Completely wireless infrastructure for distributed mm-sized neural implants

Abstract

Life-threatening medical conditions such as stroke, spinal injuries and traumatic brain injury affects millions of people worldwide. The emerging prospect of neural interfaces provides hope for these patients to regain their ability through treatment. Current examples of neural interfaces have proven their potential, with paralysed patients demonstrating control of robotic wheelchairs and prosthesis through the use of these such devices. Neural interfaces have also served as crucial research tools for neuroscientists working on deciphering the secrets of the human brain in order to reveal the causes of neurological and psychiatric disorders. However, current challenges of neural implants are tissue inflammation and cell death, which are caused by large tethered bulky centralised implanted devices. In order to reduce these detrimental effects, the prevalent concept of next-generation neural interfaces are free-floating distributed millimetre-scaled or sub- millimetre-scaled implants. This work explores the feasibility of wireless connections for distributed mm-scale neural implants, proposes a novel efficient wireless power transfer, and demonstrates an innovative method of multiple access data communication. The original contributions of this work are summarised as three aspects. Contribution 1: The selection of receiving coils is critical to the wireless connections of implantable medical devices. It determines the capability of wireless systems for electromagnetic energy delivery and data communication. To the best of author's knowledge, this work is the first time to thoroughly compare three types of millimetre-scale CMOS-compatible coils from three perspectives: electromagnetic characteristics, manufacturability and mechanical stability. Consequently, the microfabricated coil is selected as the receiving implantable coil, instead of wire-wound and CMOS coils, because of its excellent electrical properties and stable mechanical structure. Contribution 2: Inductive links and power management units are the key components in wireless power transmission systems for efficient power transfer and stable power supply. This work proposes the passive resonant arrays where are placed in multiple coupled inductive links. They boost the received voltage two times and extend power coverage four times, compared to the conventional inductive link without the resonant arrays. In addition, innovative self-regulated power management is proposed to solve unpredictable misalignments between transmitter and distributed receivers. Contribution 3: The low power multiple access data communication system ensures that hundreds of distributed implants simultaneously transmit recoding signals to an external receiver. This work demonstrates the backscatter-based data communication technique for multiple passive implantable devices. The multiple access data communication systems achieve 1.25Mbps data rate per node and 1mW power consumption per passive device. In addition, the autonomous SoC with the ASK data modulator proves the feasibility of two data carriers detection, which indicate a new direction for passive, low-power, multi-access implantable medical devices. I envision that this work could eventually be further developed into general purpose wireless infrastructure for implantable medical devices or wearable devices.