Tamper-indicating radio frequency identification antenna and sticker, a radio frequency identification antenna, and methods of using the same Number:7,102,522 from the United States Patent and Trademark Office (PTO) owispatent A tamper-indicating radio frequency identification device made of densified metal powder and to a sticker including the same device. The present invention also relates to radio frequency identification antenna made of densified metal powder and to a sticker including the same antenna. The present invention also relates to methods of indicating that a radio frequency identification antenna or sticker has been tampered with.<H identification, indicating, Tamper, indicati, 7102522.html, Patent, pto, 7102522

Title: Tamper-indicating radio frequency identification antenna and sticker, a radio frequency identification antenna, and methods of using the same

Abstract: A tamper-indicating radio frequency identification device made of densified metal powder and to a sticker including the same device. The present invention also relates to radio frequency identification antenna made of densified metal powder and to a sticker including the same antenna. The present invention also relates to methods of indicating that a radio frequency identification antenna or sticker has been tampered with.

Patent Number: 7,102,522 Issued on 09/05/2006 to Kuhns

Inventors: Kuhns; David W. (Minneapolis, MN)
Assignee: 3M Innovative Properties Company (St. Paul, MN)

Appl. No.: 10/328,989

Filed: December 24, 2002

Current U.S. Class: 340/572.7 ; 340/572.1; 340/572.6; 343/700MS; 343/790; 343/880; 343/895

Current International Class: G08B 13/14 (20060101)

Field of Search: 340/572.7,571.1,572.6,572.1 235/492 343/700MS,790,880,895

References Cited [Referenced By]

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Primary Examiner: Nguyen; Tai T.
Attorney, Agent or Firm: Buss; Melissa E.

Claims

What is claimed is:

1. A tamper-indicating radio frequency identification device, comprising: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder.

2. The tamper-indicating radio frequency identification device of claim 1, wherein the antenna responds to a signal, and wherein after the tamper-indicating radio frequency identification antenna is bent equal to or less than a radius of 25 mm, the tamper-indicating radio frequency identification antenna does not respond to the signal.

3. The tamper-indicating radio frequency identification device of claim 2, wherein the signal is sent a distance greater than 15 cm from the tamper-indicating radio frequency identification antenna.

4. The tamper-indicating radio frequency identification device of claim 1, wherein the antenna is readable by an interrogator, and wherein after the tamper-indicating radio frequency identification antenna is bent equal to or less than a radius of 25 mm, the tamper-indicating radio frequency identification antenna is not readable by the interrogator.

5. The tamper-indicating radio frequency identification device of claim 4, wherein the interrogator is at distance greater than 15 cm from the antenna.

6. The tamper-indicating radio frequency identification device of claim 1, wherein the antenna includes a resistance, and wherein the resistance of the antenna increases when the antenna is bent equal to or less than a radius of 25 mm.

7. The tamper-indicating radio frequency identification device of claim 6, wherein the resistance of the antenna significantly increases when the antenna is bent equal to or less than a radius of 25 mm.

8. The tamper-indicating radio frequency identification device of claim 1, wherein the conductivity of the antenna is reduced when the antenna is bent equal to or less than a radius of 25 mm.

9. The tamper-indicating radio frequency identification device of claim 1, wherein the conductivity of the antenna is significantly reduced when the antenna is bent equal to or less than a radius of 25 mm.

10. The tamper-indicating radio frequency identification device of claim 1, wherein the antenna is conductive, and wherein the antenna is nonconductive after the antenna is bent equal to or less than a radius of 25 mm.

11. The tamper-indicating radio frequency identification device of claim 1, wherein after the antenna is bent equal to or less than a radius of 25 mm, the antenna comprises a fracture.

12. The tamper-indicating radio frequency identification device of claim 11, wherein the fracture is small or hidden by the substrate so that it is not visible to the naked eye.

13. The tamper-indicating radio frequency identification device of claim 1, wherein the antenna comprises a conductive pattern, and wherein the conductive pattern delaminates after the antenna is bent equal to or less than a radius of 25 mm.

14. The tamper-indicating radio frequency identification device of claim 1, wherein the substrate is selected from the group consisting of paper and materials that are at least about 10% compressible.

