Radio frequency identification tag

• US 20050024287A1
• Filed: 05/28/2004
• Published: 02/03/2005
• Est. Priority Date: 05/29/2003
• Status: Active Grant

• Current Assignee: SkyCross Co., Ltd.
• Original Assignee: SkyCross, Inc.
• Inventors: Caimi, Frank M., Jo, Young-Min, Tornatta, Paul A. Jr., Farrar, John Charles
• Granted Patent: US 7,336,243 B2
• Time in Patent Office: Days
• US Class Current: 343/822
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• 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 19/07786 the antenna being of the HF type, such as a dipole
• 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 1/36 Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewithH01Q1/08, H01Q1/14 take precedence
• CPC Class Codes: H01Q 9/16 with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole H01Q9/44 takes precedence
• CPC Class Codes: H01Q 9/285 Planar dipole H01Q9/065 takes precedence; patch antenna H01Q9/0407

Abstract

A radio frequency identification tag attached to an object and comprising an antenna and an integrated circuit for providing object information to a separate reader. The antenna further comprises a pair of meanderline transmission lines each terminated at a first end for conductive connection to the integrated circuit. A shorting bar connected between the pair of meanderline transmission lines at the first ends is operative to match an antenna impedance with an integrated circuit impedance.

Claims

1. A radio frequency transponder comprising:

a substrate;

an integrated circuit disposed on the substrate

an antenna disposed on the substrate and coupled to the integrated circuit, the antenna having a physical length and an electrical length greater than the physical length and exhibiting an antenna input impedance; and

an impedance transformation element connected to the antenna for substantially matching the antenna input impedance to an impedance of the integrated circuit.

2. The radio frequency transponder of claim 1 wherein the impedance transformation element includes a shorting loop in parallel electrical orientation with the integrated circuit.

3. The radio frequency transponder of claim 1 wherein an integrated circuit impedance includes a real and a reactive component, and wherein the impedance transformation element transforms the real component to substantially match a real impedance component of the antenna and substantially cancels the reactive component at or near an antenna resonant frequency.

4. The radio frequency transponder of claim 1 wherein the antenna further comprises a conductive structure further comprising abrupt structural transitions.

5. The radio frequency transponder of claim 4 wherein an effective aperture of the antenna is increased by the abrupt structural transitions.

6. The radio frequency transponder of claim 1 wherein the antenna comprises first and second slow wave conductors configured in a spaced-apart parallel orientation.

7. The radio frequency transponder of claim 6 wherein the antenna further comprises a first and a second conductive pad disposed at a first end of each of the first and the second slow wave conductors.

8. The radio frequency transponder of claim 7 wherein the antenna further comprises a third and a fourth conductive pad disposed at a second end of each of the first and the second slow wave conductors, and wherein the integrated circuit is electrically connected between the third and the fourth conductive pads.

9. The radio frequency transponder of claim 8 wherein the impedance transformation element comprises a conductive element electrically connected between the third and the fourth conductive pads.

10. The radio frequency transponder of claim 9 wherein the conductive element further comprises conductive strip.

11. The radio frequency transponder of claim 6 wherein the first slow wave conductor comprises a first meanderline conductor and the second slow wave conductor comprises a second meanderline conductor.

12. The radio frequency transponder of claim 6 wherein the antenna comprises a substantially U-shaped structure, and wherein a first leg of the U-shaped structure comprises the first slow wave conductor and a first conductive pad disposed at a free end of the first slow wave conductor, and wherein a second leg of the U-shaped structure comprises the second slow wave conductor and a second conductive pad disposed at a free end of the second slow wave structure, and wherein the integrated circuit is disposed on a connecting bar of the U-shaped structure between the first and the second legs thereof.

13. The radio frequency transponder of claim 6 wherein each one of the first and the second slow wave conductors comprises a plurality of undulating segments, and wherein current flow in certain ones of the plurality of undulating segments of the first slow wave conductor is in the same direction as current flow in certain ones of the plurality of undulating segments of the second slow wave conductor.

14. The radio frequency transponder of claim 13 wherein current flow in the plurality of undulating segments of the first and the second slow wave conductors comprises axial current flow or radial current flow relative to the orientation of the first and the second slow wave conductors, and wherein the axial current flow produces a polarized signal along a first axis and the radial current flow produces a polarized signal along a second axis.

15. The radio frequency transponder of claim 1 wherein the impedance transformation element provides a conductive path in parallel with the integrated circuit for discharging electrostatic charge from the integrated circuit.

16. A U-shaped antenna comprising:

first and second conductive pads;

a first slow wave conductor in electrical communication with the first conductive pad forming a first leg of the U-shaped antenna;

a second slow wave conductor in electrical communication with the second conductive pad forming a second leg of the U-shaped antenna; and

a bridging conductor disposed between the first and the second slow wave conductors for completing the U-shaped antenna.

