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[] Microwave Weapons: The Dawn of the E-Bomb,

The Dawn of the E-Bomb

For the wired world, the allure and the danger of high-power microwave
weapons are both very real

By Michael Abrams

In these media-fueled times, when war is a television spectacle and
wiping out large numbers of civilians is generally frowned upon, the
perfect weapon would literally stop an enemy in his tracks, yet harm
neither hide nor hair. Such a weapon might shut down telecommunications
networks, disrupt power supplies, and fry an adversary's countless
computers and electronic gadgets, yet still leave buildings, bridges,
and highways intact. It would strike with precision, in an instant, and
leave behind no trace of where it came from.
In fact, it almost certainly is already here, in the form of high-power
microwave (HPM) weapons.
As their name suggests, HPMs generate an intense "blast" of
electromagnetic waves in the microwave frequency band (hundreds of
megahertz to tens of gigahertz) that is strong enough to overload
electrical circuitry. Most types of matter are transparent to
microwaves, but metallic conductors, like those found in metal-oxide
semiconductor (MOS), metal-semiconductor, and bipolar devices, strongly
absorb them, which in turn heats the material.

Microwave weapons researcher Edl Schamiloglu sits in front of the
Pulserad-110A accelerator, which his lab at the University of New Mexico
uses to produce single 100-nanosecond pulses of electron beams, each
pulse emitting hundreds of megawatts of power.

An HPM weapon can induce currents large enough to melt circuitry. But
even less intense bursts can temporarily disrupt electrical equipment or
permanently damage ICs, causing them to fail minutes, days, or even
weeks later. People caught in the burst of a microwave weapon would, by
contrast, be untouched and might not even know they'd been hit. (There
is, however, an effort to build a microwave weapon for controlling
crowds; a person subjected to it definitely feels pain and is forced to

"HPM sources are maturing, and one day, in the very near future, they
will help revolutionize how U.S. soldiers fight wars," says Edl
Schamiloglu, a professor of electrical and computer engineering at the
University of New Mexico in Albuquerque and one of the leading
researchers in this burgeoning field.

The fact that we seldom hear about HPM weapons only adds to their
exoticism. Last spring, stories leaked to the press suggested that the
Pentagon, after decades of research, had finally deployed such a device
in Iraq. And when news footage showed a U.S. bomb destroying an Iraqi TV
station, many informed onlookers suspected it was an electromagnetic

"I saw the detonation, and then I saw the burst?which wasn't much. If
they took the station out with that blast, I strongly suspect that we
used Iraq as a proving ground" for HPMs, says Howard Seguine, an expert
on emerging weapons technology with Decisive Analytics Corp., in
Arlington, Va.

But while the U.S. military proudly paraded assorted new war-making
technology during its conquest of Iraq, from unmanned combat aerial
vehicles to a new satellite-based tracking network, it remained
tight-lipped about this "mother of all weapons." Asked at a 5 March news
briefing to confirm the rumor, General Tommy Franks, head of U.S. forces
during the war, would only say, "I can't talk to you about that because
I don't know anything about it."

Military secrecy is nothing new, of course. What is known about
microwave weapons is that the U.S. military has actively pursued them
since the 1940s, when scientists first observed the powerful
electromagnetic shock wave that accompanied atmospheric nuclear
detonations, suggesting a new class of destructiveness.
While much of the work on HPMs remains classified, the Pentagon has also
recently sponsored a number of U.S. university laboratories to work out
the basic principles of microwave weapons, including reliable and
compact nonnuclear ways of generating microwave pulses.

Many of those results are being published in the open literature. In
fact, all you need is a reasonable grasp of physics and electrical
engineering to appreciate the ingeniousness of microwave weapons. Anyone
with a technical bent could probably also build a crude e-bomb in their
garage, a thought that security-minded folks find rather troubling.

How they work
 From the military's perspective, HPM weapons, also known as
radiofrequency weapons, have many things going for them: their blast
travels at the speed of light, they can be fired without any visible
emanation, and they are unaffected by gravity or atmospheric conditions.
The weapons come in two flavors: ultrawideband and narrowband. Think of
the former as a flashbulb, and the latter as a laser; while a flashbulb
illuminates across much of the visible spectrum (and into the infrared),
a laser sends out a focused beam at a single frequency.

