Method and system to determine physical parameters as between an RFID tag and a reader

• US 7,944,356 B2
• Filed: 03/07/2008
• Issued: 05/17/2011
• Est. Priority Date: 10/04/2007
• Status: Expired due to Fees

• Current Assignee: Round Rock Research LLC
• Original Assignee: Round Rock Research LLC
• Inventors: Tuttle, John R.
• Primary Examiner(s): Bugg; George A
• Assistant Examiner(s): MCNALLY, KERRI L
• Application Number:
  US12/044,741
• Publication Number:
  US 20090091428A1
• Time in Patent Office: 1,166 Days
• Field of Search: 340/10.1, 340/10.3, 340/10.4, 340/568.1, 340/568.5, 340/568.6, 340/568.7, 340/568.8, 340/571, 340/572.1
• US Class Current: 340/572.1
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal

Abstract

A method and system to determine physical parameters as between an RFID tag and a reader. At least some of the illustrative embodiments are methods comprising generating an antenna feed signal, and transmitting a first electromagnetic wave to a radio frequency device (by coupling the antenna feed signal to a reading antenna), receiving a backscattered electromagnetic wave from the radio frequency device to create a received signal, calculating a combined signal based on the antenna feed signal and received signal, and determining relative velocity between the radio frequency device and the reading antenna based on the combined signal.

Claims

1. A method implemented in a radio frequency identification (RFID) system, the method comprising:

an RFID reader generating an antenna feed signal and transmitting a first electromagnetic wave to an RFID tag according to the antenna feed signal;

the RFID reader receiving a backscattered electromagnetic wave from the RFID tag to create a received signal;

generating a combined signal based on the antenna feed signal and the received signal, wherein the combined signal includes a plurality of inflection points, each inflection point corresponding to a different position of the RFID tag relative to the RFID reader, wherein the plurality of inflection points comprises a first inflection point, a last inflection point, and at least one intermediate inflection point between the first inflection point and the last inflection point; and

determining a relative velocity between the RFID tag and the RFID reader by detecting the inflection points of the combined signal over a predetermined time period, wherein the predetermined time period begins at a time associated with the first inflection point and ends at a time associated with the last inflection point.

2. The method of claim 1, wherein the backscattered electromagnetic wave is received during the RFID reader interrogating the RFID tag using the antenna feed signal.

3. The method of claim 1, wherein the generating of the combined signal comprises summing the antenna feed signal and the received signal, mixing the antenna feed signal with the received signal, or performing an exclusive-OR using at least portions of the antenna feed signal and the received signal.

4. The method of claim 1, wherein the inflection points include one or more of null, minima, and maxima.

5. The method of claim 1, wherein the backscattered electromagnetic wave is generated by the RFID tag in response to a command from the RFID reader.

6. The method of claim 5, wherein the RFID tag is instructed by the command to be in a reflective state to generate the backscattered electromagnetic wave without associated data.

17. The method of claim 1, wherein the first inflection point and the last inflection point each correspond to a null value.

7. A system comprising:

a radio frequency identification (RFID) tag;

a reading antenna; and

a reader circuit coupled to the reading antenna to transmit a first electromagnetic wave to the RFID tag, based on an antenna feed signal, and to receive a received signal based on a backscattered electromagnetic wave from the RFID tag;

wherein the reader circuit generates a combined signal of the antenna feed signal and the received signal;

wherein the combined signal includes a plurality of inflection points, each inflection point corresponding to a different position of the RFID tag relative to the reading antenna;

wherein the plurality of inflection points comprises a first inflection point, a last inflection point, and at least one intermediate inflection point between the first inflection point and the last inflection point;

wherein the reader circuit determines a relative velocity between the RFID tag and the reading antenna by detecting the inflection points of the combined signal over a predetermined time period, wherein the predetermined time period begins at a time associated with the first inflection point and ends at a time associated with the last inflection point.

8. The system of claim 7, wherein the reader circuit determines the relative velocity by counting the inflection points in the combined signal.

9. The system of claim 8, wherein the inflection points include at least null points, maximum points, or minimum points in an envelope signal of the combined signal.

10. The system of claim 7, wherein the combined signal is a sum of the antenna feed signal and the received signal, a multiplication of the antenna feed signal with the received signal, or a result of an exclusive-OR applied on at least portions of the antenna feed signal and the received signal.

11. The system of claim 7, wherein the reader circuit determines identification data stored on the RFID tag and instructs the RFID tag to be in a reflective state to generate the backscattered electromagnetic wave without data.

12. The system of claim 7, wherein the RFID tag comprises a passive tag or a semi-active tag.

13. A radio frequency identification (RFID) reader, comprising:

a reading antenna; and

a reader circuit coupled to the reading antenna to receive a backscattered electromagnetic wave from an RFID tag to create a received signal, wherein the reader circuit generates an antenna feed signal corresponding to the backscattered electromagnetic wave,

the reader circuit determining a relative velocity between the RFID tag and the reader circuit based on a combined signal of the antenna feed signal and the received signal,

wherein the combined signal includes a plurality of inflection points, each inflection point corresponding to a different position of the RFID tag relative to the reading antenna,

wherein the plurality of inflection points comprises a first inflection point, a last inflection point, and at least one intermediate inflection point between the first inflection point and the last inflection point,

wherein the reader circuit determines the relative velocity by detecting the inflection points of the combined signal over a predetermined time period, wherein the predetermined time period begins at a time associated with the first inflection point and ends at a time associated with the last inflection point.

14. The radio frequency identification reader of claim 13, wherein the inflection points include at least null points, minimum points or maximum points.

15. The radio frequency identification reader of claim 13, wherein the combined signal comprises an envelope signal of a sum of the antenna feed signal and the received signal, a multiplication of the antenna feed signal with the received signal, or a result of an exclusive-OR applied on at least portions of the antenna feed signal and the received signal.

16. A non-transitory computer-readable medium storing a program that, when executed by a radio frequency identification (RFID) system, causes the system to:

generate an antenna feed signal and transmit a first electromagnetic wave from an RFID reader to an RFID tag according to the antenna feed signal;

receive a backscattered electromagnetic wave from the RFID tag to create a received signal;

generate a combined signal based on the antenna feed signal and the received signal, wherein the combined signal includes a plurality of inflection points, each inflection point corresponding to a different position of the RFID tag relative to the RFID reader, wherein the plurality of inflection points comprises a first inflection point, a last inflection point, and at least one intermediate inflection point between the first inflection point and the last inflection point; and

determine a relative velocity between the RFID tag and the RFID reader by detecting the inflection points of the combined signal over a predetermined time period, wherein the predetermined time period begins at a time associated with the first inflection point and ends at a time associated with the last inflection point.