Caracterização elétrica de tecidos biológicos e cálculo dos fenômenos induzidos no corpo humano por campos eletromagnéticos de frequência inferior a 1 GHz

Abstract

This work is part of a process aiming at evaluating and improving the performances of existing tools for the study of the interactions between the electromagnetic fields and the human body. The tools include characterisation methods to measure the macroscopic electrical properties of biological media, and numerical methods allowing to model and compute the fields induced by electromagnetic sources in the human body. The main properties of biological tissues are first described in order to explain the difficulties of their electrical characterisation. The existing characterisation methods are presented. Their specificities and operating frequency range are emphasized. Permittivity and conductivity values found in the literature are used to show the main parameters they depend on and the lack of knowledge on their accuracy. A usual characterisation method based on four-electrode impedance measurements is then studied between 10Hz and 10MHz. The measurement system is developed and tested on ionic solutions in order to build reliable and complete models. These models are used to estimate the accuracy of the measure and to optimize the characterisation method at 10Hz and 10MHz. Various numerical methods that allow modelling and computing induced electromagnetic phenomena in the body are then presented. The difficulties of the modelling are explained and linked to the unusual electrical and geometrical properties of the human body, and to the diversity of the sources of electromagnetic fields. Formulations and boundary conditions especially developed for the problem are described. Using the finite element method, and assuming the electrical properties of the body are known, various models (mesh, formulation, boundary conditions) are studied. Their efficiency is evaluated by simulating 2D and 3D representative canonical problems. The results allow estimating the accuracy of the computation and choosing the more efficient modelling for each frequency between 10Hz and 1GHz. The work gives arguments which can be used to prove the consistency of the results when studying the interaction between the electromagnetic fields and the human body. It has also direct applications in the accurate characterisation of biological media and in the establishment of new norms on human exposure to electromagnetic fields.