15. The tamper-indicating radio frequency identification device of claim 14, wherein the materials that are at least 10% compressible are selected from the group consisting of microporous materials, nonwoven materials and woven materials.

16. The tamper-indicating radio frequency identification device of claim 1, wherein the densified metal powder is selected from the group consisting of copper, tin, lead, silver, gold, platinum, aluminum, nickel, iron, steel, zinc and alloys and combinations thereof.

17. The tamper-indicating radio frequency identification device of claim 1, wherein the antenna is a loop antenna.

18. The tamper-indicating radio frequency identification device of claim 1, wherein the antenna is a dipole antenna.

19. The tamper-indicating radio frequency identification device of claim 1 further comprising a protective layer on the antenna.

20. A tamper-indicating radio frequency identification sticker, comprising: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate.

21. The tamper-indicating radio frequency identification sticker of claim 20, wherein the first layer of adhesive is attached to the second major surface of the substrate.

22. The tamper-indicating radio frequency identification sticker of claim 20 further comprising a layer of retroreflective material including a first major surface and a second major surface opposite the first major surface, wherein the first major surface is attached to the first layer of adhesive.

23. The tamper-indicating radio frequency identification sticker of claim 22 further comprising a second layer of adhesive attached to the second major surface on of the layer of retroreflective material.

24. The tamper-indicating radio frequency identification sticker of claim 23 further comprising a liner on the second layer of adhesive.

25. The tamper-indicating radio frequency identification sticker of claim 20, wherein the first layer of adhesive is attached to the antenna.

26. The tamper-indicating radio frequency identification sticker of claim 25 further comprising a layer of retroreflective material including a first major surface and a second major surface opposite the first major surface, wherein the second major surface is attached to the first layer of adhesive.

27. The tamper-indicating radio frequency identification sticker of claim 22 further comprising a second layer of adhesive attached to the second major surface on of the layer of retroreflective material.

28. The tamper-indicating radio frequency identification sticker of claim 27 further comprising a liner on the second layer of adhesive.

29. The tamper-indicating radio frequency identification sticker of claim 20 further comprising a layer of retroreflective material attached adjacent to the sticker.

30. The tamper-indicating radio frequency identification sticker of claim 20 further comprising an indicia printed on the sticker.

31. The tamper-indicating radio frequency identification sticker of claim 20, wherein the first adhesive layer comprises a first adhesive portion and a second adhesive portion, wherein the first adhesive portion includes a first adhesion strength, wherein the second adhesive portion includes a second adhesive strength, and wherein the second adhesive strength is greater than the first adhesive strength.

32. The tamper-indicating radio frequency identification sticker of claim 20 further comprising a layer of tamper-indicating optical material attached to the sticker.

33. The tamper-indicating radio frequency identification sticker of claim 32, wherein the layer of tamper-indicating optical material includes a first major surface and a second major surface opposite the first major surface, and wherein the first layer of adhesive is attached to the second major surface onto substrate and is attached to the first major surface of the layer of tamper-indicating optical material.

34. The tamper-indicating radio frequency identifications ticker of claim 32, wherein the layer of tamper-indicating optical material includes a first major surface and a second major surface opposite the first major surface, and wherein the first layer of adhesive is attached to the antenna and is attached to the second major surface of the layer of tamper-indicating optical material.

35. The tamper-indicating radio frequency identification sticker of claim 32, wherein after the sticker is removed from a surface, the layer of tamper-indicating optical material visibly indicates the sticker was removed from the surface.

36. The tamper-indicating radio frequency identification sticker of claim 20 further comprising a second integrated circuit attached to the substrate, wherein the second integrated circuit includes an antenna.

37. The tamper-indicating radio frequency identification sticker of claim 36, wherein the second integrated circuit comprises a radio frequency identification antenna.

38. The tamper-indicating radio frequency identification sticker of claim 20, wherein the antenna responds to a signal, and wherein after the tamper-indicating radio frequency identification antenna is bent equal to or less than a radius of 25 mm, the tamper-indicating radio frequency identification antenna does not respond to the signal.

39. The tamper-indicating radio frequency identification sticker of claim 38, wherein the signal is sent from a distance greater than 15 mm.

