Electromagnetic Enhancement and Decoupling

• US 20070290941A1
• Filed: 06/15/2007
• Published: 12/20/2007
• Est. Priority Date: 06/16/2006
• Status: Active Grant

• Current Assignee: HID Global Corporation (Assa Abloy AB)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Brown, James, Lawrence, Christopher
• Granted Patent: US 7,880,619 B2
• Time in Patent Office: Days
• US Class Current: 343/842
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• 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 19/07771 the record carrier comprising means for minimising adverse effects on the data communication capability of the record carrier, e.g. minimising Eddy currents induced in a proximate metal or otherwise electromagnetically interfering object
• CPC Class Codes: H01P 7/065 integrated in a substrate
• 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
• CPC Class Codes: H01Q 13/08 Radiating ends of two-conductor microwave transmission lines, e.g. of coaxial lines, of microstrip lines
• CPC Class Codes: H01Q 9/04 Resonant antennas
• CPC Class Codes: H05K 9/00 Screening of apparatus or components against electric or magnetic fields devices for absorbing radiation from an antenna H01Q17/00

Abstract

Apparatus and methods for providing a substantially surface independent tagging system are disclosed. A resonant dielectric cavity is defined between upper and lower conducting layers, and closed at one end by a conducting base portion. Incident radiation couples into the cavity and is resonantly enhanced. An electronic device or tag paced at the edge of the cavity experiences a high electric field strength on account of this enhancement and is driven into operation.

Claims

1. An electromagnetic radiation decoupler comprising a cavity structure which comprises a conducting base portion connected to a first conducting side wall and a second conducting side wall, the first conducting side wall and second conducting side wall being spaced apart and substantially parallel.

2. A decoupler according to claim 1 wherein a dielectric material is disposed within the cavity structure.

3. A decoupler according to claim 1 wherein the first conducting side wall has a continuous length of approximately λ

_d/4 measured from the conducting base portion, where λ

_d is the wavelength, in the dielectric material, of EM radiation at the frequency of operation ν

.

4. A decoupler according to claim 1 wherein the second conducting side wall has a continuous length measured from the conducting base portion which is at least as long as the length of the first conducting side wall.

5. A decoupler according to claim 1 wherein a dielectric material is disposed within the cavity structure as a continuous layer adjacent the conducting base portion which extends for substantially as long as the first conducting side wall.

6. A decoupler according to claim 1 wherein a dielectric material is disposed within the cavity structure and extends beyond the end of the first conducting side wall.

7. A decoupler according to claim 1 wherein the total thickness of the decoupler is less than λ

/10, or λ

/300 or λ

/1000.

8. A decoupler according to claim 1 wherein the total thickness of the decoupler is 1 mm or less, 2 mm or less, or 500 μ

m or less, or 100 μ

m or less.

9. A decoupler according to claim 1 wherein the length of the first conducting layer is constant across its width.

10. A decoupler according to claim 1 wherein the length of the first conducting layer varies across its width.

11. A decoupler according to claim 1 wherein the first and second conducting side walls and conducting base portion comprise a continuous layer of material.

12. A decoupler according to claim 1 having one or more different dielectric materials disposed between the two conducting side walls to form a dielectric core.

13. A decoupler according to claim 1 the decoupler comprising more than one cavity structure.

14. A decoupler according to claim 13 wherein two or more cavity structures are arranged to each maximally decouple at a different frequency.

15. A decoupler according to claim 1 further comprising a second cavity structure which comprises a conducting base portion connected to a third conducting side wall and a fourth conducting side wall, the third conducting side wall and fourth conducting side wall being spaced apart and substantially parallel and having a second dielectric material disposed within the second cavity structure wherein the conducting base portion of the first cavity structure is also the conducting base portion of the second cavity structure.

16. A decoupler according to claim 15 wherein the first conducting side wall is continuous with the third conducting side wall, and/or the second conducting side wall is continuous with the fourth conducting side wall.

17. A decoupler according to claim 15 wherein the length of the first conducting side wall, as measured from the conducting base portion to its edge, is different to the length of the third conducting side wall.

18. A decoupler according to claim 15 wherein the dielectric material disposed within the first cavity structure is different to the second dielectric material.

19. A decoupler according to claim 1 further comprising a second cavity structure which comprises a conducting base portion connected to a third conducting side wall and a fourth conducting side wall, the third conducting side wall and fourth conducting side wall being spaced apart and substantially parallel wherein the second and fourth conducting side walls comprise a continuous layer of conducting material, the edges of the first and third conducting side walls define an aperture between them and the dielectric material is also disposed within the second cavity structure.

20. A decoupler according to claim 18 wherein the first and third conducting side walls comprise a continuous layer of conducting material having an aperture extending substantially transverse to the two cavity structures to define the edges of the cavities.

