Sharhabeel Alyones

Numerical Methods for Solving the Problem of Electromagnetic Scattering by a Thin Finite Conducting Wire

Scattering, absorption and extinction by a thin finite length conducting wire are computed numerically by solving the generalized Pocklington integro-differential equation using two approaches: the method of moments (MoM) with short range pulse basis functions via the point matching scheme and the Galerkin method with long range basis functions (Legendre polynomials modified to satisfy the boundary conditions of the problem). A new development included in the computations reported here involves a more accurate rendering of wires with lower aspect (length-to-diameter) ratios. Both methods converge to the same answer and satisfy the energy balance to within one percent. A comparison is made with an existing analytical theory by Waterman and Pedersen. This theory solves a more approximate form of the Pocklington equation and is found to have anomalies for some cases. The solutions of this paper agree with the analytical theory for very thin wires, and the results yield a small but significant amplitude and resonance shift for lower aspect ratios. All three solutions are in agreement with the numerous available experimental results to within the experimental errors. The numerical approaches provide a complete direct solution to the problem and remove all the anomalies which occurred in the analytical theory by Waterman and Pedersen.

Millimeter-wavelength investigation of fibrous aerosol absorption and scattering properties

The measurements here are used to examine agreement with a recently developed theory for long-wavelength fibrous aerosol attenuative properties (extinction and components absorption, scattering). This is intended to be the final phase of a long and systematic examination of the theorys key features. In this case the parameters are high conductivities coupled with a broad range of fiber diameters. It is clear that there is a limit on the extinction efficiency or effective extinction cross section per unit fiber volume. This limit is represented by the fiber diameter of translucency, that is, the diameter at which the fiber is not completely opaque to the electromagnetic energy. The transition is approximated by the classical skin depth of the fiber. Above this diameter the peak extinction efficiency decreases with an increase in diameter at approximately the same rate for all conductors. The scattering resonance producing this peak becomes stronger as the diameter increases. Our data confirm that for fiber diameters below the skin depth the character of the attenuation is that of absorption.

Extinction efficiencies for metallic fibers in the infrared

Mass density normalized extinction has been both measured and computed throughout the infrared for distribution of well-separated synthesized silver fibers. The computational basis is a code originally generated for use with Drudian thin fibers at millimeter wavelengths and modified for application at wavelengths that include molecular and structural (crystalline) resonances as well as thicker fibers. The computation involved convolution of fiber responses over distributions for both fiber lengths and diameters. Agreement between the measured and the computed results was found to be close.

Electromagnetic Scattering by Finite Conducting Fiber: Limitation of a Previous Published Code

In this paper, the authors examine the low aspect ratio limits of a computational code whose development and application they reported several years ago. A detailed comparison has been made between this code, based on the Moment Method with point matching scheme, and the T-matrix method for the solution of the problem of electromagnetic scattering and absorption by cylinders of finite conductivity. The Alyones et al. code (A-code) has previously been shown to be applicable to relatively thin multilayered fibers, and the T-matrix method has been shown to be valid for low aspect ratios. . . both composed of bulk materials. Here the A-code is tested for low aspect ratio solid fibers and larger radial size parameters (ka) for both low and high conductivity fibrous materials. For very low values of the radial size parameter, the two codes enter agreement at lower aspect ratios, generally at a value of about 10, and as the radial size parameter increases, the agreement occurs at smaller aspect ratios until there is no convergence between the two methods. The criterion is stricter for higher conductivities. A combined code has been formed to handle the calculation of electromagnetic scattering by finite conducting fibers.

Complex conductivity of UTX compounds in high magnetic fields

We have performed rf-skin depth (complex-conductivity) and magnetoresistance measurements of antiferromagnetic UTX compounds (T=Ni and X=Al, Ga, Ge) in applied magnetic fields up to 60 T applied parallel to the easy directions. The rf penetration depth was measured by coupling the sample to the inductive element of a resonant tank circuit and then, measuring the shifts in the resonant frequency Δf of the circuit. Shifts in the resonant frequency Δf are known to be proportional to the skin depth of the sample and we find a direct correspondence between the features in Δf and magnetoresistance. Several first-order metamagnetic transitions, which are accompanied by a drastic change in Δf, were observed in these compounds. In general, the complex-conductivity results are consistent with magnetoresistance data.

Electromagnetic scattering and absorption by randomly oriented fibers

In this paper, we numerically calculate the extinction, scattering, absorption, and radar cross sections for a randomly oriented finite conducting fiber. Calculations in the long (centimeter) and short (infrared) wavelengths are presented and compared with the fixed orientation value when the incident electric field is aligned along the fiber length. The calculations presented in this paper are necessary for the parametrization of fibers to play the role of efficient obscurant and anti-radio frequency interference.

