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If I placed two devices inside of a faraday cage, one of which was a bluetooth beacon which emitted a bluetooth signal, the other was a cell phone which received bluetooth signals, would they be able to communicate?

Similarly, could two devices communicate on another radio frequency protocol?

I understand that the faraday cage would block signals from leaving the cage, or signals from coming in; what is unclear is whether there is still an electromagnetic field within the cage.

Thanks friends.

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In principle communication within the Faraday cage is fine. Electromagnetic waves can't pass through the perimeter of a Faraday cage, but can exist within it as long as the size of the cage is substantially larger than the wavelength you're interested in.

In practice, depending on the ratio of absorption to reflection for the materials in your Faraday cage and the frequencies of interest, it may be that reflected signals from the walls of the cage interfere with the operation of the transmitter.

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  • $\begingroup$ Thanks, Rob. Would you define how much 'substantially larger' should be? 1.3x, 2x, 3x, etx? $\endgroup$ – user2073336 Feb 1 '17 at 1:45
  • $\begingroup$ I have in mind 10x, but I think what happens in the small-cage case also depends on the behavior of the surface of the cage. You might test it. Bluetooth is $\lambda = c/\rm 2.4\,GHz = 0.15\,m$, about the size of most devices. Put two together in a paper bag and wrap the bag neatly and completely in a few layers of aluminum foil. If the devices can still talk to each other, they'll work in a larger enclosure as well. $\endgroup$ – rob Feb 1 '17 at 2:07

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