Multi-loop antenna for radio-frequency identification

• US 20040100413A1
• Filed: 03/03/2003
• Published: 05/27/2004
• Est. Priority Date: 11/25/2002
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Waldner, Michele A.
• Granted Patent: US 6,861,993 B2
• Time in Patent Office: Days
• US Class Current: 343/742
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

The invention provides a multi-loop antenna that produces an electromagnetic field having a magnitude of at least an interrogation threshold of a tag for a substantial portion of an interrogation region located in a plane parallel to the antenna. The antenna may include a plurality of loops, including one or more powered loops and one or more parasitic loops. The parasitic loops receive power from mutual coupling with the powered loops causing current to flow within the parasitic loops, which contributes to the profile of the magnetic field. As a result, each parasitic loop may be tuned to provide control over the magnitude of the electromagnetic field. The powered loops and the parasitic loops may be varied over the interrogation period to reduce any area of the interrogation region where the magnitude of the field remains below the interrogation threshold throughout the interrogation period. The powered loops and the parasitic loops may reside on a single layer or may be arranged on multiple layers.

Claims

1. An antenna comprising a plurality of loops oriented to produce an electromagnetic field having a magnitude of at least an interrogation threshold of a tag for a substantial portion of an interrogation region located in a plane parallel to the antenna.

2. The antenna of claim 1, wherein the loops are formed planar to one another and are oriented to produce the magnetic field such that the magnitude within the interrogation region meets or exceeds the interrogation threshold of the tag in a direction perpendicular to an orientation of the tag.

3. The antenna of claim 2, wherein a first subset of the loops are formed in a first printed circuit board, and a second subset of the loops are formed in a second printed circuit board oriented parallel to the first printed circuit board.

4. The antenna of claim 2, wherein the loops are formed in a common layer of a printed-circuit board.

5. The antenna of claim 1, wherein a subset of at least two of the loops are selectively powered over an interrogation period to achieve the magnetic field.

6. The antenna of claim 1, wherein the loops include at least one powered loop and at least one parasitic loop.

7. The antenna of claim 1, wherein the antenna is embedded within a base of a vertical file or within a shelf.

8. The antenna of claim 1, wherein the loops comprise concentric loops.

9. The antenna of claim 7, wherein the antenna includes at least three concentric loops.

10. The antenna of claim 7, wherein the antenna includes at least fifteen concentric loops.

11. The antenna of claim 1, wherein the loops comprise a plurality of planar loops formed in multiple layers of a printed-circuit board.

12. The antenna of claim 11, wherein the loops comprise one or more powered loops within a top layer, one or more powered loops within a bottom layer, and one or more parasitic loops within a layer between the top layer and the bottom layer.

13. The antenna of claim 1, wherein the electromagnetic field formed by the antenna exceeds a threshold magnitude for energizing a radio frequency identification tag for at least 50% of the dimension of the antenna.

14. The antenna of claim 1, wherein the electromagnetic field formed by the antenna exceeds a threshold magnitude for energizing a radio frequency identification tag for at least 75% of the dimension of the antenna.

15. The antenna of claim 1, wherein the electromagnetic field formed by the antenna exceeds a threshold magnitude for energizing a radio frequency identification tag for at least 90% of the dimension of the antenna.

16. A radio frequency identification system comprising:

a storage area to store items having associated radio frequency identification tags;

an antenna proximate the storage area to produce an electromagnetic field, wherein the antenna has multiple loops; and

a radio frequency identification reader coupled to the antenna to selectively power at least one of the loops of the antenna without powering the remaining loops to communicate with the radio frequency identification tags.

17. The system of claim 16, wherein the electromagnetic field produced by the multi-loop antenna has magnitude that exceeds an interrogation threshold of the tags over a time period.

18. The system of claim 17, wherein the magnitude of the electromagnetic field meets or exceeds the interrogation threshold for a substantial portion of an interrogation region located in a plane parallel to the loops of the antenna.

