Circuit Modeling for Electromagnetic Compatibility
Very simply, electromagnetic interference (EMI) costs money, reduces profits, and generally wreaks havoc for circuit designers in all industries. This book shows how the analytic tools of circuit theory can be used to simulate the coupling of interference into, and out of, any signal link in the system being reviewed. The technique is simple, systematic and accurate. It enables the design of any equipment to be tailored to meet EMC requirements. Every electronic system consists of a number of functional modules interconnected by signal links and power supply lines. Electromagnetic interference can be coupled into and out of every conductor. A review of the construction of the wiring assemblies and the functions of the signals they carry will allow critical links to be identified. Circuit modeling can be used to simulate the electromagnetic coupling mechanism of each critical link, allowing its performance to be analyzed and compared with the formal requirements. Bench testing during the development of any product will allow any interference problem to be identified and corrected, long before the manufactured unit is subjected to formal testing. Key Features: A fully outlined, systematic and dramatically simplified process of designing equipment to meet EMC requirements; Focuses on simplifications which enable electrical engineers to singularly handle EMC problems; Helps minimize time-to-market of new products and reduces the need for costly and time-consuming modifications; Outlines how general purpose test equipment (oscilloscopes and signal generators) can be used to validate and refine any model; Discusses how to use Mathcad or MATLAB® to perform analysis and assessment.
Inspec keywords: transient analysis; transmission lines; lumped parameter networks; antennas; electromagnetic compatibility
Other keywords: transmission line models; lumped parameter models; bench testing; system design; antenna models; electromagnetic compatibility; transient analysis
Subjects: Antennas; Lumped linear networks; Transmission line links and equipment; Electromagnetic compatibility and interference; General electrical engineering topics; Mathematical analysis
- Book DOI: 10.1049/SBEW502E
- Chapter DOI: 10.1049/SBEW502E
- ISBN: 9781613530207
- e-ISBN: 9781613530283
- Format: PDF
-
Front Matter
- + Show details - Hide details
-
p.
(1)
-
1 Introduction
- + Show details - Hide details
-
p.
1
–23
(23)
The development of electronic equipment has come a long way since the invention of valves and transistors, to the extent that modern society is highly dependent on the smooth functioning of the myriad systems that myriad systems now in operation. Concurrently with that development, Electromagnetic Interference (EMI) has also increased, both in the number of daily incidents and in the severity of the possible consequences. Initially, most of the effects were annoying; for example, crackles on the radio due to a nearby thunderstorm were something one learned to accept. Latterly, some of the effects could be life threatening. The phenomenon described as 'sudden unintended acceleration' could be a case in point. A succinct definition of Electromagnetic Compatibility (EMC) is 'the ability of a device, unit of equipment, or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment'.
-
2 Lumped parameter models
- + Show details - Hide details
-
p.
25
–60
(36)
A review of the method used to calculate circuit component values for three-phase power lines leads to the identification of the first step; the derivation of a formula relating the capacitance of an isolated conductor to its length and radius. This formula can be regarded as a basic building block from which the capacitive parameters of multi-conductor assemblies can be derived. In computer terminology, a low-level object or operation from which higher-level, more complex objects or operations can be constructed is termed a primitive. So it seems reasonable to use the term primitive capacitance to identify the basic relationship.
-
3 Other cross sections
- + Show details - Hide details
-
p.
61
–79
(19)
It is possible to develop the process to determine the properties of conductor assemblies of virtually any cross section. The starting point is a technique devised by researchers at Culham to predict induced voltages in aircraft cables [1.9]. In this technique, the assembly-under-review is represented by an array of parallel conductors. It is assumed that the conductors at each end are short-circuited. So the end-to-end voltage of each conductor is the same. Since the voltage along the length of one conductor of this array is determined by the currents in all the conductors, then a set of primitive equations can be defined. Solving this set of equations allows the current in each conductor to be calculated. When the currents are known, it is possible to calculate the magnetic potential of any point in the vicinity. This allows the magnetic field pattern in the region to be determined. The composite conductor can be defined as a set of elemental conductors, aligned in parallel, which enables the distribution of currents or voltages in the actual conductor to be simulated. An elemental conductor can be defined as a conductor which represents a small segment of the surface of a composite conductor. In the method described here, the primitive equations are set up and the currents in the elemental conductors are calculated, but the focus remains on the behavior of those currents.
