Efficient Metamaterial-Integrated Radiative Near-Field Wireless Power Transfer System for Scalp-Implantable Devices in IoMT Applications

Wireless power transmission to implants enables a reliable, continuous, and noninvasive energy supply, essential for the seamless operation of modern biomedical devices, particularly in the growing field of the Internet of Medical Things (IoMT). This article presents a compact, batteryless implantable system for intracranial pressure (ICP) monitoring, which consists of a metamaterial-integrated external transmitter (Tx) and an in-body receiver (Rx). The implantable Rx antenna, measuring 11x10x0 .2 mm (volume = 22 mm(3)), operates at dual frequencies of 1.7 and 2.4 GHz, supporting simultaneous wireless power reception and data telemetry. The lightweight polyimide-based mu-negative (MNG) metamaterial was employed on the body surface as a wearable device to enhance the coupling between Tx and Rx. Extensive simulations and experimental validation were conducted on minced pork tissue to verify the system's effectiveness. Significant enhancements in the transmission coefficient (S-21) were achieved using MNG metamaterial across various scenarios, including misalignments and varying Tx-Rx distances. Specifically, the integration of MNG metamaterial improved the S-21 from -24 to -17 dB, with a corresponding power transfer efficiency improvement of 1.58% at a Tx-Rx distance of 22 mm. Moreover, the antenna exhibited measured peak gains of -20.88 and -15.57 dBi, with -10-dB bandwidths of 24.6% and 19.9% at 1.7 and 2.4 GHz, respectively. Wireless communication link analysis was performed to determine the biotelemetry range, ensuring consistent and reliable data transmission. Moreover, a specific absorption rate (SAR) analysis was performed to meet safety requirements. With its advanced features and performance metrics, the proposed novel wireless power transfer-enabled biotelemetric system provides an efficient and reliable solution for wireless, battery-free ICP monitoring applications within the IoMT ecosystem.