Efficient Antenna Design of Inductive Coupled RFID-Systems with High Power Demand

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 80 mW over a distance of up to 7.6 cm by 275 mW reader output power. This system demonstrates an efficient energy supply of a high power transponder while keeping the field emissions low.