Signal cancelling transmit/receive multi-loop antenna for a radio frequency identification reader
First Claim
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 magnetic fields generated by the plurality of loops comprise a crossover point where the magnetic fields generated by the plurality of loops are equal and thereby cancel each other;
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;
wherein the antenna is oriented such that any passive RFID transponder is proximal to each of the plurality of loops in the signal cancelling antenna and the RFID reader circuit is configured to read any passive RFID transponders present when the passive RFID transponders are offset from the crossover point;
wherein a acoustically resonating metallic structure proximal to the signal cancelling antenna produces acoustic noise in an acoustic noise frequency range that cause magnetic field perturbations creating amplitude variations in a portion of the magnetic field signal emitted by the plurality of loops that is reflected by the acoustically resonating metallic structure;
wherein the acoustically resonating metallic structure is located relative to the signal cancelling antenna such that the created amplitude variations are induced equally to each loop in the plurality of loops;
wherein the passive RFID transponders are configured to transmit signals on data frequencies falling within the frequency range coincident with the acoustically resonating metallic structure frequency range;
wherein the created amplitude variations interfere with the signal transmitted by the passive RFID transponders; and
wherein the signal canceling antenna is configured to reduce electromagnetic noise interference resulting form the acoustically resonating metallic structure due to the physical arrangement of the plurality of loops causing the magnetic fields generated by the loops, when driven by the interrogation signal, to collectively cancel with increasing distance from the antenna.
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0 Petitions
Accused Products
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.
65 Citations
30 Claims
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1. A radio frequency identification (RFID) system, comprising:
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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 magnetic fields generated by the plurality of loops comprise a crossover point where the magnetic fields generated by the plurality of loops are equal and thereby cancel each other; 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; wherein the antenna is oriented such that any passive RFID transponder is proximal to each of the plurality of loops in the signal cancelling antenna and the RFID reader circuit is configured to read any passive RFID transponders present when the passive RFID transponders are offset from the crossover point; wherein a acoustically resonating metallic structure proximal to the signal cancelling antenna produces acoustic noise in an acoustic noise frequency range that cause magnetic field perturbations creating amplitude variations in a portion of the magnetic field signal emitted by the plurality of loops that is reflected by the acoustically resonating metallic structure; wherein the acoustically resonating metallic structure is located relative to the signal cancelling antenna such that the created amplitude variations are induced equally to each loop in the plurality of loops; wherein the passive RFID transponders are configured to transmit signals on data frequencies falling within the frequency range coincident with the acoustically resonating metallic structure frequency range; wherein the created amplitude variations interfere with the signal transmitted by the passive RFID transponders; and wherein the signal canceling antenna is configured to reduce electromagnetic noise interference resulting form the acoustically resonating metallic structure due to the physical arrangement of the plurality of loops causing the magnetic fields generated by the loops, when driven by the interrogation signal, to collectively cancel with increasing distance from the antenna. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 27, 28)
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24. A method of interrogating a passive transponder in the presence of metal structures vibrating at acoustic frequencies, comprising:
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positioning an antenna having a plurality of loops so that the vibrating metal structures are located at least a first distance from the antenna, where; the vibrating metal structure produces acoustic noise in an acoustic noise frequency range causing magnetic field perturbations creating amplitude variations in a portion of a magnetic field signal that is reflected by the vibrating metal structure and the amplitude variations interfere with a signal transmitted by a full-duplex transponder; the acoustically resonating metallic structure is located relative to the antenna such that the created amplitude variations are induced equally to each loop in the plurality of loops; and where magnetic fields generated by the plurality of loops comprise a crossover point where the magnetic fields generated by the plurality of loops are equal and thereby cancel each other; orienting the antenna such that any full-duplex transponders are proximal to each of the plurality of loops in the antenna, where; the full-duplex transponders are configured to transmit signals on data frequencies coincident with acoustically resonating metallic structure frequency range; and the antenna is oriented such that any passive RFID transponder is proximal to each of the plurality of loops in the antenna and the RFID reader circuit is configured to read any passive RFID transponders present when the passive RFID transponders are offset from the crossover point; driving the antenna using and interrogation signal to generate the magnetic fields having instantaneous opposite polarity that collectively cancel each other beyond the first distance from the antenna; reducing electromagnetic noise interference resulting from the acoustically resonating metallic structure using the antenna due to the physical arrangement of the plurality of loops causing the magnetic fields generated by the loops, when driven by the interrogation signal, to collectively cancel with increasing 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. - View Dependent Claims (25, 26, 29, 30)
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Specification