Method and apparatus for determining the direction of movement of RFID tags and for creating constant-width interrogation zones

• US 20070008071A1
• Filed: 06/05/2006
• Published: 01/11/2007
• Est. Priority Date: 06/06/2005
• Status: Active Grant

• Current Assignee: Seknion Incorporated
• Original Assignee: Seknion Incorporated
• Inventors: Hansen, Thorkild
• Granted Patent: US 7,605,684 B2
• Time in Patent Office: Days
• US Class Current: 340/10.300
• CPC Class Codes: G01S 13/62 Sense-of-movement determination G01S13/589 takes precedence
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal

Abstract

The disclosed inventions relate to a method and apparatus for creating one-sided interrogation zones. The disclosed inventions further relate to a method and apparatus for determining the direction of movement of tagged items that pass by an RFID reader. The disclosed inventions also relate to a method and apparatus for combining one-sided interrogation zones of two or more antenna arrays to create an interrogation zone that maintains its width over a large range of distances.

Claims

1. A method for interrogating an RFID tag using an antenna array, comprising the steps of:

transmitting a data signal having an amplitude and a time delay, wherein said data signal causes said RFID tag to respond to said antenna array;

transmitting one or more scramble signals each having an amplitude and a time delay, wherein said one or more scramble signals do not cause said RFID tag to respond to said antenna array;

selecting said data signal amplitude, said data signal time delay, said one or more scramble signal amplitudes, and said one or more scramble signal time delays so that said data signal overshadows said one or more scramble signals in a region and said one or more scramble signals overshadow said data signal outside said region, wherein said region is a one-sided region; and

,

receiving a response from said RFID tag when said RFID tag is located within said region.

2. The method of claim 1, wherein said one or more scramble signals comprise a plurality of scramble signals.

3. The method of claim 1, wherein said antenna array is a two-element array.

4. The method of claim 1, wherein said antenna array is a linear array.

5. The method of claim 1, wherein said antenna array is a ring array.

6. The method of claim 2, wherein said antenna array is a planar array.

7. The method of claim 2, wherein said antenna array is a cylindrical array.

8. The method of claim 1, wherein said selecting step further comprises determining the solution to an inverse source problem.

9. The method of claim 8 wherein said inverse source problem is solved with an iterative optimization scheme.

10. A method for determining the direction of movement of an RFID tag using an antenna array, comprising the steps of:

providing a data signal;

providing a scramble signal;

creating during a first time interval a first one-sided region in which said data signal overshadows said scramble signal;

creating during a second time interval a second one-sided region in which said data signal overshadows said scramble signal;

determining a first response of said RFID tag during said first time interval while said RFID tag is within said first one-sided region;

determining a second response of said RFID tag during said second time interval while said RFID tag is within said second one-sided region; and

,

determining the direction of movement of said RFID tag based on the temporal order of said first response and said second response.

11. The method of claim 10 wherein said first response and said second response are determined based on an average of responses by said RFID tag.

12. The method of claim 10 wherein said creating steps further comprise electronically switching antenna elements in said antenna array.

13. The method of claim 10 wherein said creating steps further comprise steering antenna elements in said antenna array.

14. A method for interrogating an RFID tag, comprising the steps of:

providing a first antenna array;

providing a second antenna array;

transmitting a data signal having an amplitude and a time delay, wherein said data signal causes said RFID tag to respond to said first antenna array;

transmitting a plurality of scramble signals each having an amplitude and a time delay, wherein said plurality of scramble signals does not cause said RFID tag to respond with said first antenna array or said second antenna array;

selecting said amplitude of said data signal, said amplitudes of said plurality of scramble signals, said time delay of said data signal, and said time delays of said plurality of scramble signals so that said data signal overshadows said plurality of scramble signals in a region and said plurality of scramble signals overshadows said data signal outside said region, wherein said region is a region of constant width; and

,

receiving a response from said RFID tag when said RFID tag is located within said region.

15. The method of claim 14 wherein said plurality of scramble signals overshadow said data signal by at least 10 dB in said region.

16. An apparatus for interrogating an RFID tag, comprising:

an antenna array;

a transmitter that transmits a data signal having an amplitude and a time delay, wherein said data signal causes said RFID tag to respond to said antenna array;

a transmitter that transmits one or more scramble signals each having an amplitude and a time delay, wherein said one or more scramble signals do not cause said RFID tag to respond to said antenna array;

a processor that selects said data signal amplitude, said data signal time delay, said one or more scramble signal amplitudes, and said one or more scramble signal time delays so that said data signal overshadows said one or more scramble signals in a region and said one or more scramble signals overshadow said data signal outside said region, wherein said region is a one-sided region; and

,

a receiver that receives a response from said RFID tag to said data signal when said RFID tag is located inside said region.

17. The apparatus of claim 16, wherein said one or more scramble signals comprise a plurality of scramble signals.

18. The apparatus of claim 16, wherein said antenna array is a two-element array.

19. The apparatus of claim 16, wherein said antenna array is a linear array.

20. The apparatus of claim 16, wherein said antenna array is a ring array.

21. The apparatus of claim 17, wherein said antenna array is a planar array.

22. The apparatus of claim 17, wherein said antenna array is a cylindrical array.