Systems and methods for stirring electromagnetic fields and interrogating stationary RFID tags

• US 8,669,874 B2
• Filed: 12/30/2010
• Issued: 03/11/2014
• Est. Priority Date: 06/21/2006
• Status: Active Grant

• Current Assignee: Smartrac Technology Fletcher, Inc. (Avery Dennison Corporation)
• Original Assignee: Neology Incorporated (OEP Technologie BV)
• Inventors: Kruest, James Robert, Bann, Gary
• Primary Examiner(s): HUNNINGS, TRAVIS R
• Application Number:
  US12/982,369
• Publication Number:
  US 20110163879A1
• Time in Patent Office: 1,167 Days
• Field of Search: 340/572.1, 340/572.7, 340/10.1
• US Class Current: 340/572.7
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/07796 arrangements on the record carrier to allow stacking of a plurality of similar record carriers, e.g. to avoid interference between the non-contact communication of the plurality of record carriers
• CPC Class Codes: G06K 19/07798 part of the antenna or the integrated circuit being adapted for rupturing or breaking, e.g. record carriers functioning as sealing devices for detecting not-authenticated opening of containers electronic seals G09F3/03
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10029 the collision being resolved in the time domain, e.g. using binary tree search or RFID responses allocated to a random time slot
• CPC Class Codes: G06K 7/10039 interrogator driven, i.e. synchronous
• CPC Class Codes: G06K 7/10475 arrangements to facilitate interaction with further interrogation devices, e.g. such that at least two interrogation devices may function and cooperate in a network of such devices
• CPC Class Codes: G06Q 10/08 Logistics, e.g. warehousing, loading or distribution; Inventory or stock management
• CPC Class Codes: H04J 3/0641 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: H05K 1/02 Details
• CPC Class Codes: H05K 1/0266 Marks, test patterns or identification means
• CPC Class Codes: H05K 1/0268 for electrical inspection or testing
• CPC Class Codes: H05K 1/142 Arrangements of planar printed circuit boards in the same plane, e.g. auxiliary printed circuit insert mounted in a main printed circuit
• CPC Class Codes: H05K 2201/0909 Preformed cutting or breaking line
• CPC Class Codes: H05K 2201/09127 PCB or component having an integral separable or breakable part
• CPC Class Codes: H05K 3/30 Assembling printed circuits with electric components, e.g. with resistor

Abstract

RFID tags are used for many purpose including tracking. RFID interrogators are used to retrieve information from tags. In many applications, RFID interrogators and RFID tags remain stationary during interrogation. Regions of low energy due to interference from either additional antenna or reflections from RFID tags and objects can impede or prohibit the reading of RFID tags residing in such regions. Stirring of the generated electromagnetic field is a method of moving around the regions of low energy, where tags can not be read, during the interrogation process. Mechanical stirring is accomplished by introducing a conductor into the electromagnetic field and moving it about in the field. Solid state stirring is accomplished by introducing a variable conductor into the field and varying the conductivity of the variable conductor. Mathematical stirring is accomplished by use of a plurality of antenna and controlling the phase difference between the antenna in a configuration known as phased antenna arrays.

Claims

1. A method of stirring an electromagnetic field to move peaks and valleys in field intensities comprising:

introducing a conductor having a width greater than the wavelength of the electromagnetic field into the electromagnetic field and a conductivity which is variable; and

varying the conductivity of the conductor.

2. The method of claim 1, wherein the conductor conductivity varies from conductor values to insulator values.

3. The method of claim 1, further comprising introducing another conductor having a width greater than the wavelength of the electromagnetic field into the electromagnetic field and a conductivity which is variable;

and varying the conductivity of the conductor independently of the first conductor.

4. The method of claim 1, wherein the conductor is a pin-diode and the step of varying the conductivity of the conductor comprises applying a voltage across the pin-diode.

5. The method of claim 1, wherein the conductor is a photoconductor and the step of varying the conductivity of the conductor comprises applying a light source to the photoconductor.

6. The method of claim 5, wherein the step of applying a light source to the photoconductor comprises transmitting light to the photoconductor using an optical fiber.

7. The method of claim 1, wherein the conductor is a piezoconductor and the step of varying the conductivity of the conductor comprises applying a mechanical force to the piezoconductor.

8. A system of stirring an electromagnetic field energy comprising:

a conductor having a width greater than the wavelength of the electromagnetic field into the electromagnetic field and a conductivity which is variable; and

stimulus for varying the conductivity of the conductor.

9. The system of claim 8, wherein the conductor conductivity varies from conductor values to insulator values.

10. The system of claim 8, further comprising:

another conductor having a width greater than the wavelength of the electromagnetic field into the electromagnetic field and a conductivity which is variable; and

another stimulus for varying the conductivity of the conductor independently of the first conductor.

11. The system of claim 8, wherein the conductor is a pin-diode and the step of varying the conductivity of the conductor comprises applying a voltage across the pin-diode.

12. The system of claim 8, wherein the conductor is a photoconductor and the step of varying the conductivity of the conductor comprises applying a light source to the photoconductor.

13. The method of claim 12, wherein the step of applying a light source to the photoconductor comprises transmitting light to the photoconductor using an optical fiber.

14. The method of claim 8, wherein the conductor is a piezoconductor and the step of varying the conductivity of the conductor comprises applying a mechanical force to the piezoconductor.

15. A system for interrogating an RFID tag comprising:

an RFID tag;

an RFID interrogator;

an antenna coupled to the RFID interrogator configured to interrogate RFID tags at a given frequency;

a variable conductor with length greater than the wavelength of the given frequency residing within the transmission range of the antenna; and

a stimulus coupled to the variable conductor that varies the conductivity of the variable conductor.

16. The system of claim 15, further comprising an enclosure within which interrogation takes place.

17. The system of claim 15, wherein the variable conductor comprises a pin-diode and the stimulus comprises an electric potential imposed across the pin-diode.

18. The system of claim 15, wherein the variable conductor comprises a photoconductor and the stimulus comprises a light source projected onto the photoconductor.

19. The system of claim 18, wherein the light source is provided by an optical fiber.

20. The system of claim 15, wherein the conductor is a piezoconductor and the stimulus comprises a mechanical force applied to the piezoconductor.

21. The system of claim 15, further comprising a network coupled to the interrogator;

and a central server coupled to the network.

22. The system of claim 15, further comprising another variable conductor with length greater than the wavelength of the given frequency residing within the transmission range of the antenna;

and another stimulus coupled to the variable conductor that varies the conductivity of the variable conductor.

23. The system of claim 22, wherein the stimuli operates independently of the each other.