Scattering from a topological insulator cylinder buried below a slightly rough surface

Electromagnetic scattering from a topological insulator (TI) cylinder buried beneath a rough surface is considered. To account for the interactions of the scattered field and the rough surface, spectral plane wave representation of fields is used along with small perturbation method. Both time-reversal symmetry TI cylinder and time-reversal symmetry broken TI cylinder are considered to evaluate the scattered-transmitted field above the rough surface for different values of the periods of the rough surface and the size of the object. It is observed that co- and cross-polarized field components show a maximum before the time-reversal symmetry is broken. The co-polarized component remains almost constant while the cross-polarized component decreases for time-reversal symmetry broken case.     

Near zone scattering and extinction properties of a left handed material cylinder buried in a semi infinite medium with rough interface

A solution utilizing the spectral plane wave representation of fields (SPRF) combined with the extended boundary condition method (EBCM) is presented to study the scattering and extinction properties of a left handed material cylinder buried in a semi infinite medium with a rough interface. The EBCM is used to evaluate the field transmitted through the interface, which excites the cylinder. The SPRF is used to study the interaction of scattered field from the cylinder with the rough interface. The effect of the negative permittivity and permeability of the cylinder on the far zone scattered field is observed. Further, the near zone scattered field is investigated, which is very helpful to characterize the scenario in which object detection is a challenging task. It is also observed that the electrical size is an important factor affecting the near zone scattered field since the extinction cross section depends upon size.     

Experimental light-scattering measurements from large-scale composite randomly rough surfaces

We present experimental measurements of the angular distribution of light scattered from large-scale composite randomly rough surfaces (oceanlike surfaces) with different statistical parameters illuminated at small and large angles of incidence. The surfaces are composed of a small-scale roughness superimposed on a slowly (large-scale) varying surface. The large-scale surfaces are diamond-machined periodic surfaces made on aluminum substrates and have either a sinusoidal or a Stokes wave profile. The small-scale roughness is added with microlithographic techniques, and the surfaces are then gold coated. For a linearly polarized incident beam, it is found that the diffusely scattered light is strongly depolarized and that its pattern is rather different for each large-scale surface profile. Enhanced backscattering is also observed.     

Monte Carlo simulations of electromagnetic wave scattering from a random rough surface with three-dimensional penetrable buried object: mine detection application using the steepest-descent fast multipole method.

We present a statistical study of the electric field scattered from a three-dimensional penetrable object buried under a two-dimensional random rough surface. Monte Carlo simulations using the steepest-descent fast multipole method (SDFMM) are conducted to calculate the average and the standard deviation of the near-zone scattered fields. The SDFMM, originally developed at the University of Illinois at Urbana-Champaign, has been modified to calculate the unknown surface currents both on the rough ground and on the buried object that are due to excitation by a tapered Gaussian beam. The rough ground medium used is an experimentally measured typical dry Bosnian soil with 3.8% moisture, while the buried object represents a plastic land mine modeled as an oblate spheroid with dimensions and burial depth smaller than the free-space wavelength. Both vertical and horizontal polarizations for the incident waves are studied. The numerical results show that the TNT mine signature is almost 5% of the total field scattered from the ground. Moreover, relatively recognizable object signatures are observed even when the object is buried under the tail of the incident beam. Interestingly, even for the small surface roughness parameters considered, the standard deviation of the object signature is almost 30% of the signal itself, indicating significant clutter distortion that is due to the roughness of the ground.     

Scattering from rough inhomogeneous media: splitting of surface and volume scattering

The intensity scattered by particles randomly placed beneath a rough interface is studied with rigorous simulations. It is shown that the angular intensity pattern is close to that obtained by adding the intensity scattered by particles under a flat surface to that scattered by a rough homogeneous surface whose permittivity is evaluated with an effective-medium theory. This heuristic splitting rule is accurate for a large range of parameters that are well beyond any perturbative treatment.     

Anisotropic speckle patterns in the light scattered by rough cylindrical surfaces

Speckle patterns in the light field scattered from the rough surface of a cylindrical object are experimentally studied. The light speckles are elongated in the direction normal to the cylinder axis. A theoretical model explains the main features of the scattered light field. The dimensions of light speckles depend on both the surface roughness and the surface curvature.     

Analytical Estimation of Radar Cross Section of Infinitely Long Conducting Cylinder Coated with Metamaterial

Aerospace structures can be approximately modeled as a combination of canonical structures such as cylinder, cone and ellipsoid. Thus the RCS estimation of such canonical structures is of prime interest. Furthermore metamaterials possess peculiar electromagnetic properties which can be useful in modifying the RCS of structures. This paper is aimed at calculating the RCS of an infinitely long PEC circular cylinder coated with one or two layers of metamaterial. The incident and scattered fields of coated cylinder are expressed in terms of series summation of Bessel and Hankel functions. The unknown coefficients of summation are obtained by applying appropriate boundary conditions. The computations are carried out for both principal polarizations. The computed results are validated against the numerical-based method of moments. Further, the variation of RCS of the metamaterial coated PEC cylinder with material parameters, frequency, aspect angle and polarization is analyzed.     

