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There are many threads on EMP and the relationship between electric and magnetic components of electromagnetic radiation, but I don't think this particular question has been asked.

It has been my understanding that in order to test the shielding effectiveness of an enclosure under EMP conditions, it's necessary to test for both electric SE and magnetic SE. But an engineer recently caused me to question this. In my understanding, his opinion is that only electric SE needs to be measured.

So my question, which exposes my lack of a background in physics, is this: In electromagnetic radiation, is it possible for either the electric or magnetic component to dominate? Specifically, is it possible that in high-altitude nuclear EMP, in which energy is transferred over long distances via electromagnetic radiation, that the electric component, which produces a field of 50 kV/m, is accompanied by a negligible magnetic component? Another way of asking this might be: is it possible that the amount of energy transferred in the magnetic component is weak in comparison to the amount of energy transferred in the electric component? Or, are the electric and magnetic components in EMR always present in some consistent ratio and always equivalent in the amount of energy they transfer?

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I learned that the basic principle of wave impedance applies. Wave impedance is the ratio of the electric and magnetic components of a wave traveling through a medium. Z = E/H. The wave impedance of EMR traveling though free space is 377 ohms. So, for all EMR traveling through air, including NEMP, the electric component is 377 times as strong as its magnetic component. Also, the engineer clarified that he didn't mean to imply that magnetic testing isn't necessary.

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