🚀 go-pugleaf

In article <1iaq83INNs2a@overload.lbl.gov> mikec@ux1.lbl.gov (Mike Chin) writes:
>A recent Smithsonian had an article about the usage of "rice-sized"
>transponders embedded into retail products for customer marketing info.
>Are these similiar to the devices that were being subcutaneously 
>implanted into dogs/cats for ID purposes? Who sells these things & how
>do they work?

	A maker of such devices gave a talk here at U. of Wa. some
years back: he was labeling salmon fry.  The transponder was a
piece of stamped stainless steel wire, injected into the nose
cartilage of the about-to-be-released fish.

	It was detected by some 3-d magnetic field sensors, that could
detect the presence of a magnetic dipole in a restricted region
(into which the snout of the caught fish was thrust).  The stamping
on the wire was read like a binary code, and served a second 
purpose as well: it strained the stainless steel so that the
tag could be magnetized (this was a nominally non-magnetic alloy).

	If one made the tag of the correct length, it would
resonate/reradiate at a sharply defined frequency, and this could
allow a simple piece of wire to be used as a transponder.
The embedding of such an antenna in a medium (like a book...)
would necessarily change its resonant frequency, though, in
a manner that would be difficult to characterize (changes with
humidity and paper age).  Not useful for tracking merchandise.

	Dallas Semiconductor makes some two-wire inventory tag devices,
but I don't know any transponder-type integrated circuit tags.

	John Whitmore