RFID tag with small aperture antenna

• US 20060250250A1
• Filed: 05/04/2005
• Published: 11/09/2006
• Est. Priority Date: 05/04/2005
• Status: Active Grant

• Current Assignee: Amtech Systems LLC (Roper Technologies, Inc.)
• Original Assignee: TC License Limited
• Inventors: Youn, Tai Won
• Granted Patent: US 7,501,947 B2
• Time in Patent Office: Days
• US Class Current: 340/572.700
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: G06K 19/0775 arrangements for connecting the integrated circuit to the antenna
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole
• CPC Class Codes: H01Q 1/1271 for mounting on windscreens
• 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 13/106 Microstrip slot antennas patch antenna elements H01Q9/0407

Abstract

A RFID tag to be attached to an object to identify the object or a characteristic or feature thereof from data stored in the tag accessible by a RFID reader includes a relatively flat structure having a small aperture antenna positioned on or proximate the tag in the form of a polygon having electrically conductive sides. The flat structure, which may be fabricated as a sticker or label, incorporates a small aperture antenna, such as a slot antenna, in the form of a polygon having electrically conductive sides. The polygon may be triangular, rectangular, square, elliptical, circular, or other polygonal figure depending on number of its plurality of sides. A constitutes the aperture of the antenna. An integrated circuit chip containing the electronics of the tag is secured to the flat structure within the boundary of the aperture constituting the central open portion within the polygon, and substantially equidistant from a pair of opposite sides of the polygon, with a pair of conductive impedance matching elements of substantially equal length confronting each other in the aperture from the opposite sides. Methods of use are disclosed.

Claims

1. A RFID tag to be attached to an object to identify the object or a characteristic or feature thereof from data stored in the tag accessible by a RFID reader, said RFID tag comprising a relatively flat structure having a small aperture antenna positioned on or proximate the tag in the form of a polygon having electrically conductive sides.

2. The RFID tag of claim 1, wherein said polygon is a square.

3. The RFID tag of claim 1, wherein said polygon is a circle.

4. The RFID tag of claim 1, wherein said polygon is a rectangle.

5. The RFID tag of claim 1, wherein said polygon is an ellipse.

6. The RFID tag of claim 1, wherein said polygon has rounded corners at the connection between each adjoining pair of its sides.

7. The RFID tag of claim 1, wherein said flat structure is a sticker for self-adhesion to an object.

8. The RFID tag of claim 1, wherein said tag is passive.

9. The RFID tag of claim 1, wherein said tag is active.

10. The RFID tag of claim 1, wherein a central open portion within said polygon constitutes the aperture of said antenna.

11. The RFID tag of claim 10, including an integrated circuit (IC) chip containing the electronics of said tag secured to said structure within the boundary of the aperture of said antenna.

12. The RFID tag of claim 11, wherein said IC chip is secured within the boundary of said aperture substantially equidistant from a pair of opposite sides of said polygon.

13. The RFID tag of claim 12, including an impedance matching circuit operatively connecting said antenna to said IC chip for delivery of RF signals therebetween.

14. The RFID tag of claim 13, wherein said impedance matching circuit comprises a pair of electrically conductive elements of substantially equal length extending toward each other from said opposite sides of said polygon into said aperture for enabling electrical interaction between said antenna and said IC chip.

15. The RFID tag of claim 14, wherein a feeding point for said antenna is located between said impedance matching elements.

16. The RFID tag of claim 14, wherein said polygon comprises an electrically conductive layer of said tag and each of said pair of impedance matching elements comprises an electrically conductive strip of said layer.

17. The RFID tag of claim 16, wherein the conductive layer forming the polygon and said pair of impedance matching elements is an etched metal layer overlying an electrically insulative sheet of said flat structure.

18. The RFID tag of claim 16, wherein the conductive layer forming the polygon and said pair of impedance matching elements is conductive ink imprinted on an electrically insulative sheet of said flat structure.

19. The RFID tag of claim 14, wherein said impedance matching circuit further comprises a second pair of elements constituting a mirror image of the first-named pair of elements, said first-named and second pairs of elements overlying opposite sides of an electrically insulative sheet of said flat structure, said polygon and first-named pair of elements overlying one side of said sheet and said IC chip and second pair of elements overlying the other side of said sheet.

20. The RFID tag of claim 19, wherein said first-named and second pairs of elements are electrically coupled through the capacitance formed by dielectric of said sheet.

21. The RFID tag of claim 19, wherein said first-named and second pairs of elements are electrically connected by a conductive path through said sheet.

22. The RFID tag of claim 1, wherein said flat structure and components thereof are encompassed within a coating for protection against damage from ambient environment.

