It sounds like the perfect weapon. Without fracturing a single brick or
spilling a drop of blood, it could bring a city to its knees. The few scientists
who are prepared to talk about it speak of a sea change in how wars will be
fought. Even in peacetime, the same technology could bring mayhem to our daily
lives. This weapon is so simple to make, scientists say, it wouldn’t take a
criminal genius to put one together and wreak havoc. Some believe attacks have
started already, but because the weapon leaves no trace it’s a suspicion that’s
hard to prove. The irony is that it’s our love of technology itself that makes
us so vulnerable.
This perfect weapon is the electromagnetic bomb, or e-bomb. The idea behind
it is simple. Produce a high-power flash of radio waves or microwaves and it
will fry any circuitry it hits. At lower powers, the effects are more subtle: it
can throw electronic systems into chaos, often making them crash. In an age when
electronics finds its way into just about everything bar food and bicycles, it
is a sure way to cause mass disruption. Panic the financial markets and you
could make a killing as billions are wiped off share values. You could freeze
transport systems, bring down communications, destroy computer networks. It’s
swift, discreet and effective.
Right now, talk of the threat of these weapons is low-key, and many want it
to stay that way. But in some circles, concern is mounting. Last month, James
O’Bryon, the deputy director of Live Fire Test & Evaluation at the US
Department of Defense flew to a conference in Scotland to address the issue.
“What we’re trying to do is look at what people might use if they wanted to do
something damaging,” he says. With good reason, this is about as much as O’Bryon
is happy to divulge.
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E-bombs may already be part of the military arsenal. According to some, these
weapons were used during NATO’s campaign against Serbia last year to knock out
radar systems. So do they really exist? “Lots of people are doing lots of work
to protect against this type of thing,” says Daniel Nitsch of the German Army
Scientific Institute for Protection Technology in Muster, Lower Saxony. “You can
make your own guess.”
Interest in electromagnetic weapons was triggered half a century ago, when
the military were testing something a lot less subtle. “If you let a nuclear
weapon off, you get a huge electromagnetic pulse,” says Alan Phelps of the
University of Strathclyde in Glasgow. If this pulse hits electronic equipment,
it can induce currents in the circuitry strong enough to frazzle the
electronics. “It can destroy all computers and communications for miles,” says
Phelps.
But the military ran into problems when it came to finding out more about the
effects of these pulses. How could they create this kind of powerful pulse
without letting off nuclear bombs? Researchers everywhere took up the
challenge.
The scientists knew that the key was to produce intense but short-lived
pulses of electric current. Feeding these pulses into an antenna pumps out
powerful electromagnetic waves with a broad range of frequencies. The broader
the range, the higher the chance that something electrical will absorb them and
burn out.
Researchers quickly realised the most damaging pulses are those that contain
high frequencies. Microwaves in the gigahertz range can sneak into boxes of
electronics through the slightest gap: vent holes, mounting slots or cracks in
the metal casing. Once inside, they can do their worst by inducing currents in
any components they hit. Lower radio frequencies, right down to a few megahertz,
can be picked up by power leads or connectors. These act as antennas, sending
signals straight to the heart of any electronic equipment they are connected to.
If a computer cable picks up a powerful electromagnetic pulse, the resulting
power surge may fry the computer chips.
To cook up high-frequency microwaves, scientists need electrical pulses that
come and go in a flash—around 100 picoseconds, or one ten-billionth of a
second. One way of doing this is to use a set-up called a Marx generator. This
is essentially a bank of big capacitors that can be charged up together, then
discharged one after the other to create a tidal wave of current. Channelling
the current through a series of super-fast switches trims it down to a pulse of
around 300 picoseconds. Pass this pulse into an antenna and it releases a blast
of electromagnetic energy. Marx generators tend to be heavy, but they can be
triggered repeatedly to fire a series of powerful pulses in quick
succession.
Deadly burst
Marx generators are at the heart of an experimental weapons system being
built for the US Air Force by Applied Physical Sciences, an electronics company
in Whitewater, Kansas. “We’re trying to put them on either unmanned aerial
vehicles or just shells or missiles in an effort to make an electromagnetic
minefield,” says Jon Mayes of APS. “If something flies through it, it’ll knock
it out.” It could also be used on a plane to burn out the controls of incoming
missiles, says Mayes. Put it on the back of a military jet and if a missile
locks onto the plane, the generator can release a pulse that scrambles the
missile’s electronics.
