Scattering by a perfect electromagnetic conductor (PEMC) plate embedded in lossy medium

In this article, we develop an analytic theory for a perfect electromagnetic conductor (PEMC) plate embedded in lossy medium. The duality transformation introduced by Lindell and Sihvola is applied to study the electromagnetic wave scattering by a PEMC plate. Perfect electric conductor and perfect magnetic conductor are the limiting cases of PEMC media. Here, we study monoscattering by PEMC plate embedded in four different soil models. Numerical results are discussed and compared with the available literature.     

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.     

Auxiliary differential equation formulation: an efficient implementation of the perfectly matched layer

An efficient algorithm for implementing the perfectly matched layer (PML) is presented for truncating finite-difference time-domain domains. The algorithm is based on incorporating the auxiliary differential equation method into the PML formulations. Simple, unsplit-field and material independent PML formulations are obtained. Two dimensional numerical examples are included to validate the proposed formulations.     

Extension and validation of a perfectly matched layer formulation for the unconditionally stable D-H FDTD method

In this letter, a modification to the recently proposed unconditionally stable D-H ADI FDTD method is presented that considerably reduces the late-time error induced by the corner cells. The PML boundary is derived from the direct discretization of the modified D-H Maxwell's equations rather than the superposition of uniaxial PML boundaries. An optimal choice of the PML conductivity profile coefficients is proposed. Results show that the reflection error of the PML is limited for increased time step size beyond the Courant-Friedrichs-Lewy stability bound, and maximum reflection errors are 15 to 20 dB lower than the original formulation.     

Perfectly matched layer for transmission line modelling (TLM)method

The authors present a development of Berenger's perfectly matched layer (PML) for direct application to the transmission line modelling (TLM) method of electromagnetic simulation     

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.     

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     

Distortion of a short quasi-monochromatic signal in a resonantly absorbing medium

Propagation of a short quasi-monochromatic electromagnetic (light or radio) signal (wave packet) is considered. The carrier frequency of the signal is close to the frequency of the absorption spectral line (or group of lines) of a medium, and the spectrum width is large relative to the width of this spectral line (or group of lines). Analytic formulas for the temporal dependence of the signal are derived and numerically confirmed for paths of various lengths. It is shown that the signal is substantially distorted long before it noticeably decays owing to absorption. The signal’s temporal dependence turns out to be rather universal with respect to the form factor of the spectral line, the optical thickness of the substance layer, and the initial temporal dependence of the signal.     

The perfectly matched layer (PML) boundary condition for the beam propagation method

The perfectly matched layer (PML) boundary condition for the Helmoltz equation is developed and applied to the finite-difference beam propagation method. Its effectiveness is verified by way of examples.     

A hybrid computational electromagnetics formulation for Simulation of antennas coupled to lossy and dielectric volumes

A heterogeneous hybrid computational electromagnetics method is presented, which enables different parts of an antenna simulation problem to be treated by different methods, thus enabling the most appropriate method to be used for each part. The method uses a standard frequency-domain moment-method program and a finite-difference time-domain program to compute the fields in two regions. The two regions are interfaced by surfaces on which effective sources are defined by application of the Equivalence Principle. An extension to this permits conduction currents to cross the boundary between the different computational domains. Several validation cases are examined and the results compared with available data. The method is particularly suitable for simulation of the behavior of an antenna that is partially buried, or closely coupled with lossy dielectric volumes such as soil, building structures or the human body.     

The fundamental electromagnetic wave of a single-wire line in a weakly absorbing medium

An approximate dispersion equation valid over a wide frequency range is obtained from the dispersion equation for the symmetric E ₀₀ wave (the Sommerfeld wave) propagating along a finite-conductance metal wire embedded in a lossy dielectric. The boundaries of this frequency range are determined. A technique is developed for solution of the obtained approximate dispersion equation in the frequency band where the pronounced skin effect is observed. The ratio of the wire radius to the thickness of the skin layer is assumed to be no less than 10. This technique is applied to calculate the longitudinal and transverse propagation constants for 1.0-and 2.5-mm-radii copper wires over the frequency range 0.5 MHz to 1000 GHz.     

Analysis of transient interaction of electromagnetic pulse with an air layer in a dielectric medium using wavelet-based implicit TDIE formulation

The interaction of transient electromagnetic pulse with an air layer in a dielectric medium is formulated in terms of a time-domain integral equation and solved numerically via the method of moments. Previous related works pointed to the inherent inadequacy of the marching-on-in-time method in this case, but suggested no remedy. This paper explains why an implicit modeling scheme would work effectively in this case. It is also noted that the use of an implicit scheme would normally involve a solution of a very large and dense matrix equation. To alleviate this drawback of the implicit scheme, the use of a wavelet-based impedance-matrix-compression technique, which has facilitated in the very recent past solutions of time-domain problems with greater efficiency, is described.     