Estimation of electromagnetic scattering patterns from sinusoidalsurfaces using FFT

The scattering of electromagnetic waves from perfectly conducting sinusoidal surfaces as prototypes of periodic rough surfaces is studied. Physical optics and Fourier methods are used to calculate the scattered far field at a function of the observation angle. The patterns for several surface parameters are evaluated and plotted. The size of the illuminated surface area is varied. Homogeneous and Gaussian field amplitude perturbation of a laser beam in TEM₀₀-mode is considered. The results are compared with other methods and show a rather good agreement. Therefore, the method may be used for far-field computation if several criteria for the validity of the Kirchhoff approximation are not violated     

Fast numerical method for electromagnetic scattering by rough layered interfaces: propagation-inside-layer expansion method

Electromagnetic scattering from a stack of two one-dimensional rough surfaces separating homogeneous media is modeled with a rigorous integral formulation solved by the method of moments. We present an efficient numerical method for computing the field scattered by such rough layers, in reflection as well as in transmission. We call this method propagation-inside-layer expansion (PILE) due to its straightforward physical interpretation. To our knowledge, it is the first method able to handle problems for this configuration with a huge number of unknowns. We study the convergence of this method versus a coupling condition and validate it by comparison with results from the literature.     

Applicability of the singular-optics concept for diagnostics of random and fractal rough surfaces

We introduce the singular-optics approach for classification of rough surfaces with large-scale inhomogeneities into random and fractal surfaces. The maps of amplitude zeros of a field versusthe parameters of the rough surfaces and the position of the observation zone are obtained and analyzed. It is shown that the local density of amplitude zeros in the scattered field serves as an appropriate parameter with which to classify the surface of interest into a surface with a height distribution that can be described as a random or a fractal process.     

Light scattering by a coated infinite cylinder in an absorbing medium

The scattering formulation for a coated infinite cylinder in an absorbing medium is presented in this paper. The cylinder is subjected to an arbitrarily polarized plane wave propagating in a general direction at the cylinder. The refractive index and magnetic permeability of the host medium, as well as those for the core and coating of the cylinder, can be real or complex. The scattering and extinction efficiencies and the scattering amplitudes are derived for both the near field and the far field. As the medium is absorbing, the "true" extinction and scattering efficiencies are derived based on the radiative energy outflow at the surface of the cylinder. The radiative efficiencies in the far field are denoted as "apparent" properties because they include absorption by the intervening medium. The influence of the refractive index and permeability of the host medium on the scattering properties of a coated cylinder is illustrated by numerical examples.     

Role of caustics in the formation of networks of amplitude zeros for partially developed speckle fields

The topology of a partially developed speckle field was studied by use of interference techniques through computer simulation. Amplitude and phase structures in the vicinity of caustics for a coherent radiation field scattered at a surface with large inhomogeneities were investigated. It was confirmed that the caustics are indispensible components of the procedure for the formation of networks of amplitude zeros for a coherent field scattered by a rough surface with large inhomogeneities. It is shown that the formation of interference forklets in the field gives evidence of changes in the field's topology, as these forklets are a diagnostic sign of transition from a caustic to a three-dimensional pattern of a diffraction catastrophe.     

Light scattering from self-affine fractal silver surfaces with nanoscale cutoff: far-field and near-field calculations

We study the light scattered from randomly rough, one-dimensional, self-affine fractal silver surfaces with nanoscale lower cutoff illuminated by s- or p-polarized Gaussian beams a few micrometers wide. By means of rigorous numerical calculations based on the Green's theorem integral equation formulation (GTIEF), we obtain both the far- and near-field scattered intensities. The influence of diminishing the size of the fractal lower-scale irregularities (from approximately 50 nm to a few nanometers) is analyzed in the case of both single realization and ensemble-average magnitudes. For s polarization, variations are small in the far field, being significant only in the higher-spatial-frequency components of evanescent character in the near field. In the case of p polarization, however, the nanoscale cutoff has remarkable effects stemming from the roughness-induced excitation of surface-plasmon polaritons. In the far field, the effect is noticed both in the speckle pattern variation and in the decrease of the total reflected energy upon ensemble averaging, as a result of increased absorption. In the near field, more efficient excitation of localized optical modes is achieved with smaller cutoff, which in turn leads to huge surface electric field enhancements.     

