My Faraday Cage Test

[The Expendable]

I've heard people talking about using steel filing cabinets as Faraday cages. Sounds logical, but how effective is it? I had some steel boxes that I was planning to use as Faraday cages, and I wanted to test them for myself. I've read that while copper is the best material to build a Faraday cage out of, aluminum is a good second choice. Although I'm not an expert by any means, I've experimented with both steel and aluminum and found aluminum to work better.

My testing used cell phones and FRS radios. I have read that the frequencies found in the E1 pulse of an EMP are similar to those found in cell phone signals. I'm not 100% sure this is true, but I needed a starting point so that is what I used.

I placed a cell phone in a cardboard box, then placed the cardboard box inside a sealed steel box. When I called the cell phone it rang. Then I took the cardboard box out of the steel box and wrapped it in aluminum foil. When I called it I was sent directly to voicemail (i.e., no signal was reaching the phone). I did the same test using FRS walkie-talkies and got the same results... I was able to send a signal to the radio in the steel box, but no signal was passed to the radio wrapped in aluminum foil.

I know this may not be conclusive, but I've ditched my steel boxes and built some Faraday cages using sturdy cardboard boxes covered with heavy duty aluminum foil and wrapped with aluminum Shurtape for strength.

This is a small Faraday cage I made out of a cell phone box. The good thing about this one is I can keep often used items in it and take them out as needed. Note how I wrapped the foil inside the lip of the box, on both the top and bottom. The inside of the box is uncovered cardboard, forming an insulating barrier between my small electronics and any EMP surge. When the box is closed, it makes a "full metal jacket", so to speak. The aluminum Suretape was used to strengthen the foil, but I could have used duct tape as well.

The bottom line is this: If you are planning on using a steel filing cabinet, or your washing machine, or your oven, or your microwave oven as a Faraday cage, put your cell phone inside it and try to call it. If it rings that means that cell signals can breach the steel structure. If cell signals can get through, your makeshift Faraday cage is not giving you any protection.