Electromagnetic bomb

INTRODUCTION
An electromagnetic bomb, or e-bomb, is a weapon designed to take advantage of this dependency. But instead of simply cutting off power in an area, an e-bomb would actually destroy most machines that use electricity.
Generators would be useless, cars wouldn't run, and there would be no chance of making a phone call. In a matter of seconds, a big enough e-bomb could thrust an entire city back 200 years or cripple a military unit. ..
An electromagnetic bomb is designed to disable electronics with an electromagnetic pulse (EMP) that can couple with electrical/electronic systems to produce damaging current and voltage surges by electromagnetic induction. The effects are usually not noticeable beyond the blast radius unless the device is nuclear or specifically designed to produce an electromagnetic pulse.



EFFECTS
These weapons are not directly responsible for the loss of lives, but can disable some of the electronic system on which industrialized nations are highly dependent.
Devices that are susceptible to EMP damage, from most to least vulnerable;
1. Integrated circuits (ICs), CPUs, silicon chips.
2. Transistors, Vacuum tubes (also known as thermionic valves.)
3. Inductors, motors.
Transistor technology is likely to fail and old vacuum equipments survive. However, different types of transistors and ICs show different sensitivity to electromagnetism: bipolar ICs and transistors are much less sensitive than FETs and especially MOSFETs. To protect sensitive electronics, a Faraday cage must be placed around the item. Some makeshift Faraday cages have been suggested, such as aluminum foil, although such a cage would be rendered useless if any conductors passed through, such as power cords or antennas.
The term electromagnetic pulse (EMP) has the following meanings:
1. Electromagnetic radiation from an explosion (especially a nuclear explosion) or an intensely fluctuating magnetic field caused by Compton-recoil electrons and photo electrons from photons scattered in the materials of the electronic or explosive device or in surrounding medium. The resulting electric and magnetic fields may couple with electrical/electronic systems to produce damaging current and voltage surges. See Electromagnetic Bomb for details on the damages resulting to electronic devices. The effects are usually not noticeable beyond the blast radius unless the devices are nuclear or specifically designed to produce an electromagnetic shockwave.
2. A broadband, high-intensity, short-duration burst of electromagnetic energy. In the case of a nuclear detonation or an asteroid impact, most of the energy of the electromagnetic pulse is distributed in the frequency band between 3Hz and 30 kHz.







PRACTICAL CONSIDERATION
The mechanism for a 400 km high altitude burst EMP gamma rays hit the atmosphere between 20-40 km altitude, ejecting electrons which are then deflected sideways by the earth’s magnetic field. This makes the electrons radiate EMP over area. Because of the curvature of earth’s magnetic field the USA, the maximum EMP occur south of the detonation and the minimum occurs to the north.

The worst of the pulse latest for only seconds, but any unprotected electrical equipment and anything connected to electrical cables, which act as giant lighting rods or antennas will be affected by the pulse. Older, vacuum tube (valve) based equipment is much less vulnerable to EMP; Soviet Cold War-era military aircraft often had avionics on vacuum tubes.
Many nuclear detonations have taken place using bombs dropped by aircraft. The aircraft that delivered the atomic weapons at Hiroshima and Nagasaki did not fall out of the sky due to damage to their electrical or electronic systems. This is simply because electrons (ejected from the air by gamma rays) are stopped quickly in normal air for bursts below 10 km, so they do not get a chance to be significantly deflected by the Earth's magnetic field (the deflection causes the powerful EMP seen in high altitude bursts), but it does point out the limited use of smaller burst altitudes for widespread EMP.

If the B-29 planes had been within the intense nuclear radiation zone when the bombs exploded over Hiroshima and Nagasaki, then they would have suffered effects from the charge separation (radial) EMP. But this only occurs within the severe blast radius for detonations below about 10 km altitude. EMP disruptions were suffered aboard KC-135 photographic aircraft flying 300 km from the 410 KT Bluegill and 410 KT Kingfish detonations (48 and 95 km burst altitude, respectively) in 1962, but the vital aircraft electronics then were far less sophisticated than today and did not down the aircraft.
Several major factors control the effectiveness of an EMP weapon. These are:
1. The altitude of the weapon when detonated;
2. The yield of the weapon;
3. The distance from the weapon when detonated;
Geographical depth or intervening geographical features,
Beyond a certain altitude a nuclear weapon will not produce any EMP, as the gamma rays will have had sufficient distance to disperse. In deep space or on worlds with no magnetic field (the moon or Mars for example) there will be little or no EMP. This has implications for certain kinds of nuclear rocket engines. See Project Orion.









