On the scattering of an obliquely incident plane wave by a biisotropic cylinder

Scattering of an obliquely incident electromagnetic plane wave by an infinitely long, homogeneous, biisotropic cylinder is addressed. The ambient host medium considered is isotropic, homogeneous and dielectric-magnetic. It is observed that the constitutive coupling of the electric and the magnetic fields in the biisotropic material causes the cross-polarization component of the scattered field not to vanish even for the normal incidence case.     

Analysis of radiation from arbitrarily oriented wire antennas over imperfect ground (Sommerfeld formulation): SomArb

The program is for analysing radiation from antenna arrays of arbitrarily oriented thin-wire antennas over the plane surface of an imperfectly conducting earth. The solution is that obtained from the E-field integral equation by the method of moments. The effects of the imperfectly conducting earth are accounted for exactly by using the Sommerfeld formulation.     

FDTDSIBC混合方法计算近地导线表面电流

通过在FDTD方法中引进时域表面阻抗界条件来研究瞬态电磁脉冲对有耗地面附近电缆线耦合问题。由频域表面阻抗出发通过拉氏变换得到时域表面阻抗边界条件（SIBC）,并将这种边界条件应用于FDTD方法中来模拟有耗地面的反射。计算结果表明了些方法的有效性。     

The effect of preventive maintenance on a system with imperfect switchover

A two-unit standby redundant system with repair, preventive maintenance and imperfect switchover is considered. The Laplace-Stieltjes transform (LST) of the survivor function (sf) of the time to the first system failure (TFSF) and the mean are derived. Finally a theorem about the effect of preventive maintenance is proved.     

The Electromagnetic Field in an EMP Simulator at a High Frequency

The electric field in the working volume of an EMP simulator has been determined experimentally in both amplitude and phase at a frequency that is high enough so that the simulator no longer behaves like a terminated-TEM-mode transmission line. Graphs of the field in the working volume are displayed and interpreted in terms of the TEM and higher parallel-plate modes. The actual field is shown to differ greatly from that characteristic of the TEM mode so that it must be expected that current and charges induced on an obstacle are also very different from those that would be observed if the excitation were an incident plane wave.     

Full-wave analysis of microwave scattering from short vegetation: an investigation on the effect of multiple scattering

A full-wave solution for polarimetric scattering from a cluster of randomly oriented three-dimensional lossy dielectric structures above an impedance surface is presented to investigate the importance of multiple scattering. The problem is formulated using an integral equation in conjunction with the exact image representation of dyadic Green's function for the half-space problem. Then, the integral equation is solved for the induced equivalent polarization currents using the method of moments. The accuracy of the numerical code is verified using other existing numerical results and experimental observations. The model is then used to examine the effect of multiple scattering among a cluster of relatively short stems and is shown that multiple scattering significantly affects the cross-polarized backscatter whereas it has a moderate effect on the copolarized backscattering depending on the stem density.     

Electric current and electric field induced in the human body whenexposed to an incident electric field near the resonant frequency

The electric field and current density induced in the human body when this is exposed to electric fields near the resonant frequency, 53 MHz, are determined analytically. Since this frequency range includes an important amateur radio band of 50-60 MHz and exposure to electric fields at this frequency has been shown to be hazardous, the study has a specific motivation. A cylindrical model of the body is used to derive formulas for the total axial current and current density induced in the body subject to skin effect. Tabulations and graphical representations illuminate the results     

Electromagnetic scattering by a dielectric slab loaded with aperiodic array of strips over a ground plane

Scattering of electromagnetic waves from a dielectric slab loaded with a periodic array of perfectly conducting strips is analyzed by a mode-matching technique. The variation of energy of significant scattered modes with various structure parameters is presented for both principal polarizations of the incident wave. The convergence and accuracy of the numerical method is evaluated. Further numerical results are obtained to show the effects of various parameters on the distribution of power in various propagating modes. The results show the usefulness of these structures as reflection-type gratings, polarizers, and filters     

Gaussian beam scattering from a conducting cylinder partially buried in a ground plane

The problem of scattering from an infinitely long conducting cylinder that is partially buried in a perfectly conducting ground plane due to an obliquely incident gaussian beam is solved by an exact procedure based on the method of images by first adopting a simplification originally proposed by Kozaki. The incident and the specularly reflected fields are expressed in terms of cylindrical vector wave functions multiplied by a weighting function which involves the beam parameters like the radial distance of the source and beam width. The scattered fields originating from the cylinder and its image in the ground plane are expressed in terms of cylindrical vector wave functions. The boundary conditions on the surface of the cylinder are then imposed and this procedure leads to a coupled infinite system of equations for the even and odd mode expansion coefficients of the scattered field. These equations are solved numerically for the case of cylinders having electrical radius in the Rayleigh and resonance regions. Both the transverse magnetic and transverse electric polarizations of the incident beam wave are considered and some representative numerical results for the scattered far-field are presented in graphical form. The magnitude of the induced current for the TM polarization is calculated and compared with the corresponding case of plane wave incidence.     

