Piergiorgio L. E. Uslenghi

Moment method with isoparametric elements for three-dimensional anisotropic scatterers

A new method for computing the frequency-domain electromagnetic fields scattered from, and penetrating into, arbitrarily shaped, three-dimensional, lossy, inhomogeneous anisotropic scatterers is presented. The method is based on a general volume integro-differential formulation of the scattering problem, and consists of the numerical solution of the coupled integral equations by the moment method and point matching. A particularly powerful feature of this method is that the numerical model of the scatterer is obtained by parametric volume elements and the basis functions used to represent the field within each element are the same used in the finite-element method. Element integration problems due to the singular kernel of the integral equations are treated in some detail. Numerical results for both the isotropic and the anisotropic spherical scatterer are presented, including comparisons with results obtained by different numerical methods for the isotropic cases considered. The capability of the numerical code presented here to deal with cases where the material parameters of the scatterer are given by singular matrices is discussed for two particular examples. >

Electromagnetic scattering from anisotropic materials, part I: General theory

Integro-differential equations are obtained for the electric and magnetic fields inside a linear, lossy, and anisotropic scatterer, in the frequency domain. The material of the scatterer is characterized by arbitrary values of the elements of the relative permittivity tensor \bar{\epsilon} , the relative permeability tensor \bar{\mu} , and the conductivity tensor \bar{\sigma} . The results are specialized to the case of oblique scattering in two dimensions, for which a numerically efficient computer code has been developed and tested, as described in a companion paper (Part II). The method developed herein is based on a comparison between macroscopic and microscopic descriptions of electromagnetic fields in material media, and is of general applicability.

Dispersion relation for bianisotropic materials and its symmetry properties

The dispersion relation for an arbitrary general bianisotropic medium is derived in Cartesian coordinates, in a form well suited to imposing the boundary conditions when dealing with layered media with planar and parallel interfaces. Special cases of practical interest are also considered. Eleven fundamental coefficient families are identified by considering in detail all the symmetries present in the dispersion relation. An ad hoc expression of the determinant of the sum of two 3*3 matrices permits the use of a simple procedure to obtain the coefficients of the dispersion equation. The discussed symmetry properties have general validity, and this technique to evaluate the coefficients may be useful in other fields of application where dispersion relations are of importance. >

Exact scattering by isorefractive bodies

The scattering by penetrable bodies whose refractive index equals the refractive index of the surrounding medium is considered. Exact solutions are obtained for scattering by penetrable isorefractive elliptic and parabolic cylinders. Extensions to other bodies are discussed.

Electromagnetic scattering from anisotropic materials, part II: Computer code and numerical results in two dimensions

The two-dimensional problem of oblique scattering by penetrable cylinders of arbitrary cross section made of materials which are linear, lossy, anisotropic and possibly inhomogeneous is considered. The materials are characterized by arbitrary tensor susceptibilities \bar{x}_{ec} and \bar{x}_{m} . The frequency-domain volume integrodifferential equations satisfied by the electric and magnetic fields and obtained in a previous paper (Part 1) are analyzed numerically. Optimal ordering of the unknowns and transverse electric-transverse magnetic (TE-TM) decomposition in the matrix formulation of the problem are discussed. The cross section of the scatterer is broken down into a triangular mesh. The field components at the vertices of the triangles are the unknowns; within each triangle, each field component is a linear combination of its values at the vertices. Computed field distributions inside the scatterer are found to be in excellent agreement with results obtained by other methods.

Reflection and Transmission for Planar Structures of Bianisotropic Media

The analysis of a layered planar structure consisting of different bianisotropic materials is performed, in the frequency domain. Reflection and transmission coefficients are determined via a chain-matrix algorithm. Numerical results are presented and discussed.

Measurements on scaled models of urban environments and comparisons with ray-tracing propagation simulation

Scaled models of simple two-dimensional (2-D) urban environments are considered in order to investigate propagation along a vertical plane. Specifically, path loss measurements are taken for different positions of the transmitting and receiving antennas at 25 GHz. Then measurement results are compared with theoretical predictions computed by a ray-tracing polygonal line simulator. The measurements indicate a very good agreement between the ray-tracing model and the experiments.

Scattering by an impedance sphere coated with a chiral layer

ABSTRACT The scattering of a plane, linearly polarized electromagnetic wave by a sphere on whose surface an impedance boundary condition holds, and that is covered with a concentric layer of chiral material, is considered. Exact, explicit expressions are derived for the scattered field coefficients. The co-polarized and cross-polarized components of the far backscattered field are determined and discussed. The value of this canonical problem as a benchmark for computer codes is pointed out.

The Inverse Problem for Biaxial Materials

Theory and measurements for the determination of the constitutive parameters of an anisotropic material are described, when a slab of the material is inserted in a rectangular waveguide. If both epsilon and µ tensors have zero off-diagonal elements (biaxial material), then the six diagonal elements can be determined by measuring amplitude and phase of reflection and transmission coefficients. If the material is nondispersive, two sets of measurements at two different frequencies are sufficient, under TE/sub 10/ excitation. In the more general case of a lossy and dispersive material, two sets of measurements at the same frequency under TE/sub10/ and TE/sub20/ excitations are needed. An experimental setup for the latter case is described.

Exact penetration, radiation, and scattering for a slotted semielliptical channel filled with isorefractive material

A semielliptical channel flush-mounted under a metal plane and slotted along the interfocal distance of its cross-section is considered. The channel is filled with a material isorefractive to the medium that occupies the half-space above the metal plane. The boundary-value problem is solved exactly in terms of Mathieu functions, when the primary source is a plane wave with arbitrary direction of incidence and polarization, or an electric or magnetic line source parallel to the channel and located either above the channel or inside it.