Showing papers on "Electromagnetic compatibility published in 1988"

Techniques for measuring the electromagnetic shielding effectiveness of materials. II. Near-field source simulation

Abstract: Shielding effectiveness relates to the ability of a material to reduce the transmission of propagating fields in order to electromagnetically isolate one region from another. Because the shielding capability of a complex material is difficult to predict, it often must be measured. A number of approaches to simulating far-field source are studied, including the use of coaxial transmission-line holders and a time-domain system. In each case, the system frequency range, test sample requirements, test field type, dynamic range, measurement time required, and analytical background are considered. Data taken on a common set of materials are presented. >

Measured electromagnetic shielding performance of commonly used cables and connectors

Abstract: The intrinsic electromagnetic property of a cable or connector shield is considered its surface transfer impedance. This is the ratio of the longitudinal open circuit voltage measured on one side of the shield (normally the inside) to the axial current on the other side (normally the outside). In cases where a high electric field is present at the surface of the shield, the transfer admittance or charge transfer elastance is also important. Measurements of typical cables, connectors, backshells, and cable terminations are presented and explained in terms of simple models. >

Transient response of a transmission line excited by an electromagnetic pulse

Abstract: The transient response of a lossless transmission line of finite length excited externally by an electromagnetic wave of an arbitrary waveform is studied. By using the Laplace transformation, a solution of the transient current is obtained as a series of analytical functions. Inspection of the solution leads to the conclusion that the response currents at terminals of the line can be equivalently expressed by the components induced at both terminals, and, in addition, the multireflected wave when the line is mismatched. Furthermore, a new equivalent circuit for the coupling phenomenon is discussed. >

Coupling between electromagnetic fields and multiconductor transmission systems using TLM

Abstract: The coupling between incident electromagnetic fields and lossless multiconductor transmission systems is studied using transmission-line modelling-(TLM) and the impedance parameters of the transmission system. This calculation is a two-stage procedure:firstly, the field problem is solved, with no conductors present, to give the incident fields; secondly, the multiconductor transmission-line problem is solved using equivalent voltage and current sources representing coupling from the incident fields. Comparison of these results with previously published work shows excellent agreement. The numerical model presented is particularly suitable for studying electromagnetic compatibility problems.

Guided waves along an unmagnetized lightning plasma channel

Abstract: The characteristics of a train of electromagnetic pulses traveling along an unmagnetized, unbounded lightning plasma column are considered. The motivation is to avoid the loss of low-flying, computer-controlled aircraft on account of very small lightning-radiated electromagnetic fields including parasitic currents in the onboard computing equipment. From Ampere's and Faraday's laws, applying appropriate boundary conditions at the edge of the channel and far away from it, the solution to the complex wave number, as well as the attenuation and phase constants of the signals traveling down the channel, is found. The results are shown to be in good agreement with observed return stroke characteristics. >

The role of shielding in interference control

Abstract: Interference in the form of extraneous noise or transients can be controlled by enclosing the circuits to be protected in an electromagnetic shield. Shielding is the primary means of protection when the source of interference cannot be controlled, although the barrier or generalized shield may be created through the use of spatial separation and orthogonalization, or may be an actual metal shield. The amount of shielding required for intrasystem compatibility can be based on local sources of interference within the system. When the equipment shield prevents the local sources from affecting its internal circuits and prevents its internal circuits from affecting the local environment, it is compatible with that environment and with all other equipment having these characteristics. This establishes intrasystem electromagnetic compatibility. >

Shielding effectiveness and electromagnetic protection

Abstract: Typical shielding effectiveness measurements and their relation to electromagnetic protection are reported. These measurements, which are based on the insertion loss when the shield is inserted between two antennas, contain the properties of the antennas and receivers inextricably commingled with the properties of the shield. For the assessment of electromagnetic protection, the shield's ability to limit the interaction of any arbitrary external source with an arbitrary internal circuit is found to be important. The assessment of protection cannot, in general, be obtained from insertion loss data. >

