Well, given the tremendous correspondence that attended the other
threads, dare I pause to offer something from the realm of the real?

Yeah, a joke given the classic divergence from topic that inhabited
them. One thing was painfully obvious in such discussion of "seeing"
or rendering reflections "invisible" that inhabited the last
discussion. Here I will offer what is taken for granted in the
optical world, solar cells are largely confined to energies that are
not visible. Very little of the Sun's energy is. This is a natural
conflict between perception and reality - but it is in harmony with
the objections I've observed. ;-)

Returning again to the solar cell, described in text as:

1w | 1/4WL |
laser-----air-----|---thin-film---|---Germanium---...
1st medium | 2nd medium | 3rd medium
n = 1.0 n = 2 n = 4.04

where the second medium might be Arsenic trisulfide glass or Lanthanum
flint glass.

When you take the intensity times the area for both the reflected and
refracted beams, the total energy flux must equal that in the incident
beam. That equation appears as:
(r² + (t² · n2² · cos(theta-t) / n1² · cos(theta-i))) = 1

It stands to reason that this can be quickly reduced without need to
use transcendentals for an angle of incidence of 0° (which results in
a refractive angle of 0°). All that needs to be known are the
coefficients which for that same angle simplify to
r = 0.667 a value that is the limit of an asymptote;
it is also invested with either a + or - sign depending
upon the polarization (another issue that was discarded
in the original discussion as more unknown than immaterial)
t = 0.667. a value that is the limit of an asymptote;
here, too, there are polarization issues we will discard as
before. All this discarding comes only by virtue of squaring:
r² = 0.445
t² = 0.445
I presume that the remainder of the math can be agreed to exhibit:
that part of the energy reflected amounts to 11%
and that part of the energy transmitted amounts to 89%.

The discussion in how the second interface does not have enough
incident energy to completely cancel the first interface reflection
has been established in earlier threads. What follows is how this
correlates to current optical designs to resolve this (industry and
academia is not shy in this effort). They, unfortunately, lack the
cavalier mentality to simply dismiss their problems as "invisible."

There are several methods of thin film construction, what has been
described above, and diffraction on periodic grating. With the work
at the Walter Schottky Institute, reflection on bare, highly polished
material varies between 11% and 60%. When married to a glass thin
film as described above, the variation smooths out to between 6% and
8%(comparable to the example above, but instead using SiGe alloys
without regard to quarterwave mechanisms).

When the same researchers employ amorphous silicon on ZnO (again with
the mechanics of layering much as described above - still without
regard to quarterwave mechanisms), then the average reflection still
resides in the region of 10%.

These results are in comparison to the native reflection values of 30%
to 50% across 80% of their BW. So, without reliance on this
presumption of interference wave mechanics, the practitioners in the
art manage to better their performance by five fold - but quite far
from absolute.

When we return to study the wave mechanics, we can understand why
developers are going for the simpler, diffraction techniques - the
wave mechanics are a bust.

Work at the National Renewable Energy Laboratory reveals the purpose
of their goal:
"Although highly efficient double and triple layer AR coatings are
available, most manufactured crystalline silicon photovoltaics
employ simple and inexpensive single layer AR coatings, with
relatively poor AR properties."
[AR meaning "Anti-Reflective"]

They are investigating Solar Cells with refractive indices of 3.5. As
evidenced in their mission statement, the wave mechanics approach is a
bust in comparison to their graded index method (a common technique in
fiber optic construction for pretty much the same purpose of
controlling energy). They construct the layers by increments of
decreasing porosity through a continuous gradient from the index of
air (1.0) through to the index of Silicon (3.5). This increases Solar
Cell performance by 25% and reflectivity falls to values within 4% to
6%.

Well, two different matching mechanisms employed and they both come to
roughly the same results as an answer to the failure of wave mechanics
in the single, double, and multiple interference layers (some up to 20
layers). It is not surprising, but let's examine the best that there
are to offer, as foretold in the mission statement offered above.

We are returning to the amorphous silicon whose native reflectance
runs at 40+%. Researchers have attempted to reduce that through
quarterwave thin layer interference mechanics, and at best have
achieved 9% to 22% reflection (in stark contrast to the "academic"
exercises offered; although conforming to the treatment above). A
MgF2+SiO double-layer coating shows better reflection characteristics
in some parts of the BW, poorer in others. Overall this species
averaged 8% (the two methods above exhibit flatter characteristics).
The best achievement through careful selection of materials (MgF2+ZnS
double-layer coating) obtained reflections on the order of 2% to 4%.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
Well, given the tremendous correspondence that attended the other
threads, dare I pause to offer something from the realm of the real?

How can anyone trust you if you don't correct your earlier
catastrophic errors before offering something new?
--
73, Cecil http://www.qsl.net/w5dxp

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Richard Clark wrote:
"Well, given the tremendous correspondence that attended the other
threads, dare I pause to offer something from the realm of the real?"

If you don`t want an EM reflection in space, the possible reflecting
object must be indistinguishable from space. It must have a resistive
characteristic impedance of 377 ohms.

377 ohms per square material spaced 1/4-wave from a reflective surface
for the purpose of completely absorbing a normally incident wave was
invented by Stanfield Salisbury at the Harvard Radio Research Laboratory
during WW-2, according to the 3rd edition of Kraus` "Antennas" on page
909, attenuation is at least 20 dB for the reflection and the bandwidth
is 1.3 to 1. Kraus gives a transmission line equivalent diagram on page
910.

Kraus derives the 377 ohms of free space on page 131. The reflecting
surface does not need to be zero or infinity ohms. The exposed surface
must be transformed to 377 ohms from whatever the underlaying surface
is.

The 377-ohm carbin cloth shown by Kraus is named Salisbury screen for
its inventor. It is placed 1/4-wavelength from the reflective surface.
The small amount of energy penetrating the screen undergoes 180-degrees
of delay in makind a round trip to the reflective surface and back to
the carbon screen. It undergoes an additional 180-degrees of delay in
peflection. The 360-degree total puts the reflected energy back in-phase
with the penetrating energy. This makes a high impedance.

A high impedance in parallel with 377 ohms leaves the 377 ohms
unchanged. It continues to match the incident energy and continues to
take a bite out of the reflected energy between the two surfaces.

Stealth aircraft, antenna laboratory. or non-reflective glass must look
like 377 ohms.

Best regards, Richard Harrison, KB5WZI

On Thu, 4 Aug 2005 11:51:07 -0500, (Richard
Harrison) wrote:

Richard Clark wrote:
"Well, given the tremendous correspondence that attended the other
threads, dare I pause to offer something from the realm of the real?"

If you don`t want an EM reflection in space, the possible reflecting
object must be indistinguishable from space. It must have a resistive
characteristic impedance of 377 ohms.

Hi Richard,

This was EXACTLY the design goal obtained by NREL with their diffusion
of a gradient of pores through the depth of the active surface. The
variation of the index of refraction went from 1.0 to 3.5 with a
smooth curve (albeit one jag at the beginning which reflects - seems
only armchair designers can do it right).

377 ohms per square material spaced 1/4-wave from a reflective surface
for the purpose of completely absorbing a normally incident wave was
invented by Stanfield Salisbury at the Harvard Radio Research Laboratory
during WW-2

And this is roughly the technique employed by diffraction techniques
which are superior to the quarterwave designs. The purpose is to
contain the energy within the active matrix.

It appears your news server truncates the Topic line, starting a new
thread each time - at least on my reader, I've noted that Google sews
the threads back together tho'.

73's
Richard Clark, KB7QHC