AOH :: EMP1.TXT
Electromagnetic Pulse Warfare - how detonating just a very few nukes can cripple a country
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EMP1.ASC
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ELECTRO MAGNETIC PULSES
------- -------- ------
Imagine a very bright flash in the sky! No one is hurt. But, your
transistor radio stops playing, your car won't start, the telephone
doesn't ring, lights stay off, and we find ourselves in the stone
age!
THE developement of modern high-tech semiconductor devices have
paralleled unsettled relations between the nations of the world with
resulting technological advances affecting the lives of every
citizen of North America. Communications have been made faster,
automobiles more fuel-efficient and maintenance-free, TV sets,
video-tape recorders, and virtually every other piece of electronics
equipment have been improved by the advent of the semiconductor and
its high-tech advancements. The relationship between nuclear
weapons and the recent electronics advances may seem unclear, but
a nuclear attack on the North American continent could make that
relationship glaringly apparent.
ALL nuclear explosions produce electromagnetic pulses (EMP's) and
the ensuing induced voltages and currents produced in conductors
( wires and cables ) are comparable in strength to the strongest of
lightning bolts. EMP's may reach 3 million volts and 10,000 amperes
for a total of 30-billion watts of energy.
The largest commercial radio stations in the U.S. and Canada radiate
50,000 watts, or approximately one-millionth that much power! The
major difference between EMP's and lightning is that EMP's are
induced simultaneously over an entire wide area, while lightning
occurs at a single location.
Significance of the Problem
------------ -- --- -------
THREE ten-megaton thermonuclear weapons detonated 250 miles ( 400
kilometers ) above the United States or Canada would produce EMP's
strong enough to knock out the entire electrical power grid of North
America including the entire civilian-telephone network, and just
about every broadcast station.
Page 1
Virtually every piece of unprotected electronic equipment in the
country -- radios, TV sets, computers, electronic controls in homes,
office buildings, factories, cars, airplanes, and instruments in
hospitals -- would be damaged, if not destroyed. The pulses would
also damage or destroy large portions of the military command's
control and communication (C3) system.
A chain reaction could be set in motion at nuclear power plants, due
to electromagnetic pulses. Although it is a point that is frequently
disputed, the possibility exists that reactor core meltdowns might
occur as a result of EMP's.
The meltdowns would be a by-product of electronic control system
failure. The control systems are used to monitor and control the
processes at the plants.
The EMP's could cause the system to fail and result in partial or
complete loss of control over vital functions, causing subsequent
melt-downs.
We know that those nuclear plants are designed to be fail safe,
but has anyone considered the possibility of every circuit breaker
in a plant failing at the same instant?
Characteristics of EMP's
--------------- -- -----
AT an altitude of 250 miles, the gamma rays produced in the first
few nano-seconds ( billionths-of-a-second ) of a nuclear explosion
can travel hundreds of kilometers before colliding with electrons in
atmospheric molecules.
That kind of collision may take place in a region 2,000 miles in
diameter and 6-miles thick. Electrons are accelerated by those
collisions, a phenomenon referred to as the Compton effect; and upon
reaching the earth's magnetic field, they set up electromagnetic
pulses that radiate downward toward earth (Fig.1).
Due to the extremely large area of collision, vast amounts of ground
area are exposed to electromagnetic fields with strengths up to
50,000-volts per meter. The ground area exposed to electromagnetic
pulses could cover the entire continental United States and most of
Canada by one nuclear blast; if not, certainly large regions such as
New England would be electrically and electronically devastated.
Page 2
FIG. 1 -- Electrons set into motion by gamma rays from a nuclear
explosion in space will produce enormous electromotive
pulses (EMP's) when the negative charges enter the Earth's
magnetic-field. It is estimated that the ideal height for
such an explosion should be 250 miles above the Earth's
surface.
:::::::::::::::::::::::::::::::::::::::
: :
: O - Nuclear Explosion :
: :
: / / :
: / / - Gamma Rays :
: --------------------------- :
: < Earth's Magnetic Field > :
: --------------------------- :
: ******* ******* ******* :
: ***** ***** ***** :
: *** EMP *** EMP *** :
: ***** ***** ***** :
: ******* ******* ******* :
: =============================== :
: EARTH :
: :
:::::::::::::::::::::::::::::::::::::::
Vulnerability
-------------
THE effects that electromagnetic pulses would have on a mass of
circuitry are difficult to predict because the interactions are
complex. But, the more complex the components, the easier they are
to damage. Power lines are one avenue for EMP damage, and a company
making a shielded tubing to go over power and signal carrying
conductors obviously had EMP in mind when they invented their
"Zippertubing". That covering acts as a partial shield to EMP's.
