On Wed, 10 Apr 2002, Tim May wrote: >> How come? True, if a bill is idealized as being planar, you'll have >> trouble on the plane. Spatial diversity will take care of that. >> Otherwise, a common note has plenty of surface to do your thing on. >> Especially at higher frequencies, like UHF and beyond. > >How come? Because I am assuming the transponders are in the same >position on each bill.
Why's that? It's easy enough to move the transponder around during the printing process as long as the exact position isn't too important and the number of positions isn't too large. Just have a rotating series of printing plates. >If you want to posit some "spatial diversity" model, that helps, but not >but a huge amount. First, "spatial diversity" is standard terminology for spatially/polarization-wise separated transmitters/receivers, used in order to fight multipath and/or antenna orientation trouble. In closed spaces, that sort of antenna configuration is probably what you'd want, anyway. >UHF is hard to launch/receive from a small, planar antenna. UWB is >easier to launch from a small (< cm) antenna, but is usually too >directional. Who's there to say the antenna has to be <cm in size? The chip would have to be, but larger conductive plastic wiring seems to be ideal for antenna work. >A stack will interfere, in the sense that planar antennas will couple to >each other (radiated signal from A will hit B square on, etc.). So they will. Still, I'm not at all sure one couldn't avoid much of the coupling by moving the antenna around in the bill. And if that's not enough, just build in ad hoc networks. Not too difficult, not too expensive once you've got silicon on-board. Note-to-note, then out. >As for the proles being too cheap, too gullible to even bother to >lightly shield, sounds like evolution in action. Not really, given that shielding could be outlawed. >True money launderers will use shielding. (Actually, this is all >oriented at "walking around money," so the vast infrastructure will >never actually get built, as there is no interest in monitoring trivial >amounts.) Who's to say the primary application would be anti-laundering? To me it seems far more likely that low-cost surveillance would be It, even if it's clear that that sort of thing isn't currently doable. >I'm done with this thread, though. Too bad. Trimming CC's. Sampo Syreeni, aka decoy - mailto:[EMAIL PROTECTED], tel:+358-50-5756111 student/math+cs/helsinki university, http://www.iki.fi/~decoy/front openpgp: 050985C2/025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2
