Types of disturbances

Solving EMC problems, by limiting controllable emissions and by improving the immunity of susceptible devices or systems, first of all involves trying to identify not only the victim equipment but also the source and the path of the disturbance between them. In practice, clear identification of the source or the path is often difficult and sometimes even impossible, but the way in which source and victim are coupled may be described in general terms as being through:

• an electric current or voltage;
• an electric field;
• a magnetic field;
• an electromagnetic field; or often
• some complex combination of these.

The IEC has classified these principal EM disturbance phenomena in six categories so that its technical committees can take a systematic approach in preparing EMC standards for all kinds of products and systems. Of the six, two are conducted, two are radiated, one is electrostatic discharge (ESD) and one covers special high-power EM transients including nuclear high-altitude electromagnetic pulse (HEMP).