40. The tamper-indicating radio frequency identification sticker of claim 20, wherein the antenna is readable by an interogator, and wherein after the tamper-indicating radio frequency identification antenna is bent equal to or less than a radius of 25 mm, the tamper-indicating radio frequency identification antenna is not readable by the interrogator.

41. The tamper-indicating radio frequency identification sticker of claim 40, wherein the interrogator is at distance greater than 15 cm from the antenna.

42. The tamper-indicating radio frequency identification sticker of claim 20, wherein the antenna includes a resistance, and wherein the resistance of the antenna increases when the antenna is bent equal to or less than a radius of 25 mm.

43. The tamper-indicating radio frequency identification sticker of claim 42, wherein the resistance of the antenna is significantly increases when the antenna is bent equal to or less than a radius of 25 mm.

44. The tamper-indicating radio frequency identification slicker of claim 20, wherein the conductivity of the antenna is reduced when the antenna is bent equal to or less then a radius of 25 mm.

45. The tamper-indicating radio frequency identification sticker of claim 44, wherein the conductivity of the antenna is significantly reduced when the antenna is bent equal to or less than a radius of 25 mm.

46. The tamper-indicating radio frequency identification sticker of claim 45, wherein the antenna is conductive, and wherein the antenna is nonconductive after the antenna is bent equal to or less than a radius of 25 mm.

47. The tamper-indicating radio frequency identification slicker of claim 20, wherein after the antenna is bent equal to or less than a radius of 25 mm, the antenna comprises a fracture.

48. The tamper-indicating radio frequency identification sticker of claim 47, wherein the fracture is not visible to the naked eye.

49. The tamper-indicating radio frequency identification sticker of claim 20, wherein the antenna comprises a conductive pattern, and wherein the conductive pattern delaminates alter the antenna is bent equal to or less than a radius of 25 mm.

50. A method of indicating a radio frequency identification sticker has been tampered, comprising steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, wherein the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; a radio frequency identification antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; sending a signal to the tamper-indicating radio frequency identification sticker attached to the first surface; receiving a response from the antenna; removing the tamper-indicating radio frequency identification sticker from the first surface; and sending the signal to the tamper-indicating radio frequency identification sticker and not receiving a response from the antenna.

51. The method of claim 50, wherein the removing step comprises bending the tamper-indicating radio frequency identification antenna less than a radius of 25 mm.

52. The method of claim 50, wherein the sending step comprises sending the signal from a distance greater than 15 cm from the tamper-indicating radio frequency identification sticker.

53. The method of claim 50, comprising after the removing step, the step of: attaching the tamper-indicating radio frequency identification sticker to a second surface.

54. The method of indicating a radio frequency identification sticker has been tampered, comprising the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, wherein the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; a radio frequency identification antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; measuring a first resistance in the antenna; bending the tamper-indicating radio frequency identification sticker less than a radius of 25 mm; and measuring a second resistance in the antenna that is higher than the first resistance of the antenna.

55. The method of claim 54, wherein the second resistance in the antenna is significantly higher than the first resistance of the antenna.

56. The method of claim 54 wherein the bending step comprises removing the tamper-indicating radio frequency identification sticker front the first surface.

57. The method of claim 56, further comprising, after the bending and removing step, the step of: attaching the tamper-indicating radio frequency identification sticker to second surface.

58. A method of indicating a radio frequency identification sticker has been tampered, comprising the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, wherein the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; a radio frequency identification antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; measuring a first conductivity in the antenna; bending the tamper-indicating radio frequency identification sticker less than or equal to a radius of 25 mm; and measuring a second conductivity in the antenna that is lower than the first conductivity of the antenna.

59. The method of claim 58, wherein the second conductivity in the antenna is significantly lower than the first conductivity of the antenna.

60. The method of claim 58 wherein the bending step comprises removing the tamper-indicating radio frequency identification sticker from the first surface.

61. The method of claim 60, further comprising, after the bending and removing step, the step of: attaching the tamper-indicating radio frequency identification slicker to a second surface.

62. A method of indicating a radio frequency identification sticker has been tampered, comprising the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, wherein the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; a radio frequency identification antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; measuring a first conductivity in the antenna; bending the tamper-indicating radio frequency identification sticker less than or equal to a radius of 25 mm; and measuring a second conductivity that indicates that the antenna is nonconductive.

