System and method for locating radio frequency identification tags using three-phase antenna

• US 6,396,438 B1
• Filed: 09/24/1999
• Issued: 05/28/2002
• Est. Priority Date: 09/24/1999
• Status: Expired due to Fees

• Current Assignee: GE Interlogix Incorporated (General Electric Company)
• Original Assignee: SLC Technologies
• Inventors: Seal, James
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/406,091
• Time in Patent Office: 977 Days
• Field of Search: 342/42,44,46,47,50,125,126,127,113,139,140,146,147
• US Class Current: 342/127
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

A system and method for determining the position of a radio frequency identification (RFID) transponder with respect to a sensor. In one embodiment, the system comprises a plurality of stationary sensors located in an array within certain physical areas. Each sensor comprises a plurality of antenna coils arranged in unique physical orientations and capable of transmitting radio frequency signals of differing phase. The RFID transponder includes an antenna which receives the plurality of signals generated by the antenna coils, and compares the phase of at least two of the signals to determine the relative position of the transponder. In a second aspect of the invention, the aforementioned antenna coils emit two direction finding mode (DFM) signals in succession; the first signal with all antenna coils turned on, the second with one of the coils turned off. The spatial relationship of the transponder antenna and individual antenna coils precludes all of the signals in each sensor from being rejected by the transponder during emission of both the first and second DFM signal. Hence, the transponder is kept in constant communication with the sensor in all orientations. In another embodiment, the location of the transponder with respect to two or more sensor(s) is determined through measurement of the intensity of the signals received by the antenna coil of the transponder. The invention also includes a system and method for transmitting data between a sensor and a dormant (motionless) RFID transponder using a hand-held high intensity RF probe.

Claims

1. A method of determining the position of a radio frequency identification (RFID) transponder with respect to a plurality of transceivers, said transceivers having a plurality of individual antennae capable of transmitting radio frequency signals, the method comprising:

transmitting a first signal having a first phase on at least one of said individual antennae of each transceiver;

transmitting a second signal having a second phase on at least one of said individual antennae of each transceiver;

receiving said first and second signals at said transponder; and

comparing the phase of at least said first and second signals in order to determine the relative position of said transponder with respect to said transceivers.

2. The method of claim 1, wherein the acts of transmitting a first signal and a second signal further each comprise transmitting signals of differing phase on each of a plurality of individual antennae within each of said transceivers.

3. The method of claim 2, wherein said individual antennae of each transceiver are orthogonal to all other antennae within the same transceiver.

4. The method of claim 1, wherein the act of comparing the phase of said at least first and second signals comprises measuring the relative intensity of each of said first and second signals.

5. The method of claim 4, wherein the act of comparing the phase further comprises calculating a ratio of the intensity of said first and second signals.

6. The method of claim 5, wherein the act of comparing the phase further comprises correlating the ratio of the intensity of said first and second signals to said relative position.

7. The method of claim 2, wherein each of said transceivers comprises three individual antennae, and the signals transmitted by each of said individual antennae of each transceiver are separated by 120 degrees of electrical phase.

8. The method of claim 1, wherein said first signal and said second signal are transmitted continuously.

9. The method of claim 8 additionally comprising:

determining when said transponder is in motion; and

processing said first and second signals by said in motion transponder so as to determine the relative position of said in motion transponder with respect to said transceivers.

10. The method of claim 8, additionally comprising:

determining when said transponder is being tampered with; and

processing said first and second signals by said tampered transponder so as to determine the relative position of said tampered transponder with respect to said transceivers.

11. The method of claim 1, wherein the relative position of said transponder with respect to said transceivers is determined within said transponder.

12. A radio frequency positioning system, comprising:

at least one radio frequency identification transponder having at least one antenna disposed therein, said at least one antenna configured to receive radio frequency signals;

a first coil oriented in a first direction relative to a given point; and

a second coil oriented in a second direction relative to said given point, said second coil being in different physical location than said first coil, said first and second coils configured to transmit first and second radio frequency signals, respectively,

wherein said first and second signals transmitted by said first and second coils are different in phase, said phase difference being used by said transponder to determine a position of the transponder relative to said first and second coils.