-
4 Transmission line models
- + Show details - Hide details
-
p.
81
–100
(20)
It is often required to extend the model to frequencies well beyond the one-tenth wavelength limit of the lumped component model. Such a task can be carried out by invoking the concepts of transmission line theory. This involves the need for circuit components to be defined in terms of W/m, F/m, H/m, and S/m. Using this approach, transmission line theory derives a pair of hybrid equations relating current and voltage at the sending end of the line to the current and voltage at the far end.
-
5 Antenna models
- + Show details - Hide details
-
p.
101
–134
(34)
EMI extends well beyond the confines of the assembly-under-review. Analysis of radiated emission and radiated susceptibility calls for a review of the properties of antennae. Fortunately, this review allows many simplifying assumptions to be invoked. Section 5.1 provides a brief overview of the textbook analysis of the half-wave dipole and identifies a very significant parameter; when connected to the output of a radio transmitter which is generating a signal at the half-wave frequency, the dipole exhibits the same characteristics as a resistive load. This has been named the `radiation resistance' and its value has been calculated to be 73 Ω.
-
6 Transient analysis
- + Show details - Hide details
-
p.
135
–174
(40)
This section describes the use of time-step analysis to simulate transient behavior. It derives a model which can simulate the emission produced by a step pulse propagated along a twin-conductor line. Such circuits should also be capable of minimizing susceptibility.
-
7 Bench testing
- + Show details - Hide details
-
p.
175
–216
(42)
It is normal practice to carry out bench tests of the functional behavior of prototype circuitry during the development of any new product. This identifies problems that had not been predicted during the feasibility study and provides an opportunity to rectify those faults. It also provides an early opportunity to check that the design requirements are being met. Since EMC is also a functional requirement, it is logical to expect that this aspect of design should be checked at the prototype stage. Two items of essential equipment are the voltage transformer and the current transformer. Several manufacturers produce such items, but they are highly expensive, and not really suitable for general-purpose use. So the transducers described in this section were assembled from components obtained from a supplier of electronic components.
-
8 Practical design
- + Show details - Hide details
-
p.
217
–244
(28)
There are a number of design concepts and techniques in existence which are aimed at improving EMC. Many of them are supported by the analytical approach. But some are not. A concept that can be traced back for many decades is that of the `equipotential ground plane'. There is no such thing. Since the 'method of images' of electromagnetic theory is often quoted as the basis for this concept, it is useful to identify the fallacies underlying the correlation. Section 8.1 does just that. Designers should resist the temptation to treat the structure as a convenient return path for signals and power. The most effective use of the conducting structure is as a shield. One deduction which is continually reinforced during the process of creating circuit models is the fact that the signal and return conductors should be as close together as possible.
-
9 System design
- + Show details - Hide details
-
p.
245
–267
(23)
Chapter 8 has identified several techniques which can be used to minimize the level of interference coupled into and out of a signal link. It is possible to glean a few simple guidelines that identify the basic concepts used in all these techniques, and these are listed in section 9.1. If implemented at the initial stage of a project, these guidelines should ensure that the EMC of the system can be achieved in a cost-effective way. This chapter discusses the design of the system that can be tailored to meet those EMC requirements.
-
Appendix A: Mathcad worksheets
- + Show details - Hide details
-
p.
269
–270
(2)
-
Appendix B: MATLAB®
- + Show details - Hide details
-
p.
271
–272
(2)
-
Appendix C: The hybrid equations
- + Show details - Hide details
-
p.
273
–276
(4)
-
Appendix D: Definitions
- + Show details - Hide details
-
p.
277
–279
(3)
-
Back Matter
- + Show details - Hide details
-
p.
(1)