Electromagnetic Interference (EMI)
Electromagnetic Interference (EMI) refers to unwanted disturbances generated by electronic devices that can degrade the performance of other equipment. In compliance terminology, EMI is referred to as emissions and, together with Electromagnetic Susceptibility (EMS), constitutes one of the two core components of Electromagnetic Compatibility (EMC).
Types of EMI
EMI is categorized by how disturbances propagate:
Conducted emissions – travel through power or signal lines, typically evaluated in the range 150 kHz–30 MHz.
Radiated emissions – electromagnetic energy emitted into free space by housings, cables, or antennas, generally measured above 30 MHz.
Understanding these emission types helps identify their typical sources.
Common Sources of EMI
Typical sources of electromagnetic interference include:
Switching power supplies (harmonics, broadband noise)
Motors, relays, and welding equipment (sparks and arcing)
Digital circuits (clock harmonics, high-speed data buses)
Lighting systems (fluorescent lamps, LED drivers)
RF transmitters (mobile phones, Wi-Fi, Bluetooth devices)
Natural phenomena (lightning strikes, solar activity)
Common design measures include filtering, shielding, and proper grounding to minimize EMI generation. Identifying EMI sources early is key to effective EMC Pre-Compliance testing during product development.
Testing and Standards
EMI is evaluated through standardized emissions testing in controlled environments using spectrum analyzers and calibrated measurement equipment.
Relevant standards include:
EN 55032 (CISPR 32) – multimedia equipment emissions
EN 61000-6-3 – residential, commercial, and light-industrial environments
EN 61000-6-4 – industrial environments
FCC Part 15 Subpart B – unintentional radiators in the United States
These standards define emission limits to ensure devices do not cause interference in residential, commercial, or industrial settings.
Managing EMI is essential for achieving EMC compliance and legal market access. Manufacturers must demonstrate that their products meet emissions limits defined in international standards.
→ See also: Electromagnetic Compatibility (EMC) and Electromagnetic Susceptibility (EMS)