Electromagnetic compatibility (EMC) engineering rests on a precise, shared vocabulary. Designers, test engineers, and standards bodies must mean the same thing when they use terms such as "disturbance," "interference," "immunity," and "susceptibility"; otherwise design reviews, test reports, and compliance discussions lose their rigor and drift into ambiguity. This reference consolidates the core EMC terminology defined in Chapter 161 of the International Electrotechnical Vocabulary (IEV), organized into three connected areas: basic concepts, disturbance waveforms, and interference control. Each entry presents the standardized English term together with its formal definition, so the material can be applied directly when writing test plans, interpreting standards, or training new engineers.
The distinctions these definitions draw carry real engineering consequences. Separating a disturbance (the cause) from interference (the effect) determines how a problem is diagnosed and where a fix should be applied. Waveform parameters such as rise time, burst duration, and click rate define what a measurement actually reports and whether a result is comparable across test houses.
Highlights:
- Electromagnetic disturbance is the cause, while electromagnetic interference (EMI) is the resulting degradation of equipment, transmission channel, or system performance.
- Immunity and susceptibility are inverse descriptions of the same behavior: a device with high susceptibility has low immunity, and vice versa.
- Waveform descriptors such as rise time, burst, click, and click rate provide the measurable parameters used to classify emissions and judge compliance.
Comprehensive Glossary of EMC Terminology
The terminology in this reference is identical to that of Chapter 161 (1990 edition) of the International Electrotechnical Vocabulary (IEV), published by the International Electrotechnical Commission (IEC). The standard defines the terms commonly used in electromagnetic compatibility (EMC), providing a consistent terminology framework for PCB EMC design, electromagnetic compatibility standards, and other technical documents. Responsibility for the vocabulary rests with IEC TC 1 (Terminology), Working Group 161, working jointly with IEC TC 77 (Electromagnetic compatibility of electrical equipment, including networks) and CISPR (the International Special Committee on Radio Interference). This vocabulary constitutes IEV Chapter 161 and replaces IEC publication 50(902) (1973).
1. Basic Concepts
The basic concepts establish the vocabulary on which every later definition depends, from the definition of the electromagnetic environment itself to the relationship between immunity and susceptibility.
1.1 Electromagnetic environment: The sum total of all electromagnetic phenomena existing in a given location.
1.2 Electromagnetic noise: A time-varying electromagnetic phenomenon that apparently does not convey information; it may be superimposed on, or combined with, wanted signals.
1.3 Unwanted signal, undesired signal: A signal that may impair the reception of a wanted signal.
1.4 Interfering signal: A signal that impairs the reception of a wanted signal.
1.5 Electromagnetic disturbance: Any electromagnetic phenomenon that may degrade the performance of a device, equipment, or system, or may adversely affect living or non-living matter. Note: An electromagnetic disturbance may be electromagnetic noise, an unwanted signal, or a change in the propagation medium itself.
1.6 Electromagnetic interference (EMI): Degradation of the performance of equipment, a transmission channel, or a system caused by an electromagnetic disturbance.
1.7 Electromagnetic compatibility (EMC): The ability of equipment or a system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbance to anything in that environment.
1.8 (Electromagnetic) emission: The phenomenon by which electromagnetic energy emanates from a source.
1.9 Emission (in radiocommunication): The phenomenon by which radio waves or signals are produced and radiated outward by a radio transmitting station.
1.10 (Electromagnetic) radiation: a. The phenomenon by which energy is radiated from a source into space in the form of electromagnetic waves; b. The propagation of energy in space in the form of electromagnetic waves. Note: The meaning of the term "electromagnetic radiation" is sometimes extended to include the phenomenon of electromagnetic induction.
1.11 Radio environment: a. The electromagnetic environment within the radio-frequency range; b. The sum total of the electromagnetic fields produced in a given location by all radio transmitters in operation.
1.12 Radio (frequency) noise: Electromagnetic noise having components in the radio-frequency range.
1.13 Radio (frequency) disturbance: Electromagnetic disturbance having components in the radio-frequency range.
1.14 Radio frequency interference (RFI): Degradation of the reception performance of a wanted signal caused by radio disturbance.
1.15 Inter-system interference: Electromagnetic interference caused to one system by electromagnetic disturbance generated by other systems.
1.16 Intra-system interference: Electromagnetic interference occurring within a system that is caused by electromagnetic disturbance originating inside that same system.
1.17 Natural noise: Electromagnetic noise originating from natural phenomena rather than from man-made devices.
1.18 Man-made noise: Electromagnetic noise originating from man-made devices.
1.19 Degradation (of performance): An undesired departure of the operating performance of a device, equipment, or system from its normal performance.