Like the flashbulb, ultrawideband weapons radiate over a broad frequency
range, but with a relatively low energy (up to tens of joules per
pulse). Their nanoseconds-long burst produces a shock that
indiscriminately disrupts or destroys any unshielded electronic
components within their reach. The bomb's destructiveness depends on the
strength of the ultrawideband source, the altitude at which it is
initiated, and its distance from the target [see "E-Bomb Anatomy"].

Narrowband weapons, by contrast, emit at a single frequency or closely
clustered frequencies at very high power (from hundreds up to a thousand
kilojoules per pulse), and some can be fired hundreds of times a second,
making an almost continuous beam. These pulses can be directed at
specific targets?say, a command and control complex positioned on the
roof of a hospital in a densely populated neighborhood?and tuned to
specific frequencies. Technologically more sophisticated than
ultrawideband sources, they are far more difficult to develop, but are
reusable and potentially of much greater use to the U.S. military.

Both versions wreak the same kind of havoc on just about any kind of
unprotected electronic equipment. Particularly vulnerable is commercial
computer equipment; anything in excess of just tens of volts can punch
through gates in MOS and metal-semiconductor devices, effectively
destroying the device, explains Carlo Kopp, a visiting research fellow
in military strategy at the Strategic and Defense Studies Centre in
Canberra, Australia, and a computer scientist who lectures at Monash
University in Melbourne. The higher the circuitry's density, the more
vulnerable it is, because less energy is required to overload and
destroy the transistors.

HPMs also produce standing waves in electrical grid wiring and telephone
and communications wiring, entering through cables, antennas, and even
ventilation grills. They can immobilize vehicles with electronic
ignition and control systems, too.

"Since the frequency is high, this permits parasitic or stray
capacitances to couple energy via paths in the circuit that may not be
protected against overvoltage," Kopp explains.

The e-bomb
You could deliver an e-bomb in a number of ways: cruise missile,
unmanned aerial vehicle, or aerial bomb. Whether ultrawideband or
narrowband, the e-bomb consists of both a microwave source and a power
source [again, see diagram]. Ultrawideband e-bombs aim to create an
electromagnetic pulse like that accompanying a nuclear detonation,
except that the nuclear material is replaced with a conventional,
chemical explosive.

The microwave source typically relies on an extremely fast switching
device, according to Kopp, who has written widely on weaponizing HPM
technology. Narrowband e-bombs might use a virtual cathode oscillator
(vircator) tube or a variant of a magnetron. Though termed narrowband,
they don't have the high coherency seen in signal-carrying applications,
Kopp says.

It takes gigawatts of power to feed an e-bomb's microwave source. For
that, the flux compression generator, or FCG, is a good choice, says
Kopp. Invented by Clarence ("Max") Fowler at Los Alamos National
Laboratory after World War II as a byproduct of research into atomic
bomb detonators, FCGs are conceptually simple. The best-known type
consists of an explosive-packed copper cylinder surrounded by a helical
current-carrying coil.

Upon detonation, the explosion flares out the cylinder, short-circuiting
the coil and progressively reducing the number of turns in the coil,
thus compressing the magnetic flux. Large FCGs have produced tens of
gigawatts, and they can be cascaded?connected end to end?so that the
output from one stage feeds the next.

Despite its simplicity, an FCG-powered e-bomb is probably too difficult
for the average terrorist to build on the cheap. For one thing, to test
the assembled apparatus, you have to blow it up. For weapons
researchers, the e-bomb poses other problems. The strength of the shock
wave dissipates rapidly as it moves out from the explosion. To knock out
an electrical power substation, for example, the weapon has to strike
within about a hundred meters.

"Like all microwave radiation, the effect follows an inverse square law
with increasing distance," Kopp notes. Though the explosion needed to
force out the current can be fairly small, it keeps the munition from
being fully nonlethal and nondetectable. Also, anything that's been
hardened or shielded against an electromagnetic pulse from a nuclear
bomb will probably emerge unscathed.

Focused like a laser
The type of narrowband HPM weapons that the U.S. military is looking at
offers everything that e-bombs do not. They're nonlethal, reuseable, and
tunable, and they can be fired from miles away. Like a laser, the
focused beam disperses only slightly over great distances. With a
frequency range that is between about 1 and 10 GHz, they can penetrate
even electronics shielded against a nuclear detonation. The deepest
bunkers with the thickest concrete walls are not safe from such a beam
if they have even a single unprotected wire reaching the surface.

