SIGNAL CANCELLING TRANSMIT/RECEIVE MULTI-LOOP ANTENNA FOR A RADIO FREQUENCY IDENTIFICATION READER

• US 20110210824A1
• Filed: 11/03/2010
• Published: 09/01/2011
• Est. Priority Date: 11/04/2009
• Status: Active Grant

• Current Assignee: MSD International GmbH (Merck & Co., Inc.)
• Original Assignee: Allflex USA Incorporated (Merck & Co., Inc.)
• Inventors: Stewart, Robert
• Granted Patent: US 8,854,188 B2
• Time in Patent Office: Days
• US Class Current: 340/10.1
• 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 7/10346 the antenna being of the far field type, e.g. HF types or dipoles
• CPC Class Codes: H01Q 1/00 Details of, or arrangements associated with, antennas arrangements for varying orientation of directional pattern H01Q3/00
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• 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

In an inductively coupled radio frequency identification (RFID) system deployed in animal and livestock applications, reading system efficacy can be compromised by animal movement on, around, or near metal structures prone to producing sonic frequencies. Such is the case, for example, when a walk-by antenna is mounted at the entry door of a livestock transport trader, and animals transit on a metallic ramp and metallic trader floor. Associated with the observable acoustic noise are subtle disturbances in the magnetic field surrounding the antenna due to vibrating metal altering the reluctance of the antenna'"'"'s magnetic field. This acoustic noise manifests itself as an electrical noise phenomenon that interferes with the signals of certain types of identification tags which rely on amplitude modulation. The detrimental effects of acoustic noise from metal structures can be mitigated by using a multi-loop antenna that limits the spatial distribution of the transmitted magnetic field and cancels close by magnetic field disturbances.

Claims

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

a signal cancelling antenna;

an RFID reader circuit configured to drive the signal cancelling antenna with an interrogation signal;

wherein the RFID reader circuit and the signal cancelling antenna are configured to detect data modulated onto the interrogation signal;

wherein the signal cancelling antenna includes a plurality of loops and at least two of the plurality of loops generate magnetic fields having opposite polarity when driven by the interrogation signal;

wherein the plurality of loops are physically arranged so that, when driven by the interrogation signal, the magnetic field proximal to each loop activates any passive RFID transponders present; and

wherein the physical arrangement of the plurality of loops causes the magnetic fields generated by the loops, when driven by the interrogation signal, to collectively cancel with increasing distance from the antenna.

2. The RFID system of claim 1, wherein the magnetic fields generated by each of the plurality of loops when driven by the interrogation signal are sufficient within a distance equal to half the largest dimension of the signal cancelling antenna for a passive RFID transponder to be activated and to modulate data onto the interrogation signal that can be detected by the RFID reader circuit.

3. The RFID system of claim 1, wherein a passive RFID transponder is incapable of being activated and modulating data onto the interrogation signal that can be detected by the RFID reader circuit at points where the magnetic fields generated by the loops of the antenna collectively cancel.

4. The RFID system of claim 1, wherein the plurality of loops of the signal cancelling antenna are connected in series.

5. The RFID system of claim 1, wherein the signal cancelling antenna includes two loops.

6. The RFID system of claim 5, wherein both of the loops have the same height, width, number of windings, and electrical current.

7. The RFID system of claim 6, wherein the two loops are connected in series.

8. The RFID system of claim 6, wherein the two loops are connected in parallel.

9. The RFID system of claim 5, wherein the magnetic fields generated by the two loops when the signal cancelling antenna is driven by the interrogation signal have instantaneous opposite polarity.

10. The RFID system of claim 5, wherein:

the first loop encloses a larger area than the second loop; and

the first loop and the second loop generate magnetic fields of equal magnitude having instantaneous opposite polarity.

11. The RFID system of claim 10, wherein the second loop includes more windings than the first loop.

12. The RFID system of claim 10, wherein the second loop carries a larger current than the first loop when the signal cancelling antenna is driven by the interrogation signal.

13. The RFID system of claim 1, wherein the signal cancelling antenna includes three loops.

14. The RFID system of claim 13, wherein the three loops are configured as an inner loop and two adjacent outer loops.

15. The RFID system of claim 13, wherein the area enclosed by a first loop is equal to the area enclosed by both the second and third loops.

16. The RFID system of claim 13, wherein the magnetic field generated by a first loop has instantaneous opposite polarity to the magnetic field generated by a second and third loop, when the signal cancelling antenna is driven by the interrogation signal.

17. The RFID system of claim 1, wherein all loops of the signal cancelling antenna have the same number of windings and carry the same electrical current, when driven by the interrogation signal.

18. The RFID system of claim 17, wherein the loops of the signal cancelling antenna are connected in series.

19. The RFID system of claim 17, wherein the loops of the signal cancelling antenna are connected in parallel.

20. The RFID system of claim 1, wherein the plurality of loops are arranged along an axis and the signal cancelling antenna is aligned so that the axis is parallel to the direction in which transponders move past the signal cancelling antenna.

21. The RFID system of claim 1, wherein the plurality of loops are configured so that the overall magnetic field generated by the signal cancelling antenna exhibits three dimensional symmetry.

22. The RFID system of claim 1, wherein the magnetic fields generated by each of the plurality of loops when driven by the interrogation signal collectively cancel at a distance at least equal to the largest dimension of the antenna.

23. The RFID system of claim 1, wherein the magnetic fields generated by each of the plurality of loops when driven by the interrogation signal collectively cancel each other at a distance at least twice the largest dimension of the antenna.

24. A method of interrogating a passive transponder in the presence of metal structures vibrating at acoustic frequencies, comprising:

positioning an antenna having a plurality of loops so that the vibrating metal structures are located at least a first distance from the antenna;

driving an antenna having a plurality of loops to generate magnetic fields having instantaneous opposite polarity that collectively cancel each other beyond the first distance from the antenna; and

detecting data modulated onto the interrogation signal by any full-duplex transponders present within the first distance during periods in which the interrogation signal is driving the antenna.

25. The method of claim 24, further comprising detecting data transmitted by any half-duplex transponders present when the interrogation signal is not driving the antenna.

26. The method of claim 25, wherein the plurality of loops of the antenna are aligned along an axis and further comprising locating the antenna so that the axis is parallel to the direction in which transponders move past the signal cancelling antenna.