Re: Focused EMP pulse?

Richard Clark wrote:
On Tue, 6 Oct 2009 10:43:10 +0100, "christofire"
<christofire@xxxxxxxxxxxxxx> wrote:

... but how much damage is a pulse of 10 GHz RF going to do?

Stand in front of an unfocussed emitter such as an open microwave oven
for 10 minutes (say, a meter back); that would be about 100,000
pulses; divide your noted effects by the same number and report back.

73's
Richard Clark, KB7QHC

More like, put your radio in a microwave and turn it on.

60 pulses/second (in the US).. 600W average power. Figure the power density is probably in the 10 W/cm^2 rough order of magnitude, or 100kW/square meter. Peak to average ratio in a microwave oven is pretty low (3?), so thermal effects on a lossy medium will be significant.


The 30kV/m (which is achievable as described earlier, a megawatt over that 2 meter circular area) is around 24 times that. I think it's safe to say that 30kV/m sorts of fields will fry stuff, in general, pretty much independent of its resonant properties. Crumpled aluminum foil sparks pretty well, as does steel wool.


As for personnel exposure..

Yep, you'll get a burn.. probably cook your eyeballs too. Although, at 100GHz, the penetration depth is small..Might just cook your skin off like a horror movie.

I don't know what the penetration scale depth at 10 GHz is, off hand. Certainly several cm (I'd expect it to scale as sqrt(1/f), and 2.45 GHz in a microwave oven clearly penetrates 10 cm at least, or you couldn't cook a big roast at all evenly)

That's the challenge, of course.. High enough fields to cause arcs/breakdown to destroy the electronics, but low enough average power that thermal effects are minimal, so you don't kill or injure the people.


1-10 MW peak powers at pulse lengths of microseconds are pretty standard radar fare. Fire it at 1pps, and the average power will be down in the few watts area, so personnel safety isn't as big a problem. There are lots of cases of folks being exposed to fields of this magnitude accidentally, and they don't die as a rule.

There is a tale in the FCC enforcement literature about a guy working on a FM broadcast tower where he noticed sparking and smoke from his protective garments after the station manager remotely turned the transmitter on to full power.


On a smaller scale, I've accidentally killed quite a few pieces of electronics with fast HV pulses. It kind of goes with the territory when you fool with Marx banks and solid state electronics. Even fairly low powered Tesla coils will do a number on garage door openers, but I think that's because the GDOs are kind of cheap designs, with long wires hanging out of them, and it doesn't take much to kill one. That's basically discharging a 50pF cap charged to 100-200kV in a few tens of ns.
.

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