Electromagnetic pulse protection can be a contentious subject among preppers. In my experience there are two dominant views on Faraday cages, and which camp you belong to depends on wither you are a ham radio operator or not. I base my ideas on the training I received when I worked as a radiological emergency response planner and the FEMA document CPG 2-17.
CPG 2-17 volume I explains the science behind electromagnetic pulse and the protection needed to mitigate this threat. Volume II and III of the CPG series deal with the construction of protection devices, as well as showing the reader how they can harden structures against Electromagnetic Pulses. Unfortunately, FEMA has discontinued the series, and the books are the “holy grail” of EMP documents and are extremely hard to find. Personally I only have been able to acquire volume one, so this article deals only with the theory behind EMP.
An electromagnetic pulse (EMP) is a burst of electromagnetic radiation. Typically we think of EMP as coming from a nuclear explosion or from the sun. However, these are not the only situations where you can get an EMP. Several types of high energy explosions as well as suddenly fluctuating magnetic fields. can produce EMP.
What you need to realize that EMP is Electromagnetic Radiation, and as such fits in the electromagnetic spectrum. This is the range of all possible frequencies of radiation emitted. Light, heat, sound, radio waves, electricity, and radiation all fit on this spectrum. The spectrum is organized by frequency, with the lower frequencies to the left and the higher on the right.
Frequency is the number of occurrences of a repeating event per unit time. Frequency is measured in hertz (Hz). 1 Hz means the cycle repeats once a second. If a light flashes at 1 HZ then it will flash 60 times a minute.
Not only is the spectrum organized by increasing frequency, increasing frequency corresponds with decreasing wavelength.
Wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings (zero crossings is where the wave crosses the center-line of the wave or 0 on the X axis)
Basically the more repetitions you cram into a span of time the smaller distance you can travel. I can make ten little hops a minute easier than I can make ten standing long jumps in a minute. The distance between when my feet leave the ground to where they land is wavelength, how many I do in a span of time is frequency.
Like I said above, we tend to think of EMP coming from nuclear detonation. As a military weapon, this works best if the nuclear warhead is detonated hundreds of kilometers above the Earth’s surface. This is called a high-altitude electromagnetic pulse (HEMP) device. Effects of a HEMP device depend on a very large number of factors, including the altitude of the detonation, energy yield, gamma ray output, interactions with the Earth’s magnetic field, and electromagnetic shielding of targets.
So lets talk a second about the mechanisms of injury that we get from EMP – what the pulse does to fry your gear.
EMP works through induction – just like a transformer – when the electromagnetic energy passes by a conductor it induces the electrons inside the conductor to move – INDUCING electricity. It works just like the wall wart you use to charge your cell phone. The electricity coming from your wall at 115volt is run into an electromagnet this electromagnetism then induces current in a coil of wire next to the magnet – the electricity from that coil is a lower voltage and allows you to charge your cell phone.
The longer the conductor the more power is induced by a pulse. Power transmission lines, large antennas, metal pipelines all will have induced electricity. Anything connected to those items could have a large surge of electricity in the event of a EMP.
This surge of electricity can cause problems by melting tiny wires in the electronics, large enough surges can overwhelm insulators and turn them into conductors (melting them in the process). It can also exceed a diode’s breakdown voltage. This is the voltage required to reverse electrical flow in a one way diode – basically ending its life as a diode. If this happens the circuit will not work
Just because something does not plug into grid power does not mean it is immune to EMP – while equipment may not receive those strong induced currents, the tiny wires inside of microcircuits do not take as much current to melt so they can receive enough induced current through its internal circuits if the EMP is strong enough.
With EMP there is some confusion – not only does it come from multiple events, it comes in several different variations.
This causes certain individuals to lump things that protect against one form of EMP and believe it protects against all types of EMP.
The International Electrotechnical Commission has categorized EMP into three types.
The E1 pulse is the fastest form of nuclear EMP. It is extremely brief but very intense electromagnetic field that can quickly induce very high voltages in electrical conductors. The E1 component causes most of its damage by causing electrical breakdown voltages to be exceeded. E1 is the component that can destroy computers and communications equipment and it changes too quickly for ordinary lightning protectors to provide effective protection against it. Lightning has a building effect where the pulse takes a few milliseconds to build and protection circuits can detect it and shut down. E1 is almost instantaneous and moves through the circuits before they can detect. Like how you slow down after the cop has you on radar…
The E1 component is produced when gamma radiation from the nuclear detonation knocks electrons out of the atoms in the upper atmosphere (Compton effect).
The E2 component is generated by the neutrons released by nuclear weapons. This E2 component is an “intermediate time” pulse that, by the IEC definition, lasts from about 1 microsecond to 1 second after the beginning of the electromagnetic pulse. The E2 component of the pulse has many similarities to the electromagnetic pulses produced by lightning. Because of the similarities to lightning coupled with the widespread use of lightning protection technology, the E2 pulse is generally considered to be the easiest to protect against.
However, since E2 happens AFTER E1, most lightning protection equipment will probably be damaged or destroyed.
E3 is different from both E1 and E2. E3 has a very slow pulse, lasting tens to hundreds of seconds.
What happens is that after a HEMP, the earth’s magnetic field thrown out of balance by the EMP, and the molten iron core of the earth that creates our magnetic field restores itself. This causes additional induction. This is the most similar to geomagnetic storms caused by a very severe CME.
This is most likely to cause induced currents in long electrical conductors, which can then damage components such as power line transformers.
Because of the similarity between solar-induced geomagnetic storms and nuclear E3, it has become common to refer to solar-induced geomagnetic storms as “solar EMP.” At ground level, however, “solar EMP” is not known to produce an E1 or E2 component.
The best way to protect against EMP is through the use of Faraday cages to shield against the pulse. While we will talk about and show some cages in a later post the are theoretically simple.
A Faraday cage is a conductor (either solid or a mesh smaller than the height of the electromagnetic wave. This cage completely encapsulates your device. It also has an insulator inside to keep the protected items from touching the cage.
Just like a rock on the beach causing waves to flow around it, EMP hits the cage and the energy is directed around your electronics rather than through it.
Some believe the cage needs to be made out of ferrous materials, but all that is needed is that the cage is a conductor, as any conductor can make an electromagnet.
Some also believe you need to ground your cage. Personally I disagree and feel the grounding wire will act as an antenna. However, it is possible for a conductor and an insulator to turn into a capacitor, and some believe a grounding rod will prevent this.
My biggest fear when it comes to Faraday cages is that any enemy that uses a HEMP against us will know some of us will have items that are protected, and will detonate a second EMP at some point (week – 10 days, a month) after the initial attack to destroy our redundant systems just like an earthquakes aftershock. This coupled with the idea that Faraday cages only protect against items that are not in use and stored properly leads me to spend time in building capability in the non-electric realm rather than spend all my resources building redundant cages stocked with redundant gear. Electronics are helpful but our civilization developed without them, and if I had too I think I can live without them (even though I am addicted to angry birds…)