63. The method of claim 62 wherein the bending step comprises removing the tamper-indicating radio frequency identification sticker from the first surface.

64. The method of claim 63, further comprising, after the bending and removing step, the step of: attaching the tamper-indicating radio frequency identification sticker to a second surface.

65. A method of indicating a radio frequency identification sticker has been tampered, comprising the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, wherein the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; a radio frequency identification antenna attached to the first major surface of the substrate wherein said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; bending the tamper-indicating radio frequency identification sticker less than or equal to a radius of 25 mm; and forming a fracture in the radio frequency identification antenna.

66. The method of claim 65 wherein the bending step comprises removing the tamper-indicating radio frequency identification sticker from the first surface.

67. The method of claim 66, further comprising, after the bending and removing step, the step of; attaching the tamper-indicating radio frequency identification sticker to a second surface.

68. A method of indicating a radio frequency identification sticker has been tampered, comprising the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, wherein the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; a first radio frequency identification antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; a second integrated circuit attached to the substrate, wherein the second integrated circuit comprises a second antenna; and a first layer of adhesive attached to the substrate; sending a signal to the tamper-indicating radio frequency identification sticker attached to the first surface; receiving a response from the first antenna and from the second antenna; removing the tamper-indicating radio frequency identification sticker from the first surface; sending the signal to the tamper-indicating radio frequency identification sticker; and receiving a signal from the second antenna and not receiving a response from the first antenna.

69. The method of claim 63, further comprising, after the removing step, the step of: attaching the tamper-indicating radio frequency identification sticker to a second surface.

70. A tamper-indicating radio frequency identification sticker, comprising: a substrate including a first major surface and a second major surface opposite the first major surface, wherein the substrate is selected from the group consisting of paper and materials that are at least about 10% compressible, and wherein the materials that are at least 10% compressible are selected from the group consisting of microporous materials, nonwoven materials and woven materials; and a radio frequency identification loop antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder, wherein the densified metal powder is selected from the group consisting of copper, tin, lead, silver, gold, platinum, aluminum, nickel, iron, steel, zinc and alloys and combinations thereof; and wherein the metal powder comprises metal particles in the shape of spheres, oblongs, and polyhedra; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; wherein the antenna responds to a signal sent a distance greater than 15 cm from the tamper-indicating radio frequency identification sticker, and wherein after the tamper-indicating radio frequency identification sticker is bent equal to or less than a radius of 25 mm, the tamper-indicating radio frequency identification loop antenna does not respond to the signal and the antenna comprises a fracture that is not visible to the naked eye.

71. A radio frequency identification antenna, comprising: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, wherein said antenna comprises densified metal powder.

72. The radio frequency identification antenna of claim 71, wherein the substrate is selected from the group consisting of paper and materials that are at least about 10% compressible.

73. The radio frequency identification antenna of claim 72, wherein the materials that are at least 10% compressible are selected from the group consisting of microporous materials, nonwoven materials and woven materials.

74. The radio frequency identification antenna of claim 71, wherein the densified metal powder is selected from the group consisting of copper, tin, lead, silver, gold, platinum, aluminum, nickel, iron, steel, zinc and alloys and combinations thereof.

75. The radio frequency identification antenna of claim 71, wherein the antenna is a loop antenna.

76. The radio frequency identification antenna of claim 71, wherein the antenna is a dipole antenna.

77. The radio frequency identification antenna of claim 71 further comprising a protective layer on the antenna.

78. A radio frequency identification sticker comprising a radio frequency identification antenna of claim 71, and further comprising: a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate.

79. The A radio frequency identification sticker of claim 78, further comprising a layer of retroreflective material including a first major surface and a second major surface opposite the first major surface, wherein the second major surface is attached to the first layer of adhesive.

Description

TECHNICAL FIELD

The present invention relates to a tamper-indicating radio frequency identification device made of densified metal powder and to a sticker including the same antenna. The present invention also relates to radio frequency identification antenna made of densified metal powder and to a sticker including the same antenna. The present invention also relates to methods of indicating that a radio frequency identification antenna or sticker has been tampered with.

