Implantable Reconfigurable FSS for Wireless Protection of Implantable Cardiac Devices in the ISM Band

This paper presents a novel reconfigurable electro-magnetic shield for securing cardiac Implantable Medical Devices (IMDs) against unauthorized access over the 2.45 GHz Industrial, Scientific, and Medical (ISM) band. The proposed shield is conceived to be permanently implanted and placed above the pacemaker within the subcutaneous pocket, thereby providing continuous protection without affecting patient comfort or device usability. The shield is implemented as a wireless reconfigurable Frequency Selective Surface (FSS) incorporating varactor diodes and Radio Frequency Identification (RFID) Integrated Circuits (ICs) to enable dynamic switching between transparent (ON) and shielded (OFF) states. The FSS unit cell comprises a Jerusalem Cross surrounded by an inductive grid, ensuring polarization-independent operation and parallel biasing of the varactors. Fullwave electro-magnetic simulations of the unit cell inserted in a layered human body model confirm the feasibility of the idea, showing a variation in the transmission coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S_{21}$</tex> exceeding 28 dB between the OFF and ON states and insensitivity to linear and circular polarization.