Finite-Difference Time-Domain Analysis of Time Reversal Technique for Electromagnetic Fields Focusing on Human Head

The interaction between electromagnetic fields and human body has been studied for a long time, accounting for one of the most operative areas in theoretical and applied research concerning with the technologies of electromagnetism. Initially, the studies of the scientific community were focused on the possible harmful effects of the interaction between electromagnetic fields and the human body, forming a branch of physics named as radiation dosimetry. For some years now, the innovative idea of using this phenomenon to produce a specific effect has been taken into consideration. This innovation has met with great success in medical branch thanks to the nature of non-ionizing electromagnetic fields, their ability to penetrate matter, and the specificity of the electromagnetic properties of the different human tissues, also according to the several pathological conditions. Consequently, some diagnostic and therapeutic technologies have been introduced into clinical routine. Some examples are the Magnetic Resonance Imaging and the Tomographic Microwave Imaging for diagnostic applications and Microwave-induced hyperthermia and Radar therapy for the treatment of some diseases. Other methodologies are being developed to cooperate with those currently in use to enhance the quality of the diagnosis or the therapeutic efficacy for certain diseases. New approaches to overcome the limitations of current methodologies are based on the usage of the Time Reversal (TR) technique. Recently applied on electromagnetism, the TR exploits the principle of reciprocity to focus wave energy to a selected point in space and time. In the present thesis, we propose a numerical study of TR principles to focus, both spatially and temporally, electromagnetic fields on human head. The computation is done by own-made Finite-Difference Time-Domain (FDTD) code, capable to account for tissues permittivity. A human numerical model from the Virtual Family project is used and permittivity values are assigned to each tissue according to Cole-Cole equation. A gaussian pulse is broadcasted by a monopole antenna, spread out by reverberation chamber, and measured, by FDTD code, on a point in the head in which we desire to focus energy. The FDTD-computed signal is then time reversed and rebroadcasted to target tissue. Promising results are obtained. This thesis extends the previous works, by introducing FDTD simulations of a finer map of human body on high-performance computers, enhancing the design of applicators based on TR technique, to focus energy on the target tissue, while minimizing the side effects on the surrounding ones.