BACKGROUND OF THE INVENTION

Radio frequency identification technology has become widely used in virtually every industry, including transportation, manufacturing, waste management, postal tracking, airline baggage reconciliation, and highway toll management. An RFID system is made up of two components, the transponder and the interrogator or reader. The essential components of a transponder are the data carrying device--generally referred to as an integrated circuit or an electronic microchip, and a coupling element--such as an antenna. A transponder that contains its own power supply, generally a battery, is know as an active tag, while a transponder that does not contain its own power supply is known as a passive tag, sticker or label. The interrogator or reader contains a radio frequency module (transmitter and receiver), a control unit and a coupling element--an antenna. Power and data exchange between the transponder and the interrogator are achieved through magnetic or electromagnetic fields.

An example of a radio frequency identification sticker is disclosed in U.S. Pat. No. 6,121,880 (Scott et al.), "Sticker Transponder for Use on Glass Surface." This patent discloses a sticker transponder adapted to be affixed to a glass surface, such as a vehicle windshield, including a RFID transponder enabling the storage and retrieval of vehicle related data. The sticker transponder comprises a flexible circuit substrate having an antenna formed thereon and a transponder circuit disposed on the substrate and coupled to the antenna. An adhesive layer is coupled to a first surface of the flexible circuit substrate. An indicia layer is coupled to a second surface of the flexible circuit opposite from the first surface. The indicia layer comprises a space permitting indicia to be printed thereon. The antenna has a characteristic impedance defined in part by a dielectric constant of the glass surface. As a result, a proper impedance match between the antenna and the transponder circuit is achieved only when the sticker is affixed to the glass surface. The sticker transponder further comprises a release liner affixed to the adhesive layer, the release liner being selectively removable to permit the sticker transponder to be affixed to the glass surface. The transponder circuit further includes a memory having a read-only portion and a re-writable portion.

An example of a tamper indicating radio frequency identification label is disclosed in PCT Publication WO 01/71848A1 (Atherton), "A Tamper Indicating Radio Frequency Identification Label." This publication discloses a label which may include RFID components and a tamper track coupled to the RFID components. The tamper track should be constructed from a destructible conducting path. Additionally, the tamper rack can be formed such that it is damaged when the label is tampered. In one embodiment, adhesion characteristics of the tamper track (102) are adapted to break apart the tamper track when the label is tampered, for example, by removal from an object. The RFID components may retain their RF capability and detect when the tamper track (102) has been damaged to indicate that the label has been tampered. Alternatively, the RFID capability of the RFID components may be disabled when the tamper track is damaged, indicating tampering.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a tamper-indicating radio frequency identification device. The radio frequency identification device comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder. In one preferred embodiment of the above tamper-indicating radio frequency identification device, the antenna responds to a signal, and after the tamper-indicating radio frequency identification antenna is bent equal to or less than a radius of 25 mm, the tamper-indicating radio frequency identification antenna does not respond to the signal.

Another aspect of the present invention provides a tamper-indicating radio frequency identification sticker. The tamper-indicating radio frequency identification sticker comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate. In one preferred embodiment of the above tamper-indicating radio frequency identification sticker, the antenna responds to a signal, and after the tamper-indicating radio frequency identification antenna is bent equal to or less than a radius of 25 mm, the tamper-indicating radio frequency identification antenna does not respond to the signal.

Another aspect of the present invention provides a method of indicating that a radio frequency identification sticker has been tampered. The method comprises the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, where the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; sending a signal to the tamper-indicating radio frequency identification sticker attached to the first surface; receiving a response from the antenna, removing the tamper-indicating radio frequency identification sticker from the first surface; and sending the signal to the tamper-indicating radio frequency identification sticker and not receiving a response from the antenna. In one preferred embodiment of the above method, the removing step comprises bending the tamper-indicating radio frequency identification antenna less than or equal to a radius of 25 mm.

Yet another aspect of the present invention provides an alternative method of indicating a radio frequency identification sticker has been tampered. This method comprises the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, where the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; measuring a first resistance in the antenna; bending the tamper-indicating radio frequency identification sticker less than or equal to a radius of 25 mm; and measuring a second resistance in the antenna that is higher than the first resistance of the antenna.

