Protecting your favorite electronics
from electromagnetic pulse destruction

You just experimented with different capacitor and resistor values until getting it right. You debugged the last code error in your microcontroller project and the excitement and pride are huge as the program finally executes perfectly. Just then AC/DC’s "High-Voltage Rock ‘n’ Roll" gets interrupted on your radio by a civil defense announcement warning of an approaching atmospheric object – possibly an EMP weapon previously warned about by intelligence sources. What do you do? You’re not about to lose all your hard work to those miserable war pigs. Believe it or not, you could safely protect it by throwing it in the garbage can. A metal one, that is.

The can, if enclosed with a lid, would serve as a Faraday cage and could protect its contents from much of the damaging electromagnetic radiation. A Faraday cage shields against electric fields, most electromagnetic fields, but not purely magnetic fields. For example, a magnetic compass will operate inside a Faraday cage.

Starfish Prime: In July of 1962 the US government detonated a 1.4-megaton nuclear warhead 250 miles above the Pacific Ocean. It was a test designed to measure the effects of electromagnetic pulse on electrical and electronic equipment. The EMP was much greater than expected and knocked out streetlights and communications in Hawaii. The detonation and afterglow were widely visible.
Watch declassified test video

So what makes up a weaponized electromagnetic pulse and how well would a Faraday cage protect against it? According to the International Electrotechnical Commission (IEC) there are 3 parts to a nuclear EMP:

E1 is a very brief, but intense, electromagnetic field that’s generated when gamma radiation knocks electrons from their atoms in the atmosphere. This creates a very strong electrostatic charge that can cause over-voltage breakdowns of insulation and semi-conductors, resulting in short-circuit damage to equipment components.

E2 lasts up to 1 second and is produced when the gamma rays are scattered in the atmosphere. Its effect is very similar to the electromagnetic pulse from a nearby lightning discharge that would occur naturally. This is considered to be the least threatening of the 3 parts because it has the lowest intensity and can be protected against using conventional lightning protection equipment.

E3 lasts up to several minutes and is produced when the explosion displaces the Earth’s magnetic field, similar to what happens during a geomagnetic storm. When the Earth’s magnetic field is displaced, and then returns back to its normal state, the massive movement of the field can induce very strong electrical currents in long conductors, such as power and telecommunication lines. This effect from an EMP weapon would also likely be stronger than from a natural geomagnetic storm.

A Faraday cage is known to protect very well against electrostatic discharge (as in E1) and the type of electromagnetic pulse described in E2. Because a Faraday cage does not block magnetic fields it would not prevent the type of induction described in E3, but the induced currents would likely be small because of the short conductor lengths of the device circuitry. It’s very possible, then, that a Faraday cage-type container would prevent the damage of its contents even though the protection would not be complete.

Links:
"High-Altitude Electromagnetic Pulse (HEMP): A Threat to Our Way of Life"
"A Very Scary Light Show: Exploding H-Bombs In Space"