Talk:Electromagnetic pulse

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[edit] Magnetic stripes

Does anyone know if an EMP would have an effect on magnetic stripe cards? - BlackWidower 00:32, 18 January 2006 (UTC)

I wouldn't be surprised. A lot in physics seems to have two sides to the coin. Just as a magnetic field can induce current in a wire, current passing through a wire generates a magnetic field. The MythBusters actually busted a relevant myth, but not for the same reasons.--Drat (Talk) 12:17, 23 January 2006 (UTC)

While I don't know if the actual cards would be effected by am EMP, the machines that read them would be, thus rendering the card useless anyway. Jen

The EMP from a high air burst is never strong enough at the Earth's surface to do this, see: [1]. The strongest EMP was produced by the Hardtack-Teak shot, not the Starfish test. (Teak was 3.8 Mt and was detonated at 77 km. EMP field strength (but not area coverage) is maximised for a burst at 40 km altitude, so Teak at 77 km would have produced a stronger ground level EMP than Starfish at 400 km.) The prompt EMP electric field from Teak was not measured due to instrument failure, but the late-time magnetic field variation was measured in a laboratory which studies solar storms:

"... the Apia Observatory at Samoa recorded the ‘sudden commencement’ of an intense magnetic disturbance – four times stronger than any recorded due to solar storms – followed by a visible aurora along the earth’s magnetic field lines (reference: A.L. Cullington, Nature, vol. 182, 1958, p. 1365)." - [2]

Since this EMP covered vast areas (though not as wide as those from Starfish), if the magnetic field was strong enough to wipe magnetic information off swipe cards, it would in 1962 have wiped magnetic audio and data tapes (a swipe card is just a plastic card with a strip of magnetic tape stuck on it). This didn't happen. If you think about it, the electromagnetic radiation which propagates is governed by Maxwell's equations (like visible light), and the magnetic field component of such a light velocity wave is given by:

B = E / c

Inserting the commonly used value for EMP of E = 50,000 volts/metre for the prompt field with a rise time of about 20 nanoseconds [3], the magnetic field strength is seen to be B = 0.000167 Teslas. This is only 2.9 times the natural magnetic field strength in Washington D.C. according to [4] which says the natural field there is 0.0000571 Testa. However, the ability to erase magnetic tape or credit card strip information depends on the field intensity in Orested not the field strength in Teslas:

"QUESTION: What is the danger that my tape will accidentally be erased?
"ANSWER: Standard open reel audio tapes have a coercivity of approximately 360 Oersteds. It takes an even greater magnetic field (approaching 900 Oersted) to completely erase a tape. For a comparison: The earth's magnetic field is 0.6 Oersted." [5]

EMP can't directly wipe out magnetic information. However, it could wipe magnetic information indirectly, if it induced a large current in a long conductor which runs near magnetic tape. Any conductor carrying an induced pulse of electric energy creates a magnetic field around it, which can easily be much stronger than the magnetic field of the EMP in free space. For example, a long overhead power transmission line, subjected to 50,000 v/m peak EMP will typically give a pulse with a peak of 1 million volts at 10,000 Amps. This will create tremendous magnetic fields. When these pulses go into transformers at the end of the power line, the transformer can explode or catch fire, but some of the energy is passed on before that happens, and can end up in home power systems. Any loop of cable connected to the mains will be a source of a powerful magnetic field which could wipe nearby magnetic tape, cards, and discs. 172.212.17.34 21:03, 30 March 2006 (UTC)

[edit] Why is this article titled Electromagnetic pulse?

Why is the title of the article Electromagnetic pulse when the article seems to be exclusively about EMP weapons? --hitssquad 06:26, 28 January 2006 (UTC)

Probably because the way that a powerful EMP has to be generated, in real-life, typically involves some sort of weapon, like a nuke. By the way, please sign your comments.--Drat (Talk) 06:32, 28 January 2006 (UTC)
I understand that Earth impactors may also create powerful Source Region EMP's within the 2-psi overpressure threshold, just like ground-level nuclear explosions do. L. Foschini. Electromagnetic interference from plasmas generated in meteoroid impacts. Europhysics Letters 43 (1998) 226. The article seems to me jump to the conclusion -- and to assume that everyone already knows -- that powerful EMP is exclusively a weapon effect. If it is indeed the case that powerful EMP's can only be created by weapons, perhaps the article should introduce that critical point before continuing to the rest of the article which is excusively about weapons. As it is it, looks as bizarre as would an article supposedly about cars that first introduces the topic of cars in a reasonable manner but then exclusively discusses Mercedes as if Mercedes are the only types of cars in existence -- or even possible -- and that everyone already knows this so well that it would be pointless to even mention the fact. --hitssquad 10:07, 5 February 2006 (UTC)
Then improve the article as you see fit. As it is, you know well more than I do on the subject, in terms of physics and all that.--Drat (Talk) 14:12, 5 February 2006 (UTC)
Another option may be to split this article in two, one named "Electromagnetic pulse (weapon)" and another one named "Electromagnetic pulse (telecommunications)", or something. -- Bovineone 08:06, 5 March 2006 (UTC)

