"Waves of Average Power"
 

Guess it's time to re-post a posting I made on this newsgroup on April
9. Here it is:

-----------------------------

I'd vowed that I wouldn't hit this tarbaby yet again. But here I go.

Among the junk science being bandied about here is the following
supposition:

Suppose you have beams from two identical coherent lasers which, by a
system of (presumably partially reflective and partially transmissive)
mirrors, are made to shine in exactly the same direction from the same
point (which I'll call the "summing point"). Further, suppose that the
paths from the two lasers to this summing point differ by an odd number
of half wavelengths. So beyond the summing point, where the laser beams
exactly overlie each other, there is no beam because the two exactly
cancel. Or, in other words, the sum of the two superposed fields is
zero. The recurring argument is that because each laser is producing
energy and yet there is no net field and therefore no energy in the
summed beams, something strange has happened at the summing point (or
"virtual short circuit"), and creative explanations are necessary to
account for the "missing energy". One such proposed explanation is that
the mere meeting of the two beams is the cause of some kind of a
reflection of energy, and that each wave somehow detects and interacts
with the other.

Well, here's what I think. I think that no one will be able to draw a
diagram of such a summing system which doesn't also produce, due solely
to the reflection and transmission of the mirrors, a beam or beams
containing exactly the amount of energy "missing" from the summed beam.
No interaction(*) of the two beams at or beyond the summing point is
necessary to account for the "missing" energy -- you'll find it all at
other places in the system. Just as you do in a phased antenna array,
where the regions of cancelled field are always accompanied by
complementary regions of reinforced field. Somewhere, in some bounce
from a mirror or pass through it, the beams will end up reinforcing each
other is some other direction. My challenge is this: Sketch a system
which will produce this summation of out-of-phase beams, showing the
reflectivity and transmissivity of each mirror, and showing the beams
and their phases going in all directions from the interactions from each
mirror. Then show that simple interaction of the beams with the mirrors
is insufficient to account for the final distribution of energy.

Next, do the same for a transmission line. Show how two coherent
traveling waves can be produced which will propagate together in the
same direction but out of phase with each other, resulting in a net zero
field at all points beyond some summing point. But also calculate the
field from waves reflected at the summing point and elsewhere in the
system due to simple impedance changes. Show that this simple analysis,
assuming no interaction between the traveling waves, is insufficient to
account for all the energy. A single case will do.

Until someone is able to do this, I'll stand firm with the unanimous
findings of countless mathematical and practical analyses which show
superposition of and no interaction between waves or fields in a linear
medium.

(*) By "interaction" I mean that one beam or wave has an effect on the
other, altering it in some way -- for example, causing it to change
amplitude, phase, orientation, or direction. I'm not including
superposition, that is the fact that the net field of the two waves is
the sum of the two, in the meaning of "interaction".

-------------------

As far as I know, nobody has been able to do this. But I see that hasn't
done anything to dampen Cecil's claims. Apparently having waves be able
to detect other waves and bounce off of them when need be is necessary
in order to get some other creative theories to work out. So I can
understand why it's hard to let go of such a compelling idea.

Roy Lewallen, W7EL

"Waves of Average Power"
 

Roy Lewallen wrote:
As far as I know, nobody has been able to do this.

Good grief - the *interaction* between two waves that causes
wave cancellation is what makes non-reflective glass work
and has been described tens of times on this newsgroup. Here
it is again:

www.mellesgriot.com/products/optics/oc_2_1.htm

"Clearly, if the wavelength of the incident light and the thickness of
the film are such that a phase difference exists between reflections of
p, then reflected wavefronts interfere destructively, and overall
reflected intensity is a minimum. If the two reflections are of equal
amplitude, then this amplitude (and hence intensity) minimum will be
zero." (Referring to 1/4 wavelength thin films.)

"In the absence of absorption or scatter, the principle of conservation
of energy indicates all 'lost' reflected intensity will appear as
enhanced intensity in the transmitted beam. The sum of the reflected and
transmitted beam intensities is always equal to the incident intensity.
This important fact has been confirmed experimentally."

micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/waveinteractions/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."

Two waves interact and their combined energy is redistributed in a
new direction. In a transmission line, the two waves of equal amplitude
and opposite phase cease to exist in one direction. Their energy is
redistributed in the only other direction possible, i.e. the opposite
direction. The conservation of energy principle will allow nothing else.
If reflected energy stops flowing in one direction at a Z0-match in a
transmission line, it must flow in the only other direction possible.

Superposition does not always result in interference but sometimes
it does. Interference does not always result in wave cancellation
but sometimes it does. Wave cancellation is a subset of interference.
One wave cannot be canceled. It takes the interaction of two waves
in order to cancel both and the energy has to go somewhere.
--
73, Cecil http://www.w5dxp.com

"Waves of Average Power"
 

Christopher Cox wrote:
There's always heat....

I suspect the heat generated at the surface of non-reflective
glass is negligible.
--
73, Cecil http://www.w5dxp.com

"Waves of Average Power"
 

On Nov 1, 8:51 pm, Cecil Moore wrote:

Good grief - the *interaction* between two waves that causes
wave cancellation is what makes non-reflective glass work

Ah, very interesting. So you're saying that the "non-reflective
glass" is a non-linear medium, then. I'm very happy to have learned
that little tidbit. Thank you.

