Signal line structure for a radio-frequency identification system

• US 20090085746A1
• Filed: 09/27/2007
• Published: 04/02/2009
• Est. Priority Date: 09/27/2007
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Banerjee, Swagata R., Erickson, David P., McGee, James P., Waldner, Michele A.
• Granted Patent: US 8,289,163 B2
• Time in Patent Office: Days
• US Class Current: 340/572.100
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10316 using at least one antenna particularly designed for interrogating the wireless record carriers antennas in general H01Q1/22
• CPC Class Codes: G06Q 10/08 Logistics, e.g. warehousing, loading or distribution; Inventory or stock management
• 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 13/106 Microstrip slot antennas patch antenna elements H01Q9/0407
• CPC Class Codes: H01Q 21/0025 Modular arrays
• CPC Class Codes: H01Q 21/28 Combinations of substantially independent non-interacting antenna units or systems multiple beam H01Q25/00

Abstract

The invention provides one or more signal line structures that produce an electromagnetic field having a magnitude of at least an interrogation threshold of a radio frequency identification (RFID) tag for a substantial portion of an interrogation region. The signal lines may be made from copper and laid across a shelf in a storage area. The electromagnetic field may cause the tag to backscatter radio frequency (RF) signals to an RFID reader via the signal line.

Claims

1. A radio frequency identification (RFID))-enabled shelf comprising:

a substrate providing a shelf for items having RFID tags; and

a signal line structure comprising;

a plurality of signal lines affixed to a first side of the substrate to generate one or more radio frequency (RF) electromagnetic fields for interrogating one or more of the RFID tags;

an electrical conductor providing an electrical ground plane on a second side of the substrate opposite the plurality of signal lines; and

an electrical load coupling at least one of the plurality of signal lines and the ground plane.

2. The RFID enabled-shelf of claim 1, wherein the ground plane has a width that is at least twice a width of the signal line.

3. The RFID enabled-shelf of claim 1, wherein the ground plane has a width that is at least four times a width of the signal line.

4. The RFID enabled-shelf of claim 1, wherein the signal lines have a width of at least 0.312 inches (7.92 mm) and the ground plane has a width of at least 1 inch (25.4 mm) in width.

5. The RFID enabled-shelf of claim 1, wherein the signal lines have a width of at least 1.0 inches (25.4 mm) and the ground plane has a width of at least 4 inch (101.6 mm) in width.

6. The RFID-enabled shelf of claim 1, further comprising a first connector connected to a first end of a signal line of the plurality of signal lines are a second connector connected to a second end of the signal line to electrically couple the signal line structure of the RFID enabled shelf to signal line structures of one or more additional shelves.

7. The RFID-enabled shelf of claim 1, wherein the signal lines and the ground plane comprise a copper tape affixed to the substrate.

8. The RFID-enabled shelf of claim 1, wherein the electrical load coupling the at least one of the plurality of signal lines and ground plane is a 50 ohm resistor.

9. The RFID-enabled shelf of claim 1, further comprising an electrical connector for electrically coupling the at least one of the plurality of signal lines to an RFID reader.

10. The RFID enabled-shelf of claim 1,

wherein the plurality of signal lines extend longitudinally along a length of the shelf, and

wherein the electrical ground plane extends longitudinally along the length of the substrate on the second side of the substrate opposite the plurality of signal lines.

11. The RFID-enabled shelf of claim 1,

wherein the plurality of signal lines are substantially equally spaced apart and located at different depths of the shelf.

12. The RFID-enabled shelf of claim 1, wherein at least one of the plurality of signal lines is a parasitic signal line that is not electrically coupled to the ground plane.

13. The RFID-enabled shelf of claim 1, wherein all of the plurality of signal lines extend longitudinally along substantially an entire length of the shelf.

14. The RFID-enabled shelf of claim 1,

wherein a first subset of the plurality of signal lines extends longitudinally along substantially an entire length of the shelf, and

wherein a second subset of the plurality of signal lines extends longitudinally along only a partial length of the shell.

