Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!sparrms!sparatd!mb
From: mb@sparrms.ists.ca (Mike Bell)
Newsgroups: sci.electronics
Subject: Anti-shoplifting devices
Message-ID: <1991May9.135021.22131@sparrms.ists.ca>
Date: 9 May 91 13:50:21 GMT
References: <050691.224256WDBURNS%MTUS5.BITNET> <19934@slice.ooc.uva.nl>
Organization: Spar Aerospace Ltd, Toronto, Canada
Lines: 22

Further to the discussion of library anti-theft tags, I recently 
took to pieces a store anti-theft tag, and I'm stuck on how this
one works:

It consists of a rather bulky plastic self-adhesive package, about 40mm
x 13mm. Inside are two mettalic strips. One is a rectangle 38mm x 12.2
mm. The other is a parallelogram:

        __________________ 
       /                 /     ^
      /                 /      |12.2mm
     /_________________/       |

    <    29mm         >

The angle is 45 degrees. All dimensions are +/- 0.25mm

The two strips are separated by a plastic membrane. 

Anybody able to explain the principle of operation?

What are the relevant frequencies of operation?