Search

A novel high-efficient two-step finite-difference time-domain (FDTD) method is proposed to analyze the lightning-induced voltages on transmission lines (TLs) in this paper. The proposed method includes two steps. The first step is to calculate, using the 2-D FDTD method, electromagnetic fields that are radiated from a vertical lightning channel and illuminate the nearby TLs. The second step is to calculate, using the 3-D FDTD method, the electromagnetic response of the TL that is illuminated by the incident electromagnetic fields added at the total field–scattered field connecting the boundary of the 3-D space. To validate the proposed two-step FDTD method, the results calculated using the two-step FDTD method are compared with those calculated with Agrawal coupling model, and with those calculated using the 3-D FDTD method. The two-step FDTD method shows high computational efficiency in analyzing lightning-induced voltages on TLs. [ABSTRACT FROM AUTHOR]

In this paper, a time-domain variant of the generalized telegrapher's equations for transient electromagnetic field coupling to a finite-length wire above a lossy half-space is derived. The approach is fully based on the thin-wire antenna theory. The lossy ground effects are taken into account by means of the reflection coefficient approximation. The obtained equations are handled numerically via the Galerkin–Bubnov indirect boundary element method. Computational examples are presented for the case of a single-wire line excited by an electromagnetic pulse excitation source. The obtained results for the induced current along the line are compared with those obtained using 1) the method of moments solution of the electric field integral equation implemented in the numerical electromagnetics code (NEC-4), and 2) the transmission line (TL) theory. It is shown that the results obtained by the proposed method are in excellent agreement with those of NEC-4. It is also shown that the TL approximation yields in general results which are in reasonably good agreement with the full-wave results, especially for the early time response and even beyond the limits of the accuracy of the TL theory. The TL theory can, however, give accurate results only for times before the arrival of the first reflection from the TL terminations and it fails to reproduce accurately the dispersion effects occurring after the first reflection. [ABSTRACT FROM AUTHOR]

Modeling the combined electromagnetic (EM)/quantum transport problem in graphene circuits requires the development of novel concepts and novel unified tools. In this paper, we further explore the correlation between Dirac and Maxwell equations, in the time domain, where we derive the transmission-line equations, valid for both EM and quantum current. This is a step forward toward an effective integration of the Dirac theory in the numerical simulation of EM field problems and introducing EM concepts and simulators to describe quantum transport. We show that the familiar Telegrapher's equations can be readapted in order to investigate the mechanisms that govern the space–time evolution of Dirac spinors; two significant examples, having a double quantum/EM meaning, are provided. Final considerations about associated quantum current have also been reported. [ABSTRACT FROM AUTHOR]

The calculation of voltages induced by external electromagnetic fields on multiconductor transmission lines (MTLs) has been the subject of several studies. In this paper, discrete equations for MTLs exposed to incident fields are derived based on the time-domain finite-element method and the backward differentiation formula. Based on these equations, a value-delivery table characterizing the MTLs is presented. Combining this table with modified node analysis formulation, it is convenient for analyzing the responses of transmission lines composed of complex termination networks or complex transmission-lines networks. The validity and efficiency of the proposed algorithm is demonstrated using several examples. Finally, a 1-km 35 kV overhead line above an imperfectly conducting ground is studied, and the influences of ground wire and a metal-oxide arrester to the lightning-induced voltage are both discussed. [ABSTRACT FROM PUBLISHER]

Exploration of the terahertz (THz) portion of the electromagnetic spectrum has recently expanded due to advances in ultrafast optical laser systems. The application of THz imaging to detect explosive materials (and other chemical agents) is a promising potential application because of the unique spectral signatures found for many explosives in the THz band. However, since the wavelength of THz radiation is on the order of tens to hundreds of micrometers, the rough interface between materials and the granular nature of material mixtures (such as explosives) may cause frequency-dependent scattering, which could mask the spectral signature. Thus, to evaluate the effectiveness of THz imaging systems, it is necessary to characterize the combined volume and rough-surface scattering effects. Because of the complexity of the media and the requirement for broadband modeling, the finite-difference time-domain (FDTD) formulation is an ideal tool. In this paper, transmission measurements through granular media and reflection measurements from controlled rough surfaces are shown to be in good agreement with FDTD results. Methods for extracting the material spectral peaks from a limited number of measurements are presented and discussed. [ABSTRACT FROM AUTHOR]