FOR each component, damage would come from the internal pickup of
the circuit itself, as well as surges fed to it by all other
attached conductors (power lines, other circuits,and metal parts).
ANOTHER concern is that generators and motors with their numerous
internal windings of copper wire could be rendered useless in an EMP
attack; and with subsequent inoperative water pumping stations,
desert population-centers could persih. In the dead of winter,
motors in heating units would be destroyed and the chilling freeze
in the northern portions of the North American continent would bring
those areas to a standstill. Food and fuel shipments would halt
because fusible links and electronic ignitions would be destroyed in
cars and trucks. It's difficult to conceive a family anywhere on
the continent not suffering extreme hardships.
THE more complex the electronics components, the more vulnerable
they are to electromagnetic pulses. Hardness describes the
vulnerability of an electrical device and it is best for old-style
vacuum tubes, less for semi-conductors, and even less for
microcircuitry.
It would take 100 times more EMP energy to damage the tubes than
integrated circuits. Computers may be upset through memory erasure
with 100 times less energy than required to damage integrated
circuits; refer to Fig. 3. Aircraft in the air
and parked on open surfaces would be disabled, because electronics
controls
the crafts' flight instruments and control surfaces.
:::::::::::::::::::::::::::::::::::::::
:(-8)(-6)(-4)(-2) (1) (2) (4) (6) (8) :
:::!:::!:::!:::!:::!:::!:::!:::!:::!:::
: ###### :
: :
: $$$$$$$$ :
: :
: %%%%%%% :
: :
: &&&&&&& :
: :
:::!:::!:::!:::!:::!:::!:::!:::!:::!:::
:(-8)(-6)(-4)(-2) (1) (2) (4) (6) (8) :
:( Powers of TEN) <Fig. 3> :
:::::::::::::::::::::::::::::::::::::::
: RANGE OF THRESHOLD ENERGY, JOULES :
:::::::::::::::::::::::::::::::::::::::
: # = Motors and Transformers :
: $ = Vacuum Tubes :
: % = Low-Power Transistors :
: & = Integrated Circuits :
:::::::::::::::::::::::::::::::::::::::
Hardening Communications Equipment
--------- -------------- ---------
HARDENING of electronics communications equipment is vital to the
military, and, to a lesser extent, the civilian populace. The
Department of Defense has established an Electromagnetic
Compatibility Program (EMCP) to ensure that all military
Communication-Electronic (CE) equipment subsystems, and systems are
protected from electromagnetic interference of all kinds.
That program was implemented to ensure that electromagnetic
compatibility is maintained through design, acquistion, and
operational phases. Numerous semiconductor manufacturers now
produce what are called "radiation-hardened" integrated circuits,
just for that reason.
THERE are three major design criteria which must be considered when
hardening against EMP's. They are cost, the equipment's ability to
survive EMP, and failure rates of the shielding components. COST
includes both installation and maintenance. Some protection
practices, such as shielding the entire communication site, may be
attractive from a technical point of view, but are impractically
expensive.
THE electronic equipment's ability to survive an EMP attack must be
measured in order to determine how much EMP protection is needed. A
testing device for measuring the radiated electromagnetic
susceptibility of an electronic device is a Transverse
Electromagnetic Mode (TEM) cell.
A TEM cell consists of a group of electronic instruments and a
special specimen holder that simulates an environment of free space.
Page 4
The TEM cell is used for performing electromagnetic
interference/electromagnetic compatibility (EMI/EMC) measurements
and evaluating protection devices.
Shielding Methods
--------- -------
IN order to predict the effect of an electromagnetic pulse on
electronic equipment, it is necessary to assess the enviroment. The
structures housing the electronic equipment are made in various
shapes and sizes, and are connected to the outside world by
conductors such as utility lines and pipes, communication lines, and
access and ventilation structures.(Refer to fig.5)
:::::::::::::::::::::::::::::::::::::::
: EMP Lightning :
: //// V V V :
: ------------------------------ :
: !* Building ! :
:P--+** ! :
: !* ! :
: ! EMP Penetration ! :
: ! ! :
: ! ! :
: +-+ * ! :
: ! ! *** ! :
: ! -----!------------------------ :
: ! ! :
:=!======!========================== :
:Gnd ! - Buried Cable :
:--------+ :
:::::::::::::::::::::::::::::::::::::::
: P = Power Lines Fig. 5. -- :
: -- A sealed metal box is an ideal :
: structure for eliminating EMP pen- :
: etration. However, power lines and :
: signal cables require entry ports :
: thus compromising the integrity of :
: a shielded building. Obviously, it :
: is apparent that doors and windows :
: would have a greater leakage effect.:
:::::::::::::::::::::::::::::::::::::::
Page 5
That combination of criteria makes the exact determination of the
interaction of an EMP with such a variety of structures extremely
difficult. However, for complex systems, it is convenient to have
several layers of shielding. (Refer to Fig. 6).