Marx generators have the advantage of being able to operate repeatedly. But
to generate a seriously powerful, one-off pulse, you can’t beat the oomph of
old-fashioned explosives. The energy stored in a kilo or two of TNT can be
turned into a huge pulse of microwaves using a device called a flux compressor.
This uses the energy of an explosion to cram a current and its magnetic field
into an ever-smaller volume. Sending this pulse into an antenna creates a deadly
burst of radiowaves and microwaves.
Simplicity is one of the flux compressor’s big attractions. Just take a metal
tube, pack it with explosives, and stick a detonator in one end. Then fix the
tube inside a cylinder of coiled wire, which has a wire antenna attached at the
far end. Finally, pass a current through the coil to set up a magnetic field
between the metal tube and the coil, and you’re ready to go
(see Diagram).
Setting off the detonator triggers the charge, sending an explosion racing
along the tube at almost 6000 metres per second. If you could slow this down,
you’d see that in the instant before the explosive pressure wave begins to
shatter the device, the blast flares out the inner metal tube. The distorted
metal makes contact with the coil, causing a short circuit that diverts the
current—and the magnetic field it generates—into the undisturbed
coil ahead of it. As the explosive front advances, the magnetic field is
squeezed into a smaller and smaller volume. Compressing the field this way
creates a huge rise in current in the coil ahead of the explosion, building a
mega-amp pulse just 500 picoseconds wide. Finally, just before the whole weapon
is destroyed in the blast, the current pulse flows into an antenna, which
radiates its electromagnetic energy outwards. The whole process is over in less
than a tenth of a millisecond, but for an instant it can spray out a terawatt of
power.
Tom Schilling of TPL, an electronics company in Albuquerque, New Mexico, is
working along similar lines with the microwave weapons he’s developing for the
US Air Force. “We’re using explosive flux generators to generate the power, then
sending that straight into an antenna,” he says. “One of the systems we’re
looking at is a guided bomb that can be dropped off a plane. Targets would be
things like command and control centres—we should be able to shut those
down with little or no collateral damage.” Schilling’s company is also looking
at putting flux compressors into air-to-air missiles. It’s an appealing idea, as
even a near miss could bring down a plane.
It certainly ought to be practical. As long ago as the late 1960s, scientists
sent a pair of flux compressors into the upper atmosphere aboard a small rocket
to generate power for an experiment to study the ionosphere. “You can build flux
compressors smaller than a briefcase,” says Ivor Smith, an electrical engineer
at Loughborough University who has worked on these devices for years.
Perhaps the biggest benefit of these weapons is that they carry the tag
“non-lethal”. You could take out a city’s communications systems without killing
anyone or destroying any buildings. In addition to the obvious benefits for the
inhabitants, this also avoids the sort of bad press back home that can fuel
opposition to a war. But that doesn’t make these weapons totally safe,
especially if they’re being used to mess up the electronics of aircraft. “If
you’re in an aeroplane that loses its ability to fly, it’s going to be bad for
you,” points out James Benford of Microwave Sciences in Lafayette,
California.
Another big plus for people thinking of using these weapons is that
microwaves pass easily through the atmosphere. This means that you can set off
your weapon and inflict damage without having to get close to your target.
“People think in terms of a kilometre away,” says Benford. According to some
estimates, a flux compressor detonated at an altitude of few hundred metres
could wipe out electronics over a 500-metre radius.
Electromagnetic weapons can be sneaky, too. You don’t have to fry everything
in sight. Instead you can hit just hard enough to make electronics
crash—they call it a “soft kill” in the business—and then quietly do
what you came to do without the enemy ever knowing you’ve even been there. “That
could be useful in military applications when you just want to make [the
opposition] lose his electronic memory for long enough to do your mission,”
Benford says. “You can deny you ever did anything,” he adds. “There’s no
shrapnel, no burning wreckage, no smoking gun.”
Did it work?
The downside is that it can sometimes be hard to tell when an electromagnetic
weapon has done its job. This is compounded by the fact that unless you know
exactly what kind of electronics you are attacking, and how well protected they
are, it’s hard to know how much damage a weapon will do. This unpredictability
has been a major problem for the military as it tries to develop these weapons.
“Military systems have to go through an enormous amount of development,” says
Benford. “The key thing is that it has to have a clearly demonstrated and robust
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Tests like this are close to the heart of Nigel Carter, who assesses aircraft
for their sensitivity to microwaves at Britain’s Defence Evaluation and Research
Agency in Farnborough, Hampshire. Microwaves can easily leak between panels on
the fuselage, he says. “You’ve also got an undercarriage with hatches that open,
there’s leakage through the cockpit, leakage through any doors.”
