EMC glossary

Common EMC terms, abbreviations and measurement concepts.

AAN (asymmetric artificial network): A network used to measure common-mode conducted disturbance on communication cables, presenting a defined common-mode impedance (also called ISN).
Absorber (RF absorber): A material that converts electromagnetic energy to heat, used to line chambers so that walls do not reflect. Common types are pyramidal foam and ferrite tiles, often combined (hybrid).
ALSE: Absorber-lined shielded enclosure; the room for automotive component tests (CISPR 25, ISO 11452-2).
AMN: Artificial mains network; see LISN.
Anechoic: "Without echo": a room whose surfaces absorb rather than reflect radio waves.
Antenna factor: The ratio of the incident field strength to the voltage at the antenna terminals, used to convert a receiver reading to field strength.
Approved body: The British counterpart of a notified body, designated to carry out conformity assessment under UK product regulations.
Average detector: A detector that gives the average value of the signal envelope; used with the quasi-peak detector in emission limits.
BCI (bulk current injection): An immunity method that injects a radio-frequency current into a cable bundle through a clamp (ISO 11452-4, ISO 11451-4).
Bonding: A low-impedance electrical connection between metal parts so that they are at the same potential at high frequencies; essential for shields, enclosures and ground planes.
Broadband disturbance: A disturbance whose spectrum is wider than the measurement bandwidth (for example from sparking motors).
Burst (EFT): A train of fast transient pulses used in IEC 61000-4-4.
CDN (coupling/decoupling network): A device that injects a test disturbance on a cable while isolating auxiliary equipment.
CE marking: The EU conformity marking by which a manufacturer declares compliance with applicable EU law, including the EMC Directive.
CISPR: International Special Committee on Radio Interference (an IEC committee), the source of the emission standards and of the measuring-instrument specifications (CISPR 16).
Class A / Class B: Emission limit classes: Class A for commercial and industrial environments; Class B (stricter) for residential environments.
Common mode (CM): Current or voltage that appears the same on all conductors of a cable with respect to ground; a major cause of radiated emissions.
Common-mode choke: Two or more windings on one magnetic core that present a high impedance to common-mode current and almost none to differential-mode current.
Compatibility level: The specified level of disturbance an environment is expected not to exceed.
Conducted disturbance: Disturbance carried along conductors (mains, signal and data cables).
Coupling path: The way interference travels from a source to a victim: conducted, capacitive, inductive or radiated.
Declaration of conformity: A formal statement by the manufacturer (or supplier) that a product meets the applicable requirements.
Decoupling: Placing capacitors (or other components) so that a local current demand does not disturb a shared supply.
Differential mode (DM): Current or voltage between the conductors of a pair.
DUT / EUT: Device or equipment under test.
E mark: The approval mark of the UN 1958 Agreement: a circled capital E with the number of the approving country, followed by the approval number.
EFT: Electrical fast transient; see burst.
EMC: Electromagnetic compatibility.
EMI: Electromagnetic interference, the disturbance itself.
EMI receiver: A measuring receiver with the detectors and bandwidths required by CISPR 16-1-1.
ESA (electrical/electronic sub-assembly): In automotive regulation, an electrical or electronic device or set of devices intended to be part of a vehicle.
ESD: Electrostatic discharge.
Expanded uncertainty: The combined standard uncertainty of a measurement multiplied by a coverage factor (typically 2, for about 95 % confidence); quoted in dB for EMC emission measurements.
FAR / FAC: Fully anechoic room / chamber; absorber on all six surfaces.
Far field: The region far enough from a source that the electromagnetic wave has a fixed ratio of electric to magnetic field.
Ferrite: A magnetic ceramic that absorbs high-frequency energy; used in cable clamps, chokes and absorber tiles.
Field uniformity: The property of a calibrated test field to be nearly the same over the test area (IEC 61000-4-3).
Flicker: Perceptible variation of light output caused by voltage fluctuations on the supply.
Ground plane: A large conductive surface used as the reference potential and the return path for high-frequency currents, in a PCB, a test setup or a site.
GTEM cell: Gigahertz transverse electromagnetic cell; a tapered TEM cell with an absorbing termination.
Harmonics (mains): Currents or voltages at integer multiples of the mains frequency, limited by IEC 61000-3-2 and related standards.
Harmonised standard: In the EU, a European standard whose reference has been published in the *Official Journal*, giving a presumption of conformity.
