System and method of enhancing range in a radio frequency identification system

• US 20070096881A1
• Filed: 10/28/2005
• Published: 05/03/2007
• Est. Priority Date: 10/28/2005
• Status: Active Grant

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Inventors: Pillai, Vijay
• Granted Patent: US 7,482,926 B2
• Time in Patent Office: Days
• US Class Current: 340/10.51
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• 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

Abstract

A radio frequency identification (RFID) system includes a plurality of RFID tags each having adjustable tag resonant frequency, and an RFID reader configured to transmit interrogation and change frequency RF signals. The interrogation and change frequency RF signals are transmitted at the current tag resonant frequency. The plurality of RFID tags modify the tag resonant frequency to a new tag resonant frequency in response to the change frequency RF signals. RFID tag identification rates may be enhanced by interrogating the plurality of RFID tags at the tag resonant frequency for a dwell time, receiving response RF signals, determining a new tag resonant frequency, and transmitting a change frequency RF signal that causes the RFID tags to change the tag resonant frequency to the new tag resonant frequency. The new resonant frequency may be based on the number of received responses.

Claims

1. A radio frequency identification reader operable to communicate with RFID tags, the radio frequency identification reader comprising:

a reader antenna;

a variable radio frequency source operable to generate carrier waves at a plurality of carrier wave frequencies;

a controller operable to from time-to-time, determine a new carrier wave frequency, the new carrier wave frequency being different from a current carrier wave frequency that at least approximately matches a current tag resonant frequency of at least one of the RFID tags, and generate change frequency instructions indicative of an instruction to change a tag resonant frequency from the current tag resonant frequency to at least approximately match a new tag resonant frequency; and

a transmitter configured to modulate the carrier waves having the current carrier wave frequency with the change frequency instructions to transmit a change frequency radio frequency signal via the reader antenna.

2. The radio frequency identification reader of claim 1 wherein the change frequency radio frequency signal encodes the new tag resonant frequency.

3. The radio frequency identification reader of claim 1, further comprising:

a receiver to receive response radio frequency signals transmitted by the plurality of radio frequency identification tags.

4. The radio frequency identification reader of claim 3 wherein the controller is further operable to determine the new carrier wave frequency based upon the received response radio frequency signals.

5. The radio frequency identification reader of claim 3 wherein the controller is operable to estimate a radio frequency identification tag population based upon a number of the received response radio frequency signals and to determine the new carrier wave frequency based upon the estimated radio frequency identification tag population.

6. The radio frequency identification reader of claim 5 wherein the new carrier wave frequency is selected from a first subset of frequencies of the plurality of carrier wave frequencies when the estimated tag population is at least equal to a predefined population threshold, the first subset of frequencies including long-range tag resonant frequencies.

7. The radio frequency identification reader of claim 5 wherein the new carrier wave frequency is selected from a second subset of frequencies of the plurality of carrier wave frequencies when the estimated tag population is less than a predefined population threshold, the second subset of frequencies including shorter-range tag resonant frequencies.

8. The radio frequency identification reader of claim 1 wherein the variable radio frequency source is a voltage-controlled oscillator.

9. The radio frequency identification reader of claim 1 wherein the controller is a microprocessor.

10. The radio frequency identification reader of claim 1 wherein the controller is operable to change an impedance of the reader antenna to at least approximately match the new tag resonant frequency after the change frequency radio frequency signal is transmitted via the reader antenna.

11. A radio frequency identification tag operable to communicate with a radio frequency identification reader, the radio frequency identification tag comprising:

an adjustable impedance block; and

a signal processing/memory section coupled to the adjustable impedance block and configured to receive a change frequency radio frequency signal from the radio frequency identification reader and to change a tag resonant frequency to a new tag resonant frequency by modifying an impedance of the adjustable impedance block in response to the change frequency radio frequency signal.

12. The radio frequency identification tag of claim 11 wherein the adjustable impedance block comprises at least one switched capacitor.

13. The radio frequency identification tag of claim 12, further comprising:

an antenna;

a first antenna line coupled to the antenna; and

a second antenna line coupled to the antenna, and wherein the at least one switched capacitor comprises at least two capacitors and at least one switch operable to selectively electrically couple at least one of the capacitors across the first and the second antenna lines.

