| 摘要 |
The present invention provides an antitheft system to detect the presence of an object which has a label affixed thereto when said object passes through a surveillance zone comprising an oscillatory electromagnetic interrogation field having three separate and distinct vector components produced by driving the transmitting coils located in housing on either side of said surveillance zo ne with an alternating power source repetitively in and out of phase with respect to one another so as to form magnetic lines of flux having one vector component in the out-of-phase mode. The signals generated by the label are received by coils in said housing and are processed by electronic circuitry adapted to distinguis h said label signals from spurious signals with a high degree of accuracy. The labe l can be deactivated so as to pass through the surveillance zone without triggerin g a system response.
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