Honeycomb vent: A ventilation opening built from many short metal tubes that acts as a waveguide below cut-off and so attenuates radio waves while letting air through.
Immunity: The ability of equipment to operate as intended in the presence of an electromagnetic disturbance (also called susceptibility).
Insertion loss: The attenuation a filter or component adds to a circuit, measured in decibels in a defined system.
ISN (impedance stabilisation network): See AAN.
Isotropic probe: A field probe that responds equally to all directions of the field.
LISN: Line impedance stabilisation network (also AMN): a device that gives the EUT a defined RF impedance and provides a measuring port for conducted noise.
Narrowband disturbance: A disturbance whose spectrum is narrower than the measurement bandwidth (for example a clock harmonic).
Near field: The region close to a source, within roughly λ/2π, where electric and magnetic fields are not related like a free wave.
Notified body: An organisation designated by an EU Member State to carry out conformity assessment tasks under EU product law; optional for the EMC Directive.
NSA (normalised site attenuation): Measure of site quality for emission measurements below 1 GHz.
OATS: Open-area test site.
Performance criteria (A, B, C): Classes that describe what degradation of function is acceptable during or after an immunity test.
Power factor correction (PFC): A circuit that makes the input current of a power converter follow the supply voltage, reducing harmonic currents.
Pre-compliance test: An informal or reduced test done during development to find problems before the formal test.
Pst / Plt: Short-term (10 minutes) and long-term (2 hours) flicker severity indices defined for the assessment of voltage fluctuations.
Quasi-peak detector: A detector with defined charge and discharge time constants that weights disturbances by their repetition rate; used in emission limits below 1 GHz.
Radiated disturbance: Disturbance carried through the air as electromagnetic fields.
RE / CE / RI / CI: Common abbreviations for radiated emissions, conducted emissions, radiated immunity and conducted immunity.
RED: The EU Radio Equipment Directive 2014/53/EU.
Return current: The current that flows back to a source along the path of least impedance; at high frequency this path is directly beneath the signal conductor.
Reverberation chamber: A shielded room with a moving stirrer that creates a statistically uniform field.
Rise time: The time a signal takes to go from 10 % to 90 % of its final value; a shorter rise time means more high-frequency content.
SAC: Semi-anechoic chamber; absorber on walls and ceiling, reflective floor.
SDoC (supplier's declaration of conformity): A conformity route in which the supplier declares, after testing and documentation, that a product meets the applicable requirements, used for many unintentional radiators in the USA.
Shielding effectiveness (SE): The attenuation of a shield, in decibels, for a given field type and frequency.
Skin depth: The depth at which the current in a conductor has fallen to about 37 % of its surface value; it shrinks with frequency and determines how thin a shield can be.
Spread-spectrum clocking: Slowly varying a clock frequency so that its energy is spread over a wider band, lowering the peak reading on the measurement detector.
Surge: A slow, high-energy transient, for example from lightning or switching (IEC 61000-4-5).
SVSWR (site voltage standing-wave ratio): Measure of reflections in a test volume above 1 GHz.
Technical documentation: The file a manufacturer prepares to show that a product meets the requirements: description, assessment, test reports and references to standards.
Technical service: In vehicle type approval, the laboratory designated by an approval authority to carry out the tests.
TEM cell: Transverse electromagnetic cell, a transmission line enclosure with a uniform field between its plates.
Transfer impedance: A measure of how much of the current on the outside of a cable shield appears as a voltage on the inside; lower is better.
Transient: A short-lived change of voltage, current or field.
TVS diode: A transient-voltage-suppression diode that clamps a voltage spike by conducting when the voltage exceeds its threshold.
Type approval: Approval of a product type by an authority, as in UN Regulation No. 10 for vehicles and components, shown by an approval mark and number.
UKCA marking: The conformity marking used in Great Britain.
UT (nominal supply voltage in dip tests): The rated supply voltage used as the reference for the depth of voltage dips in IEC 61000-4-11.
Varistor: A voltage-dependent resistor that conducts heavily above a threshold voltage and is used to absorb surges.
VCP / HCP: Vertical / horizontal coupling plane used in indirect ESD tests.
Victim: The equipment or circuit that malfunctions because of interference.
Voltage dip: A short reduction of the supply voltage, tested in IEC 61000-4-11.
X capacitor / Y capacitor: Filter capacitors connected across the lines (X) or from the lines to protective earth (Y); Y capacitors are limited by leakage-current safety rules.