EMP. The letters spell burnt out computers and other electrical systems and perhaps even a return to the dark ages if it were to mark the beginning of a nuclear war. But it doesn’t need to be that way. Once you understand EMP, you can take a few simple precautions to protect yourself and equipment from it. In fact, you can enjoy much of the “high tech” life style you’ve come accustomed to even after the use of a nuclear device has been used by terrorists–or there is an all-out WWIII.

EMP (Electro-Magnetic Pulse), also sometimes known as “NEMP” (Nuclear Electromagnetic Pulse), was kept secret from the public for a long time and was first discovered more or less by accident when US Military tests of nuclear weapons started knocking out phone banks and other equipment miles from ground zero.

EMP is no longer “top secret” but information about it is still a little sketchy and hard to come by. Adding to the problems is the fact that its effects are hard to predict; even electronics designers have to test their equipment in powerful EMP simulators before they can be sure it is really capable of with standing the effect.

EMP occurs with all nuclear explosions. With smaller explosions the effects are less pronounced. Nuclear bursts close to the ground are dampened by the earth so that EMP effects are more or less confined to the region of the blast and heat wave. But EMP becomes more pronounced and wide spread as the size and altitude of a nuclear blast is increased since the ground; of these two, altitude is the quickest way to produce greater EMP effects. As a nuclear device is exploded higher up, the earth soaks up fewer of the free electrons produced before they can travel some distance.

The most “enhanced” EMP effects would occur if a nuclear weapon were exploded in space, outside the Earth’s atmosphere. In such a case, the gamma radiation released during the flash cycle of the weapon would react with the upper layer of the earth’s atmosphere and strip electrons free from the air molecules, producing electromagnetic radiation similar to broad-band radio waves (10 kHz-100 MHz) in the process. These electrons would follow the earth’s magnetic field and quickly circle toward the ground where they would be finally dampened. (To add to the confusion, we now have two more EMP terms:

“Surface EMP” or “SEMP” which refers to ground bursts with limited-range effects and “High-altitude EMP” or “HEMP” which is the term used for a nuclear detonation creating large amounts of EMP.)

Tactically, a space-based nuclear attack has a lot going for it; the magnetic field of the earth tends to spread out EMP so much that just one 20-MT bomb exploded at an altitude of 200 miles could–in theory–blanket the continental US with the effects of EMP. It’s believed that the electrical surge of the EMP from such an explosion would be strong enough to knock out much of the civilian electrical equipment over the whole country. Certainly this is a lot of “bang for the buck” and it would be foolish to think that a nuclear attack would be launched without taking advantage of the confusion a high-altitude explosion could create. Ditto with its use by terrorists should the technology to get such payloads into space become readily available to smaller countries and groups.

But there’s no need for you to go back to the stone age if a nuclear war occurs. It is possible to avoid much of the EMP damage that could be done to electrical equipment–including the computer that brought this article to you–with just a few simple precautions.

First of all, it’s necessary to get rid of a few erroneous facts, however.

One mistaken idea is that EMP is like a powerful bolt of lightning. While the two are alike in their end results–burning out electrical equipment with intense electronic surges–EMP is actually more akin to a super-powerful radio wave. Thus, strategies based on using lightning arrestors or lightning-rod grounding techniques are destined to failure in protecting equipment from EMP.

Another false concept is that EMP “out of the blue” will fry your brain and/or body the way lightning strikes do. In the levels created by a nuclear weapon, it would not pose a health hazard to plants, animals, or man PROVIDED it isn’t concentrated.

EMP can be concentrated.  That could happen if it were “pulled in” by a stretch of metal. If this
happened, EMP would be dangerous to living things. It could become concentrated by metal girders, large stretches of wiring (including telephone lines), long antennas, or similar set ups. So–if a nuclear war were in the offing–you’d do well to avoid being very close to such concentrations. (A safe distance for nuclear-generated EMP would be at least 8 feet from such stretches of metal.)

