ELECTRONIC ARTICLE SECURITY SYSTEM EMPLOYING VARIABLE TIME SHIFTS

摘要

A pulse-listen electronic article security (EAS) system (10) for detecting the presence of a security tag (42) within a detection zone is disclosed. The EAS system includes a transmitter (20) for radiating a first electromagnetic signal into the detection zone. The first electromagnetic signal is a time sequence of RF bursts emitted during each of a plurality of contiguous frame intervals in which the duration of each of the frame intervals is one of a plurality of different values. The EAS system also includes a receiver (24) synchronized with the transmitter (20) for receiving a second electromagnetic signal re-radiated from a security tag (42) in the detection zone in response to the first electromagnetic signal. The receiver provides an output signal if a security tag is detected. The values of the plurality of the frame interval durations are selected to be different from the values of frame interval durations of other EAS systems thereby rendering the EAS system substantially free of false alarms or blockages caused by the operation of other EAS systems.