Re: Experimental Update- Emdrive/Relativity Drive- unspun
- From: "nuny@xxxxxxx" <Alien8752@xxxxxxxxx>
- Date: Sat, 26 Apr 2008 00:18:30 -0700 (PDT)
On Apr 25, 3:26 pm, Douglas Eagleson <eaglesondoug...@xxxxxxxxx>
wrote:
I decided to try the emdrive idea without spinning it first. I just
went to the goodwill store and bought a $25 Dawoo microwave oven.
It is complicated control computer affair so I think I will just start
off cutting a larger hole in the side. I will then insert a waveguide
and tape it to the oven. The side exactly opposite the microwave
window to the oven area is unpopulated by electronics or anything,
just metal siding.
NO!! It is not "just metal siding", it is the wall of the COOKING
CAVITY! It is a CRITICAL COMPONENT that ought not be altered in ANY
FASHION unless you plan on removing the magnetron from the existing
guide/cavity setup and adding a completely new one that can be
connected as you need.
I will use good practices in RF shielding and use copper foil to cover
all cracks between the cut hole and the tubular waveguide. I will
ensure good ground contact with the foil.
THIS IS NOT A SIMPLE MATTER OF GROUNDING AS IN DC OR LOW FREQUENCY
CIRCUITS!!! A cavity, just like a waveguide, is a RESONANT STRUCTURE
that contains a particular number of half-waves per given length along
its structure. At what are called "nodes" there is no voltage but
there is current alternating at the microwave's operating frequency;
more than two billion times per second, AT THE FULL POWER THE
MAGNETRON PUTS OUT! Similarly at antinodes there is no current, but
voltage that alternates as above, ALSO CARRYING THE FULL POWER! YOU
DARE NOT RISK THAT KIND OF POWER BEING SAFELY CARRIED BY THE BOND
BETWEEN THE METAL CAVITY WALL AND YOUR COPPER FOIL!!
I am not trying to dissuade you from going ahead with your extension
of Shawyer's experiments. What I do not want is to read about how you
severely burned or killed yourself! Remember what a microwave oven can
do to a bit of hamburger; do you want to risk that with your own
flesh?
You may believe that a gap too small to see or an "unimportant"
irregularity in the wall you cut or your added waveguide/horn
structure is safe, but YOU DO NOT WANT TO FIND OUT YOU WERE WRONG THE
HARD WAY!
Look here:
http://www.tpub.com/content/et/14092/css/14092_80.htm
which illustrates a standard rotating waveguide joint. Can you build
something like that which will maintain concentricity between the
rotating and stationary parts to a tolerance of a few millimeters?
Notice the "slot" on the second drawing and notice that it extends
into an annular space around the joint seen in the top cross-section.
It isn't there for decoration, it's there to reflect any microwave
energy that spills into it back into the guide, and its dimensions
relative to the wavelength are critical for safe, effective operation.
Note also that the text warns against dents which can cause
"standing waves" which is basically microwave energy from the
magnetron that gets trapped in a short secion of waveguide and damages
the guide by heating it or even arcing. There is PLENTY of power
available in that cheap oven you bought to burn right through a poorly-
built guide and burn YOU!
Also there is something called "modes" to consider, which basically
means which way the electric and magnetic fields point at various
locations in the guide/cavity system and how many reversals of those
fields you will find per unit length. You need to determine what the
mode(s) must be in the conical cavity to get your desired result, then
you must determine the mode(s) your guide will carry to get the energy
to the cavity, and then the fun part; designing the port (where the
guide enters the cavity) so that energy is transferred smoothly into
the cavity.
It helps to know the physics.
Speaking of that, where does all that microwave energy go once it
enters the cavity? That's something Shawyer apparently dismisses but I
can't accept that; either it is "converted" to something else (and I
know of no physics involving his described setup that will do that) or
it just builds up (or is reflected back to the magnetron) and
eventually causes catastrophic failure.
Ignoring that for the moment- physics is good, but engineering can
keep you ALIVE and UNHURT!! The site hosting the page I pointed you to
is a pretty good general overview of the task you are facing.
PLEASE read through it (you can read all of it online and do not have
to spend any money) and determine what you DO NOT yet know to do a
safe experiment, and LEARN THAT! But be aware that microwave
engineering is NOT a simple discipline and you may have to extend your
schedule a bit.
Mark L. Fergerson
.
- References:
- Experimental Update- Emdrive/Relativity Drive- unspun
- From: Douglas Eagleson
- Experimental Update- Emdrive/Relativity Drive- unspun
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