This concentration of EMP by metal wiring is one reason that most electrical equipment and telephones would be destroyed by the electrical surge. It isn’t that the equipment itself is really all that sensitive, but that the surge would be so concentrated that nothing working on low levels of electricity would survive.

Protecting electrical equipment is simple if it can be unplugged from AC outlets, phone systems, or long antennas. But that assumes that you won’t be using it when the EMP strikes. That isn’t all that practical and–if a nuclear war were drawn out or an attack occurred in waves spread over hours or days– you’d have to either risk damage to equipment or do without it until things had settled down for sure.

One simple solution is to use battery-operated equipment which has cords or antennas of only 30 inches or less in length. This short stretch of metal puts the device within the troughs of the nuclear-generated EMP wave and will keep the equipment from getting a damaging concentration of electrons. Provided the equipment isn’t operated close to some other metal object (i.e., within 8 feet of a metal girder, telephone line, etc.), it should survive without any other precautions being taken with it.

If you don’t want to buy a wealth of batteries for every appliance you own or use a radio set up with longer than 30-inch antenna, then you’ll need to use equipment that is “hardened” against EMP.

The trick is that it must REALLY be hardened from the real thing, not just EMP-proof on paper. This isn’t all that easy; the National Academy of Sciences recently stated that tailored hardening is “not only deceptively difficult, but also very poorly understood by the defense-electronics community.” Even the US Military has equipment which might not survive a nuclear attack, even though it is designed to do just that.

That said, there are some methods which will help to protect circuits from EMP and give you an edge if you must operate ham radios or the like when a nuclear attack occurs. Design considerations include the use of tree formation circuits (rather than standard loop formations); the use of induction shielding around components; the use of self-contained battery packs; the use of loop antennas; and (with solid-state components) the use of Zener diodes. These design elements can eliminate the chance an EMP surge from power lines or long antennas damaging your equipment. Another useful strategy is to use grounding wires for each separate instrument which is coupled into a system so that EMP has more paths to take in grounding itself.

A new device which may soon be on the market holds promise in allowing electronic equipment to be EMP hardened. Called the “Ovonic threshold device”, it has been created by Energy Conversion Devices of Troy, MI. The Ovonic threshold device is a solid-state switch capable of quickly opening a path to ground when a circuit receives a massive surge of EMP. Use of this or a similar device would assure survival of equipment during a massive surge of electricity.

Some electrical equipment is innately EMP-resistant. This includes large electric motors, vacuum tube equipment, electrical generators, transformers, relays, and the like. These might even survive a massive surge of EMP and would likely to survive if a few of the above precautions were taking in their design and deployment.

At the other end of the scale of EMP resistance are some really sensitive electrical parts. These include IC circuits, microwave transistors, and Field Effect Transistors (FET’s). If you have electrical equipment with such components, it must be very well protected if it is to survive EMP.

One “survival system” for such sensitive equipment is the Faraday box.

A Faraday box is simply a metal box designed to divert and soak up the EMP. If the object placed in the box is insulated from the inside surface of the box, it will not be effected by the EMP traveling around the outside metal surface of the box. The Faraday box simple and cheap and often provides more protection to electrical components than “hardening” through circuit designs
which can’t be (or haven’t been) adequately tested.

Many containers are suitable for make-shift Faraday boxes: cake boxes, ammunition containers, metal filing cabinets, etc., etc., can all be used.  Despite what you may have read or heard, these boxes do NOT have to be airtight due to the long wave length of EMP; boxes can be made of wire screen or other porous metal.

The only two requirements for protection with a Faraday box are: (1) the equipment inside the box does NOT touch the metal container (plastic, wadded paper, or cardboard can all be used to insulate it from the metal) and (2) the metal shield is continuous without any gaps between pieces or extra-large holes in it.

