Desensitizing apparatus for electromagnetic article surveillance system

• US 5,285,182 A
• Filed: 09/03/1992
• Issued: 02/08/1994
• Est. Priority Date: 09/03/1992
• Status: Expired due to Term

• Current Assignee: 3M Company, NEC Corporation
• Original Assignee: 3M Company
• Inventors: Zarembo, Peter J.
• Primary Examiner(s): DONOVAN, LINCOLN D
• Application Number:
  US07/940,007
• Time in Patent Office: 523 Days
• Field of Search: 335/284, 335/306, 340/551, 340/572
• US Class Current: 335/284
• CPC Class Codes: G08B 13/2411 Tag deactivation

Abstract

A desensitizing apparatus for magnetizing a desensitizable marker used with an electromagnetic article surveillance system. The apparatus includes a rectangular, non-metallic plate positioned so that its length is perpendicular to a likely direction of travel of the marker to be magnetized. A row of X-shaped arrays of elongated magnets is embedded on the plate. A marker passing over the row of magnets will be desensitized regardless of its orientation or direction of travel over the magnets.

Claims

1. A desensitizing apparatus for magnetizing a desensitizable marker used with an electromagnetic article surveillance system, including:

a housing having a surface adapted to support an article as a marker secured thereto is moved past the apparatus, wherein the surface is further adapted to constrain said an article along a direction of travel over the housing; and

an elongated, high density magnet positioned in a plane proximate to and substantially parallel with the surface of the housing adapted to support said an article, wherein the length of the magnet is substantially perpendicular to said a direction of travel of said a marker to be moved past the apparatus, wherein the magnet provides a magnetic field aligned substantially normal to its length, wherein the strength of the magnetic field decreases by about 1/r², for r greater than 1 mm, where r is a distance above the magnet, thereby enabling the marker to be remanently magnetized without altering the magnetic state of the article to which the marker is affixed, and wherein the magnetic field is sufficiently strong to magnetize the marker but does not subject the marker to a back field which would partially resensitize the marker.

2. The desensitizing apparatus of claim 1, wherein the magnet is a rare earth, transition metal alloy magnet.

3. The desensitizing apparatus of claim 1, wherein the magnet has a peak magnetic energy product of at least about 25 Megagauss-oersteds and behaves like a dipole having north and south poles located on opposite surfaces of the magnet.

4. The desensitizing apparatus of claim 1, wherein the magnet has a square-shaped cross-section perpendicular to its length having dimensions of less than about 1.3 mm by 1.3 mm.

5. The desensitizing apparatus of claim 2, wherein the rare earth, transition metal alloy magnet comprises neodynium-iron-boron.

6. The desensitizing apparatus of claim 1, wherein the plane of the magnet is coplanar with the surface adapted to support said an article, whereby said an article may contact the magnet as the article is moved past the apparatus.

7. The desensitizing apparatus of claim 1, wherein the housing is adapted to be hand-held for transporting the apparatus relative to said an article to which said a marker is affixed.

8. A desensitizing apparatus for magnetizing a desensitizable marker used with an electromagnetic article surveillance system including:

a housing having a surface adapted to support an article as a marker secured thereto is moved past the apparatus; and

first and second elongated magnets positioned in a plane proximate to and substantially parallel with the surface of the housing adapted to support said an article, wherein the lengths of the two magnets are substantially perpendicular to each other, wherein each magnet provides a magnetic field aligned substantially normal to its length and parallel to the surface of the housing adapted to support said an article, and wherein said a marker which passes over each of the magnets will be magnetized and thereby desensitized regardless of its orientation relative to the magnets.

9. The desensitizing apparatus of claim 8, wherein the length of the first elongated magnet is oriented at an angle of about 45°

with respect to a likely direction of travel of said a marker to be magnetized.