1.20 Immunity (to a disturbance): The ability of a device, equipment, or system to operate without degradation of performance in the presence of an electromagnetic disturbance.
1.21 (Electromagnetic) susceptibility: The inability of a device, equipment, or system to avoid degradation of performance in the presence of an electromagnetic disturbance. Note: High susceptibility corresponds to low immunity.
2. Disturbance Waveforms
Disturbance waveforms are described by parameters that make emissions measurable and comparable. The definitions below cover transient events, pulse shapes, spectral components, and the coefficients used to quantify ripple and harmonic content.
2.1 Transient (adjective and noun): A physical quantity or physical phenomenon that changes between two adjacent steady states, with a transition time smaller than the time scale of interest.
2.2 Pulse: A physical quantity that changes abruptly within a short time and then returns rapidly to its initial value.
2.3 Impulse: A pulse that, for a given application, approximates a unit pulse or a Dirac function.
2.4 Spike: A unidirectional pulse of relatively short duration.
2.5 Rise time (of a pulse): The time interval during which the instantaneous value of a pulse first rises from a specified lower limit to a specified upper limit. Note: Unless otherwise specified, the lower and upper limits are set at 10% and 90% of the pulse amplitude, respectively.
2.6 Rate of rise: The average rate of change of a quantity with time over a specified range, from 10% to 90% of its peak value.
2.7 Burst (of pulses or oscillations): A sequence of a limited number of distinct pulses, or an oscillation of limited duration.
2.8 Impulsive noise: Noise appearing at a specific device as a sequence of distinct pulses or transients.
2.9 Impulsive disturbance: Electromagnetic disturbance appearing at a specific device or equipment as a sequence of distinct pulses or transients.
2.10 Continuous noise: Noise whose effect on a specific device cannot be resolved into a sequence of distinct effects.
2.11 Continuous disturbance: Electromagnetic disturbance whose effect on a specific device cannot be resolved into a sequence of distinct effects.
2.12 Quasi-impulsive noise: Noise equivalent to the superposition of impulsive noise and continuous noise.
2.13 Discontinuous interference: Electromagnetic interference occurring within defined time intervals separated by interference-free intervals.
2.14 Random noise: Noise whose instantaneous value at a given moment cannot be predicted.
2.15 Click: Electromagnetic disturbance whose duration, when measured by a specified method, does not exceed a specified value.
2.16 Click rate: The number of clicks per unit time (usually per minute) that exceed a specified level.
2.17 Fundamental (component): The first-order component of the Fourier series of a periodic quantity.
2.18 Harmonic (component): A component of the Fourier series of a periodic quantity whose order is higher than one.
2.19 Harmonic number: The integer ratio of a harmonic frequency to the fundamental frequency. Note: The harmonic number is also called the harmonic order.
2.20 nth harmonic ratio: The ratio of the r.m.s. value of the nth harmonic to the r.m.s. value of the fundamental.
2.21 Harmonic content: The quantity obtained by subtracting the fundamental component from an alternating quantity.
2.22 Fundamental factor: The ratio of the r.m.s. value of the fundamental component to the r.m.s. value of the alternating quantity to which it belongs.
2.23 (Total) harmonic factor: The ratio of the r.m.s. value of the harmonic content to the r.m.s. value of the alternating quantity to which it belongs.
2.24 Pulsating: A term used to describe a periodic quantity having a non-zero mean value.
2.25 Alternating component: The quantity obtained by removing the direct component from a pulsating quantity. Note: The alternating component is sometimes called ripple content.
2.26 Peak-ripple factor: The ratio of the difference between the peak and the trough of the ripple of a pulsating quantity to the absolute value of its direct component.
2.27 r.m.s.-ripple factor: The ratio of the r.m.s. value of the ripple content of a pulsating quantity to the absolute value of its direct component.
3. Interference Control
Interference control terms describe how disturbance is coupled into equipment, quantified at defined points, and ultimately limited. They cover mains-borne coupling, cabinet radiation, the distinction between internal and external immunity, and the levels at which compliance is judged.
3.1 Level (of a time-varying quantity): The mean or weighted value of a time-varying quantity such as power or a field parameter, determined in a specified manner over a specified time interval. Note: The level may be expressed logarithmically, for example as decibels relative to a reference value.
3.2 Mains-borne disturbance: Electromagnetic disturbance transmitted to a device via the supply mains.
3.3 Mains immunity: Immunity to mains-borne disturbance.
3.4 Mains decoupling factor: The ratio of the voltage applied at a specified point on the supply mains to the voltage applied at a specified input terminal of the device that produces the same disturbance effect on that device.
