Electromagnetic Pulse: Pure Hollywood?

Imagine you’re in charge of a major heist. Right as your crew is about to rob the main vault, you need all of the electronics in the building to fail at exactly the right moment with no other collateral damage (except, maybe, to your raggedy panel van). Obviously you will turn to one of the entertainment industry’s tired tropes, the electromagnetic pulse! The only problem is that if you were to use a real one rather than a Hollywood prop either there would be practically no effect, a large crater where the vault used to be, or most of humanity would be in deep trouble. After all, the real world isn’t quite as convenient as the movies make it seem.

emp-electromagnetic-pulse-jra-1cg_wq4mp4-shot0001Our curiosity into this phenomenon was piqued when we featured an “EMP generator” from [FPS Weapons]. The device doesn’t create an enrapturing movie-esque EMP pulse suitable for taking down a casino or two, but it does spew a healthy amount of broadband electromagnetic interference (EMI) in every direction. It probably also doesn’t send the EMI very far; as we’ve seen in many other projects, it’s hard to transfer energy through the air. It got us wondering, though: what is the difference between being annoying and creating a weapon? And, is there any practical use for a device like this?

Nuisance EMP

While there’s no explicit dividing line between causing your neighbor’s wireless router to drop a few packets and destroying the electrical grid, many things produce an EMP in the course of their normal operation. You probably operate a machine that produces thousands of tiny EMPs per minute: your car. Every time a spark plug operates, a little EMP is generated.

8c297991-9a67-4d7c-832c-26d43734ab03While most governments regulate the amount of EMI that these devices can radiate, there are some areas where even a tiny bit is intolerable and anyone nearby must drive diesel vehicles that don’t have spark plugs. Usually these areas are near radio telescopes that are sensitive enough to be affected by the tiniest electromagnetic noise of any kind.

Nature’s EMP

A spark plug is just one thing that uses a spark gap to do something useful. Spark gaps are used in some old radio transmitters (although their use is now heavily regulated to the point of near-extinction), and even as high voltage protection devices in electrical substations. Each of these devices will produce a relatively small EMP as a side effect when they operate. For larger EMP, however, we first have to turn to mother nature and her own spark gap: lightning strikes.

For a spark gap protection device on a high-voltage power line, there might be a voltage of 500 kV and a fault current in the thousands of amps for a few milliseconds. In a lightning strike, however, the voltage can exceed a billion volts and carry a stroke current in the hundreds of thousands of amps. The EMP released from a lightning strike can damage anything from common household devices to electric motors. Even if a device isn’t plugged in, it can still be damaged by EMP from a lightning strike provided it has a long enough conductor within. Any conductor can act as an antenna for an EMP, and the broadband nature and high energy content of the EMP from a lightning strike means that anything metal can be affected, heating up as current is induced within.

Weapons Grade EMP

e-bomb-detonationThis is the crux of why someone would want to develop an EMP weapon. In modern times, disabling electric and electronic devices is crippling to almost everyone. Since any conductor can and will absorb the energy from an EMP, almost everything will be affected. Militaries around the world have come up with some interesting ways to generate EMP pulses in order to disable their enemies without the collateral damage of explosives. The more powerful EMP devices are driven by explosives, though, so there will still be a sizable blast to deal with.

Of course, these types of weapons are very targeted and would affect only a small area. As we have seen already, it’s difficult to keep energy focused over long distances. To really do some damage, the beam has to be very tight or the device nearby. Or, a nuclear weapon could be deployed. A side effect of detonating any nuclear device is an incredibly large EMP. Compared to a non-nuclear device, these produce a million times stronger EMP for a given weight.

starfish_prime_aurora_from_honolulu_1In the early days of the atomic bomb it wasn’t quite understood just how severe this problem was, but the United States quickly found out. During the Starfish Prime test, a 1.44 megaton nuclear bomb was detonated at 400 kilometers above the Pacific Ocean. The EMP was strong enough to cause damage in Hawaii, over 1,400 kilometers away from the blast. The ramifications of a weapon of this sort detonated over a major city are certainly a concern, especially to a nation’s electric grid which would bear the brunt of the force and almost certainly be destroyed. The only good thing about this is that access to nuclear weapons and access to a delivery system (a rocket) is quite hard to come by for the average person and there are much easier ways to take out large parts of the electric grid if you’re so inclined.

