Showing papers in "IEEE Transactions on Electromagnetic Compatibility in 1998"

Plane wave integral representation for fields in reverberation chambers

Abstract: A plane wave integral representation is presented for well-stirred fields in a reverberation chamber. The representation automatically satisfies Maxwell's equations in a source-free region and the statistical properties of the fields are introduced through the angular spectrum, which is taken to be a random variable. Starting with fairly simple and physically appropriate assumptions for the angular spectrum, a number of properties of the electric and magnetic fields and the power received by an antenna or a test object are derived. Many of these properties and test object responses are in agreement with other theories or with measured results. An important result for radiated immunity testing is that the ensemble (stirring) average of received power is equal to the average over plane wave incidence and polarization.

Review and evaluation of lightning return stroke models including some aspects of their application

Abstract: Four classes of models of the lightning return stroke are reviewed. These four classes are: (1) the gas dynamic models; (2) the electromagnetic models; (3) the distributed-circuit models; and (4) the "engineering" models. Validation of the reviewed models is discussed. For the gas dynamic models, validation is based on observations of the optical power and spectral output from natural lightning. The electromagnetic, distributed-circuit, and "engineering" models are most conveniently validated using measured electric and magnetic fields from natural and triggered lightning. Based on the entirety of the validation results and on mathematical simplicity, we rank the "engineering" models in the following descending order: MTLL, DU, MTLE, BG, and TL. When only the initial peak values of the channel-base current and remote electric or magnetic field are concerned, the TL model is preferred. Additionally discussed are several issues in lightning return-stroke modeling that either have been ignored to keep the modeling straightforward or have not been recognized, such as the treatment of the upper, in-cloud portion of the lightning channel, the boundary conditions at the ground, including the presence of a vertically extended strike object, the return-stroke speed at early times, the initial bi-directional extension of the return stroke channel, and the relation between leader and return stroke models. Various aspects of the calculation of lightning electric and magnetic fields in which return stroke models are used to specify the source are considered, including equations for fields and channel-base current, as well as a discussion of channel tortuosity and branches.

Analytical formulation for the shielding effectiveness of enclosures with apertures

Abstract: An analytical formulation has been developed for the shielding effectiveness of a rectangular enclosure with an aperture. Both the magnetic and electric shielding may be calculated as a function of frequency, enclosure dimensions, aperture dimensions and position within the enclosure. Theoretical values of shielding effectiveness are in good agreement with measurements. The theory has been extended to account for circular apertures, multiple apertures, and the effect of the enclosure contents.

The US National Lightning Detection Network/sup TM/ and applications of cloud-to-ground lightning data by electric power utilities

Abstract: Lightning is a significant cause of interruptions or damage in almost every electrical or electronic system that is exposed to thunderstorms. The problem is particularly severe for electric power utilities that have exposed assets covering large areas. We summarize the basic properties of cloud-to-ground (CG) lightning, the primary hazard to structures on the ground, and then we discuss methods of detecting and locating such discharges. We describe the US National Lightning Detection Network/sup TM/ (NLDN), a system that senses the electromagnetic fields that are radiated by individual return strokes in CG flashes. This network provides data on the time of such strokes, their location and polarity and an estimate of the peak current. We discuss the network detection efficiency and location accuracy and some of the limitations that are inherent in any detection system that operates with a finite number of sensors with fixed trigger thresholds. We also discuss how NLDN data have benefited utilities by providing lightning warnings in real time and information on whether CG strokes are the cause of faults, documenting the response of fixed assets that are exposed to lightning, and quantifying the effectiveness of lightning protection systems. We conclude with some general observations on the use of lightning data by power utilities and we provide some guidelines on the uncertainties in lightning parameters that are acceptable in the industry.

A channel model for the residential power circuit used as a digital communications medium

Abstract: A channel model for the residential power circuit used as a carrier for telecommunications signals is presented. This model is based on the results of an extensive measurement campaign executed in the city of Amsterdam, The Netherlands. As a basis for the channel model, the time-variant linear filter model is used. Channel noise is shown to be a summation of four noise types. Figures on channel-input impedance as well as signal attenuation are given. Finally, the phase shift introduced by the channel is considered.

