It seems from the video on that site that most of the advantages they claim are not RF-related (strength, water resistance, etc.) However, they do mention scanning "RFID" cards as you say. A true Faraday cage would have no holes in it and be made of perfectly conductive material :) It would block all EM radiation in or out in that case. Any deviation from this will allow some EM through. Let's look at the several aspects of this aluminum clamshell design: 1) 5mm gap around edges - this will act like both a waveguide and as a dipole/slot antenna. It would severely compromise the integrity of the shielding for GHz-range signals, perhaps even down to 100MHz or so. I say this mainly from experience of trying to shield these frequencies. The size of any hole must be less than a 1/2 wavelength to be at all effective in shielding at a particular frequency. Even if it is smaller than this, it simply creates a highly-attenuating path so that the path length through the hole will determine the final attenuation value. In this case, this is worse than just a hole because it sounds like the slot goes most of the way around the wallet, so that the two halves are only connected on one side. I'm not 100% sure of the effect of this but my guess is that it would make a nice antenna at frequencies where the dimensions of the wallet are about 1/2 wavelength. 2) conductivity between halves - if the two halves are not electrically connected, then they also have the distinct possibility of forming a short dipole antenna which could be a very effective radiator even down into the 10s of MHz. 3) magnetic shielding - as the material of the cage gets less conductive and thinner, it will begin to fail to shield against low frequency magnetic fields. This could make this wallet shield ineffective at blocking the 100s of kHz range inductive-coupled RFID. The tongue and groove fit you mention would be ideal, especially if there was an electrical connection all the way around the tongue and groove (i.e., the metal was not plated with a non-conductive coating so that the two halves made contact all around the tongue and groove joint). It would be best of the tongue and groove were split into small segments like metal "fingers" so that there were many points of contact all along each joint. My best guess is that this wallet would not be very effective shielding against any of the RFID technologies out there. Sean On Mon, Jul 4, 2011 at 1:24 PM, YES NOPE9 wrote: > www.alumawallet.tv > > I have looked at this wallet at Walgreens. =A0There are two aluminium cla= m-shells that do not quite fit together. On the edges of the clam-shells is= a plastic ring that supplies at latching mechanism and hinges. =A0This mak= es an approximately 5mm gap between the clam shells. > > The wallet is claimed to block "scanning attempts" of the contents of the= wallet. > > Are the qualities of a Faraday cage related to the wavelength of the scan= ning radiation versus hole sizes in the cage ? > Do the two clam-shell halves require electrical continuity ? > Would an aluminium clam-shell which mated with it's opposite ..... using = a tongue and groove fit .... be a much better Faraday cage or is this unnec= essary ? > > What level of conductivity is required to establish a Faraday cage ? =A0W= ould a carbon fiber composite with copper particles work ? > > One item this wallet should protect is NFC cards that operate at 13.56 MH= z. > > 99guspuppet > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .