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.

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.

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.

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.

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.