Coded surveillance system having magnetomechanical marker

摘要

A magnetic article surveillance system marker is adapted, when armed, to resonate at preselected frequencies provided by an incident magnetic field applied within an interrogation zone. The marker is a plurality of elongated ductile strips of magnetostrictive ferromagnetic material each of the strips being disposed adjacent to a ferromagnetic element which, upon being magnetized, magnetically biases the strips and arms them to resonate at the preselected frequencies. A substantial change in effective magnetic permeability of the marker at the preselected frequencies provides the marker with signal identity.