ISSN : 1796-2021
Volume : 2    Issue : 6    Date : November 2007

Efficient Antenna Design of Inductive Coupled RFID-Systems with High Power Demand
Christian Reinhold, Peter Scholz, Werner John, and Ulrich Hilleringmann
Page(s): 14-23
Full Text:
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In contrast to pure identification labels, passive inductive coupled RFID transponders with
enhanced functionality have an increased power consumption. A nonoptimized antenna design for
high power transponders may lead to a poor efficiency and high magnetic field emissions.
Therefore, in this work, the energy transmission of inductive coupled systems is investigated,
enabling an optimized system design. The RFID system is modeled by network elements in order
to optimize the energy transmission. Next to a brief review of different methods for the antenna
parameter determination, a new modification of the PEEC method is derived enabling an
accelerated and accurate computation of the mutual coupling of the reader and the transponder
antenna. Along with the simplification of the transformed transponder impedance and the
investigation of the reader matching, consecutive design steps are deduced. The influence of the
location-dependent antenna coupling on the energy transmission is characterized. Two case
studies are carried out showing a successful transmission of 80mW over a distance of up to 7.6 cm
by 275mW reader output power. This system demonstrates an efficient energy supply of a high
power transponder while keeping the field emissions low.

Index Terms
RFID System, Antenna Design, Inductive Coupling, Wireless Energy Transmission, Quality Factor,
Inductance Calculation, PEEC