Magnetic marker anti-shoplifting system for supermarket - has evaluator responding to content of energy levels in band to indicate marker presence

摘要

An interrogator creates a magnetic field at a selected frequency in a monitor zone. It includes a receiver establishing disturbances in the field of the zone to give out a characteristic signal. The receiver has a channel for giving out a signal content characteristic for the energy levels in one resp. band of a number of bands of the signal. An evaluator responds to the signal contents to compare the energy levels which are characterised by the signal content, with the object of evaluating whether there is an article present in the zone. There are pref. at least three bands, and the first signal content for a resp. band of the number of bands, has signal levels which are characteristic for the energy in that band. The evaluator, in the course of evaluation compares these levels.