Differences between lightning and nuclear electromagnetic pulse interactions

Abstract: Some important differences between the system interactions of electromagnetic transients from lightning (LEMP) and from high-altitude nuclear explosions (HEMP) are discussed. Interactions with small systems, such as aircraft, and large systems, such as electric power grids, are considered. Effects of factors like lightning channel attachment and the relatively local nature of the lightning excitation are contrasted with the broad-area effect of the HEMP interaction. It is concluded that although protective approaches and techniques for LEMP and HEMP are often similar, the two phenomena are sufficiently different that protection against one does not necessarily imply protection against the other. >

Measurement procedures for electromagnetic compatibility assessment of electroexplosive devices

Abstract: Electroexplosive devices (EEDs) are electrically fired explosive initiators used in a wide variety of applications. A new and rigorous approach for characterizing EED firing levels is developed in the context of statistical linear models and is demonstrated. The authors combine statistical theory and methodology with thermodynamic modeling to determine the probability that an EED of a particular type fires when excited by a pulse of a given width and amplitude. Methods for assessing model validity and for obtaining probability plots, called firing likelihood plots (FLPs), are included. The results provide information that is crucial for evaluating the effects of currents induced by impulsive electromagnetic fields of short duration relative to the thermal time constant of an EED. Methods of measuring the thermal time constant of an EED and the energy needed to fire an EED with a single current impulse are given. These parameters are necessary not only to determine suitable ranges in the design of the statistical experiment, but also to assess the effect of pulses on EED's in EMC analyses. >

Calculation of lightning's EM effects on surrounding structure

Abstract: A high-intensity current that is drained to the soil by a lightning protection system generates electromagnetic interference in its immediate surroundings. A mathematical model is presented for evaluating the electromagnetic fields induced in a device (simulated by an open square turn) positioned in a vulnerable area. The model is based on the dynamic analysis of the protection system's response to a lightning stroke. It takes into account the complete simulation of the complex phenomenology tied to the partial discharges of the ground electrode. >

Magnetic field generated by lightning protection system

Abstract: A lightning protection system for today’s civil buildings must be electromagnetically compatible with the electronic equipment present in the building. This paper highlights a mathematic model which analyzes the electromagnetic effects in the environment in which the lightning protection system is. This model is developed by means of finite elements of an electrical circuit where each element is represented by a double pole circuit according to the trapezoidal algorithm developed using the finite difference method. It is thus possible to analyze the electromagnetic phenomena associated with the transient effects created by the lightning stroke even for a high‐intensity current. Referring to an elementary system comprised of an air terminal, a down conductor, and a ground terminal, numerical results are here laid out.

Review of EMC practice for launch vehicle systems

Abstract: Case histories, design and test practice in the field of advanced electromagnetic compatibility (EMC) are reviewed. Failures caused by lightning, electrostatic discharge (ESD), and electromagnetic interference (EMI) and radiofrequency interference (RFI) are discussed. System and equipment design and analysis are examined, including lightning and ESD protection and computer-aided EMC analysis. Testing of a number of rockets and spacecraft is described. >

A role model for electromagnetic systems design

Abstract: The authors discuss the antenna test range at the US Naval Ocean Systems Center, which provides solutions to some formidable electromagnetics problems on ships. They describe the measurement approach; the pattern range, a 160 ft diameter ground plane constructed of prestressed concrete covered with a very thin coating of lead; the impedance range, which has a subterranean instrument room that houses the measurement equipment and personnel during the test; and the time-domain measurement range. The authors then examine computer modelling of antennas and analysis of the EMC (electromagnetic compatibility) problem. The modelling approach as presented is not limited to ships; it can work for power lines, buildings, and even mountains. >

Models for circuit simulators to analyze crosstalk and radiation into wires

Abstract: A procedure is presented for analyzing digital pulse distortion, unintentional electromagnetic coupling (crosstalk), and the pickup of an incident electromagnetic field by transmission lines, using suitable models for commercial circuit simulators such as ASTAP, SPICE, and SABER. Transmission-line effects and field-to-cable coupling are represented in the circuit simulator by voltage sources for AC and transient analysis. AC computations can be done with distributed parameters, instead of lumped parameters, producing good accuracy and saving time. This type of analysis is very useful in the case of a periodic signal and linear loads. A description of these models and a comparison with experimental results are given. >

