Method and Apparatus for Testing RFID Tags for Mass Production

• US 20110202299A1
• Filed: 02/12/2010
• Published: 08/18/2011
• Est. Priority Date: 02/12/2010
• Status: Active Grant

• Current Assignee: Amtech Systems LLC (Roper Technologies, Inc.)
• Original Assignee: TC License Limited
• Inventors: Youn, Tai Won
• Granted Patent: US 8,392,137 B2
• Time in Patent Office: Days
• US Class Current: 702/85
• 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

Abstract

A testing system and method for testing glass-mounted RFID tags such as tags mounted on vehicle windows. A testing carrier for use in a test chamber simulates the effect on the tag of the mounting glass. The test chamber and carrier are calibrated by first mounting the tag on the test carrier and making sensitivity measurements and then mounting the tag on glass that is representative of the actual production environment. Comparisons are made between the two measurements and calibration factors are derived to compensate for differences between the actual mounting glass and the test carrier. The test carrier is designed to provide uniform pressure against the tag to minimize any distortions that would alter the sensitivity of the tag.

Claims

1. A carrier assembly for testing RFID tags, the tags having front and back faces and a thickness that is the distance between the front and back faces, the carrier assembly comprising:

a flat carrier comprising a carrier cut-out;

a bottom glass plate;

a flat spacer having a spacer cut-out that is larger than the faces of the tag;

a resilient insert that fits inside said spacer cut-out;

a top glass plate;

a plate fastener;

wherein the said bottom glass plate is placed over said carrier cut-out;

said spacer is placed on top of said bottom plate with said spacer cut-out generally aligned with said carrier cut-out;

said tag is placed inside said spacer cut-out;

said resilient insert is placed on top of the tag;

said top glass plate is placed on top of said spacer and said resilient insert; and

said plate fastener compresses said flat carrier against said bottom glass plate, said bottom glass plate against said spacer and the tag, and said spacer and said resilient insert against said top glass plate.

2. The carrier assembly of claim 1, wherein said spacer is thicker than said tag thickness and the combination of the thickness of said resilient insert and the tag is greater than the thickness of said spacer.

3. The carrier assembly of claim 1 wherein said resilient insert provides a generally uniform pressure across the tag to produce consistent mechanical contact between the bottom glass and the tag.

4. The carrier assembly of claim 1, wherein said tag operates in an operating frequency range and said resilient insert is comprised of a material selected based on its dielectric properties to have a minimal effect on said tag in said tag operating frequency range.

5. The carrier assembly of claim 1, wherein said carrier and said spacer are made of a dielectric material.

6. The carrier assembly of claim 1, wherein said plate fastener comprises a plurality of threaded nylon fasteners that are adjustably tightened with nuts or wing nuts.

7. The carrier assembly of claim 1, wherein at least one dimension or material of at least one said flat carrier, bottom glass plate, flat spacer, resilient insert or top glass place that fits inside said spacer cut-out is selected by

testing a plurality of tags on said carrier assembly to produce a first set of sensitivities for a first standard deviation;

testing said plurality of tags by adhering them to glass to produce a second set of sensitivities for a second standard deviation; and

selecting said dimension or material of said at least one of said flat carrier, bottom glass plate, flat spacer, resilient insert or top glass place that fits inside said spacer cut-out when said first standard deviation is the closest to said second standard deviation.

8. A tag testing system comprising:

a tag carrier;

an RF anechoic testing chamber;

an antenna; and

a tag interrogator;

wherein the tag is placed on the tag carrier inside said testing chamber and a signal is transmitted to the tag through said antenna by said tag interrogator and a signal is received from the tag by said interrogator through said antenna.

9. The tag testing system of claim 8 wherein said anechoic testing chamber is characterized with calibration constants at a plurality of frequencies.

10. The tag testing system of claim 8, wherein said calibration constants are established by

measuring the sensitivities of a plurality of tags on said tag carrier in said RF anechoic testing chamber to produce a first set of sensitivities;

measuring the sensitivities of said plurality of tags adhered to glass in a reference test site to produce a second set of sensitivities and establishing said calibration constants to minimize the difference between said first and second sets of sensitivities.

11. A method for testing glass-mounted RFID tags comprising:

measuring first set of sensitivities of a plurality of sample RFID tags on a test carrier without adhering the tags to glass;

adhering said plurality of sample RFID tags to glass

measuring second set of sensitivities of said plurality of sample RFID tags adhered to said glass;

deriving a calibration factor to relate said first and second sets of sensitivities,

measuring a production sensitivity of a production RFID tag on said test carrier; and

applying said calibration factors to said production sensitivity.

12. The method of claim 11 further comprising:

calculating a first standard deviation for said first set of sensitivities;

calculating a second standard deviation for said second set of sensitivities;

and deriving said calibration factor based on said first and second standard deviations.

13. The method of claim 11, wherein said measuring of said first set of sensitivities is conducted at a plurality of frequencies and said measuring of said second set of sensitivities is conducted at a plurality of frequencies, and further comprising

calculating a first standard deviation at each of said plurality of frequencies for said first set of sensitivities so as to create a first set of standard deviations;

calculating a second standard deviation at each of said plurality of frequencies for said second set of sensitivities so as to create a second set of standard deviations; and

deriving said calibration factor based on said first and second sets of standard deviations.