Protect Your Electronics From an EMP

S2-E6-Faraday-Cage

Electromagnetic pulses occur at various frequencies depending on how they’re caused, and you need various strategies to protect your electronics.

EMP Bullet Points

  • You don’t need a Faraday cage to protect small electronics from EMPs caused by lightning or solar flares. These EMPs cause damage by driving voltage spikes into things that are plugged into your electrical outlets.
  • A Faraday cage is necessary to protect electronics from a nuclear EMP, which occurs at short wavelengths that can couple energy into integrated circuits and “fry” them.
  • The components to be protected must be completely enclosed in the Faraday cage.
  • The components inside the cage must be electrically isolated from the conductive material of the cage; wrap them in a towel or a rubber material, or set them on an old mouse pad.
  • You must not have any gaps larger than about 1 millimeter.
  • You may use a wire mesh to build your cage, as long as the mesh is smaller than 1 millimeter.
  • You do not need to ground the cage.

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EMP In-Depth Explanation

Faraday cages are not necessary to protect small electronics from solar coronal mass ejections (solar flares) or lightning, because they occur at low frequencies (long wavelengths) which can’t couple energy into small circuits, unless long wires are entering the system. The best protection is simply to unplug them, or use high voltage surge protectors.

Lightning strikes and solar flares create EMPs at frequencies ranging from 3 Hz to 30 KHz, which is far too low a frequency to couple directly with your small electronics. The wavelengths involved range from several miles to 100,000 miles in length, so they can’t couple with the short wiring circuits in a cell phone, a thumb drive, or a radio. However, they do couple with long power lines and create huge voltage surges which are transmitted through power cables connected to the electrical grid, so if you have something plugged into the power outlet in your wall, it can be damaged. The best protection is to unplug your electronics, but use a surge protector in case you’re not there to unplug everything.

A nuclear EMP, on the other hand, can damage electronic devices by coupling energy with their integrated circuits. These occur at frequencies of around 1 GHz, which corresponds to a wavelength of .3 meters, or about 1 foot. Cell phones, computers, thumb drives, and even some modern flashlights are vulnerable. LED bulbs are vulnerable. To protect them, you need a Faraday cage. In this context, a Faraday cage is a container made of conductive material that completely surrounds your electronics.

Because of the so-called skin effect, the conductive material can be very thin. You can make your own Faraday cage by placing your electronics in a cardboard box and wrapping the box with heavy-duty aluminum foil, which is about 24 microns thick. It is important to completely wrap the box. Very small gaps are OK, but to offer protection, they must be significantly smaller than the wavelength of the EMP; in the case of a nuclear EMP, the greatest gap you want is about 1 millimeter.

A microwave oven will offer excellent protection. Modern ovens operate at a frequency of 2.45 GHz, and their built-in shielding will exclude all frequencies below that, including nuclear EMPs.

Faraday cages do not need to be grounded.

Small Electronics Vulnerable to a Nuclear EMP

  1. Thumb drive with critical information
  2. Cell phone
  3. Laptop
  4. Emergency radio
  5. Flashlight. One thing I neglected to mention in the video is that LED bulbs are highly susceptible to EMP damage. Add to the the fact that many modern flashlights have electronic circuits that control the output, and your flashlight is definitely an item you want to protect.
  6. Car “brains.” Unless you intend to build a Faraday cage in your garage, your only option is to have a vehicle that is entirely mechanical, like the old 12-valve Cummins Dodges. Even they had some electronic components, but none of them are required to start and run the engine. The fuel shutdown solenoid can easily be replaced with a choke cable.

Make Your Own Faraday Cage

In the video, I demonstrate a DIY Faraday cage made from a cardboard box and heavy duty aluminum foil. It must be heavy duty foil, which is 24 microns thick, and I use two layers just to be sure.

  1. Choose a cardboard box large enough to hold the items you want to protect.
  2. Place the items inside and isolate them from the container with a towel or rubberized material.
  3. Include a pack of desiccant to absorb moisture.
  4. Wrap with two layers of heavy duty (24-micron) aluminum foil.
  5. Tape shut to hold the foil tight, avoiding gaps.

Other suitable Faraday cages:

  1. Metal trash can.
  2. Ammo box. Close the gaps around the lid with metal tape or aluminum foil.
  3. Altoids can for thumb drives and SD cards.
  4. Old microwave oven.
  5. Anti static bags offer some protection, and those certified to MIL-PRF-8170 or MIL-PRF-131 offer the most. Avoid Mylar like that used in metalized food storage bags. The aluminum is  only 6 microns thick —  too thin.

Resources:

The EMP Threat: Fact, Fiction, and Response — a technical paper discussing EMP threat from nuclear devices and solar flares

Skin Depth Calulator — to determine how thick your conductive material must be in your Faraday cage

~SnoMan

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