The diffraction of an inhomogeneous plane wave by an impedancewedge in a lossy medium

The diffraction of an inhomogeneous plane wave by an impedance wedge embedded in a lossy medium is analyzed. The rigorous integral representation for the field is asymptotically evaluated in the context of the uniform geometrical theory of diffraction (UTD) so that the asymptotic expressions obtained can be employed in a ray analysis of the scattering from more complex edge geometries located in a dissipative medium. Surface wave excitations at the edge and their propagation along the wedge faces are discussed with particular emphasis on the effects of losses     

Generalisation of the partial-power law (Brown's identity) to waveguides with lossy media

The partial-power law, otherwise known as Brown's identity, which relates the product of the phase velocity of a mode on a lossless waveguide to the time-average power and momentum carried by the mode, is generalised to be applicable to lossy waveguides as well.     

Alternating-direction implicit (ADI) formulation of the finite-difference time-domain (FDTD) method: algorithm and material dispersion implementation

The alternating-direction implicit finite-difference time-domain (ADI-FDTD) technique is an unconditionally stable time-domain numerical scheme, allowing the /spl Delta/t time step to be increased beyond the Courant-Friedrichs-Lewy limit. Execution time of a simulation is inversely proportional to /spl Delta/t, and as such, increasing /spl Delta/t results in a decrease of execution time. The ADI-FDTD technique greatly increases the utility of the FDTD technique for electromagnetic compatibility problems. Once the basics of the ADI-FDTD technique are presented and the differences of the relative accuracy of ADI-FDTD and standard FDTD are discussed, the problems that benefit greatly from ADI-FDTD are described. A discussion is given on the true time savings of applying the ADI-FDTD technique. The feasibility of using higher order spatial and temporal techniques with ADI-FDTD is presented. The incorporation of frequency dependent material properties (material dispersion) into ADI-FDTD is also presented. The material dispersion scheme is implemented into a one-dimensional and three-dimensional problem space. The scheme is shown to be both accurate and unconditionally stable.     

Effect of finite size of ground plane on the impedance of a monopole immersed in a lossy medium

The effect of finite size of the ground plane on the impedance of a monopole immersed in a lossy medium is studied. The theoretical results show that for water medium and for the ratio of the ground-plane radius to free-space wavelength equal to and greater than 0.2, the effect of ground plane on the monopole impedance is negligible.     

Generation of lossy mode resonances (LMR) using perovskite nanofilms

The results presented here show for the first time the experimental demonstration of the fabrication of lossy mode resonance(LMR) devices based on perovskite coatings deposited on planar waveguides. Perovskite thin films have been obtained by means of the spin coating technique and their presence was confirmed by ellipsometry, scanning electron microscopy, and X-ray diffraction testing. The LMRs can be generated in a wide wavelength range and the experimental results agree with the theoretical s...     

Protection effect of a SiO_2 layer in Al_(0.85)Ga_(0.15)As wet oxidation

正The Al_(0.85)Ga_(0.15)As layers buried below the GaAs core layer with and without the SiO_2 layer were successfully oxidized in a wet ambient environment.The experimental results show that the SiO_2 layer has little impact on the lateral-wet-oxidation rate of the Al_(0.85)Ga_(0.15)As layer.The contrast of the SEM image of the oxidized regions and the absence of As-related Raman peaks for samples with the SiO_2 layer arise from the removal of As ingredients with the largest atomic number,which leads to improvements in the thermal stability of the oxidized layer.The PL intensities of samples with the SiO_2 layer are much stronger than those without the SiO_2 layer.The PL emission peak is almost unshifted with a slight broadening under the protection of the SiO_2 layer.This is attributed to the SiO_2 layer preventing oxidation damage to the GaAs capping layer.     

Application of a new MPIE formulation to the analysis of adielectric resonator embedded in a multilayered medium coupled to amicrostrip circuit

A new mixed-potential integral-equation (MPIE) formulation is developed for the analysis of electromagnetic problems due to conducting or dielectric objects of arbitrary shape embedded in a planarly stratified medium. In the new MPIE formulation, the dyadic kernel of the vector potential is kept in the simple form originally developed by Sommerfeld. The scalar potential, which is related to the vector potential via the Lorenz gauge, is then represented by a double dot product of a dyadic kernel with a dyadic charge density. An extra line integral term, which is well behaved and nonsingular, will appear when the object penetrates an interface. The numerical implementation of the double dot product is found to be trivial if one takes advantage of the well-established basis functions in which the unknown current density is expressed. The new MPIE formulation is employed in conjunction with the triangular patch model to treat the problem of a dielectric resonator (DR) excited by microstrip circuit. A matched-load simulation procedure has been used to extract the network S-parameters of a DR microstrip circuit. The diameters of the Q circles have been measured to determine the coupling coefficients and the Q factors of the DR excited by a microstrip circuit. The validity of the new MPIE formulation and the numerical procedure have been verified by comparing the obtained S-parameters, with available measurement data