Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!rice!uw-beaver!milton!whit
From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Anti-shoplifting devices
Message-ID: <1991May13.201605.17091@milton.u.washington.edu>
Date: 13 May 91 20:16:05 GMT
References: <1991May9.135021.22131@sparrms.ists.ca> <1990021@hpldsla.sid.hp.com>
Organization: University of Washington, Seattle
Lines: 17

In article <1990021@hpldsla.sid.hp.com> tonya@hpldsla.sid.hp.com (Tony Arnerich) writes:
>I dissected one of these gizmos that was on a CD box. 
>
>It has two curved elements (antenna?), an hourglass detail that was
>blistered at the junction (burned out fuse for disabling), two exposed
>circles of circuit trace (connection to disabling wand?) and a VERY
>tiny silicon chip. There were two wires going into the chip, so I figured
>that it might be a diode.

	With either a varactor or a PIN diode, this could easily
be a frequency doubler/tripler; send out an interrogation pulse and
look for a triple-the-frequency response, and you've located
a tag that hasn't been disabled.
	At a guess, the curved elements would be resonant at the
interrogation frequency and the tripled frequency, respectively.

	John Whitmore