Another aspect of the present invention provides another alternative method of indicating a radio frequency identification sticker has been tampered. This method comprises the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, where the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; measuring a first conductivity in the antenna; bending the tamper-indicating radio frequency identification sticker less than or equal to a radius of 25 mm; and measuring a second conductivity in the antenna that is lower than the first conductivity of the antenna.

Another aspect of the present invention provides yet another alternative method of indicating a radio frequency identification sticker has been tampered. This method comprises the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, where the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; measuring a first conductivity in the antenna; bending the tamper-indicating radio frequency identification sticker less than or equal to a radius of 25 mm; and measuring a second conductivity that indicates that the antenna is nonconductive.

Another aspect of the present invention provides another alternative method of indicating a radio frequency identification sticker has been tampered. This method comprises the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, where the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; bending the tamper-indicating radio frequency identification sticker less than or equal to a radius of 25 mm; and forming a fracture in the radio frequency identification antenna.

Another aspect of the present invention provides another alternative method of indicating a radio frequency identification sticker has been tampered. The method comprises the steps of: attaching a tamper-indicating radio frequency identification sticker to a first surface, where the tamper-indicating radio frequency identification sticker, comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a first radio frequency identification antenna attached to the first major surface of the substrate where said antenna comprises densified metal powder; a first integrated circuit attached to the antenna; a second integrated circuit attached to the substrate, where the second integrated circuit comprises a second antenna; and a first layer of adhesive attached to the substrate; sending a signal to the tamper-indicating radio frequency identification sticker attached to the first surface; receiving a response from the first antenna and the second antenna; removing the tamper-indicating radio frequency identification sticker from the first surface; sending the signal to the tamper-indicating radio frequency identification sticker; and receiving a signal from the second antenna and not receiving a response from the first antenna.

Another aspect of the present invention provides a tamper-indicating radio frequency identification sticker. The tamper-indicating radio frequency identification sticker comprises: a substrate including a first major surface and a second major surface opposite the first major surface, where the substrate is selected from the group consisting of paper and materials that are at least about 10% compressible, and where the materials that are at least 10% compressible are selected from the group consisting of microporous materials, nonwoven materials and woven materials; and a radio frequency identification loop antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder, where the densified metal powder is selected from the group consisting of copper, tin, lead, silver, gold, platinum, aluminum, nickel, iron, steel, zinc and alloys and combinations thereof; and where the metal powder comprises metal particles in the shape of spheres, oblongs, and polyhedra; a first integrated circuit attached to the antenna; and a first layer of adhesive attached to the substrate; where the antenna responds to a signal sent a distance greater than 15 cm from the tamper-indicating radio frequency identification sticker, and where after the tamper-indicating radio frequency identification sticker is bent equal to or less than or equal to a radius of 25 mm, the tamper-indicating radio frequency identification antenna does not respond to the signal and the antenna comprises a fracture that is not visible to the naked eye.

Yet another aspect of the present invention provides a radio frequency identification antenna. The radio frequency identification antenna comprises: a substrate including a first major surface and a second major surface opposite the first major surface; and a radio frequency identification antenna attached to the first major surface of the substrate, where said antenna comprises densified metal powder.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further explained with reference to the appended Figures, wherein like structure is referred to by like numerals throughout the several views, and wherein:

FIG. 1 is a top view of one embodiment of a radio frequency identification device;

FIG. 2 is a top view of one embodiment of a tamper-indicating radio frequency identification sticker including the device of FIG. 1;

FIG. 3a is cross-sectional view of the tamper-indicating radio frequency identification sticker of FIG. 2 taken along line 3 in FIG. 2;

FIG. 3b is cross-sectional view of another embodiment of the tamper-indicating radio frequency identification sticker taken along line 3 in FIG. 2;

FIG. 4a is cross-sectional view of the tamper-indicating radio frequency identification sticker of FIG. 2 applied to a surface and a portion of the sticker is bent at a radius R.sub.1;

FIG. 4b is cross-sectional view of the tamper-indicating radio frequency identification sticker of FIG. 4a a portion of the sticker is bent at a radius R.sub.2, taken along line 4b in FIG. 6a;

FIG. 5a is a cross-sectional view of an alternative embodiment of the tamper-indicating radio frequency identification sticker taken along line 5 in FIG. 2;

