Anisotropic Surface Impedance Research Articles

A UTD solution for the diffraction at an edge in a planar anisotropic impedance surface: Oblique incidence case

Electromagnetic scattering of plane waves obliquely incident on the edge of a planar anisotropic impedance surface is analyzed. A rigorous analytical solution, obtained by applying a procedure similar to that originally proposed by Maliuzhinets, is derived with reference to a couple of particular geometrical configurations. These latter are relevant to the case in which the anisotropic impedance surface is truncated to originate on either the edge of a half-plane, the other face being perfect electric conductor, or on a planar junction between the same anisotropic surface and a perfectly conducting plane. The exact integral representation for the total field is then asymptotically evaluated in the context of the uniform geometrical theory of diffraction (UTD). The particular kind of anisotropic surface impedance considered for the loaded face is suitable for modeling corrugated surfaces or strip-loaded grounded dielectric slabs, when the direction of either corrugations or strips is perpendicular to the edge. © 1996 John Wiley & Sons, Inc.

A UTD solution for the diffraction at an edge in a planar anisotropic impedance surface: Oblique incidence case

Electromagnetic scattering of plane waves obliquely incident on the edge of a planar anisotropic impedance surface is analyzed. A rigorous analytical solution, obtained by applying a procedure similar to that originally proposed by Maliuzhinets, is derived with reference to a couple of particular geometrical configurations. These latter are relevant to the case in which the anisotropic impedance surface is truncated to originate on either the edge of a half-plane, the other face being perfect electric conductor, or on a planar junction between the same anisotropic surface and a perfectly conducting plane. The exact integral representation for the total field is then asymptotically evaluated in the context of the uniform geometrical theory of diffraction (UTD). The particular kind of anisotropic surface impedance considered for the loaded face is suitable for modeling corrugated surfaces or strip-loaded grounded dielectric slabs, when the direction of either corrugations or strips is perpendicular to the edge. © 1996 John Wiley & Sons, Inc.

Electromagnetic scattering from a circular cylinder with an anisotropic surface impedance due to an obliquely incident plane wave

AbstractThe series solution of the electromagnetic scattering from a circular cylinder with an anisotropic surface impedance due to an arbitrary plane‐wave incidence is given. The solution can be used as a canonical problem, and for validation of more general numerical methods or for exact calculations of the cylinder with the actual dimension of the realization of the surface impedance. Examples are given for verification purposes. © 1995 John Wiley & Sons, Inc.

UTD solution for plane wave diffraction at an edgeinan artificially hard surface: Oblique incidence case

The three-dimensional plane wave scattering from an anisotropic wedge is described. The particular kind of anisotropic surface impedance considered for the wedge faces is suitable for modelling the artificially hard boundary condition.

Image theory for DC problems involving a conducting half-space bounded by a perfect anisotropic impedance surface

Image theory is developed for the canonical direct current problem involving a point current source in a conducting half-space bounded by a planar perfect anisotropic surface (PAS). The anisotropy of the surface is perfect in the sense that it has infinite conductivity in one direction and zero conductivity in the perpendicular direction. A PAS plane can be realized by a layer of perfectly conducting parallel wires isolated from one another. It is seen that the image of a current point source is a quadrupole transverse-magnetic current extending along a half-infinite line.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Image theory for DC problems involving a conducting half‐space above an anisotropic impedance surface

A novel image theory is introduced, applicable to dc problems involving current sources in an isotropic conducting half‐space bounded by a planar, reciprocal, anisotropic impedance surface. The theory is a generalization of dc problems involving an isotropic impedance surface or a perfect anisotropic impedance surface with zero and infinite resistivities in two orthogonal directions on the plane, previously analyzed by these authors. The image for a point current source is a combination of an electric line current source and a transverse quadrupole magnetic line current source. The magnetic current component vanishes for vanishing anisotropy, while the electric current component vanishes for perfect anisotropy, of the impedance surface.

Static image principle for anisotropic conducting half‐space problems: Impedance boundary

The image principle developed for static problems involving an anisotropic half‐space and bounded by either a perfect electric or magnetic conductor is extended to problems with an anisotropic surface impedance boundary. Such a boundary can be applied to approximate a thin layer of anisotropic conducting material above the anisotropic half‐space. The problem is limited by requiring similar anisotropy for the surface impedance and the transverse part of the resistivity dyadic of the half‐space. It is seen that, instead of a point image for a point source, the image consists of a combination of a point image and a line image obeying an exponential law. The effect of the impedance surface on the potential field of a point source is considered in terms of a numerical example.

Waveguides filled with general biisotropic media

Guided waves in a general class of waveguides with biisotropic filling are studied. The biisotropic medium is the most general isotropic linear medium, that is, nonreciprocal chiral medium. Field equations are derived first for arbitrary waveguide cross sections and then applied for a special circular cross section. The following special boundary impedance conditions have been covered: ideally conducting surface, isotropic, and anisotropic impedance surface and open surface. Some general properties of the eigenwaves are established, and the influence of nonreciprocity together with chirality and losses is discussed. Calculated curves are shown for biisotropic circular waveguides with ideally conducting and isotropic impedance surfaces.

