In-body power transfer and data communication for active neural implants

Abstract

The advent of active implantable medical devices has led to a paradigm shift from previous solutions to medical conditions. The remarkable success of early therapeutic devices, such as the cardiac pacemaker, has encouraged the development of more advanced systems, expanding the reach and ambition of implantable devices - now targeting significantly more complex diseases and treatments. Neural implants, which are able to effectively interact with the nervous system, are an important example of this progress. Such medical devices have demonstrated a significant impact on the quality of life of millions of patients worldwide, e.g. with treatments of Parkinson’s disease and Epilepsy. Neural implants have evolved in the years, transitioning from open-loop neuromodulators to closed-loop neuromodulators. These includes also a monitoring function in addition to stimulation. This method allows to activate the intervention only when required and to receive feedback on the effectiveness of the treatment. More recently, to target the limitations of the single-module implants new generations of AIMDs are emerging that are based on a multi-module approach: the system is now partitioned and distributed across multiple implants, each with specific functions and located at different sites. Distributed systems promise to give clear advantages, paving the way for numerous medical applications requiring high-channel stimulation and sensing to/from many locations in the body. However, they introduce a new set of challenges, both at the development and deployment stages. These are related to additional design considerations specific to the presence of multiple modules within an implanted system. This thesis investigates power transfer and data communication between multiple implanted devices and the development of interfacing circuits, which will contribute towards the implementation of a modular closed-loop AIMD for treating refractory focal Epilepsy. The specific objectives of this investigation have been framed to address the key challenges in the creation of a medical device for clinical trials, thus prioritising adequate performance of the medical functions, while ensuring implant system reliability in a human body. A custom protocol has been developed – the 4WiCS – and circuits for inter-module connectivity have been designed, implemented, and fabricated in CMOS and PCB technology. These have been tested within an end-to-end platform, informing further design of a novel fully-integrated System-on-Chip – the CANDO4 SoC – fabricated as part of the CANDO project neural implant.