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

• I
• timber1969
In summary, EM waves propagate in free space as a waveform consisting of electric and magnetic fields in phase. However, when the waves are near a material or object they may have a phase shift depending on the location.
timber1969
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

berkeman

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.

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)

Dale and vanhees71
thank you SO much to all of you :)

vanhees71, Delta2 and berkeman

## 1. What is an EM wave?

An EM (electromagnetic) wave is a type of energy that is created by the movement of electrically charged particles. It consists of two components, an electric field and a magnetic field, which oscillate perpendicular to each other and travel through space at the speed of light.

## 2. How do EM waves propagate?

EM waves propagate through space in a straight line. They are able to travel through a vacuum, as well as through various materials, such as air, water, and solids. The strength of the wave decreases as it travels further away from its source.

## 3. What is the phase of an EM wave?

The phase of an EM wave refers to the position of the wave at a given point in time. It is determined by the relative positions of the electric and magnetic fields, and can be described as either in-phase or out-of-phase.

## 4. How does the phase of the E and M fields affect EM wave propagation?

The phase of the E and M fields determines the direction and polarization of the wave. In-phase fields create a wave that propagates in a straight line, while out-of-phase fields create a wave that is circularly polarized. This can affect how the wave interacts with different materials and objects it encounters.

## 5. Can the phase of an EM wave be manipulated?

Yes, the phase of an EM wave can be manipulated through various methods, such as using antennas or reflectors to change the direction and polarization of the wave. This is important in many applications, such as wireless communication and radar systems.

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