🚀 go-pugleaf

In article <1118@cameron.egr.duke.edu> wdp@dukee.egr.duke.edu (William D.
Palmer) writes:
>Friday, 12 OCT 90
>
>Simon Kravis writes:
>
>> From: skravis@csis.dit.csiro.au (Simon Kravis)
>> Subject: Stock control tags
>> Date: 12 Oct 90 04:48:01 GMT
>> 
>> Does anyone know how the detection system for the metallic tags attach
d to
>> CDs and other small and valuable items in shops works? ...
>
>The tags of this type that I have seen are LC tank circuits.  A flat coi
 is 
>made of copper (or some other non-magnetic material) with a capacitor (s
mply
>two layers of foil separated by an insulator) made of some magnetic meta
 in
>the center.  The coil and capacitor are connected in parallel.  When the

>magnetic material in the center is demagnetized, the flat coil will have
a 
>certain inductance, producing one resonant frequency for the tank.  Magn
tize 


Looks like there are different types of detectors...the tags that I took
apart do have the L-C resonant tank circuit but also have a small diode
which I assume acts as a frequency doubler or tripler and re-radiates
a signal on a harmonic which is then picked up as an alarm.

 



















-- 
Bill Hester, Ham Radio N0LAJ, Denver CO., USA
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