Electromagnetic Bomb: The Lethality

… A Weapon of Electronic Mass Destruction Part 3

by Carlo Kopp
Defense Analyst

Page 1 2 3 4 5 6

The Lethality of Electromagnetic Warheads

The issue of electromagnetic weapon lethality is complex. Unlike the technology base for weapon construction, which has been widely published in the open literature, lethality related issues have been published much less frequently.

While the calculation of electromagnetic field strengths achievable at a given radius for a given device design is a straightforward task, determining a kill probability for a given class of target under such conditions is not.

This is for good reasons. The first is that target types are very diverse in their electromagnetic hardness, or ability to resist damage. Equipment which has been intentionally shielded and hardened against electromagnetic attack will withstand orders of magnitude greater field strengths than standard commercially rated equipment. Moreover, various manufacturer’s implementations of like types of equipment may vary significantly in hardness due the idiosyncrasies of specific electrical designs, cabling schemes and chassis/shielding designs used.

The second major problem area in determining lethality is that of coupling efficiency, which is a measure of how much power is transferred from the field produced by the weapon into the target. Only power coupled into the target can cause useful damage.

Coupling Modes

In assessing how power is coupled into targets, two principal coupling modes are recognised in the literature:

  • Front Door Coupling occurs typically when power from a electromagnetic weapon is coupled into an antenna associated with radar or communications equipment. The antenna subsystem is designed to couple power in and out of the equipment, and thus provides an efficient path for the power flow from the electromagnetic weapon to enter the equipment and cause damage.
  • Back Door Coupling occurs when the electromagnetic field from a weapon produces large transient currents (termed spikes, when produced by a low frequency weapon ) or electrical standing waves (when produced by a HPM weapon) on fixed electrical wiring and cables interconnecting equipment, or providing connections to mains power or the telephone network. Equipment connected to exposed cables or wiring will experience either high voltage transient spikes or standing waves which can damage power supplies and communications interfaces if these are not hardened. Moreover, should the transient penetrate into the equipment, damage can be done to other devices inside.

A low frequency weapon will couple well into a typical wiring infrastructure, as most telephone lines, networking cables and power lines follow streets, building risers and corridors. In most instances any particular cable run will comprise multiple linear segments joined at approximately right angles. Whatever the relative orientation of the weapons field, more than one linear segment of the cable run is likely to be oriented such that a good coupling efficiency can be achieved.

It is worth noting at this point the safe operating envelopes of some typical types of semiconductor devices. Manufacturer’s guaranteed breakdown voltage ratings for Silicon high frequency bipolar transistors, widely used in communications equipment, typically vary between 15 V and 65 V. Gallium Arsenide Field Effect Transistors are usually rated at about 10V. High density Dynamic Random Access Memories (DRAM), an essential part of any computer, are usually rated to 7 V against earth. Generic CMOS logic is rated between 7 V and 15 V, and microprocessors running off 3.3 V or 5 V power supplies are usually rated very closely to that voltage. Whilst many modern devices are equipped with additional protection circuits at each pin, to sink electrostatic discharges, sustained or repeated application of a high voltage will often defeat these.

Communications interfaces and power supplies must typically meet electrical safety requirements imposed by regulators. Such interfaces are usually protected by isolation transformers with ratings from hundreds of Volts to about 2 to 3 kV.

It is clearly evident that once the defence provided by a transformer, cable pulse arrestor or shielding is breached, voltages even as low as 50 V can inflict substantial damage upon computer and communications equipment. The author has seen a number of equipment items (computers, consumer electronics) exposed to low frequency high voltage spikes (near lightning strikes, electrical power transients), and in every instance the damage was extensive, often requiring replacement of most semiconductors in the equipment.

HPM weapons operating in the centimetric and millimetric bands however offer an additional coupling mechanism to Back Door Coupling. This is the ability to directly couple into equipment through ventilation holes, gaps between panels and poorly shielded interfaces. Under these conditions, any aperture into the equipment behaves much like a slot in a microwave cavity, allowing microwave radiation to directly excite or enter the cavity. The microwave radiation will form a spatial standing wave pattern within the equipment. Components situated within the anti-nodes within the standing wave pattern will be exposed to potentially high electromagnetic fields.

Because microwave weapons can couple more readily than low frequency weapons, and can in many instances bypass protection devices designed to stop low frequency coupling, microwave weapons have the potential to be significantly more lethal than low frequency weapons.

What research has been done in this area illustrates the difficulty in producing workable models for predicting equipment vulnerability. It does however provide a solid basis for shielding strategies and hardening of equipment.

The diversity of likely target types and the unknown geometrical layout and electrical characteristics of the wiring and cabling infrastructure surrounding a target makes the exact prediction of lethality impossible.

A general approach for dealing with wiring and cabling related back door coupling is to determine a known lethal voltage level, and then use this to find the required field strength to generate this voltage. Once the field strength is known, the lethal radius for a given weapon configuration can be calculated.

A trivial example is that of a 10 GW 5 GHz HPM device illuminating a footprint of 400 to 500 metres diameter, from a distance of several hundred metres. This will result in field strengths of several kiloVolts per metre within the device footprint, in turn capable of producing voltages of hundreds of volts to kiloVolts on exposed wires or cables. This suggests lethal radii of the order of hundreds of metres, subject to weapon performance and target set electrical hardness.

Maximising Electromagnetic Bomb Lethality

To maximise the lethality of an electromagnetic bomb it is necessary to maximise the power coupled into the target set.

The first step in maximising bomb lethality is is to maximise the peak power and duration of the radiation of the weapon. For a given bomb size, this is accomplished by using the most powerful flux compression generator (and Vircator in a HPM bomb) which will fit the weapon size, and by maximising the efficiency of internal power transfers in the weapon. Energy which is not emitted is energy wasted at the expense of lethality.

Page 1 2 3 4 5 6

About Luis Miranda
The Real Agenda is an independent publication. It does not take money from Corporations, Foundations or Non-Governmental Organizations. It provides news reports in three languages: English, Spanish and Portuguese to reach a larger group of readers. Our news are not guided by any ideological, political or religious interest, which allows us to keep our integrity towards the readers.

Comments are closed.