Metamaterial Inspired Geometries for Wireless Power Transfer to Biomedical Implants

Wireless charging of biomedical implants will make the life of patients with implants much easier. However, it is associated with significant design challenges - efficiency degradation and the need to meet standards for exposure to electromagnetic fields. Biomedical tissue dielectric and conductive properties affect the electrical performance of an inductor, which appears on increased effective inductance, reduced quality factor, and reduced self-resonance. Building a wireless power transfer (WPT) system using such inductors leads to low efficiency and low power that limit specific absorption rate. In this work, we study the characteristics of inductance in biomedical tissue and present a theory to maintain the effective inductance with the same value in the air and biomedical tissue. Finally, to overcome these issues, we propose a metamaterial inspired geometry with near-zero permeability. This metamaterial inspired geometry is stacked split ring resonator metamaterial fed by a driving inductive loop and acts as a WPT transmitter for an in-tissue implanted WPT receiver. The presented demonstrations have confirmed that the proposed metamaterial inspired WPT system outperforms the conventional one. Also, the resonance frequency of the proposed metamaterial inspired TX is negligibly affected by the tissue characteristics, which is of great interest from the design and operation prospects. Furthermore, the proposed WPT system can be used with more than twice the input power of the conventional one while complying with the safety regulations of electromagnetic waves exposure.