Letter Re: EMP Shielding

HJL,

Hi! Can anyone tell me why parking your vehicle in a metal building will not provide the same EMP shielding as a metal ammo box or trash can? If my building is all steel, with no windows and has a metal roll up door, then where is the wave penetration? I was wondering if any experts out there knew the answer. Thanks. – R.M.

HJL Responds: The key to a Faraday cage is that the construction has good electrical conductivity across the entire surface and that there are no “holes” that are large enough to allow significant leakage through the barrier. This is usually accomplished with press fit seals on doors and windows along with solid connections on the seams. A metal garage is usually put together with standard construction practices that may or may not meet the criteria required for good electrical conductivity and minimization of gaps or holes. The metal panels are usually screwed together with standard hardware and the screws are spaced based on the mechanical strength rather than the electrical properties. They are generally too far apart and they may not even make a good electrical connection. If there is an electrical connection, it can change over time as the exposed metal corrodes. In addition, the floor usually does not have any shielding in it, allowing significant leakage that way.

It is possible to build a metal building with the right properties, but you have to start out knowing that is what you want, because it can be difficult to retrofit afterwards.

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