Faraday Protection

December 4, 2012

in Manage Risk

The primary means of protecting electronic devices from a strong ElectroMagnetic Pulse (EMP) is to prevent the pulse from reaching the equipment. This is done by placing the device inside a cage, box or other container that does not allow the wave to penetrate inside the perimeter or to induce current in anything in contact with the device. This kind of protection is known as a “faraday box” or “faraday cage” or even “faraday room”.
[because Michael Faraday discovered the principle of electromagnetic induction]

Faraday protection has different requirements for different electromagnetic wavelengths. A conductive metal mesh screen with a hole size of 1/4 of the wavelength will often prevent penetration of the waveform inside the screen. A crude mesh screen (like that found in window and door screens) will prevent a long wavelength from penetrating, but will not protect against high frequency waves with shorter wavelengths.

An EMP produced by a nuclear blast exudes three distinctly different waves:

  • E-1 is high frequency (up to several Ghz and possibly higher), only lasts for a few microseconds, and is the primary concern for faraday shielding
  • E-2 is intermediate frequency (from 1 hz to 100 Khz), lasts for about 1/10 second, and is similar to a lightening strike in threat profile
  • E-3 is low frequency, lasts for many seconds, and is mostly a threat to long lines

The primary job of faraday shielding is to protect against the E-1 high frequency, short wavelength pulse. This pulse can be expected to contain a lot of energy compressed into a microsecond duration window and if there is any small gap or leak in the faraday shielding that allows it through, it will destroy delicate electronic circuits inside the protection.

The shielding itself does not have to be anything special. Layers of tinfoil and/or a fine metallic screen mesh can do the job. The important parts are to make sure gaps are eliminated (particularly where the cage/box opens and closes, and to insulate the electronic devices inside from contact with any of the conducting shielding material.

A metallic container might be a good starting place, and the opening/closing method will be critical to seal off any gaps. Metal drums, metal garbage cans, metal boxes, almost any metal based container is a good start, specially if it closes with a tight seal. (a tight conductive seal) A non-metallic container will work too if it is lined with some conductor like aluminum foil (use several layers and press them into place so there are no gaps or wrinkles that might let EM get through) and then sealed carefully. Store devices to be protected in some insulating material (plastic bag, plastic, wood, paper, cloth container or wrapping material) then place it inside the shielded container and seal it with great diligence. If the container is opened, it must be carefully resealed. If any cracks are not sealed that might allow radio waves to penetrate the shield, it can fail.

Some simple tests can demonstrate some of the principles involved with this. There are a lot of videos available, but many of them are incomplete. Using an AM/FM radio to test faraday shielding will demonstrate the ability of the shielding to stop that fairly low frequency radio, but not higher frequency waves. Using a cell phone tests frequencies in the Ghz range but still has some serious limitations because E-1 pulses can generate frequencies far above that. If a normal radio or a cellphone can penetrate your shielding, you can be sure an E-1 pulse will, but silencing them is no guarantee the same thing will happen with EMP.

Another key factor to consider with using faraday shielding is that there is not likely to be any warning about an EMP attack. This means that the electronic devices that are to be protected by the shielding will need to be in the protected area all of the time, relegating their role to a reserve backup device. It will be necessary to weigh how critical the need of the device is anticipated to be after an EMP takes out most other electronics versus the cost of redundancy. Protecting a TV may not make much sense if there will be no television signal to receive and watch.

Here is a suggestion list to consider for faraday protection:

  • Flashlights and other LED lights
  • Battery charger – solar and/or handcrank
  • Radio – multi-band, shortwave+ receiver that runs from batteries or a handcrank.
  • Data – data storage for critical data, flash drive, hard drive (remember to think about how it will be accessed)
  • Laptop – a small laptop might be useful, but think about how it will be used and what information might be useful (a library of survival info on CD/DVD?)
  • A small DVD player might be cheaper and easier to protect than a laptop, but just as functional (depending upon your needs)
  • GPS – a small GPS unit and power to run it (assuming GPS satellites survive)
  • Solar power setup – panels, charge controller, batteries, inverter (this will take up a lot of space)

Scenario: ElectroMagnetic Pulse (EMP) and Solar Flares

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