On Fri, 23 Nov 2007 19:33:01 -0500, axolotl
wrote:

Winston wrote:

My question
is: if we provide a 30" diameter field that has a power density of 2 W
at 24" and we are radiating at the resonant frequency of the initiator,
would that reliably disarm or failing that, trigger the device?


I don't know. The MIL-STD for EEDs is MIL-STD-1576. The "safe current"
(the max current/power/time for the squib not firing) listed in the spec
is 1A/1W/5min. Do the bad guys use parts made to the same spec? Do you
want to have to get within 24" for it to work?

A Friis equation calculator is available he

http://www.learningmeasure.com/cgi-b...ators/friis.pl

When you start playing with power/frequency/and antenna gain, it backs
you into path loss and radiator size.

You will have a polarization mismatch (circular (presumably) to
something random), and what is probably a lousy match between squib and
antenna.

It would be interesting to experiment, and the task is a worthy one.

You could measure the result of your effort the way EEDs are checked on
aircraft. An optical fiber coated with temperature dependent phosphor is
brought into contact with the squib active element. The other end of the
fiber is coupled to a flashtube and a sensor. The phosphor is flashed
and the decay time of the phosphor is measured. the decay time is
proportional to temperature. You hit the aircraft with 200V/meter and
check the squib for a temperature rise.


Kevin Gallimore

200 V/meter is only about 106 W/m^2. That'd be a pretty good radar
smack on an airframe so it's certainly a reasonable level for the test
you describe ... but it isn't necessarily telling here.

The Friis equation and other path loss calculations assume far field,
not the case here.

The squib will be a good match to its antenna at some frequency,
because Zo of a dipole depends on length /wavelength.

An xmit antenna or feed working against a reflector of about 1 sq
meter will have a footprint not much larger than that at distance
comparable to reflector dimensions, so if the xmtr is 1KW then
there'll be power density of about 1 KW/m^2 beneath it. This need
not be a parabolic reflector, could be a planar array. If the squib
+ lead separation is ca. 60 mm (length of a flashlight battery), then
aperture might be ca. 3.6E-03 m^2, capturing 3.6 watts per kilowatt.
3.6 watts is more than ample to fire a cap.

Again, I don't assert that this is the best or even a viable
approach, but only a politician, bureaucrat or seat-of-pants "expert"
could dismiss it out of hand with arguments presented thus far.
Shielding would certainly be an issue, though achieving effective
shielding is not nearly as easy as it has been made out to be by most
here.

I agree that some experiments would be interesting and that some
investigation is merited. It's probably most likely to happen by
motivated and skilled people on the ground working with a scrounged
radar, a bit of expertise and more than a bit of creativity.