Posted: 7/21/2007 4:25:52 PM EDT
| I was watching a old show on the SciFi network this afternoon and a question came to mind about a nuclear air blast that would create EMP waves knocking out all electrical circuits. My question is this. If an electronic device was off, would it still be damaged? Would any electrical device survive such a blow. Would it matter if the devices were in an underground shelter? Just wondering about geiger counters and such and if they would work after an nuclear blast. |
there are so many factors which affect this question that it is nearly impossible to say, with any certainty, whether a given device will continue to function post-NEMP. as i wrote some time ago here in the SF, archive.ar15.com/forums/topic.html?b=1&f=123&t=521338&page=3
that said, in all likelihood, most all portable, battery operated, handheld devices (such as ham HT's, geiger counters, and the like) will not be affected by EMP. the distance-reduced field intensity and the minimal capture area will prevent any permanent damage, although there may be minor transient issues. here is what an ARRL report on the EMP effects to ham radios says:  as you can see, as long as there are no long power cables or antennas connected to the device, it should survive an EMP. ar-jedi former EMC/EMI/ESD/EFT/TEMPEST engineer. ps: i have a test chamber where i work:    |
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ETA: from page one of the link posted above:
ar-jedi |
| Thank you for an informed post. It's great to get info from people who actually have real knowledge in the area. "Weaponology" demonstrated an EMP effect on a car by driving one directly under an EMP generator. So if I get this right then many vehicles (and other devices) may survive a high altitude EMP burst due to distance from point-of-origin, atmospherics and other variables ? |
I've read a lot of conflicting info. Do you or don't you have to ground your homemade Faraday Cage. Some sites say not necessary (as long as it's not on concrete) and some say it's a must. Whats the truth??? "Consequently, storage of equipment in Faraday boxes on wooden shelves or the like does NOT require that everything be grounded. (One note: theoretically non-grounded boxes might hold a slight charge of electricity; take some time and care before handling ungrounded boxes following a nuclear attack.) " www.aussurvivalist.com/nuclear/empprotection.htm |
If you don't ground it the surge doesn't go anywhere. The Faraday cage could act like a (crappy) capacitor until the charge bleeds off naturally. A grounded cage would get rid of its charge much faster. BSW |
no.
no. let's work up an example. what happens when an airplane in flight is struck by lightning? clearly, the airplane isn't grounded. ar-jedi |
I'm not an airplane guy: I suppose that a charge builds up on the skin of the airplane. As long as there is no path to ground, no potential, no current flow. It's the same reason birds can sit on a 50kV HV line, the bird is at 50kV in respect to ground, but at 0V with respect to the line. BSW |
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file this under "Sucks to be me" - In the case of a EMP, there is one device that is quite sensitive to an EMP. The Pacemaker...... Yup, you will be able to tell who is pacemaker dependent when it hits.... Folks like me, not as big a deal as it could be. BUT - there are many, many people of ALL ages (some as young as 14) who are 100% pacemaker dependent. That means EVERY beat of their heart is instructed by the device. Therefore, when the EMP scrambles the pacer, - they're done. Many of those people may be driving cars when it happens..... |
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I hope you are joking. His statement was correct. These guys are working on a live line by raising the potential of their insulated truck to the line's potential:  |
but consider that a moment later the airplane is now charged at a potential which can ionize the air in the gap to the ground. there is another discharge, originating at the plane and ending on the ground. www.youtube.com/watch?v=w69vfMvpeBc so there is current flow (and a high current flow at that) through the plane, specifically through the skin of the plane. if the surface area of the plane is sufficiently conductive, and there is enough conductive area to avoid localized heating (i.e., melting of aluminum), there will be no damage to the aricraft. what we've talked about so far is a situation where a large current passes through an ungrounded structure. let's take this onward. suppose the bolt does not hit the plane, but instead passes some 100yards to one side of it. what happens then? we know that any current flow (especially a big current flow like a lightning bolt) produces electromagnetic (EM) energy -- turn on an AM/FM radio during a thunderstorm and you can hear it (much more so on AM than FM, btw, for the simple reason that FM is much more resistant to atmospheric disturbances). the current flow in the bolt creates an electric field (conceptually a wave front, sometimes referred to as a "flux") and a magnetic field. these two are referred to as an E-field and an H-field respectively. for simplicity here, take my word that the E-field and H-field travel together but at a right angle to one another. if you want to learn more about EM energy, google for Maxwell, Gauss, Faraday, and Michelson. the lightning discharge can be thought of as an impulse; that is, a very short duration high energy pulse. again, for reasons a bit complicated to type up, such an impulse generates a broad range of electromagnetic energy -- which i'll translate to say that the lightning produces a wide bandwidth "bump" of powerful EM energy that spans many frequencies. as the invisible electromagnetic wave produced by the lightning passes by the airplane, a current is generated on the surface of the plane. this is conceptually no different than the current that is produced on the antenna of your car -- an EM wave is transmitted by your favorite radio station, and your car antenna picks up this signal and converts it to audio. the magnitude of the current on the skin of the airplane is a product of many factors, including the E- and H-field strengths, the spectral content of the wave, the angle of incidence, and the conductivity of the aluminum skin. nevertheless, because of a principle put forth by Faraday, assuming the skin is reasonably electrically contiguous up to the highest frequency impinging on it, the inside of the structure will not suffer any effects of the wave. this is true whether the structure is grounded or not.
this is correct. the protein nonsense written above is just that, nonsense. ar-jedi |