Scattering from composite materials: a first-order model

The nonspecular electromagnetic scattering from finite composite laminates is investigated. The composite material is modeled as planar lamina composed of undirectional collimated fibers with regular spacings between the elements. The fibers, perfectly or partially conductive, are assumed to be embedded in a resin matrix translucent to electromagnetic radiation. For the partially conductive case, the Schelkunoff Ansatz is used. The case of two-plied laminates with skewed fiber orientation is discussed. The mathematical formulation is based on the electric-field integral equation solved with an entire-domain Galerkin expansion. Results are obtained for laminates with both finite and infinite numbers of elements. For the latter, the Floquet-Galerkin solution for periodic structures is used. The effect of truncation of the panels is discussed for arbitrary angles of illumination. It is shown that in many cases implementation of the Floquet-Galerkin solution using diagonal system matrices yields accurate results for the nonspecular cross sections of the laminates. The theoretical results are confirmed by experimental data     

Electromagnetic scattering from ducts with irregular edges. II.Noncircular case

For pt.I see ibid., vol.AP-36, no.3, p.383-97 (1988). Electromagnetic scattering from finite noncircular ducts terminated with irregular edges is investigated. An edge-dependent entire-domain Galerkin expansion is proposed for the current variation on the duct wall, rigorously satisfying the edge conditions. The electric field integral equation is solved using this expansion for arbitrary noncircular ducts. Convergence of these solutions is examined and compared to results obtained with a simpler edge-independent formulation. The solutions are shown to agree with previously published results for circular ducts and recently obtained experimental data     

Scattering properties of an impedance-matched, ideal, homogeneous, causal "left-handed" sphere

The plane-wave scattering properties of a sphere of material having an ideal, homogeneous, and causal permittivity epsilon(f), and permeability mu(f) were investigated through detailed three-dimensional finite-difference time-domain, method-of-moments, and series-solution simulations. A Lorentzian functional form was chosen for epsilon(f) and mu( f), as it yields causal responses and allows us to study the physics of the left-handed-medium (LHM) regime. Our interest lies mainly in the frequency range where negative refraction [Re(n) < 0] is observed. We found that when operating in the LHM regime, an impedance-matched sphere responds with scattering features strikingly different from those found in ordinary materials. In particular, we found zero back-scattering and forward scattering that exceeds that of a metal sphere of similar size. The equality of E- and H-plane patterns was proved analytically and numerically, and the possibility of internal subwavelength focusing with a zero index sphere is also reported.     

Electromagnetic scattering from axially inhomogeneous bodies of revolution

The electromagnetic scattering from partially or totally penetrable bodies of revolution (BOR) is formulated in terms of coupled Fredholm integral equations, solved by the method of moments (MM). The scatterers can have axial inhomogeneities, formed by dissimilar dielectric materials. The case of conducting bodies with axially discontinuous coatings is also treated. The penetrable regions can be lossy, characterized by complex permeability and permittivity. Boundary conditions are rigorously treated everywhere including the intersection of the various regions. The solutions are expressed in terms of combinations of two special matrices arising from the Galerkin technique. These solutions are implemented numerically for a class of generic axially inhomogeneous BOR scatterers. Numerical results given for various conducting/dielectric cylinder combinations using this formulation are compared with experimental data. For special cases where comparisons are possible, the present analysis replicates the results of the Mie theory.     

Scattering from partial bodies of revolution

The electromagnetic scattering from classes of partial bodies of revolution formed by the presence of perfectly electrically or magnetically conducting (PEC or PMC) planes is investigated. It is found that when the Galerkin technique is used with a harmonic circumferential expansion, there is a modal decoupling of the integral operators. The choice of these expansions is determined by the angle subtended by the intersecting planes and by whether these planes are PEC, PMC, or a combination of the two. In this analysis, the partial bodies can be either PEC or penetrable. Examples illustrating this formulation are given for conducting and dielectric hemispherical geometries and for a modified corner reflector. Measured and calculated data are compared for the case of a half-cylinder on a finite ground plane