Grounding a Faraday box is NOT necessary and in some cases actually may be less than ideal. While EMP and lightning aren’t the “same animal”, a good example of how lack of grounding is a plus can be seen with some types of lightning strikes. Take, for example, a lightning strike on a flying airplane. The strike doesn’t fry the plane’s occupants because the metal shell of the plane is a Faraday box of sorts. Even though the plane, high over the earth, isn’t grounded it will sustain little damage.

In this case, much the same is true of small Faraday cages and EMP.  Consequently, storage of equipment in Faraday boxes on wooden shelves or the like does NOT require that everything be grounded. (One note: theoretically non-grounded boxes might hold a slight charge of electricity; take some time and care before handling ungrounded boxes following a nuclear attack.)

The thickness of the metal shield around the Faraday box isn’t of much concern, either. This makes it possible to build protection “on the cheap” by simply using the cardboard packing box that equipment comes in along with aluminium foil. Just wrap the box with the aluminum foil (other metal foil or metal screen will also work); tape the foil in place and you’re done. Provided
it is kept dry, the cardboard will insulate the gear inside it from the foil; placing the foil-wrapped box inside a larger cardboard box is also wise to be sure the foil isn’t accidentally ripped anywhere. The result is an “instant” Faraday box with your equipment safely stored inside, ready for use following a nuclear war.

Copper or aluminium foil can help you insulate a whole room from EMP as well. Just paper the wall, ceiling and floor with metal foil. Ideally the floor is then covered with a false floor of wood or with heavy carpeting to insulate everything and everyone inside from the shield (and EMP). The only catch to this is that care must be taken NOT to allow electrical wiring connections to pierce the foil shield (i.e., no AC powered equipment or radio antennas can come into the room from outside). Care must also be taken that the door is covered with foil AND electrically connected to the shield with a wire and screws or some similar set up.

Many government civil defence shelters are now said to have gotten the Faraday box, “foil” treatment. These shelters are covered inside with metal foil and have metal screens which cover all air vents and are connected to the metal foil. Some of these shelters probably make use of new optical fibre systems–protected by plastic pipe–to “connect” communications gear inside the room to the “outside world” without creating a conduit for EMP energy to enter the shelter.

Another “myth” that seems to have grown up with information on EMP is that nearly all cars and trucks would be “knocked out” by EMP. This seems logical, but is one of those cases where “real world” experiments contradict theoretical answers and I’m afraid this is the case with cars and EMP. According to sources working at Oak Ridge National Laboratory, cars have proven to be resistant to EMP in actual tests using nuclear weapons as well as during more recent tests (with newer cars) with the US Military’s EMP simulators.

One reason for the ability of a car to resist EMP lies in the fact that its metal body is “insulated” by its rubber tires from the ground. This creates a Faraday cage of sorts. (Drawing on the analogy of EMP being similar to lightning, it is interesting to note that cases of lightning striking and damaging cars is almost non-existent; this apparently carries over to EMP effects on vehicles as well.)

Although Faraday boxes are generally made so that what is inside doesn’t touch the box’s outer metal shield (and this is especially important for the do-it-yourself since it is easy to inadvertently ground the Faraday box–say by putting the box on metal shelving sitting on a concrete floor), in the case of the car the “grounded” wiring is grounded only to the battery. In practice, the entire system is not grounded in the traditional electrical wiring sense of actually making contact to the earth at some point in its circuitry. Rather the car is sitting on insulators made of rubber.

It is important to note that cars are NOT 100 percent EMP proof; some cars will most certainly be effected, especially those with fiberglass bodies or located near large stretches of metal. (I suspect, too, that recent cars with a high percentage of IC circuitry might also be more susceptible to EMP effects.)

The bottom line is that all vehicles probably won’t be knocked out by EMP. But the prudent survivalist should make a few contingency plans “just in case” his car (and other electrical equipment) does not survive the effects of EMP. Discovering that you have one of the few cars knocked out would not be a good way to start the onset of terrorist attack or nuclear war.

