EMC Question of the Week: October 12, 2020

Three essential elements of an EMC problem: Source, Coupling Path, Victim.

Which EM coupling mechanism is proportional to the source voltage, rather than the source current?

  1. common-impedance coupling
  2. electric-field coupling
  3. magnetic-field coupling
  4. radiated coupling


The best answer is "b". Electric fields are proportional to voltage differences. They are relatively independent of currents, except to the extent that the currents produce voltage differences.

Common-impedance coupling, magnetic-field coupling and radiated coupling all tend to be determined by the source currents. This is particularly true when a weak-coupling assumption can be made (i.e. the victim circuit's impedance does not appreciably affect the source circuit voltages and currents). 

Of course, there are generally many voltages and currents in a given source circuit, and they are not independent of one another. Determining which voltage or current is responsible for the coupling is a key step in identifying and modeling the interference.

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