14. The radio frequency identification tag of claim 11 wherein the signal processing/memory section, comprises:

an energy storage device;

a memory coupled to the energy storage device;

a digital state machine coupled to the memory; and

an analog block coupled to the digital state machine.

15. The radio frequency identification tag of claim 14 wherein the signal processing/memory section further comprises:

a DC power source configured to supply power to the memory, the digital state machine, and the analog block.

16. The radio frequency identification tag of claim 14, further comprising:

a radio frequency front end coupled to the adjustable impedance block and the energy storage device and configured to rectify an interrogation radio frequency signal received from the radio frequency interrogation reader and to supply at least a portion of the resulting power to the energy storage device.

17. The radio frequency identification tag of claim 14 wherein the digital state machine is coupled to the adjustable impedance block and configured to modify the impedance of the adjustable impedance block based upon the change frequency radio frequency signal.

18. A radio frequency identification tag operable to communicate with a radio frequency identification reader, the radio frequency identification tag comprising:

radio frequency signal receiving means for receiving a radio frequency signal from the radio frequency identification reader;

signal processing means for determining whether the received radio frequency signal is an instruction to change a tag resonant frequency of the radio frequency identification tag; and

tag resonant frequency changing means for changing a tag resonant frequency to a new tag resonant frequency in response to the signal processing means determining that the received radio frequency signal is an instruction to change the tag resonant frequency of the radio frequency identification tag.

19. The radio frequency identification tag of claim 18 wherein the radio frequency signal receiving means and the signal processing means each comprise respective portions of a signal processing/memory section.

20. The radio frequency identification tag of claim 18 wherein tag resonant frequency changing means comprises an adjustable impedance block coupled to the signal processing means for control thereby.

21. The radio frequency identification tag of claim 20 wherein an impedance of the adjustable impedance block is modified according to a value encoded in the radio frequency signal that is determined to be an instruction to change the tag resonant frequency to a new tag resonant frequency.

22. The radio frequency identification tag of claim 18 wherein the radio frequency signal receiving means comprises an antenna, and wherein the adjustable impedance block comprises a plurality of switched capacitors selectively electrically couplable in parallel across the antenna.

23. A radio frequency identification system, comprising:

a plurality of radio frequency identification tags each having a tag resonant frequency that is adjustable and configured to wirelessly communicate at a current tag resonant frequency; and

a radio frequency identification reader operable to transmit interrogation radio frequency signals and change frequency radio frequency signals, the interrogation radio frequency signals and the change frequency radio frequency signal being transmitted at the current tag resonant frequency, and the plurality of radio frequency identification tags further configured to modify the tag resonant frequency to a new tag resonant frequency based upon the receipt of change frequency radio frequency signals.

24. The radio frequency identification system of claim 23 wherein the change frequency radio frequency signal encodes an indication of the new tag resonant frequency.

25. The radio frequency identification system of claim 23 wherein the radio frequency identification reader is further operable to receive response radio frequency signals transmitted by the plurality of radio frequency identification tags.

26. The radio frequency identification system of claim 25 wherein the radio frequency identification reader is further operable to estimate a radio frequency identification tag population based upon a number of response radio frequency signals received by the radio frequency identification reader and to determine the new tag resonant frequency based upon the estimated radio frequency identification tag population.

27. The radio frequency identification system of claim 26 wherein the radio frequency identification reader determines the new tag resonant frequency to be a long-range tag resonant frequency when the estimated RFID tag population is greater or equal to a predefined population threshold.

28. The radio frequency identification system of claim 26 wherein the radio frequency identification reader determines the new tag resonant frequency to be a shorter-range tag resonant frequency when the estimated radio frequency identification tag population is less than a predefined population threshold.