Diffraction of cylinders with longitudinal surface structures

We present a model to determine the light scattered by a metallic cylinder with longitudinal structures when the cylinder is illuminated by a Gaussian light beam in oblique incidence. The model is based on an approximate solution to the Helmholtz-Kirchhoff integral by means of the stationary-phase method. We have studied the variations of the diffraction pattern in terms of the size of the defect and other geometrical parameters. The width of the beam and the misalignment between the beam and the cylinder have also been considered, as well as the optical properties of the surface.     

粗糙表面散射基模高斯光束的散射特性实验研究

本文介绍良导体二维粗糙表面对红外激光束的散射分布;讨论不同偏振方式入射时散射光的分布特点,以及中等粗糙表面和弱粗糙表面散射能量在不同入射角下的变化趋势;分析表面参数对分布的影响。文章对观察到的弱粗糙表面散射在镜反射方向附近的边凸现象作了简述;这一现象由散射光的相干叠加而引起,有深入研究的价值。     

An Efficient Inverse Scattering Algorithm for a Complex Cylinder Buried in a Three Layer Structure

In this paper, we present a computational approach to the imaging of a complex cylinder object buried in three layers by the unrelated illumination method. The electromagnetic imaging for a complex cylinder object buried in three layers by transverse electric (TE) wave illumination is investigated. A dielectric cylinder of unknown permittivities coated on a conductor with known cross section are buried in the second layer and scatter a group of unrelated TE waves incident from the first layer where the scattered field is recorded. By proper arrangement of the various unrelated incident fields, the difficulties of ill-posedness and nonlinearity are circumvented, and the permittivity distribution can be reconstructed through simple matrix operations. The algorithm is based on the moment method and the unrelated illumination method. Numerical results show that good reconstruction has been obtained both with and without Gaussian noise in measured data. In addition, the effects of noise are also investigated.     

Wave Scattering from Fractal Surfaces

Abstract

In this paper, a normalized band-limited Weierstrass function is presented for modelling 2D fractal rough surfaces. Some conventional statistical parameters, namely the root mean square and the correlation length of rough surfaces, are used to assess between fractal parameters and the roughness of surfaces. An analytic solution of the scattered light field from these fractal surfaces is derived based on Kirchhoff theory. Three statistical parameters, namely the average scattering coefficient, the average intensity of scattered field, and the root mean square of scattered field, are introduced to study the influence of various fractal parameters on the scattered field by theoretical analysis and numerical calculations.     

Controlled formation of dielectric chain aggregates on material surfaces

This paper investigated the formation of chain aggregates from fine particles suspended in gas stream onto material surfaces under the action of electric field. The results showed that the shape of aggregate formed on material surface was greatly influenced by the field intensity and the surface condition of materials. In a weak electric field without corona discharge, particles tended to form clustered aggregates on a metal plate with smooth surface, but on a metal mesh and a porous alumina substrate, to form chain aggregate. On the other hand, in a corona discharge field, these surfaces were coated uniformly. Consequently, for forming chain aggregates on material surface, an electric field without corona discharge and a rough surface are necessary conditions. On rough surface, chain aggregates of dielectric particles or conductive particles grew from the protrusions of the surface and could form a rough and porous layer. When the external electric field was removed, the chain aggregates remained long time due to the Van der Waals forces. After sintered at proper temperature, the chain aggregates became fiber-like. The results indicate that the formation of chain aggregate can be controlled by electrostatic force, and sintering can be used as a method for increasing their mechanical strength.     

Statistical moments for rough surface scatter from two-way parabolic integral equation at low grazing angles

The moments of a plane wave scattered at low grazing angles from a one-dimensional perfectly reflecting rough surface are considered. The mean intensity and autocorrelation of the scattered field and the corresponding angular spectrum are obtained to second order in surface height. The derivations are based on an operator expansion of the extended (two-way) parabolic integral equation solution. The resulting operator series describes successively higher-order surface interactions between forward and backward going components. The expressions derived may be regarded as backscatter corrections to those obtained via the standard (one-way) parabolic integral equation method.     

Multi-parameter identification and shape reconstruction for unbounded fractal rough surfaces with tapered wave incidence

In this paper, we study the inverse scattering of tapered waves from sound soft surfaces or horizontally polarized electromagnetic waves from perfectly conducting surfaces. By the related Fréchet derivative with respect to a given surface of the solution of direct scattering problems, an efficient algorithm is proposed to reconstruct the parameters of unbounded rough surfaces from a set of scattered field measurements. Tapered wave is introduced to realize the asymptotic truncation for unbounded fractal rough surface. In order to improve the results of reconstruction, multi-angle and multi-frequency incidence strategy has been used. The numerical results show that the method yields satisfactory reconstructions for some rough surface profiles.