Electromagnetic resonances of a free ferrite sphere

Calculation of the axial-symmetric modes of the electromagnetic resonances in an open ferrite sphere is described. The diameter of the sphere and the wavelength of the field are of the same order, and the electric field cannot be neglected, necessitating the solution of an eigenvalues problem subject to Maxwell's equations.     

Electromagnetic scattering by an exponentially inhomogeneous plasma sphere

The mathematical analysis of electromagnetic wave scattering by radially inhomogeneous spherical objects is treated. Numerical integration of the differential equations for the separated radial wave functions has been carried out for the case of a plasma with an exponential electron density gradient, Parametric calculations of bistatic scattering have given many interesting results. The range of validity of the Born approximation has been demonstrated by comparing it with computed results.     

Electromagnetic waves excited by elementary sources and scattered by a finite circular conducting cylinder

A finite circular magnetodielectric conducting cylinder located in a conducting medium with arbitrary permittivity and permeability is considered. The method of induced currents is applied to analyze scattering of electromagnetic waves by this cylinder in the case when the incident field is excited by elementary sources. The effect of the parameters of the cylinder on the meridional and azimuthal components of the total electric field produced by a radial electric dipole is investigated numerically.     

Electromagnetic resonances and Q factors of a chiral sphere

A study of electromagnetic resonances of an isotropic chiral sphere is presented. The characteristic equation of a chiral sphere, which is complex and transcendental, is obtained by forming solutions of the electromagnetic field for a chiral sphere in terms of the spherical vector wave functions. The characteristic equation is solved by using a computer. Resonant frequencies and Q factors of the first few modes for relative permittivities of two and ten are reported and discussed. These modes are hybrid modes. They are classed as either hybrid electric (HE) modes or hybrid magnetic (HM) modes. Chirality is observed to have a significant effect on the resonances of a sphere.     

Plane wave pulse backscattering from a low-density dielectric sphere

The solution to the scattering problem of a pulse incident on a low-density dielectric sphere is presented. Pulse modulated harmonic carriers and dc pulses are considered.     

Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere of multilayers

Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere is formulated and obtained, where the inhomogeneous plasma anisotropic sphere is divided into (s-1) homogeneous anisotropic spherical layers. The electromagnetic fields in the inner spherical multilayers and outer free space of the inhomogeneous plasma anisotropic spherical structure can be expanded in terms of the spherical vector wave functions in plasma anisotropic medium and in isotropic medium, respectively. By applying the continuous boundary conditions of electromagnetic fields on the spherical interfaces of the (s-1)-layered homogeneous anisotropic plasma medium, the unknown expansion coefficients of fields in the multilayered plasma spherical structure are obtained, and then the electromagnetic field distributions are calculated. Numerical results for the very general inhomogeneous plasma dielectric material sphere are given and the data in a special case are obtained using the present method and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach and compared to each other to verify the correctness and applicability of the present analysis.     

Electromagnetic scattering from a dielectric-coated sphere with anembedded impedance film

The electromagnetic scattering from a multilayered sphere modal solution of Wait (1963) is modified to allow the inclusion of infinitesimally thin impedance films at layer boundaries. The modified solution is implemented in a computer algorithm and the scattering from an aluminum sphere coated with a dielectric Delrin^TM layer containing an embedded impedance film is computed. This target was fabricated and laboratory measurements performed in the 2-18 GHz region are in good agreement with computations     

Electromagnetic pulse propagation in a weakly nonlinear plasma

An investigation of the propagation of electromagnetic pulses in a weakly nonlinear, cold, collisionless plasma is described. It is found that a transverse electromagnetic pulse generates, through nonlinear effects, a small amplitude, longitudinal electric pulse field. The transient behavior of this longitudinal electric field is studied. One particular case is considered in detail: the nonlinear generation of a longitudinal electric field by a transverse electromagnetic pulse which is excited by a suddenly turned-on cosinusoidal electric field of frequencyomega_{0}. Computer plots of numerical calculations of the second-order transient longitudinal field are presented.     

Electromagnetic pulse generation by an impedance loaded dipole antenna

A theoretical study is made for obtaining the pulse radiated from an impedance loaded dipole. Numerical results are presented for an antenna that is slowly charged and suddenly shorted at the terminals. The impedance loadings are chosen as those on an existing antenna located at Sandia Laboratory, Albuquerque, N. Mex.     

