Wireless Power Systems Design for Implantable Biomedical Devices

The daily demand of a technology-driven society, focused on innovation and continuous re-invention of almost every product we use in our daily life has led to the tremendous amount of progress we have experienced in the last century. We have continuously shifted, year after year, from a product that was considered "perfect" to something even better. From landline, to mobile phones, to portable computers, everything keeps changing and evolving. With this continuous technological progress driven by demand, wireless power has recently become one of the most urgent needs in many applications, ranging from automotive to consumers electronic, also covering sectors such as military and healthcare.

The starting point of this PhD project aims to tackle the main challenges associated with Wireless Power Charging in the field of Implantable Biomedical Devices.

This is in line with the EPSRC research area of Power Electronics, under the strategic themes of Engineering and Healthcare Technologies.

The initial research will focus on assessment of health and safety risks for Pacemaker users, aiming to prove compatibility of existing inductive power transfer systems with the emissions limits stated in ICNIRP 1998 and BSI 60601/45502.

One of the most significant differences from other Wireless Power Transfer systems is the presence of a metallic body in close proximity of the receiver coil. This affects multiple design choices for the optimization of wireless power links, ranging from optimal coil geometry for maximum coupling of the two coils to quality factor's optimization.

A reduction of the equivalent quality factor of the receiver coil due to the pacemaker body implies the need of operating at a higher frequency to bring the link efficiency to reasonable values; this leads to the development of Wireless Power system that operate in the ISM band Mega-Hertz range, focusing mainly on 6.78 MHz, 13.56 MHz and 27.12 MHz.

The uncertainty in the position of a small coil inside the body and the presence of surrounding organic material can lead to a significant decrease in coupling factor. This aspect is not only relevant in terms of efficiency loss, but can also affects correct operation of the transmitter side. Because of the potentially big variation in coupling factor, there will be a significant effect on reflected impedance to the primary side, leading to tuning issues.

We aim to investigate synchronous rectification as a potential solution to this issue, essentially replicating a DC-AC inverter architecture with a gate-switching signal constantly operating with a 90 degrees phase shift from the transmitter's side. One of the main challenges of this lays in the practical implementation of a high frequency synchronization system that is capable to produce a high-precision gate signal, minimizing losses from potential phase mismatches.

This specific aspect of the PhD research project has a high potential and versatility, finding applications in a wide range of low-coupling systems. Not only this technology is easily transferable, but it could also be an interesting starting point for high frequency bidirectional wireless power charging through phase control, arbitrarily switching the operating mode of either of the two sides of the system from transmitter to receiver.

Given the wide amount of applications and optimizable aspects in the discussed topics of wireless power, I believe this research has the potential of offering new and interesting results for the enhancement of both pre-existing and emerging technologies.