Scaling laws for coupling quantities on EMP

Abstract: A set of scaling laws relating three-potential electromagnetic coupling quantities to three electromagnetic pulse (EMP) characteristics is derived. The electromagnetic coupling quantities are an attempt to characterize, in a very rough sense, the ability of an electromagnetic wave to induce an electronic upset in an electric circuit. The coupling quantities used are chosen based on voltage transients, power transients, and energy-induced overload as mechanisms for electronic upset. The independent quantities in the scaling laws are chosen to be the pulse rise time, peak field, and total energy density. >

SHF/EHF field-to-wire coupling model

Abstract: Method-of-moments calculations have provided a database for deriving an empirical algorithm to characterize SHF/EHF coupling. The data show that the maximum field-to-wire current coupled into a port saturates as a function of height above the ground plane and that the saturation level can be simply characterized. The most important parameter in determining the saturation current is the near-port termination impedance. A computationally efficient algorithm is derived and can be incorporated into electromagnetic-compatibility (EMC) surveying/culling tools such as the IEMCAP code. The algorithm has been verified by coupled current measurements in an anechoic chamber. Cable-grounding conditions, port-termination resistance, and cable transmission loss are treated as input parameters in the algorithm. >

The evolution of MININEC (method of moments computer program for antenna analysis)

Abstract: The Mini Electromagnetics Code, or MININEC, is a method-of-moments computer program for the analysis of thin-wire antennas. A Galerkin procedure is applied to an electric-field integral equation to solve for the wire currents. This formulation results in an unusually short computer program suitable for implementation on a microcomputer. Hence, MININEC is written in BASIC, which is compatible with many popular microcomputers. MININEC capabilities include determination of impedance and currents, calculation of near and far fields, and calculation of radiation patterns. The solution includes all electromagnetic interactions between conductors, so the code can be used to determine antenna-to-antenna coupling, a necessary requirement for the electromagnetic compatibility (EMC) assessment of a cosite antenna environment. The development of MININEC from its conception is described. The capabilities are described and illustrated with examples. Future developments are included. >

Force calculation in electromagnetic devices

Abstract: In this paper the authors show how the Maxwell stress tensor can be used, in practice, in order to determine local magnetic forces distribution in an electromagnetic system. An experimental set-up has been designed in view of comparing the theoretical results with the measurements.

Transient response of a receiving dipole array: bounds and maximization

Abstract: The optimum solution for a receiving array of dipole antennas connected to a load through a feed network is obtained. It is given in terms of the incident electric field waveform that maximizes, at a specific time t/sub 0/, the received voltage across a specified load impedance. This result is used to set an upper limit on the peak voltage that the antenna can deliver to a load, thus providing guidelines for the design of pulse-protection circuits. The analysis uses the method of moments to approximate the currents induced in the wires by the incident field and S-parameter techniques to describe the feed incident electromagnetic plane waves. The Lagrange multiplier technique is then used to maximize the receive load voltage. The solutions presented are based on an idealized model for the feed network; however, the analysis can be extended easily to account for loss and asymmetry of physically realizable feed networks. >

Malfunctions of high impedance circuits caused by electrostatic discharges

Abstract: An electrostatic discharge is known to be a noise source and causes the malfunction of electronic circuits. As a result, most of the studies to date have been made on electromagnetic noise radiated by electrostatic discharges. Here, the authors focus on the effect of an electrostatic field on electronic circuits. The electrostatic field strength of discharges was investigated theoretically and experimentally, and it was found that the electrostatic field is also a source of noise and causes the malfunction of an electronic circuit terminated with high impedance. Results obtained from analyses and experiments are presented. >

Transient protection for highway traffic control equipment

Abstract: Electronic traffic control equipment is subjected to a wide range of electromagnetic threats. The electromagnetic environment, which includes lightning, electrostatic discharge, internally and externally generated inductive-switching transients, and radiated electromagnetic interference (EMI) from radio, TV, radar, and mobile communication transmitters, is described. Powerlines and cables interconnecting equipment to sensors, communications systems, or peripheral hardware provide a direct path for the conduction of disruptive and damaging electrical transients and other EMI into traffic control equipment. The relative levels of the various threats are integrated into a set of recommended test waveforms for traffic control equipment. >

