Method and system for detecting an object within a magnetic field interrogation zone

摘要: This specification discloses a marker for being secured to an object enable the detection of within interrogation zone having magnetic field periodically varying at predetermined fundamental frequency. The includes first elongated ferromagnetic element object. has relatively low coercivity and is operable generate detectable signal containing harmonics frequency when placed in zone. further second disposed adjacent greater than element. Deactivation structure provided selectively magnetize impose plurality pairs alternate poles on order deactivate marker. deactivated does not desired passes through In preferred embodiment invention, constructed so as be magnetized by oriented any direction Also embodiment, deactivation which checks insure that been prior allowing energization auxiliary device such cash register or like.