:::::::::::::::::::::::::::::::::::::::
: Shield 1 :
: ******************** :
: * Zone 1 (internal) * :
: * ============== * :
: * = Zone 2 =----* :
: * g = ########## = g * :
: * r = ############ = r * :
: * o =--###ZONE 3### = o * :
: * u = ############--= u * :
: * n = ########## = n * :
: * d = (cabinet- = d * :
: *---= environment) = * :
: * ============== * :
: * Shield 2 * :
: ****************** :
: !------! :
: ! :
: ! Zone 0 (External- :
: ! Environment) :
:----!--------------------------------:
: = EARTH :
: :
:::::::::::::::::::::::::::::::::::::::
: Fig. 6 -- More than one shield can :
: be used to secure the environment of:
: the machinery and electronic mat- :
: erial contained within a building. :
: The building can provide the initial:
: shield. Shielded rooms or metal cab-:
: inets may provide a second shield. :
: A third shield (not diagrammed) :
: would protect entry cables from :
: violating the shielded area of :
: zone 3. :
:::::::::::::::::::::::::::::::::::::::
Shield 1
------ -
A structure composed of a great deal of metal is well shielded
against electro-magnetic pulses, while a building made primarily of
wood is virtually unshielded against EMP's. Continuous, closed
sheet-metal shields are, by far, the most effective electromagnetic
shields.
It is imperative that the internal environment of zone 1 be
connected to the outside world. That fact makes a closed sheet-
metal shield impossible. Apertures in shield 1 create a special
problem in protecting communication sites from EMP penetration.
Page 6
THE electromagnetic field penetration depends on the aperature size.
If a given area of wall opening is subdivided into ten small
openings having the same total area, the penetrating EMP fields at
an interior point will be 1/SQR(10) as large as for a single large
opening of the same total area. (Refer to Fig. 7).
:::::::::::::::::::::::::::::::::::::::
: !! !! :
: ###### !! ######## !! :
: # !! # !! :
: EMP *==!! # !! :
: # !! # !! :
: # !! E *==!! :
: EMP *==!! M **==!! :
: # !! P **==!! :
: # !! *==!! :
: EMP *==!! # !! :
: # !! # !! :
: # !! # !! :
: EMP *==!! # !! :
: # !! # !! :
: # # :
: ###### ######## :
: Shield Shield :
:::::::::::::::::::::::::::::::::::::::
: Fig. 7 -- The electromagnetic field :
: penetration into a ported shield is :
: minimized by reducing the size of :
: the openings. In the diagram the :
: open area of the port of the example:
: on the right is equal to the sum of :
: the areas in the example at left. :
: The diagram clearly shows that the :
: penetration of an EMP is less when :
: equal areas are summed from several :
: small ports. :
:::::::::::::::::::::::::::::::::::::::
Therefore, it is better for a structure to have more small openings
than just a few larger openings. A common treatment for such
openings is to cover them with a conducting screen or mesh so that
the large opening is converted to a multitude of small openings, or
use a glass impregnated with metal. That glass, despite having
metal in it, offers approximately the same degree of visual
attenuation or lack of clarity as looking through a screen door from
within the house.
Shields 2 and 3
------- - --- -
THE second-level shield seperates the internal environment from the
sensitive small-signal circuits within the electronic equipment
found within Zone 2. Shielding here may be accomplished by
electrically grounding the metal cabinets and equipment.
SHIELD 3 involves the shielding of the interconnection of the
equipment. That could involve elaborate design of interconnecting
signal transmission lines. Fiberoptic signal transmission shows
Page 7
great promise here because it is not effected by any type of
electromagnetic interference.
Hardening Aircraft and Missles
--------- -------- --- -------
GENERALLY, the EMP interaction with electrical systems inside
structures such as aircraft and missles depends upon a multitude of
factors. Aircraft and missles usually have a nearly complete
metallic exterior covering that serves as a shield from
electromagnetic fields. However, that shield alone is not enough
protection against electromagnetic pulses.
Missles and Aircraft are equipped with computers that cannot be
upset even for an instant. They must be partically well hardened.
AT the present time, there is no agreement on the most effective
ways to harden aircraft and missles. Heavy shielding, like the type
used at communication sites, is obviously impractical because of the
added weight that the aircraft has to carry.
Instead, EMP resistance is designed into the aircraft's equipment.
One example of that would be in the area of circuit design. Small
loops make better antennas for EMP's than short straight lines;
therefore, circuits are designed in tree or branching layouts rather
than in more conventional circuit loops.
