Adaptive coupler for reactive near field RFID communication
An adaptive near field electromagnetic coupler for coupling electromagnetic power to a plane metallic trace (inlay) independently of the inlay geometry and/or orientation without external control algorithms. This is achieved by employing a microstructure of phase altering elements suitable for creating a constant phase field distribution along a top surface of the coupler structure. This is advantageously applicable to printing devices having a function of encoding RFID layers printed on a medium. In view of the provided flexibility, the coupler arrangement can be employed in a variety of printers of different mechanical design.
1. A multi-layer electromagnetic coupler arrangement for coupling electromagnetic power to a planar metallic trace of arbitrary geometric shape, the electromagnetic coupler arrangement comprising:
a top surface layer forming a top surface of the electromagnetic coupler arrangement, said top surface layer being arranged closest to said metallic trace to which the electromagnetic power is to be coupled;
a dielectric layer having a surface covered by said top surface layer;
an input signal source layer for providing an AC electromagnetic input field signal; and
a one- or a two-dimensional array of phase altering elements sized and mutually arranged such as to provide phase compensation for a spatial change of position between each of said phase altering elements and a neighboring said phase altering element for transforming said input field signal into a distributed electromagnetic field with substantially constant phase across said top surface;
wherein said one- or two-dimensional array of phase altering elements is provided between said input signal source layer and said dielectric layer;
said input signal source layer provides a guided wave input signal having a target wavelength, the target wavelength being a wavelength of propagation in a homogeneous dielectric of the material of said dielectric layer; and
a size of each of said phase altering elements is significantly smaller than one half of the target wavelength.
2. A multi-layer electromagnetic coupler arrangement according to claim 1 , wherein said top surface layer comprises a metallic material with at least one of apertures and a microstructure.
3. A multi-layer electromagnetic coupler arrangement according to claim 2 , wherein at least one of a size of said microstructure and dimensions and distances between said apertures is substantially smaller than said guided wavelength of said electromagnetic field in said dielectric layer.
4. A multi-layer electromagnetic coupler arrangement according to claim 1 , wherein said one- or two-dimensional array of phase altering elements comprises a transmission line network.
5. A multi-layer electromagnetic coupler arrangement according to claim 4 ,
wherein said transmission line network comprises plural transmission line layers, and
wherein the coupler arrangement further comprises dielectric layers positioned between said transmission line layers, and between a transmission line layer that is most distant from said top surface and said input signal source layer.
6. A multi-layer electromagnetic coupler arrangement according to claim 1 , wherein said one- or two-dimensional array of phase altering elements comprises a metallic layer with apertures, said metallic layer being arranged between said dielectric layer and said input signal source layer.
7. A multi-layer electromagnetic coupler arrangement according to claim 6 , further comprising a further dielectric layer between said metallic layer with said apertures and said input signal source layer.
8. A multi-layer electromagnetic coupler arrangement according to claim 1 , comprising a further dielectric and a further metallic layer arranged as a ground plane layer on a side of said input signal source layer opposing said one- or two-dimensional array of phase altering elements,
wherein said ground plane layer thereby forms a bottom layer of the entire said multi-layer electromagnetic coupler arrangement on a side opposing said top surface layer.
9. A multi-layer electromagnetic coupler arrangement according to claim 1 , wherein said input signal source layer comprises a strip transmission line.
10. A multi-layer electromagnetic coupler arrangement according to claim 1 , wherein said input signal is a standard guided wave input signal provided by a 50Ω coaxial cable system.
11. A multi-layer electromagnetic coupler arrangement according to claim 1 , wherein each of said phase altering elements forms, together with a transmission line segment having a predetermined electrical length, a phase compensated element and includes a network of lumped or distributed components for achieving phase compensation for the predetermined electrical length of said transmission line segment.
12. A multi-layer electromagnetic coupler arrangement according to claim 11 , wherein said components comprise an inductive component and at least one capacitive component.
13. A multi-layer electromagnetic coupler arrangement according to claim 12 , wherein said inductive components of said phase altering elements are realized in distributed form as inductive loops,
wherein said loops are disposed on one side of a three layer printed circuit board, and said transmission layer segments are disposed on the opposite side, and said intermediate layer of said printed circuit board acts as a ground plane.
14. A multi-layer electromagnetic coupler arrangement according to claim 12 , wherein said inductive components of said phase altering elements are realized in distributed form as inductive loops,
wherein said planar metallic trace is part of an RFID inlay, and said inductive loops are adapted to be used for reactive near field coupling towards said RFID inlay.
15. A multi-layer electromagnetic coupler arrangement according to claim 11 , wherein said planar metallic trace is part of an RFID inlay, and said transmission line segments are adapted to be used for reactive near field coupling towards said RFID inlay.
16. A multi-layer electromagnetic coupler arrangement according to claim 1 , wherein said planar metallic trace is part of an RFID inlay, and said multi-layer electromagnetic coupler arrangement is adapted to encode said RFID inlay by coupling electromagnetic power thereto.
17. A multi-layer electromagnetic coupler arrangement according to claim 1 , configured for being employed in a printer wherein said RFID inlays to be encoded are arranged on a medium guided in the printer along a media path,
wherein a shape of said multi-layer electromagnetic coupler arrangement can be flexibly adapted so as to achieve a constant distance between said top surface and said media path of said printer at all positions of said top surface.
18. An RFID printer/encoder comprising a multi-layer electromagnetic coupler arrangement according to claim 1 .
19. An RFID printer/encoder according to claim 18 , wherein electromagnetic coupling for transferring coding information to an RFID inlay occurs in the reactive near field.