3.5 Cabinet radiation: Radiation produced by the enclosure of equipment, excluding radiation from connected antennas or cables.
3.6 Internal immunity: The ability of a device, equipment, or system to function normally without degradation of performance when electromagnetic disturbance is present at its normal input terminals or antenna.
3.7 External immunity: The ability of a device, equipment, or system to function normally without degradation of performance when electromagnetic disturbance enters by paths other than the normal input terminals or antenna.
3.8 Limit of disturbance (permissible value): The maximum permitted level of electromagnetic disturbance for a specified measurement method.
3.9 Limit of interference (permissible value): The maximum permitted degradation of performance of a device, equipment, or system caused by electromagnetic disturbance.
Electromagnetic Compatibility Level
The specified maximum electromagnetic disturbance level expected to be applied to a device, equipment, or system under specified conditions. This level serves as a reference for comparing emission and immunity margins. Note: in practice, the electromagnetic compatibility level is not an absolute maximum and may be exceeded with a small probability.
Emission Level (of a Disturbance Source)
The level of a given electromagnetic disturbance emitted by a specific device, equipment, or system, measured by a specified method. The emission level therefore describes the actual disturbance produced by the source under the defined measurement conditions.
Emission Limit (from a Disturbance Source)
The specified maximum emission level for an electromagnetic disturbance source. The emission limit defines the permitted upper bound against which the measured emission level is assessed.
Emission Margin
The difference between the electromagnetic compatibility level of a device, equipment, or system and the emission limit. The emission margin indicates how much separation exists between the compatibility reference level and the permitted emission boundary.
Immunity Level
The maximum disturbance level at which a given electromagnetic disturbance applied to a device, equipment, or system still allows normal operation and maintenance of the required performance level. It characterizes the disturbance level that the equipment can withstand under the specified conditions.
Immunity Limit
The specified minimum immunity level. The immunity limit establishes the required lower bound for immunity performance and is used as the reference for assessing whether the equipment meets the specified immunity requirement.
Immunity Margin
The difference between the immunity limit of a device, equipment, or system and the electromagnetic compatibility level. The immunity margin shows the separation between the required minimum immunity level and the compatibility reference level.
(Electromagnetic) Compatibility Margin
The difference between the immunity level of a device, equipment, or system and the emission limit of the disturbance source. This margin relates the immunity capability of the equipment to the permitted emission level of the source.
Coupling Factor
In a given circuit, the coupling factor is the ratio of the electromagnetic quantity at a defined destination position to the corresponding electromagnetic quantity at the defined source position when coupling occurs from one specified position to another. The electromagnetic quantity is usually voltage or current.
Coupling Path
The path through which part or all of the electromagnetic energy is transmitted from a specified source to another circuit or device. The coupling path identifies the route by which electromagnetic energy reaches the victim circuit or equipment.
Earth-Coupled Interference, Ground-Coupled Interference
Electromagnetic interference caused when electromagnetic disturbance is coupled from one circuit to another through a common ground or ground circuit. The common ground or ground circuit therefore acts as the coupling route between the circuits.
Earthing Inductor, Grounding Inductor
An inductor connected in series with the grounding conductor of equipment. The earthing inductor is placed in the ground path rather than in the signal or power path.
Disturbance Suppression
Measures taken to weaken or eliminate electromagnetic disturbance. Disturbance suppression targets the disturbance itself before or during its coupling to the affected circuit or equipment.
Interference Suppression
Measures taken to weaken or eliminate electromagnetic interference. Interference suppression addresses the interference condition that affects the circuit or equipment.
Suppressor, Suppression Component
A component designed specifically to suppress disturbance. The suppressor is dedicated to reducing or eliminating the disturbance rather than performing a general circuit function.
Screen
A measure used to reduce the penetration of a field into a specified region. The screen limits the field that reaches the protected region.
Electromagnetic Screen
A screen made of conductive material that reduces the penetration of an alternating electromagnetic field into a specified region. The conductive material provides the shielding action against the alternating electromagnetic field.
Related Reading:
EMC Engineer Skills and Common Components: Chokes, Ferrite Beads, Filter Capacitors
EMC Design Principles and EMI/EMC Questions for PCB Engineers
PCB EMC Design Q&A: Differential Pairs, Grounding and Filtering
FCC and EMC Compliance Requirements Explained for PCB Design
Ferrite Beads vs. Inductors for High-Frequency Filtering on PCBs
Class-D Amplifier PCB Routing: EMC, Power, and ESD Essentials
EMC Measurement, Equipment Classification, and Transceiver Terms
Power Control, Supply Impedance, and Flicker Terminology Explained
Internal EMC Design and PCB Layout Techniques for Electronic Products
