Stuffs used for detection

[Remo Pini]

At 09:52 PM 7/12/96 +0800, you wrote:
>In our school library, there is a depository area wherein you deposit your
things and get the tag. Since the library doesn't allow those tags to be
brought out from the library, everytime you brought it out and pass by the
door, it will alarm. Does anyone know what stuff is that? How come it is
alarmed? I brought some metals but it wouldn't alarm... Why those tag would
alarm them???
>

Most of these systems are made of an oszillator (basically a few windings of
a wire with a capacitor:

 ------
/      \
¦--¦¦--¦
\      /
 ------

This acts like an ordinary RLC-Oszillator. When you put it in a electrical
field with the right frequency, it will effect the field strong enough to be
detectable.

So, if you shield it, you win.
----------< fate favors the prepared mind >----------
Remo Pini                      Fon 1: +41 1 350 28 82
mailto:rp at rpini.com            Fon 2: +41 1 465 31 90
http://www.rpini.com/remopini/ Fax:   +41 1 350 28 84
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