A microwave beam is created much like a laser beam. Between the
batteries (or other power source) and the beam sit three elements:
capacitors that turn the stored energy into an electron beam of
nanosecond bursts, a microwave source that converts the electron beam
into focused, high-frequency electromagnetic waves, and an antenna that
points and shoots the beam.

Kirtland Air Force Base, in Albuquerque, N.M., is considered the
epicenter of the Pentagon's research on pulsed-power electromagnetic
weapons. There, its premier pulsed-power system, the Shiva Star, is
housed behind meter-thick walls [see photo]. An Air Force spokesperson
refused to comment on what goes on in their pulsed-power programs, but a
fact sheet on the Web site of Kirtland's Directed Energy Directorate
describes the Shiva Star as capable of producing "120 thousand volts and
10 million amps for down to one millionth of a second to produce a power
flow equivalent to a terawatt."

The Kirtland machine isn't used to investigate HPM weapons per se, and
its massive size makes it clearly impractical for delivering microwave
beams to any spots of real military interest. Indeed, one big push in
microwave weapons has been toward portability. "Back in the 1960s and
1970s, the attitude was, 'Yeah, we can do it?but we need Hoover Dam as
our power supply,' " says Seguine. But just as batteries for cellphones
and laptops have shrunk and gained capacity, so have sources for
microwave weapons.

In the 1990s, the U.S. Air Force Office of Scientific Research set up a
five-year Multidisciplinary University Research Initiative (MURI)
program to explore microwave sources. One of those funded was the
University of New Mexico's Schamiloglu, whose lab is located just a few
kilometers down the road from where the Shiva Star sits behind tightly
locked doors.

Thanks in large part to his and his colleagues' efforts, the fundamental
capabilities and limitations of high-power microwave sources are now
better understood and appreciated.
Amidst the lead bricks and clutter in Schamiloglu's basement lab lies
his masterwork: the Sinus-6.

"A lot of laboratories come up with very cute names for these devices,"
Schamiloglu notes with a smile. "We never did." With a huge cylinder at
one end connected to the long microwave source, the Sinus-6 looks like a
giant torch lying on its side [see photo]. The big cylinder contains a
Tesla transformer, whose two coils vibrate in resonance and amplify the
incoming voltage "with nearly 100-percent efficiency," Schamiloglu says.
Once the pulse has been transformed into an electron beam, it is guided
by a strong axial magnetic field through the long tube that will turn it
into microwaves.

The Sinus-6 can fire a several-gigawatt pulsed beam 200 times a second
in 10-nanosecond bursts. "It has to be pulsed power because what you're
after is high peak power," says Schamiloglu. "The power in the
microwaves is going to depend on the electric field squared, so if you
generate very large power, then the electric field is going to be big."

How big? To drive the Sinus-6's beam continuously for an entire second,
you'd need to supply about 25 gigajoules?"the entire output of a
typical coal-fired electrical plant for 10 full seconds," Schamiloglu
says. Another reason for pulsed rather than continuous power is to avoid
a problem at the output end: the air around the antenna would heat to a
plasma that in turn would interfere with a continuous beam at these
power levels.

The key to reaching gigawatts of power is dumping all the energy in one
gigantic, nearly instantaneous pulse. A pressurized gas switch prevents
the Tesla transformer from prematurely dumping as it builds up for the
next pulse. The switch is filled with highly compressed and
nonconducting nitrogen gas. When the transformer coils reach 700 kV, the
nitrogen gas breaks down, and the pulse leaps through to the
electron-beam diode.

"Once you've fired the switch, it conducts, it generates a pulse," says
Schamiloglu. "It conducts because you've made a plasma channel out of
the gas. Then you have to wait for that plasma to recombine and form a
neutral gas again. A typical time scale for this thing to recombine and
fizzle out and be a neutral gas again is probably on the order of

Among the best candidates for supplying microwaves is the backward wave
oscillator; it has the advantage of being tunable (plus or minus 20
percent) and producing output in the 4-10-GHz range. To turn the kinetic
energy from the Sinus-6's electron beam into high-power microwaves, the
oscillator uses a rippled-wall waveguide, also called a slow-wave
structure [see photo].

