Mike Monett wrote:
Roy Lewallen wrote:

[...]

The traces are drawn in the order Eh, Ee, and total. During the
initial forward wave, Eh and Ee are equal, so the Ee overwrites
the Eh trace.

Good - thanks.

[...]

My problem here is someone wrote a web page that claims the
electric and magnetic fields are orthogonal:

http://www.play-hookey.com/optics/tr...etic_wave.html

You're making the same error that Cecil often does, confusing time
phase with directional vector orientation. The orthogonality of E
and H fields refers to the field orientations of traveling plane
TEM waves in lossless 3D space or a lossless transmission line, at
the same point and time.

Now you are confusing me with Cecil. I have no difficulty with the E
and H field orientation.

The E and H fields of these traveling waves are always in time
phase, not in quadrature.

Yes, that's what I tried to explain to him also.

The graphs show the magnitudes of the waves at various points
along the line. These represent neither the time phase nor the
spatial orientation of the E and H fields.

I tried sending him an email to show if the fields were
orthogonal as he claims, it would look like a pure reactance, and
no energy would be transmitted. But he is stuck on his idea and
won't budge.

Good for him - he's absolutely correct.

There is a bad mixup here. He claims:

"Note especially that the electric and magnetic fields are not in
phase with each other, but are rather 90 degrees out of phase. Most
books portray these two components of the total wave as being in
phase with each other, but I find myself disagreeing with that
interpretation, based on three fundamental laws of physics"

He claims the E and H fields are in quadrature. I claim he is wrong.

And you're right. I apologize. "Orthogonal" usually refers to spatial
orientation, so when you said that he said they're orthogonal, my
reaction was that it's correct. But I didn't look at the web page. I see
by looking at it that he also says the two are in time quadrature, which
of course is incorrect as you say. His "fundamental laws of physics" are
certainly different from everyone else's. Thanks for providing a good
example of the pitfalls of relying on the web for information.

Again my apology. You do indeed have it right. Incidentally, it's not
possible for a medium to have a purely reactive (imaginary) Z0 at any
non-zero frequency.

Roy Lewallen, W7EL

Roy Lewallen wrote:

[..]

And you're right. I apologize. "Orthogonal" usually refers to
spatial orientation, so when you said that he said they're
orthogonal, my reaction was that it's correct. But I didn't look
at the web page. I see by looking at it that he also says the two
are in time quadrature, which of course is incorrect as you say.

His "fundamental laws of physics" are certainly different from
everyone else's. Thanks for providing a good example of the
pitfalls of relying on the web for information.

Again my apology. You do indeed have it right. Incidentally, it's
not possible for a medium to have a purely reactive (imaginary) Z0
at any non-zero frequency.

Roy Lewallen, W7EL

Thanks very much, Roy. It was probably my mistake, using the word
"Orthogonal" when quadrature would probably have worked better.

Can you explain your last sentence? Why does this happen?

I have been following these threads with some interest, and I very
much appreciate your analysis, as it adds greatly to my
understanding. Thank you very much for taking the time to write so
clearly.

There is one point I still have trouble with. The concept of power
flowing in standing waves where the superposition goes to zero, and
yet the energy flow is unaffected and continues in opposite
directions on either side of the null point.

Anyway, I have googled until my fingers get sore, and I haven't
found a good explanation of why this happens. Everyone says it is
well understood from basic undergraduate theory, but the only
references I can find are from graduate studies in Quantum
Electrodynamics. This is not much help.

So I have to form some image in my mind of why these waves do not
interact. Here is a partial pictu

1. Electromagnetic waves travel at the speed of light in whatever
medium they are in. For them to interact, there must be some advance
information they are about to collide. But that would require
transferring information faster than the speed of light, which is
forbidden.

2. The fields in electromagnetic waves are at right angles to the
direction of propagation. There is no longitudinal component, and
therefore the waves have no advance warning they are about to
collide. There is no vector component that is common to both that
would allow any interaction, so there is no way this can happen.

3. Photons carry no charge. They are not deflected by electrostatic
or electromagnetic fields, and do not interact with other photons.
Electromagnetic waves are made up of photons. Since photons do not
interact, EM waves also do not interact with each other.

The above concepts seem to make sense, and allow me to get some
sleep at night. Can you tell me if they are valid, and if there are
other ways of explaining this phenomenon?

Regards,

Mike Monett

Mike Monett wrote:
Since photons do not
interact, EM waves also do not interact with each other.