Study of the ground bounce caused by power plane resonances

Abstract: We describe Delta-I noise caused by power plane resonances in multilayer boards. First, we study the effect of power plane resonances on the ground bounce of the system by performing finite-difference time-domain (FDTD) simulations. We simulate the voltage fluctuations at one point of the printed circuit board (PCB) due to a current surge between the power planes in a different point. Next, two methods to prevent this ground bounce effect are investigated. The first method consists of adding lumped capacitances to the design. The effect of one large capacitor is compared to the effect of adding a "wall" of smaller capacitors. A second approach is to isolate the chips by etching a slot around the sensitive integrated circuits (ICs) and connecting both sides by a small inductor. Both methods provide excellent protection against power plane resonances.

Reduction of power converter EMI emission using soft-switching technique

Abstract: Measurements of conducted and radiated electromagnetic interference (EMI) emission from hard-switched and soft-switched buck, boost, and flyback converters of similar power ratings are presented. Results indicate that EMI emission can be substantially reduced by using a soft-switching technique in power converters. Thus, the soft-switching technique provides a practical and useful solution to reduce EMI emission from switched-mode power circuits. A comparison of EMI emission on the three classes of converters is also included. The flyback converter is found to be the least EMC friendly among the converters tested.

Lightning-induced overvoltages in power lines: validity of various approximations made in overvoltage calculations

Abstract: The validity of different approximations used in the calculation of induced overvoltages in power lines are investigated. These approximations are as follows: (1) neglect the distortions introduced by the finitely conducting ground on the electromagnetic (EM) fields; (2) the horizontal electric field at ground level is calculated by using the wavetilt approximation, which is valid for radiation fields and for grazing incidence; (3) the horizontal field at the line height is obtained by adding the horizontal field calculated at ground level to the horizontal field at the line height calculated over a perfectly conducting ground; (4) the transmission line equations derived by assuming that the ground is perfectly conducting are used with the horizontal field present over a finitely conducting ground as a source term in calculating the induced overvoltages; and (5) the propagation effects on the transients as they propagate along the line are either neglected or modeled by replacing the line impedance due to the ground by a constant resistance. The results presented show that in the calculation of induced overvoltages the approximation (3) is justified and approximation (2) is justified if the interest is to estimate the peak value of the induced overvoltage. Approximation (4) is probably justified for short lines and/or for highly conducting grounds. But it can introduce significant errors if the line is long and ground conductivity is low. Approximations (1) and (5) may lead to significant errors in the peak value, risetime, and derivative of the lightning-induced overvoltages.

Lightning characteristics based on data from the Austrian lightning locating system

Abstract: We compare various lightning characteristics measured by the Austrian lightning locating system [Austrian Lightning Detection and Information System (ALDIS)] with those found in the literature. The latter are typically based on measurements of lightning electric fields. We show that lightning peak electric fields due to subsequent strokes measured by the ALDIS are similar to those in the literature. However, the ALDIS data do not show the usual ratio of about 2:1 between the median values of the field peaks for first and subsequent strokes. Although the flash detection efficiency of the ALDIS system in the area of investigation is estimated to be higher than 90%, one of the best for such systems all over the world, the observed percentage of single-stroke flashes and the average number of strokes per flash seem to suggest that the stroke detection efficiency is appreciably less than 90%. The ALDIS data indicate that larger strokes are preceded by longer interstroke intervals. The mean flash duration of 175 ms measured by ALDIS is similar to the typical flash duration found in the literature. Strokes with larger field peaks tend to have higher average field rates of rise. Since many lightning parameters show a large scatter for different thunderstorm days, long-term data from lightning locating systems are more representative of average lightning compared to data derived from electric field measurements typically performed during a few thunderstorms.

Lightning current and magnetic field parameters caused by lightning strikes to tall structures relating to interference of electronic systems

Abstract: In order to protect electronic devices against the effects of lightning strikes to tall structures, detailed information about the lightning currents and the radiated electromagnetic fields are necessary For this purpose, coordinated lightning current and field measurements are performed at the telecommunication tower on the mountain Hoher Peissenberg in the south of Germany The instrumentation is described Of special interest are the detailed waveforms of the lightning currents and the corresponding magnetic fields as well as their respective derivatives Electronic systems are mainly affected by the impulse current components in a lightning strike to a tall structure The lightning current and corresponding field waveforms are discussed and detailed statistical evaluations of different parameters are presented

Net and partial inductance of a microstrip ground plane

Abstract: A knowledge of the net inductance of the ground plane can aid in the analysis and investigation of printed circuit board emissions. In this paper, we present a method, based on the concept of partial inductance, to determine the net inductance of the ground plane associated with a microstrip line. This method is based on a previously derived expression for the current density on the ground plane. We show calculations for the net, self-partial, and mutual-partial inductance of the ground plane for various trace geometries of practical interest. We also illustrate how the classical transmission line inductance of a microstrip line can be obtained from the concept of partial inductance. Comparisons to different experimental results are also given.

