Electromagnetic Weapons

Long article in IEEE Spectrum.

Posted on September 2, 2014 at 11:08 AM • 33 Comments


Mark JohnsonSeptember 2, 2014 11:31 AM

Working behind a panel of networked factory controls I noticed I could reset boards by just keying a 5W FM walkie-talkie. That was years ago though.

I don't know what to think about EMP because some say the threat is exaggerated and nuclear weapons have already been exploded in the atmosphere without hurling us into the dark ages. Another says it's the biggest threat of all.

AlfredoSeptember 2, 2014 11:32 AM

If I remember correctly, electromagnetic weapons (and I believe they meant EM induction weapons, as laser weapons are also electromagnetic but their effect is mainly thermal) is a controlled export tech in the US and a restricted technology because of its military use. It would be cool to see more public research about the matter.

ReSeptember 2, 2014 11:47 AM

The fall-off with range is significant. However, at higher frequencies, you can get very directional emissions.

What they're talking about are HERF weapons. High Energy Radio Frequency. Beware the dangers. At the frequencies and power they're talking about, human exposure is not safe.

Google for HERF Weapon. You'll find lots of descriptions, and do it yourself projects. Some of these weapons will shut down a car at a considerable distance.

AnuraSeptember 2, 2014 11:51 AM

@Mark Johnson

"I don't know what to think about EMP because some say the threat is exaggerated and nuclear weapons have already been exploded in the atmosphere without hurling us into the dark ages. Another says it's the biggest threat of all."

It's not necessarily all atmospheric detonations that are the problem, it's high altitude detonations. They have been known to knock out satellites as well as ground electronics for a very long distance because of their line of sight. Stone age? Probably not. Significant economic damage if detonated within line of sight of a high population area? Definitely. Satellites in geosynchronous orbit are probably safe (barring a nuclear explosion designed to take them out), although those in low earth orbit are at risk; luckily GPS and most communication satellites are in geosynchronous orbit.

CassandraSeptember 2, 2014 3:00 PM


Be careful, geosynchronous doesn't mean what you think it means.

A lot of communications satellites are in geostationary orbits, which means that they appear to hover over a fixed equatorial point on the earth's surface, as their orbital period is 24 hours.

However, geosynchronous simply means that the satellite's orbital period is 24 hours. The spot on the earth's surface directly under the satellite traces a path over the earth, rather than staying in the same place. If the satellite's orbit is tilted (inclined) with respect to the plane of the equator, the path moves north and south of the equator. GPS satellites are in such inclined orbits, but their orbital periods are shorter than geosynchronous satellites - they are closer to the earth (in medium earth orbit) rather than geostationary orbit.

Iridium communication satellites are in low earth orbit (at roughly 780 kilometres above the Earth's surface)
GPS satellites are in medium earth orbit (roughly 20,200 kilometres, giving an orbital period of just under 12 hours) (Glonass, Galileo, and BeiDou are in similar orbits)
Many communications satellites are in geostationary orbit at 35,786 kilometres.

name.withheld.for.obvious.reasonsSeptember 2, 2014 4:55 PM

Two things shock me about this issue (electromagnetic pun intended) and the coverage given thus far (IEEE included). Back in the late 1990's and early 2000's I had the chance to work in this area, research based on high energy RF Marx's generators and unique power sources and "ladders". What was apparent by way of our research was the lack of background data that could demonstrate both R^2 losses and impacts of linear and non-linear time-domain based repetition technigues. Of interest (source "guns" demonstrated corona decays over time) was the "skin effects" respecting dielectrics of various types. For example, a system that included any non-insulated conductor (typically metallic) became an attenuation surface. Using various techniques it was possible to induce "summing" on known surface types.

Another feature of our research also demonstrated the political nature of the "business". We, in our efforts, were primarily interested in non-leathal weapons systems for DoS purposes. Others in the field performed similar research but clearly had motives that were about the continuation of contracts and not results. A contractor dilebrately "lied" about "figures of merit" and used this information to "eliminate" competitors. It was very disappointing to witness this kind of behavior and should be disturbing to others when worthwhile and earnest work is deliberated derailed by dishonest vendors and scientific research organizations.

