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The superphone

Something isn't right. Our laboratory facilities contain a couple of Faraday-shielded rooms. The idea is that electromagnetic radiation can't get in (or, for that matter, out). That means mobile phones shouldn't work in there. And they don't. Mine has no reception at all - others in our research group report either no reception or 'one-bar' reception occasionally, and that with the door open. At least, that used to be the case. Then a summer student arrived. With him came an extremely new 4G phone which WORKS JUST FINE inside the Faraday shield with the door closed. Not only that, but the student reports that he gets better reception in the room than at home. THIS IS NOT SUPPOSED TO HAPPEN. 

For sure, we don't expect the room is perfect. It needs to have holes in it, such as letting internet cables through (no wireless reception, obviously) and, a little more importantly, air. But there shouldn't be much radiation at all. In fact, we have two shielded rooms across a corridor from each other - one is used for electrophysiology (where we look at very tiny voltage signals) and the other for simulating lightning strikes on electronic equipment (where voltages are very high). The fact that the lightning experiments don't interfere with the electrophysiology ones shows that it's working. So how does my student's phone get really good reception? This is still a bit of a mystery. 

 

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3 Comments

Not sure if this is a rhetorical question. I'm no expert on Faraday cages and know nothing about what makes 4G different to 3G or 2G or anything. but my guess is the 4G has wireless capability that enables it to make use of the internet connections and equipment you have inside the Faraday cage. The equipment includes wireless modem or anything like that? Have you tried removing the internet/wireless/modems from the room and seeing if the phone still works?

Yes - I think 4G is designed to talk to devices with wireless modems directly. However, if this is happening, there is something very wrong with the security on our computer network. The phone in question 'knows' no network passwords or anything like that.

Different phone networks use different frequency bands (about 1 - 2.5 GHz is what I think is typically used - that's about 12-30 cm in wavelength). It may be that its frequency is particularly conducive to this room. It is maybe conceivable that the grate in the door is acting as a slot antenna.

However, given that the room does what it is designed to do (keeps our experiments nearly noise-free) it isn't something we'll lose a lot of sleep on just yet. A puzzle, not a problem.

Sorry, I didn't explain it well, I gathered you weren't finding it a problem. I was thinking more along the lines of wireless capacity of equipment already connected to the internet (presumably by cable!). Like laptops, printer, wireless mouse, etc. For example, do students connect their own laptop/netbook to the internet. Even if the connections are all via cable that does not automatically mean the wireless capability of the device is disabled. Just wondering...

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