The following quote sounds like an interaction of photons to me.

http://micro.magnet.fsu.edu/primer/j...ons/index.html

"... when two waves of equal amplitude and wavelength that are
180-degrees ... out of phase with each other meet, they are not
actually annihilated, ... All of the photon energy present in
these waves must somehow be recovered or redistributed in a new
direction, according to the law of energy conservation ... Instead,
upon meeting, the photons are redistributed to regions that permit
constructive interference, so the effect should be considered as
a redistribution of light waves and photon energy rather than
the spontaneous construction or destruction of light."

I suspect that coherent photons can interact at an impedance
discontinuity which causes reflections.
--
73, Cecil http://www.w5dxp.com

Mike Monett wrote:
Roy Lewallen wrote:
. . .
Again my apology. You do indeed have it right. Incidentally, it's
not possible for a medium to have a purely reactive (imaginary) Z0
at any non-zero frequency.

Roy Lewallen, W7EL

Thanks very much, Roy. It was probably my mistake, using the word
"Orthogonal" when quadrature would probably have worked better.

Can you explain your last sentence? Why does this happen?

The "non-zero" was unnecessary, and a result of a too-quick evaluation
of an equation, although the meaning of Z0 at DC isn't clear anyway.

There are at least two related ways to show that a medium can't have a
purely imaginary Z0 (more correctly, intrinsic impedance). One is to use
the telegrapher's equation for a transmission line immersed in the medium:

Z0 = sqrt((R + jwL)/(G + jwC)) (w = omega, the rotational frequency)

For Z0 to be purely imaginary, the quantity under the radical has to be
purely real and negative. A little algebraic manipulation shows that
this requires that RG + w^2LC 0. All the quantities are positive, so
it can't happen.

You can also use

Zc = sqrt(mu/ceps) where ceps = the complex permittivity, mu = the
permeability of the medium, and Zc the intrinsic impedance.

The complex permittivity ceps = eps - j*sigma/w

where eps = the real (DC) permittivity
sigma = the conductivity of the material

You end up with the same situation, where for Zc to be purely imaginary,
the quantity under the radical has to be purely real and negative, which
requires that mu * eps 0. Remember that mu and eps here are the actual
permeability and permittivity, not the relative values we often use.

A little further research reveals that there are some fairly recently
created man-made materials which have a negative permeability. Those
could presumably have a purely imaginary intrinsic impedance, provided
that they have a positive permittivity. So there might be an exception
to my statement, although it isn't something you're likely to encounter
for some time to come.

I have been following these threads with some interest, and I very
much appreciate your analysis, as it adds greatly to my
understanding. Thank you very much for taking the time to write so
clearly.

There is one point I still have trouble with. The concept of power
flowing in standing waves where the superposition goes to zero, and
yet the energy flow is unaffected and continues in opposite
directions on either side of the null point.

Anyway, I have googled until my fingers get sore, and I haven't
found a good explanation of why this happens. Everyone says it is
well understood from basic undergraduate theory, but the only
references I can find are from graduate studies in Quantum
Electrodynamics. This is not much help.

Please exclude me from the "everyone" in "everyone says". I don't say
that power flows, period. We've seen the serious traps people have
fallen into by making this assumption and trying to build from it.
That's why you won't find it in texts.

So I have to form some image in my mind of why these waves do not
interact. Here is a partial pictu

1. Electromagnetic waves travel at the speed of light in whatever
medium they are in. For them to interact, there must be some advance
information they are about to collide. But that would require
transferring information faster than the speed of light, which is
forbidden.

You don't need a reason for them to not interact, you need a reason for
them to do so. In a linear medium, there is none.

2. The fields in electromagnetic waves are at right angles to the
direction of propagation. There is no longitudinal component, and
therefore the waves have no advance warning they are about to
collide. There is no vector component that is common to both that
would allow any interaction, so there is no way this can happen.

3. Photons carry no charge. They are not deflected by electrostatic
or electromagnetic fields, and do not interact with other photons.
Electromagnetic waves are made up of photons. Since photons do not
interact, EM waves also do not interact with each other.

The above concepts seem to make sense, and allow me to get some
sleep at night. Can you tell me if they are valid, and if there are
other ways of explaining this phenomenon?

I'm glad they work for you. I'll have to leave it to others to comment
on their validity, since I don't buy into the notion of flowing power in
the first place.

Roy Lewallen, W7EL