Most susceptible to EMP damage would be cars with a lot of IC circuits or other “computers” to control essential changes in the engine. The very prudent may wish to buy spare electronic ignition parts and keep them a car truck (perhaps inside a Faraday box). But it seems probable that many vehicles WILL be working following the start of a nuclear war even if no precautions have been taken with them.

One area of concern are explosives connected to electrical discharge wiring or designed to be set off by other electric devices. These might be set off by an EMP surge. While most citizens don’t have access to such equipment, claymore mines and other explosives would be very dangerous to be around at the start of a nuclear box if they weren’t carefully stored away in a Faraday box. Ammunition, mines, grenades and the like in large quantities might be prone to damage or explosion by EMP, but in general aren’t all that sensitive to EMP.

A major area of concern when it comes to EMP is nuclear reactors located in the US. Unfortunately, a little-known Federal dictum prohibits the NRC from requiring power plants to withstand the effects of a nuclear war. This means that, in the event of a nuclear war, many nuclear reactors’ control systems might will be damaged by an EMP surge. In such a case, the core-cooling controls might become inoperable and a core melt down and breaching of the containment vessel by radioactive materials into the surrounding area might well result. (If you were needing a reason not to live down wind from a nuclear reactor, this is it.)

Provided you’re not next door to a nuclear power plant, most of the ill effects of EMP can be over come. EMP, like nuclear blasts and fallout, can be survived if you have the know how and take a few precautions before hand.

And that would be worth a lot, wouldn’t it?

Some initial thoughts on EMP protection from the US military packaging division.

A continuously sealed metal barrier has proven to be very effective in preventing EM/HPM energy from reaching susceptible electronic or explosive components. Exterior packaging fabricated from plastic, wood or other fibre materials provides almost no protection form EM/HPM threats. The metal enclosure can be very thin provided there are no openings (tears, pin holes, doors, incomplete seams) that would allow microwaves to enter. Sealed barrier bags that incorporate a thin layer of aluminium foil and are primarily used to provide water vapour proof protection to an item, can add a great deal of resistance to EM/HPM penetration.

A number of cylindrical and rectangular steel containers have been developed by the Packaging Division for a wide range of munitions, weapon systems and associated components. The cylindrical containers are end opening and the rectangular containers are top opening. All the containers have synthetic rubber gaskets that allow them to maintain a +3 psi environmental seal to the outside environment. The containers are constructed using seam welding to provide for continuous metal contact on all surfaces of the body assembly. The cover openings have been held to a minimum and the sealing gaskets positioned in a manner to allow overlapping metal parts to add additional protection to these areas. Microwaves are very adept at bouncing around and working their way into even the smallest opening. Tests of the cylindrical and rectangular steel containers used by this organization have demonstrated a high level of protection in preventing EM/HPM energy from entering the container.

The key is to use a metal enclosure and eliminate or minimize any openings. Where openings are needed they should be surrounded to the greatest extent possible by continuous metal and in the case of a gasket, metal sheathing or mesh can be placed around the elastometer material or conductive metal moulded into the gasket. The closer the surrounding container comes to a continuous metal skin the more protection that will be provided.

High quality gaskets, utilizing either a mesh or embedded conductive metal design, are very expensive. They add a magnitude of cost to a normal gasket and can easily double the price of a container similar to the ones mentioned above.

The National Communications System (NCS), a governmental entity made up from 22 different Federal agencies, wants ham radio operators and their gear to survive an EMP (Electro-Magnetic Pulse) generated “nuclear event.”

NCS engineers have simulated the EMP phenomenon in the laboratory and have subjected various pieces of current amateur radio gear to its effect.

The people at NCS came to some rather surprising conclusions.

In their report they say, “It was concluded that modern solid-state amateur radio equipment was more survivable in an EMP transient environment than had been previously anticipated.”