Total-field absorbing boundary conditions for the time-domain electromagnetic field equations

Abstract: A method is described for generating absorbing boundary conditions (ABCs) that can be applied to the total fields rather than the usual scattered fields. As compared with the traditional use of ABCs for total-field formulations, this method has the advantages that it does not require the introduction of a mathematical connection surface between the total-field region and the scattered-field region; the total field is computed in the entire domain of computation. The incident field is accounted for by augmenting the ABC used. The resulting code is much simpler than one using ABCs for scattered fields together with a connection surface and the numerical results are much more easily interpreted since they consist of total fields only.

PEEC modeling of lightning protection systems and coupling to coaxial cables

Abstract: This paper proposes a partial element equivalent circuit (PEEC) model for the analysis of the electromagnetic environment inside a building during a direct or nearby lightning strike A PEEC model for the lightning protection system (LPS) is developed in conjunction with a PEEC model for braided coaxial cables A two-step matrix solution of the whole set of equations describing the LPS and cables allows one to predict the current distribution in the downconductors and the induced voltages and currents on the cables' shield and loads Results are given in frequency and time domain for direct and nearby lightning strikes and for different positions of the cables inside the LPS volume

Measurement results of the electric fields in cloud-to-ground lightning in nearby Munich, Germany

Abstract: This report gives an overview of the electric fields measured in cloud-to-ground lightning in nearby Munich, Germany between 1984 and 1993. The electric fields and their derivatives during the onset of return strokes were recorded with three different measuring systems during three measuring periods. The statistical results include the initial peaks of the return-stroke field as well as the maximum values and the full widths on half maximum of their derivatives. Based on the measured fields of multiple-stroke flashes and negative flashes containing continuing currents statistics about the interstroke intervals, the numbers of return strokes and the duration of continuing currents are presented.

A spectral approach for the determination of the reverberating chamber quality factor

Abstract: A simple and effective approach for the evaluation of the chamber quality factor is presented. It is based on the averaged periodogram and permits a complete spectral characterization of the efficiency of reverberating chambers. A meaningful set of experiments is performed and discussed.

Electromagnetic chaos in mode-stirred reverberation enclosures

Abstract: We study a simple (ray optical, scalar) model of mode-stirred electromagnetic reverberating enclosures. Extensive numerical simulations reveal consistently that spatial-field homogenization and (wide-sense) deterministic chaos occur together, as the time-harmonic peak displacement of the mode-stirring wall becomes comparable to the electromagnetic wavelength. Reverberation properties can thus be synthetically gauged by Lyapounov exponents. Semiquantitative design optimization criteria are obtained and possible generalizations are discussed.

Evaluation of LEMP effects on complex wire structures located above a perfectly conducting ground using electric field integral equation in time domain

Abstract: In this paper, a novel approach for the implementation of scattering theory is proposed in order to evaluate the electromagnetic effects of lightning return stroke on complex wire structures (lightning EM pulse - LEMP). An electric field integral equation (EFIE) in the time domain is employed to describe the electromagnetic transients from lightning. The proposed approach is applied to a single-phase, three-phase as well as a Y-shaped transmission line located above a perfectly conducting ground. The simulation results reproduce accurately experimental data available in the literature. The proposed method provides new possibilities in estimation of lightning indirect effects on complex networks as an example "radial transmission systems tapped from main switching substations" are investigated.

The specific absorption rate in a spherical head model from a dipole with metallic walls nearby

Abstract: The head of the user of a mobile telephone is modeled by a lossy dielectric sphere excited by the near field of a dipole antenna and the effects of a metallic wall placed close to this system are analyzed. Three wall orientations are used and the changes in specific absorption rate (SAR) with wall or antenna distance from the sphere are investigated. When the wall is closer than 100 mm to the dipole-sphere system, it can have a strong influence on the input impedance of the antenna and can cause significant increases in the SAR in the head. When a constant radiated power of the dipole antenna is assumed, the maximum value of SAR averaged over 10 g of tissue within the sphere is increased by 60% when the wall is as close as 30 mm from the surface of the sphere. For a dipole excited by a constant current source, the increase is less than 10% and occurs when the wall is 120 mm from the surface of the sphere. Although the distances and configurations analyzed may not represent the way the majority of people use mobile telephones, it is important to examine unusual situations to determine the extent of the SAR enhancement problem.

