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EM and Thermal Modelling of the Human Eye

The purpose of this work is to investigate the influence of high frequency time harmonic electromagnetic fields on the human eye. As it is well known, the most noted effect of high frequency fields on biological tissues is the thermal rise due to absorbed electromagnetic power. The task performed in this thesis was two-fold ; as a first step the total electric field and resulting SAR (specific absorption rate) inside an eye and surrounding tissues is calculated. The data from field distribution and SAR calculation is then provided as an input to bio-heat transfer equation to obtain the temperature field distribution inside an eye. An eye was not considered as the system isolated from the rest of the head ; it is rather modeled together with the part of the head which can considerably influence the electric field distribution inside an eye at the given frequency. The consequence of this was the greater number of tissues involved. Dispersion of electric parameters of the tissues at various frequencies is well known and is usually approximated using 4-Cole-Cole extrapolation. Moreover the conductivity and permittivity parameters of the tissues were obtained from measurements performed either in vivo or from autopsies. This data was collected systematically by other researchers and used in this thesis for the purpose of modeling the human tissues. Next, a plane wave incident on the eye and on the part of the head containing it was considered as an electromagnetic scattering problem. For this reason, the hybrid BEM/FEM formulation was used in order to calculate correctly the scattering of electromagnetic fields. Another reason why hybrid method was used is in inhomogenity of tissues involved. The inhomogenity issue was resolved via direct treatment of Maxwell’s equations. Furthermore, this hybrid formulation was altered in a way that discontinuous boundary elements were used with hybrid formulation thus providing the better accuracy of the method and resolving the problem of non-uniqueness of the fluxes at the corners. The justification of the method and the comparison with other methods is provided as well. Finally, specific absorption rate (SAR) was calculated from the distribution of electric field inside an eye for the frequency range from 0.7 GHz to 4.4 GHz. This data was then fed into bio-heat transfer equation for steady state to obtain the temperature field distribution at the given frequency range. The results from this research may have various applications ranging from medical to safety applications. The data and the methodology used may eventually have practical applications in medicine such as hyperthermia treatment of rare eye cancer forms or it can be used to re-asses the exposure limits to electromagnetic fields for the human tissues.

Hybrid BEM/FEM ; Computational electromagnetics ; Bioelectromagnetics ; Thermal modeling

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