On Thu, 31 Mar 2005, Major Variola (ret) wrote:
> At 10:08 PM 3/31/05 +0200, Eugen Leitl wrote:
> > government plan to insert remotely readable chips in American
> > passports, calling the chips [2]homing devices for high-tech
> > muggers,
>
> So the market for faraday-cages for your passport will grow to
> equilibrium. A cage will cost less than a buck in parts, easily
> affordable by the clueful. The damage to the clueless will
> quickly be the best advertising for the product. Since we
> have been wearing conductive mesh burkhas for some time,
> the only inconvenience will be for the terahertz voyeurs
> employed by the TSA.
Beware of one gotcha. Faraday cage will shield only the electrical
component. Low-frequency tags (125 kHz, typically) are magnetically
coupled. Experiments shown that such tag is readable, even if entirely
wrapped in aluminum foil. Laying a tag on top of a feromagnetic surface
(iron sheet) does not help (probably only diminishes the range, didn't do
the exact measurements yet); the sheet has to be between the tag's coil
and the reader coil to be effective.
Putting the tag into an enclosure made of a feromagnetic material helps,
though. Altoids can proved to be a pretty effective shielding.
