Dual status thin-film eas marker having multiple magnetic layers

• US 5,580,664 A
• Filed: 01/04/1995
• Issued: 12/03/1996
• Est. Priority Date: 12/23/1992
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Tsai, Ching-Long
• Primary Examiner(s): Ryan, Patrick
• Assistant Examiner(s): Jewik, Patrick
• Application Number:
  US08/368,748
• Time in Patent Office: 699 Days
• Field of Search: 428/607, 428/611, 428/622, 428/626, 428/650, 428/651, 428/679, 428/212, 428/457, 428/900, 340/551, 340/572
• US Class Current: 428/457
• CPC Class Codes: G08B 13/2411 Tag deactivation
• CPC Class Codes: G08B 13/2437 Tag layered structure, processes for making layered tags
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details
• CPC Class Codes: Y10S 428/90 Magnetic feature
• CPC Class Codes: Y10T 428/12465 having magnetic properties, or preformed fiber orientation coordinate with shape
• CPC Class Codes: Y10T 428/12535 with additional, spatially distinct nonmetal component
• CPC Class Codes: Y10T 428/31678 Of metal

Abstract

A dual status marker for use with a magnetic-type EAS system has a signal-producing layer including at least one magnetic thin-film of high permeability and low coercive force such as permalloy, and a signal-blocking layer including at least one remanently magnetizable thin-film such as an Fe-Cr alloy. The remanently magnetizable thin-film or thin-films should have a total thickness at least equal to, and preferably at least twice, the total thickness of the magnetic thin-film or thin-films of high permeability. By doing so, the marker is more reliably deactivated when the signal-blocking layer is magnetized. For even greater assurance of deactivation, the signal-blocking layer should include more than one remanently magnetizable thin-film, thus giving it a squarer B-H loop and greater assurance against false alarms.

Claims

1. A dual status marker for use with a magnetic electronic article surveillance system, which system produces in an interrogation zone alternating magnetic fields having average peak intensities of less than 20 Oersteds, the dual status marker comprising:

a signal-producing layer having a differential permeability above 5000 and a coercive force less than the average peak intensities encountered in the interrogation zone, such that upon exposure to the alternating magnetic fields, the magnetization state of the signal-producing layer is periodically reversed thus producing an alarm signal; and

a signal-blocking layer in substantial contact with the signal-producing layer, the signal-blocking layer comprised of a plurality of remanently magnetizable deposition film layer, the signal blocking layer further having a coercivity above 25 Oe and providing magnetic flux such that the signal-producing layer is prevented from producing the alarm signal in the interrogation zone when the signal-blocking layer is magnetized.

2. A dual status marker as defined in claim 1 wherein said plurality of remanently magnetizable deposition films comprises an Fe-Cr alloy having a Cr content up to about 20 atomic percent.

3. A dual status marker as defined in claim 2 wherein the Cr content of said plurality of remanently magnetizable deposition films is from 1 to 15 atomic %.

4. A dual status marker as defined in claim 1 wherein said plurality of remanently magnetizable deposition films has a total thickness from 2 to 5 times the total thickness of the signal-producing layer.

5. A dual status marker as defined in claim 1 wherein the total thickness of the plurality of remanently magnetizable deposition films is from 0.8 to 1.2 μ

m.

6. A dual status marker as defined in claim 1 wherein the remanently magnetizable deposition films are discontinuous.

9. A dual status marker as defined in claim 1 wherein the signal-blocking layer further comprises alternating layers of remanently magnetizable deposition films and non-magnetic deposition films.

10. A dual status marker as defined in claim 9 wherein discontinuities of the at least one remanently magnetizable deposition film are segments of substantially uniform size and shape.

11. A dual status marker as defined in claim 10 wherein each of the segments has an area of from 1 to 100 mm².

12. A dual status marker as defined in claim 1 further including a substrate adapted to support the signal-producing layer and the signal-blocking layer.

13. A dual status marker as defined in claim 12 wherein the substrate is a flexible web.

14. A dual status marker as defined in claim 12 wherein the substrate comprises an article that is to be protected against theft.

15. A dual status marker as defined in claim 1 wherein the marker has an area of from 2 to 10 cm².

16. A dual status marker as defined in claim 12 wherein each of the nonmagnetic deposition films is no greater than 20 nm in thickness.

7. A control element which affords dual status to a marker having a signal-producing layer that produces an alarm signal when the marker is passed through an interrogation zone of a magnetic electronic article surveillance system, the control element comprising:

a plurality of remanently magnetizable deposition film layer having a coercivity above 25 Oe and providing magnetic flux such that, when placed in substantial contact with the signal-producing layer, the signal-producing layer is prevented from producing the alarm signal in the interrogation zone when the plurality of remanently magnetizable deposition films are magnetized.

8. A marker-deactivating product as defined in claim 7 wherein said plurality of remanently magnetizable thin-films have a total thickness of from 0.8 to 1.2 μ

m.