Method and apparatus for authenticating a record medium consisting of applying two different strength magnetizing fields and monitoring the remanent fields
First Claim
1. A system for examining a record medium expected to include a magnetic material storage layer exhibiting an inherent pattern of magnetic remanence difference between a part of the layer and another part of the layer when both parts are subjected to a uniform magnetising field includingmeans for applying to the layer in turn at least two different strength magnetising fields along the same direction,means for measuring the relative remanent magnetisation in said part and said another part for each said magnetising field, andmeans responsive to the measurements to assess the authenticity status of the medium, the relative remanent magnetisations differing for said different strength magnetising fields for an authentic medium.
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Accused Products
Abstract
Apparatus to examine a magnetic storage layer expected to contain a magnetic watermark includes means to magnetize the layer with a unidirectional field of a selected strength without saturating it and means to detect any distinct region of magnetic remanence. The apparatus may further include means to record the resultant remanence levels (or their ratio) for such a region and another part of the layer, means to magnetize the layer with a unidirectional field of a different selected strength, means to detect any then-existing such distinct region or regions, means to measure the remanence levels (or their ratio) for the then-existing such region and another part of the layer, and means to compare the measured and recorded levels (or their ratios) and indicate from the result of the comparison whether or not this represents a layer having a magnetic watermark of regions of distinctly aligned anisotropic magnetic particles. The use of different amounts of magnetization will produce different ratios of remanence in a layer having such a watermark but not in an homogenous layer.
135 Citations
11 Claims
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1. A system for examining a record medium expected to include a magnetic material storage layer exhibiting an inherent pattern of magnetic remanence difference between a part of the layer and another part of the layer when both parts are subjected to a uniform magnetising field including
means for applying to the layer in turn at least two different strength magnetising fields along the same direction, means for measuring the relative remanent magnetisation in said part and said another part for each said magnetising field, and means responsive to the measurements to assess the authenticity status of the medium, the relative remanent magnetisations differing for said different strength magnetising fields for an authentic medium.
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9. A method of examining a record medium expected to include a magnetic material storage layer exhibiting an inherent pattern of magnetic remanence difference between a part of the layer and another part of the layer when both parts are subjected to a uniform magnetising field, including
applying to the layer in turn at least two different strength magnetising fields, measuring the relative remanent magnetisations in said part and said another part for each said field and assessing the authenticity of the medium from the measurements, the relative magnetisation differing for different strength magnetising fields for an authentic medium.
Specification