An equivalent circuit model for designing wireless programmable FSS for WPT EMI suppression and secure communication of implanted devices

Wireless Power Transfer (WPT) has emerged as a crucial technology for Implantable Medical Devices (IMDs), addressing the limitations of traditional batteries by enabling contactless and continuous energy delivery. Moreover, such wireless-enabled IMDs also allow remote monitoring and programming within the Medical Implant Communication Service (MICS) band (401-406 MHz). However, since WPT can happen in the same band, the electromagnetic emissions from WPT systems could interfere with the IMD, and the wireless channel also makes them vulnerable to various physical and cyber threats. To address these challenges, this paper describes the design of a programmable Frequency Selective Surface (FSS) in the MICS band, providing dual functionality: shielding the implanted device from unauthorized electromagnetic fields by default (OFF state) and enabling wireless power transfer and secure communication upon authentication (ON state). The synthesis procedure is based on an Equivalent Circuit Model (ECM) that offers a closed-form analytical framework for designing an FSS that meets the required frequency filtering specification (e.g., working frequency and transmission bandwidth). The ECM is validated through full-wave simulations, highlighting its accuracy and computational efficiency.