Diffraction by a half-plane with two face impedances uniform asymptotic expansion for plane wave and arbitrary line source incidence

A uniform asymptotic expansion (UAE) of Maliuzhinets' exact solution for incident plane wave diffraction by a half-plane with two face impedances has been obtained using Van der Waerden's method. This solution has been further extended to the case of arbitrary line source incidence using a heuristic approach.     

Circular TEM cell for generating standard electromagnetic fields

A circular TEM (CTEM) cell for achieving the radiated EMC test without any rotation of the equipment under test is proposed. The authors also analyse field uniformity inside the cell and characteristic impedance by using a moment method (MM) which can determine the number of segments per line efficiently     

Electromagnetic plane wave scattering by a system of two uniformlylossy dielectric prolate spheroids in arbitrary orientation

By means of modal series expansions of electromagnetic fields in terms of prolate spheroidal vector wave functions, an exact solution is obtained for the scattering by two uniformly lossy dielectric prolate spheroids in arbitrary orientation embedded in free space, the excitation being a monochromatic plane electromagnetic wave of arbitrary polarization and angle of incidence. Rotational-translational addition theorems for spheroidal vector wave functions are employed to transform the outgoing wave from one spheroid into the incoming wave at the other spheroid. The field solution gives the column vector of the unknown coefficients of the series expansions of the scattered and transmitted fields expressed in terms of the column vector of the known coefficients of the series expansions of the incident field and the system matrix which is independent of the direction and polarization of the incident wave. Numerical results in the form of curves for normalized bistatic and monostatic radar cross sections are given for a variety of two-body system of uniformly lossy dielectric prolate spheroids in arbitrary orientation having resonant or near resonant lengths and different distances of separation     

Electromagnetic beam wave scattering by arbitrary cross-sectional conducting cylinder using N circular cylindrical models

Rigorous expression of the electromagnetic beam wave scattering by N circular cylindrical models is described. To check this method, comparison between exact solution and this model composed of N=24 circular cylinders is presented for a single circular conducting cylinder. Numerical results of conducting square cylinder has been also checked with well-known result (B.E.M).     

Diffraction of a normally incident plane wave by three parallel half-planes with different face impedances

The diffraction problem of plane waves by a set of three parallel half-planes one of which is placed in the opposite direction and having characterized with different surface impedances on upper and lower faces is solved by mode-matching method where available and Fourier transform technique elsewhere. The solution includes two independent Wiener-Hopf equations each involving infinite number of expansion coefficients which satisfy an infinite system of linear algebraic equations. After the determination of these coefficients numerically, some graphical results are presented showing the influence of the surface impedances and the distances between the half-planes on the diffracted and transmitted waves.     

程控任意波形功率电源的研究

采用了以单片机为核心,应用大规模集成逻辑器件FPGA、高速D/A转换器MAX5885和功率放大电路的方案设计了一款任意波形功率驱动电源.系统由单片机控制各个模块,频率合成电路合成所需的不同频率的时钟作为控制地址计数器的时钟信号,而地址计数器的计数输出提供读取存储的数字波形数据的地址,数据经数模转换为模拟信号并经过功率放大后输出.该电源可以双路输出1 H～-1 MHz频率范围内幅度、频率和相位可调的任意波形,同时将输出信号进行功率放大以达到有效驱动负载的目的.测试结果表明,该电源在最大输出电流为2A时最大输出功率为200 W.     

Electromagnetic wave scattering by an infinite plane metallicgrating in case of oblique incidence and arbitrary polarization

A novel spectral-domain method combined with a sampling theorem is applied to the rigorous analysis of this quasi-two-dimensional problem. The accuracy and convergence of the method are examined numerically taking into account errors in comparison with extrapolated values, errors in the power relation, and the duality relationship. It is found that the numerical results exhibit good convergence. Another formulation related to Babinet's principle is discussed, and a relationship between the fields of an original and its complementary gratings is demonstrated. Numerical calculations are carried out showing that the method provides precise numerical results not only for the far fields, such as transmitted and reflected powers, but also for the near fields, such as surface current distribution on a strip and electric field intensity in a slit. Some numerical results related to the dual problem are provided     

Electromagnetic field measurements a millimeter wave linearaccelerator

Perturbational field strength measurements suitable for use on a proposed 120-GHz 50-MeV electron linear accelerator are described. The measurements are used to determine the R/Q of the device, where R is the shunt impedance. The perturbation is achieved by the use of hollow metallic cylinders with diameters ranging from 25 to 127 μm which are approximately 500 μm long. The cylinders were fabricated by sputtering aluminum through a shadow mask onto silica optical fibers as well as nylon surgical thread. The perturbational “form factors” for such a geometry are experimentally determined using a pillbox cavity. The measured values for the form factors are compared to theoretical estimations, which result in simple analytical expressions. The measured form factors are also compared to values calculated from a finite difference model of the perturbing object. The R/Q for various accelerating modes is measured on a 12-GHz model of the 120-GHz structure. Results are compared to predictions from a finite difference model of the accelerating structure     

Resonance suppression in a TEM cell

All TEmnp resonances in a TEM cell have been suppressed by cutting the cell walls longitudinally. The TMmnp resonances and propagating TEM mode were not affected. The suppressed resonances have a residual interaction with a biological body inside the cell. Because of this, the modified cell can only be used for bioeffects dosimetry studies at a small number of frequencies above the upper limit for the original cell. Where an accuracy of only +/- 5 dB is required, such as in some EMC studies, the effective bandwidth of the modified cell is twice that of the original cell.     

