Method and system for standing wave detection for radio frequency identification marker readers

• US 20080074268A1
• Filed: 09/25/2006
• Published: 03/27/2008
• Est. Priority Date: 09/25/2006
• Status: Active Grant

• Current Assignee: Sensormatic Electronics LLC (Johnson Controls International plc)
• Original Assignee: Sensormatic Electronics Corporation (Johnson Controls International plc)
• Inventors: Shafer, Gary Mark
• Granted Patent: US 8,120,462 B2
• Time in Patent Office: Days
• US Class Current: 340/572.4
• 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
• CPC Class Codes: G06K 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device

Abstract

A method and system for determining the absence and presence of items in an RFID interrogation zone. At least one RFID reader transmits interrogation signals in an interrogation zone. Each RFID reader transmits interrogation signals having a forward amount of RF energy and receives response signals from the items in the interrogation zone having a reflected amount of RF energy. A detection circuit determines the presence and absence of items within the interrogation zone based at least in part on the reflected amount of RF energy.

Claims

1. A system for determining the absence and presence of items in an RFID interrogation zone, the system comprising:

at least one RFID reader transmitting interrogation signals in an interrogation zone, wherein each RFID reader transmits interrogation signals having a forward amount of RF energy and receives response signals from the items in the interrogation zone having a reflected amount of RF energy; and

a detection circuit, the detection circuit determining the presence and absence of items within the interrogation zone based at least in part on the reflected amount of RF energy.

2. The system of claim 1, wherein each RIFD reader comprises:

an RF source for generating RF signals;

an antenna coupled to the RF source, the antenna transmitting the forward RF energy within the interrogation zone; and

a receiver for receiving the reflected RF energy,

wherein the detection circuitry compares an amount of the reflected RF energy with an amount of the forward RF energy at the antenna.

3. The system of claim 2, wherein the detection circuitry provides an output signal representing a ratio between the amount of reflected RF energy and the amount of forward RF energy.

4. The system of claim 3, wherein the system further comprises a processor for receiving the output signal from the detection circuitry and for processing the signal in order to determine the presence and absence of the items within the interrogation zone.

5. The system of claim 4, wherein the processor is located in the RFID reader.

6. The system of claim 3, wherein the output signal is forwarded to an external computer in order to determine the presence and absence of items within the interrogation zone.

7. The system of claim 1, wherein if it is determined that no items are in the interrogation zone, the reader reduces the intensity of the transmitted interrogation signals.

8. The system of claim 1, wherein the detection circuitry determining the presence and absence of items within the interrogation zone analyzes the DC component of the responsive signals.

9. The system of claim 1, wherein the detection circuitry for determining the presence and absence of items within the interrogation zone analyzes the AC component of the responsive signals.

10. The system of claim 1, wherein the detection circuitry includes a dual directional coupler.

11. The system of claim 1, further comprising one or more RFID markers, wherein the one or more RFID readers transmit interrogation signals to the one or more RFID markers within the interrogation zone.

12. A method for determining the absence and presence of items within an RFID interrogation zone, the method comprising:

transmitting interrogation signals within the interrogation zone, the interrogation signals having a forward RF energy;

receiving responsive signals in response to the transmitted interrogation signals, the response signals having a reflected RF energy; and

analyzing the reflected RF energy to determine whether any items within the interrogation zone have been removed.

13. The method of claim 12, wherein analyzing the reflected RF energy includes analyzing a DC component of the responsive signals.

14. The method of claim 12, wherein analyzing the reflected RF energy includes analyzing an AC component of the responsive signals.

15. The method of claim 12, further comprising:

comparing the reflected RF energy with the forward RF energy; and

determining if items within the interrogation zone have been removed based on the comparison of the reflected RF energy with the forward RF energy.

16. The method of claim 15, further comprising determining a ratio between the reflected RF energy and the forward RF energy and determining if items within the interrogation zone have been removed based on the ratio of the reflected RF energy and the forward RF energy.

17. The method of claim 16, further comprising providing an output signal representing the ratio of the reflected RF energy and the forward RF energy.

18. The method of claim 17, further comprising processing the output signal in order to determine the presence and absence of the items within the interrogation zone.

19. The method of claim 12, wherein if it is determined that items are not present within the interrogation zone, further comprising providing instructions to replenish the items.

20. The method of claim 12, wherein if it is determined that items are not present within the interrogation zone, reducing the transmitting power of the interrogation signals.

21. The method of claim 15, wherein comparing the reflected RF energy with the forward RF energy is performed by detection circuitry located within an RFID reader.

22. An RFID reader for determining the absence and presence of items in an RFID interrogation zone, the reader comprising:

an RF source for generating RF signals;

an antenna coupled to the RF source, the antenna transmitting forward RF energy within the RFID interrogation zone;

a receiver for receiving reflected RF energy from items in the RFID interrogation zone; and

a detection circuit, the detection circuit comparing an amount of the reflected RF energy with an amount of the forward RF energy at the antenna to obtain a standing wave ratio, the standing wave ratio usable to determine if items have been removed from the interrogation zone.

23. The RFID reader of claim 22, further comprising a processor, wherein the detection circuit monitors changes in the standing wave ratio and forwards a signal representing the changes in the standing wave ratio to the processor, the processor determining if items have been removed from the interrogation zone.