more on "Smart Dust" gets Zarqawi?

[David Farber <dave () farber net>]

Begin forwarded message:

From: Brad Templeton <btm () templetons com>
Date: June 11, 2006 8:16:23 PM EDT
To: David Farber <dave () farber net>
Cc: ip () v2 listbox com
Subject: Re: [IP] "Smart Dust" gets Zarqawi?

On Sun, Jun 11, 2006 at 02:25:32PM -0400, David Farber wrote:
> Highly interesting.  I haven?t seen this mentioned anywhere else.
> It?d be interesting to see if any other press picks up on it and
> investigates.  (I like the quote about ?magic dust? that appears in
> the article?)

Without knowing anything about whatever fabulous classified
technology is out there, generally the laws of physics demand that
passive RFID signals fall of as the 4th power of the distance from
transmitter to receiver.

4th power is a lot.  If you are 10 times as far away, the signal will
be 10,000 times weaker.   100 times as far away means 100 million
times weaker.

Designers of RFID systems often spec them to be readable only a few
inches or feet away from the reader.   This is misleading because
better readers can indeed detect them a fair bit farther through the
use of higher power, directional antennas, more sensativity and lower
tolerances.   But troops are not going to be reading them from
long distances.

This does not, however, mean that you could not create a mesh network
of readers along "choke points" -- narrow roadways, gates, doors,
intersections, and use it to track people with RFID chips hidden on
their bodies or cars.   You could also get around the 4th power law
by having different transmitters and receivers.  For example you could
have a smaller number of small transmitters pulsing hundreds of
megawatts, and a much larger of (now less detectable) self-powered
read-only readers at the chokepoints.   This would not allow the  
iterative
algorithms commercial RFIDs use to read multiple devices in their area.

Active RFIDs go down with the square of the distance, but that's based
on the battery in them, and they are not tiny.


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