Analysis of Impact of Bioimpedance on Performance of Implant Coil of Artificial Retina for Optimizing Q Factor & Bandwidth

Spiral coils are indispensable part of implantable electronics for facilitating wireless power and data transfer. Although many advanced high Q receiver design have emerged, implementing and retaining high Q in biological medium so as to improve link efficiency is challenging. This article bridges the gap between advanced techniques towards improving link efficiency and the tissue losses that deteriorates the Q factor of coil in heterogeneous tissue medium. The purpose of this research is to improve the Q factor and bandwidth of the coil in tissue medium by reducing the net conductance of the coil in tissue medium, which is comparable to the net conductance in air. Bioimpedance of each layer of the eye is modelled to identify the highly capacitive and highly conductive tissue layer in the eye. To investigate the worst-case and best-case scenario, Q factor and bandwidth of the implant coil is analysed in the eye with and without aqueous humor which is a highly conductive and capacitive tissue layer in the eye. The coil is encapsulated with breast fat which possess lowest permittivity of all body tissue. After removing the high conductive tissue layer from the implantation zone, the Q factor and bandwidth of the coil is improved by 87.5% and 97.7% respectively. It is observed that 100% Q at 10 MHz and 76.75% of bandwidth is recovered in tissue medium after using breast fat as encapsulation layer. This demonstration of coil for various test cases in tissue medium aids to device a reliable, safe and efficient wireless power/data transfer system for artificial retina.