Pilferage detection systems
First Claim
1. A system for detecting removal of articles from a protected area comprising:
- a magnetic marker associated with each article, each marker including a remanently magnetized control element of relatively high coercivity and a switching element of relatively low coercivity, at least a portion of which is magnetized by said remanently magnetized control element in the absence of other magnetic fields of sufficient strength to counteract the effect of said remanently magnetized control element;
means for generating a periodic magnetic field in a region through which an article must pass to leave the protected area for periodically altering the magnetization of the switching element of a marker in said region, said periodic magnetic field having a first frequency and being free of a detectable amount of a predetermined even harmonic of said first frequency;
means for detecting said predetermined even harmonic of said first frequency in the magnetic field produced by the switching element of a marker in response to said periodic magnetic field; and
means for demagnetizing the control element of a marker sufficiently to preclude the aforesaid production of said predetermined even harmonic when the associated article is to leave the protected area undetected.
4 Assignments
0 Petitions
Accused Products
Abstract
In a pilferage detection system employing apparatus for generating a magnetic field of alternating polarity and predetermined fundamental frequency through which articles subject to pilferage must pass to leave a protected area and a magnetic marker associated with each article in the protected area, markers are provided which generate both odd and even harmonics of the fundamental frequency in response to the alternating magnetic field when the marker is active (i.e., a control element of the marker is magnetized) and which generate only odd harmonics of the fundamental frequency when the marker is inactive. The presence of an active marker in the alternating magnetic field is therefore detected by detecting a predetermined even harmonic of the fundamental frequency. Apparatus is also provided for demagnetizing the control element of the marker associated with an article authorized for removal from the protected area to permit that article to pass through the alternating magnetic field undetected.
45 Citations
37 Claims
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1. A system for detecting removal of articles from a protected area comprising:
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a magnetic marker associated with each article, each marker including a remanently magnetized control element of relatively high coercivity and a switching element of relatively low coercivity, at least a portion of which is magnetized by said remanently magnetized control element in the absence of other magnetic fields of sufficient strength to counteract the effect of said remanently magnetized control element; means for generating a periodic magnetic field in a region through which an article must pass to leave the protected area for periodically altering the magnetization of the switching element of a marker in said region, said periodic magnetic field having a first frequency and being free of a detectable amount of a predetermined even harmonic of said first frequency; means for detecting said predetermined even harmonic of said first frequency in the magnetic field produced by the switching element of a marker in response to said periodic magnetic field; and means for demagnetizing the control element of a marker sufficiently to preclude the aforesaid production of said predetermined even harmonic when the associated article is to leave the protected area undetected. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system for detecting pilferage of articles from a protected area comprising:
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a magnetic marker associated with each article, each marker including a first longitudinal marker element of magnetic material which is magnetically relatively soft and a second marker element of magnetic material which is magnetically relatively hard, said second marker element being disposed adjacent said first marker element and being remanently magnetized in a direction parallel to the longitudinal axis of said first marker element when said marker is active to protect the associated article from pilferage, the magnetic force exerted by said second marker element on said first marker element when said marker is active being great enough to magnetize at least a portion of said first marker element but not great enough to prevent reversal of the polarity of said portion of said first marker element by an external magnetic field of magnitude less than the magnitude required to affect the magnetization of said second marker element; means for generating a magnetic field of alternating polarity in an area through which an article associated with a marker must pass to leave the protected area, said alternating magnetic field having a predetermined fundamental frequency and being free of a detectable amount of a predetermined even harmonic of said fundamental frequency, the amplitude of said alternating magnetic field being great enough to cause reversal of the polarity of the first element of an active marker entering said field during a portion of each period of oscillation of said alternating magnetic field for at least a fraction of the possible locations and orientations of said marker in said alternating magnetic field, the amplitude of said alternating field being insufficient to affect the magnetization of the second element of said marker to such a degree as to cause a detectable change in the operation of said marker for any of the possible locations and orientations of said markers in said field; means for detecting said predetermined even harmonic of said fundamental frequency in the magnetic field produced by the first element of an active marker in said alternating magnetic field; and means for demagnetizing the second element of a marker sufficiently to preclude the aforesaid production of said predetermined even harmonic when the associated article is authorized for removal from the protected area to permit the article and the associated marker to pass through said alternating magnetic field without said marker producing said predetermined even harmonic of said fundamental frequency detected by said means for detecting. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. For use in a pilferage detection system in which a magnetic marker associated with an article to be protected from pilferage is detected when the marker is active and the associated article enters an alternating magnetic field by a characteristic of the magnetic field produced by the marker in response to the alternating magnetic field, an improved magnetic marker comprising:
- a first longitudinal element of magnetic material which is magnetically relatively soft and a second element of magnetic material which is magnetically relatively hard, said second element being disposed adjacent said first element and being remanently magnetized parallel to the longitudinal axis of said first element when said marker is active and demagnetized when said marker is inactive, the magnetic force of said second element on said first element when said marker is active being great enough to magnetize a portion of said first element but not great enough to prevent reversal of the polarity of said portion of said first element by a properly aligned external magnetic field of magnitude less than the magnitude required to affect the magnetization of said second marker element.
- View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
Specification