Radiofrequency Magnetic Field Devices for Biomedical Applications: Magnetic Hyperthermia - Magnetic Resonance Imaging - Wireless Power Transfer

In the present work, the attention is drawn towards magnetic field applications for biomedical devices, exploiting the radiofrequency (RF) range from 300 kHz to 300 MHz. In this range, a lot of different applications have been proposed in the literature; in particular, the dissertation will cover three main topics: Magnetic Particle Hyperthermia (MPH), Magnetic Resonance Imaging (MRI) and resonant inductive Wireless Power Transfer (WPT). In detail, Chapter 1 is devoted to present the work about Magnetic Particle Hyperthermia developed in collaboration with the Italian National Research Council Institute of Clinical Physiology (IFC-CNR) and with the research center of Colorobbia S.p.A. (Ce.Ri.Col, Sovigliana Vinci, Firenze). We first address the development of a fast and efficient electromagnetic characterization method for colloidal magnetic fluids with nanoparticles, which is a fundamental step for optimizing their use; secondly, the design of a novel focusing RF radiating system to perform safe and efficient hyperthermic treatments for superficial tumors is investigated. In Chapter 2, the inductive mutual coupling, arising when arrangements of multiple RF MRI coils are used, is faced. In particular, we propose an innovative approach to solve this issue, employing small spiral resonators, precisely designed and positioned between the RF coils. Hence, the electromagnetic characterization of the employed resonators has been firstly carried out, developing a method to extract an accurate and reliable lumped equivalent circuital model. Then, this step has been followed by the analytical formulation of a framework to design a decoupling filter using such resonators; in particular, this study was conducted in collaboration with the University of L’Aquila (L’Aquila, Italy). Chapter 3 introduces the topic about resonant inductive Wireless Power Transfer. We present the design of an extremely compact, low-frequency metasurface, able to bring significant benefits to WPT applications, despite the ultra-thin thickness. After that, the possibility to finely control efficiency, gain and magnetic field distribution in a WPT device is investigated and an analytical framework to design arrays of concentric non-resonant loops for tunable WPT devices is presented. The author has conducted the WPT research activities at the Keck School of Medicine of University of Southern California (Los Angeles, California, USA), under the supervision of Prof. Gianluca Lazzi, during a 1 year research appointment as a visiting Research Scholar (1 May 2018 – 30 April 2019).