FIG. 5b is a cross-sectional view of another alternative embodiment of the tamper-indicating radio frequency identification sticker taken along line 5 in FIG. 2;

FIG. 6a is a top view of the tamper-indicating radio frequency identification sticker of FIG. 4b with the adhesive layer removed for clarity; and

FIG. 6b a top view of another embodiment of a tamper-indicating radio frequency identification sticker with the adhesive layer removed for clarity.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates one preferred embodiment of a radio frequency identification ("RFID") device 10. The RFID device 10 includes a substrate 14, which has a first major surface 16 and a second major surface 18 opposite the first major surface (shown in FIG. 3a). The substrate 14 is preferably a compressible material. As used herein, compressible means that a substrate reduces in its dimension parallel to an applied pressure and that the total volume of the substrate is also reduced by a similar amount. When used herein as a quantitative measure, X % compressible means that the dimension of a substrate measured parallel to an applied pressure of 30 MPa is [(100-X)/100] times its dimension in this direction at 0.07 MPa and the total volume of the substrate at 30 MPa is [(100-X)/100] times its volume at 0.07 MPa. If the dimension change in the direction of the applied pressure and the volume change yield different values of X, then the smaller X of the two values is used to define the quantitative compressibility of the material. Preferably, following release of an applied pressure, substrates 14 still show dimension and volume changes of at least 10%, more preferably they show dimension and volume changes that are at least 50% of the percent compressibility observed at 30 MPa, and most preferably they maintain dimension and volume changes that are at least 75% of the percent compressibility achieved at 30 MPa.

Preferably, substrate 14 is made of paper and compressible fibrous and non-fibrous materials, including those manufactured from synthetic or naturally occurring polymers, or combinations thereof. Suitable forms of these substrates include nonwovens including dry-lay and wet-lay nonwovens, nonwovens made by melt-blown fiber, spun bond or spun lace processes, woven and knit fabrics, membranes, foams (preferably open-cell foams) and expanded webs, and webs comprised of cast fibers.

Paper is one preferred substrate 14 and a variety of papers are suitable, including, but not limited to, kraft paper, stationery paper, copier paper, filter paper, newsprint, cardstock, folder stock, printing paper, specialty papers, paper products such as pulp board and the like. Suitable papers may be made by various processes and may contain fillers, sizing agents, pigments, dyes, and others additives as known to those skilled in the art. Suitable papers may be calendered or non-calendered, processed to provide various finishes and coated or uncoated.

Suitable nonwoven substrates can include membranes or porous materials, such as, for example, ultrafiltration membranes, microporous materials, cast polymeric membranes, and thermally induced phase transition materials (TIPS), which are described in U.S. Pat. Nos. 4,247,498 and 4,867,881. One suitable substrate is a particle-filled, microporous material, commercially available from PPG Industries, Pittsburgh, Pa., under the trade designation Teslin. Teslin is described by its manufacturer as a dimensionally stable, polyolefin based, microporous, printing sheet with 60% of its weight including a non-abrasive filler and with 65% of its volume including air.

Suitable substrate materials may be fibrous and fiber-like materials including silk and cellulosic or lignocellulosic materials, such as for example, flax, hemp, cotton, jute, or synthetic cellulosic or lignocellulosic materials such as rayon.

Suitable substrates can be made from a variety of polymers, including thermoplastic, thermoset, elastomeric, and crosslinked polymers. Examples of suitable polymers include polyamides, polyurethanes, polyolefins (e.g., polyethylene and polypropylene), polystyrene, polycarbonate, polyethers, polyvinylchloride, silicones, fluoropolymers, polysulfones, nylons, cellulose acetate, ethylenically unsaturated polymers, and suitable combinations thereof.

RFID device 10 includes a densified metal powder layer 12. The densified metal powder layer 12 in FIG. 1 is illustrated in a pattern of a loop. However, the densified metal powder layer may be in any pattern. The pattern of densified metal powder layer 12 is formed on the substrate by at least one of the methods taught in U.S. patent application Ser. No. 09/952,239, "Method for Making Conductive Circuits Using Powdered Metals," (Koskenmaki et al.), filed on) Sep. 10, 2001, the entirety of which is hereby incorporated by reference, and which is co-owned by the assignee of the present invention. To summarize at least one of these methods described in this applicati