SAR SIMULATION FOR CHIRAL WAVES IN HEAD MODEL
A numerical model of an electromagnetic wave, propagating in a chiral media, characterized by the Born-Fedorov formalism, is presented. FDTD numerical method, adapted to chiral media, is used. The classical Yee algorithm, implemented by several authors for non chiral media, does not provide, for the same time instant, knowledge of the transverse field components (both incident and induced by the chirality). This problem is solved by the authors, delaying one of the field components when it incides in the achiral-chiral interface, storing the values corresponding to the times n and n -1, in order to solve for the the field at time n+1. The simulation results of propagating Gaussian pulses in chiral media, in the range of microwaves, show the chiral curl of the polarization plane. The results show that the use of the box model in combination with a realistic model of the head derived of a resonance image, is important for accurate determination of the near chiral fields induced in the head. It was found that, through SAR (Specific Absorption Rate) parameter, about 20% of the antenna input power is absorbed in the head. It is proposed that the chiral effect is due to a microscopic mechanism, where the typical cell membrane is a fairly fluid bilipid layer, with a few big protein molecules embedded in it. Every protein molecule is polar and will tend to align itself with an electric field and often rotate helically in its socket, so any volume of brain tissue must have a few cells bearing protein molecules that happen to resonate at its rotation frequency.