To find out how bad that leakage is, Carter could simply put the plane in a
field and fire away at it with microwaves. But he has to be careful. “If we go
blatting away at a very high level at hundreds of frequencies, people in the
nearest town get a bit upset because they can’t watch TV any more,” says Carter.
“It’s very unpopular.”
To avoid annoying the neighbours, Carter beams very low-power microwaves at
the plane. Sensors on board—linked by fibre optics to data recorders so
they are immune to the microwaves—record the currents induced in the
plane’s electronics.
Knowing what currents are produced by weak microwaves, Carter calculates what
kinds of currents are likely to be produced if the plane is hit by a more
powerful pulse of microwaves. “You can then inject those currents directly into
the electronics,” he says. The results can be dramatic. “The sort of effects you
might expect to get if it’s not protected are instrumentation displaying wrong
readings, displays blanking out and you could, in the worst case, get
interference with your flight controls,” he says.
The idea of weapons like these being used in warfare is disturbing enough,
but what if criminals get their hands on them? According to Bill Radasky, an
expert in electromagnetic interference with Metatech in Goleta, California, they
may have already done so. A basic microwave weapon, he says, can be cobbled
together with bits from an electrical store for just a few hundred dollars. Such
a system would be small enough to fit in the back of a car and could crash a
computer from 100 metres away.
Other systems are even easier to acquire. Some mail-order electronics outlets
sell compact microwave sources that are designed to test the vulnerability of
electronics. But they could just as easily be used in anger. “We’ve done
experiments that show it’s very easy to do,” says Radasky. “We’ve damaged a lot
of equipment with those little boxes.” If some reports are to be believed,
they’re not the only ones.
Criminals may have already used microwave weapons, according to Bob Gardner
who chairs the Electromagnetic Noise and Interference Commission of the
International Union of Radio Science in Ghent, Belgium. Reports from Russia
suggest that these devices have been used to disable bank security systems and
to disrupt police communications. Another report suggests a London bank may also
have been attacked. While these incidents are hard to prove, they’re perfectly
plausible. “If you’re asking whether it’s technologically reasonable that
someone could do something like this,” says Gardner, “then the answer is
.”
Gardner’s claims are backed by Nitsch. He is investigating how vulnerable
computers and networks are to powerful bursts of microwaves. Surprisingly, he
has found that today’s machines are far easier to crash than older models. He
says computer manufacturers used to be more worried about electromagnetic
interference, so they often put blocks of material inside to absorb stray
signals, and ran strips of copper around the joins in the casing to keep
microwaves out.
That modern computers have less protection is bad enough. But they are also
more susceptible because they are more powerful. To push signals around faster,
you must reduce the voltage to ensure that the extra current doesn’t make the
processor chips overheat. In the 1980s, most computers operated at 5 volts.
Today’s machines operate at nearer 2 volts, says Nitsch, making their signals
easier to disrupt. Networks are particularly susceptible, he adds, because the
hundreds of metres of cabling connecting their workstations can act as an
efficient radiowave receiving antenna.
Secret attacks
So are businesses taking the threat seriously? Radasky knows of only one
European company that has protected its control centre against microwave
weapons. Gardner believes it will take a high-profile attack to raise awareness
of the issue. But combine the lack of evidence left by microwaves with
companies’ reluctance to admit their systems have been breached and you’d expect
attacks to go unreported.
The good news is that protection isn’t too difficult if it’s done at the
design stage, says Carter. The first thing to do is make sure you’ve got
well-constructed circuits. This means using strong signals that can easily be
distinguished from the fuzz of noise generated by microwaves. “You also want to
make sure your circuitry only responds at the frequency it’s supposed to,” he
says. So if your computer is intended to respond to signals coming in at 500
megahertz, you want to make sure it won’t also respond to signals at twice that
frequency—the kind that could be induced by microwaves. Another step is to
wire in filters that absorb large surges of current—much like those used
to protect against glitches in the mains power supply following lightning
strikes.
Regardless of whether these weapons have been used yet, they highlight the
way our dependence on electronics could become our Achilles’ heel. The next time
your computer crashes, don’t automatically blame Bill Gates. Just wander over to
the window and look out for that unmarked van that sometimes parks across the
street. Could there be someone inside sending a blast of microwaves your
way?
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