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Registered Member #3324
Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276
i would personaly think that it depends on the size and range of the EMP, the feather away it is, the less current and voltage it induces in the wires after all... a very strong one, theoreticly could totaly destroy the faraday cage, after all, from what i know a EMP works like a huge, giant pulse transformer as far as im concerned and a large enough pulse of EM could induce a current large enough to melt the metal cage
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
There is a big difference between EMP and an E Field. The laptop in my video was only hit with an E field or more specifically I passed current through it but the E field around it was rather weak.
For an EMP you need a supper strong supper short blast of Electromagnetic energy, this would induce currents in all of the little traces in the integrated circuits causing them to heat up and fail. In close proximity to an atomic or thermal nuclear blast this would kill most unshelled integrated circuits (including laptops). an EMP can also be created with a capacitor discharge bank if set up correctly.
In my video the laptop is not really being hit with EMP.
Registered Member #2887
Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107
Dunno, but if it if connected to its charger, the cable will act as a nice antenna. I know someone has damaged a laptop with a Marx generator because of this.
I can only assume other cables (usb mouse) would also do the same.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
One interesting little titbit I found online. Its possible to make an "EMP Simulator" using a modified microwave with a high voltage rated vacuum relay in series with the -5KV from the capacitor. (DANGER WARNING LETHAL VOLTAGE ETC YADAYADA)
Needless to say, it only works with industrial sized (i.e. physically large) microwaves, and it is essential to leave the interlocks etc intact so it won't turn on by accident.
The heater coil is left intact and connected to the existing control circuitry so that it shuts off correctly when the power turns off. This ensures that the heater is kept hot, so switching the relay briefly will yield a short pulse of microwaves consistent with an EMP or accidental sweep with a high power millimetre wave radar.
You can even set the pulse width from a few ms to seconds, which is handy indeed for chemistry synthesis etc where precise average power needs to be maintained.
With a few more modifications the magnetic component can also be simulated, winding a multilayer coil and coating it with BiSnPb connected to the cavity then placing it directly under the equipment under test would work. Best to put the coil where the existing rotator and plate went, as the existing hole(s) can then be used. Needs feedthroughs to keep the microwave energy inside the cavity though..
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
Ah, so that's what I was doing when I was applying sparks to a magnetron at college and blipping out all the speakers in my apartment. I wonder if it would "simulate" better if I discharged a hv capacitor bank into it via spark gap.
I'm not sure about laptops, but most other compact high tech devices I've taken apart have many layers to them with shielding in between (more to shield one region from the next internally I think, but I suppose it would work for external emp)
While the melting current emp is an interesting idea, I imagine the repulsive force between the current and the emp would rip the shield/device apart before it could melt. Oo that actually gives me an idea to counter what I just said using metal leaf on a block of wood placed on an induction launcher...
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
I think a MWO magnetron (or a radar transmitter) generates an EMP qualitatively very different from a high altitude nuclear detonation.
The former produces E and H fields alternating at GHz frequencies, with an envelope that builds up and then decays over many cycles. The spectrum is dominated by the microwave oscillator frequency; shielding and damage effects would depend on target behavior at that frequency.
The latter is not fundamentally oscillatory. A ball of air absorbs x-rays/gamma rays, resulting in fast electrons which leave the positive ions far behind. Would be radially symmetric if near sea level (like conundrum's avatar image!). At the near-vacuum density hundreds of km up, it's bigger than the scale height of Earth's atmosphere. That makes the charge separation unsymmetric. I bet the effect of the geomagnetic field is not too significant in the first microseconds.
So I bet the E and H waveforms are more like monopulses, perhaps followed by some overshoot in the opposite direction. The spectrum from 100 MHz down to kHz or lower would be (AFAIK) pretty much the Fourier transform of the envelope.
Here's an article about a contemporary risk assessment. [edit] In response to the thread title question: I think small gadgets like smart phones, maybe even laptops, could be undamaged. Unless plugged into their charger at the time. Land line and wireless comm networks, and the electric power grid, and grid powered computers are what the planners worry about.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
I remember QST having an article a year or two back relating to the protection of equipment from an EMP burst, and how to implement it yourself. I'll see if I can dig it up from the stack, and maybe share a few details.
However, I think a laptop or desktop on its own would not survive even with the metal shielding for reasons mentioned by others and due to the fact that most cables going into and out of a machine would not be able to adequately protect against generating current going into the machine.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
With North Korea about to launch a satellite, it seems to be a topical issue for discussion. I was thinking today how to shield a weather balloon with attached wifi and radiation monitoring from EMP. I expect that a simple double shield where all the components are well isolated would stop most if not all of the energy. Maybe retract the antenna except when it is being used and use optical comms to send telemetry?
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