One side note, there is little to describe what we discovered in our research that spoke more to the issue of the "shape" of the source then the total energy realized at the end of the "gun". I'd like to go deeper but out of respect for Bruce's generosity I need to keep it simple (unclassified). It's seems there is enough here to enpanel a senate committee on this type of abuse of the DoD research process.

Clive RobinsonSeptember 2, 2014 7:25 PM

I get the feeling that the author or one of his sources has read this blog at some point, as untill recently this blog and the Cambridge Labs blog were the only places on the Internet that talked about active EM attacks using lower frequency modulation on a higher frequency EM carrier to get through ventilation etc slots. It is a subject that I've investigated on and off since the early 1980s

Further there is a lot of "guess work" on the Internet by people about EM Weapons and many of the designs are like those you can find for "personal jet belts" etc, they look like they should work but they don't in practice or are extreamly dangerous to use (the directed output of a microwave oven for instance can cook your eyes and nervous system beyond use in seconds).

Outside of the specialist and mainly ineffective chemical, biological and malware weapons, conventional and EM weapons are all about directing energy at a target to impare it's function temporarily or permanently. This can be done as either a radiating system (ie a blast wave) or as a kinetic system (ie a projectile) of the two a kinetic weapon is usually more efficient against a distant target.

EM weapons that are used are nearly all radiant weapons and suffer from an energy drop off proportional to a portion of a surface of an expanding sphear and thus drops in the far field (ie inversly to the square of the distance). In the near field the energy drops to one fiftieth of the power within two wavelengths for two isotropic radiators, which means that to direct the energy to a given target needs a high gain antenna.

Very roughly for a TV type yagi-uda array antenna, which is one of the more space efficient antennas, count the number of quaterwave spaced directing elements on the boom and muliply the number by three to get a crude ball park estimation of the forward gain. That is the gain of of a yagi antenna is proportional to the boom length that holds unobstructed directors, but after a relativly few directors (20) they become an engineering nightmare for little extra gain. Which is why for microwave and above frequencies large reflector antennas such as parabolic dishes are used which are mechanicaly simple to design and build and can offer very high gains. Either way high directionality antennas are large compared to the wavelength in use and this makes for an unwieldy weapon at anything below the higher microwave frequences.

EM weapons can be broadly classified as CW or Pulse systems, both of which can be used to disrupt or damage a target electronic system. For various reasons disruption is prefered to damage, one pragmatic reason is that disruption can usually be easily obtained at less than one thousandth of the radiated power needed to cause destruction which gives an effective range increase of over thirty times.

Destruction can happen in one of several ways the two most commonly considered are I^2R heating and electrostatic breakdown of device junctions. In both cases low impeadence short track length circuits are a good place to start along with low impedence screening around sensitive electronics.

Pulse based EM weapons utilise very fast rising edges, that contain energy across a very wide range of frequencies, the problem is that due to the relativly low speed of voltage limiting components such as varistors considerable energy can get through before they start to work, even transorbs and zener circuits will be much slower than modern RF FETs. The way to deal with this is by multiple filters before and after the active limiting devices, though care needs to be excercised to prevent ringing. That said the energy has to go somewhere, and this is where earth circulating currents etc need to be considered in some detail.

The subject of protection small electrical equipment against lightning strikes and protection of implanted medical electronics against defibulators is a good place to get a feel for the issues involved.

The subject of designing equipment to protect against EM weapons is one that would fill several text books. Equally so is how to design EM weapons such that they don't kill, maim or disable the operators of the weapons.

Chris AbbottSeptember 2, 2014 7:49 PM

You could shield all wiring and either put electronics in a basement with shielding on a ceiling or use a shielded safe room. I like the basement idea, but that's not always possible. I have no idea what to do with satellites. Other equipment that has to use RF would be impossible to protect, unless you could figure out a way to make a one way RF system, but this seems unlikely.

Chris AbbottSeptember 2, 2014 7:52 PM

Come to think of it, back in high school, my buddy took a microwave magnetron and put it in a tube to directionalize it and you could destroy any electronic device you pointed it at. This was back in the late 90's and early 2000's, so EMP isn't really anything new.