17. The antenna of claim 16 wherein a material of the first and the second slow wave conductors and a material of the first and the second conductive pads comprises conductive material further comprising one or more abrupt transitions formed therein.

18. The antenna of claim 16 wherein a effective aperture of the antenna is increased by the abrupt transitions.

19. The antenna of claim 16 wherein the first and the second conductive pads comprise a generally rectangular shape.

20. The antenna of claim 16 wherein the first and the second slow wave conductors comprise first and second meanderline transmission lines.

21. The antenna of claim 20 wherein each of the first and the second meanderline transmission lines comprises a plurality of undulating conductive segments, and wherein current flow in certain ones of the plurality of undulating segments of the first meanderline transmission line is in the same direction as current flow in certain ones of the plurality of undulating segments of the second meanderline transmission line.

22. The antenna of claim 21 wherein current flow in the plurality of undulating segments of the first and the second meanderline transmission lines comprises axial current flow in a direction of the first and the second legs of the U-shaped antenna or radial current flow perpendicular to the first and the second legs of the U-shaped antenna, and wherein the axial current flow produces a polarized signal in a first direction and the radial current flow produces a polarized signal in a second direction.

23. The antenna of claim 22 wherein current flow is in a same direction in the first and the second conductive pads.

24. The antenna of claim 16 wherein each one of the first and the second slow wave conductors exhibits an electrical length greater than a physical length.

25. An antenna comprising a slow wave section and a radiating section, wherein the slow wave section is located at or near a current minimum at or near a resonant frequency so as to reduce heating losses and improve radiation efficiency of the antenna.

26. An antenna responsive to a transmitting/receiving component, comprising:

first and second spaced-apart slow wave conductors each including first and second terminal ends thereof;

a first pad connected to the first terminal end of the first slow wave conductor;

a second pad connected to the first terminal end of the second slow wave conductor; and

wherein the transmitting/receiving component is electrically connected between the first and the second pads.

27. The antenna of claim 26 wherein the first and the second slow wave conductors are disposed in a substantially parallel orientation.

28. The antenna of claim 26 for transmitting and receiving electromagnetic energy, wherein current flow is in a substantially same direction in the first and the second pads, and wherein the first and the second pads comprise the primary radiating elements of the antenna.

29. The antenna of claim 26 further comprising a third pad connected to the second terminal end of the first slow wave conductor and a fourth pad connected to the second terminal end of the second slow wave conductor.

30. The antenna of claim 26 further comprising a conductive segment electrically connected between the first and the second pads.

31. The antenna of claim 30 wherein the conductive segment is disposed in an electrically parallel relation to the transmitting/receiving component.

32. The antenna of claim 31 wherein an impedance of the transmitting/receiving component impedance includes a real component and a reactive component, and wherein the conductive segment transforms the real component to substantially match a real impedance of the antenna and substantially cancels the reactive component at or near an antenna operating frequency.

33. The antenna of claim 30 wherein the conductive segment provides a low impedance electrical path around the transmitting/receiving component for limiting electrostatic discharge into the transmitting/receiving component.

34. The antenna of claim 30 wherein the conductive segment and the transmitting/receiving component each exhibit an impedance, and wherein the electrical properties of the conductive segment are determined to substantially match the transmitting/receiving component impedance to the impedance seen by the transmitting/receiving component at or near an antenna operating frequency.

35. The antenna of claim 26 wherein the first and the second slow wave conductors and the first and second pads comprise one or more linear edges.

36. The antenna of claim 26 wherein the first and the second slow wave conductors and the first and second pads comprise abrupt structural transitions for increasing an effective antenna aperture.

37. The antenna of claim 26 wherein the first and the second pads each comprise a rectangular shaped pad.

38. The antenna of claim 26 wherein the first slow wave conductor comprises a first meanderline transmission line and the second slow wave conductor comprises a second meanderline transmission line.

39. The antenna of claim 38 wherein each one of the first and the second meanderline transmission lines comprises a plurality of undulating conductive segments, and wherein current flow in certain ones of the plurality of undulating conductive segments of the first meanderline transmission line is in the same direction as current flow in certain ones of the plurality of undulating conductive segments of the second meanderline transmission line.

40. The antenna of claim 26 wherein the antenna comprises an electrical length greater than a physical length.

41. The antenna of claim 26 wherein the transmitting/receiving component is physically disposed between the first and the second pads.

