EM wave propagation: respective phase of E and M field

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  • #1
timber1969
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TL;DR Summary
are E and M field in phase (far field)?
Hi alltogether,

I have been confused about a certain topic of EM wave propagation:

it´s clear to me that E and M field are perpendicular to each other (I know Maxwell´s equations well).

But:
sometimes you can find on the internet that both fields are in phase:
https://i.stack.imgur.com/aeoHQ.jpg

... whereas in other cases there is a phase shift of pi/2 respective to each other:
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRSjCbPyMVkBNOOJXtZ3o0cO7T1xXp58OZ2Cg&usqp=CAU

So my question is: what is correct and why?

Thank you very much in advance and best regards,
Tim
 

Answers and Replies

  • #3
timber1969
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thank you very much for your quick and informative reply :smile::biggrin:
 
  • #4
jtbell
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... whereas in other cases there is a phase shift of pi/2 respective to each other:
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRSjCbPyMVkBNOOJXtZ3o0cO7T1xXp58OZ2Cg&usqp=CAU
What is the context of this diagram? Does it describe propagation outward from a localized source (in which case one would expect the wave amplitude to decrease with distance, as shown)? Or does it describe propagation through a medium that absorbs or attenuates the wave? Or what?

Can you provide a link or reference to the original source?
 
  • #5
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Summary: are E and M field in phase (far field)?

So my question is: what is correct and why?
For a wave propagating in free space far from any sources they will be in phase. However, in materials and in the near field the phase may be different. Your second image might be showing the near field of some specific antenna design.
 
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  • #6
Delta2
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Yes as @Dale said, in the far field E and B are in phase. But in the near field all sorts of "crazy" things can happen, the fields having phase difference up to ##\frac{\pi}{2}##, that's exactly what happens in the fields of an ideal electric radiating dipole (Hertzian dipole)
 
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  • #7
timber1969
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thank you SO much to all of you :)
 
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