Keeping the peace

Abstract: Discusses problems in ensuring compatibility between the electromagnetic environment and electronic and electrical devices. >

Implementation of an SHF/EHF field-to-wire coupling model into IEMCAP

Abstract: An SHF/EHF field-to-wire coupling model has been implemented in the Intrasystem Electromagnetic Compatibility Analysis Program (IEMCAP), which is a widely used code for intrasystem EMC modeling and analysis. IEMCAP includes a coupling model for an external field incident on a wire over a ground plane. This model incorporates a bounding algorithm based on transmission line theory. High frequencies or large distances above the ground plane cause the transmission line model to break down. The new model handles field-to-wire coupling from 1 GHz to 40 GHz. The model was verified experimentally. Tests in an anechoic chamber showed the same sensitivity of shielding effectiveness to port termination condition and the lack of sensitivity to cable length predicted by the model. Measurements of the current coupled into a bare wire above a ground plane, for a variety of illumination conditions, show excellent agreement with the theoretically derived bounds for the bare-wire coupling. >

Generation of ESD wave pulse and its space propagation characteristics

Abstract: An electrostatic discharge (ESD) between a metal object of large aspect ratio, charged at a low voltage, and another metal object emits electromagnetic energy, which is propagated in an impulsive form in the spatial medium around the metal objects. Sometimes, this phenomenon interferes with a computer system located in this spatial medium. The electromagnetic interference (EMI) in this case, recognized as indirect ESD, has been found by the present author to be proportional, not to the charged energy in the metal object, but to the acceleration component of the electromagnetic energy which has been emitted. An experimental study of the waveform and spatial propagation characteristics of the electromagnetic radiation emitted is reported. >

Computer modelling for vehicle electromagnetic compatibility

Abstract: It is likely that in the future strict regulations will be imposed on electromagnetic emission from automobiles and electromagnetic interference susceptibility levels for electronic equipment in automobiles. It is necessary therefore that there should be a good understanding of the factors affecting electromagnetic compatibility in vehicles both from the design and testing points of view. Computer simulation of the interaction of electromagnetic waves with structures and the coupling of electromagnetic fields into cables offers considerable insight into EMC mechanisms.

A new port spectrum modeling approach and the design of non-average power receptor models for IEMCAP

Abstract: The result of a technical effort for the design, development, and implementation of an enhanced spectrum-modeling algorithm in the US Air Force Intrasystem ElectroMagnetic Compatibility Analysis Program (IEMCAP) are summarized. The authors also define and design analytical models in IEMCAP to assess the EMC of receptors sensitive to nonaverage power (e.g. energy, peak voltage/current, and risetime). >

An EMC prediction and protective margin calculation program for the DEC VAX computer series

Abstract: A program that analyzes proposed shipboard electronic-equipment configurations for potential electromagnetic interference (EMI) problems and aids in solving these problems is presented. The program makes its calculations using EMI models or narrowband MIL-STD-461-type EMI data. This code provides designers and installers with a tool for examining configurations and establishing electromagnetic compatibility (EMC) before an installation is begun. >

The Design, Construction, Performance and Calibration of Pulse Generators to Fulfill the Requirements of Specifications Defense Standard 59-41, FS(F)510 and FS(F)457

Abstract: : This Memorandum describes the construction, performance and calibration of pulse generators to fulfill the electromagnetic transient test requirements of the Defence Standard 59-41 (June 1986), RAE Technical Memorandum FS (F) 510 and FS (F) 457 (Issue 2). Three pulse generators are described, Type 1A which produces damped sinusoidal waveforms in the frequency range 2 to 30MHz, Type 2 which is fixed frequency 100kHz generator, and Type 3 which produces two waveforms for ground voltage lightning effects simulation. The generators have been designed to enable electronic systems to be assessed for immunity to the effects of EMC, LEMP and NEMP. The NEMP capabilities of the Type 1A generator meet the Airside requirements of the Defence Standard. Great Britain.