Electromagnetic Pulse Excitation Research Articles

Analytical Correlation Between Time and Frequency Domain Shielding Effectiveness of Metallic Enclosures With Apertures

Time domain shielding effectiveness (SE) of metallic enclosures with apertures against electromagnetic pulse excitation has been analytically estimated and correlated to the frequency domain characteristics. The method is based on the analysis of the transient process at the aperture and an equivalent magnetic current source, to derive the initial peak amplitude appearing at the very beginning of the coupled field waveforms. The equivalent circuit model is utilized to analytically describe the frequency domain SE data. Then, a simple correlation formula has been derived, which relates the peak value reduction of the E-field and H-field to the specified spectral data minus a specially defined factor. Especially, the correlation for the E-field is shown to link the spectral SE data near the fundamental resonant frequency of TE101 mode with the peak amplitudes in time domain. A series of numerical and experimental cases have been checked to confirm the applicability of the analytical formulas. Comparisons between the data and the analysis exhibit reasonable agreements.

A mathematical model of photochemical transformations: Analysis of the influence of basic characteristics of the model

Basic aspects of the choice of parameters entering a system of differential equations that simulate the sequence of chemical transformations in the case of initiation of a reaction by electromagnetic pulse excitation of reactant molecules are discussed. These parameters are the probabilities of spontaneous and stimulated dipole–dipole transitions and the frequency of quantum beats that lead to the reaction. A method for an a priori estimation of optimum values of these frequencies on the basis of fundamental characteristics of intramolecular processes has been specified. It has been noted that in theoretical prediction of the course of chemical reactions, the solution of the problem in the natural coordinate system (distance between the atoms), rather than Cartesian coordinates, can be more appropriate.

Electromagnetic pulse excitation of finite- and infinitely-long lossy conductors over a lossy ground plane

This paper details a model for the response of a finite- or an infinite-length wire interacting with a conducting ground to an electromagnetic pulse excitation. We develop a frequency–domain method based on transmission line theory that we name ATLOG – Analytic Transmission Line Over Ground. This method is developed as an alternative to full-wave methods, as it delivers a fast and reliable solution. It allows for the treatment of finite or infinite lossy, coated wires, and lossy grounds. The cases of wire above ground, as well as resting on the ground and buried beneath the ground are treated. The reported method is general and the time response of the induced current is obtained using an inverse Fourier transform of the current in the frequency domain. The focus is on the characteristics and propagation of the transmission line mode. Comparisons with full-wave simulations strengthen the validity of the proposed method.

Time-Domain Generalized Telegrapher's Equations for the Electromagnetic Field Coupling to Finite Length Wires Above a Lossy Ground

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.

TIME DOMAIN ANALYTICAL MODELING OF A STRAIGHT THIN WIRE BURIED IN A LOSSY MEDIUM

This paper deals with an analytical solution of the time domain Pocklington equation for a straight thin wire of ¯nite length, buried in a lossy half-space and excited via the electromagnetic pulse (EMP) excitation. Presence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The analytical solution is carried out using the Laplace transform and the Cauchy residue theorem. The EMP excitation is treated via numerical convolution. The obtained analytical results are compared to those calculated using the numerical solution of the frequency domain Pocklington equation combined with the Inverse Fast Fourier Transform (IFFT).

A multiconductor model for determining the response of power transmission and distribution lines to a high altitude electromagnetic pulse (HEMP)

A method for determining the response of a multiwire transmission or distribution line to a high altitude electromagnetic pulse excitation is discussed. An above ground multiconductor model is developed to take into account wire-to-wire coupling, the earth reflection and line propagation effects, as well as the effects of periodic grounding of shield or neutral conductors along the line. Sample numerical results are also presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pulse excitation technique for determining frequency response of machine tools using an on-line mini computer and a non-contacting electromagnetic exciter

An electromagnetic pulse excitation technique for the determination of receptance data is presented. The relative performance of this in relation to the conventional stepped and swept sine methods was established in tests carried out on a horizontal milling machine. Good correspondence between the three techniques was noted, thus confirming the reliability of the electromagnetic pulse technique. The pulse excitation technique was then used for determining the relative response data of a cylindrical grinding machine. These experiments required the development of a new type of magnetic exciter with which a relative force pulse can be applied to the grinding spindle and the workpiece under conditions simulating actual grinding conditions.