Desensitizer for ferromagnetic markers used with electromagnetic article surveillance systems
First Claim
1. A desensitizer apparatus adapted for use with an electronic article surveillance system for detecting a desensitizable marker secured to an article the presence of which within an interrogation zone is desirably known, said marker including an elongated section of low coercive force, high permeability ferromagnetic material having proximate thereto at least one section of a remanently magnetizable high coercive force material which when magnetized magnetically biases the elongated section of low coercive force material and thereby alters the detectability of the marker, said desensitizer apparatus comprising a permanent magnet assembly which includes at least one section of ferromagnetic material having two substantially opposed major surfaces and which is substantially uniformly magnetized to present one magnetic polarity at one of said major surfaces and the opposite polarity on the other major surface, and a pair of pole pieces each of which is proximate to and extends over a major portion of said major surfaces and terminates proximate to the other pole piece to provide a gap of substantially constant width extending along said section for concentrating external magnetic lines of flux resulting from said magnetized material near the gap such that the resultant external magnetic field decreases rapidly with increasing distance from the gap, thereby enabling a said marker to be moved relative to said gap to remanently magnetize the section of said high coercive force material within the marker, the external field intensity extending beyond a short distance from the gap being insufficient to alter magnetic states such as may exist within an article to which the marker is secured.
1 Assignment
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Accused Products
Abstract
A desensitizer apparatus for use with magnetically based electronic article surveillance systems having a marker containing at least one magnetizable section which when magnetized, alters the response of the marker produced by an alternating magnetic field provided in an interrogation zone. The apparatus includes a magnet assembly having an elongated permanent magnet section and a pair of elongated pole pieces which concentrate external fields produced by the magnet sections near a gap extending the length of the magnet section, the external field near the gap being sufficient in intensity to magnetize the magnetizable section of a marker positioned proximate thereto, and being rapidly attenuated a short distance from the gap. Accordingly, magnetically sensitive articles such as prerecorded magnetic recording cassettes to which the markers are affixed are not affected.
23 Citations
8 Claims
- 1. A desensitizer apparatus adapted for use with an electronic article surveillance system for detecting a desensitizable marker secured to an article the presence of which within an interrogation zone is desirably known, said marker including an elongated section of low coercive force, high permeability ferromagnetic material having proximate thereto at least one section of a remanently magnetizable high coercive force material which when magnetized magnetically biases the elongated section of low coercive force material and thereby alters the detectability of the marker, said desensitizer apparatus comprising a permanent magnet assembly which includes at least one section of ferromagnetic material having two substantially opposed major surfaces and which is substantially uniformly magnetized to present one magnetic polarity at one of said major surfaces and the opposite polarity on the other major surface, and a pair of pole pieces each of which is proximate to and extends over a major portion of said major surfaces and terminates proximate to the other pole piece to provide a gap of substantially constant width extending along said section for concentrating external magnetic lines of flux resulting from said magnetized material near the gap such that the resultant external magnetic field decreases rapidly with increasing distance from the gap, thereby enabling a said marker to be moved relative to said gap to remanently magnetize the section of said high coercive force material within the marker, the external field intensity extending beyond a short distance from the gap being insufficient to alter magnetic states such as may exist within an article to which the marker is secured.
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8. A desensitizer apparatus adapted for use with an electronic article surveillance system for detecting a desensitizable marker secured to a housing containing a prerecorded magnetic tape, the presence of which within an interrogation zone is desirably known, said marker including an elongated section of low coercive force, high permeability ferromagnetic material having proximate thereto at least one section of a remanently magnetizable high coercive force material which when magnetized magnetically biases the elongated section of low coercive force material and thereby alters the detectability of the marker, said desensitizer apparatus comprising a permanent magnet assembly which includes at least one section of a permanent magnet ferromagnetic material having two substantially opposed major surfaces and which is substantially uniformly magnetized to present one magnetic polarity at one of said major surfaces and the opposite polarity on the other major surface, and a pair of pole pieces each of which is proximate to and extends over a major portion of said major surfaces and terminates proximate to the other pole piece to provide a gap of substantially constant width extending along said section for concentrating external magnetic lines of flux resulting from said magnetized material near the gap such that the resultant external magnetic field decreases rapidly with increasing distance from the gap, thereby enabling a said marker to be moved relative to said gap to remanently magnetize the section of said high coercive force material within the marker, the external field intensity extending beyond a short distance from the gap being insufficient to appreciably alter the prerecorded magnetic patterns on the tape when the assembly is moved relative to a surface of the housing having a said marker affixed thereto and the marker is resultantly desensitized.
Specification