EMC Question of the Week: August 27, 2018
What is the main criteria used to distinguish between electric-field coupling and radiated coupling?
- source frequency
- source impedance
- distance from source to victim in wavelengths
- minimum size of the source and victim in wavelengths
Answer
The correct answer is "c". Radiated coupling requires that the victim be located in the radiated far field of the source. If the victim is too close to the source relative to a wavelength, it will be in the reactive near field and any field coupling will be either electric- or magnetic-field coupling. The source-victim distance must also be greater than the Fraunhofer distance (2D2/λ) for radiated coupling. So while the source frequency and the size of the source and victim are important parameters, it is ultimately the distance from the source to the victim that determines whether the coupling is field coupling or radiated coupling.
It is important to recognize the difference between field coupling and radiated coupling, because the options for reducing the coupling are very different. The best options for reducing field coupling generally involve relatively minor adjustments to the distance or orientation of the source and/or victim circuits. Adjustments can also be made to the circuit impedance that have a significant effect on field coupling. On the other hand, radiated coupling is most effectively mitigated by identifying and modifying the unintentional "antennas" responsible for the coupling.
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