Back to Reality

Besides as a weapon or a nuisance to radio astronomers, there aren’t too many things that actually make use of EMP to do useful work. There are some metalworking shops that use a technique called electromagnetic forming to shape objects using EM pulses, and there are some piezoelectric generators that can convert a large force into an EMP to form a spark for a lighter or camping stove, for example. There are also some purpose-built radio jammers that can perform a similar action as an EMP, but these are very specialized to work in a controlled manner and in a narrow frequency range rather than the broadband effect that EMPs generally have.

It’s rare that we recommend against exploring some topic for DIY research, but it may be the case that EMPs are just too difficult and too dangerous to play around with. Unless you want a surprise visit from the FCC, the FBI, or any other ominous three-letter agency, you may either want to leave these devices alone unless you’re creating the next summer blockbuster movie.

61 thoughts on “Electromagnetic Pulse: Pure Hollywood?

      1. The way it’s built, not much microwave is getting out of their horn gun. They do produce emi as can be seen in the video. A proper way to build a microwave oven gun would be with a rectangular waveguide and mounting the magnetrons in-line with the proper 1/2 wave spacing so they’d tune to same frequency and be in phase. Use a proper power supply. I don’t think you can run a magnetron off pulses from a capacitor bank as need micro seconds to start oscillating after poweron. Then put a larger horn antenna on it and they could light up incandescent bulbs 30ft away and disable wifi in half the city.

        1. It eyeballs about right for a cantenna type cavity (Readjust your gut if you think it should look like a pringles can, they’re actually too narrow at 2.4ghz) and injection point eyeballs about right from the end. The question would be whether non-synchronous use of the magnetrons 120 degrees apart around it is cancelling each other out or not… but it wouldn’t be easy to mount them 1/2 a wavelength inline because they’re fatter than that… without more waveguidey extensions then coupling loss, chance of impedance mismatch, blah blah. Though you could probably get some 3-4″ duct and have them X+1/2 wavelengths apart. Then I guess the business end is getting ungainly..

          The EMI on the camera could have been incidental from the sparking of whatever device was switching the magnetrons on, connect up a bake element and might have got the same thing.

        2. You absolutely *can* run a magnetron pulsed as long as the filament is kept hot. For airport surveillance RADAR one does pulses down to about 50 – 100 nano seconds (0.1 usec). 15 years ago I built a modulator for this, which worked, and still works, around the world.

          Nowadays, it’s all modulated CW and signal processing-, software defined radio components and systems are so cheap and reliable that that a system performance, which is only limited by the antennas used and of course physics, can be achieved for “normal money”, about 3000 EUR. The military can afford good antennae, their electronics is the same.

      2. A weaponized can-tenna, I love it! It has to be a very creative fake, though. 4×18650’s isn’t nearly enough power to fully energize one of the masers, much less 3. And GY6 type scooters just naturally explode, it’s a feature of the design.

        1. Its not CW, they are using the 18650s to heat the filaments and then charge high voltage caps somehow. When the voltage gets high enough it breaks over and dumps the caps into the magnetrons. So you get short high power pulses.

          1. Makes sense. I have a radar magnetron that is really not that big and rated for something like 100kw pulses. As long as the average power if not high you wont overheat the magnetrons.

    1. I think it is likely faked but really well presented. The lighting of the neon and CFL lamps in the garage, – plausible. The disruption of the bug transmitter? – Maybe. The EMI to the video camera? Most Likely. The rest was for show. Note that while blowing up the stereo there was an expensive laptop in the room unprotected. Despite this, it was entertaining and thought provoking. Could a pulsed magnetron EMI disrupter be built by a hobbyist? Most definitely. I don’t see it blowing up stereos or scooters, but it would wreak havoc on anything electronic, and some devices it would actually fry because of the nature of the waveforms and power levels they normally switch.

  1. Just do what the US gov’t does. Play out in the desert.

    I don’t see why a bedroom sized faraday cage wouldn’t allow the hobbyist to at least dabble at the lower end of the EMP spectrum without inconveniencing their neighbors & local emergency services.