Chris AbbottSeptember 2, 2014 8:07 PM


My friend only used his device twice because the second time he did heat up a bit. The stuff he destroyed was only 2 or 3 feet away. You would have to activate it remotely. That could injure people nearby I'm guessing. I just gave away my age with the last post, which sometimes makes me feel both young and old. Oh well.

Iain MoffatSeptember 2, 2014 9:15 PM

@Chris Abbott: Radio systems have had the problem of EM pulse protection for decades because people put antennas on towers, hilltops and tall buildings which leads to lightning strikes. Professional radio systems use voltage-dependent devices on the antenna input (solid state voltage dependent resistors and gas discharge tubes)which become a short circuit to ground once the input voltage exceeds the threshold of the device - this short circuit keeps lightning and nuclear EMP current pulses from entering the radio. The challenge with Nuclear EMP is a rise time at least an order of magnitude faster than for lightning.


JeffHSeptember 3, 2014 3:47 AM

Considering how little actual work typically goes into EM compatibility, it's not terribly surprising that we're seeing electronics built that would be disrupted by deliberate EM efforts - even when the engineers in question knew better.

Designing a good protocol/circuit that takes what is effectively jamming into account and survives it is hard & expensive, more so the bigger the EM threat. No wonder companies often don't invest in it. Who hasn't come across a cheap network switch that intermittently had problems, and you discover an AC contractor had left their mobile phone on top of it (and it has a plastic case to save money...). How about the military radar domes that shut cars down as you drive within a few miles of them?

Commercial shielding is usually non-existent; the concept of a separate common ground is one that usually has a lot of electronic engineers going 'what's that?'. Even for those that have a grasp, trying to protect against all the ways in which your circuit might fail if exposed to EM of different kinds (ranging from lightning induction to EM pulses to a nearby Bluetooth transmitter being brought too close) is non-trivial. Clive covered the technical stuff far better than I could.

Our use of the wireless spectrum is just as guilty - why does your Bluetooth signal reduce when someone is cooking in the kitchen? Bluetooth shares a lot of the same spectrum as microwave ovens (along with cordless phones, wireless video cameras, outdoor microwave links, wireless game controllers, Zigbee devices, fluorescent lights, and WiMAX). The signal to noise is such that it doesn't take much leakage (even taking inverse square into account) to reduce effective range.

The article highlighted one of the most critical measures that we as a society still mostly refuse to take - use optical fiber for all communications. Not only is the current approach wasteful of copper, but fiber isn't susceptible to a host of these problems, and isolates your system from others that might be attacked or disrupted.

vas pupSeptember 3, 2014 10:57 AM

"It’s not enough to patch holes that bad actors have discovered; we must also try to anticipate attacks that haven’t yet occurred."
This extract from the article caught my attention because it is clearly pointed to necessity of switching from reactive security paradigm to proactive. Proactive one required creativity (anticipation) to develop concept first. Unfortunately, on the surface US globally still following Napoleon motto: "It is important to engage in the battle first, then proceed accordingly". I was recently pleased to hear from current POTUS (regardless you like him or not) necessity on concept first(related to actions against ISIS).

GarrettSeptember 3, 2014 2:32 PM

Does anybody have suggestions on what's required for a residence to become resistant to EMP attacks, assuming that they aren't the direct target? What's cost-effective?
I have a wired network using Cat5e UTP. Is that resilient on its own? What happens if I wrap the existing wiring in aluminum foil? Wrap metal duct-work around the longer section runs? Convert to Cat6?


AnuraSeptember 3, 2014 3:04 PM

It doesn't matter how your devices are connected if the devices themselves are vulnerable to EMP attacks. Consumer electronics in general are not designed to protect against them, so you would need to shield each device. Personally, I don't think it's a big enough threat to worry about. That said, power surges, which can be caused by EMP but are much more likely to occur for other reasons, are the main concern if your devices aren't fried by a direct EMP burst, and the best way to protect against them is with a surge protector. If you are worried about ethernet, you can get surge protectors for those as well (many mid-end surge protectors have ethernet surge protectors built in).