线缆网络中的电磁脉冲传输

电磁拓扑理论在分析电磁干扰(EMI)问题中具有重要的应用价值。本文利用电磁拓扑理论研究了线缆网络的电磁脉冲瞬态响应求解方法,并进行了实验验证。实验利用同轴线建立简单线缆网络,选用方波脉冲作为激励源,先由Fourier变换求得方波脉冲的频谱,根据频域上的BLT超矩阵方程求出线缆网络在方波脉冲作用下各节点的电压,然后再由Fourier逆变换就可求出各节点电压的瞬态响应。通过实验对比说明了此方法的有效性,为进一步研究电磁脉冲在复杂线缆网络中的传输规律打下基础。     

Electromagnetic pulse signal representation using orthonormalLaguerre sequences

The notion of representing discrete-time electromagnetic pulse (EMP) signals using orthonormal Laguerre sequences is introduced. The motivation for doing so is that EMP signals and Laguerre sequences are both characterized by decaying exponentials. It is shown a that very efficient Laguerre representation of EMP signals is possible using this approach     

Electromagnetic pulse transmission in homogeneous dispersive rock

The effect of the frequency dependence of the conductivity and permittivity of rock for pulse transmission is considered. These high-frequency dispersive effects appear to play a major role in determining the transient response of the medium. A quantitative understanding is achieved by adopting a dispersion model that consists of multiple Debye relaxation processes. It is shown that the results differ significantly from earlier transient calculations that assume frequency independent permittivities and conductivities.     

Scattering by a ferrite-coated conducting sphere

The theory for scattering by a perfectly conducting sphere with a coating of lossy, homogeneous, isotropic ferrite material is presented. In addition to the rigorous eigenfunction formulation, the physical optics (PO) and geometrical optics (GO) approximations are also included. Numerical results are shown in graphical form to illustrate the backscatter echo area versus the radius of the sphere, as well as the bistatic scattering patterns.     

Scattering by a rotating dielectric sphere

The scattering of a plane wave by a rotating dielectric sphere of arbitrary radius,epsilon_{r}andmu_{r}is investigated. A relativistically correct solution is found for the scattered fields and the fields inside the sphere. This solution is valid in the limit of "small" angular velocities. Attention is focused on the fields at large distances. The depolarization of the backscattered signal and the scattering in the low frequency limit are treated in some detail.     

Scattering by a rotating conducting sphere

The scattering of a plane wave by a rotating sphere with finite conductivity is investigated. The problem is solved by means of the "instantaneous rest-frame" hypothesis. It is shown that a surface current must be taken into account to calculate the jump in the tangential magnetic field at the surface of the sphere, even in the case of finite conductivity. The analytical solution shows that the influence of the rotation becomes negligible in the limit of a perfectly conducting sphere.     

Electromagnetic imaging of two-dimensional perfectly conducting cylinders with transverse electric scattered field

Electromagnetic imaging of two-dimensional perfectly conducting cylinders using measured transverse electric scattered field is studied in this paper. The contours of cylinders are denoted by local shape functions /spl rho//sub i/=F/sub i/(/spl theta//sub i/) in local polar coordinates which are then approximated by closed cubic B-splines instead of trigonometric series. By using the boundary condition of vanishing tangential electric field on surfaces of perfectly conducting cylinders, a set of electric field integral equations governing the scattering problem is derived. The scattering problem is solved by a point-matching method with pulse basis and Dirac delta testing functions. The inverse problem is reformulated as an optimization problem and solved by a real-coded genetic algorithm with closed cubic B-splines local shape function. Numerical examples show good agreement between the true profiles and the reconstructed results.     

Electromagnetic field distribution and developed losses inside a finite cylinder and sphere under MRI conditions

The control of the thermal losses dissipated inside the human body during magnetic resonance imaging (MRI) is very important, since it is directly related to patient safety. The authors give the exact solution to the problem of the electromagnetic energy dissipation and distribution inside a conductive sphere and a finite conductive cylinder, considered as the closest models to the human anatomy. The high-frequency alternating magnetic field is produced by a current loop. Numerical results are given for alternating fields from 6 to 100 MHz and various excitation geometries. The results, which take into account the magnetic field inhomogeneities and the finite dimensions of the conductive models, apply not only to the MRI experiments but also to any similar eddy-current problem.     

Microwave scattering by a plasma covered sphere

Laboratory measurements of the scattering of microwaves by a plasma covered sphere are presented for forward scattering angles. The radial electron density variation is deduced from these data and a simple model of the experiment.     

Electromagnetic dyadic Green's function for a layered homogeneouslossy dielectric sphere as head model for numerical EMC investigation

An improved head model for numerical EMC investigation using the method of moments is proposed. Making use of an electromagnetic dyadic Green's function for a layered homogeneous lossy dielectric sphere user's interaction with antennas of hand-held mobile telephones can be investigated efficiently