DETERMINING THE THREE-DIMENSIONAL READ ACCURACY OF AN RFID TAG USING A POWER SCALING FACTOR

• US 20070296586A1
• Filed: 04/27/2007
• Published: 12/27/2007
• Est. Priority Date: 04/28/2006
• Status: Active Grant

• Current Assignee: University of Pittsburgh of The Commonwealth System of Higher Education
• Original Assignee: University of Pittsburgh of The Commonwealth System of Higher Education
• Inventors: Greene, Charles, Mickle, Marlin
• Granted Patent: US 7,528,696 B2
• Time in Patent Office: Days
• US Class Current: 340/572.1
• 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 7/0095 Testing the sensing arrangement, e.g. testing if a magnetic card reader, bar code reader, RFID interrogator or smart card reader functions properly testing of electrical circuits G01R31/28
• CPC Class Codes: G06K 7/10465 the interrogation device being capable of self-diagnosis, e.g. in addition to or as part of the actual interrogation process testing of electrical circuits in general G01R31/28

Abstract

A method of generating a normalized matrix for use in determining one or more read accuracies of an RFID tag at selected points in space relative to a transmitter associated with the RFID tag. The method may further include using the normalized matrix to determine a particular read accuracy of the RFID tag at a particular point in space relative to the transmitter. Also, a method of generating a power scaling factor for determining the read accuracy of an RFID tag.

Claims

1. A method of generating a power scaling factor for use in determining a read accuracy of an RFID tag, comprising:

defining a 3-D matrix for said RFID tag, wherein a first axis in said matrix represents theta values for said RFID tag according to a first discretization, a second axis in said matrix represents phi values for said RFID tag according to a second discretization, and a third axis in said matrix represents polarization values for said RFID tag according to a third discretization, and wherein each position in said 3-D matrix identified by a particular theta, phi and polarization is a gain variable for said RFID tag;

determining a gain value for each said gain variable when said RFID tag is located at a first point in space to create a solved 3-D matrix;

defining a first set of values including a transmitter gain, a transmitted power, and a wavelength for a transmitter associated with said RFID tag and a minimum operating power for said RFID tag;

varying the distance between the RFID tag and said transmitter to locate said RFID tag at a second point in space;

calculating the power received by the RFID tag at said second point for all gain and polarization combinations specified in the solved 3-D matrix using the first set of values and a distance between said second point and said transmitter;

determining the maximum of said calculated powers; and

determining said power scaling factor by dividing said maximum of said calculated powers by said minimum operating power for said RFID tag.

2. The method according to claim 1, wherein said first point in space is an optimum, most favorable point in space for said RFID tag relative to said transmitter.

3. The method according to claim 1, further comprising using said power scaling factor to determine a read accuracy of all possible orientations according to said first and second discretizations and polarizations according to said third discretization of said RFID tag at a selected point in space relative to said transmitter.

4. The method according to claim 1, further comprising using said power scaling factor to determine a volume in space relative to said transmitter at which said RFID tag will have at least a specified read accuracy.

5. The method according to claim 4, wherein said power scaling factor corresponds to said specified read accuracy.

6. The method according to claim 1, wherein said first and second discretizations are each a specified degree and wherein said third discretization is a specified relative angle.

7. The method according to claim 1, wherein said first and second discretizations are each one degree.

8. The method according to claim 1, further comprising using said power scaling factor to determine an amount of power that said RFID tag must receive at a selected point in space relative to said transmitter when said RFID tag is in an optimum position at said selected point in order to be read at a specific read accuracy.

9. A method of generating a normalized matrix for use in determining one or more read accuracies of an RFID tag at selected points in space relative to a transmitter associated with said RFID tag, said RFID tag having a minimum operating power, the method comprising:

generating a first 3-D matrix for said RFID tag, wherein a first axis in said first 3-D matrix represents theta values for said RFID tag according to a first discretization, a second axis in said first 3-D matrix represents phi values for said RFID tag according to a second discretization, and a third axis in said first 3-D matrix represents polarization values for said RFID tag according to a third discretization, and wherein each position in said first 3-D matrix is a power value determined by solving the Friis equation for said RFID tag at a first selected point in space relative to said transmitter using the particular theta value, phi value and polarization value of said position in said first 3-D matrix;

determining the maximum of said power values in said first 3-D matrix;

generating a scaling factor by dividing said maximum of said power values by said minimum operating power;

generating a second 3-D matrix by dividing each of said power values in said first 3-D matrix by said minimum operating power to thereby create a plurality of second 3-D matrix values in said second 3-D matrix; and

generating said normalized matrix by dividing each of said second 3-D matrix values by said scaling factor to thereby create a plurality of normalized matrix values in said normalized matrix.

10. The method according to claim 9, wherein said transmitter has a given transmitter gain and a given transmit power and wavelength and wherein said step of solving the Friis equation for said RFID tag uses said given transmitter gain and said given transmit power and wavelength.

11. The method according to claim 9, further comprising using said normalized matrix to determine a particular read accuracy of said RFID tag at a particular point in space relative to said transmitter.

12. The method according to claim 11, wherein said step of using said normalized matrix to determine a particular read accuracy of said RFID tag at a particular point in space relative to said transmitter comprises determining a maximum power received by said RFID tag at said particular point in space, said maximum power received being a power received when said RFID tag is in an optimum, most favorable position at said particular point in space, determining a second scaling factor by dividing said maximum power received by said minimum operating power, generating a third 3-D matrix by multiplying each of said normalized matrix values in said normalized matrix by said second scaling factor to thereby create a plurality of third 3-D matrix values in said third 3-D matrix, and generating said particular read accuracy by determining the percentage of said third 3-D matrix values that are greater than or equal to one.

13. A computer readable medium having computer executable instructions for performing the method recited in claim 9.

14. A computer readable medium having computer executable instructions for performing the method recited in claim 12.