Currents induced in a wire cross by a plane wave incident at an angle

The currents induced in a thin-wire cross with equal mutually perpendicular arms by an incident plane electromagnetic wave are determined when the normal to the wave front is perpendicular to the horizontal wire and is at an anglethetawith respect to the vertical wire; the direction of the electric vector in the wave front is arbitrary. The analysis is formulated in general terms but explicit formulas are obtained only for the zero-order currents which are generally adequate to determine the scattered field of very thin wires. The relatively simple formulas consist of even and odd parts for both the vertical and horizontal wires; they include components due to mutual coupling as well as those excited directly by the incident field.     

Multiple scattering effect on backscattering from a random medium

The backscattering from a random medium is analytically studied. The result gives a mathematical foundation to the cumulative forward-scatter single-backscatter (CFSB) approximation proposed by de Wolf. The multiple scattering effects on backscattering of a plane wave incidence are examined for both Fresnel and Fraunhofer scatterings with various correlation functions of turbulence. As a result, it is found that the multiple scattering effect on the backscattering is sensitive to the statistical properties of the fluctuating medium.     

The effect of topography on radar scattering from vegetated areas

The ways in which radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation are discussed. It is shown, using a discrete scatterer model, that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal. For a horizontal ground surface, for example, the total scattering may be dominated by scattering off the tree trunks, followed by a reflection off the ground surface. For a relatively small tilt in the ground surface, the ground-trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism. The effect of the topography is more pronounced for scattering by longer wavelengths, and the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric SAR data are discussed. The effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the NASA/JPL three-frequency polarimetric SAR over the Black Forest in Germany     

Electromagnetic scattering from a coaxial dielectric circularcylinder loading a semicircular gap in a ground plane

An exact dual series solution of a plane wave incident on a coaxial dielectric circular cylinder imbedded in a semicircular gap of a ground plane is presented. Both TM and TE cases are considered here. The scattered field is represented in terms of an infinite series of cylindrical waves with unknown coefficients. By applying the boundary conditions and employing the partial orthogonality of the trigonometric functions the scattering coefficients are obtained. The resulting infinite series is then truncated to a finite number of terms to produce numerical results. For the sake of comparison with the published data some special cases are introduced first. The comparisons showed excellent agreement in all cases     

地平面上方垂直磁流元电磁场的精确解析表达式

利用倍特曼（Bateman)展开公式，地平面上方垂直磁流元电磁场中的索末菲型积分被表达成快速、绝对收敛的球面波展开式；应用超几何函数的巴恩斯（Barnes)积分表达式，展开系数被表达成以复介电常数为宗量的雅可比多项式。该展开式是此类索末菲半空间问题精确解答，它能够为相关电磁场问题研究提供方便、准确的解析表达式。     

An efficient approach for evaluating Sommerfeld integrals encountered in the problem of a current element radiating over lossy ground

Efficient numerical evaluation of the Sommerfeld integrals, arising from the problem of a current element radiating over a lossy half-space, is considered. An integration technique based on the method of steepest descent is investigated. The details for computing possible pole and branch cut contributions resulting from the deformation of the path of integration are presented. A computer program for evaluating Sommerfeld integrals is developed on the analysis presented. Numerical results and estimates of computational efficiency of the method are given and a comparison with other available works in the literature is included.     

Simple deterministic solutions for cables over a ground plane or in an enclosure

The use of statistical electromagnetics to determine cable currents in an enclosure consists of two basic parts: (1) determination of the probability density function (PDF) for the ambient electromagnetic fields and (2) substitution of this field PDF in cable-coupling formulas to evaluate the PDF for the cable currents. The application of the work reported here pertains to the second of these operations. Previously, determination of cable-current PDFs was a fairly tedious process involving the solution of finite-difference-like transmission-line equations. Unlike the field-distribution PDFs, the cable-current PDFs could not be expressed, or even approximated, in closed form. The contribution reported here relates the unknown cable-current PDFs to the known field PDFs in closed form and does not require the manipulation of finite-difference entities. Additionally, it turns out that some rather arcane issues concerning the autocorrelation of the electromagnetic cable-driving fields as functions of position or frequency no longer seem to matter.     

Development and numerical solution of integral equations forelectromagnetic scattering from a trough in a ground plane

We develop a set of scalar integral equations that govern the electromagnetic scattering from a two-dimensional (2-D) trough in an infinite perfectly conducting ground plane. We obtain accurate and efficient numerical solution to these equations via the method of moments (MoM). Our numerical implementation compares favorably to popular methods such as the finite element/boundary integral (FE/BI) method, generalized network formulation (GNF), and electric field integral equation (EFIE) techniques     

High-frequency surface currents induced on a perfectly conducting cylindrical sheet by an obliquely incident plane wave

Explicit expressions for the surface currents of different kinds induced on a perfectly conducting cylindrical sheet by an obliquely incident high-frequency plane wave are derived. The results are in such forms that they can both be used directly in numerical applications and permit us to understand the structure of the induced surface current. It is shown that the components due to the surface and edge diffractions propagate along certain geodesic lines on which the transfer coefficients as well as the attenuation constants are dependent only on the curvature radius.