Is Shielding Help on the Way?
-- --------- ---- -- --- ----
IN the last decade, electronic devices have proliferated in all
areas of our lives. That influx of products has caused a problem:
Noise Pollution, or EMI/RFI ( electromagnetic/radio frequency
interference). Over 80,000 cases of noise pollution were reported
to the FCC (Federal Communications Commission) in 1982.
STRANGE as it may sound, the plastics industry is coming to the
rescue with plastic electronic-equipment enclosures specifically
designed for both EMI containment and shielding. Obviously, with
EMP's as an external disturbance, the containment of a field is
academic, but the shielding from an outside field is crucial.
The parameter describing that is Shielding Effectiveness (SE) and
the equation for shielding effectiveness is
SE = A + R,
or shielding effectiveness equals Absorbed plus Reflected energy.
HIGHLY conductive materials such as pure metal shields reflect
approximately 99 percent of the energy and adsorb 1 percent. But
plastics with metallic composite fillers, metallic paints and
sprays, or even impregnated wire meshes still reflect 80 percent of
the energy and absorb 20 percent.
If EMP's and the disturbing effects of electromagnetic fields still
seem like an abstraction or a physicist's dream, consider that
event.
A manufacturer of buses designed for city use had just delivered a
fleet when, during a test drive, a problem was discovered. After
Page 8
going over the top of a hill, the driver tried to brake, only to
discover he had no brakes until he got to the bottom of the hill.
Upon logical investigation of that problem, field-strength meters
demonstrated that a local television station had a lobe-shaped
radiation pattern that intersected the hill's apex.
The microprocessor-controlled anti-skid braking system on the bus
had sensitive circuitry that became inoperative because of the TV
signal. The bus, though, was made safe by properly shielding the
enclosure housing the electronics. Graphite, a moderately good
conductor, is fabricated within large plastic sheets for
applications such as that.
IF a signal as small as that can effect circuitry that drastically,
you can imagine what an EMP could do and likewise you can see how
crucial EMI shielding is. But will EMI shielding be universally
implemented into new equipment?
The Military's Involvement
--- ---------- -----------
THE military is very concerned with EMP's. The Army has established
its Aurora Tree test facility in Aldelphi, Maryland. The Navy has
the Casino and Gamble-2 x-ray emitting facilities, but the Air Force
probably has the most interesting project of all. It is the
Trestle, after the railroad structure it resembles.
THAT 12-story (118 feet) high, 58-meter (200-foot) square deck is
flanked by a 50-foot wide adjoining ramp upon which aircraft to be
tested are rolled up. The Trestle can support aircraft weighing
550,000 pounds and is built with one-foot by one-foot wooden columns
using no nails or metal of any kind. That largest glue-laminated
structure in the world uses 250,000 wooden bolts to hold its six-
million board feet of lumber together --- enough for 4,000 frame
houses. The structure at Kirtland Air Force Base, New Mexico cost
approximately 58-million dollars.
THE Trestle has two 5-million volt pulsers that discharge energy
into wire transmission lines surrounding the aircraft under test.
Sensors capture aircraft response signals and fiber-optic channels
transmit that sensor data to computers for processing.
The processing equipment, though, naturally resides inside a very
well shielded structure. The B-52G's OAS (Offensive Avionics
System) is one of numerous studies directed primarily at testing the
electronic hardening of military systems.
The Future
--- ------
THE effects of EMP on our lives is becoming known to many on the
North American continent as it is being discovered by all the
citizens of the free world. Its political implications are not the
topic here, but rather the facts in this article reveal to what EMP
is and what it can do to the technological devices we rely on every
minute of the day.
Page 9
The next time a solar flare disrupts radio communications around the
world for a few hours, or maybe a few days, recall that man with one
nuclear device can outshine the damage old Sol creates by many fold.
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GLOSSARY OF TERMS
-----------------
ElectroMagnetic Pulse (EMP): An electromagnetic field of high
intensity and short duration that may be caused by a nuclear
explosion.
-----------------------------------
Electromagnetic Field: A magnetic field produced by electricity
(the flow of current in a wire or electrons through a medium
such as a vacuum). It is usually expressed in volts per meter.
-----------------------------------
ElectroMagnetic Compatibility (EMC): The ability of an electronic
device to deal with electromagnetic interference and function
properly.
-----------------------------------
ElectroMagnetic Interference (EMI): Any adverse effect on electronic
equipment due to an electromagnetic field.
-----------------------------------
Shielding or Hardening: A method used to protect electronic devices
from EMP interruption or damage.
-----------------------------------
Written: Art Reichert / March 21, 1988
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