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Comment by ascuttlefish | Hacker News Reader

A friend of mine recently made me a duct-tape wallet lined with tinfoil. The theory is that this will act as a Faraday cage to protect my Mastercard with Paypass. I haven't tested it yet, but next time I'm at a Paypass place, I'm going to give it a try. Anyone have any idea if this is sound physics, or just paranoia?

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That sounds like a great DIY way of doing what this "steel mesh" wallet does. I have heard though that different RFID chips broadcast on different frequencies that render certain materials less effective at blocking.

Here's another great product catalog with far cheaper prices for similar stuff: http://www.idstronghold.com/

I didn't know that different frequencies would affect blocking effectiveness, but it makes sense. My initial design was for some kind of copper mesh, but my friend, practical and cost-cutty as he is, said to go with tinfoil to get a similar effect. Those idstronghold wallets look a touch more professional than my duct-tape wallet.

I'm not a physicist, but doesn't the conductor need to fully encircle the card to make a Faraday cage? I would think that something U-shaped (in one dimension or another) like a typical wallet would just act as a waveguide. Even if it does act as a waveguide, it might make it safe enough. There might be a way to put some sort of flap that closes over the card.

There's also one other important requirement: it must be GROUNDED. So unless you're willing to wear a wire from your wallet down to the bottom of your shoe, this won't be too effective.

No, so long as it is electrically completely enclosed, signals won't get in or out. Doesn't matter if it is floating at +/- 13.89 v ac/dc above ground.

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