This handbook outlines the factors that must be considered in designing circuits, equipment, and systems for electromagnetic compatibility (EMC). It teaches circuit and system designers practical approaches to thwart the ever present culprit of electromagnetic interference (EMI). By emphasizing the fundamentals, it provides information that will help readers understand the rationale that forms the basis for many of the EMC practices and procedures. There is much information about these topics available in disparate forms (journal articles, symposia proceedings, etc.) but this book brings the critical knowledge into a single source for battling EMI. The goal of all device and system designs that must function in an electromagnetic environment (i.e. radio, TV, radar, navigation, and communications) is to operate without adversely affecting other electronic equipment or systems. The inverse is also true. The requirement for sharing spectrum has reached international levels of concern and it must be dealt with in proportion to the safety and economic impact involved, Designing Electronic Systems for EMC outlines how.
Inspec keywords: electric connectors; bonding processes; cables (electric); electromagnetic compatibility; electromagnetic shielding
Other keywords: ferrite; grounding; protection technique; isolator; transient suppressor; bonding; shielding theory; filter; electronic system design; cable; EMC; connector
Subjects: General electrical engineering topics; Wires and cables; Connectors; Electromagnetic compatibility and interference
The primary purpose of this book is to provide an understanding of EMI problems and techniques for mitigating these problems. Careful application of these techniques at appropriate stages in the system life cycle will ensure EMC without either the wasteful expense of overengineering or the uncertainties of underengineering.
A number of specialized terms are applicable to the characterization, specification, and/or measurement of electromagnetic interference (EMI). It is particularly important that individuals responsible for ensuring that equipments and/or systems operate in an electromagnetically compatible manner be familiar with the basic terms and definitions that are widely used throughout the electromagnetic compatibility (EMC) community. This chapter presents a discussion of the basic terms and definitions that are important to the EMC engineer or technician.
This chapter identifies potential EMI problems that may occur between transmitters and receivers. The emphasis in this chapter is specifically oriented toward EMI signals that are generated by potentially interfering transmitters, propagated and received via antennas, and that cause EMI in receivers associated with communication systems.
The basic EMC requirement is to plan, specify, and design devices, equipments, and systems that can be installed in their operational environments without creating or being susceptible to interference. In order to satisfy this requirement, careful consideration must be given to a number of factors that influence EMC. In particular, it is necessary to consider major sources of electromagnetic interference (EMI), modes of coupling, and points or conditions of susceptibility. The electronic equipment or system designer should be familiar with the basic tools (including prediction, analysis, measurement, control, suppression, specifications, and standards) that are used to achieve EMC. The first step in the system-level EMC design process is to define the ambient environment. During this step, it is necessary to identify culprit EMI sources and victim circuits and specify the EMI emissions from sources and the susceptibility of victims. Information about the environment EMI sources and victims may be provided by applicable regulations and standards (i.e., EMC, safety, etc.). The next step in system-level EMC design is to identify major EMI coupling mechanisms and determine EMI suppression and control requirements that are necessary to achieve EMC. Trade-off considerations (i.e., EMI vs. safety, shielding vs. circuit design, etc.) should be addressed, and the applicable EMI fixes should be selected and incorporated. Measurements should be performed throughout the design and development process to verify compliance.
The objective of this chapter is to help engineers, designers, and technicians to optimize the functionality and reliability of their equipment by providing an orderly systems approach to grounding. Such an approach is highly preferable to the empirical and sometimes contradictory approaches that are often employed.
Shielding is a major means of EMI control at all levels of EMC. This chapter presents shielding theory, shielding materials, and some mathematical models of shielding effectiveness. The performance of shields is a function of whether the source appears as an electric or magnetic field in the near-in induction region or an electromagnetic field in the far-field region.
Electrical bonding refers to the process by which parts of an assembly, equipments, or subsystems are joined together in a manner such that they provide low contact impedance. The objective is to make the joined structures homogenous with respect to the flow of RF currents. This mitigates electrical potential differences that can produce EMI among metallic parts.
There are several different types of EMI control devices that may be placed in a conducted path (either signal or power lines) to selectively pass intended signals and reject unintended EMI signals. The rejection is provided on the basis of some characteristics of the EMI signal, which differs from the intended signal. Thus, these EMI control devices provide a means of suppressing conducted interfering signals that have certain characteristics. Filters, which are discussed in Section 8.1, discriminate between desired and interfering signals on the basis of frequency. Ferrites may also be used to provide frequency selectivity, and these devices are discussed in Section 8.2. Isolators, which are discussed in Section 8.3, discriminate between common-mode and differential-mode signals existing in the conducted path. Transient suppressors, which are discussed in Section 8.4, discriminate between signals on the basis of signal level. All four of these device types are very important in system applications, because they can usually be used at equipment inputs or outputs to control EMI problems that occur as a result of integrating the equipment into a system.
Several basic electromagnetic interference (EMI) principles determine whether an equipment will experience EMI or electromagnetic compatibility (EMC) as a result of exposure to the electromagnetic (EM) fields that are present in the equipment environment. These basic EMI principles are influenced by the way that the system is configured, including the cables. To achieve EMC, it is necessary to be careful to configure the cables in a way that does not create EMI problems. The basic EMI considerations and the resulting impact of the configuration of the cables are discussed in this chapter.
Control of EMI between sources and susceptible devices is essential if EMC is to be achieved in a complex electronic system. The electronic system designer must give careful consideration to the components that are used in the system and must define their EMI interactions with each other and with the system operational environment. The system designer must define the EMI suppression and control requirements that are necessary to achieve EMC. Also, the system designer must define the various EMI/EMC regulations and standards that apply to the system and must design the system so it satisfies these regulations and standards.
This appendix provides the basic approach to predicting capacitive and inductive cable-to-cable crosstalk based on cable lengths, wire separation, wire heights above ground, load impedances, and frequency. Figures show the circuit representation of capacitive and inductive coupling between parallel wires or circuits.