Multi-loop antenna for radio frequency identification (RFID) communication

• US 20040183742A1
• Filed: 02/20/2004
• Published: 09/23/2004
• Est. Priority Date: 02/20/2004
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Lieffort, Seth A., Goff, Edward D., Stolberg, Leroy
• Granted Patent: US 7,417,599 B2
• Time in Patent Office: Days
• US Class Current: 343/867
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 6/1225 comprising photonic band-gap structures or photonic lattices
• CPC Class Codes: G06K 7/10178 including auxiliary means for focusing, repeating or boosting the electromagnetic interrogation field comparable booster antennas integrated on the record carrier itself G06K19/07794
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: G06K 7/10346 the antenna being of the far field type, e.g. HF types or dipoles
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 21/29 Combinations of different interacting antenna units for giving a desired directional characteristic H01Q25/00 takes precedence
• 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 multi-loop antenna is described having a plurality of conductive loops to produce an electromagnetic field for radio frequency identification (RFID) communication with RFID tags. The conductive loops are spaced apart at least a distance that is selected based on a dimension of the RFID tags with which the antenna communicates. In this manner, the loops are positioned and spaced in a manner that reduces the size of the holes within the resulting magnetic field. In addition, the configuration of the described dual-loop antenna increases the coverage of the antenna, and decreases inter-winding capacitance, thereby increasing overall read range achieved by the antenna.

Claims

1. An antenna comprising a plurality of conductive loops to produce an electromagnetic field for radio frequency identification (RFID) communication with RFID tags, wherein the conductive loops are spaced apart at least a distance D that is selected based on a dimension of the RFID tags with which the antenna communicates.

2. The antenna of claim 1, wherein the distance D is selected to exceed a maximum dimension of the RFID tags.

3. The antenna of claim 1, wherein the RFID tags have a dimension of length M, and the distance D between each of the plurality of conductive loops is selected such that D≧

M.

4. The antenna of claim 1, wherein D≧

2.54 cm.

5. The antenna of claim 1, wherein D≧

5.08 cm.

6. The antenna of claim 1, wherein the plurality of conductive loops form a dual-loop structure having an inner loop and an outer loop.

7. The antenna of claim 1, wherein the plurality of conductive loops are electrically coupled so that a common current flows through the loops.

8. The antenna of claim 7, wherein the plurality of conductive loops are located in parallel planes and formed with concentric traces, and the plurality of conductive loops are electrically coupled so that the common current flows through the loops in the same direction.

9. The antenna of claim 1, wherein the plurality of conductive loops are formed in a single printed circuit board.

10. The antenna of claim 1, further comprising a tuning circuit for tuning the plurality of loops to a single operating frequency.

11. The antenna of claim 10, wherein the tuning circuit tunes the plurality of antennas to the operating frequency of approximately 13.56 megahertz (MHz).

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

an RFID tag associated with an article; and

an antenna having a plurality of conductive loops to produce an electromagnetic field for communication with the RFID tag, wherein the conductive loops are spaced at least a distance that is selected based at least in part on a dimension of the RFID tag.

13. The RFID system of claim 12, further comprising:

an RFID interrogation device coupled to the antenna, wherein the interrogation device interrogates the RFID tag to obtain information regarding the article; and

a computing device to process the information retrieved from the RFID interrogation device.

14. The RFID system of claim 12, wherein the plurality of conductive loops are electrically coupled so that the interrogation device drives a common current through the loops.

15. The RFID system of claim 14, wherein the plurality of conductive loops are formed with concentric traces, and the plurality of conductive loops are electrically coupled so that the common current flows through the loops in the same direction.

16. The RFID system of claim 12, wherein each of the conductive loops are spaced at least a distance D that is selected to meet or exceed a maximum dimension of the RFID tag.

17. The RFID system of claim 12, wherein the RFID tag has a dimension of length M, and the distance D between each of the plurality of conductive loops is selected such that D≧

M.

18. The RFID system of claim 17, wherein D≧

2.54 cm.

19. The RFID system of claim 17, wherein D≧

5.08 cm.

20. The RFID system of claim 12, wherein the plurality of conductive loops form a dual-loop structure having an inner loop and an outer loop.

21. The RFID system of claim 12, wherein the antenna has a substantially planar form.

22. The RFID system of claim 21, further comprising a substantially-contiguous conductive shield positioned around the antenna and within a plane parallel to the antenna.

23. The RFID system of claim 21, wherein the conductive shield shapes the electromagnetic field to extend substantially in a direction perpendicular to the antenna, and prevents the electromagnetic field from forming substantially over the conductive shield.

24. The RFID system of claim 23, wherein the conductive shield comprises planar conductive regions oriented to form a non-shielded inner region, and further wherein the antenna is disposed within the non-shielded inner region and parallel to the planar conductive regions.