As this forum seems to be chock full
o' people who know a thing or two or three about
microwaves, I figure I'd ask the following questions.
Please keep in mind that I'm a laser jock by trade
and my practical microwave experience is limited
to nuking tv dinners for the most part.
I am working on an inhouse project
to build a microwave based Chemical Vapor Deposition
system. Basically all that is being done is to use
microwave ebergy to dissasociate reactant gas at
sub atmospheric pressure to coat a substrate with
the thin film of your dreams. I have modeled my
efforts thusfar after the work done on microwave
based diamond cvd as there is alot of effort put
into that field. the first reactors used for this
kind of work were called NIRIM systems, after the
japaneese agency that developed the reactor design
- basically a piece of fused sillica stabbed through
a waveguide. This doesnt work well for a number
of reasons and cant reach high power density.
The next generation systems basically used
an antenna to couple microwave radiation into a
cavity, part of witch was under reduced pressure.
some of the more novel designs used tricks such
as elliptical cavities with an antenna at one foci
and the product deposition area at the other to
increase power density and remove the plasma from
the cavity walls (a major source of contamination).
Essentially all of this work has been done
using 2450 or 915 microwaves.
To use the
words of my favorite tv cheif - i'd like to kick
things up a notch or two. I happen to have in my
hot little hands a 20kw source at 18 gig - previously
I had been playing with a 100kw source at 915, but
since i care about power density and not power I
think the shorter wavelength will ahve more pros
than cons. What i would like to do is take the output
of my klystron to a horn or dish and then refocus
the the enegy with an off axis parabolic reflector
to a point where as much of that 20kw is concentrated
into a region ideally no more than a few cm in diameter...
A smallish stainless steel reaction vessel will
be located at this focal point and ideally the paraolic
reflector will be as 'fast' as possible to keep
the e field gradient near the focus as steep as
possible to avoid the problem of plasma comming
into contact with the chamber walls or pressure
now... cosidering my desire for
optimum efficency in energy transport from the tube
to my product, my desire for highest power density
possible, the need to keep plasma away from the
chamber walls and the philosophy that this is applied
research funded on a small busines budget so therefore
must be as cheap as relitivly possible - would anyone
care to comment on anything that they see that jumps
out that I might be ignoring, not thinking of, alternate
Lastly, I am boardering
on paranoid when it comes to saftey with 2450 and
915 - i know the military has done some non lethal
areal denial weapons testing with mm wave sources
- 95 gig iirc - what kind of hazards are present
with roughly 18 gig? Will it cook ya just the same
as the lower frequency stuff?
If you would prefer to contact
me via email please do so at