Comparison of different integral equation formulations for bodies of revolution with anisotropic surface impedance boundary conditions

To obtain an accurate solution in the method of moments it is vital that an appropriate integral equation be used. In solving the problem of scattering from bodies of revolution with anisotropic surface impedance boundary conditions, different answers may result from seemingly minor differences in the integral equation formulations used. Different kinds of integral equations are compared with one another when they are applied to bodies of revolution.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radiation patterns of “scalar” lightpipes

At long wavelengths, diffraction effects cause condensing lightpipes to have a significant response in directions within the geometric optics shadow zone. Here, using an analogy with the corrugated “scalar” horns often used in antenna engineering, we point out that a lightpipe with anisotropic surface impedance on its interior surfaces can have substantially reduced sidelobe levels. This may be important for measurements requiring high dynamic range, particularly in the far-infrared.

Radiation from vertical electric dipole located over laterally anisotropic groundplane

We consider a Hertzian vertical dipole at height h over an infinite plane which is characterised by an anisotropic surface impedance. An exact integral formulation is presented which is evaluated asymptotically to give the radiation patterns for the components of the elliptically polarised far zone field.

Launching vertically polarised ground waves from a vertical magnetic dipole over an anisotropic surface

While a vertical magnetic dipole will radiate horizontally polarised waves over a homogeneous isotropic earth, the effect of anisotropy will convert some of the radiated energy to vertical polarisation. An analysis of this situation is outlined employing an anisotropic surface impedance model.

Definition of artificially soft and hard surfaces for electromagnetic waves

The widely used transversely corrugated surfaces and other alternative surfaces having the same anisotropic surface impedance deserve a common name. Here it is proposed to call them soft surfaces by analogy with the soft surfaces in acoustics. In the same way artificially hard surfaces are defined. Cylindrical hard waveguides of any cross-sectional shape can support TEM waves.

Electromagnetic fields of corrugated conical horns with elliptical cross section described by Lamé functions

The corrugated conical horn with elliptical cross section is investigated. Use is made of the analytical solutions of the Lamé differential equations. In the investigations we use the anisotropic surface impedance model. The problem of wave propagation in an anisotropic elliptical cone is formulated as an eigenvalue problem. This problem is solved, and plots are given of the separation constant as a function of the opening angle of the cone with the aspect ratio of the elliptical cross section as a parameter. The radiation of an anisotropic elliptical horn excited by a hybrid mode is determined using the spheroconal wave expansion method. Satisfactory agreement between computations and measurements is obtained. It is found that with this type of horn it is theoretically possible to perfectly generate circularly polarized radiation patterns of elliptical cross section.

Complex Reciprocity Theorem for Multiregions, with Piezoelectric Media and Surface Impedance

It is shown that the complex reciprocity theorem holds for regions bounded by inhomogeneous anisotropic impedance surfaces and composed of Iossless inhomogeneous and piezoelectric media. Also, the complex reciprocity theorem is obtained in the quasi-electrostatic form.

Reciprocity Theorem for a Region with Inhomogeneous Bianisotropic Media and Surface Impedance (Short Papers)

It is shown that the modified reciprocity theorem holds for a region bounded by inhomogeneous anisotropic impedance surfaces and composed of regions with lossless inhomogeous bianisotropic media; and besides, the reciprocity theorem holds for the case a condition.

Reciprocity theorem for a region with inhomogeneous anisotropic media and with surface impedance

The validity of the reciprocity theorem for a region bounded by inhomogeneous anisotropic impedance surface and composed of regions with lossless inhomogeneous anisotropic media whose parameters vary with position is discussed.

Attenuation in an elliptic waveguide

The formula for the anisotropic axial surface impedance, specified by Falciasecca et al. as necessary for agreement with the classical attenuation computation of Chu, gives an erroneous result for a much elongated ellipse. This error is attributed to the form of the asymptotic expansion of the radial Mathieu functions of the fourth kind that is used in the waveguide wall. Corrected expressions for the axial and transverse surface impedances and for the TE and TM mode attenuation are elaborated.

Rectangular Waveguides with Impedance Walls

The propagation of guided waves in a rectangular geometry having impedance boundary conditions is investigated. An impedance compatibility relation is derived that must be satisfied in order that a separable modal solution exists for a given impedance configuration. Several new rectangular waveguides are developed; among them are 1) a tall rectangular waveguide operating in a dominant H/sub 10/ mode with no H/sub 0N/ modes; 2) a rectangular waveguide with two parallel anisotropic impedance surfaces; 3) a rectangular waveguide with two parallel walls having isotropic impedance surfaces, the other two walls being anisotropic; 4) a rectangular waveguide supporting only E modes; and 5) rectangular coaxial systems containing impedance surfaces. The modal structure of rectangular waveguides with impedance boundary conditions offers advantages over the conventional waveguide. The potential of oversizing for low-loss and high-power applications is enhanced because of the additional modal control provided by the impedance surfaces. Other applications are suggested.

Scattering from cylinders with arbitrary surface impedance

This paper presents an integral equation method for the solution of the field scattered by a set of cylinders with arbitrary cross-sectional shape, and arbitrarily varying anisotropic surface impedance. The integral equations are given for an arbitrary source with arbitrary harmonic variation along the cylinder axis. The scattering problem can be solved for arbitrary three-dimensional sources by expansion of the source in a Fourier integral over the axial propagation constant. The integral equations have been programmed for a CDC 1604A computer. The program developed has been used to solve a great variety of scattering, antenna, and propagation problems, and, depending upon accuracy desired, will handle cylinders up to about 150-wavelengths total perimeter. Numerical results on scattering from cylinders with specific cross sections are presented to illustrate the utility of the program developed.