Flexible Metasurface-Coupled Efficient Wireless Power Transfer System for Implantable Devices

Wireless power transfer (WPT) is a promising technology for enabling the long-term operation of advanced implantable medical devices (IMDs). This article presents a highly efficient near-field WPT system for wirelessly driven or rechargeable miniaturized IMDs, comprising an off-body transmitter (Tx), a flexible on-body mu-negative (MNG) metasurface slab, and an in-body receiver (Rx). The Rx element with dimensions 7.5 \times 7.15 \times 0.75 mm ^3 exhibits dual-band characteristics (i.e., 433 and 915 MHz) for simultaneous wireless power reception and data telemetry. The flexible MNG slab serves as a wearable device, focusing the magnetic field toward the Rx, thereby increasing the efficiency of the proposed WPT system. Simulation and measurements are conducted to analyze the systems performance. Interestingly, the MNG-coupled WPT system offered significant improvement in the power transmission efficiency (PTE) in various realistic scenarios, including misalignments and varying Tx-Rx separations. Remarkably, an increment of approximately 17% is achieved in the PTE from 3.37% to 20.36% at a 10 mm distance. In addition, a wireless communication link analysis is conducted to specify the range for biotelemetry. Moreover, a compact rectenna system is developed incorporating a rectifier with a power conversion efficiency (PCE) of 73.7% at 6 dBm input power. Simulation and real-time experimental results demonstrate the effectiveness of the proposed flexible metasurface-coupled WPT system for compact implantable biotelemetric devices.