Schormans, Matthew James; (2019) Inductive Links for Biomedical Wireless Power and Data Telemetry: Circuits and Methods. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Implantable medical devices (IMDs) have been a subject of much commercial and academic interest and research since their inception in the form of the first pacemakers. Over time they have been developed to perform a wide range of functions, including neurostimulation, pressure sensing, and neural recording, to name a few. A key building block of IMDs is telemetry; they must have some way to receive power from, and communicate with, the outside world. One of the most common methods of providing this telemetry is through an inductive link. While inductive telemetry has existed in some form since the inception of IMDs, it is still a subject of research today; there is increasing pressure to design links that are more power efficient, more resilient, and that can carry more data. This thesis contributes developments to the field of inductive link based telemetry for IMDs in the form of analyses and methods, as well as circuit and system designs. Firstly, the theory behind inductive links is extensively discussed and built upon, in order to provide a series of simple methods that can be used for inductive link design. A free software tool, the Coupled Coil Configurator (CuCCo) was produced to accompany the analyses, and aid in the design of inductive links. Secondly, a system was developed for tracking the optimum frequency of an inductive link, for use in powering passive implants. This system was fabricated and tested, and found to greatly improve the resilience of the link against coupling variations when overcoupled. Third, a methodology and system were developed together to allow a remote capacitive sensor to be easily interrogated through an inductive link. A proof-of-concept device was fabricated in 180 nm CMOS, and was found to agree well with the theory when measured, with a low power consumption. Fourth, the principles of stagger tuning for inductive links were investigated, and a dual-purpose power and data link was constructed using stagger-tuning. This approach was confirmed to greatly reduce the sensitivity of the link to coupling variations, as well as improving its performance when transferring data. Finally, a novel impulse-based system for data transfer via an inductive link was developed, allowing for high-speed low-power data transfer, without the need for carriers or local oscillators. This system was fabricated using 0.35 µm CMOS, and confirmed to achieve data transfer at up to 52 Mbps, with a power consumption of 8.11 pJ/b.

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