600431 Disclosed is a radio frequency identification (RFID) system. The system includes a signal cancelling antenna (400) and an RFID reader circuit configured to drive the signal cancelling antenna (400) with an interrogation signal. The RFID reader circuit and the signal cancelling antenna (400) are configured to detect data modulated onto the interrogation signal. The signal cancelling antenna (400) includes a plurality of loops (401, 402) and at least two of the plurality of loops (401, 402) generates magnetic fields having opposite polarity when driven by the interrogation signal. The magnetic fields generated by the plurality of loops (401, 402) comprise a crossover point where the magnetic fields generated by the plurality of loops (401, 402) are equal and thereby cancel each other. The plurality of loops (401, 402) is physically arranged so that, when driven by the interrogation signal, the magnetic field proximal to each loop activates any passive RFID transponders present. The antenna (400) is oriented such that any passive RFID transponder is proximal to each of the plurality of loops (401, 402) in the signal cancelling antenna (400) 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. An acoustically resonating metallic structure proximal to the signal cancelling antenna (400) produces acoustic noise in an acoustic noise frequency range that causes magnetic field perturbations creating amplitude variations in a portion of the magnetic field signal emitted by the plurality of loops (401, 402) that is reflected by the acoustically resonating metallic structure. The acoustically resonating metallic structure is located relative to the signal cancelling antenna (400) such that the created amplitude variations are induced equally to each loop in the plurality of loops (401, 402). 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. The created amplitude variations interfere with the signal transmitted by the passive RFID transponders; and the signal cancelling antenna (400) is configured to reduce electromagnetic noise interference resulting from the acoustically resonating metallic structure due to the physical arrangement of the plurality of loops (401, 402) causing the magnetic fields generated by the loops (401, 402), when driven by the interrogation signal, to collectively cancel with increasing distance from the antenna (400).
Signal cancelling transmit/receive multi-loop antenna for a radio frequency identification reader