Electromagnetic Interference (EMI)

Electromagnetic interference (EMI) is the degradation of equipment performance caused by an electromagnetic disturbance. Such disturbances may originate from electrical or electronic equipment or from natural sources. In electromagnetic compatibility (EMC) assessment, emissions describe disturbances produced by a source, while immunity describes equipment’s ability to operate as intended in their presence. Electromagnetic susceptibility (EMS) describes the corresponding vulnerability to those disturbances.

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 IEC 61000-6-3:2021 – equipment in residential environments and at other locations outside the scope of EN IEC 61000-6-8 and EN IEC 61000-6-4; in cases of doubt, EN IEC 61000-6-3 applies

• EN IEC 61000-6-8 – professional equipment in commercial and light-industrial environments where no more specific product or product-family standard applies

• 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)