SURVEILLANCE SYSTEM HAVING MAGNETOMECHANICAL MARKER

摘要

SURVEILLANCE SYSTEM HAVING MAGNETOMECHANICAL MARKER A magnetic article surveillance system marker is adapted, when armed, to resonate at a frequency provided by an incident magnetic field applied within an interrogation zone. The marker is an elongated ductile strip of magnetostrictive ferromagnetic material disclosed adjacent to a ferromagnetic element which, upon being magnetized, magnetically biases the strip and arms it to resonate at said frequency. A substantial change in effective magnetic permeability of the marker at the resonant frequency provides the marker with signal identity.