29. The radio frequency identification system of claim 23 wherein the radio frequency identification reader comprises:

a reader antenna;

a variable radio frequency source operable to generate carrier waves at a selected resonant frequency from a plurality of tag resonant frequencies;

a controller configured to determine the new tag resonant frequency and generate change frequency instructions, the change frequency instructions including the new tag resonant frequency; and

a transmitter configured to modulate a carrier wave generated by the variable radio frequency source with the change frequency instructions to generate the change frequency radio frequency signal and transmit the change frequency radio frequency signal via the reader antenna, the carrier wave having a frequency at least approximately matching the current tag resonant frequency.

30. The radio frequency identification system of claim 23 wherein the radio frequency identification tag comprises:

an adjustable impedance block; and

a signal processing/memory section coupled to the adjustable impedance block and configured to receive the change frequency radio frequency signal from the radio frequency identification reader and modify the tag resonant frequency to the new tag resonant frequency by modifying an impedance of the adjustable impedance block.

31. The radio frequency identification system of claim 30 wherein the adjustable impedance block comprises at least one switched capacitor.

32. The radio frequency identification system of claim 30 wherein the radio frequency identification tag further comprises:

a first antenna line;

a second antenna line;

a tag antenna electrically coupled to the adjustable impedance block via the first and the second antenna lines, and wherein the adjustable impedance block comprises at least one switched capacitor selectively electrically couplable in parallel between the first and the second antenna lines.

33. A method of operating a radio frequency identification reader to enhance radio frequency identification tag identification rates for a plurality of radio frequency identification tags operating at a variable tag resonant frequency, the method comprising:

interrogating the plurality of radio frequency identification tags at a current tag resonant frequency for a dwell time;

receiving response radio frequency signals transmitted by the plurality of radio frequency identification tags at the tag resonant frequency during the dwell time;

determining a new tag resonant frequency at which the radio frequency identification tags and the radio frequency identification reader will communicate; and

transmitting a change frequency radio frequency signal for instructing the radio frequency identification tags to change the tag resonant frequency to the new tag resonant frequency.

34. The method of claim 33 wherein transmitting a change frequency radio frequency signal for instructing the radio frequency identification tags to change the tag resonant frequency to the new tag resonant frequency comprises transmitting the change frequency radio frequency signal encoding the new tag resonant frequency.

35. The method of claim 33, wherein determining the new tag resonant frequency further comprises:

determining the new tag resonant frequency based upon the received response radio frequency signals.

36. The method of claim 33, further comprising:

estimating a radio frequency tag population based upon a number of the received response radio frequency signals.

37. The method of claim 36 wherein determining the new tag resonant frequency further comprises determining the new tag resonant frequency based upon the estimated radio frequency identification tag population.

38. The method of claim 37 wherein the new tag resonant frequency is selected from a first subset of carrier frequencies when the estimated radio frequency identification tag population is at least equal to a predefined population threshold, the first subset of carrier frequencies including long-range tag resonant frequencies.

39. The method of claim 37 wherein the new tag resonant frequency is selected from a second subset of carrier frequencies when the estimated radio frequency identification tag population is less than a predefined population threshold, the second subset of carrier frequencies including shorter-range tag resonant frequencies.

40. The method of claim 33, further comprising:

determining the dwell time based upon the received response radio frequency signals.

41. A method of operating a radio frequency identification tag in communication with a radio frequency identification reader to enhance radio frequency identification tag identification rates, the method comprising:

receiving a radio frequency signal from the radio frequency identification reader;

determining whether the received radio frequency signal is an instruction to change a tag resonant frequency of the radio frequency identification tag; and

changing a tag resonant frequency to a new tag resonant frequency in response to determining that the received radio frequency signal is an instruction to change the tag resonant frequency of the radio frequency identification tag.

42. The method of claim 41 wherein changing a tag resonant frequency to a new tag resonant frequency comprises adjusting an impedance of an adjustable impedance block.

43. The radio frequency identification tag of claim 42 wherein adjusting an impedance of an adjustable impedance block comprises selectively electrically coupling at least one of a plurality of switched capacitors in parallel across an antenna of the radio frequency identification tag.

44. The method of claim 41 wherein changing a tag resonant frequency to a new tag resonant frequency comprises adjusting an impedance of an adjustable impedance block according to a value encoded in the received radio frequency signal that is determined to be an instruction to change the tag resonant frequency to a new tag resonant frequency.