Wide-band electromagnetic scattering from a dielectric BOR buriedin a layered lossy dispersive medium

A method of moments (MoM) analysis is developed for electromagnetic scattering from a dielectric body of revolution (BOR) embedded in a layered medium (the half-space problem constituting a special case). The layered-medium parameters can be lossy and dispersive, of interest for simulating soil. To make such an analysis tractable for the wide-band (short-pulse) applications of interest here, we have employed the method of complex images to evaluate the Sommerfeld integrals characteristic of the dyadic layered-medium Green's function. Example wide-band scattering results are presented, wherein fundamental wave phenomenology is elucidated. Of particular interest, we consider wide-band scattering from a model plastic mine, buried in soil, with the soil covered by a layer of snow     

Quasiparticle description of pulse propagation in a lossy dispersive medium

It has been known from extensive saddle point analysis that pulses propagating in a lossy dispersive Lorentzian medium exhibit a high frequency forerunner and frequency chirping. The quasiparticle approximation permits an accurate and numerically efficient calculation of the forerunner frequency chirping with a simple physical explanation. For the case of a Gaussian incident pulse, the error in the second order quasiparticle approximation becomes smaller as the pulse propagates; hence one may apply the quasiparticle method for a wide range of propagation distances with error estimates that can be readily calculated.     

Multidomain pseudospectral time-domain simulations of scattering by objects buried in lossy media

A multidomain pseudospectral time-domain (PSTD) method with a newly developed well-posed PML is introduced as an accurate and flexible tool for the modeling of electromagnetic scattering by 2-D objects buried in an inhomogeneous lossy medium. Compared with the previous single-domain Fourier PSTD method, this approach allows for an accurate treatment of curved geometries with subdomains, curvilinear mapping, and high-order Chebyshev polynomials. The effectiveness of the algorithm is confirmed by an excellent agreement between the numerical results and analytical solutions for perfectly conducting as well as permeable dielectric cylinders. The algorithm has been applied to model various ground-penetrating radar (GPR) applications involving curved objects in a lossy half space with an undulating surface. This multidomain PSTD algorithm is potentially a very useful tool for simulating antennas near complex objects and inhomogeneous media.     

Closed form expression of the Green's function for the time-domain wave equation for a lossy two-dimensional medium

The Green's function that relates the electric field to a line current source in a conductive, homogeneous medium is evaluated in the space-time domain in closed form. Early and late time asymptotes are supplied.     

Moment-method modeling of short-pulse scattering from and theresonances of a wire buried inside a lossy, dispersive half-space

A frequency-domain method-of-moments (MoM) algorithm is used to model short-pulse plane-wave scattering from a wire buried inside a lossy, dispersive half-space with the time-domain scattered fields computed via the Fourier transform. Further, the complex resonant frequencies of such targets are also calculated via the MoM. The phenomenology associated with scattering from a buried wire is investigated in detail, and it is demonstrated that the time-domain scattered fields and the target resonances depend on the buried-wire orientation as well as the electrical properties of the half-space     

Wave scattering by a prism made of a lossy metamaterial

The results of rigorous calculation of the scattering pattern of a Gaussian beam incident onto a finite prism made of a metamaterial are presented for different values of the refractive index n _r < 0 and loss factor ν of the medium. It is shown that geometric optics can correctly predict the tilt of the scattering-pattern maximum, while consideration for the medium’s loss factor 0.001 ≤ |ν| ≤ 0.1 affects the amplitudes of the transmitted and reflected fields.     

High-frequency scattering by objects buried in lossy media

The uniform geometrical theory of diffraction (UTD) is extended so that it can be used to calculate the scattering from an object buried in a lossy medium. First, the accuracy of this high frequency method is examined by comparing numerical results for the scattering by a polygonal cylinder in a lossy medium of infinite extent with calculations based on a method of moments (MoM) solution. Next, the more difficult scattering problem of a polygonal cylinder in a lossy half space is treated. The UTD solution for the unbounded region is employed together with the fields of rays introduced by the interface between air and the lossy medium to obtain expressions for the scattered field in air and in the lossy medium     

Practical problems in the time-domain probing of lossy dielectric media

Interest in time-domain probing of a lossy dielectric medium by means of optimization processes has been shown in former papers. Some problems related to the application of such techniques to realistic situations are envisaged. Screening effects due to losses are first investigated, and a setup (perturbed line) is presented to reduce them. The influence of a finite extent of the illumination, implied by classical wave applicators, is then discussed.     

Enhanced electromagnetic power deposition in a lossy medium

It is demonstrated that an aperture antenna, excited by a leaky wave, will transfer power into an homogeneous lossy half-space at levels exceeding expectation. However, such local enhancements are only possible in the near-field region in the central part of the array. With the proper choice of parameters, enhancements of the order of 15 dB can be achieved. The calculated results are relevant to hyperthermic heating in cancer therapy and to related problems in biological hazards     

Physical limitations of antennas in a lossy medium

The dissipated power and the directivity of antennas in a homogeneous, lossy medium are systematically analyzed in this paper. The antennas are ideal and located inside a lossless sphere. In the lossy space outside the sphere, the electromagnetic fields are expanded in a complete set of vector wave functions. The radiation efficiency, the directivity, and the power gain are defined for antennas in a lossy medium, and the optimal values of these quantities are derived. Simple relations between the maximal number of ports, or channels, an antenna can use and the optimal directivity and gain of the antenna are presented.     

