Field-shaping shielding for radio frequency identification (RFID) system

• US 7,421,245 B2
• Filed: 02/20/2004
• Issued: 09/02/2008
• Est. Priority Date: 02/20/2004
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Lieffort, Seth A., Goff, Edward D.
• Primary Examiner(s): Maung; Nay
• Assistant Examiner(s): NGUYEN, TUAN HOANG
• Application Number:
  US10/784,109
• Publication Number:
  US 20050186902A1
• Time in Patent Office: 1,656 Days
• Field of Search: 455/41.1, 455/296, 455300-301, 343741-742, 343/867, 343/841, 340/572.7
• US Class Current: 455/41.1
• 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: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: G06K 7/10346 the antenna being of the far field type, e.g. HF types or dipoles
• CPC Class Codes: H01Q 1/22 by structural association with other equipment or articles
• CPC Class Codes: H01Q 1/2208 associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems methods or arrangements for sensing record carriers, e.g. for reading patterns G06K7/00; record carrier for use with machines and with at least a part designed to carry digital markings G06K19/00
• CPC Class Codes: H01Q 1/526 Electromagnetic shields
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

A radio frequency identification (RFID) system is described that utilizes a substantially-contiguous conductive shield to shape an electromagnetic field formed by an antenna for communication with RFID tags. The antenna and the conductive shield have substantially planar forms, and may be mounted to a surface of a check-in/check-out area. The conductive shield is positioned around the antenna and within a plane parallel to the antenna, e.g., within the same plane. The conductive shield shapes the electromagnetic field to extend substantially in a direction perpendicular to the antenna, and prevents the electromagnetic field from forming substantially over the conductive shield.

Claims

1. A radio frequency identification (RFID) system comprising:

an antenna that forms an electromagnetic field that defines a communication zone in which RFID tags can be read, wherein the antenna has a substantially planar form; and

a substantially-contiguous conductive shield positioned a distance from the antenna within a plane parallel to the antenna to define an outermost region of the communication zone within the plane parallel to the antenna, wherein the conductive shield has a width that extends in the plane parallel to the antenna such that the electromagnetic field at any region beyond the conductive shield is below a threshold level for communication with the RFID tags, and

wherein the conductive shield comprises planar conductive regions oriented to form a non-shielded inner region, and further wherein the antenna is disposed within the non-shielded inner region and parallel to the planar conductive regions.

2. The RFID system of claim 1, wherein the width of the conductive shield within the plane parallel to the antenna shapes the electromagnetic field to extend substantially in a direction perpendicular to the antenna, and prevents the electromagnetic field from forming substantially over the conductive shield.

3. The RFID system of claim 1, wherein the conductive regions define at least one disconnect area that prevents the conductive shield from forming a closed conductive loop around the antenna.

4. The RFID system of claim 1, wherein the antenna comprises one or more conductive loops including an outer loop, and the conductive regions of the conductive shield are located at least a distance D from an outer loop of the antenna that is selected based on a radius of the outer loop.

5. The RFID system of claim 1, wherein the antenna has a first conductive loop having a radius D1 and a concentric second conductive loop having a radius D2, and the conductive regions of the conductive shield are located at least a distance D3 from the outer loop, and wherein D3 is selected as approximately the average of D1 and D2.

6. The RFID system of claim 1, wherein each of the conductive regions have respective widths extending outward from the antenna, and further wherein each of the widths are selected based at least in part on the threshold level of the magnetic field necessary for RFID communication between the antenna and the RFID tags.

7. The RFID system of claim 6, wherein each of the widths are selected to extend sufficiently in directions parallel to and outward from the antenna to prevent the electromagnetic field from forming in or above the conductive regions until the strength of the magnetic field reduces to below the threshold level.

8. The RFID system of claim 1, wherein the antenna and the conductive shield are mounted to a working surface of an RFID check-in/check-out area.

9. The RFID system of claim 8, wherein the working surface has a recessed area and a non-recessed area, and further wherein the antenna is mounted to the recessed area of the working surface and the conductive shield is mounted to the non-recessed area.

10. The RFID system of claim 1, wherein the conductive shield and the antenna are co-planar.

11. The RFID system of claim 1, wherein the conductive shield and the antenna are located in two different parallel planes.

12. The RFID system of claim 1, further comprising:

an RFID interrogation device coupled to the antenna, wherein the interrogation device interrogates the RFID tags to obtain information regarding associated articles; and

a computing device to process the information retrieved from the RFID interrogation device.

13. The RFID system of claim 1, wherein the antenna comprises a plurality of conductive loops to produce the electromagnetic field, and wherein the conductive loops are spaced apart at least a distance D that is selected based on a dimension of the RFID tags with which the antenna communicates.

14. The RFID system of claim 13, wherein the distance D is selected to exceed a maximum dimension of the RFID tags.

15. The RFID system of claim 13, wherein the RFID tags have a dimension of length M, and the distance D between each of the plurality of conductive loops is selected such that D≧

M.

16. The RFID system of claim 1, further comprising

an RFID reader that incorporates the antenna;

and

a computing device to control the RFID reader.

17. A method comprising:

providing an antenna that forms an electromagnetic field that defines a communication zone in which RFID tags can be read, wherein the antenna has a substantially planar form;

selecting a width of a substantially-contiguous conductive shield such that when the conductive shield is positioned a distance from the antenna within a plane parallel to the antenna to define an outermost region of the communication zone within the plane parallel to the antenna, the electromagnetic field at any region beyond the conductive shield is below a threshold level for communication with the RFID tags;

orienting planar conductive regions of the conductive shield to form a non-shielded inner region; and

positioning the substantially-contiguous conductive shield having the selected width round the antenna within the non-shielded inner region a distance from an outer hoop of the antenna and parallel to the planar conductive regions.

18. The method of claim 17, wherein selecting the width of the substantially-contiguous conductive shield comprises selecting the width to shape electromagnetic field to extend substantially in a direction perpendicular to the antenna and prevent the electromagnetic field from forming substantially over the conductive shield.

19. The method of claim 17, further comprising selecting each of the widths of each of the conductive regions based at least in part on the threshold level of the magnetic field necessary for RFID communication between the antenna and the RFID tags.

20. The method of claim 19, wherein selecting each of the widths comprises selecting each of the widths to extend sufficiently in directions parallel to and outward from the antenna to prevent the electromagnetic field from forming in or above the conductive regions until the strength of the magnetic field reduces to below the threshold level.

21. The method of claim 17, further comprising mounting the antenna and the conductive shield to a working surface of an RFID check-in/check-out area.

22. The method of claim 21,

wherein the working surface has a recessed area and a non-recessed area, and

wherein mounting the antenna and the conductive shield comprises mounting the antenna to the recessed area of the working surface and mounting the conductive shield to the non-recessed area.

23. The method of claim 17, further comprising:

interrogating the RFID tags with an RFID interrogation device coupled to the antenna to obtain information regarding articles associated with the RFID tags;

retrieving the information from the RFID interrogation device with a computing device, and

processing the information with the computing device.

24. The method of claim 17, further comprising:

determining a dimension M of the RFID tags for use within an RFID system;

selecting a distance D based on the dimension M; and

positioning a plurality of conductive loops of the antenna the selected distance D apart for communication with the RFID tag within the RFID system.