Forward-backward method for scattering from imperfect conductors

The previously developed forward-backward method for calculating scattering from perfectly conducting azimuthally homogeneous surfaces is extended to imperfect conductors, where the dielectric constant has a large imaginary part such as sea water at X-band (10 GHz). An example shows that highly accurate results at X-band are obtained for the case of a steepened sea wave     

Low-frequency scattering from cylindrical structures at obliqueincidence

Classical Rayleigh scattering theory is extended to the case of a homogeneous dielectric cylinder of arbitrary cross section whose transverse dimensions are much smaller than the wavelength. By assuming that the surface fields can be approximated by those of the infinite cylinder, the far zone scattered field is expressed in terms of polarizability tensors, whose properties are discussed. Numerical results are presented for circular, semicircular, triangular, and square cylinders. The results are applicable to the remote sensing of twigs, stalks, and vegetation needles at centimeter and millimeter wavelengths     

Low-frequency scattering by rectangular cylinders

An integral equation formulation is used to investigate potential problems associated with low-frequency scattering by both dielectric and perfectly conducting cylinders of rectangular cross section. Induced dipoles and scattering cross sections are obtained for 1) waves withbar{E}orbar{H}parallel to the axis, and 2) directions of propagation perpendicular and parallel to the broad side of the rectangle.     

Electromagnetic scattering from anisotropic plasma-coated perfect electromagnetic conductor cylinders

The scattering of electromagnetic waves by a perfect electromagnetic conductor (PEMC) cylinder coated with a homogeneous plasma anisotropic material is studied in this paper. Both of the transverse electric and the transverse magnetic polarizations of the incident waves have been analyzed and formulated. The presented analysis and formulations are general for any perfect conductor cylinder (PEC, PMC, or PEMC) with general isotropic/anisotropic material coatings that include plasma and metamaterials. The co-polarized and the cross-polarized components of the scattered fields are computed for different cases of the anisotropic plasma coated PEMC cylinders and for an anisotropic plasma column. Bistatic echo widths for the cases of PEMC, PEC (perfect electric conductor) and PMC (perfect magnetic conductor) cores have been computed and compared. The behavior of the monostatic echo width with the variation of the admittance parameter for the co-polarized and the cross polarized fields is also investigated. The comparisons of the computed results of the presented formulations with the published results of some special cases confirm the accuracy of the presented analysis.     

Transient scattering from two-dimensional dielectric cylinders ofarbitrary shape

The problem of transient scattering by arbitrarily shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time technique. The dielectric problem is approached via the surface equivalence principle. Two coupled integral equations are derived by enforcing the continuity of the electric and magnetic fields which are solved by using the method of moments. Numerical results are presented for two cross sections, viz. a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution     

Inverse scattering for conductors by the equivalent source method

The inverse scattering for two-dimensional conductors is investigated. Assume that an incident wave is incident upon conducting cylinders of unknown shape and the scattered field is measured outside. By properly processing the scattering data, the position and shape of the conducting scatterers can then be reconstructed. The proposed theory of inverse scattering is a combination of the diffraction tomography and the equivalent source method. To overcome the ill-posedness, the condition of the measured scattered field and the boundary condition on the conductor surfaces are combined and recast into an optimization problem using the least-squares concept. By comparing the reconstructed and the prescribed results, the inversion algorithms are numerically examined. Note that if a priori information of the shape is sufficient and the equivalent sources are properly placed, the algorithms can be flexibly applied to the cases of multiple conductors. Also the effects of noise contamination and multiple scattering on the reconstruction result are numerically investigated     

二维fBm随机分形界面的电磁散射特性

应用二维fBm（分形布朗运动）模拟了这种既非完全周期的也非完全随机的实际粗糙界面，用Kirchhoff方法计算了电磁波在随机分形界面的散射特性。数值结果表明随着分形维数的增加，散射场中非相关分量逐渐增大，旁瓣增多并在镜面方向周围不断展宽。     

Far field in transient two-dimensional scattering

A heuristic definition of far field is given for time-domain two-dimensional scattering that simplifies the expression of the scattered far field as an integral over the sources. The meaning of this definition and of the ensuing simplifications is clarified by Fourier transforming the approximate time-domain result to compare it with well-known frequency-domain expressions in the Fresnel and Fraunhofer approximations.     

Rules for field plotting in a class of two-dimensional inhomogeneous conductors

Rules for graphically plotting fields in a class of two-dimensional inhomogeneous conductors are shown which are an extension of the rules for field plotting in homogeneous conductors by the method of curvilinear squares. A graphical solution for a particular example is illustrated.     

Test for two-dimensional scattering Hurwitz polynomials

Tests for the discrete scattering Hurwitz property of two-dimensional (2-D) polynomials are suggested. Results belonging to two different categories are presented. The first procedure uses a finite number of rational operations and relies on the so-called polynomial resultant algebra. Alternative methods of testing, which are computationally less complex to implement are also developed.The work described in this paper was carried out during a visit of the first named author under the sponsorship of the Alexander von Humboldt Foundation at the Lehrstuhl für Nachrichtentechnik, Ruhr-Universität Bochum. The authors gratefully acknowledge the support received from this foundation.     

海水包裹空心椭球体的低频散射场计算及分析

为了分析水下金属壳体目标的散射场,提出了一种基于移位算子时域有限差分方法的加速计算方法.利用该方法对海水、空气和金属三种媒质材料进行了建模,并计算了水下金属椭球状壳体目标低频散射场的空间分布和起伏海面对低频电磁波传播的影响.通过数值算例测试了所提方法的加速性能,可以得到接近线性的加速比和95%以上的加速效率.计算结果表明,海面会影响水下壳体目标散射场的空间分布,特别是对于电场的空间分布影响比较大,并且由于水下电导率的存在导致海面上方散射场的传播速度要比海面下方的快.     

