Radio frequency identification (RFID) tag location systems and methods

• US 8,519,823 B2
• Filed: 10/31/2006
• Issued: 08/27/2013
• Est. Priority Date: 10/31/2006
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Rinkes, Charles
• Primary Examiner(s): Bugg, George
• Assistant Examiner(s): SMALL, NAOMI J
• Application Number:
  US11/589,938
• Publication Number:
  US 20080100439A1
• Time in Patent Office: 2,492 Days
• Field of Search: 340/7.32, 340/502, 340/505, 340/572.4
• US Class Current: 340/7.32
• 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 7/10079 the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions
• CPC Class Codes: G06K 7/10217 parameter settings controlling the transmission power of the interrogator

Abstract

Methods, systems, and apparatuses for ways of locating tags are described. A power level of a RFID communication signal transmitted by a RFID device, such as a reader, is adjusted to hone in on a specific tag. For example, the power level may be decreased or increased, depending on the situation, to hone in on the tag. The RFID device may be repositioned to aid in further honing in on the tag. Transmitting RFID communication signals, adjusting transmit power levels, and repositioning the RFID device may be iterated as needed to hone in on the tag.

Claims

1. A method for locating a radio frequency identification (RFID) tag, comprising:

identifying a desired RFID tag at a distance to be located among a plurality of RFID tags;

transmitting a plurality of interrogation signals from a transmitter in a portable RFID reader at a selected transmit power level to determine a group of tags present within a region and a relative read rate of the desired RFID tag, the group including the desired RFID tag, wherein a physical location of the desired RFID tag is unknown, and wherein the read rate of the desired RFID tag comprises a rate of response to the plurality of interrogation signals;

performing each of the following steps at least once to hone in on the physical location of the desired RFID tag using the transmitter;

lowering the transmit power level based at least on a number of tags present in the determined group and the relative read rate, until the desired RFID tag'"'"'s read rate is low;

transmitting a subsequent interrogation signal from the transmitter at the adjusted transmit power level to determine a subsequent group of tags present within a subsequent region and a subsequent relative read rate of the desired RFID tag, and

repositioning the transmitter.

21. The method of claim 1, further comprising:

using a crescent shaped region defined by the repositioning of the transmitter to locate the desired RFID tag.

2. A method for locating a radio frequency identification (RFID) tag, comprising:

identifying a desired RFID tag at a distance to be located;

selecting a first transmit power level;

transmitting a plurality of interrogation signals from a transmitter at the first transmit power level to determine a first group of tags present within a first region and a read rate of the desired RFID tag if the desired RFID tag is present in the first group, wherein the read rate is based upon transmit power of the transmitter and a distance of the desired RFID tag from the transmitter, and wherein the read rate comprises a rate of response to the plurality of interrogation signals; and

lowering the first transmit power level to a second transmit power level based on a number of tags present in the first group and on the read rate of the desired RFID tag if the desired RFID tag is present in the first group, and until the desired RFID tag'"'"'s read rate is low.

3. The method of claim 2, wherein said adjusting step further comprises:

selecting the second transmit power level to be less than the first transmit power level if the first group includes the desired RFID tag; and

selecting the second transmit power level to be greater than the first transmit power level if the first group does not include the desired RFID tag.

4. The method of claim 2, wherein said adjusting step further comprises:

adjusting the first transmit power level to a second transmit power level based on a relative value of the read rate of the desired RFID tag if the desired RFID tag is present in the first group.

5. The method of claim 2, further comprising:

transmitting a second at least one additional interrogation signal from the transmitter at the second transmit power level to determine a second group of tags present within a second region and a second read rate of the desired RFID tag; and

adjusting the second transmit power level to a third transmit power level based on a number of tags present in the second group and on the second read rate of the desired RFID tag.

6. The method of claim 2, further comprising:

iterating at least one of the transmitting step and the adjusting step at least once to hone in on a physical location of the desired RFID tag using the transmitter.