15. The RFID-enabled shelf of claim 1, wherein the plurality of signal lines comprises signal lines that each extend to a different longitudinal position along a length of the shelf.

16. The RFID-enabled shelf of claim 1,

wherein the plurality of signal lines extend along a width of the shelf in a direction from a front of the shelf to a back of the shelf.

wherein the plurality of signal lines are substantially equally spaced a lateral distance apart along a length of the shelf and are configured for selective powering for determining longitudinal position of an item placed on the shelf.

17. The signal line structure of claim 1, wherein the plurality of signal lines extend substantially across an entire width of the shelf.

18. The signal line structure of claim 1, wherein the plurality of signal lines comprise an alternating scheme of a first signal line that extends substantially an entire width of the shelf, and a second signal line of the plurality of signal lines that extends less than the entire width of the shelf.

19. A radio frequency identification (RFID) system, comprising:

a plurality of RFID-enabled shelves for storing items having RFID tags, each of the shelves having a substrate and signal line structure that includes a plurality of signal lines on a first side of the substrate to generate one or more radio frequency (RF) electromagnetic fields for interrogating one or more of the RFID tags and an electrical conductor providing in electrical ground plane on a second side of the substrate opposite the plurality of signal lines; and

an electrical load coupling at least one of the plurality of signal lines of a last one of the shelves to the ground plane of the last shelf.

wherein each of the shelves is physically connected to at least one adjacent shelf.

wherein at least one of the plurality of signal lines of each of the shelves is coupled to at least one of the plurality of signal lines of at least one adjacent shelf, and

wherein the ground plane of each of the shelves is coupled to a ground plane of at least one adjacent shelf.

20. The signal line structure of claim 19, wherein at least one of the plurality of signal lines of a first one of the shelves is capable of being physically and electrically coupled to an RFID reader.

21. A radio frequency identification (RFID) system comprising:

an RFID reader;

a radio frequency identification (RFID)-enabled shelf electrically coupled to the RFID reader to generate a radio frequency (RF) electromagnetic field when powered by the RFID reader, the RFID-enabled shell comprising;

a substrate providing a shelf for items having RFID tags;

a signal line structure comprising;

a plurality of signal lines affixed to a first side of the substrate to generate one or more radio frequency (RF) electromagnetic fields for interrogating one or more of the RFID tags;

an electrical conductor providing an electrical ground plane on a second side of the substrate opposite the plurality of signal lines; and

an electrical load coupling at least one of the plurality of signal lines and ground plane.

22. A method for detecting the presence of a particular item of interest within a radio frequency identification (RFID) system, comprising:

outputting a first output signal from an RFID reader to a signal line structure of an RFID-enabled shelf to generate one or more radio frequency (RF) electromagnetic fields for interrogating one or more of the RFID tags associated with items located on a shelf, the signal line structure comprising a plurality of signal lines affixed to a first side of the shelf, an electrical conductor providing an electrical ground plane on a second side of the substrate opposite the plurality of signal lines and an electrical load coupling at least one of the plurality of signal lines and ground plane, wherein the first output signal is outputted to a first signal line of the plurality of signal lines;

receiving a response RF signal from at least one of the RFID tags via the signal line structure; and

determining, based on the response RF signal, whether an item of interest is stored on the shelf.

23. The method of claim 22, wherein the first output signal creates a first RF electromagnetic field substantially along the first signal line of the plurality of signal lines the method further comprising:

outputting a second output signal to the signal line structure to create a RF electromagnetic field substantially along a second signal line of the plurality of signal lines;

determining a location of the item on the shelf up based on whether the response RF signal is received via the first signal line in response to the first output signal or via the second signal line in response to the second output signal.

24. The method of claim 22, wherein the plurality of signal lines extend longitudinally along a length of the shelf, and wherein determining a location comprises determining a depth that the item is positioned on the shelf.

25. The method of claim 22, wherein the plurality of signal lines extend across a width of the shelf along a direction from a front of the shelf to a back of the shelf, and wherein determining a location comprises determining a longitudinal position for the item along a length of the shelf.