13. The system of claim 12, further comprising:

a third coil oriented orthogonal to said first coil;

a fourth coil oriented orthogonal to said first and third coils, said first, third and fourth coils being physically co-located;

a fifth coil oriented orthogonal to said second coil; and

a sixth coil oriented orthogonal to said second and fifth coils, said second, fifth, and sixth coils being physically co-located;

wherein said third, fourth, fifth, and sixth coils are each configured to transmit radio frequency signals.

14. The system of claim 13, wherein said first, third, and fourth coils transmit signals which differ in electrical phase.

15. The system of claim 14, wherein said second, fifth, and sixth coils transmit signals which differ in electrical phase.

16. The system of claim 12, wherein said transponder measures the relative intensity of said first and second signals in order to determine said position of the transponder.

17. The system of claim 13, wherein at least one of said first, third and fourth coils are arranged in a Helmholz configuration.

18. The system of claim 12, wherein said first and second radio frequency signals are transmitted continuously.

19. The system of claim 18, wherein said transponder includes a motion sensor operable to determine when said transponder is in motion, such that when it is determined that said transponder is in motion, said first and second signals are processed by said transponder so as to determine the relative position of said transponder with respect to said transceivers.

20. The system of claim 18, wherein said transponder includes a tamper detector operable to determine when said transponder is being tampered with, such that when it is determined that said transponder is being tampered with, said first and second signals are processed by said transponder so as to determine the relative position of said transponder with respect to said transceivers.

21. A method of determining the position of a radio frequency identification (RFID) transponder with respect to a transceiver, said transponder having an antenna coil configured to receive a radio frequency signal, said transceiver having a first sensor and a second sensor in different locations, said first and second sensors further including at least one antenna coil, the method comprising:

positioning said transponder in a first spatial relationship with respect to said first and second sensors;

transmitting a first signal having a first phase from said at least one antenna coil of said first sensor;

transmitting a second signal having a second phase from said at least one antenna coil of said second sensor; and

determining the position of said transponder relative to said first and second sensors based on the phase relationship between said first and second signals received by said antenna coil of said transponder.

22. The method of claim 21, wherein the act of transmitting further comprises transmitting signals of differing phase on each of a plurality of individual antenna coils within each of said sensors.

23. The method of claim 22, wherein said individual antenna coils of each sensor are orthogonal to all other antenna coils within the same sensor.

24. The method of claim 21, wherein the act of determining the position of said transponder comprises measuring the relative intensity of each of said first and second signals.

25. The method of claim 24, wherein the act of measuring the relative intensity further comprises calculating a ratio of the intensity of said first and second signals.

26. The method of claim 22, wherein each of said sensors comprises three individual antenna coils, and wherein the signals transmitted by each of said individual antenna coils are separated by 120 degrees of electrical phase.

27. The method of claim 21, wherein the determining of the position of said transponder is performed by said transponder.

28. The method of claim 21, wherein said first signal and said second signal are transmitted continuously.

29. The method of claim 28 additionally comprising:

determining when said transponder is in motion; and

processing said first and second signals by said in motion transponder so as to determine said relative position of said in motion transponder with respect to said transceivers.

30. The method of claim 28 additionally comprising:

determining when said transponder is being tampered with; and

processing said first and second signals by said tampered transponder so as to determine the relative position of said tampered transponder with respect to said transceivers.

31. A method of determining a position of a radio frequency transponder regardless of its orientation, the method comprising:

providing at least two sensors each having a plurality of transmit coils capable of transmitting radio frequency energy within a predetermined frequency band;

placing each of said transmit coils of each of said at least two sensors in a different orientation with respect to a given reference point;

providing a receiver coil within said transponder;

generating radio frequency emissions from each of said transmit coils of each of said at least two sensors, said emissions being shifted in electrical phase from each other; and

measuring the phase of signals received by said receiver coil to determine the position of the transponder.

32. The method of claim 31, wherein said transmit coils are orthogonal to all other transmit coils within the sensor.

33. The method of claim 31, wherein said sensor comprises three individual transmit coils, and wherein the emissions generated by each of said individual transmit coils are separated by 120 degrees of phase.

34. The method of claim 31, wherein measuring the phase of signals received by said receiver coil is performed by said transponder.

35. The method of claim 31, wherein said radio frequency emissions from each of said transmit coils of each of said at least two sensors are emitted continuously.

36. The method of claim 35, additionally comprising:

determining when said transponder is in motion; and

processing said radio frequency emissions by said in motion transponder so as to determine the relative position of said in motion transponder with respect to said at least two sensors.

37. The method of claim 35, additionally comprising:

determining when said transponder is being tampered with; and

processing said radio frequency emissions by said tampered transponder so as to determine the relative position of said tampered transponder with respect to said at least two sensors.

38. A radio frequency positioning system, comprising:

a radio frequency identification (RFID) transponder having an antenna coil configured to receive radio frequency signals;

a first sensor including at least one antenna coil, said first sensor capable of transmitting a first signal having a first phase from said at least one antenna coil of said first sensor;

a second sensor including at least one antenna coil, said second sensor capable of transmitting a second signal having a second phase from said at least one antenna coil of said second sensor; and

means for determining the position of said transponder relative to said first and second sensors based on the phase relationship between said first and second signals received by said antenna coil of said transponder.

39. The system of claim 38, wherein said second sensor is at a different location than said first sensor.

40. The system of claim 38, wherein said transponder is in a predetermined spatial relationship with respect to said first and second sensors.

41. The system of claim 38, wherein one of said sensors is further capable of transmitting signals of differing phase on each of a plurality of individual antenna coils.

42. The system of claim 41, wherein said at least one antenna coils of said first and second sensors are orthogonal to all other antenna coils within the same sensor.

43. The system of claim 41, wherein each of said sensors comprises three individual antenna coils, and wherein the signals transmitted by each of said individual antenna coils are separated by 120 degrees of electrical phase.

44. The system of claim 38, wherein the means for determining the position of said transponder comprises means for measuring the relative intensity of each of said first and second signals.

45. The system of claim 38, wherein the position of said transponder relative to said first and second sensors is determined within said transponder.

46. The system of claim 38, wherein said first signal and said second signal are continuously transmitted.

47. The system of claim 46, wherein said transponder includes a motion sensor operable to determine when said transponder is in motion, such that when it is determined that said transponder is in motion, said first and second signals are processed by said in motion transponder so as to determine the relative position of said in motion transponder with respect to said first and second sensors.

48. The system of claim 46, wherein said transponder includes a tamper detector operable to determine when said transponder is being tampered with, such that when it is determined that said tampered transponder is being tampered with, said first and second signals are processed by said tampered transponder so as to determine the relative position of said tampered transponder with respect to said first and second sensors.

49. A positioning system, including:

an identification transponder having at least one antenna disposed therein, said at least one antenna configured to receive communication signals;

a first coil oriented in a first direction relative to a reference point; and

a second coil oriented in a second direction relative to said reference point, said second coil being in a different physical location than said first coil, said first coil and said second coil being configured to continuously transmit a first and a second communication signal, respectively, wherein said first and second communication signals transmitted by said first and second coils are different in phase;

wherein said transponder includes a motion sensor operable to determine when said transponder is in motion, and wherein in response to said determination that said transponder is in motion, said transponder uses said phase difference to determine a position of said transponder relative to said first and second coils.

50. The positioning system of claim 49, wherein said transponder operates in the radio frequency (RF) domain.

51. The positioning system of claim 49, further including a tamper detector operable to determine when said transponder is being tampered with, wherein in response to said determination that said transponder is being tampered with, said transponder determines a position of said transponder relative to said first and second coils based upon said phase difference.