RFID devices having self-compensating antennas and conductive shields

• US 20060054710A1
• Filed: 10/11/2005
• Published: 03/16/2006
• Est. Priority Date: 04/10/2003
• Status: Active Grant

• Current Assignee: Avery Dennison Retail Information Services LLC (Avery Dennison Corporation)
• Original Assignee: Avery Dennison Corporation
• Inventors: Forster, Ian J., Farr, Adrian N., Howard, Norman A., Holman, Andrew W.
• Granted Patent: US 7,652,636 B2
• Time in Patent Office: Days
• US Class Current: 235/492
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• 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 1/52 Means for reducing coupling between antennas; Means for reducing coupling between an antenna and another structure absorbing means H01Q17/00

Abstract

A radio frequency identification (RFID) tag includes an antenna configuration coupled to an RFID chip, such as in an RFID strap. The antenna configuration is mounted on one face (major surface) of a dielectric material, and includes compensation elements to compensate at least to some extent for various types of dielectric material upon which the antenna configuration may be mounted. In addition, a conductive structure, such as a ground plane or other layer of conductive material, may be placed on a second major surface of the dielectric layer, on an opposite side of the dielectric layer from the antenna structure.

Claims

1. An RFID device comprising:

a dielectric layer;

an antenna structure atop a first face of the dielectric layer; and

an RFID chip coupled to the antenna structure;

wherein the antenna structure includes one or more compensating elements that compensate at least in part for effects of an operating environment in proximity to the antenna structure.

2. The device of claim 1, wherein the compensating elements include an inter-digital capacitor.

3. The device of claim 1,

wherein the compensating elements include a meander inductor;

wherein the antenna structure includes antenna elements; and

wherein the meander inductor is located between the RFID chip and one of the antenna elements.

4. The device of claim 1,

wherein the compensating elements include a meander inductor;

wherein the meander inductor includes multiple turns of conductive material; and

wherein at least some of the multiple turns are capacitively coupled with one another.

5. The device of claim 1, wherein the compensating elements interact with dielectric material of the dielectric layer, providing different operating characteristics for the compensating elements based on characteristics of the dielectric material.

6. The device of claim 1, further comprising a conductive plane atop a second face of the dielectric layer, wherein the dielectric layer is interposed between the conductive plane and the antenna structure.

7. The device of claim 6, wherein the antenna structure and the conductive plane are formed on a different parts of a single substrate, which is folded over and attached to opposite sides of the dielectric layer.

8. The device of claim 1, wherein the dielectric layer is a portion of a container.

9. The device of claim 8, further comprising a conductive plane atop a second face of the dielectric layer, wherein the dielectric layer is interposed between the conductive plane and the antenna structure.

10. The device of claim 9, wherein the conductive plane is between the antenna structure and an inner volume of the container.

11. The device of claim 9, wherein the portion is an overlapped portion of the container, with the antenna structure on one face of the portion, and the conductive plane on an opposite face of the portion.

12. The device of claim 1,

wherein the antenna structure includes a pair of antenna elements coupled to the RFID chip;

and

wherein the dielectric layer has a non-uniform thickness, the dielectric layer having a thinner portion and a thicker portion; and

wherein a portion of one of the antenna elements is on the thinner portion.

13. The device of claim 12,

further comprising a conductive plane atop a second face of the dielectric layer, wherein the dielectric layer is interposed between the conductive plane and the antenna structure;

wherein the portion of the antenna element on the thinner portion of the dielectric layer is capacitively coupled to the conductive plane.

14. The device of claim 12, wherein the antenna elements are each coupled to the RFID chip at feedpoints differing in location on each of said two antenna elements.

15. The device of claim 1,

further comprising a conductive plane atop a second face of the dielectric layer, wherein the dielectric layer is interposed between the conductive plane and the antenna structure;

wherein the conductive plane extends at least about 6 mm in extent beyond the antenna structure.

16. The device of claim 1, wherein the dielectric layer includes an expandable material.

17. The device of claim 1, wherein the one or more compensating elements aid in maintaining a closer impedance match between the chip and the antenna structure over a range of operating environments in proximity to the antenna structure.

18. A method of configuring an RFID device, the method comprising:

placing an antenna structure of the RFID device and a conducting plane of the RFID device opposed to one another on opposite sides of a dielectric layer; and

re-tuning the antenna structure to compensate at least in part for effects of the dielectric layer on performance of the antenna structure;

wherein the re-tuning is an automatic re-tuning performed by compensating elements of the antenna structure in response to being placed in proximity to the dielectric layer.

19. The method of claim 18, wherein the compensating elements include one or more capacitive elements.

20. The method of claim 18, wherein the compensating elements include one or more inductive elements.

21. The method of claim 18, wherein the placing includes placing the antenna structure and the conducting plane on opposite sides of a container.

22. The method of claim 21, wherein the placing includes placing the conducting plane on an inside surface of the container, thereby at least partially shielding the antenna structure from effects of contents of the container.

23. The method of claim 21, wherein the placing includes placing the antenna structure and the conducting plane on opposite sides of an overlapping portion of the container.

24. A method of employing an RFID device, the method comprising:

providing the RFID device, wherein the RFID device includes;

an RFID chip; and

an antenna structure coupled to the RFID chip, wherein the antenna structure includes one or more compensating elements;

placing the RFID device in proximity to one or more dielectric materials and/or conductive materials, wherein the placing causes alteration of operating characteristics of the antenna structure, away from impedance matching between the antenna structure and the RFID chip; and

compensating for the alteration of the operating characteristics of the antenna structure, through automatic action of the compensating elements in response to the proximity to the one or more dielectric materials and/or conductive materials, to bring the antenna structure and the RFID chip toward impedance matching.

25. The method of claim 24,

wherein the one or more compensating elements an impendence matching network between the RFID chip and antenna elements of the antenna structure;

and

wherein the compensating includes compensating includes using the impedance matching network to bring the antenna structure and the RFID chip toward impedance matching.

26. The method of claim 24, wherein the compensating includes changing effective length of antenna elements of the antenna structure.

27. The method of claim 24, wherein the placing includes placing the RFID device on a container.

28. The method of claim 27, wherein the one or more dielectric materials and/or conductive materials includes a wall of the container.

29. The method of claim 28, further comprising placing a conductive structure on the wall on an opposite side of the wall from the antenna structure and the chip.

30. The method of claim 29, wherein the placing of the conductive structure includes placing the conductive structure is on an interior side of the container, closer to contents of the container than the antenna structure and the chip.

31. The method of claim 29, wherein the placing of the conductive structure and the placing of the RFID device results in the conductive structure substantially overlapping the antenna structure and the chip.

32. The method of claim 27, wherein the placing the RFID device on the container includes placing the RFID device on an overlapping portion of a carton.

33. The method of claim 27, wherein the one or more dielectric materials and/or conductive materials include contents of the container.

34. An RFID device comprising:

a dielectric layer;

an antenna structure atop a first face of the dielectric layer; and

an RFID chip coupled to the antenna structure;

wherein the antenna structure includes an electrical conductor that forms a capacitance element that interacts with contents of a container in proximity to the antenna structure to compensate at least in part for the effects such contents have on the antenna structure.

35. An RFID device comprising:

a dielectric layer;

an antenna structure atop a first face of the dielectric layer; and

an RFID chip coupled to the antenna structure;

wherein the antenna structure includes an electrical conductor having a gap that interacts with contents of a container in proximity to the antenna structure to render the antenna structure less sensitive to the effects such contents have on the antenna structure.