Load isolated article surveillance system and antenna assembly
First Claim
1. An electronic article surveillance system for detecting the unauthorized movement of protected articles, said system comprisinga transmitter antenna assembly including a transmitter loop antenna lying in a flat plane and a capacitor connected to said transmitter loop antenna to form a resonant circuit therewith,a flat panel of electrically conductive material extending parallel to and aligned with said transmitter antenna,a receiver loop antenna arranged parallel to and aligned with said transmitter antenna and located on the same side of said panel as said transmitter antenna,a signal generator arranged to drive said transmitter antenna assembly at its resonant frequency,a receiver connected to said receiver loop antenna to process electrical signals generated by said receiver loop antenna and to detect those signals which result from the presence of a detectable target in the vicinity of said antennas, said receiver including gates synchronized with said signal generator to permit detection only of signals which occur at predetermined phase relationships relative to the phase of the signal generator,said gate being synchronized with said signal generator such that it does not pass signals during intervals of the driving of the transmitter antenna assembly which correspond to the occurrence of received disturbances caused by the presence of targets on the opposite side of said panel from said transmitter loop antenna.
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Accused Products
Abstract
An electronic theft detection system with a transmitter antenna assembly which includes a flat electrically conductive panel positioned close to a transmitter loop antenna to preload it and isolate it from the loading effects of nearby metal objects and a receiver arranged with a signal gate synchronized to the transmitter antenna energization to prevent detection of targets located on the opposite side of the panel from the transmitter loop antenna.
34 Citations
1 Claim
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1. An electronic article surveillance system for detecting the unauthorized movement of protected articles, said system comprising
a transmitter antenna assembly including a transmitter loop antenna lying in a flat plane and a capacitor connected to said transmitter loop antenna to form a resonant circuit therewith, a flat panel of electrically conductive material extending parallel to and aligned with said transmitter antenna, a receiver loop antenna arranged parallel to and aligned with said transmitter antenna and located on the same side of said panel as said transmitter antenna, a signal generator arranged to drive said transmitter antenna assembly at its resonant frequency, a receiver connected to said receiver loop antenna to process electrical signals generated by said receiver loop antenna and to detect those signals which result from the presence of a detectable target in the vicinity of said antennas, said receiver including gates synchronized with said signal generator to permit detection only of signals which occur at predetermined phase relationships relative to the phase of the signal generator, said gate being synchronized with said signal generator such that it does not pass signals during intervals of the driving of the transmitter antenna assembly which correspond to the occurrence of received disturbances caused by the presence of targets on the opposite side of said panel from said transmitter loop antenna.
Specification
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- Resources
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Current AssigneeKnogo North America, Inc. (Sentry Technology Corp.)
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Original AssigneeKnogo Corp (Johnson Controls International plc)
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InventorsKinnaer, Christian, Cooper, Michael N., Minasy, Arthur J.
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Primary Examiner(s)EISENZOPF, REINHARD
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Application NumberUS07/226,136Time in Patent Office1,411 DaysField of Search340/572, 340/551, 340/941, 343/841, 343/842US Class Current340/551CPC Class CodesG08B 13/2474 Antenna or antenna activato...G08B 13/2488 Timing issues, e.g. synchro...
