Deactivatable coded marker and magnetic article surveillance system
First Claim
1. A deactivatable coded marker for use in article surveillance systems wherein coded markers are carried by monitored articles, the marker comprising:
- at least one core of soft magnetic material;
at least one electrically conductive element at least partly surrounding the core, by reason of which the marker will generate a phase-shifted harmonic signal responsive to a reference signal; and
,at least magnetizable element of high coercivity adjacent to and overlying the electrically conductive element, the marker generating the phase-shifted harmonic signal when the high coercivity element is not magnetized but generating a non-phase-shifted harmonic signal responsive to the reference signal when the high coercivity element is magnetized, whereby the high coercivity element neutralizes the effect of the electrically conductive element when magnetized.
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Accused Products
Abstract
A deactivatable coded marker for use in article surveillance systems has a core of soft magnetic material. An electrically conductive element at least partly surrounds the core, by reason of which the marker will generate a phase-shifted harmonic signal responsive to a reference signal. A magnetizable element of high coercivity is adjacent to and overlying the electrically conductive material, the marker generating the phase-shifted harmonic signal when the high coercivity element is not magnetized but generating a non-phase-shifted harmonic signal responsive to the reference signal when the high coercivity element is magnetized, whereby the high coercivity element neutralizes the effect of the electrically conductive element when magnetized. The deactivatable marker may have a plurality of cores, a plurality of electrically conductive elements and a plurality of separately magnetizable elements, forming respective and independently activatable and deactivatable marker parts. An article surveillance system for use with such deactivatable markers has an automatic gain control for continuously adjusting the intensity of transmitted reference signals responsive to the intensity of the received harmonic signals to compensate for the variation due to marker presence in a detection zone, thereby preventing random variation in the phase shift of the harmonic signals.
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Citations
20 Claims
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1. A deactivatable coded marker for use in article surveillance systems wherein coded markers are carried by monitored articles, the marker comprising:
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at least one core of soft magnetic material; at least one electrically conductive element at least partly surrounding the core, by reason of which the marker will generate a phase-shifted harmonic signal responsive to a reference signal; and
,at least magnetizable element of high coercivity adjacent to and overlying the electrically conductive element, the marker generating the phase-shifted harmonic signal when the high coercivity element is not magnetized but generating a non-phase-shifted harmonic signal responsive to the reference signal when the high coercivity element is magnetized, whereby the high coercivity element neutralizes the effect of the electrically conductive element when magnetized. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An article surveillance system, comprising:
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means for generating and transmitting phase locked reference signals in a detection zone; a plurality of deactivatable coded markers, each marker having; at least core of soft magnetic material; at least one electrically conductive element at least partly surrounding the core, by reason of which the marker will generate harmonic signals of predetermined phase shift responsive to the reference signals; and
,a magnetizable element of high coercivity adjacent to and overlying the electrically conductive element, the presence of a coded marker in the detection zone tending to cause a variation in the transmitted reference signals which tends to induce a certain random variation in the phase shift of the harmonic signals; means for receiving the phase-shifted harmonic signals generated by active coded markers in the detection zone; means for automatically adjusting the transmitted reference signals responsive to a characteristic of the received harmonic signals to compensate for the variation due to marker presence in the detection zone and thereby prevent the random variation in the phase shift of the harmonic signals; means for determining the relative phase shift between the reference signals and the harmonic marker signals; and
,means for generating a control signal responsive to identification of a valid code by the determining means. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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15. A method for conducting surveillance of articles in a detection zone, comprising the steps of:
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providing each article with a deactivatable coded marker having means for generating harmonic signals of a predetermined phase shift responsive and relative to reference signals and having means for preventing generation of the harmonic signals; transmitting phase locked reference signals at a fundamental frequency into the detection zone; receiving phase shifted harmonic signals generated by each marker in the detection zone responsive to the phase locked reference signal, the presence of a coded marker in the detection zone tending to cause a variation in the transmitted reference signals which tends to induce a certain random variation in the phase shift of the harmonic signals; continuously adjusting the transmitted reference signals responsive to a characteristic of the received harmonic signals to compensate for the variation due to marker presence in the detection zone and thereby prevent the random variation in the phase shift of the harmonic signals; and
,measuring the phase shift between the reference signals and the harmonic marker signals, the degree of phase shift being related to positive identification of an active marker in the detection zone. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification