SECURITY TAG UTILIZING RFID REFLECTIVITY MODE POWER RATIONING

• US 20110084814A1
• Filed: 10/07/2010
• Published: 04/14/2011
• Est. Priority Date: 10/08/2009
• Status: Abandoned Application

• Current Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Original Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Inventors: Ramsch, Karl Georg
• Application Number:
  US12/900,100
• Publication Number:
  US 20110084814A1
• Time in Patent Office: Days
• US Class Current: 340/10.32
• CPC Class Codes: G06K 19/0724 the arrangement being a circuit for communicating at a plurality of frequencies, e.g. for managing time multiplexed communication over at least two antennas of different types
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• 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 7/10019 resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08

Abstract

An RFID security tag which changes its reflectivity after receiving an interrogation signal is provided. The RFID security tag changes its reflectivity so that it becomes transparent to RF power of the RFID reader interrogation signal once the RFID security tag responds, thereby permitting surrounding RFID security tags to absorb the interrogation signal and to respond thereto. These surrounding RFID security tags then, in turn, change their reflectivity so that RFID security tags surrounding that second set of RFID security tags can absorb the interrogation signal and can also respond thereto. In this manner, a large plurality of RFID security tags, such as those associated with merchandise loaded on a palette, can be interrogated accurately.

Claims

1. A radio frequency identification (RFID) system comprising:

a reader for emitting an interrogation signal and for receiving response signals based thereon; and

a first tag for emitting a respective response signal based upon receipt of said interrogation signal and defining a first reflectivity that casts a shadow on at least a second tag, said first tag comprising circuitry that alters said first reflectivity state to a second reflectivity state that makes said first tag substantially transparent to said interrogation signal such that said interrogation signal can illuminate said second tag without physically moving either said first or second tag.

2. The system of claim 1 wherein said second reflectivity is temporary.

3. The system of claim 1 wherein said second tag comprises circuitry that alters a first reflectivity of said second tag, which casts a shadow on a third or more tags, to a second reflectivity that makes said second tag substantially transparent to said interrogation signal such that said interrogation signal can illuminate a third or more tags without physically moving either said second or third or more tags.

4. The system of claim 2 wherein said second reflectivity of said second tag is temporary.

5. The system of claim 1 wherein each of said first, second, or more tags comprises:

a single open loop; and

an RFID chip, coupled across said opening of said single open loop, and wherein said RFID chip effects the alteration between said first and second reflectivities.

6. The system of claim 5 wherein said RFID chip comprises a digital timing circuit for controlling the alteration between said first and second reflectivities.

7. The system of claim 5 wherein said RFID chip comprises an analog timing circuit for controlling the alteration between said first and second reflectivities.

8. The system of claim 5 wherein said analog time circuit comprises a floating gate MOSFET switch.

9. The system of claim 5 wherein said RFID chip comprises a variable impedance device.

10. The system of claim 5 wherein said RFID chip comprises a signal processing unit that comprises digital memory and program code stored therein.

11. The system of claim 5 wherein said RFID chip comprises a high Q value.

12. The system of claim 5 wherein said RFID chip comprises variable capacitors.

13. The system of claim 1 wherein each of said first, second, or more tags comprises:

two dipole antenna elements; and

an RFID chip, coupled between said two dipole antenna elements, that effects the alteration between said first and second reflectivities.

14. The system of claim 13 wherein said RFID chip includes a variable impedance device for effecting the alteration between said first and second reflectivities.

15. The system of claim 14 wherein said RFID chip includes a pair of switches for controlling the variable impedance device.

16. The system of claim 1 wherein each of said first, second, or more tags comprises:

a loop antenna; and

an RFID chip, coupled to said loop antenna, that effects the alteration between said first and second reflectivities.

17. The system of claim 16 further comprising a capacitive element that is switched in or out by said RFID chip for effecting the alteration between said first and second reflectivities.

18. The system of claim 16 further comprising a switch element that open circuits or close circuits said loop antenna for effecting the alteration between said first and second reflectivities.

19. The system of claim 2 wherein a period during which the tag is transparent to said interrogation signal is defined by a time said reader takes to complete communications with one or more other tags in a field of said reader.

20. A method of interrogating a group of RFID tags comprising:

(a) emitting a first reader signal from a reader toward the group of RFID tags;

(b) energizing a first tag having an RFID chip and tuned to a reader frequency for defining a first reflectivity state of said first tag;

(c) listening to instructions within said first reader signal by said first tag to determine if said first reader signal is an initial encounter or a repeat encounter;

(d) generating a reflected response signal from said first RFID tag if said first reader signal is an initial encounter;

(e) temporarily altering the reflectivity of said first RFID tag to a second reflectivity state to render said first RFID tag substantially transparent to said first reader signal, thereby permitting a second tag located in a shadow of said first RFID tag to receive said first reader signal, said second tag being in a first reflectivity state for receiving said first reader signal; and

(f) said second tag comprising an RFID chip and generating its own reflected signal from said first reader signal; and

(g) said first tag restoring itself to said first reflectivity state after temporarily altering said reflectivity.