What makes those sophisticated and delicate transistors and ICs so survivable?

The secret is in having two EMP surge protection devices.  One is needed on the end where the power comes into the radio and the other on the antenna end where the RF signal goes out.

The NCS tested various commercially available suppression devices designed for both lightning and EMP and, in a move surprising for any governmental agency, issued a report telling which ones worked and which ones didn’t.

Their findings and recommendations are outline in a 105-page publication entitled “Electromagnetic Pulse/Transient Threat Testing of Protection Devices for Amateur/Military Affiliate Radio System Equipment”–otherwise known as NCS Technical Information Bulletin 85-10.

When considering EMP protection for transient voltage spikes coming in through commercial power lines, the folks at NCS recommend the TII model 428 plug-in power line protector, an item which costs only $45.  But for those a little strapped for cash (and what survivalist isn’t), the report shows how you can make one yourself for an estimated cost of only $11.

For EMP protection on the antenna side of a rig, NCS recommends the Fisher series of spikeguard suppressors.  They come in a variety of different clamping voltages, depending on the characteristics of a specific station.

The bulletin provides a mathematical formula to determine which fisher model is correct for your radio.

The Fisher devices cost $55, thus giving hams total effective EMP protection for their radios with off-the-shelf items for only $100.

If your radio has a power output of 100 watts or less, a second coax protector was recommended, the PolyPhaser products.  They proved to be just as effective as the fisher products but cost somewhat more–$82.95 each.  Because of their lower clamping voltages, they are recommended only for lower wattage transmitters.

But again, for those handy with electronics, NCS shows you how to make a simple home-made protection device for your antenna system for only $9.

It was interesting to note that two relatively inexpensive devices simply did not work.  The Archer (Radio Shack brand) AC line protector was NOT recommended.  Nor was the Alpha Delta brand “Transi Trap” coax protector, commonly advertised in ham radio magazines.

Other interesting findings made by NCS engineers were that portable generators, such as Honda types, were not likely to be adversely effected by EMP at all.  Neither were hand-held walkie-talkie type portable radios, particularly those with short stubby “rubber duck” antennas.

The importance of a proper grounding system for amateur radio stations was discussed in the report with specific recommendations for maximum effectiveness.

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 development 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. 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 meltdowns. 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 nanoseconds ( 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.

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 (powerlines, 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 semiconductors, 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.

:::::::::::::::::::::::::::::::::::::::
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:( Powers of TEN) :
:::::::::::::::::::::::::::::::::::::::
: 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.

Three 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. 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) 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).

:::::::::::::::::::::::::::::::::::::::
: 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.:
:::::::::::::::::::::::::::::::::::::::
: 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 electromagnetic 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. Aperatures in shield 1 create a special problem in protecting communication sites from EMP penetration.

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).

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.

:::::::::::::::::::::::::::::::::::::::
: !! !! :
: ###### !! ######## !! :
: # !! # !! :
: 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. :
:::::::::::::::::::::::::::::::::::::::

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 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 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. 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.

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 elect-
ricity (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

Of the many fables of nuclear war that has been worn out in an effort to convince us all of the futility of it all is EMP. When understood, the problem can take on realistic proportions. When a nuclear explosion occurs, a very broad spectrum of energy is released. It ranges from nearly DC (o KHZ) to beyond 1021 hertz (gamma rays). The portion concerned with here ranges from 0 KHZ to 1000 GHZ (beyond radar uses).

Two basic sorts of damage can occur as a result of EMP. The first being what we will call ” power line ” type of damage, and the other being what I’ll call ” radio ” damage. Power line damage is resultant from the induction of high levels of current into relatively long wires such as home or shelter wiring, electrical generating system wiring such as the cables running to and from PV ( photovoltaic ) panels, generators, windmills, and of course in the already famous auto electronic ignition system. This type of damage can be virtually eliminated by a multi-level approach, that provides front line defenses, and various levels of backup systems in the event that EMP should overcome the first level of defense. This layered defense method has proven highly reliable in commercial communications systems where radio towers are subject to severe direct lightning strikes. Even with such severe EMP and direct surge conditions which excede most predicted EMP conditions, the communications systems survive often for years of storm seasons.

