RF identification transponder

• US 5,945,938 A
• Filed: 11/12/1997
• Issued: 08/31/1999
• Est. Priority Date: 11/14/1996
• Status: Expired due to Term

• Current Assignee: National University of Singapore
• Original Assignee: National University of Singapore
• Inventors: Au, Tsien Ming, Chia, Yan Wah
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/968,381
• Time in Patent Office: 657 Days
• Field of Search: 342/42, 342/44, 342/50, 342/51, 342/175
• US Class Current: 342/42
• CPC Class Codes: G01S 13/756 using a signal generator for modifying the reflectivity of the reflector G01S13/758 takes precedence
• CPC Class Codes: G01S 13/78 discriminating between different kinds of targets, e.g. IFF-radar, i.e. identification of friend or foe G01S13/75, G01S13/79 take precedence
• CPC Class Codes: G06K 19/0672 with resonating marks
• 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: 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 21/061 Two dimensional planar arrays
• CPC Class Codes: H01Q 21/065 Patch antenna array
• CPC Class Codes: H01Q 3/2652 Self-phasing arrays
• CPC Class Codes: H01Q 5/42 using two or more imbricated arrays H01Q5/49 takes precedence
• CPC Class Codes: H01Q 9/0464 Annular ring patch
• CPC Class Codes: H01Q 9/265 Open ring dipoles; Circular dipoles

Abstract

An RF identification transponder comprises a substrate layer, and an array of M*N antenna elements formed on the substrate layer, where M and N are integers. The antenna elements have a common predetermined resonant frequency f_r. The resonant frequency of the transponder'"'"'s antenna element array allows it to be identified apart from other transponders, each having an antenna element array with a different resonant frequency.

Claims

1. In a transponder reader system, a plurality of RF identification transponders each of which comprises:

a substrate layer; and

an array of M*N antenna elements formed on the substrate layer, wherein the antenna elements have a common predetermined resonant frequency f_r and M and N are integers,

each of the transponders in the system having a different predetermined resonant frequency, wherein the respective different resonant frequencies of the antenna elements allow identification of the transponders.

2. A transponder according to claim 1, wherein each antenna element is connected to another one of the antenna elements by a connection line.

3. A transponder according to claim 2, wherein the connection lines are all of equal length.

4. A transponder according to claim 2, wherein the connection lines are of unequal length.

5. A transponder according to claim 2, wherein each connection line has a length of r1_g ±

(p1_g /2), where r and p are integers.

6. A transponder according to claim 2, wherein the connection lines are routed in or on the substrate to minimise mutual RF coupling therebetween.

7. A transponder according to claim 2, wherein the connection lines do not cross one another in or on the substrate layer.

8. A transponder according to claim 2, wherein the connection lines are spaced apart by at least a quarter of the guided wavelength.

9. A transponder according to claim 2, wherein the connection lines are connected directly to the antenna elements.

10. A transponder according to claim 2, wherein the connection lines are separated from the antenna elements by at least a portion of the substrate layer and are proximity coupled to the antenna elements through the substrate layer.

11. A transponder according to claim 1, wherein the resonant frequency f_r is determined by the size of the individual antenna elements.

12. A transponder according to claim 1, wherein the resonant frequency f_r is determined by the dimensions (M*N) of the individual antenna elements.

13. A transponder according to claim 1, wherein each antenna element comprises a loop element or a patch element.

14. A transponder according to claim 13, wherein one or more of the antenna elements comprise multiple loop elements such that each antenna element has more than one predetermined resonant frequency f_r.

15. A transponder according to claim 13, wherein the antenna elements are of a polygonal or circular configuration.

16. A transponder according to claim 13, wherein the antenna element comprises a C-type loop element.

17. A transponder according to claim 16, wherein the C-type element is a thin rectangular loop formed with a discontinuity or gap.

18. A transponder according to claim 1, wherein one or more further arrays of antenna elements carried on respective substrate layers are provided, respective arrays comprising antenna elements having common predetermined resonant frequencies f_r1,f_r2,f_r3, . . . f_rn, the transponder thereby having at least two resonant frequencies f_r1,f_r2.

19. A transponder according to claim 18, wherein the respective substrate layers carrying the arrays are stacked on top of one another.

20. A transponder according to claim 1, wherein a stub is provided on one or more of the antenna elements.

21. A transponder according to claim 1, wherein the substrate is formed on a ground plane.

22. A transponder according to claim 1, wherein the substrate is a dielectric material.

23. A transponder according to claim 22, wherein the resonant frequency f_r is determined by the relative permitivity of the dielectric.

24. A transponder according to claim 1, wherein the substrate is a ferrite, isotropic or anisotropic materials.

25. A transponder according to claim 24, wherein the resonant frequency f_r is determined by the relative permeability of the ferrite material.

26. A transponder according to claim 1, wherein the array of antenna elements is divided into a number of macrocells, each macrocell containing antenna elements of a common predetermined resonant frequency, each macrocell thereby having a resonant frequency.

27. A transponder according to claim 26, wherein the resonant frequencies of the macrocells in an array of antenna elements are different from one another.

28. A transponder according to claim 1, wherein the antenna array comprises a plurality of unit cells each consisting of a block of C-type antenna elements rotated with respect to one another within each unit cell.

29. A transponder according to claim 28, wherein each unit cell comprises a block of our antenna elements rotated at 90°

with respect to one another.

30. An RF transponder reader in combination with a transponder according to claim 1, the reader comprising:

means for generating and transmitting signals at a range of frequencies f₁,f₂,f₃, . . . f_n, wherein at least one of the frequencies in the range of frequencies f₁,f₂,f₃, . . . f_n is substantially equal to the or each resonant frequency f_r of the transponder; and

means for detecting said one or each resonant frequency f_r.