7. The method of claim 2, wherein said transmitting step comprises:

transmitting the first at least one interrogation signal from the transmitter at a first location.

8. The method of claim 7, further comprising:

repositioning the transmitter from the first location to a second location; and

transmitting a second interrogation signal from the transmitter at the second location and at the second transmit power level to determine a second group of tags present within a second region and a second read rate of the desired RFID tag.

9. The method of claim 2, further comprising:

repositioning the transmitter from a first location to a second location; and

iterating at least one of the transmitting step, the adjusting step, and the repositioning step at least once to hone in on a physical location of the desired RFID tag.

10. The method of claim 2, further comprising:

enabling a user to interact with a user interface associated with the transmitter to perform said adjusting of the first transmit power level.

20. The method of claim 2, further comprising:

using an annular shaped region defined by the first transmit power level and the second transmit power level to locate the desired RFID tag.

11. A method for locating a radio frequency identification (RFID) tag, comprising:

transmitting a plurality of interrogation signals from a transmitter at a first location to determine a first group of tags present within a first region and a read rate of a desired RFID tag at a distance that has been identified to be located, wherein the read rate is based upon transmit power of the transmitter and a distance of the desired RFID tag from the transmitter, and comprises a rate of response to the interrogation signals;

selecting a second location to be located within the first region if the first group includes the desired RFID tag or to be located outside of the first region if the first group does not include the desired RFID tag;

repositioning the transmitter from the first location to a second location, wherein the repositioning and the selecting is responsive to signals received from the transmitter; and

transmitting a second plurality of interrogation signals from the transmitter at the second location to determine a second group of tags present within a second region;

selecting the second transmit power level to be less than the first transmit power level when the first group includes the desired RFID tag; and

wherein the second transmit power level based on a relative value of the read rate of the desired RFID tag if the desired RFID tag is present in the first group; and

continuing to lower the second transmit power level based on the read rate of the desired RFID tag until the desired RFID tag'"'"'s read rate is low.

12. The method of claim 11, further comprising:

performing one or more of the following steps at least once to hone in on a physical location of the desired RFID tag;

repositioning the transmitter to a subsequent location, and

transmitting a subsequent interrogation signals from the transmitter at the subsequent location to determine a subsequent group of tags present within a subsequent region and a subsequent read rate of the desired RFID tag.

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

an antenna;

a radio frequency identification (RFID) module coupled to the antenna, wherein the RFID module is configured to generate a plurality of interrogation signals that are transmitted by the antenna at a transmit power level, and the RFID module is configured to demodulate tag response signals received by the antenna in response to the interrogation signals to determine a group of tags present within a region and a read rate of a desired RFID tag at a distance that has been identified to be located, wherein the read rate is based upon transmit power of the transmitter and a distance of the desired RFID tag from the transmitter, and comprises a response rate of the desired RFID tag to the plurality of transmitted interrogation signals; and

a power ranging module configured to lower the transmit power level of the interrogation signals to enable an operator of the RFID communications device to hone in on a physical location of the desired RFID tag based upon the read rate and the at least one tag response signal, until the desired RFID tag'"'"'s read rate is low.

14. The RFID communications device of claim 13, wherein the RFID communications device is mobile, thereby enabling an operator of the RFID communications device to reposition the RFID communications device to hone in on the physical location of the desired RFID tag.

15. The RFID communications device of claim 13, further comprising:

a user interface configured to enable an operator to interact with the power ranging module to adjust the transmit power level.

16. The RFID communications device of claim 13, wherein the RFID communications device is a RFID reader.

17. The RFID communications device of claim 13, wherein the RFID communications device is an RFID module that is attachable as an accessory to a handheld device.

18. The RFID communications device of claim 13, wherein transmit power level is decreased if a first at least one tag response signal received by the antenna determines that the desired RFID tag is present within the region.

19. The RFID communications device of claim 13, wherein transmit power level is increased if a first at least one tag response signal received by the antenna determines that the desired RFID tag is not present within the region.