电离层时域散射与逆散射的数值

采用具有四阶精度的时域有限差分法计算了电离层对时域脉冲的散射,然后应用小波变换求出了反射信号的时频分布.这一时频分布就相当于电离层的频高图.最后利用POLAN程序重建了等离子体剖面,重建剖面非常接近原始剖面.     

Electromagnetic-pulse propagation in a simple dispersive medium

Using a simple model, the resulting distortion for a transient plane wave propagating through a dissipative and dispersive medium is considered. The analysis is exact for the chosen form of the frequency dependence of the complex `relative permittivity?. The results have some relevance to the propagation of electromagnetic pulses through geological media.     

Synchronous communications in a lossy medium using transient waves

The problem of detecting an electromagnetic signal with the initial time variation of a rectangular pulse is presented. The medium between the transmitter and the receiver is assumed to introduce ohmic losses. The implication of additive thermal noise on the error probability and the detectable propagation velocity is investigated. The results are shown for a synchronous binary communications model in which the receiver has knowledge of the starting time of each observation interval. A correlator receiver is assumed for optimal signal detection in the mean-square-error sense. It is shown that the observable propagation velocity of the signal is a function of the receiver characteristics and the parameters of the signal used. Formulas relating the pulse width, signal-to-noise ratio, propagation distance, error probability, and the observed propagation velocity are derived. Plots for specific examples are presented     

UTD solution for electromagnetic scattering by a circular cylinderwith thin lossy coatings

A uniform geometrical theory of diffraction (UTD) solution is obtained for the field exterior to a two-dimensional circular cylinder with a thin lossy dielectric coating. The solution is convenient for engineering applications due to its simple ray format. In the lit region, the geometrical optics (GO) solution consists of the direct incident ray and the reflected ray. In the shadow region, the geometrical theory of diffraction (GTD) uses the creeping-wave format to calculate the diffracted field. In the transition regions adjacent to the shadow boundaries, where the pure ray optical solution fails, a `universal' transition integral is used for the UTD solution to calculate the field. Numerical values for the essential transition integral are deduced, by a heuristic approach, from alternative representations of the Green's function for a circular cylinder with coating. Numerical results obtained from the UTD solution show excellent agreement with the eigenfunction results for cylinders with thin dielectric coatings     

Absorbing surface impedances of lossy layers in the finite difference time-domain method

In this paper the time-domain surface impedances of an homogeneous absorber layer, are given for the vertical and horizontal polarizations, or respectively for the electric field perpendicular or parallel to the incidence plane. It turns out that the application of the concept in finite difference time-domain (FDTD) in absorbing surface impedances boundary conditions, gives results in good agreement with analytical Fresnel reflection coefficients.     

Nonlinear differential equation for the reflection coefficient ofan inhomogeneous lossy medium and its inverse scattering solutions

Nonlinear differential equations for the reflection coefficients of an inhomogeneous lossy medium illuminated by both TE-polarized and TM-polarized electromagnetic plane waves are derived using a microwave networking technique, which can be approximately solved by a nonlinear renormalization method. Considering the equivalent microwave network of the permittivity profile discontinuity at the interface of free space with the medium, two novel inverse scattering solutions for the permittivity profile and the conductivity profile are further investigated in closed forms. Closed-form and numerical reconstruction examples show the availability of this scheme     

Magnetic dipole excitation of a long conductor in a lossy medium

A formulation is presented for the excitation of currents on an infinitely long conductor by electric or magnetic dipoles of arbitrary orientation. The conductor can be either insulated or bare to model ungrounded or grounded conductors. Specific calculations are presented for a vertical magnetic dipole source because this source produces the appropriate horizontal polarization and could be used in a borehole-to-borehole configuration. Numerical results for the induced current and secondary magnetic field indicate that long conductors produce a strong anomaly over a broad frequency range. The secondary magnetic field decays slowly in the direction of the conductor and eventually becomes larger than the dipole source. Results have been presented for frequencies from 20 kHz to 2 MHz, and the entire frequency range appears to be useful     

Propagation characteristics of a dielectric-coated coaxial helicalwaveguide in a lossy medium

In this paper, the authors discuss the propagation characteristics of a dielectric-coated coaxial helical waveguide in a lossy medium. The authors place emphases on the phase constant, propagation modes, magnetic fields distribution, and attenuation constant, when permittivity of the internal region is relatively small, two propagation modes exist and dominant components of their magnetic fields are different. Lastly, the authors discuss the relation between the attenuation constant and permittivities