Discussion of Electromagnetic interference
Electromagnetic interference can come from a number of different sources and be categorized in a number of different ways. EMI sources can be natural or man-made. They can be categorized by duration like continuous interference or impulse “noise” (noise meaning interference), or categorized by bandwidth (narrow or broad band). How does EMI happen? Normally EMI occurs from a coupling mechanism (or path) caused by one of the following models.
Conduction by electric current effect: Conducted noise is coupled between two or more components through interconnecting wires like a power supply or ground wires. Common impedance coupling is caused when currents from two or more circuits flow through the same component or circuit. Most conducted coupling between pieces of equipment occurs through AC power lines.
Radiation by electromagnetic effect: In the near field condition, E field (electric) and H field (magnetic) coupling are diagnosed separately (mainly for electric field issues). In the far field condition, coupling is treated as a plane wave (mainly for radiated electromagnetic field issues).
Induction by electric field or magnetic field effect: -- Inductive Coupling: Magnetic field coupling is caused by current flow in conductors. The coupling mechanism may be modeled by a transformer.
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