金属衬底多层各向异性介质电波反射特性研究

通过分析和计算多层各向异性介质的电磁波传输矩阵,导出了金属衬底上多层各向异性介质的电磁波反射系数计算方法,举例验证了该计算方法的正确性.作为一个应用例子,初步分析了金属衬底上各向异性材料的极化转换特性,为复杂电磁材料的电磁散射近似计算提供了理论基础.     

Characterisation of arbitrary media in fields

An obstacle in a field may be uniquely defined by a linear operator, provided that its constituent media are time-invariant, linear and passive. The properties, measurement and uses of this operator are discussed, and examples are given.     

Electromagnetic scattering from arbitrary configurations of wires

A general formulation is presented for the treatment of electromagnetic scattering from an arbitrary configuration of thin wires. A system of integral equations is derived for obtaining the currents in the wires.     

Electromagnetic wave transmission in a well logging cable-theory

A well logging cable is idealized as a uniform cylindrical structure consisting of N axial dielectric-coated thin wires in a lossy medium, all encased by a metallic sheath. A general modal equation which is specialized to low frequencies where quasi-static conditions prevail is developed. It is pointed out that the line parameters are spatially dispersive, in addition to being frequency dependent. The formulation differs from most multiconductor transmission theories because of the presence of the lossy filler material, which actually allows for a simplification of the working mode equation, which is an N-order polynomial     

Electromagnetic wave diffraction using a finite volume method

The authors describe a finite volume time domain (FVTD) method for the resolution of electromagnetic diffraction by `complex' structures. Results obtained for an aircraft by this technique which allow a conformal meshing are compared with results from a classical FDTD code     

Electromagnetic wave propagation on a double-layer dielectric film

The nature of the eigenvalues characterising the electromagnetic wave propagation in a homogeneous isotropic double-layer dielectric structure of infinite extent on a perfectly conducting ground plane is discussed.     

EM fields generated by lightning channels with arbitrary locationand slope

It is well known that lightning discharges follow a tortuous path; therefore, a general technique able to evaluate the electromagnetic (EM) fields associated with discharge currents flowing into tortuous channels seems to be worthy of consideration. Two techniques have been adopted to find the EM field generated by a current pulse traveling along a single line radiator with arbitrary slope and location above the ground. The first one employs the Fraunhofer approximation, which can provide useful information only on distant radiated fields. The second technique is exact, but applies only to the case of a velocity of propagation v of the current pulse equal to c (velocity of light). Even this solution is indeed inadequate for our purposes since v相似文献   

Diffraction by a wedge with anisotropic face impedances

When boundary conditions on a surface of a wedge are anisotropic impedance ones, the problem of diffraction is reduced to a coupled system of Maliuzhinets’ equations via Sommerfeld integral. For weak anisotropy a regular asymptotic method is developed to compute the leading terms and the first correction of spectral functions. Electromagnetic field which arises due to anisotropy is presented in closed form. Analytic properties of spectral functions are investigated. Uniform asymptotics for the scattered field are constructed via matching of local asymptotic expansions.     

Diffraction of an arbitrary plane electromagnetic wave by a half-plane

The asymptotic form of the diffracted field produced by a plane electromagnetic wave of arbitrary polarization incident obliquely on a conducting half-plane is expressed very simply in terms of the incident and reflected wavesF_{1}andF_{2}, respectively, rotated to bring their wave vectorsk_{1}andk_{2}onkin the direction of observation. The diffraction coefficients becomepm(sin psi_{i}/2)^{-1}wherepsi_{i}is the angle betweenk_{i} (i = 1,2)and the direction of observationk.     

Electromagnetic fields near a concave perfectly conducting cylindrical surface

Although no shadowing or diffraction effects occur, the surface fields excited by a high frequency source located on a perfectly conducting concave cylindrical boundary cannot be analyzed by geometrical optics since the caustics for rays, which have experienced many reflections, accumulate. In a previous study, alternative field representations in terms of whispering gallery (WG) modes, canonical integrals, and hybrid ray-mode combinations have been explored to compensate for the failure of geometrical optics. As the source and/or observation points move off the boundary, the number of relevant multiply reflected rays decreases, and the caustics eventually become separated sufficiently to be treated as isolated. Ray optics is then expected to apply provided that uniform corrections near caustics and their endpoints are included. This conjecture is confirmed in the present investigation, which tracks the field continuously from the "boundary layer" near the concave surface, where ray optics is invalid, to off-surface points where it applies, by generalizing the alternative field representations used previously. A rich variety of hybrid ray-mode combinations exists for off-surface source and observation points. Especially intriguing is the possibility of choosing a hybrid mix that completely avoids the need for the caustic (and endpoint) correction functions in a purely ray-optical formulation. The utility, accuracy, and range of validity of the various field representations is assessed by numerical comparison with a reference solution in terms of WG modes plus a continuous spectrum.