Clive RobinsonSeptember 3, 2014 5:48 PM

@ Garret,

Does anybody have suggestions on what's required for a residence to become resistant to EMP attacks, assuming that they aren't the direct target? What's cost-effective?

As I pointed out above EM weapons are in general either very short range or highly directional or both. The well known exception is as a result of the EM frequency step down from a nuclear device.

As Anura points out I would not worry about an EMP attack, that is not specifically aimed at you, because the chances are you have far bigger things to worry about.

A direct lightning strike to a power or communications node is more likely to happen and stoping that is difficult enough that few bother to even try. You have to make the choice between protection and replacment, and most business continuity plans opt for reliable backups and insurance replacment of equipment.

Decent backup tapes stored in lightning proof containers stored in two or more geographical seperated places is the main factor along with clearly written re-instalation and setup guides. It also helps if you have thought about how you are going to initialy setup the computers, such as seperate drive partitions for system / swap / apps / data to aid in easy backup and reinstalation, also having original media for the OS and apps stored in a lightning proof storage container in two or more places would be desirable, especially for software that's more than a year old. Further think about what data formate you are going to save in, proprietary data file formats are a disaster waiting to happen, standard well documented and supported formats like CSV, RTF are better also avoid "object linking" it was, is now and for ever more a bad idea unless you set it up correctly (even then it's still best to avoid as changes happen).

If you opt to protect then you have a difficult as well as expensive job on your hands... Firstly identify all direct and indirect earths and check they are correctly electricaly bonded, 99.99 to 100% of domestic systems are not, nor are office or light industrial. You can see this by the way ordinary electricians "neatly coil up" the earth bonding wires. That coil is an inductor which will be a very high impedence to even moderatly low frequencies, which means it might as well be an open circuit to the main energy of a lightning bolt, even when short "straps" are used the bonding may not be good enough. Those big thick connectors you see on lightning conductors are more for low inductance than their current carrying capacity. Properly earth bonding is an art as any amateur / ham radio operator that runs high power will tell you. You must have only one point of earthing and all equipment must be "star configuration" on power and earthing, that is no ring circuits etc where conductors are shared directly or indirectly. Likewise you need to correctly seperate power conductors and signal conductors, good practice says atleast a metre apart and parallel runs should be no more than two metres to keep the coupling factor down (remember we are talking voltage and currents beyond sensible comprehension, that fuse soil to glass like objects upto a foot long, and blow mighty trees to smouldering fragments).

All equipment should be galvanicaly issolated both for power and communications, which means no copper network cables all star connected fiber without metal sheathing. Power should come through a proper all conductor filter followed by a varistor over voltage protection before going into an isolation transformer. The equipment side of the transformer should have a varistor protector followed by a filter followed by a communications grade spark gap overload protector and multiple transorbs or equivalent. This isolator alone will cost more than a fairly good desktop or laptop computer to buy and install correctly. Which is why the replace rather than protect option makes more financial sense.

Further setting up a properly thought out and implemented backup&replace procedure will protect you from other much more likely events such as fire, theft, malware, accidental damage, and having the very poor MTTF of consumer electronics bite you etc...

Wesley ParishSeptember 4, 2014 3:34 AM

If, as is usually the case, the walls are mere masonry, without metal shielding, the fields will attenuate only slightly.

If the building is mere masonry with no internal reinforcing that can operate as shielding, the owners may be playing with the lives of the people inside: in the 2011 Christchurch earthquake those were the buildings hardest hit. So I'm sure the California building code is more than adequate for protection against all but the mightiest of electromagnetic pulse weapons.

Now OT: Lockheed Martin Shows Off High-Power Fiber Laser Weapon

These weapons are precisely the tools one would need to change the orbit of an asteroid that is on a collision course with Planet Earth. The chances they could be made small enough to fit inside a Soyuz chassis to match orbits with such an asteroid and change its orbit to one non-threatening. But the chance that anyone in Lockheed or Boeing or the US Navy or the US Air Force would be public-spirited enough to make them available for such a mission? I'm sure I could count up to twenty on the fingers of my right foot, or the toes of my left hand before they would ever let such a thought within a gigaparsec of their minds ...