Predicting the spatial and temporal variation of the electromagnetic fields, currents, and speeds of subsequent return strokes

Abstract: A mathematical model with a physical basis is introduced to describe the subsequent return strokes in lightning flashes. The input parameters of the model are the channel-base current and the charge distribution along the leader-term-stroke channel. Once these have been specified, the model can be used to describe how the current, speed, and the electromagnetic (EM) fields of the return strokes vary in space and time. It predicts that the current risetime increases with increasing height along the channel while the value of its peak decreases. According to the model simulations, the return-stroke speed reaches its highest value within a few meters of ground level after which it decreases monotonically with increasing height. The EM fields generated by the model reproduce most of the features observed in measured fields and the model predicted return-stroke speed profile agrees with the data obtained in experimental observations. The model predicts that E/sub p/=32I/sub p//D where I/sub p/ is the peak current (in Amperes) and E/sub p/ (in V/m) is the peak radiation field observed at distance D (in meters).

Systematic approach for the analysis of the electromagnetic environment inside a building during lightning strike

Abstract: This paper defines a systematic approach considering the lightning current at the base of the channel as the input function, and the spatial distribution of the electromagnetic (EM) field inside the building, or the overvoltages induced at the open ends of loops as the output functions. A parametric analysis of the influence of the lightning protection system on the output functions is carried out in the frequency domain. The systematic approach allows one to take into account the probabilistic nature of the input function, which transforms the values of the outputs from a deterministic to a distribution of probability. This is extremely useful for all electromagnetic compatibility (EMC) engineers dealing with realistic systems' designs or maintenance problems.

Ray analysis of electromagnetic field build-up and quality factor of electrically large shielded enclosures

Abstract: A high-frequency asymptotic ray solution is investigated for predicting the electromagnetic field build up and steady-state parameters of shielded enclosures or cavities, which are large with respect to wavelength. It is found that the ray solution can deterministically predict the early-time field build up after the source is switched on, but cannot predict the steady-state fields of high-Q enclosures because of the intractably large number of ray reflections required for convergence. However, it is demonstrated that the steady-state Q factor may be predicted from the early-time energy density build up at a point by coherently summing the power in each ray. The Q factor is obtained via its relationship to the cavity time constant, which may be extracted from the early time energy density curve. A clear indication of polarization diversity throughout the enclosure may also be obtained by plotting the polarization components of the early-time fields and energy density build up at different points. The advantage of the ray method is that it can be used to treat large closed cavities of relatively arbitrary shape.

Harmonic balance simulation of RF injection effects in analog circuits

Abstract: RF noise immunity is becoming a serious problem for integrated circuits (ICs). We have found a frequency-domain simulator [harmonic balance (HB)] to be useful for analyzing the undesired IC behavior, especially the DC output shift under the large RF injection. The simulator has the following advantages in comparison with a conventional time-domain simulator such as SPICE: (1) DC output shifts can be simulated in a very short time using a conventional bipolar transistor model and (2) steady-state current or voltage waveforms at each node in an IC are directly and easily obtained. This paper describes the methods and results of the DC shifts analysis of a bipolar transistor or a differential amplifier using the HB simulator.

Statistical response of EM-driven cables inside an overmoded enclosure

Abstract: This paper deals with probabilistic modeling of the electromagnetic (EM) response of cables inside a complex cavity subjected to well overmoded EM penetration. Theoretical studies indicate that the field amplitudes and cable currents squared both should have a /spl chi/-square distribution with two degrees of freedom, but our observations indicate that a log normal fit is empirically better unless the data, if experimentally obtained, is first passed through a carefully tailored trend-removing filter. If a cable model is driven by statistically simulated enclosure fields, similar extreme care must be taken with the numerical generation of these driving fields. The major innovation reported here is the development of an algorithm that models cable-drive fields simultaneously having a /spl chi/-square power-flux distribution and the physically mandated local autocorrelation at a spatial point as the frequency is swept or at a fixed frequency as the power flux sensor is moved around to map the cavity response. Nature is quite adept at creating a cable drive with these simultaneous attributes, but computer emulation had proved very exasperating. Our algorithm, as an unplanned bonus, also has the capability to transform random numbers from one distribution to another. For instance, one can input normally distributed power-flux values and obtain as the output /spl chi/-square or log normally distributed power-flux values. The reverse transformations are also allowed.

