nuckolls.bob(at)aeroelect
Guest
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 Posted: Sun Jun 06, 2010 8:52 am Post subject: PolyFiber silver coats and their effect on radio signals |
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| Quote: | I can see where such a semi-solid layer of aluminum flakes could
affect some radio waves. I chose to not do the bottom
surfaces. (They got their share of sealer/paint, etc)
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Perhaps some consideration of electro-magnetic wave behavior
is useful here . . .
If you were to seal yourself up in a 55-gallon drum
and weld the lid on. A hand held vhf radio would be
useless in terms of communicating with the
outside world. If you added a hole in the drum (but
didn't stick the antenna through the hole), the hole
would have to be enlarged to about 10% of a wavelength
(120 MHz is 2.5 meters or 100 inches. 10% is about
10 inches) to have significant communication with the
outside world but would become really "transparent" at
50% or 50 inches in diameter.
Now consider the effects of suspending particles of
aluminum, probably less than .001" in diameter, in
the path between a transmitting and receiving antenna.
These tiny "shields" are about 1/100,000th of a
wavelength at VHF comm frequencies and 1/10,000th
at transponder frequencies. They are a SIGNIFICANT
part of a wavelength at the frequency of light and
thus offer useful attenuation by reflection of the
effects of light on the surface.
The only way you can make these particle a useful
tool for affecting VHF radio is to electrically bond
the particles together such that the sheet resistance
approaches that of a solid material like aluminum
skin. This simply cannot and does not happen when
dispersed throughout a fluid polymer intended to
be a component of paint.
Some of you may recall a discussion I had with
Greg Richter some years ago wherein he offered
that spray-on conductive coatings were suitable
for adding a ground plane to the inside surface of
a non-conducting skin. There too we considered the
exceedingly difficult task of purposefully increasing
conductivity of an applied coating. In the case
of PolyFiber coatings, there's no interest whatsoever
in the electrical conductivity of the finished
coating.
It's the size of aluminum particles compared with
the wavelength of ultra-violet light that makes
the coating magic . . . it's effectiveness as
a conductor at radio frequencies is very low
and as demonstrated . . . not noticeable in terms
of antennas buried under the skin.
Bob . . .
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