by Dr. Arthur Bradley, author of Disaster Preparedness for EMP Attacks and Solar Storms
Many people are looking for an inexpensive Faraday cage to protect personal electronics from a nuclear-generated EMP. Unfortunately, it requires quite a bit of test equipment to determine shielding effectiveness. On the transmit side, it requires a signal generator, a high-power amplifier, and a broadband antenna. The receive side requires a small, battery-operated spectrum analyzer. I’ve done quite a bit of testing on various makeshift Faraday cages, and this article discusses the effectiveness of a metal garbage can.
A baseline open air measurement is first taken to determine the ambient field levels at some predetermined frequency (i.e. 500 MHz in this case). The levels at the spectrum analyzer are shown to be at -36 dBm.
When placed inside the garbage can, the measurement is shown to be -46 dBm, meaning that the can offered 10 dB of shielding. Not too great!
Much of the energy was believed to be coming in through the seam around the lid. It was, therefore, taped with conductive tape and the measurement repeated.
Next, the spectrum analyzer is placed into a metal garbage can, and the measurement is repeated.
The new measurement was shown to be at -77 dBm, meaning that the taped can offered 41 dB of protection. Much better!
This experiment showed that a metal garbage can can serve as a very good Faraday cage, but only if the seams are taped. Remember, it is not small holes that matter most, but rather long narrow slots, such as those around the lid’s seam. Expensive EMI copper tape and cheap aluminum duct tape both worked equally well, so a quick stop at the hardware store will get you what you need.
To learn more about EMP protection, check out Disaster Preparedness for EMP Attacks and Solar Storms. Also, to find the highest quality EMP bags, see http://disasterpreparer.com.