Electromagnetically Induced Absorption in Metamaterials in the Infrared Frequency

In this paper, the author studies, through numerical simulation, the classical analog of the electromagnetically induced absorption/re∞ection (EIA) in a planar metamaterial structure in the near infrared spectral region. The structure is designed by transforming an electromagnetically induced transparency (EIT) structure into an EIA structure using Babinets principle. The structure exhibits a coupling between a bright mode (a complementary ring resonator (CRR)) and a dark mode (pair of parallel straight slits) imprinted on a glass substrate. A narrow absorption window, induced in a wide transparent window, is achieved by the structure and the strength of coupling is tuned by the degree of breaking symmetry and relative displacement of the two mode elements. Electromagnetically induced transparency (EIT) is a quantum mechanical phenomenon in which an absorption is transformed into a transparency, and this is associated with strong dispersion that reduces the group velocity (1{3). This phenomena has many potential applications in signal processing, optical flltering and sensing technologies (4{7). The classical analog of the EIT has been achieved and reported by many researchers using a planar metamaterial structures that are generally composed of two metallic elements imprinted on a dielectric substrate. The two elements are metallic resonators that act either as two bright modes or a bright and dark mode. A bright mode element couples strongly with the incident excitation fleld while the dark element does not couple with the incident fleld but couples with the magnetic fleld induced by the bright element. Several EIT metamaterial structures have been employed and reported in the microwave, terahertz and optical frequency regions (8{14). In this paper, we propose a new EIT structure that achieves a more pronounced narrow transparency window sandwiched between two absorption bands compared with a similar structure proposed in (14). Also compared with (14), the structure proposed here is independent of the polarization orientation with respect to the bright mode element. Then we transform this structure into an EIA structure using Babinets principle (15,16), where a narrow absorption/re∞ection window is sandwiched between two transparency bands. The structures proposed here may be used as obscurant particles that allow the passage of a speciflc window/windows of the electromagnetic spectrum and obscure the neighboring frequencies, for this reason the transmission spectrum will be discussed and addressed for the potential obscurant applications. Although the orientational average response of the structure is what matters, it is of good beneflt to get the behavior in a given orientation. The EIT structure is composed of a metallic ring resonator (RR) which acts as a bright mode and a pair of metallic rods that act as a dark mode. Here we overlap the RR wide antenna resonance and the narrow line width quadrupole rod resonance, which in turn produces the EIT-like efiect. The structure is transformed into an EIA structure by replacing the metallic RR and the pair of rods resonator with complementary ring resonator (CRR) and

DESIGN OF METAPARTICLES AS SHARP FREQUENCY- SELECTIVE OBSCURANT AEROSOLS

In this article, artiflcial aerosol metaparticles are investigated. These particles are based on interacting single split rectangular resonators (SRRs) imprinted on a one-sided thin dielectric substrate. These particles produce sharper transmission bandstops with adjustable bandwidths compared to conventional artiflcial aerosol obscurants like flbers, spheres, discs. The particle design is performed in the microwave region with the intention to be scalable to the infrared. Particles with couplings between two, three, and four SRRs are introduced. Numerical simulations and experimental measurements of the transmission parameter of the particles are introduced and compared with flbrous aerosols. These particles may be used as good electromagnetic obscurants in the atmosphere.

Curved Fiber Scattering

Extinction and backscattering from thin curved fibers of finite conductivity are computed by solving the Pocklington integrodifferential equation using the Moment Method with point matching scheme. For simplicity of interpretation these computations were performed at long wavelengths, in the Drude domain. The effect of the degree of curvature on the cross sections is examined for high and low fiber conductivities, and for two incident geometries: normal and parallel to the plane of the curved fiber. The computations show a narrowing and decreasing cross sections with increased fiber curvature for both low and high conductivities. The normal geometry produces larger cross sections than the parallel case.

Selective-Band Metaparticle Based on Bright-Bright Mode Coupling for Obscuration Applications

In this paper, we propose a planar metamaterial particle that consists of two bright elements imprinted on a dielectric substrate in the microwave region. The two bright elements are a circular ring resonator (CRR) and an asymmetric single-split rectangular resonator (ASRR). The structure exhibits a narrow transparency band in a wide absorption/reflection band through coupling between the two bright modes. We study the proposed structure through numerical simulation and experiment. We also test different orientations of the structure for possible application as an efficient frequency selective-band obscurant.