EMI (Electromagnetic Interference)

Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning.

In the case of a data path, these effects can range from an increase in error rate to a total loss of the data. Both man-made and natural sources generate changing electrical currents and voltages that can cause EMI: ignition systems, cellular network of mobile phones, lightning, solar flares, and auroras (Northern/Southern Lights).

EMI frequently affects AM radios. It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy. EMI can be used intentionally for radio jamming, as in electronic warfare.

Types of EMI

Electromagnetic interference can be categorized as follows:

  • Narrowband EMI or RFI interference typically emanates from intended transmissions, such as radio and TV stations or mobile phones.
  • Broadband EMI or RFI interference is unintentional radiation from sources such as electric power transmission lines.

Conducted electromagnetic interference is caused by the physical contact of the conductors as opposed to radiated EMI, which is caused by induction (without physical contact of the conductors). Electromagnetic disturbances in the EM field of a conductor will no longer be confined to the surface of the conductor and will radiate away from it. This persists in all conductors and mutual inductance between two radiated electromagnetic fields will result in EMI.

In accordance with ITU RR (article 1) variations of interference are classified as follows:

  • Permissible interference
  • Acceptable interference
  • Harmful interference
Related Articles