particular the power conservation and associated optical relations are investigated in detail, in view of a complete lack of theories on this aspect. Results of specific problems are extensively summarised, including scattering cross-section per unit area and detailed optical relations inherent between various quantities involved, with several examples not only for a scalar wave but also for electromagnetic waves.

Scattering from an elliptic cylinder loaded with an active or passive continuously variable surface impedance

Recently it has been shown that a plane wave reflected from an active surface may be amplified [1]. The active surface was theoretically assumed to be a corrugated planar structure with slots properly loaded with negative conductance material (e.g., Gunn, tunnel, or IMPATT diodes). If the corrugations are sufficiently close, such surfaces, whether active or passive, can be modeled in terms of an equivalent surface impedance. From the boundary-value point of view this makes the problem amenable to easy computation. In this communication, an example is discussed where a plane electromagnetic wave scatters from an elliptic cylinder loaded by a continuously variable surface impedance. For negative surface conductance, significant amplification of the backscattered field is obtained. Results are also shown for passive surface impedances.

VLF Wave Propagation Along a Mixed Path in the Curved Earth‐Ionosphere Waveguide

An investigation of VLF radio‐wave propagation across a land‐sea boundary has been completed. The influence of the homogeneous ionosphere and the curvature of the earth, as well as the ground discontinuity, are considered. The problem of finding the field strength due to a horizontal line source is first formulated as a Wiener‐Hopf type problem via the concept of equivalent surface impedance and is subsequently solved in the Fourier‐transform plane. This solution has direct correspondence with that for dipole excitation and is expressed analytically in terms of the reflection and transmission coefficients of modes in the two sections of the earth‐ionosphere waveguide.