G - Physics – 08 – B
Patent
G - Physics
08
B
340/124.3
G08B 13/24 (2006.01)
Patent
CA 1294017
Abstract of the Invention A deactivatable coded marker for use in article surveillance systems has an electrically conductive element at least partly surrounding the core, by reason of which the marker will generate a phase shifted harmonic signal responsive to a reference signal. A magnetizable element of high coercivity is adjacent to and overlying the electrically conductive material, the marker generating the phase shifted harmonic signal when the high coercivity element is not magnetized but generating a non phase shifted harmonic signal responsive to the reference signal when the high coercivity element is magnetized, whereby the high coercivity element neutralizes the effect of the electrically conductive element when magnetized. The deactivatable marker may have a plurality of cores, a plurality of electrically conductive elements and a plurality of separately magnetizable elements, forming respective and independently activatable and deactivatable marker parts. An article surveillance system for use with such deactivatable markers has an automatic gain control circuit for continuously adjusting the intensity of transmitted reference signals responsive to the intensity of the received harmonic signals to compensate for the variation due to marker presence in a detection zone, thereby preventing random variation in the phase shift of the harmonic signals.
567411
Cassan Maclean
Controlled Information Corporation
Weaver Jon N.
LandOfFree
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