# Analyzing the SAR in Human Head Tissues under Different Exposure Scenarios
## 2 Materials and Methods
### SAR Simulations  
In order to investigate the effects of exposure to RF-EMFs of various intensities on the human head and tissues, we used a specific anthropomorphic mannequin (SAM) which has the same geometry as described in IEEE 1528-2013 standard [31] and computational human models. Because it is aimed at determining the effect of an electric field on tissues, the SAR values obtained at the laboratory were transferred and used as a reference for simulations. The equivalent of the phantom and tissue equivalent fluids used in the laboratory are found in CST program under the name SAM, and its relative permittivity and conductivity values are given in Table 2. As seen from the table dielectric properties of SAM are very similar to liquids used in the laboratory. CST's SAM head model is a simplified homogeneous human model that consists of the outer shell and the tissue-equivalent liquid. Its dielectric parameters are determined by averaging the dielectric properties of an anatomical head. The relative permittivity and conductivity values of the outer shell are independent of frequency (\(\epsilon_{\tau}=3.5\), \(\sigma=0.0016\) S/m). However, tissue equivalent fluid's dielectric properties change by frequency. In order to use SAR laboratory measurement results as a reference, SAR calculations were performed for SAM in CST, and correct antenna position and excitation signal levels were determined for further evaluations. As this study aims to determine the SAR on different tissues; computational human models, which have been developed from tomographic data of real individuals, were used in simulations beside SAM. These models are a mathematical description of the envelope of the human body shape as well as the borders of the internal tissues and organs. In the CST voxel family, there are seven human models of different ages, sizes, and gender [32]. In computational human models, each biological organ and tissue is defined by electromagnetic properties that vary with frequency. Detailed information about the electromagnetic properties of biological tissues and organs is necessary to understand the interaction between electromagnetic fields and the human body. These electromagnetic properties are available only for the 100 MHz and 900 MHz frequencies in CST. The electrical properties of the tissues for 1800 MHz were adjusted according to the values given in [33]. It is very important to determine the number of cells when working with computational human models. A thinner network means more elements and more accurate results but may, however, require more powerful hardware. The calculation time changes depending on the number of cells used. Therefore, an appropriate balance must be found between the accuracy and calculation time. To model the RF-EMF source in the simulations, two monopole antennas that have the same properties as the antennas of the generators were designed for 900 and 1800 MHz. The designed antenna models consist of feeding pins, ground planes, copper wires as radiating elements, and Teflon coatings for insulation. The antenna is fed through a 50 \(\Omega\) \begin{table}
\begin{tabular}{c c c c c} \hline  & **Frequency** & **Relative Permittivity** & **Relative Permittivity** & **Conductivity** \\  & **(MHz)** & **(Real Part)** & **(Imaginary Part)** & **(S/m)** \\ \hline \multirow{2}{*}{SAR Lab.} & 901.95 & 39.77 & 18.53 & 0.93 \\ \cline{2-5}  & 1803.20 & 38.30 & 13.87 & 1.39 \\ \hline \multirow{2}{*}{CST} & 900 & 41.50 & 19.37 & 0.97 \\ \cline{2-5}  & 1800 & 40.00 & 13.98 & 1.40 \\ \hline \end{tabular}
\end{table} 
Table 3: Dielectric properties of materials used at the laboratory and the simulations. connector.