Response of long lines to nuclear high-altitude electromagnetic pulse (HEMP)

Abstract: During high-altitude nuclear testing in 1962 over Kazakhstan, several system effects were noted due to the high-altitude electromagnetic pulse (HEMP). In particular a 500-km-long aerial communications line experienced a failure due to the damage of its protective devices. This failure is examined in detail beginning with the calculation of the incident HEMP environments, including those from the early- and late-time portions of the HEMP. In addition, the currents and voltages induced on the line are computed and the measured electrical characteristics of the protection devices are presented. With this information it is possible to determine which portions of the HEMP environment were responsible for particular protection failures. The paper concludes with recommendations for further work required to understand the best ways to protect power lines from HEMP in the future.

Reliable protection of electronics against lightning: some practical applications

Abstract: The classical lightning conductor, which must prevent fire, has to have a sufficiently small resistance. An analogous condition can be formulated for the new challenge: the protection of sensitive electronics against lightning. In this case, the so-called transfer impedance, which gives the interference voltages across a sensitive input per ampere lightning current, must be made small. The arguments for this approach are described. A theoretical description is available and practical experience has been built up over the years, also in high-voltage (HV) research and in power engineering measurements in the field. This approach was used to greatly improve the lightning protection of several installations: a marine radio station, the peripheral equipment of a nuclear power plant, and an electronic siren for a nationwide public warning system. Detailed investigations were requested by our contract partners, together with suggestions for economically acceptable improvements that could be carried out in reasonable time. Later, the correctness of the renovations had to be demonstrated. In the validation measurements, we injected currents into the installation or into relevant parts thereof. The current waveform was chosen fast enough so that inductive effects determined the current distribution. At present, lightning position and tracking system (LPATS) data on lightning strikes near the marine radio station and the nuclear power plant are available to verify the effectiveness of the protection. After our improvements no more damage was reported.

Surface transfer impedance measurement: a comparison between current probe and pull-on braid methods for coaxial cables

Abstract: Theoretical models to compute the surface transfer impedance of cables often rely on simplifying assumptions This, together with the fact that surface transfer impedance can vary considerably between cable samples of the same type, means that measurements become necessary In this way an average performance may be determined Many transfer impedance measurement methods have been proposed over the years and each has its own relative strengths Two frequency-domain measurement methods are compared: the current probe method and the pull-on braid method Both methods are inexpensive and can be set up very quickly without expensive cable preparation Moreover, they operate over a broad frequency range with high accuracy This is shown by the good agreement obtained between measurements carried out with the two methods

Electromagnetic ground-wave field of vertical antennas for communication at 1 to 30 MHz

Abstract: Radio communication over the spherical surface of the Earth and sea makes use of vertical antennas in the frequency range from 1 to 30 MHz. For distances that extend beyond the approximation of a planar Earth, use must be made of the ground-wave. Following a description of antennas used on shipboard, their radiated fields are analyzed in the planar- and spherical-Earth regions. The latter involves new formulas for the field of vertical dipoles over the spherical surface of the sea.

Effect of logic family on radiated emissions from digital circuits

Abstract: Radiated emissions were measured for simple digital circuits designed to operate with various logic families. Emissions in the near and far field were found to depend both on the circuit layout and the choice of logic family. However, the difference in peak emissions between any two logic families was found to be independent of the circuit layout. The greatest difference in peak emissions was between high-speed 74ACT logic and low-speed 4000 CMOS logic devices, with a mean value of approximately 20 dB. Emissions from a more complex circuit were compared with the measurements on simple loop circuits. Test circuits were used to measure the propagation delay, the rise and fall times, the maximum operating frequency and the transient switching currents between two successive logic gates for each logic family. Empirical formulas have been derived that relate relative peak emissions to these switching parameters. It is hoped that these will assist designers to assess the effect of choice of logic family on electromagnetic compatibility.

Power spectrum of unbalanced NRZ and biphase signals in the presence of data asymmetry

Abstract: The impact of data unbalance and asymmetry on the power spectral density of nonreturn-to-zero (NRZ) and biphase baseband modulations is presented. Previously reported results for this problem assumed an incorrect model for the shape and number of elementary pulse shapes that characterize an arbitrary random data stream and thus led to erroneous computations of these power spectra. This paper provides the correct analytical model and then use it to obtain theoretical power spectrum results that are in full agreement with those obtained from computer simulation.

Electromagnetic scattering by the Luneberg lens with reflecting cap

Abstract: The near-field distribution in the case of the normal incidence to the Luneberg lens reflector is numerically obtained by using the modal expansion technique and point-matching method. As a model of the Luneberg lens, six different homogeneous media is used. A microwave experiment was also performed.