The bymoment method for two-dimensional electromagnetic scattering

The bymoment method is presented for analyzing two-dimensional electromagnetic wave scattering in an unbounded region. The method introduces a conforming surface to geometrically decouple the interior region containing the scatterer from the exterior region extending to infinity. The solution in the interior is generated using the standard finite-element solution of an interior Dirichlet boundary-value problem. The interior solution is then coupled to the exterior using Green's theorem in the unbounded exterior region. The validity of the method and the associated computer program is demonstrated by comparing the results to those of other methods for scattering by various cylindrical geometries     

Numerical Simulation of scattering of electromagnetic waves from traveling and/or vibrating perfect conducting planes

This paper presents the one-dimensional computational results for electromagnetic waves scattered from traveling and/or vibrating perfect conducting planes via the application of the characteristic-based method. Relativistic boundary conditions combined with the characteristic variable boundary conditions are employed to account for relativistic effects due to the very high-speed motion of the conductor. The variations in both magnitude and frequency of the reflected electric field were investigated by comparing the computational results with the theoretical double-Doppler shift values. A maximum error percentage of less than 0.50% was found. It is also concluded that when the perfect conducting plane travels and vibrates simultaneously, the Doppler effects in frequency that are impressed on the reflected fields can be predicted, on the basis of computational results, simply dividing the vibrating frequency of perfect conducting plane by the factor (1+/spl beta//sub t/) where /spl beta//sub t/ is the ratio of the traveling velocity to the speed of light.     

Polarimetric scattering from two-layered two-dimensional random rough surfaces with and without buried objects

A three-dimensional polarimetric analysis of the two-layered rough ground with and without buried objects is investigated here. A rigorous electromagnetic surface integral-equation-based model is used in this analysis. The statistical average of the polarimetric scattering matrix elements is computed based on the Monte Carlo simulations for both the vertically and horizontally polarized incident waves. The results show a significant impact on the scattered intensities due to the two-layer nature of the ground. However, these intensities show almost no difference between the ground signature with or without the object. On the other hand, the statistical average of the covariance matrix elements shows a distinct difference between these two signatures despite the small size of the buried object.     

RCS of two-dimensional structures consisting of both dielectricsand conductors of arbitrary cross section

The problem of determining the electromagnetic field scattered by two-dimensional structures consisting of both dielectric and conducting cylinders of arbitrary cross section is considered. The conductors may be in the form of strips and the dielectrics may be in the form of shells. The conductors may be partially or fully covered by dielectric layers, while the dielectrics may be partially covered by conductors. Only homogeneous dielectrics are studied. Both the transverse electric (TE) and the transverse magnetic (TM) cases are considered. The problem is formulated in terms of a set of coupled integral equations involving equivalent electric and magnetic surface currents radiating in unbounded media. The method of moments is used to solve the integral equations. Simple expansion and testing procedures are used. Numerical results for scattering cross sections are given for various structures     

A multiresolution study of two-dimensional scattering by metalliccylinders

The application of wavelet transforms in method of moments (MoM) solutions for scattering problems is extended to cases involving metallic cylinders whose periphery contains a variety of length-scale features ranging from smoothly varying large-scale features (characterized by a radius of curvature of several wavelengths) to rapidly varying small scale ones (characterized by a radius of curvature that is small compared with the wavelength). The basic idea is to first consider a periodic extension of the equivalent current in the arc-length variable with a period identical to the scatterer circumference, and then to expand this representation using a set of periodic wavelets derived from a conventional basis of wavelets by a periodic extension. Using a Galerkin method and subsequently applying a threshold operation, a substantial reduction in the number of elements of the moment-method matrix is attained without virtually affecting the solution accuracy. The proposed extension is illustrated by a numerical analysis of TM (transverse magnetic) and TE (transverse electric) scattering from a cylinder of elliptic cross section. A thorough study is carried out showing how the solution accuracy improves with increasing resolution level, and how this accuracy is affected by a thresholding process which renders the moment matrix sparsely populated     

Noncoherent spatial/spectral optical CDMA system with two-dimensional perfect difference codes

In this paper, the family of newly constructed codes, named 2-D perfect difference codes, is proposed to suppress the phase-induced intensity noise (PIIN) in noncoherent spatial/spectral optical code division multiple access (OCDMA) systems. A novel spatial/spectral transceiver structure employing the new codes to eliminate the multiuser interference (MUI) by using the MUI cancellation property of the new codes is also presented. Compared with the systems employing modified quadratic congruence codes (MQC codes) and maximal-area matrices codes (M-matrices codes), numerical results verify that our proposed system can more effectively suppress the PIIN and eliminate MUI. Hence, the number of simultaneous users and total transmission rate increase significantly.     

Magnetoresistance of two-dimensional ballistic microcontacts with electron-electron scattering

In the semiclassical approximation we calculate corrections to the Sharvin conductance of two-dimensional ballistic microcontact. They are caused by electron-electron interactions outside the contact, the main contribution to the corrections are made by the collisions of electrons with almost opposite momenta. The corrections are positive, increase with temperature and are strongly suppressed by a magnetic field. We assume that the anomalous positive magnetoresistance observed in a recent experiment may be a consequence of this suppression.     

Family of two-dimensional correcting codes on a basis of perfect binary array

We consider a family of two-dimensional correcting E(N)-codes on a basis of perfect binary arrays H(N), and we show correcting possibilities of E(N)-codes in comparison with corresponding BCH-codes with maximal length are essentially better with regard to correction of package (correlated) errors, at that, uncorrelated errors are corrected identically.