Electromagnetic interference: a tutorial

The treatment of electromagnetic interference (EMI) problems is perceived by many engineers as a generally unscientific, hit or miss, procedure. The intent of this tutorial is to present a practical, understandable, and straightforward approach to solving interference problems. The paper will address the concepts of circuit-to-world mutual isolation and effective energy-blocking boundaries between equipment and environment, and will cover in some detail problem detection, problem analysis, and possible problem. The emphasis will be on electromagnetic compatibility between equipment and its environment, including neighboring equipment and EMI test specification limits, in a cost-effective manner with reasonable margins of safety. The need to analyze a problem before attempting to solve it will be stressed. Common fix methods will be discussed, including grounding, bonding, filtering, and shielding. Common mistakes will be discussed. Both "rules of thumb" and simple, but helpful, equations will be listed. The EMI implications of ever increasing digital computer clock speeds and lowered logic voltages on future emissions and susceptibility fix methods will be presented. The author has extensive professional experience in aerospace and military EMI control (since 1973), yet the concepts presented in the paper are equally applicable to medical, and industrial Specification limits, test methods, and allowed fixes in these diverse fields vary, but the physical laws involved are identical.