21. The method of claim 20 further comprising the steps of:

(h) returning to step (c) following step (g); and

(i) temporarily altering said reflectivity of said first tag again to said second reflectivity state if said tag determines a repeat encounter in step (c).

22. The method of claim 20 wherein said step of temporarily altering the reflectivity comprises using a predetermined period of time that is monitored by said RFID chip.

23. The method of claim 22 wherein said first RFID tag restores itself to said first reflectivity state just before total power is lost which occurs at the end of said predetermined period.

24. The method of claim 20 further comprising the step of said second tag temporarily altering the reflectivity of said second RFID tag to a second reflectivity state to render said second RFID tag substantially transparent to said first reader signal, thereby permitting a third or more tags located in a shadow of said second RFID tag to receive said first reader signal.

25. The method of claim 24 further comprising the steps of said second tag

(j) listening to instructions within said first reader signal by said second tag to determine if said first reader signal is an initial encounter or a repeat encounter;

and

(k) returning to its second reflectivity state if said second tag determines a repeat encounter.

26. The method of claim 25 wherein said step of temporarily altering the reflectivity of said second tag comprises using a predetermined period of time that is monitored by said RFID chip in said second tag.

27. The method of claim 26 wherein said second RFID tag restores itself to said first reflectivity state just before total power is lost which occurs at the end of said predetermined period.

28. The method of claim 20 wherein said step of temporarily altering the reflectivity of said first RFID tag to a second reflectivity state comprises introducing a variable impedance into said first tag.

29. The method of claim 20 wherein said step of temporarily altering the reflectivity of said first RFID tag to a second reflectivity state comprises opening a loop of said first RFID tag.

30. The method of claim 20 wherein said RFID chip comprises variable capacitors and wherein said step of temporarily altering the reflectivity of said RFID tag comprises utilizing said variable capacitors.

35. The RFID tag of claim 29 wherein said antenna comprises a loop and wherein said tag reflectivity circuitry comprises a switch that open circuits or close circuits said antenna by said RFID chip for effecting the alteration between said first and second reflectivity states.

31. A radio frequency identification (RFID) tag comprising:

an antenna; and

an RFID chip coupled to said antenna, said RFID chip comprising tag reflectivity circuitry, said tag reflectivity circuitry permitting said tag to become temporarily detuned from a first RFID reader signal emitted by an RFID reader once said RFID security tag has responded to said first RFID reader signal and then to re-tune said RFID security tag to said RFID reader.

32. The RFID tag of claim 31 wherein said tag reflectivity circuitry comprises a digital timing circuit for effecting said temporarily detuned tag from a first reflectivity state wherein said tag is tuned to said RFID reader to a second reflectivity state wherein said tag is detuned from said RFID reader.

33. The RFID tag of claim 31 wherein said tag reflectivity circuitry comprises an analog timing circuit for effecting said temporarily detuned tag from a first reflectivity state wherein said tag is tuned to said RFID reader to a second reflectivity state wherein said tag is detuned from said RFID reader.

34. The RFID tag of claim 31 wherein said antenna comprises a loop and wherein said tag reflectivity circuitry comprises a capacitive element that is switched in or out by said RFID chip for effecting the alteration between said first and second reflectivity states.

36. The RFID tag of claim 31 wherein said RFID chip comprises variable capacitors for tuning and detuning said tag.

37. A method of automatically altering the reflectivity of an RFID tag comprising:

(a) providing an antenna coupled to an RFID chip to form the RFID tag and wherein said RFID tag is initially tuned to an RFID reader frequency, defining a first reflectivity state;

(b) energizing said RFID tag upon receipt of an RFID reader signal having a frequency to which said RFID tag is tuned;

(c) listening, by said RFID chip, to instructions within said RFID reader signal by to determine if said reader signal is an initial encounter or a repeat encounter;

(d) generating a reflected response signal from said RFID tag if said first reader signal is an initial encounter;

(e) temporarily altering the reflectivity of said RFID tag to a second reflectivity state to render said RFID tag substantially transparent to said RFID reader signal; and

(f) restoring said RFID tag to said first reflectivity state.

38. The method of claim 37 further comprising the steps of:

(g) returning to step (c) following step (e); and

(h) temporarily altering said reflectivity of said RFID tag again to said second reflectivity state if said RFID tag determines a repeat encounter in step (c).

39. The method of claim 38 wherein said step of temporarily altering said reflectivity comprises using a predetermined period of time that is monitored by said RFID chip.

40. The method of claim 38 wherein first RFID tag restores itself to said first reflectivity state just before total power is lost which occurs at the end of said predetermined period.

41. The method of claim 37 wherein said RFID chip comprises variable capacitors and wherein said step of temporarily altering the reflectivity of said RFID tag comprises utilizing said variable capacitors.