Subgridding methods are often used to increase the efficiency of the wave propagation simulation with the Finite-Difference Time-Domain method. However, the majority of contemporary subgridding techniques have two important drawbacks: the difficulty in accommodating dispersive media and the inability for physical interfaces to cross the subgridding interface. This paper presents an extension of the frequency-dependent Huygens subgridding method from one dimension to three dimensions. Frequency dependency is implemented via the Auxiliary Differential Equation approach using the one-pole Debye relaxation model. Numerical experiments indicate that subgridding interfaces can be placed in various Debye media as well as across the physical interface . [ABSTRACT FROM PUBLISHER]

In this paper, a general domain expression is developed to calculate the horizontal electric field at the ground surface. The expression satisfies stricter conditions than the Cooray–Rubinstein (C-R) and Wait formulae. We proved that the new expression can be reduced into the first approximation of the C-R and Wait formulae. An evaluation that utilized the numerical results obtained by the three formulae was conducted to investigate the error caused by the assumptions made in the C-R and Wait formulae. Finally, the approximate method proposed by Caligaris, Delfino, and Procopio was utilized to evaluate the new formula and the C-R formula through comparison with the results obtained conventionally using the C-R formula. [ABSTRACT FROM PUBLISHER]

This paper presents SPICE models for the prediction of effects on shielded cables induced by nonuniform fields. Based on the transmission line theory, these models can be utilized to analyze shielded cables terminated with nonlinear or time-varying loads excited by nonuniform fields in the time domain. Two examples, a coaxial shielded cable and a two-parallel-wire shielded cable, both inside a cavity with a slot excited by an incident wave, are studied with the proposed models. The finite-difference time-domain method is employed to calculate the excitation fields of the cables, and then, the SPICE models are utilized to obtain the disturbances induced by the incident wave on the cables. The results obtained by the proposed models agree well with those obtained through other methods. [ABSTRACT FROM AUTHOR]

The transmission-line matrix (TLM) method, in time domain, is extended to account for the presence of anisotropic and dispersive media in electromagnetic structures or devices. The model is thoroughly constructed by using Maxwell's equations that make it a unified general TLM formulation. Numerical results are compared with experimental measurements; hence, in the case of ferrite-based structures, validating the model and showing the accuracy of the approach. [ABSTRACT FROM AUTHOR]

Electromagnetic scattering by general bi-isotropic objects is calculated by using the time-domain integral equations which are incorporated with the Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) formulations. By introducing a pair of equivalent electric and magnetic sources, electromagnetic fields inside a homogeneous bi-isotropic region can be represented by these sources over its boundary after applying fields splitting method. A series of coupled surface integral equations are obtained after imposing boundary conditions. These equations are then solved numerically using the method of moment (MoM) which involves separate spatial and temporal testing procedures. The Rao-Wilton-Glisson (RWG) functions are used as the spatial expansion and testing functions, and the weighted Laguerre functions are derived as the temporal basis and testing functions. Numerical results such as transient currents, far scattered fields, and normalized radar cross sections are presented and compared with analytical results as well as MoM-based frequency-domain analysis, and good agreements are observed. [ABSTRACT FROM PUBLISHER]

Analytic time-domain expressions are derived for the pulsed electromagnetic field radiated by a wide slot antenna with a dielectric layer in a two-dimensional model configuration. In any finite time window of observation, exact pulse shapes for the propagated, reflected and refracted wave constituents are constructed with the aid of the modified Cagniard method (the Cagniard-DeHoop method). Numerical results are presented for field pulse shapes at the dielectric/free-space interface, the pulse time widths of the excitation being chosen such that the separate arrivals from the two edges of the slot can be distinguished. Applications are found in any system whose operation is based on pulsed electromagnetic field transfer and where digital signals are detected and interpreted in dependence on their pulse shapes. [ABSTRACT FROM AUTHOR]