Bill Kimmel

Like it or not, most electronic designs today are subject to formal EMI testing. So even if you are new to EMI/EMC (electromagnetic interference/compatibility), you need to understand what is involved and how to best prepare for a trip to the EMI test lab.

It’s been said that nobody grows up wanting to be an EMC engineer. Rather, it usually just happens. Maybe you had incriminating information on your resume, such as being a radio ham. “You’ve created interference, so you must know how to stop it, right?” Maybe you showed a knack for EMC troubleshooting, and suddenly you’re now the company expert - whether you want to be or not.

Sooner or later, anyone involved with EMI will be involved in troubleshooting an EMI problem, wherever it may surface. Most commonly, the problems will be uncovered during EMI testing, generally very late in the product design cycle, resulting in costly patches and schedule delays. It is best if preliminary EMI testing is done early in the design stage - EMI problems can be uncovered early enough that corrective action can be done in a timely fashion, ideally at the circuit board level. On the back end, EMI problems are often encountered in the field - perhaps because the environment is harsher than that expected by the regulatory agencies or because of an installation problem.

Considering EMC techniques during the design phase will minimize EMC problems and avoid disasters uncovered at EMC test time. At this time, the remedial measures are usually very painful.

In the typical case, where the electronic equipment is contained within a single enclosure, enclosure shielding along with cable filtering or shielding are commonly employed to meet EMC requirements.

Every EMI (electromagnetic interference) problem ultimately starts or ends at an electronic circuit. And since electronic components are the building blocks of circuits, it only makes sense to pay attention to the EMI impact of those individual components.

Probably the most important thing to remember about electronic components is that nothing is ideal. Components change values with frequency, current, voltage, and even physical size. And those changes may be nonlinear, adding a new level of complexity. Like a pilot, you need to know the limits so you stay within the envelope of safe performance.

Shielding to control EMI is a staple in modern electronics, playing a major role in military applications. Internal design practices can do much to control EMI in commercial and industrial electronics, but there is a limit to how much you can do. The EMI demands in military electronics are such that good internal design practices are inadequate - shielding is usually needed.