10. The desensitizing apparatus of claim 9, further including a third elongated magnet, identical to the second elongated magnet, coplanar with the first and second magnets, wherein the second and third elongated magnets are each approximately one-half the length of the first elongated magnet, and wherein the lengths of the second and third magnets are substantially perpendicular to the length of the first elongated magnet and intersect the first magnet on opposite sides of the magnet at the midpoint of its length, thereby forming an X-shaped array of elongated magnets in the plane of the magnets.

11. The desensitizing apparatus of claim 10, further including a plurality of additional X-shaped arrays of elongated magnets, wherein the X-shaped arrays meet at their ends to form a straight row of X'"'"'s, wherein the row is substantially perpendicular to said likely direction of travel of said a marker to be magnetized.

12. The desensitizing apparatus of claim 8, wherein each magnet has a peak magnetic energy product of at least about 25 Megagauss-oersteds and behaves like a dipole having north and south poles located on opposite surfaces of the magnet, and wherein said a marker passing the magnets is not exposed to a back field that would partially resensitize the marker.

13. The desensitizing apparatus of claim 12, wherein the magnets are rare earth, transition metal alloy magnets.

14. The desensitizing apparatus of claim 13, wherein the magnets comprise neodynium-iron-boron.

15. The desensitizing apparatus of claim 8, wherein the magnets each have a square-shaped cross-sectional area perpendicular to their length of less than about 1.5 mm by 1.5 mm.

16. The desensitizing apparatus of claim 8, wherein the plane of the magnets is coplanar with the surface adapted to support said an article, whereby said an article may contact the magnets as the article is moved past the apparatus.

17. A desensitizing apparatus for magnetizing a desensitizable marker used with an electromagnetic article surveillance system, including:

a housing having a surface adapted to support an article as a marker secured thereto is moved past the apparatus;

a rectangular, non-magnetic plate positioned in the housing in a plane proximate to and substantially parallel with the surface of the housing adapted to support said an article, wherein the length of the plate is substantially perpendicular to a likely direction of travel of said a marker to be magnetized, whereby the marker on said an article passing over the apparatus will also pass over the plate; and

a plurality of X-shaped arrays of elongated magnets embedded on the plate, wherein each elongated magnet provides a magnetic field aligned substantially normal to its length and parallel to the plate, and wherein the X-shaped arrays meet at their ends to form a straight row of X'"'"'s, wherein the row is parallel to the length of the plate.

18. The desensitizing apparatus of claim 17, wherein each of the X-shaped arrays of elongated magnets comprises:

a first elongated magnet oriented at an angle of about 45°

to the length of the plate; and

second and third elongated magnets, each of which is about one-half the length of the first elongated magnet, wherein their lengths are perpendicular to the length of the first magnet, they meet the first elongated magnet at the midpoint of its length, and wherein they are on opposite sides of the first elongated magnet.

19. The desensitizing apparatus of claim 17, wherein the surface adapted to support said an article does not cover the non-magnetic plate and the magnets embedded therein, whereby said an article may contact the plate as the article is moved past the apparatus.

20. The desensitizing apparatus of claim 17, wherein the magnets are rare earth, transition metal alloy magnets.

21. The desensitizing apparatus of claim 20, wherein the magnets comprise neodynium-iron-boron.

22. The desensitizing apparatus of claim 17, wherein the magnets each have a cross-sectional area perpendicular to their length of less than about 1.5 mm by 1.5 mm.

23. The desensitizing apparatus of claim 17, wherein each magnet has a peak magnetic energy product of at least about 25 Megagauss-oersteds and behaves like a dipole having north and south poles located on opposite surfaces of the magnet, and wherein said a marker passing the magnets is not exposed to a back field that would partially desensitize the marker.

24. The desensitizing apparatus of claim 17, wherein the strength of the magnetic field decreases by about 1/r², for r greater than 1 mm, where r is a distance above the magnets, thereby enabling said a marker to be remanently magnetized without altering the magnetic state of said an article to which the marker is affixed.