RFID DEVICE WITH CONDUCTIVE LOOP SHIELD

• US 20090309703A1
• Filed: 06/11/2008
• Published: 12/17/2009
• Est. Priority Date: 06/11/2008
• Status: Active Grant

• Current Assignee: Avery Dennison Retail Information Services LLC (Avery Dennison Corporation)
• Original Assignee: Avery Dennison Corporation
• Inventors: Forster, Ian J.
• Granted Patent: US 8,289,165 B2
• Time in Patent Office: Days
• US Class Current: 340/10.100
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole
• CPC Class Codes: G06K 7/10178 including auxiliary means for focusing, repeating or boosting the electromagnetic interrogation field comparable booster antennas integrated on the record carrier itself G06K19/07794
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 7/04 Screened antennas H01Q7/02, H01Q7/06 take precedence

Abstract

A radio frequency identification (RFID) device includes a conductive loop shield for a loop antenna. The shield may overlap the conductive loop antenna. The preferred frequency of operation may be a frequency or range of frequencies within the ultra high frequency (UHF) range of frequencies. The conductive loop shield provides a distributed capacitance to the loop antenna, which brings the inductance of the combined system of the loop antenna and the conductive shield down to an inductance level that allows impedance matching with the RFID chip (at the desired impedance or range of impedances). The use of the conductive loop allows the RFID device to function as a near-field magnetic communication device, utilizing a loop antenna having a larger area than would normally be possible for impedance-matching with RFID chip. The loop antenna and the conductive shield loop may be on opposed major surfaces of a dielectric material layer.

Claims

1. An RFID device comprising:

an RFID chip having an input capacitance, and having a predetermined UHF frequency or range of frequency of operation for sending and receiving signals;

an RFID loop antenna electrically coupled to the RFID chip, wherein the RFID loop antenna has an enclosed area greater than 1 cm², wherein the antenna on its own has an unmodified inductance that is at least 20% greater than a desired inductance or range of inductances that would achieve resonance with the input capacitance, at the frequency or range of frequencies; and

a conductive loop operatively coupled to the RFID, without being in contact with the RFID loop antenna;

wherein the RFID loop antenna and the conductive loop together couple to a chip with a modified inductance that is within 5% of the desired inductance or range of inductances.

2. The RFID device of claim 1, further comprising a dielectric material between the RFID loop antenna and the conductive loop.

3. The RFID device of claim 2,

wherein the dielectric material is a dielectric layer;

and

wherein the RFID loop antenna and the conductive loop are on opposite major surfaces of the dielectric layer.

4. The RFID device of claim 3, wherein the dielectric layer has a thickness of 1 mm or less.

5. The RFID device of claim 3, wherein the dielectric layer is a folded-over layer, with the RFID loop antenna and the conductive loop on the same side of the folded-over layer prior to the folding of the folded-over layer.

6. The RFID device of claim 1, wherein the conductive loop overlaps at least 90% of the RFID loop antenna.

7. The RFID device of claim 6, wherein a width of the conductive loop is at least 1.5 times a width of the RFID loop antenna.

8. The RFID device of claim 7, wherein a width of the conductive loop is between 1.5 and 15 times a width of the RFID loop antenna.

9. The RFID device of claim 7, further comprising an additional conductive loop that overlaps at least 90% of the RFID loop antenna.

10. The RFID device of claim 9, wherein the conductive loops are substantially parallel to one another, offset on opposite sides of the RFID loop antenna.

11. The RFID device of claim 1, wherein the conductive loop has a conductive loop gap therein.

12. The RFID device of claim 11, wherein the conductive loop gap is on an opposite side of the conductive loop from a portion of the conductive loop that is closest to where the chip is coupled to the RFID loop antenna.

13. A method of configuring an RFID device, the method comprising:

selecting an RFID chip having an input capacitance, and having a predetermined UHF frequency or range of frequency of operation for sending and receiving signals;

selecting an RFID loop antenna to be electrically coupled to the RFID chip, wherein the RFID loop antenna has an enclosed area greater than 1 cm², wherein the antenna on its own has an unmodified inductance that is at least 20% greater than a desired inductance or range of inductances that would achieve resonance with the input capacitance, at the frequency or range of frequencies; and

selecting a conductive loop to be operatively coupled to the RFID to reduce inductance of the RFID loop antenna to within 5% of the desired inductance or range of inductances.

14. The method of claim 13, wherein the selecting the conductive loop includes modeling.

15. The method of claim 14, wherein the modeling includes modeling with an electromagnetic simulator.

16. The method of claim 13, wherein the selecting the conductive loop includes limiting far field range.

17. The method of claim 13, wherein the selecting includes selecting a width of the conductive loop to achieve the reduction of the inductance of the RFID loop antenna.

18. A method of forming an RFID device, the method comprising:

forming an RFID loop antenna and a loop shield on a major surface of a dielectric material substrate;

electrically coupling an RFID chip to the RFID loop antenna; and

folding the dielectric material substrate so that the loop shield overlaps the RFID loop antenna.