Journal
IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT
Volume 60, Issue 8, Pages 2797-2803Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TIM.2011.2122390
Keywords
Antenna accessories; impedance matching; loop antennas; magnetic devices; magnetic-variable control
Funding
- Austrian Science Fund (FWF) [L356-N14]
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Systems for radio-frequency identification (RFID) realize a bidirectional wireless communication between a reader device and cheap passive tags (e. g., an RFID chip with an antenna printed on badges for access-control systems) in the near field of an antenna. This paper deals with the automatic and fast tuning of the resonant reader antennas in the widely used 13.56-MHz frequency band, resulting in a performance improvement and an increased READ/WRITE range. A novel RFID reader system is proposed with a tuning transformer for the automatic adjustment of the resonant circuit center frequency. This is achieved by shifting the magnetic operating point (i.e., the biasing direct-current (dc) magnetization) of a Ni-Zn ferrite transformer by means of an additional dc winding. The operation principle and the performance potential of this device are demonstrated by measurements on a prototypical RFID system.
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