Abstract-Passive UHF RFID tag consists of a microchip attached directly to an antenna. Proper impedance match between the antenna and the chip is crucial in RFID tag design. It directly influences RFID system performance characteristics such as the range of a tag. It is known that an RFID microchip is a nonlinear load whose complex impedance in each state varies with the frequency and the input power. This paper illustrates a proper calculation of the tag power reflection coefficient for maximum power transfer by taking into account of the changing chip impedance versus frequency.
Abstract-Novel reconfigurable frequency selective surfaces (RFSS) are designed using a finite-difference time-domain with periodic boundary condition (FDTD/PBC) algorithm.The FSS are reconfigured using two techniques: the first technique providing a wide frequency tuning range is based on using diodes to change the current distribution over the FSS surface, and the second technique exhibiting a finer frequency tuning resolution is based on changing the grid orientation of the FSS mechanically. Simulation results are provided to validate the concept of RFSS. The results show that these designs provide a wide dynamic range of reconfigurability and a large degree of freedom in controlling the FSS frequency response.
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