David HendersonSeptember 4, 2014 11:32 AM

There is an IEEE paper that says the EMP threat is way overblown.

"Effect of the FAST NUCLEAR ELECTROMAGNETIC PULSE on the Electric Power Grid Nationwide: A Different View" by Mario Rabinowitz, Electric Power Research Institute Palo Alto, California 94303


This paper primarily considers the potential effects of a single high-altitude nuclear burst on the U.S. power grid. A comparison is made between EMP and natural phenomena such as lightning. This paper concludes that EMP is no more harmful to the power grid than its counterparts in nature. An upper limit of the electric field of the very fast, high-amplitude EMP is derived from first principles. The resulting values are significantly lower than the commonly presented values. Additional calculations show that the ionization produced by a nuclear burst severely attenuates the EMP.

Thomas_HSeptember 5, 2014 3:28 AM

@ keiner:

So that happened to other people too? I noticed that several other sites had trouble loading as well at the same time, including a forum I use that for some reason did not seem to get its CSS and images loaded. Just like Bruce's blog it is hosted in the USA.

RE: EM weapons: I think I first read about such things in the late 1980s-early 1990s in a popular science journal (and figured both unidirectional and area-effect versions of such weapons could be handy to take out enemies, vehicles or living). It's also a topic that generally comes up when discussing the aftereffects of nuclear weapons - although I just realized that in most recent popular-science articles about the subject that aspect tends to be ignored. IIRC, one of the points that usually gets raised is that reinforced concrete, as used in a lot of modern constructions, shields the inside of a building up to a degree from such weapons. Although I guess that depends on the type of armature used (amount of metal + grid structure), and won't be of much help in most typical buildings where only the side walls of each building unit are reinforced concrete, with the front and rear of the building being mostly wood and bricks.

divSeptember 5, 2014 9:22 AM

@keiner, @Thomas_H

Yup. As far as I could tell, http:// attempts were serving valid redirectins to https://, but then the main page and various "indexy" type pages were serving blank responses. Valid cert, 200 OK, with Content-Length: 0.

(Which means the various sites that tell you whether it's "just you", which tend to just try to get a 200 response, would have believed that it was still up whether the problem was global or more localised.)

Direct links to articles, from Google or the twitter feed, still worked. Comment submission resulted in a 500 error.

Lasted for about a day.

Perhaps temporary anti-DDoS protection?

YoshiSeptember 8, 2014 12:48 PM

This topic interests me but primarily because I believe I have been a victim of physical abuse via electromagnetic weaponry. Don't laugh; prejudice is irrelevancy. It was traumatic.

I experienced painful burning sensations and sometimes spasms and what felt like bubbling in parts of my that implied a very sadistic operator. My genital area and nipples and sometimes internal organs were painfully hurt. I experienced a combination of pain, discomfort, anxiety, fear, depression, anger, irritation/irritability, and disgust.

Believe me, it was horrible. It was the worst sensations I have ever felt in my life.

A related sidebar...

I remember when there was actually some public news about a new (a few years ago) weapon being developed for use in the mideast to deter terrorists in Iraq for example. They actually joked and talked about it on CNN and showed volunteer people getting extremely uncomfortable when it was directed at them. That particular technology was considered non-lethal and "safe"(?), but it was a clear demonstration that these things exist. The source was several yards away from the demo targets if not further away. After the news debuted, it was hushed up again and I never saw anything about it again.

I'm not critical of the US military nor government about this technology, but I worry about people who have access to this type of technology getting out of hand sometimes and abuses happening by sociopaths and people who just don't give a damn.

Ultimately, I fear that there are some sadistic people somewhere who have used this technology in inhumane, terrible ways to disrupt people's lives and/or to use them as human experiment subjects against their will.

Until it happens to you, you are skeptical, but believe me, after it happens to you, your whole perspective is changed in a bad way.

Coincidentally, some of the attacks to my body seemed to stop after I contacted both federal law enforcement and a branch of the military. I'm not joking. It's a serious thing.

