An Optimised Approach to Wireless Power Transfer for an Artificial Retina Implant

Abstract

An artificial retina can replace some of the functionality of the eye in people that have experienced partial or complete loss of vision. Loss of vision is associated with many negative effects in one’s life and can be a debilitating condition. Artificial retinas in the form of a chip thus offer the potential to greatly improve people’s lives.

A wireless implementation is much preferred to the wired alternative, as it reduces the risks associated with implantable devices while also being less invasive to the patient. Wirelessly powering an artificial retina implant requires careful consideration of the impact on tissue heating as this is the fundamental
limit in how much power an implantable device can consume.

This thesis provides an optimal implementation of wireless power transfer in the framework of an artificial retina implant with the explicit goal of reducing tissue heating. A literature study forms the basis for identifying the key metrics and providing a switched capacitor power converter (SCPC) topology needed to realise the final system performance. The key innovations are a first-of-its-kind design of an ctive rectifier, a novel system-level optimisation and an SCPC to implement the o ptimised system approach while simultaneously enabling a novel, efficient, low-overhead closed-loop control of the link. It was shown that a 30 % reduction in radiated power can be realised for a given system while maintaining the same output load power. The designed active rectifier can achieve orders of magnitude faster settling compared to the state of the art, allowing rapid amplitude-shift keyed data transfer to be employed on the wireless power transfer link. The active rectifier achieves a simulated voltage conversion ratio of 92.0 % and a power conversion efficiency of 90.1 % for a 500 Ω load. an SCPC as designed and fabricated to achieve a load transformation to the calculated optimum load. A simulated 80 % efficiency at a power density of 29 mW/mm2 was achieved, with a conversion range of 0.7 − 1.8. Measurement results proved to be inconclusive. The SCPC was shown not to work and the active rectifier’s performance couldn’t be precisely verified. An improved measurement setup and additional debugging options in the chip design are among the proposed improvements for future work.