Electromagnetic Pulse (EMP)

Electromagnetic Pulse (EMP)

This advanced project shows how to produce a multi — megawatt pulse of electromagnetic energy that can cause irreversible damage to computerized and sensi­tive communication equipment. A nuclear detonation causes such a pulse, which must be countermeasured lo protect electronic devices. This project requires lethal amounts of electrical energy storage and must not be attempted unless in a qualified laboratory environment. Such a device can be used to deactivate

the computer systems in automobiles, avoiding dan­gerous high-speed chases. Sensitive electronic equip­ment can be tested for susceptibility to lightning and potential nuclear detonations.

The project is semidetailed with references made only to the major components. A low-cost, open-air spark switch is shown but will provide only limited results. A gas-filled or isotope doped switch is required for optimum results (see Figure 25-1).

Basic Description

Shockwave generators are capable of producing focused acoustic or electromagnetic energy that can break up objects such as kidney stones and other sim­ilar materials. Electromagnetic pulse (EMP) genera­tors can produce pulses of electromagnetic energy that can destroy the sensitive electronics in comput­ers and microprocessors. Destabilized inductive and capacitive (LC) circuits can produce multigigawatt pulses by using an explosive wire disruption switch. These high-power pulses can be coupled into parallel plate transmission lines for EMP hardness testing, parabolic and elliptical antennas, horns, and so on for directional far-field effects.

For example, research is currently being under­taken to develop a system that would disable a car during a dangerous high-speed chase. The trick is generating a high enough power pulse to fry the elec­tronic control processor modules. This would be a lot simpler if the vehicle were covered in plastic or fiber­glass rather than metal. The shielding of the metal body offers a challenge to the researcher developing a practical system. A device could be built to do this, but it would be costly and could produce collateral damage to friendly targets.

Project Objective

The objective here is to generate a high-peak power pulse of electromagnetic energy to test the hardness of sensitive electronic equipment. Specifically, this project explores the use of such a device for disabling vehicles by jamming or destroying computerized con­trol chips. We’ll experiment with disruptive LCR cir­cuits with focused Shockwave capabilities.

Hazards

The project uses deadly electrical energy that can kill a person instantly if improperly contacted. The high — energy system that will be assembled uses exploding

wires that can create dangerous shrapnel-like effects. A discharge of the system can severely damage nearby computers and other related equipment.

Theory

A capacitor (C) is charged from a current source to an energy source over a period of time. Once it reaches a certain voltage corresponding to a certain energy level, it is allowed to discharge quickly into a resonant circuit. A wire now is made to explode, dis­rupting this high-peak current through the circuit inductance. A powerful, undampened wave is now generated at the natural frequency and at the associ­ated harmonics of this resonant circuit. The induc­tance (L) of the resonant circuit may consist of a coil and associated lead inductance, along with the intrin­sic inductance of the capacitor, which is around 20 nanohenries. The capacitor of the circuit determines the energy storage and also has an effect on the reso­nant frequency of the system.

Radiation of the energy pulse can be made via a conductive conic section or a metal, horn-like struc­ture. Some experimenters have used lumped, half­wave elements center-fed by a coil coupled to the coil of the resonant circuit. This half-wave antenna con­sists of two quarter-wave sections tuned to the reso­nant circuit frequency. These are in the form of coils wound with an approximate length of wire equal to a q uarter-wavelength. The antenna has two radiation lobes parallel to its length or broadside. Minimum radiation occurs at points axially located or at its ends, but we have not validated this approach. For example, a gas discharge lamp, such as a household fluorescent lamp, will flash brightly at a distance from the source, indicating a powerful directional pulse of electromagnetic energy.

Our test pulse system produces conservative, multimegawatt electromagnetic pulses (1 megawatt of broadband energy) and is radiated preferably via a conical section antenna consisting of a parabolic reflector of 100 to 300 millimeters in diameter. A 25- X 25-centimeter-square metallic horn, flaring out to 100 centimeters square, will also provide a degree of performance. A.5-microfarad, special. low —

inductance capacitor charges up in about 20 seconds with the ion charger described in Chapter 1, “Anti­gravity Project.” and is modified as shown. Faster charging rales can be obtained by a higher-current system available on special request for more serious research Irom www. amazingl. com.

A high-power radio frequency pulse can be gener­ated where the output of the pulser may also be cou­pled to a full-size, center-fed. half-wave antenna tuned between 1 and 1.5 MHz. The actual length at 1 МН/ is over 150 meters (492 feet) and may be too large for many experiments. However, it is normal­ized for a radiation coefficient of 1, with all other schemes being less. The actual elements may be reduced in length by using tuned quarterwave seo tions consisting of a 75-meter (246-foot) length of wire spaced and wound on 2- to 3-meter pieces of polyvinyl chloride (PVC) tubing. This scheme pro­duces a pulse of low-frequency energy.

Please note, as stated, that the pulse output of this system will cause damage to computers and any devices using microprocessors or similar circuitry up to a considerable distance. Always use caution when testing and using this system—just being close can damage sensitive electronic equipment. Figure 25-2 provides a description of the strategic parts used in our lab-assembled system.

Capacitor

The capacitor (C) used for this type of application must have very low inherent inductance and dis­charge resistance. At the same time, the part must have the energy storage sufficient to produce the nec­essary high-powered pulse at the target frequency. Unfortunately, these two requirements do not go hand in hand. Higher-energy capacitors always will have more inductance than lower-energy units. Another important point is the use of relatively high — discharge voltages (V) to generate high-discharge currents. These values are required to overcome the inherent complex loss impedance of the series induc­tance and resistance of the discharge path.

The capacitor used in our system is.5 mfd at 50,000 volts with a.03-microhenry series inductance. Our tar­get fundamental frequency for the low-power nondis — ruptive circuit is 1 MHz. The system energy is400 joules, as determined by E = Ч2 CV?, with E at 40 Kv.

Inductor

The inductor can be easily made for a low-frequency radio puIse. The inductance shown as LI is a lumping of all stray connecting leads, the spark switch, the exploding wire disrupter, and the inherent inductance of the capacitor. This inductance resonates at a wide band of frequencies and must be able to handle the high-discharge current pulse (1 j. The value of the lumped value is around.05 to.1 Uh. The conductor sizes must take into effect the high pulse current, ide­ally equal to V X (C/L)b2.This fast current transition wants to flow on the conductor surface due lo the high-frequency skin effect.

You may use an inductor ot several turns for experimenting at Ihe lower frequencies along wilh a coupled antenna. Dimensions are determined by the air inductance formula: L = (10 X D — X N2 )/l, where D is the diameter in centimeters, 1 is the length in centimeters, and N is the number ol turns. A coil from 3 turns of 10 millimeters (.375 inches) of copper tub­ing on a 7.5-cenlimeter (З-inch) diameter spread out lo 15 centimeters (6 inches) will have a calculated inductance of.3 Uh.

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