Effects of averaging procedures for electrical properties at the interface of dissimilar tissues in the human head with finite-difference time-domain modelling

The finite-difference time-domain method builds a problem space out of finite-sized Yee cells. The interfaces between heterogeneous materials can be treated in different ways. The ways of calculating the effective permittivity and conductivity at dissimilar tissue interfaces are investigated. Both homogeneous and anatomically realistic heads are considered. Importantly, it is found that although the effects of the different averaging techniques are small for homogeneous heads, they are significant with anatomically realistic heads. The effects are particularly apparent if internal structures in the head are near resonance. It is shown that the choice of averaging technique has an impact on results and therefore should be explained as a parameter of the simulation technique. Data for 0.9, 1.5 and 1.8 GHz are included here.