Most of the victim folklore on the internet about it though, is overshadowed by fiction and propaganda and exaggerated and misguided speculations. I remember it wasn't as bad in previous years. About the only info left on the internet is bad bad stuff, fiction, or nothing at all.

Anyways, I would like to get more access to information about documented human health risks, because I can't find very much info by myself yet.

Last but not least, around the same time of the physical bodily attacks, which I consider criminal acts, there were unexplained interruptions to some of my pro audio electronics which were not physically faulty, yet had intermittent failures unless for some reason I turned my portable fan on. This of course, made no sense. It was't hot. I think somebody was just messing with me and trying to interrupt my work.

Anyways, thanks for the article and maybe reconsider redacting some of the technical details so you don't end up teaching more people how to create weapons! But I'm OK with sharing info on how to make Faraday chambers and shielded rooms and such.

Peace is the only way.

_JimSeptember 16, 2014 5:39 PM

Clive Robinson • September 2, 2014 7:25 PM

"that talked about active EM attacks using lower frequency modulation on a higher frequency EM carrier to get through ventilation etc slots."

What does this mean exactly?

In transit, EM energy is essentially transparent to ANY other waves transiting that same space; there is no possibility of a 'low frequency' wave riding atop a higher frequency in order to avoid the WGBC (Wave Guide Beyond Cutoff) effect vis-a-vis a high frequency signal facilitating a low frequency signal's entering into a "room" via a "ventilation slot".

Surely you weren't attempting to describe AM modulation of a high frequency carrier signal with lower frequency modulating signal? This would still not allow a low frequency RF energy to enter the room (the result would still be the RF carrier +- the modulating frequency.)


Clive RobinsonSeptember 17, 2014 3:06 AM

@ Jim,

What do you know about point contact and metal oxide diodes?

The full answer to your question would require a considerable response, so I will give a very brief outline.

Put overly simply, any modulated EM carrier that is considered to be in the usable part of the RF EM spectrum when it meets a conductor will impart part of that energy into the wire, in sympathy with the carrier.

Now if the conductor is electricaly issolated it will re radiate the energy it has had imparted to it. The amount of energy it has imparted to it is very roughly proportionate to it's effective impedence and orientation to the carrier.

If however the conductor is connected to some kind of load, then some of the imparted energy will appear at the load.

If the load has some kind of diode like behaviour then the RF energy will be partialy demodulated and cause a baseband signal to be produced. Depending on other charecteristics of the load a current proportional to the baseband signal will flow. If sufficiently high in frequency the basband signal will reradiate from the wire.

Most IC's have protective diodes at their I/O pins, so a PCB trace will act just like the conductor. The resulting baseband signal will thus appear on the IC input and power supply and will get into many parts of the IC internals.

With regards the modulation it can be AM as you enquire but it can also be FM due to conductors behaving differently when near their resonant points.

There is an interesting side effect to this, in that if a conductor already has a signal on it, this can be super imposed onto any other current in the conductor. The result is both the reradiated EM carrier and it's reradiated baseband signal will be modulated with the signal. It's this effect that the TAO catalogue RADAR reflectors work on, and they trace their ancestry back through the "Thing" or "Great Seal Bug" developed by Theramin, but first written up publicaly by the man who analysed it. He was Peter Wright and the book Spy Catcher, which your local library should be able to get you a copy of.

Whilst there is information about these effects in engineering text books, you almost have to read between the lines to find it. There has been little or nothing published academicaly about active EM attacks, back in the early 1980s when I first started playing with them against the likes of electronic wallets and pocket gambling machines, not only was there no academic write ups, the academics were not interested in doing work on it.

And that's how it stayed untill fairly recently when a couple of students over at the UK's Cambridge Computer labs squirted a 10GHz carrier at a comercial TRNG and brought it's effective entropy from 2^32 to less than 2^7. What they did not do was --as I suggested-- follow it up by modulating the carrier. Which would have enabled them to induce values into the TRNG such that whilst the output would look like 2^32 again it would in reality follow a sequence they had induced. Which would have attracted more interest, especialy with the later NSA debacle over fixing standards etc.

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