[edit] Affected devices

I don't think that it's really made clear what devices are vulnerable -- as of right now the page says any unprotected electronic equipment but I'm sure there are things that are not vulnerable due to their small size and thus no 'antenna' to amplify the signal into the device. (By antenna, I mean anything that might serve to cause the device to absorb more EMP shock.) It might be worthwhile to note a few common electronics that would be vulnerable, such as cell phones -- speaking of which, are small personal electronic devices necessarily vulnerable? Home appliances most certainly are, as well as anything connected to the power grid due to the large EMP collecting abilities of the multitude of wiring. And -- are batteries necessarily vulnerable to EMP? I don't see how. I will do research later, if someone doesn't get to it first. - S. Komae (talk) 18:28, 29 March 2006 (UTC)

Microchips are vulnerable. In the 1950s and 1960s, America tested weapons at Nevada with yields up to 74 kilotons in air bursts and near surface bursts, which just produced 'clicks' on car radios. If you see B. J. Stralser's declassified 30 April 1961 EG&G report, Electromagnetic Effects from Nuclear Tests, you see that there is no damage to anything unless it was connected physically to a cable which had induced an EMP. Hence, in tower test, wth cables running from bomb to control point 50 km away, after serious damage in a 1951 test they had to switch off mains power and go over to diesel generators at shot time. In the 1958 Teak test the 3.8 Mt bomb exploded 77 km directly over Johnston Island, producing a massive EMP, but again no portable radios were destroyed. In the 1962 Starfish test, and also three Russian tests, lots of things were damaged but only if they were connected to long wires [6]. Portable radios working off batteries were OK. Although modern microchips are up to a million times more sensitive than valve/vacuum tube radios, the aerial size in a UHF cellular phone is really tiny compared to the long aerials of old HF valve/vacuum tube radios, so things balance out. I agree that anything you can fit in your pocket is not likely to be damaged by EMP, unless it is being recharged from the mains when the bomb exploded. (Batteries could only be damaged if they were being recharged at the time.) However, a safe, working cellular radio wouldn't be any use to you if the network (running from mains electricity) was zapped by EMP! 172.212.17.34 21:24, 30 March 2006 (UTC)

In the same vein, is it possible to build fuses or breakers that would protect devices plugged into the power grid? Also, are automobile electronics safe? BertW 05:53, 24 May 2006 (UTC)

[edit] Specific effects of High Altitude EMP blast

For the purposes of a novel, I am wondering if anyone has a good guess about the effects if a large nuclear weapon or EMP weapon was detonated at GPS level, say 24,000 miles or so.

Basically wondering about the range of the effects. Would it affect all of the GPS satellites within the visible horizon? How about regular staellites that are at only 100 - 300 miles up?

Thanks!

4.178.238.32 18:25, 11 April 2006 (UTC)

The effective blastradius of the EMP field generated by a nuclear weapon, does not change when going into high altitude, if you know any specific data on the efectiveness of an EMP blast at ground level, it is safe to say that in space, or in high altitude, the effects would be the same. It is arguable that sattelites are built to withstand more galactic radiation then ground based electronic devices, maybe this has some shielding effect?

crashmatrix 23:05, 11 April 2006 (GMT+2)

Thanks for the reply. In reading today, however, several websites mentioned that High altitude blasts were visible from literally thousands of miles away, and I thought there was also an effect on blast radius with the lack of air resistance. What connection am I missing?

Thanks again!

4.178.45.132 03:24, 12 April 2006 (UTC)

Well, I'm not a 100% sure on this one, but the resistence in the atmosphere for EMP fields is non-existant or negligible, the fact that a high altitude blast is visible appearently implies that scientist (?) where 'listening' with sensitive equipment for EMP spikes, but at thousands of miles the impact is not great enough to affect normal equipment. A EMP field theoreticly extends into infinity, however the impact it makes deminishes over distance, so with equipment sensitive enough you could detect a EMP spike from the other way of the galaxy (if there where no background stellar radiation).

crashmatrix 00:49, 20 April 2006 (GMT+2)

High-altitude electromagnetic pulses (HEMP) produced by high-altitude bursts occur in an area of the atmosphere where the density of the air is low. Because of this, the gamma rays can travel very far before they are absorbed. These rays travel downward into the increasingly dense atmosphere. Here, they interact with the air to form ions as previously described. This region, called the deposition or source region, is roughly circular. It is thick in the middle and thinner toward the edges. It extends horizontally very far creating source regions that are over 1000 miles in diameter.(10) The size of it depends on the height of the burst and the yield of the weapon. The EMP in this source region gets deflected downward towards the earth due to the earth’s magnetic field. Although the fields produced from a high-altitude burst are not as great as those for a near-surface burst, they affect a much larger area.(11) Because of this huge potential, high-altitude bursts could be the most dangerous type of EMP. (http://www.geocities.com/capecanaveral/5971/emp.html) There hasn't been much experimentation with HEMPs in recent years so the effect on orbiting satelites is uncertain. --141.158.28.46 22:16, 25 April 2006 (UTC)

