RFID TAGS HAVING FERROMAGNETIC PATCHES

• US 20090015376A1
• Filed: 09/07/2006
• Published: 01/15/2009
• Est. Priority Date: 09/08/2005
• Status: Active Grant

• Current Assignee: SRI International, Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Xiang, Xiao-Dong, Yu, Zhi-Gang, Wang, Huan-Hua
• Granted Patent: US 8,018,345 B2
• Time in Patent Office: Days
• US Class Current: 340/10.100
• CPC Class Codes: G06K 19/0672 with resonating marks

Abstract

RFID tags and devices disclosed herein make use ferromagnetic films to store information. The tags include patches of ferromagnetic materials, each patch having a particular ferromagnetic resonance frequency determined by the composition of the ferromagnetic film. When stimulated, the patches emit microwave or RF signals at their resonance frequencies and at intensities proportional to the patch sizes. The signals are read and the frequency spectrum of the tag may be determined by using a FFT. Identity and other information may be provided by the spectrum.

Claims

1. An RFID tag comprising:

(a) at least one permanent magnet providing a substantially homogeneous magnetic field to a region of the RFID tag; and

(b) one or more ferromagnetic patches provided in the region of substantially homogeneous magnetic field;

wherein each patch has a defined ferromagnetic resonance frequency and size such that when exposed to microwave or radio frequency stimulation;

it emits a signal at the defined resonance frequency at an intensity proportional to the size.

2. The tag of claim 1 wherein the ferromagnetic patches comprise one or more ferromagnetic materials selected from yttrium iron garnet, bismuth iron garnet, bismuth iron oxide, and doped versions thereof.

3. The tag of claim 1 wherein the ferromagnetic patches comprise yttrium iron garnet.

4. The tag of claim 1 wherein the ferromagnetic patches comprise a ferromagnetic material doped with a material selected from Al, Ca, Ga and Si.

5. The tag of claim 1 wherein the ferromagnetic layer comprises at least 2 patches.

6. The tag of claim 1 wherein the tag has an information capacity of at least 96 bits.

7. The tag of claim 1 wherein each patch has a unique resonance frequency and size.

8. The tag of claim 1 wherein the permanent magnet is provided as a layer having a thickness between about 100 nm-100 μ

m.

9. The tag of claim 1, wherein the permanent magnet is provided with a gap or as two separate magnets separated by said gap, wherein the substantially homogeneous magnetic field is provided in the gap.

10. The tag of claim 1, further comprising a non-conductive and non-magnetic substrate on which at least one of the permanent magnet and one or more ferromagnetic patches are provided.

11. The tag of claim 10, wherein the permanent magnet is provided as at least one permanent magnet layer above the substrate.

12. The tag of claim 10, wherein the permanent magnet substantially surrounds the substrate and includes a gap where the one or more ferromagnetic patches are provided on the substrate.

13. The tag of claim 10, wherein the one or more ferromagnetic patches are provided on a ferromagnetic layer above the substrate.

14. An RFID communication system comprising:

a) a station having a receiver and a transmitter; and

b) an RFID tag configured to communicate with the station;

the RFID tag comprising;

(i) at least one permanent magnet providing a substantially homogeneous magnetic field to a region of the RFID tag; and

(ii) one or more ferromagnetic patches provided in the region of substantially homogeneous magnetic field;

wherein each patch has a defined ferromagnetic resonance frequency and size such that when exposed to microwave or radio frequency stimulation;

it emits a signal at the defined resonance frequency at an intensity proportional to the size.

15. The RFID communication system of claim 14, further comprising:

c) an antenna for receiving an interrogation signal and transmitting an RFID tag signal.

16. The RFID communication system of claim 14, wherein the ferromagnetic patches of the RFID tag comprise one or more ferromagnetic materials selected from yttrium iron garnet, bismuth iron garnet, bismuth iron oxide, and doped versions thereof.

17. The RFID communication system of claim 14, wherein the ferromagnetic patches of the RFID tag comprise one or more ferromagnetic materials doped with a material selected from Al, Ca, Ga and Si.

18. The RFID communication system of claim 14, wherein the RFID tag has an information capacity of at least 96 bits.

19. The RFID communication system of claim 14, wherein the permanent magnet of the RFID tag is provided with a gap or as two separate magnets separated by said gap, wherein the substantially homogeneous magnetic field is provided in the gap.

20. A method of identifying an object comprising:

a) sending a broadband signal to an RFID tag attached to the object to excite ferromagnetic patches on the tag;

b) receiving resonance signals associated with the patches; and

c) determining a frequency spectrum of the tag.

21. The method of claim 20, further comprising sending one or more additional pulses of the broadband signal to the RFID tag after (a).

22. The method of claim 20, wherein the ferromagnetic patches of the RFID tag comprise one or more ferromagnetic materials selected from yttrium iron garnet, bismuth iron garnet, bismuth iron oxide, and doped versions thereof.

23. The method of claim 20, wherein the ferromagnetic patches of the RFID tag comprise one or more ferromagnetic materials doped with a material selected from Al, Ca, Ga and Si.

24. The method of claim 20, wherein the RFID tag has an information capacity of at least 96 bits.

25. The method of claim 20, wherein the RFID tag comprises one or more permanent magnets providing a substantially homogeneous magnetic field to the patches.

26. The method of claim 25, wherein the permanent magnet of the RFID tag is provided with a gap or as two separate magnets separated by said gap, wherein the substantially homogeneous magnetic field is provided in the gap.