Electromagnetic compatibility (EMC) is the branch of electrical sciences which studies the unintentional generation, propagation and reception of electromagnetic energy with reference to the unwanted effects (Electromagnetic Interference, or EMI) that such energy may induce. The goal of EMC is the correct operation, in the same electromagnetic environment, of different equipment which use electromagnetic phenomena, and the avoidance of any interference effects.
In order to achieve this, EMC pursues two different kinds of issues. Emission issues are related to the unwanted generation of electromagnetic energy by some source, and to the countermeasures which should be taken in order to reduce such generation and to avoid the escape of any remaining energies into the external environment. Susceptibility or immunity issues, in contrast, refer to the correct operation of electrical equipment, referred to as the victim, in the presence of unplanned electromagnetic disturbances.
Interference, or noise, mitigation and hence electromagnetic compatibility is achieved primarily by addressing both emission and susceptibility issues, i.e., quieting the sources of interference and hardening the potential victims. The coupling path between source and victim may also be separately addressed to increase its attenuation.
Types of Interference
Electromagnetic interference divides into several categories according to the source and signal characteristics.
The origin of noise can be man made or natural.
Continuous Interference
Continuous Interference arises where the source regularly emits a given range of frequencies. This type is naturally divided into sub-categories according to frequency range, and as a whole is sometimes referred to as "DC to daylight".
Audio Frequency, from very low frequencies up to around 20 kHz. Frequencies up to 100 kHz may sometimes be classified as Audio. Sources include:
Mains hum from power supply units, nearby power supply wiring, transmission lines and substations.
Radio Frequency Interference, RFI, from 20 kHz to a limit which constantly increases as technology pushes it higher. Sources include:
Wireless and Radio Frequency Transmissions
Television and Radio Receivers
Industrial, scientific and medical equipment
High Frequency Circuit Signals (For example microcontroller activity)
Broadband noise may be spread across parts of either or both frequency ranges, with no particular frequency accentuated. Sources include:
Solar Activity
Continuously operating spark gaps such as arc welders
Pulse or Transient Interference
Electromagnetic Pulse, EMP, also sometimes called Transient disturbance, arises where the source emits a short-duration pulse of energy. The energy is usually broadband by nature, although it often excites a relatively narrow-band damped sine wave response in the victim.
Sources divide broadly into isolated and repetitive events.
Sources of isolated EMP events include:
Switching action of electrical circuitry.
Electrostatic Discharge (ESD), as a result of two charged conductors coming into close proximity or even contact.
Lightning Electromagnetic Pulse (LEMP)
Nuclear Electromagnetic Pulse (NEMP), as a result of a nuclear explosion.
Non-Nuclear Electromagnetic Pulse, NNEMP weapons.
Power Line Surges/Pulses
Sources of repetitive EMP events, sometimes as regular pulse trains, include:
Electric Motors
Electric Fast Transient/Bursts (EFT)
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