Omnidirectional Magnetoelectric Wireless Power Transfer for Implantable Intracranial Pressure Monitoring.

Abstract

Wireless power transfer is attractive for battery-free intracranial pressure (ICP) monitors, but practical operation is often limited by angular misalignment between the external transmitter and the implanted receiver. Magnetoelectric (ME) receivers offer a compact, sub-MHz, and high-sensitivity alternative to conventional receivers, but a single ME element still suffers from a severe power drop near 90-degree misalignment because of its anisotropic magnetic response. Here, we present a three-axis ME wireless power receiver that provides robustness against transmitter-receiver angular misalignment for battery-free ICP monitoring. The receiver integrates three orthogonal Metglas/PMN-PT/Metglas ME elements, each with a compact size of 6 × 2 × 0.65 mm³ and a voltage sensitivity of 0.17 V_p/μT near 200 kHz. To improve rectifier driving capability, a C-L step-up impedance matching network was designed for the high-impedance ME source, increasing the rectified output voltage by 3.2-fold under the tested condition. A voltage-balanced parallel energy-combining circuit was used to suppress inter-axis clamping and combine harvested currents across orthogonal axes. The integrated receiver achieved a peak received power of 4 mW at a 20-mm transmission distance and maintained an angular tolerance index of 95.7%. A 10 × 10 × 8 mm³ encapsulated prototype was validated in the epidural space of an ex vivo porcine head model, maintaining >3.15 mW output across full 0°-180° spatial rotations of the external transmitter and enabling uninterrupted Bluetooth telemetry with 0% packet loss at 50 cm.