System for minimizing coupling nulls

• US 20080048834A1
• Filed: 07/30/2007
• Published: 02/28/2008
• Est. Priority Date: 08/23/2006
• Status: Active Grant

• Current Assignee: HID Textile Services SARL
• Original Assignee: Tagsys SAS (Mojix Inc)
• Inventors: Lenevez, Yves
• Granted Patent: US 7,956,751 B2
• Time in Patent Office: Days
• US Class Current: 340/10.3
• 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

A system is disclosed for minimizing coupling nulls between an electromagnetic field derived from one or more sources and a plurality of randomly oriented RFID tags, wherein the electromagnetic field is rotated relative to the tags such that no tag is persistently located in a coupling null relative to the field. The source of the electromagnetic field may include a passive antenna or loop that changes its orientation relative to a direction of movement of the tags. The source of the electromagnetic field may further include an active antenna or loop that is electromagnetically coupled to the passive antenna or loop. A method for minimizing coupling nulls between the electromagnetic field and the randomly oriented tags is also disclosed.

Claims

1. A system for at least minimizing coupling nulls between an electromagnetic field derived from one or more sources and a plurality of randomly oriented RFID tags, wherein said electromagnetic field is rotated relative to said tags such that no tag is persistently located in a coupling null relative to said field.

2. A system according to claim 1 wherein the or each tag is translated relative to said electromagnetic field.

3. A system according to claim 1 wherein the or each source includes a main axis that is oriented obliquely relative to a direction of movement of said plurality of tags.

4. A system according to claim 3 wherein the or each source of the electromagnetic field includes at least one passive antenna, loop or portal that is arranged such that its main axis changes orientation relative to said direction of movement of said tags.

5. A system according to claim 3 wherein said passive antenna, loop or portal is arranged to rotate relative to said direction of movement of said tags.

6. A system according to claim 4 wherein the or each source of the electromagnetic field includes at least one active antenna, loop or portal that is electromagnetically coupled to said passive antenna, loop or portal.

7. A system according to claim 6 wherein the or each antenna, loop or portal includes an aperture through which the plurality of tags may pass.

8. A system according to claim 3 wherein said main axis is oriented at an acute angle relative to said direction of movement.

9. A system according to claim 8 wherein said main axis is oriented substantially at 45 degrees relative to said direction of movement.

10. A system according to claim 4 wherein the or each tag is arranged to rotate relative to the or each antenna, loop or portal during movement of said tags in said direction.

11. A method for at least minimizing coupling nulls between an electromagnetic field derived from one or more sources and a plurality of randomly oriented RFID tags, said method including the step of rotating said electromagnetic field relative to the or each tag such that the or each RFID tag is not persistently located in a coupling null relative to said field.

12. A method according to claim 11 including translating the or each tag relative to said electromagnetic field.

13. A method according to claim 11 including orienting a main axis of the or each source obliquely relative to a direction of movement of said plurality of RFID tags.

14. A method according to claim 13 wherein the or each source of the electromagnetic field includes at least one passive antenna, loop or portal that is arranged such that its main axis changes orientation relative to said direction of movement of said tags.

15. A method according to claim 14 wherein said passive antenna, loop or portal is arranged to rotate relative to said direction of movement of said tags.

16. A method according to claim 14 wherein the or each source of the electromagnetic field includes at least one active antenna, loop or portal that is electromagnetically coupled to said passive antenna, loop or portal.

17. A method according to claim 13 wherein the or each antenna, loop or portal includes an aperture through which the plurality of tags may pass.

18. A method according to claim 13 wherein said main axis is oriented at an acute angle relative to said direction of movement.

19. A method according to claim 18 wherein said main axis is oriented substantially at 45 degrees relative to said direction of movement.

20. A method according to any one of claim 11 including rotating the or each tag relative to the or each antenna, loop or portal during movement of said tags in said direction.