    1. This youtube video makes you think about how vulnerable modern society is. Not even emergency broadcast would work for public information as noone have a battery powered transistor radio, in a tin can, anymore as a backup. My latest phonebook from 15 years ago actually had that exact advice for emergency preparedness before they stopped printing phone books.

      1. If it’s as “powerful as a nukular bomb” and you have to be within 50ft of it to stop your car, I don’t think it’s the EMP you really need to worry about..

        Doing something like nuking the magnetosphere is another level though, compared to surface detonation effects.

    1. There is a sweet spot in altitude for any particular bomb’s gamma radiation yield. The 400km of this test was close to optimal for that bomb. A really big one built for high gamma output would be pretty wild. So far, such things as fusion bombs and rockets that can carry one to 400km or greater are way beyond the means of terrorists and most countries.

      1. And then there’s just this ugly, not so little thing called R-36M2 (or as NATO refers to it: SS-18 mod 6)…
        A 211t liftoff weight ICBM with an estimated 20Mt warhead that purposely detonates above the atmosphere…even though they were pulled out of active duty, the warheads are probably still around and most likely can be easily bolted on to it’s (only slightly) less destructive MIRV-type brothers, which still are in active service.

        One of those alone could probably destroy the US as we know it without ever coming into US airspace and severely cripple/destroy most of Western and Central EU, with negative effects being felt around the whole world.
        Anything non-nuclear is limited to precision strikes, but stuff like this is pure doomsday device. That’s what scares me…

        1. pure doomsday how?

          EMP events happen in nature as well, AFAIK there has been quite a few blackouts linked to solar storms and the effect is similar, so stuff like the grid in europe is built to withstand that kind of punishment, several grid equipment manufacturers directly test their products to handle even nuclear emp’s.

          1. the difference is this type of emp is already inside the magnetic field so it won’t protect usw like it would from a solar flair. but even small solar flair scares the heck out of all power grids and satellites mangers, these systems are designed to turn off when a big flair hits but an emp attack would come with no warning

            all satellites in range would be dead and power grids will overload blowing out the chip in most electronics.

            world wide communication would be down and power grids you take years of work to be fixed the, world would never recover from something like this.

          2. that is the myth i am trying to dispel, see below where others have also discussed it but you are describing something out of fiction.

            the earths magnetic field might not provide as much protection, but a nuclear bomb also doesn’t provide the same flux as a large solar storm, again, this is something that modern grid equipment is actually designed for, yes sometimes old equipment is turned off because it minimizes risk, this is because the emp itself actually isn’t powerful enough by itself to permanently destroy or even damage most electronics, but they can induce errant behaviour in a circuit that causes the circuit to kill itself, and that is why you pre emptively turn off equipment.

            of course stuff would break but it isnt the doomsday scenario most people are led to believe by hollywood, it would only be a percentage of stuff that would break permanently, far lower than 50% at any range where the fireball wouldn’t fry you anyway or the pressure wave crush your lungs.

  2. In the runup to Y2k and through to the 2010s I had a book author connection in the survivalist nut movement who would feed me paranoids with big cash for private consultation and sometimes even very expensive besopke fabrication or design projects. It just got too crazy with the (friendly) wacko creeps and constant creative changes and feature creep way past that stage of the project.
    Those survival guys have rewatched The Day After too many times and just imagine a wave of holy EMP magic wiping out all post-age of steam tech except their stuff in trash can Faraday cages and setting them up with their bazillion bullets and MREs as the new local feudal barrons, or quickly transported to white-right-gun heaven.
    I used to try to explain the tech and mil-specs, but these guys believe in the magic(or teh white Revelations gun-Jesus waves) and have the dream of being the only ones smart enough to be prepared for X.
    I did write a few articles pointing out that even crude boosted fission devices are unlikely/ineffective EMP devices and that it takes a superpower to design and loft a good Megaton+ H-bomb EMP activator, but I feel like I did brought the Carrington Event Solar storm to the fore of the EMP cult’s mind in the early to mid 2000s, a dubious honor.

    1. It takes at least a 700 gauss magnetic field *in motion* to alter the data on a credit card magnetic stripe. Mythbusters tested fields to thousands of gauss without effect on test cards.

