A MAGNETOMECHANICAL ELECTRONIC ARTICLE SURVEILLANCE SYSTEM AND METHOD USING SIDEBAND DETECTION

摘要

An electronic article surveillance (EAS) system and method utilizing two transmitted signals to generate and detect a marker signal is provided. The first signal is set at or near the resonance of the marker so its energy can be transmitted and stored in the marker. The second signal is a low frequenc y magnetic field that changes the resonant frequency of the marker. Because th e marker's resonant frequency is constantly varying in repsonse to the low frequency magnetic field, the marker's response to the first transmitted signal also changes. As a result, the marker performs a modulation on the first transmitted signal. Detection of a sideband of the modulated signal indicates the presence of the marker within an interrogation zone formed by the two transmitted signals. Multiple interrogation zones can be implemented by transmitting multiple low frequency signals, one low frequency signal for each interrogation zone.