19. The system of claim 16, wherein the antenna comprises at least one powered loop and at least one parasitic loop.

20. The system of claim 16, wherein the antenna comprises concentric loops.

21. The system of claim 16, wherein the antenna comprises loops formed in a common plane.

22. The system of claim 16, wherein the antenna comprises loops formed on a single layer of a printed-circuit board.

23. The system of claim 16, wherein the antenna is embedded within the storage area.

24. The system of claim 16, wherein the antenna comprises a plurality of planar loops formed in multiple layers of a printed-circuit board.

25. The system of claim 16, wherein the radio frequency identification reader selectively powers at least two of the loops of the antenna at different times during an interrogation period.

26. The system of claim 16, further comprising a file tracking system to receive the information from the radio frequency identification reader and store the information within a database.

27. The system of claim 26, further comprising a remote computer coupled to the file tracking system to present the information to a remote user.

28. The system of claim 16, wherein the storage area includes at least one of a shelving unit, a cabinet, a vertical file separator, a smart cart, and a desktop reader.

29. The system of claim 16, wherein the information received from the radio frequency identification tags includes location information for the items within the storage area.

30. The system of claim 16, wherein the items having associated radio frequency identification tags include at least one of files and documents.

31. A method comprising:

selectively powering at least one loop of a multi-loop antenna without powering the remaining loops to produce an electromagnetic field proximate to a storage area during an interrogation period; and

obtaining information during the interrogation period from one or more radio frequency identification tags fixed to items within the storage area.

32. The method of claim 31, wherein powering the multi-loop antenna includes selectively powering two or more loops of the multi-loop antenna at different times during the interrogation period to produce the electromagnetic field to have a magnitude of at least an interrogation threshold of the tags for a substantial portion of an interrogation region located in a plane parallel to the antenna.

33. The method of claim 31, wherein powering the multi-loop antenna includes powering one or more loops of the multi-loop antenna to produce the electromagnetic field to have a magnitude that meets or exceeds the interrogation threshold of the tag in a direction perpendicular to an orientation of the tag.

34. The method of claim 31, further comprising storing the information from the radio frequency identification tags within a database.

35. The method of claim 31, further comprising presenting the information from the tags to a remote user.

36. The method of claim 31, wherein obtaining information from the energized radio frequency identification tags includes obtaining location information for items to which the radio frequency identification tags are fixed, and further wherein the items include one of books, files and documents located within the storage area.

37. The method of claim 31, wherein the multi-loop antenna includes at least one powered loop and at least one parasitic loop, and powering the multi-loop antenna further comprises selectively powering the powered loop to create the electromagnetic field and induce a current in the parasitic loop via mutual coupling with the powered loop to contribute to a profile of the electromagnetic field.

38. The method of claim 31, wherein powering the multi-loop antenna further comprises:

powering a first subset of the loops to create a first electromagnetic field during a first portion of the interrogation period; and

powering a second subset of the loops to create a second electromagnetic field during a second portion of the interrogation period, wherein the contributions of the first and second electromagnetic fields produce an electromagnetic field having a magnitude over the interrogation period of at least an interrogation threshold of a tag

39. The method of claim 38, wherein the first and second portions of the interrogation period are non-overlapping.

40. The method of claim 38, wherein the first and second sets of the loops reside in a common plane.

41. The method of claim 38, wherein the first and second sets of the loops reside within multiple layers.

42. The method of claim 31, wherein a magnitude of the electromagnetic field exceeds a threshold magnitude for energizing the radio frequency identification tags for at least 50% of an interrogation region located in a plane parallel to the antenna.

43. The method of claim 31, wherein a magnitude of the electromagnetic field exceeds a threshold magnitude for energizing the radio frequency identification tags for at least 75% of an interrogation region located in a plane parallel to the antenna.

44. The method of claim 31, wherein a magnitude of the electromagnetic field exceeds a threshold magnitude for energizing the radio frequency identification tags for at least 90% of an interrogation region located in a plane parallel to the antenna.