Which signals (Wi-Fi, mobile phone, and GPS) can reliably be blocked by aluminum foil?

Question

There seems to be conflicting information regarding which signals can be effectively blocked by wrapping the device in aluminum foil.

With effectively blocked I mean block the signal as such that the service becomes unavailable.

Faraday bags exist, but they have been shown to be rather expensive and will become unusable after wear and tear. Also, most bags do not specify which signals are reliably blocked by the bag.

Aluminum foil seems a viable alternative, but I could not find any reputable source investigating the issue.

Answer 1

Tim is absolutely correct. I am an EMC engineer and use aluminum foil on occasion to wrap equipment to prove whether emissions of equipment are from the unit or its power cable (or other cables).

In theory if the aluminum shield were perfect this would give infinite attenuation at all frequencies, but in practice this isn’t the case. If the foil is well wrapped and taped at all the seams I can usually get in the order of 40dB of attenuation up to ~1Ghz. Past that the attenuation drops because the wave lengths get shorter and any small seam acts like a slot antenna (albeit a poor one).

So to answer your question, all of those signals can be blocked reliably by aluminum foil if you are diligent about how well you wrap them and close the seams. Oxidation is also an issue because you need good contact at the seams, but in practice this is not normally a much of issue unless you want very high attenuation or you are working at very high frequencies.

Answer 2

Aluminum foil is more than thick enough to block plane waves of these frequencies (ballpark 1GHz) to a high ratio.

It is not easy to employ in practice, however. Seams are transparent to RF fields, unless they are a particular width of overlap, or the seams have been shorted over with conductive EMI tape.

Note that it's not enough to simply lay foil together, or use generic aluminum (actual-duct) tape: the surfaces may be coated or oxidized, or a layer of adhesive insulates the foil backing. Special care must be taken to create a contiguous conducting shield.

Finally, for full shielding, the device to be shielded must be sealed inside the shield. A room lined with foil must be completely lined, floor to ceiling, with no gaps or seams, and any openings, doors, windows, etc. must be covered over with mesh or foil, and spring strip around the seams so they seal when closed every time. Outlets, lights and other connections that penetrate the shield, must be filtered for RF, lest they carry signals in as well.

To enclose just a single device, the best bet is to make a foil pouch by folding a sheet in half lengthwise, then crimping the sides down, and finally crimping down the end. Hopefully, the crimping action creates an electrical seal, but you will need some way to verify that this is the case.

Even a five-side-sealed pouch geometry isn't enough, because as long as the opening of the pouch is wide enough to transmit wavelengths of interest, energy can be exchanged with the device within. The frequency of 5G for example might be 5GHz or more, and the critical opening width (wavelength) is just a few inches.