The structure sets up standing electromagnetic waves in such a way that
energy is rapidly transferred to them from the incoming beam of
relativistic electrons from the Sinus-6. This growing energy initially
propagates in the opposite direction of the beam's movement?hence the
device's name?and is then reflected forward and radiated in the form
of high-power microwaves. Backward wave oscillators, by the way, are
also being tested as a way to push giant sails into outer space, to
detect space debris, and to clear minefields.

Being able to tune an HPM weapon comes in handy when a particular target
proves invulnerable to a particular frequency.

"Experience has shown that if the frequency is slightly altered,
measurable effects are discerned," Schamiloglu notes. People used to
believe that varying the frequency of HPMs wasn't practical, but
Schamiloglu and his students proved them wrong.

Coincidence and curiosity led to their discovery. Schamiloglu first
acquired the Sinus-6 from Russian researchers in the early 1990s. (The
Soviet Union once boasted a sophisticated program to develop microwave
weapons; after its collapse, parts of that legacy were put up for sale,
to the delight of researchers like Schamiloglu.) But once the apparatus
was assembled in his New Mexico lab, he couldn't get it to operate as
promised, so Russian colleagues flew over to help.

"One of them took the RF structure [the rippled-wall waveguide] and
started hammering on the thing," Schamiloglu recalls. When they tried it
again, everything worked. "I was baffled why manhandling this RF
structure?ramming it in?could affect the power so much," says
Schamiloglu. So he started a series of experiments in which he slightly
displaced the backward wave oscillator by increments. With a little
experimentation assisted by computer simulations, his team found that
the frequency could be adjusted by changing the distance between the
diode and the microwave source.
The result is that the backward wave oscillator is now one of the few
pulsed-power HPM sources that can be tuned.

Smaller is better
One disadvantage of this oscillator, however, is that it needs an
external magnetic field to create the microwave beam, a major hurdle to
making the whole system smaller. The size of the Sinus-6 and attendant
equipment in Schamiloglu's basement suggests that the U.S. military is
nowhere near fielding a narrowband HPM weapon.

"When I first started working on high-power narrowband sources, we joked
that you can do more damage dropping this equipment on someone than you
can by using it," he recalls. "People know how to make microwave sources
in the laboratory. The challenge is to take this and package it into an
autonomous platform and have it function at the same parameter levels."

Schamiloglu is now hard at work under a new MURI program to study the
possibilities of making a compact pulsed-power source. Current
narrowband generators are typically several meters long, batteries not
included. Schamiloglu and his colleagues are studying how to incorporate
novel ceramics into pulsed-power systems, which they believe will allow
the length of such sources to be halved.
The trick is identifying materials with a high dielectric constant that
can also survive the harsh electric fields. "Materials will be an
important part in making the next giant leap," he says.

Life in a glass house
Among those agreeing that narrowband HPM weapons will need more refining
before they become truly useful to the military is Loren B. Thompson,
chief operating officer of the Lexington Institute, a military think
tank based in Arlington, Va. He looked at the technology as principal
investigator of "Directed-Energy Weapons: Technologies, Applications and
Implications," a report that the institute put out in February.

"We have some fairly rudimentary weapons that we're ready to use,"
Thompson says. "This is going to be a very important weapons technology,
and the basic physical principles are well understood. But the military
is having some difficulty in assimilating them."

Thompson's report speaks of a future with satellites delivering
missile-debilitating microwaves, unmanned vehicles that fly by and
destroy communications systems, and war without civilian casualties. But
the fact remains that it's the U.S. military?as well as U.S. financial
institutions, PCs, and Game Boys?that will be the most susceptible to
such weapons.

"One of the things that happened during the last 10 years?as the
Pentagon fell in love with network-centered warfare?is that we
purchased a lot of very fragile digital systems off the shelf from
commercial sources," Thompson notes. Such moves were taken in the name
of cost and efficiency, but the resulting equipment is almost certainly
more vulnerable to electromagnetic attack than the vacuum tubes and
heavy metal-encased electronics of yesteryear.

