Magnetic tags or markers
First Claim
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1. A magnetic marker or tag, which comprises:
- a first layer of magnetic material characterised by high permeability, low coercivity and a non-linear B-H characteristic;
wherein said first layer of magnetic material is coated with a second layer of magnetic material which is capable of being permanently magnetised, so as to have a non-uniform magnetic field pattern, said second layer of magnetic material comprising at least three discrete regions of magnetic bias material, wherein each of said discrete regions exhibits a different level and direction, such that during interrogation by a constant frequency alternating magnetic field, the magnetic bias levels of each of said discrete regions are overcome at different times in the interrogation cycle.
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Abstract
A magnetic tag or marker is described which is capable of functioning as a multi-bit information carrying tag. The tag may be attached to an article and then used as a means of identifying that article, generally as it enters or is positioned within an interrogation zone. The tag comprises (a) a first magnetic material characterized by high permeability, low coercivity and a non-linear B-H characteristic; and (b) a second magnetic material which is capable of being permanently magnetized, the second magnetic material being magnetized with a non-uniform field pattern (A, B, C). Detection systems for use with such tags, and write/read system using them, are also disclosed.
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Citations
36 Claims
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1. A magnetic marker or tag, which comprises:
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a first layer of magnetic material characterised by high permeability, low coercivity and a non-linear B-H characteristic;
wherein said first layer of magnetic material is coated witha second layer of magnetic material which is capable of being permanently magnetised, so as to have a non-uniform magnetic field pattern, said second layer of magnetic material comprising at least three discrete regions of magnetic bias material, wherein each of said discrete regions exhibits a different level and direction, such that during interrogation by a constant frequency alternating magnetic field, the magnetic bias levels of each of said discrete regions are overcome at different times in the interrogation cycle. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 28, 29)
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27. A method of coding articles so as to make it possible to distinguish between different classes of articles and/or to distinguish between different classes of articles and/or to distinguish between individual articles within a given class, which comprises (1) applying to said articles a magnetic marker or tag comprising a first layer of magnetic material characterised by high permeability, low coercivity and a non-linear B-H characteristic, wherein said first layer of magnetic material is coated with a second layer of magnetic material which is capable of being permanently magnetised;
- and (2) generating a predetermined, non-uniform permanent magnetic field pattern in said second magnetic material by magnetising said second layer of magnetic material either before or after it has been applied to said article, said magnetic field pattern comprising at least three discrete regions of magnetic bias material, wherein each of said discrete regions exhibits a different combination of magnetisation level and direction, such that during interrogation by a constant frequency alternating magnetic field, the magnetic bias levels of each of said discrete regions are overcome at different times in the interrogation cycle, and wherein said magnetic field pattern is selected so as to be readable with suitable configured apparatus and to be distinctive of said article or of the class to which said article belongs when so read.
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30. A magnetic marker or tag, which comprises a first layer of magnetic material characterised by high permeability, low coercivity and a non-linear B-H characteristic wherein said first layer of magnetic material is coated with a second layer of magnetic material which is capable of being permanently magnetised, characterised in that said second layer of magnetic material is magnetised with a non-uniform field pattern;
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said first magnetic material having an extrinsic relative permeability greater than 103 and a coercivity not more than 10 A/m;
said first layer of magnetic material being in the form of a thin film; and
said thin film material being in the form of one or more patches, each having an area in the range 1 mm2 to 500 mm2. - View Dependent Claims (31, 32)
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33. A data storage and retrieval system which comprises:
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a plurality of magnetic markers or tags, each said marker or tag comprising a first layer of magnetic material characterised by high permeability, low coercivity and a nonlinear B-H characteristic wherein said first layer of magnetic material is coated with a second layer of magnetic material which is capable of being permanently magnetised, characterised in that said second layer of magnetic material is magnetised with a non-uniform field pattern;
a detection system comprising (i) first means for generating an alternating magnetic field;
(ii) second means for detecting harmonics generated by the interaction between the first layer of magnetic material of the tag and the alternating magnetic field produced in use by said first means; and
(iii) third means for correlating the detection of harmonics by said second means with the alternating magnetic field generated by said first means; and
said third means being arranged to determine the amplitude and phase of the harmonics generated by the interaction of the first layer of magnetic material of the tag and the alternating magnetic field, the harmonics of interest being selected from harmonics in the range of 2 to 100.
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34. A data storage and retrieval system which comprises:
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a plurality of magnetic markers or tags, each said marker or tag comprising (a) a first layer of magnetic material characterised by high permeability, low coercivity and a nonlinear B-H characteristic wherein said first layer of magnetic material is coated with a second layer of magnetic material which is capable of being permanently magnetised, characterised in that said second magnetic material is magnetised with a non-uniform field pattern;
a detection system comprising (i) first means for generating an alternating magnetic field;
(ii) second means for detecting harmonics generated by the interaction between the first magnetic material of the tag and the alternating magnetic field produced in use by said first means; and
(iii) third means for correlating the detection of harmonics by said second means with the alternating magnetic field generated by said first means; and
said third means being arranged to determine the characteristics of said harmonics produced by the marker and to compare the detected characteristics with information in a data bank, said information serving to correlate the detected characteristics with known characteristics relating to items on an inventory.
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35. A data storage and retrieval system which comprises:
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a plurality of magnetic markers or tags, each said marker or tag comprising (a) a first layer of magnetic material characterised by high permeability, low coercivity and a non-linear B-H characteristic wherein said first layer of magnetic material is coated with a second layer of magnetic material which is capable of being permanently magnetised, characterised in that said second magnetic material is magnetised with a non-uniform field pattern;
a detection system comprising (i) first means for generating an alternating magnetic field;
(ii) second means for detecting harmonics generated by the interaction between the first magnetic material of the tag and the alternating magnetic field produced in use by said first means; and
(iii) third means for correlating the detection of harmonics by said second means with the alternating magnetic field generated by said first means; and
said detection system being arranged to determine the characteristics of harmonic bursts produced by the marker and to compare the detected characteristics with information in a data bank, said information serving to correlate the detected characteristics with known characteristics relating to items on an inventory. - View Dependent Claims (36)
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Specification