      It was only when Adam took the card off the electromagnet before Jaime turned it off that they figured it out. Then they re-did the tests and zeroed in on 700 gauss as the minimum.

      If you just stuck a card in a swipe slot then twiddled the read/write head with pulses, it wouldn’t do a thing to the stripe. You have to slide the card while the write pulses are happening.

    1. Interesting. They mention taking out electronics “even before the first troops arrive”. When I heard this was using microwaves to take out electronics I wondered if these would be powerful enough to harm humans passed over by the beam. That statement makes me thing that yes, it would be.

      1. I think that was more likely related to OSHA regulations (excluding humans from the test site). Taking out humans involves complex issues with neuro-electrochemical reactions. It’s way easier to fry electronics. Taking out command and control centers before troops arrive drastically lowers battlefield mortality. That is what I read.

  3. When I was a kid, our dog had one of those invisible fence collars and he’d go nuts when he was in the car when it was started. My dad realized pretty quickly that the ignition was setting off the collar, so we always remembered to take it off the dog on car rides after that.

  4. You didn’t include Electrical Discharge Machining (EDM) in your list. EDM uses a controlled spark gap to burn away metal, and is commonly used in the tool & die world. EDM is an effective way to machine some of the common tool steels that are either really brittle, really tough, or both. And because the spark gap can be precisely set, some very tight tolerances can be achieved.

    A company I used to work for grinds custom screw threads. They had some tool & die customers who occasionally had them put very accurate threads on a set of graphite rods. These were used in an EDM machine to burn a thread-shaped cavity in a tool-steel mold to be used for plastic injection. This allowed the plastic company to make injection molded screws in one operation, which is much cheaper and faster than cutting a thread with a die on a blank plastic cylinder.

    What I don’t know is how much harmful EMI an EDM machine produces, or what its range would be. Anything using an electric spark to burn away hardened tool steel has to have some serious current flowing through it, so I imagine it’s large enough to either be somehow contained or otherwise regulated.

  5. There is a nice website, which had brought me to write this comment. A brilliant man, by the name of Robert Iannini who has an “amazing” website: http://www.amazing1.com also known as Information Unlimited. His H.E.R.F. and EMP weapons are amazing. I have purchased quite a few items in my time from his site, and even the plans for some H.V. gear. You never know when you need a few kilo-volts to drive a nice tube amp for my ham radio gear. Give his sight a bit of a once over, and check out his EMP videos as well.

    1. I remember those ads from the electronics magazines of the ’90s. I’m sure some of their stuff is legit, but the ads had an “Amaze Your Friends with X-ray Glasses!!!” vibe that suggested otherwise.

    1. … emit surprisingly small/inconsequential pulses. Friend of mine did that trick at an annual physics picnick. It caused glitches on the screens of digital cameras, but no more. I can’t remember the capacity, but it was at 15-20 kV on a capacitor as big as a large suitcase.

      OTOH, the thick copper coil that broke through the cinderblock that contained it was pretty impressive. I hid behind a tree.

  6. “The EMP was strong enough to cause damage in Hawaii, over 1,400 kilometers away from the blast.”

    The Starfish Prime electromagnetic pulse also made those effects known to the public by causing electrical damage in Hawaii, about 1,445 kilometres (898 mi) away from the detonation point, knocking out about 300 streetlights, setting off numerous burglar alarms and damaging a telephone company microwave link. The EMP damage to the microwave link shut down telephone calls from Kauai to the other Hawaiian islands.

    The microwave link was restored by replacing fuses. And the 300 streetlights were all on a single circuit that a single transformer blew that was suspected to be weak already.. My father was stationed in Hawaii when it happened, he had some really cool photos of the glow in the sky that my mother hopefully still has.

    More REAL data on the starfish test and detailed results of an EMP can be found at http://ed-thelen.org/EMP-ElectroMagneticPulse.html

    Basically, Unless you are within the bomb blast radius, the communists will not be EMP attacking your CB radio and trying to squelch freedom.

  7. I disagree with “It’s rare that we recommend against exploring some topic for DIY research”, if used responsibly inside of shielding at low power. You can’t design systems that are protected against natural or man made EMP, without having access to the cause of the problem.