The first layer of EMP defense is the THYZORB. This is a solid state single junction device similar to an avalanch diode. Its maker is National Semiconductor, and it is distributed by Square D. You should purchase these devices specifically matched to the type of system voltage you wish to protect. For instance, if you wish to protect a 12 VDC PV system, you should consider that the open circuit voltage of most PV panels is around 19 VDC so a 25 VD C THYZORB would provide excellent protection. Also remember that as the amount of current through the device increases, so does the voltage drop across the device. Generally about 10 VDC is to be expected at maximum rating, thus we can expect that no more than 35 VDC will develop at the protected area.

I would place a Thyzorb on each panel at the output terminals and then one more at the junction of the panels where your main feed line is connected. The THYZORB is available in many power ratings from 1.5 KW to 15 KW. Generally you should be safe with the small ones on the panels, and the 15 KW unit at the junction point. At the other end of the feedline add another THYZORB just as the first one at the junction point was. The device only has two connections on it which are placed directly across the lines to be protected. Under normal conditions, the unit has no effect on the circuitry. The unit is reliable and re-useable. After thousands of operations, it will still be as good as new. The reaction time for those who wonder about such things is about 10 nano seconds. In the event your cables are longer than ten feet or so, it wouldn’t hurt to add a THYZORB every ten feet. THYZORBS are available in many voltages and in AC or DC. This means you should be installing them in any AC lines such as inverter outputs or generator outputs. I would put one in every wall outlet and light fixture also. Now for the layered effect I mentioned earlier.

In the event the THYZORB fails you need to have another device in place to soak up the balance of the surge. In low voltage DC systems your choices are somewhat limited. You could use an MOV ( metal oxide varistor ). These are devices made by General Electric. They are widely available at stores like Radio Shack. The only problem with MOV’s is that every time they fire (see a surge) they drift in value a little. Pretty soon your surge stopper isn’t turning on at the right time or worse yet fails altogether. In low voltage systems, you can’t really use a gas discharge tube, since they only work at 150 volts or higher. By then your low voltage equipment will be fried. Instead, at the risk of sounding redundant, I recomend another THYZORB but selected at a slightly higher voltage. Five volts higher would be a good choice since the second one would only fire if the first one were working at 1/2 of its full capacity. This would cause a current sharing condition and increase overall device reliability. You could in theory go several layers in this manner until you felt completely safe, or you ran out of EMP money. The actual connections would be to earth ground the negative (-) side of your DC power system in several locations. Use long bronze, brass, or copper rods with heavy, short cables to the power system. Next attach the negative (-) side of the protection device, ( THYZORB or other ), to the ground system. Finally, attach the positive side of the protection device to the positive side of the power system. In an AC system, you can do exactly the same as above with proper device selection. You may also use a gas discharge tube here since we are dealing with a high voltage to start with. In this case you will have three wires to deal with; one for each side of the AC, and one for earth ground. Additional preventive measures include grounding the frame of the PV panel and grounding generator frames. A good earth ground is very important if you use gas discharge tubes. If scenes from the ” DAY AFTER ” have you paranoid about being trapped in an immobile car, then take heart. You can EMP proof your auto electrical system the same way as your low voltage DC system. Just put a couple layers of THYZORBS or MOV’s across the DC input to the ignition system. A few more sprinkled here and there like the power wires of your CB radio, or your AM/FM receiver will work wonders. An easy way to reduce the risk of appliance damage in your home or shelter, if it is an AC device is to use a personal computer style surge protector. They are cheap and very easy to install. Most of these devices use MOV’s or better yet THYZORBS or avalanch diodes.