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

• US 7,884,725 B2
• Filed: 06/21/2007
• Issued: 02/08/2011
• 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): Mehmood; Jennifer
• Application Number:
  US11/766,752
• Publication Number:
  US 20080024273A1
• Time in Patent Office: 1,328 Days
• Field of Search: 3405721-5729, 340 101- 106, 343757-766, 343/893, 343/894, 438/107, 438/108, 438761-763
• 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 during RFID tag interrogation to move peaks and valleys in field intensities, thereby allowing information to be retrieved from an RFID tag during the interrogation, the method comprising:

introducing a first conductor having a width greater than the wavelength of the electromagnetic field into the interrogating electromagnetic field; and

moving the position of the first conductor within the interrogating electromagnetic field.

2. The method of claim 1, wherein the first conductor is a piece of metal.

3. The method of claim 1, wherein moving the position of the first conductor comprises rotating the first conductor about an axis.

4. The method of claim 1, wherein moving the position of the first conductor comprises oscillating the position of the first conductor along a path.

5. The method of claim further comprising:

introducing a second conductor having a width greater than the wavelength of the electromagnetic field into the interrogating electromagnetic field; and

moving the second conductor within the interrogating electromagnetic field.

6. The method of claim 5, wherein moving the second conductor within the electromagnetic field comprises moving the second conductor independently of the motion of the first conductor.

7. The method of claim 5, wherein the second conductor comprises a piece of metal.

8. The method of claim 5, wherein moving the position of the second conductor comprises rotating the second conductor about an axis.

9. The method of claim 5, wherein moving the position of the second conductor comprises oscillating the position of the second conductor along a path.

10. A system of interrogating RFID tags comprising:

an RFID tag;

an RFID interrogator;

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

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

a first movement mechanism coupled to the first conductor that moves the first conductor,

wherein moving the first conductor causes an electromagnetic field to be stirred during interrogation of the RFID tags to move peaks and valleys in peak intensities, thereby allowing information to be retrieved from the RFID tag during the interrogation.

11. The system of claim 10, further comprising an enclosure within which interrogation takes place.

12. The system of claim 10, wherein the first movement mechanism comprises an axis and a motor.

13. The system of claim 10, wherein the first conductor comprises a piece of metal.

14. The system of claim 10, further comprising:

a network coupled to the interrogator; and

a central server coupled to the network.

15. The system of claim 10, further comprising:

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

a second movement mechanism coupled to the second conductor that moves the second conductor.

16. The system of claim 14, wherein the second movement mechanism operates independently of the first movement mechanism.

17. A method for interrogating RFID tags in a static interrogation environment comprising:

providing an antenna for transmitting and receiving RF signals to and from RFID tags;

generating an electromagnetic field of a predetermined frequency in the interrogation environment; and

varying the electromagnetic field in the interrogation environment, by

introducing a conductor into the interrogation environment; and

moving the conductor in the interrogation environment,

wherein moving the conductor causes an electromagnetic field to be stirred during interrogation of the RFID tags to move peaks and valleys in peak intensities, thereby allowing information to be retrieved from the RFID tags during the interrogation.

18. The method of claim 17, wherein the step of moving the conductor in the interrogation environment is continuously moving the conductor in the interrogation environment.

19. The method of claim 17, wherein the step of moving the conductor in the interrogation environment comprises rotating the conductor.

20. The method of claim 17, wherein the conductor is a piece of metal having a length greater than the wavelength of the electromagnetic field.