    Suppose you designed some opto-isolated onion layed attenuation system, with no means of testing if it worked, or or how well it worked, it is not really a product that could ever be brought to market.

    1. “if used responsibly inside of shielding at low power” was not the spirit of the article. Small sparks are cool, and it’s important to test electronics against interference.

      The point was just that large/disruptive EMP blasts, from immobilize-a-vehicle on up, are completely out of the realm of the DIY, and probably even most evil masterminds or bank robbers, Hollywood be damned.

  8. There was more bad Hollywood EMP-ness on last week’s Agents of S.H.I.E.L.D. Terrorists set up EMP pulse generators in seven large cities, pumping out a pulse every two seconds.

    When the things got turned off by shield, everything worked again. They also used the trope of it not affecting things which weren’t powered up.

    Even worse was the maps of the affected areas. In Sci-Fi you can Gerrymander how magnetic fields work. ;) The zones should have been circular.

    The one thing they got halfway right was the pulses not affecting Ghost Rider’s old car, except Daisy said that cars before 1980 don’t have electronics. Oh so wrong-o! Except for some heavy trucks, vehicles in the USA had to have electronic ignition starting in 1974. By 1976, every new gasoline powered road vehicle had electronic ignition. (1974 was also when every new passenger vehicle, except ones for which 1974 was a model’s final year, were required to have front disc brakes.)

    What’s real odd in the real world is that diesel powered semi-trucks hash my ATSC TV antenna reception when they drive past my house. Just the diesels! How the hell are they producing RFI?

    I’m pretty close to a railroad track and the engines also have some effect on TV reception, but they have the reason of massive generators and motors working with a lot of electricity and strong magnetic fields. Since the track is farther away than the road, the noise strength gets reduced a bunch by distance, and the concrete and masonry buildings blocking much of the lines of sight between track and house.

    Sucks that digital TV is far less fault tolerant than analog. NTSC could degrade quite a bit and still be watchable. ATSC either works or it doesn’t, no in between.

    1. There was a study done and after a emp most cars will restart by resetting the cars computer by disconnecting the battery.

      As for the RFI from the trucks, maybe the alternator?

    2. Diesel engines today have electric injection valves, either piezo or electromagnetic. And they have to be really fast as several short injections during one piston stroke are used. So we are talking about a power range of a kW pulse peak power. Perhaps this is the source of EMI.

    3. “”Oh so wrong-o! Except for some heavy trucks, vehicles in the USA had to have electronic ignition starting in 1974. By 1976, every new gasoline powered road vehicle had electronic ignition. (1974 was also when every new passenger vehicle, except ones for which 1974 was a model’s final year, were required to have front disc brakes.)””

      Um… source? My 1978 VW convertible, sold in the USA in ’78, has points and drum brakes all around. Bug hardtops were sold until 1976 with drum fronts and point type ignitions. Buses got the disc brakes in front in ’71, but no electric ignition until the Vanagon in 1980. (49 state.. Cali may have been different)

      Rabbits in 1976 had points also. But they did have disc brakes in front. :)

    4. EMP’s have to be far more powerful than nuclear to guarantee most electronics wont work, even nuclear emp’s cant actually destroy something like the European grid permanently, I don’t know where this myth that any emp at all instantly means northing electronic will ever work again, comes from, but it is false.

    5. “What’s real odd in the real world is that diesel powered semi-trucks hash my ATSC TV antenna reception when they drive past my house. Just the diesels! How the hell are they producing RFI?”

      I would be more inclined to believe what your seeing is more the effect of mutli-path than RFI. Trucks like that have large flat metal surfaces that are going to reflect TV signals. Multi-path is a big issue with OTA digital TV signals.

  9. A lot of confusion going on with EMP vs. EMI… I think posting articles where you have zero idea as to what you are talking about is a bad idea on the interwebs where there are no shortage of Wikipedia and Google “smarts” that read something and then go with whatever their little imaginations dream up, and that’s how myths start and get spread.

    If you have a couple of thousand dollars and the time, Texas Tech has short course on pulsed power that covers a lot of this in depth. They may even take you out to the range for some live fire demos and they’ll stuff you with Texas BBQ to boot!

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