23. The RFID tag according to claim 1, wherein said small aperture antenna is a slot antenna.

24. The RFID tag of claim 1, adapted to be applied wherein said object is a vehicle and said surface is the windshield of the vehicle, for RF communication of said tag with a RFID reader in the vicinity of said vehicle.

25. A radio frequency identification (RFID) tag, comprising:

a flat structure with an integrated circuit (IC) chip containing electronic circuitry of said tag on a major side and a small aperture antenna in the shape of a polygon with a central aperture on the other major side, and an impedance matching circuit with elements on both sides operatively connected between said antenna and said IC chip for complex impedance matching between the two.

26. The RFID tag according to claim 25, wherein said impedance matching circuit has a shunt impedance to circuit ground sufficiently large to simulate an open circuit and a substantially smaller series impedance between said antenna and said IC chip.

27. The RFID tag according to claim 25, wherein said small aperture antenna is a slot antenna.

28. The RFID tag according to claim 25, wherein said flat structure is a sticker adapted for adhesion to an object to be identified by characteristics or features stored in the tag during RF communication with a RFID reader in stationary to high speed applications.

29. The RFID tag according to claim 28, wherein said sticker is adapted for adhesion to a vehicle.

30. The RFID tag according to claim 29, wherein said sticker is adapted for adhesion to the windshield of the vehicle, as authorization, by virtue of data stored in said tag, for participation by the vehicle in an on-the-fly roadway toll collection system in which at least one RFID reader is positioned for RF communication with said tag with respect to a toll collection lane of the roadway for automated toll collection with each passage of said vehicle through said lane.

31. The RFID tag according to claim 30, wherein said tag is adapted to transmit backscatter RF signal with elements of said stored data from said antenna in response to an interrogating RF signal incident on said antenna from said at least one RFID reader.

32. The RFID tag according to claim 25, wherein the size of said antenna is smaller than one-half wavelength of the RF communication frequency designated for operation of said tag.

33. A method of enabling a vehicle to be detected automatically as being authorized for passage through a restricted lane equipped with a RFID reader, which comprises the step of making available to the vehicle a RFID tag in the form of a planar compact sticker that incorporates a storage medium programmed with authorization data that identifies the vehicle as being permitted to pass through said lane without stopping, said sticker further including a small aperture antenna implemented as a polygon with central aperture for optimized communication of the stored authorization data from said antenna in a backscatter RF signal in response to an interrogating RF signal from said RFID reader when within RF communication range of said RFID tag.

34. The method according to claim 33, including the step of affixing said sticker to the windshield of the vehicle.

35. The method according to claim 33, wherein said restricted lane is for vehicle passage to or from a parking facility.

36. The method according to claim 33, wherein said storage medium is programmed with authorization data that uniquely identifies the vehicle as being permitted to pass through said lane.

37. The method according to claim 36, wherein said restricted lane is for vehicle passage to or from a secure facility.

38. The method according to claim 36, wherein said restricted lane is a payment collection lane for automatic debiting of payment due with each passage of the vehicle therethrough.

39. The method according to claim 36, wherein said restricted lane is a toll collection lane for automatic on-the-fly roadway toll collection with each passage of the vehicle therethrough.

40. The method according to claim 36, wherein said restricted lane is a track of a railway system for asset tracking by RFID tag identification of each passage of a railcar on said track past said RFID reader.

41. An antenna configuration, comprising a small aperture antenna formed as a polygon having electrically conductive sides on a major surface of an electrically insulative sheet, and at least a portion of an impedance matching circuit on said surface electrically connected to said polygon for coupling said antenna to a load, for substantial impedance matching over a band of frequencies in which said antenna is designed to operate.

42. The antenna configuration of claim 41, wherein said at least a portion of the impedance matching circuit comprises a pair of conductive elements projecting along said major surface in confronting spaced relation from substantially opposite sides of said polygon into a central opening of said polygon constituting the aperture of said antenna.

43. The antenna configuration of claim 42, including a second pair of conductive elements constituting a substantial mirror image of the first-mentioned pair of conductive elements of the impedance matching circuit, said second pair overlying the opposite major surface of said sheet for coupling as a feed to the load when placed in or adjacent the gap formed by the confronting spaced relation of said second pair of elements.

44. The antenna configuration of claim 43, wherein said second pair of elements is capacitively coupled to the first-mentioned pair of elements of the impedance matching circuit through the dielectric of said insulative sheet.

45. The antenna configuration of claim 43, wherein the combination of said small aperture antenna and said impedance matching circuit is adapted to optimize power delivery to a load having a highly reactive impedance.

46. The antenna configuration of claim 43, wherein said load is the electronics of a RFID tag.