WEAPON ALTIITUDE
How the peak EMP on the ground varies with the weapon yield and burst altitude. The yield here is the prompt gamma ray output measured in kilotons. This varies from 0.115–0.5% of the total weapon yield, depending on weapon design. The 1.4 Mt total yields 1962 Starfish Prime test had an output of 0.1%, hence 1.4 KT of prompt gamma rays. (The blue 'pre-ionization' curve applies to certain types of thermonuclear weapon, where gamma and x-rays from the primary fission stage ionize the atmosphere and make it electrically conductive before the main pulse from the thermonuclear stage. The pre-ionization in some situations can literally short out part of the final EMP, by allowing conduction current to immediately oppose the Compton current of electrons.)
A high-altitude nuclear detonation produces an immediate flux of gamma rays from the nuclear reactions within the device. These photons in turn produce high energy free electrons by Compton scattering at altitudes between (roughly) 20 and 40 km. These electrons are then trapped in the Earth's magnetic field, giving rise to an oscillating electric current. This current is asymmetric in general and gives rise to a rapidly rising radiated electromagnetic field called an electromagnetic pulse (EMP). Because the electrons are trapped essentially simultaneously, a very large electromagnetic source radiates coherently.
The pulse can easily span continent-sized areas, and this radiation can affect systems on land, sea, and air. The first recorded EMP incident accompanied a high-altitude nuclear test over the South Pacific and resulted in power system failures as far away as Hawaii. A large device detonated at 400–500 km (250 to 312 miles) over Kansas would affect all of the continental U.S. The signal from such an event extends to the visual horizon as seen from the burst point.
Thus, for equipment to be affected, the weapon needs to be above the visual horizon. Because of the nature of the pulse as a large, long, high powered, noisy spike, it is doubtful that there would be much protection if the explosion were seen in the sky just below the tops of hills or mountains.
The altitude indicated above is greater than that of the International Space Station and many low Earth orbit satellites. Large weapons could have a dramatic impact on satellite operations and communications; smaller weapons have less such potential.

WEAPONS YIELD
Typical nuclear weapon yields quoted in such scenarios are in the range of 20 megatons. This is roughly 1,000 times the sizes of the weapons the United States used in Japan at Hiroshima and Nagasaki.

WEAPONS DISTANCE
The major energy in an EMP is electromagnetic, and radiates out from the point of detonation in a sphere. EMP is electromagnetic radiation. The intensity of these fields decreases in proportion to the circumference and distance from explosion. The actual amount of EMP energy deposited per unit area is entirely different, and that falls off as the inverse-square of distance.

How the area affected depends on the burst altitude.

Radius in Miles

Circumference

Relative
Strength

10

62.83

100% or 1

20

125.66

50% or 1/2

30

188.50

33.3% or 1/3



251.32

40

25% or 1/4

The range of gamma rays in the atmosphere is assumed to be 10 miles, which is appropriate for a 1 megaton burst at an altitude of about 10 miles. The size of the perimeter of this circle grows in proportion to the radius of the circle, and so the electric field strength weakens as the circle grows. By simple mathematics the electrical field strength does not fall as the inverse square law, but is instead a simple inverse linear relationship.

The range of deposition of gamma rays would be smaller for a surface burst because of the greater air density, which shields the initial gamma rays that cause the EMP. Conversely, for a burst at greater altitudes, the range of the deposition would be far greater than 10 miles, because the gamma rays could travel much further in the low density air before being stopped. The actual energy deposited per unit area, if emitted from an isotropic point source, is always governed by the inverse-square law.
But the damaging effect of EMP is determined largely by the peak electric field (measured in volts/meter), which falls only inversely with distance. The amount of EMP energy passing through a unit of area is proportional to the square of the field strength. Within the range of gamma ray deposition, these simple laws no longer hold as the air is ionized and there are other EMP effects such as a radial (non-radiated) electric field due to the separation of Compton electrons from air molecules, and other complex phenomena. So its energy = 1/d^2









NON-NUCLEAR ELECTROMAGNETIC PULSE
Non-nuclear electromagnetic pulse (NNEMP) is an electromagnetic pulse generated without use of nuclear weapons. There are a number of devices to achieve this objective, ranging from a large low-inductance capacitor bank discharged into a single-loop antenna or a microwave generator to an explosively pumped flux compression generator. To achieve the frequency characteristics of the pulse needed for optimal coupling into the target, wave-shaping circuits and /or microwave generators are added between the pulse source and the antenna. A vacuum tube particularly suitable for microwave conversion of high energy pulses is the victor.
A right frond view of a Boeing E-4 advanced airborne command post on the electromagnetic pulse (EMP) simulator for testing.
Non-nuclear electromagnetic pulse (NNEMP) generators can be carried as a payload of bombs and cruise missiles, allowing construction of electromagnetic bombs with diminished mechanical, thermal and ionizing radiation effects and without the political consequences of deploying nuclear weapons.
NNEMP generators also include large structures built to generate EMP for testing of electronics to determine how well it survives EMP. In addition, the use of ultra-wideband radars can generate EMP in areas immediately adjacent to the radar; this phenomenon is only partly understood.

USS Estocin (FFG-15) moored near an Electro Magnetic Pulse Radiation Environmental Simulator for ship (EMPRESS) facility.





CONCLUSION
An electromagnetic Bomb is designed to disable electronics with an electromagnetic pulse (EMP) that can couple with electrical/electronic system to produce damaging current and voltage surges by electromagnetic induction. The effects are usually not noticeable beyond the blast radius unless the device is nuclear or specifically designed to produce an electromagnetic pulse.






REFERENCES

1. http://www.wikipedia.com/
2. http://www.answers.com/
3. WWW.IEEE.ORG/MDH.HTML
4. http://www.gogle.com/