"Computers become more vulnerable as the voltage at which they operate
becomes smaller," says Victor Granatstein, professor of electrical
engineering at the University of Maryland in College Park, who is
studying the effects of microwave pulses on integrated electronics.
"When our opponent was the Soviet Union, the electronics were much more
robust because they weren't miniaturized. Now they have very thin oxide
layers that can easily break down." Wireless networking makes matters
worse. Computers and other communications devices now have antennas
attached, giving an electromagnetic pulse a direct pathway to its guts.

Meanwhile, the U.S. Navy no longer requires that all its hardware be
hardened against nuclear electromagnetic pulses. It deemed that
maintaining those standards was too costly and slowed down the
integration of new technology. The presumption was that after the Cold
War, nobody would be using nuclear bombs, says the Lexington Institute's
Thompson. "Whenever I ask the admirals, 'Well, what if someone did use a
nuclear bomb?,' I just get this kind of blank
I-don't-have-an-answer-for-that sort of look."

In the wrong hands
The scariest part of microwave weapons may be that crude forms of the
technology are readily available to anyone right now. "Any nation with a
1950s technology base capable of designing and building nuclear weapons
and radars" can build an e-bomb, says military analyst Kopp. Indeed,
more than 20 countries now have programs to develop some type of RF

"The more widespread the technology is, the more likely that people with
nefarious purposes will have access. It's just an inescapable fact,"
says Thompson. "I don't know what we're going to do. Nobody in
Washington knows. I imagine that the way the clear thinking starts is
with a catastrophe."

Criminals and pranksters have already started exploiting that weakness.
In one of the more harmless applications, a Japanese scam artist rigged
up a weak microwave generator inside a suitcase to rip off a pachinko
parlor. When he placed the suitcase next to one of the machines (which
is something like a cross between a slot machine and a pinball machine)
and turned it on, the pachinko machine went haywire and disgorged a pile
of coins. The perp managed the trick several times before he was caught.

Other press accounts hint at electromagnetic weapons being deployed by
Chechen troops, and by an unnamed assailant trying to topple London's
futures market [see "Don't Try This at Home"].

Thankfully, protecting yourself against the microwave-enabled goofballs
of the world isn't too difficult. "It is analogous to existing
techniques used to trap RF interference inside equipment, except that
the higher power levels require special measures," Kopp notes. Rooms or
equipment chassis must become electrically sealed Faraday cages, and
protective devices must be added wherever cables enter the protected
volume. "Optical fibers are very useful in this game."

Such protective measures are a lot cheaper to design in from the
beginning than to add on afterward, says Howard Seguine. "The general
rule of thumb is that if you do the hardening during the design phase,
it increases the cost roughly 1 percent. If you do it afterward, it may
cost as much as 30 percent more."

But maybe hardening is a waste of time. Arthur Varanelli, a Raytheon Co.
engineer who has helped write several IEEE standards for electromagnetic
field measurement, human exposure, and safety, is skeptical that a
malicious prankster could exploit the technology.

"Some of this stuff is just so far out there," Varanelli says. "I just
don't see people running around with Buck Rogers ray guns. It's great
for a science fiction writer, great to prey upon people's fears." He
scoffs at the suggestion that a do-it-yourselfer could build a microwave
weapon potent enough to do real damage.
"People can put tacks in the road. Are we worried about electronic tacks
in the air?"

The wide disparity in opinions and the uncertainty about microwave
weapons, from Loren Thompson on one end to Arthur Varanelli on the
other, are all part of what makes them so powerful, says military
analyst John Pike, who is director of (Alexandria,

"It all depends on the complex interactions between the weapon and the
target," he notes. "I can set up a strap-down chicken test that makes
[an HPM weapon] look pretty good. But as soon as I start getting into
real-world targets, maybe it doesn't work so well."

"Part of the story is we don't know what the story is," Pike says.
"These are weapons that by their nature seek the shadows. And unlike
cluster bombs or atomic bombs, they aren't going to leave behind
unambiguous evidence of their use."

To Probe Further

For a detailed technical discussion of high-power microwaves, see
High-Power Microwave Sources and Technologies, edited by IEEE Fellows
Robert J. Barker and Edl Schamiloglu (Wiley-IEEE Press, 2001).

Schamiloglu is also coauthor, with James Benford and John Swegle, of the
forthcoming High-Power Microwaves, 2nd edition (Institute of Physics,

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