Magnetic tags or markers

• US 6,371,379 B1
• Filed: 10/09/1998
• Issued: 04/16/2002
• Est. Priority Date: 07/17/1995
• Status: Expired due to Fees

• Current Assignee: Flying Null, Ltd.
• Original Assignee: Flying Null, Ltd.
• Inventors: Dames, Andrew Nicholas, Crossfield, Michael David
• Primary Examiner(s): Frech, Karl D.
• Application Number:
  US08/983,385
• Time in Patent Office: 1,285 Days
• Field of Search: 235/493, 235/492, 235/488, 235/449, 235/462.01
• US Class Current: 235/493
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• CPC Class Codes: G11B 5/00804 magnetic sheets rotating sheets G11B5/012

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.

Claims

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.

2. A magnetic marker or tag as claimed in claim 1, characterised in that the field pattern in said second material varies in amplitude.

3. A magnetic marker or tag as claimed in claim 1, characterized in that the field pattern in said second material varies in amplitude and/or direction.

4. A magnetic marker or tag as claimed in claim 1, characterised in that said second magnetic material is formed of discrete, magnetised sections of a magnetic bias material.

5. A magnetic marker or tag as claimed in claim 1, characterised in that said second magnetic material is formed by writing a magnetic field pattern onto a strip or tape of magnetic bias material.

6. A magnetic marker or tag as claimed in claim 5, characterised in that said magnetic field pattern varies across the width of said strip or tape.

7. A magnetic marker or tag as claimed in claim 1, characterised in that said first magnetic material has an extrinsic relative permeability greater than 10³ and a coercivity not more than 10 A/m.

8. A magnetic marker or tag as claimed in claim 7, characterised in that said first magnetic material is in the form of an elongate strip or wire.

9. A magnetic marker or tag as claimed in claim 8, characterised in that said strip-has dimensions in the ranges:

width—

from 0.1 mm to 10 mm; and

thickness from 5 μ

m to 500 μ

m.

10. A magnetic marker or tag as claimed in claim 9, characterised in that said strip has dimensions in the ranges:

width—

from 0.5 mm to 5 mm; and

thickness from 10 μ

m to 100 μ

m.

11. A magnetic marker or tag as claimed in claim 7, characterised in that said first magnetic material is in the form of a thin film.

12. A magnetic marker or tag as claimed in claim 1, characterized in that said first and second magnetic materials are in the form of layers supported by a substrate formed of paper or a plastics material.

13. A magnetic marker or tag as claimed in claim 1, characterised in that the marker is adapted to be secured to an article to serve as an identifying tag for that article.

14. A magnetic marker or tag as claimed in claim 13, characterised in that the marker or tag serves as an antipilferage or anti-counterfeiting tag.

15. A magnetic marker or tag as claimed in any claim 13, characterised in that the marker or tag serves as a verification tag.

16. A data storage and retrieval system which comprises a plurality of magnetic markers or tags as claimed in claim 1 and 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.

17. A data storage and retrieval system as claimed in claim 16, characterised in that said first means is arranged so that, in use, it generates a first, high frequency alternating magnetic field and a second, low frequency alternating magnetic field.

18. A system as claimed in claim 17, characterised in that said first means is adapted to generate a high frequency alternating magnetic field at a frequency in the range of from 250 Hz to 20 kHz.

19. A system as claimed in claim 18, characterised in that said first means is adapted to generate an alternating magnetic field at a frequency in the range of from 3 kHz to 10 kHz.

20. A system as claimed in claim 16, characterised in that said third means is arranged to determine the number of harmonic bursts detected by said second means per cycle of the alternating field generated by said first means.

21. A system as claimed in claim 20, characterised in that said third means is arranged to determine the point or points within each cycle of said alternating field at which harmonic bursts are detected by said second means.

22. A system as claimed in claim 16 characterized in that said first means is adapted to generate an alternating magnetic field at a frequency in the range of from 50 Hz to 20 kHz.

23. A system as claimed in claim 17, characterised in that first means is adapted to generate a low frequency alternating magnetic field at a frequency in the range of from 1 Hz to 250 Hz.

24. A system as claimed in claim 23, characterised in that said first means is adapted to generate a low frequency alternating magnetic field at a frequency in the range of from 5 Hz to 50 Hz.

25. A system as claimed in claim 24, characterised in that said first means is adapted to generate a high frequency alternating magnetic field at a frequency in the range of from 1 kHz to 10 kHz and a low frequency alternating magnetic field at a frequency in the range of from 8 Hz to 50 Hz.

26. A system as claimed in claim 25, characterised in that said first means is adapted to generate a high frequency alternating magnetic field at a frequency in the range of from 4 kHz to 8 kHz and a low frequency alternating magnetic field at a frequency in the range of from 10 Hz to 20 Hz.

28. A method of detecting the presence of an article within a predetermined interrogation zone, which comprises (A) attaching to or incorporating into the article, before the article reaches said interrogation zone, a magnetic marker as claimed in claim 12 and which carries a unique magnetic code so as to be distinctive of the article;

(B) determining the magnetic interaction between said magnetic marker and an applied magnetic field capable of interacting with said magnetic marker to generate a detectable response;

(C) recording in a directory the correlation between said article, said magnetic marker and its magnetic interaction determined by step B; and

(D) subjecting the volume defined by said interrogation zone to substantially the same magnetic conditions as were used in step B while one or more unknown articles are located within said zone, and determining the resultant magnetic interaction(s);

(E) comparing the detected interaction(s) with data in said directory; and

(F) generating a response indicating the nature of the article whenever correlation data in said directory provides a match between the magnetic interaction generated in step (D) and that in step (B).

29. A method according to claim 28, characterised in that said applied magnetic field comprises (i) a first alternating, low frequency magnetic field and (ii) a second alternating, high frequency magnetic field.

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.

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;

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.

31. A magnetic marker or tag as claimed in claim 30, characterised in that said one or more patches each have an area in the range from 10 mm² to 100 mm².

32. A magnetic marker or tag as claimed in claim 30, characterised in that said one or more patches each have a thickness in the range from 0.1 μ

m to 10 μ

m.

33. A data storage and retrieval system which comprises:

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.

34. A data storage and retrieval system which comprises:

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.

35. A data storage and retrieval system which comprises:

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.

36. A system as claimed in claim 35 characterised in that said detection system is 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, and also characterised in that said detection system is arranged to measure the shape of the envelope of said harmonic bursts.