A graph showing the EMP as a function of bomb power, bomb design and burst altitude has just been added to the article, based on an unclassified 1975 computer simulation. 172.202.130.162 11:35, 7 May 2006 (UTC)

[edit] Trivia about uses in fiction

What is the purpose of this section, other than being an indiscriminate collection of facts? Is the fact that MacGyver can make an EMP generator or that "EMP" is the name of a magic spell in an N64 game supposed to help a reader understand what an electromagnetic pulse is? Why shouldn't this section be deleted? -- Centrx 22:27, 4 June 2006 (UTC)

I see your point. Dealt with the problem.--Drat (Talk) 07:40, 5 June 2006 (UTC)
I must say, even if this section was deemed trivia and not fit to stay in the main article, entirely deleting it without saving the list first by splitting it in its own article (which is now done with the Electromagnetic pulse in fiction article) was irrespectuous of the work done by the various contributors who had compiled this section, and borderline vandalism.
St Fan 13:30, 10 June 2006 (UTC)
Not if that article does not belong in an encyclopedia. It may very well be deleted for being an indiscriminate collection of information. -- Centrx 23:25, 12 June 2006 (UTC)

[edit] Shielding

The Boeing E-4 is apparently 'shielded' to be protected from EMP - how would this be done? Joffeloff 18:01, 12 July 2006 (UTC)

I would guess a faraday cage Rewt241
The plane could have negative pulse projectors but that would take massive amounts of energy since the pulse itself is powered through magnetism and shockwaves. Also, i would say that the shield could only work if it sense the pulse within a specific radius.—The preceding unsigned comment was added by 69.158.71.24 (talk • contribs).

[edit] Wouldn't an EMP have some effects?

Why does an article about electromagnetic pulse not discuss the effects of a scenario in which, somehow, electric equipment were in the radius of one? Would electric equipment be destroyed/damaged and would you then not be able to use it afterwards, or would the effects only be temporary, etc.? Kamikaze Highlander 03:57, 21 July 2006 (UTC)

Also, effects on animals and humans? AFAIK, electric impulses are used to transmit signals across the neurons in nervous system and whatever. So, I'd think EMP could at least disrupt those signals temporarily, if not outright damage the neurvous system or anything else (bioelectricity?). --Acolyte of Discord 22:11, 30 August 2006 (UTC)

I never really payed attention in physics, and haven't even really read most of the article, but I guess it would have something to do with the powerful magnetic field generating powerful electrical current in wires (basic physics), hence devices being damaged. Living things, of course, don't have wires. It'd be different if you were a cyborg, but for now that's mostly in the realms of fiction.--Drat (Talk) 09:30, 31 August 2006 (UTC)
Please look here[7] for some description of the effects of an EMP. As for the effects of EMP on humans etc? From the same site, "Electromagnetic weapons may be productively used against all elements in this model, and provide a particularly high payoff when applied against a highly industrialised and geographically concentrated opponent. Of particular importance in the context of strategic air attack, is that while electromagnetic weapons are lethal to electronics, they have little if any effect on humans. This is a characteristic which is not shared with established conventional and nuclear weapons." --Madbrood 15:28, 20 September 2006 (UTC)
Can someone add something about the effects to the article? I am really amazed that the article managed to be so long without offering even one example of something which might happen as a result of an EMP. For example, the 1985 tv film The Day After showed the cars and motorcycles were permanenetly disabled by the EMP of a nuclear blast occurred. I really thought that this article would tell whether that was fact or fiction, and if fact, offer an explanation of how it all works. But I came here to find nothing of that sort in the article, only here in the discussion. Can someone upgrade the article please? Thanks! --Keeves 00:48, 24 December 2006 (UTC)
I agree, I think the bulk of this article should be in an article called "Technical requirements for the use of an electromagnetic pulse as a weapon" which is probably not of sufficient interest to comprise the near entirety of the main article. Can someone rewrite? --70.247.192.110 19:30, 24 February 2007 (UTC)

[edit] Mad Explosions

I'm not a science-type fellow, but I'm assuming EMP waves don't cause mad explosions, fires, destruction, and such? (Any destruction might be the result of the trigger, but not the EMP?) JimmmyThePiep 04:10, 24 March 2007 (UTC)

That's science fiction/artistic licence for you.--Drat (Talk) 04:20, 24 March 2007 (UTC)

[edit] Defense

Add to the article how to defend or shield against EMP.—The preceding unsigned comment was added by Frap (talk • contribs).

Only with reliable sources. No Sci-fi/made-up stuff.--Drat (Talk) 11:00, 26 March 2007 (UTC)
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