Glossary term
Electromagnetic Interference
Unwanted electromagnetic energy that degrades, disturbs, or disrupts the operation of electrical or electronic equipment.
Definition
phenomenonUnwanted electromagnetic energy that degrades, disturbs, or disrupts the operation of electrical or electronic equipment.
Electromagnetic interference is a system-level compatibility problem involving a source, coupling path, and susceptible receiver. It may be conducted or radiated, continuous or transient, narrowband or broadband, and it can affect measurements, communication links, control systems, computing hardware, and power electronics.
Electromagnetic interference is unwanted electromagnetic coupling that causes equipment to behave incorrectly or with degraded performance. The classic model has three parts: a source that emits energy, a coupling path, and a victim or receiver that is susceptible to that energy.
Engineering role
EMI matters in power electronics, radio systems, medical devices, industrial automation, automotive electronics, aircraft systems, sensors, data links, and high-speed digital hardware. It can cause false readings, communication errors, resets, audible noise, unstable control loops, failed compliance tests, or unsafe actuator behaviour.
Coupling paths
Conducted EMI travels through cables, power lines, grounds, shields, and common impedance paths. Radiated EMI travels through electromagnetic fields. Capacitive coupling is associated with electric fields and high voltage change rates. Inductive coupling is associated with magnetic fields and high current change rates. Common-mode currents on cables are a frequent radiated-emissions mechanism.
Sources and susceptibility
Typical sources include switching converters, motor drives, relays, contactors, electrostatic discharge, lightning surges, digital clocks, RF transmitters, welding equipment, and long cables. Susceptible circuits include high-impedance sensors, analog front ends, communication receivers, reset lines, poorly filtered power rails, and circuits with weak grounding or shielding.
Mitigation
Mitigation can target the source, coupling path, or receiver. Common measures include filtering, shielding, grounding strategy, bonding, cable routing, differential signalling, twisted pairs, ferrites, snubbers, slower edge rates, proper PCB return paths, isolation, surge protection, and enclosure design. Good EMC design is usually cheaper when built in early rather than patched after testing.
Common mistakes
Common mistakes include adding shields without terminating them properly, treating ground as an ideal zero-voltage node, and testing only in a quiet lab environment. Another frequent error is fixing emissions while creating immunity problems, or vice versa. EMI diagnosis should be based on measurements, frequency content, current paths, and repeatable test conditions rather than guesswork.