Metallic Inductive Coupling Frame-based HF RFID Cards

Abstract

A coupling frame-based HF RFID card is composed of a metallic coupling frame with a slot and a module (contains a small coil and an integrated circuit). This provides higher coupling and better performance in comparison to the standalone module. Such design eliminates the need for a mechanical connection between the module and card body (metal frame) which leads to reduced manufacturing costs. Further, it enhances the card's robustness against mechanical stress. We explain the operation of such a design from first principles and highlight the effect of the slot on the performance. Additionally, a circuit model for the card is derived. Furthermore, we propose an enhancement to the card design which improves the card's performance with two variations either in terms of better transferred voltage (up to 3 times higher) or more bandwidth (up to double). The enhancement is shown by HFSS simulations, circuit simulations and corresponding measurements including the HF RFID integrated circuit. Finally, a double coupling frame-based design is proposed and analyzed which simultaneously achieves increased bandwidth and higher transferred voltage. The results are compared to those of conventional HF RFID cards with galvanic coupling to the integrated circuit.