42. An antenna having a resonant frequency and responsive to a transmitting/receiving component, comprising:

first and second spaced-apart slow wave conductors each including first and second terminal ends thereof, at least one of the first and the second slow wave conductors including a conductive tuning region, wherein the resonant frequency is responsive to an area of the conductive tuning region;

a first pad connected to the first terminal end of the first slow wave conductor;

a second pad connected to the first terminal end of the second slow wave conductor; and

wherein the transmitting/receiving component is electrically connected between the first and the second pads.

43. The antenna of claim 42 wherein the first and second slow wave conductors each further comprise undulating segments, and wherein the first slow wave conductor comprises a first conductive tuning region and the second slow wave conductor comprises a second conductive tuning region, and wherein the first and the second tuning regions are each disposed between two successive segments of the first slow wave conductor, and wherein the second conductive tuning region is disposed between two successive segments of the second slow wave conductor.

44. The antenna of claim 42 wherein the first and second slow wave conductors each further comprise undulating segments and wherein the first slow wave conductor comprises a first conductive tuning region and the second slow wave conductor comprises a second conductive tuning region, and wherein the first conductive tuning region is disposed between the first pad and an adjacent undulating segment of the first slow wave conductor, and wherein the second conductive tuning region is disposed between the second pad and an adjacent undulating segment of the second slow wave conductor.

45. The antenna of claim 42 further comprising a third pad connected to the first terminal end of the first slow wave conductor and a fourth pad connected to the first terminal end of the second slow wave conductor, and wherein the first and second slow wave conductors each further comprise undulating segments, and wherein the first slow wave conductor comprises a first conductive tuning region disposed between the third pad and an adjacent undulating segment of the first slow wave conductor, and wherein the second slow wave conductor comprises a second conductive tuning region disposed between the fourth pad and an adjacent undulating segment of the second slow wave conductor.

46. An item identification system comprising:

a radio frequency transponder affixed to an object comprising;

a substrate;

a transmitting/receiving element disposed on the substrate

an antenna disposed on the substrate and coupled to the transmitting/receiving element, the antenna having a physical length and an electrical length greater than the physical length and exhibiting an antenna input impedance;

an impedance transformation element connected to the antenna for substantially matching the antenna input impedance to an impedance of the transmitting/receiving element; and

an interrogation device for transmitting information to and receiving information from the transponder.

47. The item identification system of claim 46 wherein the antenna exhibits a substantially omnidirectional radiation pattern for receiving information from and transmitting information to the transponder for reducing signal degradation effects related to physical orientation of the transponder relative to the interrogation device.

48. The system of claim 46 wherein the antenna comprises first and second slow wave conductors configured in a spaced-apart parallel orientation.

49. The system of claim 48 wherein the antenna further comprises a first and a second conductive pad disposed at a first end of each of the first and the second slow wave conductors and a third and a fourth conductive pad disposed at a second end of each of the first and the second slow wave conductors, and wherein the transmitting/receiving element is connected between the first and the second conductive pads.

50. The system of claim 49 wherein the impedance transformation element comprises a conductive element electrically connected between the first and the second conductive pads.

51. The system of claim 52 wherein the information relates to a condition of the object.

52. The system of claim 46 wherein the antenna exhibits an electrical length greater than a maximum substrate dimension.

53. The system of claim 46 wherein the antenna comprises first and second slow wave conductors configured in a spaced-apart parallel orientation providing first and second current flow paths, wherein the antenna further comprises a frequency tuning element for changing an electrical length of one or both of the first and the second slow wave conductors such that a current path length is changed thereby.

54. The system of claim 53 wherein the current path length is determined in response to object properties that affect a resonant frequency of the antenna.

55. The system of claim 54 wherein the current path length is selected to provide operation of the transponder at a predetermined resonant frequency.

56. A radio frequency tag comprising:

a conductive sheet having a plurality of shaped contiguous openings formed therein, wherein the openings form first and second parallel spaced-apart meanderline transmission lines, first and second apertures disposed at a first terminal end of each of the first and the second meanderline transmission lines, respectively, and third and fourth apertures disposed at a second terminal end of each of the first and the second meanderline transmission lines, respectively, and a bridge opening connecting the first and the second apertures; and

an integrated circuit electrically connected to the conductive sheet and bridging the bridge opening.

57. The tag of claim 56 wherein the first and the second meanderline transmission lines comprises a plurality of undulating segments.

58. The tag of claim 56 wherein the first, second, third and fourth apertures each comprise an opening having a polygonal, circular or elliptical shape.

59. An antenna comprising:

a conductive sheet having a plurality of shaped openings formed therein, wherein the openings form first and second parallel spaced-apart meanderline transmission lines, first and second apertures disposed at first terminal ends of the first and the second meanderline transmission lines, respectively, and third and fourth apertures disposed at second terminal ends of the first and the second meanderline transmission lines, respectively, and a bridging opening connecting the first and the second apertures.