Cheers,
Tom

"Waves of Average Power"
 

Roy Lewallen wrote:

My challenge is this: Sketch a system
which will produce this summation of out-of-phase beams, showing the
reflectivity and transmissivity of each mirror, and showing the beams
and their phases going in all directions from the interactions from each
mirror. Then show that simple interaction of the beams with the mirrors
is insufficient to account for the final distribution of energy.

That is the crux of the issue. The problem as I see it Roy, is that a
very well respected (and deservedly so) member of the group has
written an otherwise excellent book in which it is proposed that
reflectivity is dependent to an extraordinarily large extent upon the
way reflective surfaces are irradiated. And further, that these
surfaces can change from being partially reflective in both directions
to being 100% reflective in one direction and totally non-reflective
in the other dependent upon the relative phase of waves impinging upon
the surface. I believe that, to a large extent, it is from this idea
that the whimsical explanations may have derived.

73, ac6xg

"Waves of Average Power"
 

K7ITM wrote:
Cecil Moore wrote:
Good grief - the *interaction* between two waves that causes
wave cancellation is what makes non-reflective glass work

Ah, very interesting. So you're saying that the "non-reflective
glass" is a non-linear medium, then.

I am saying no such thing!

If there were anything non-linear about wave cancellation
the result would be harmonic generation but we know that
no harmonics are generated by the *linear* phasor addition
of two coherent sine waves of equal amplitude and opposite
phase collinear in the same direction. In a transmission line,
the energy involved in wave cancellation of two coherent waves
is "redistributed to regions that permit constructive
interference" (per the FSU web page). In a transmission
line, only one other direction is available for the
"redistribution of energy", i.e. the direction opposite from
the direction of the canceled waves, and the resultant
redistributed energy wave continues to be coherent with the
original two canceled waves. There is no non-linearity!

If two waves traveling in one direction in a transmission
line are canceled, their energy cannot continue in the
same direction and that energy cannot be destroyed. Since
there are only two directions available in a transmission
line, it is a no-brainer to figure out which direction the
energy goes.
--
73, Cecil http://www.w5dxp.com

"Waves of Average Power"
 

Jim Kelley wrote:
That is the crux of the issue. The problem as I see it Roy, is that a
very well respected (and deservedly so) member of the group has written
an otherwise excellent book in which it is proposed that reflectivity is
dependent to an extraordinarily large extent upon the way reflective
surfaces are irradiated. And further, that these surfaces can change
from being partially reflective in both directions to being 100%
reflective in one direction and totally non-reflective in the other
dependent upon the relative phase of waves impinging upon the surface.
I believe that, to a large extent, it is from this idea that the
whimsical explanations may have derived.

I agree 100% with the above. Given the surfaces, they
cannot change from being partially reflective. Reflections
from those surfaces are fixed by the *physical* mediums
chosen which result in a fixed *physical* reflection
coefficient. Any reflection coefficient that deviates
from the *physical* reflection coefficient is a
virtual result and is not needed. The virtual reflection
coefficient looking forward into a Z0-match is 0.0.
The virtual reflection coefficient looking backward
into a Z0-match is 1.0. That is the crux of the
problem. Neither one of those virtual reflection
coefficients bare any relationship to *physical*
reality. They are the resulting artifacts of the model
being used and not causes of anything. Virtual reflection
coefficients cannot cause anything. Virtual impedances
cannot cause anything.

I am preparing a picture that hopefully will be worth
a thousands words. I'll try to have it posted to my
web page by tomorrow.
--
73, Cecil http://www.w5dxp.com

"Waves of Average Power"
 

Cecil Moore wrote:

The virtual reflection
coefficient looking forward into a Z0-match is 0.0.
The virtual reflection coefficient looking backward
into a Z0-match is 1.0. That is the crux of the
problem. Neither one of those virtual reflection
coefficients bare any relationship to *physical*
reality. They are the resulting artifacts of the model
being used and not causes of anything. Virtual reflection
coefficients cannot cause anything. Virtual impedances
cannot cause anything.

You've just dismissed the only plausible mathematical support for your
theory, Cecil.

I am preparing a picture that hopefully will be worth
a thousands words.

There are far too few such pictures in the world in my opinion.

I'll try to have it posted to my
web page by tomorrow.

Thanks. I am interested in seeing it.

73, ac6xg

"Waves of Average Power"
 

Jim Kelley wrote:
You've just dismissed the only plausible mathematical support for your
theory, Cecil.

That just proves that you do not understand it
(and never have).

It is the many reflections from the *physical*
impedance discontinuity with its physical-based
reflection coefficient during the transient state
that add up to the final steady-state result. No
reflection coefficients are required besides the
original single fixed physical reflection coefficient.

The first transient internal reflection reduces the
magnitude of the external reflection an amount predicted
by the irradiance/interference equation. The same thing
happens for subsequent transient internal reflections.
--
73, Cecil http://www.w5dxp.com

"Waves of Average Power"
 

On Nov 2, 12:24 pm, Cecil Moore wrote:
K7ITM wrote:
Cecil Moore wrote:
Good grief - the *interaction* between two waves that causes
wave cancellation is what makes non-reflective glass work

Ah, very interesting. So you're saying that the "non-reflective
glass" is a non-linear medium, then.

I am saying no such thing!


Ah, so then you're saying that there is not any actual interaction,
only summation in the normal way. Thank you for that clarification.