I EM wave propagation: respective phase of E and M field

AI Thread Summary
In electromagnetic wave propagation, the electric (E) and magnetic (M) fields are in phase when propagating in free space, as indicated by the intrinsic impedance of free space being real. However, in the near field or within certain materials, a phase shift of π/2 can occur between the fields. This phase difference is particularly evident in specific antenna designs, such as the ideal electric radiating dipole. The discussion highlights that while the far field behavior is consistent, the near field can exhibit complex interactions. Understanding these distinctions is crucial for accurately interpreting electromagnetic wave behavior.
timber1969
Messages
3
Reaction score
5
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
 
  • Like
Likes berkeman
Physics news on Phys.org
thank you very much for your quick and informative reply :smile::biggrin:
 
timber1969 said:
... 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?
 
timber1969 said:
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.
 
  • Like
Likes Delta2, vanhees71 and alan123hk
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)
 
  • Like
Likes Dale and vanhees71
thank you SO much to all of you :)
 
  • Like
Likes vanhees71, Delta2 and berkeman
Back
Top