21. A decoupler according to claim 18 wherein the combined length of the two cavities is λ

_d/2 and the aperture between the first and third conducting side walls is located at λ

_d/4 from either conducting base portion.

22. A decoupler according to claim 1 wherein the second side wall of a first cavity structure forms the second side wall of a second cavity structure disposed to the side of the first cavity structure.

27. A decoupler according to claim 1, wherein the conducting base portion is curved.

28. A decoupler according to claim 27, wherein the first conducting side wall forms a segment of a circle and wherein the base portion is connected to the circumferential edge of said segment.

29. A decoupler according to claim 28, wherein the first conducting side wall forms a 90 degree quadrant.

30. A decoupler according to claim 29, wherein the vertex of said quadrant is truncated.

31. A decoupler according to claim 28, wherein said first conducting side wall is semicircular.

32. A decoupler according to claim 31, wherein a slit is provided in said first conducting side wall.

33. A decoupler according to claim 32 wherein said slit extends radially outwards from the centre of the diameter of said semicircle.

34. A decoupler according to claim 33 wherein said slit extends perpendicularly from the diameter of said semicircle.

35. A substantially surface independent EM tag comprising an EM tag mounted on a decoupler as claimed in claim 1.

36. A tag as claimed in claim 35 wherein the EM tag is mounted in the vicinity of the edge of the first conducting side wall.

37. A tag as claimed in claim 35 wherein the tag is located, at least partly, on the first conducting side wall so that the tag antenna is located at the edge of the first conducting side wall opposite the conducting base portion.

38. A tag as claimed in claim 37 comprising a spacer between the EM tag and the decoupler material.

39. A tag as claimed in claim 38 wherein the total gap between the metal part of the EM tag and the decoupler is in the range of from 100 to 1000 microns, or in the range from 175 to 800 microns, or 300 to 800 microns, or 300 to 600 microns.

40. A tag as claimed in claim 35 wherein the EM tag is located across or within the open end of the cavity structure.

41. A tag as claimed in claim 40 wherein the EM tag is at least partly embedded or located within the dielectric material.

42. A tag as claimed in claim 35 wherein the EM tag and decoupler are be in part covered or enveloped by a protective housing.

43. A tag as claimed in claim 42 wherein the housing is a non-conducting material deposited on the surface of the EM tag and the decoupler.

44. A tag as claimed in claim 35 wherein the EM tag is a low Q-tag having a small, untuned antenna.

45. The use of a decoupler as claimed in any claim 1 as a mount for an RF tag.

46. The use of a decoupler as claimed in claim 1 with a low Q RF tag to enable useful read ranges.

23. An electromagnetic radiation decoupler for decoupling an electronic device from a conducting surface comprising a first conducting side wall connected to a conducting end portion and means for spacing the first conducting side wall from the conducting surface such that the conducting end portion makes contact with the conducting surface.

24. A decoupler according to claim 23 wherein the means for spacing the first conducting side wall from the conducting surface is at least one layer of dielectric material that will, in use, be located between the first conducting side wall and conducting surface.

25. A decoupler according to claim 23 wherein the means for spacing the first conducting side wall from the conducting surface comprises one or more spacers.

26. A decoupler according to claim 23 wherein the length of the first conducting side wall is approximately one quarter of the wavelength of the radiation of intended operation.

47. Use of apparatus comprising a resonant dielectric cavity defined between first and second substantially parallel conducting side walls, and closed at one edge by a conducting base portion electrically connected between said first and second side walls, to enhance an incident electric field at an open edge of said cavity.

48. Use according to claim 47, wherein said enhanced electric field powers an electronic device at said open edge of said cavity.

49. Use according to claim 48, wherein said electronic device is an RFID device.

50. Use according to claim 47, wherein said electronic device is powered by differential capacitive coupling.

51. Use according to claim 47, wherein said incident electric field is enhanced by a factor greater than or equal to 50, greater than or equal to 100, or greater than or equal to 200.

52. Use according to claim 47, wherein said incident electric field is enhanced to produce a peak value greater than or equal to 200V/m.

53. Apparatus comprising:

a resonant dielectric cavity defined between first and second substantially parallel conducting side walls, said resonant cavity being closed at one edge by a conducting base portion electrically connected between said first and second side walls, and

an electronic device located adjacent to an open edge of said cavity, said electronic device being responsive to an electric field.

54. Apparatus according to claim 53, wherein said resonant cavity is adapted to enhance an incident electric field at an open edge of said cavity, and wherein said electronic device is located at least partially in a region of enhanced electric field at said open edge.

55. Apparatus according to claim 54, wherein at least part of said electronic device is located within 5 mm, 10 mm or 20 mm from an open edge of said cavity.

56. Apparatus according to claim 53, wherein said open edge is substantially opposite said conducting base portion.

57. Apparatus according to claim 53, wherein said electronic device is an RFID device.

58. Apparatus according to claim 53, wherein said electronic device has no electrical contact with said first or second side walls.