## 3 Results  
The simulations with the abovementioned models were performed to make the comparative study of shielding properties of conductive structures. The power density distribution resulting from an incident wave from the distant base station was simulated (the direction of propagation is in this case approximately horizontal). The results are presented at the cross-section of the model in the \(x\)-\(y\) plane at the eye level. The wave incidence angle was \(\varphi=0^{\circ}\), \(\theta=90^{\circ}\). The reference results for the uncovered head  
Figure 8: Model of head with wire shield. Figure 7: Power density distribution in the \(x-y\) (\(z=0\)) plane for the four wire array (the length of wires: 47 mm, conductivity: 500 S/m. Values given in logarithmic scale with reference value 10 W/m\({}^{2}\). The power density for the frequency of 3600 MHz and the uncovered head is presented in Figure 11. Figure 12 presents corresponding data for the head covered with the metal surface shield. The results for the wire shield are presented in Figure 13.  
Figure 11: Power density for uncovered head, 3600 MHz (in the logarithmic scale with reference value equal to 10 W/m\({}^{2}\)). Figure 12: Power density for conductive shield, 3600 MHz (in the logarithmic scale with reference value equal to 10 W/m\({}^{2}\)). The specific absorption rate (\(SAR\)) is the parameter commonly used to determine the interaction of electromagnetic fields with the human body in terms of absorbed energy by the mass of tissue. This is defined by the following equation:  
\[SAR=\frac{\sigma|E|^{2}}{\rho} \tag{1}\]  
where:  
\(\sigma\)--electrical conductivity (S/m)  
\(E\)--electric field strength (V/m)  
\(\rho\)--tissue density (kg/m\({}^{3}\))  
This parameter is often used in various regulations of electromagnetic field exposure limits, defined in terms of \(SAR\) averaged over a volume of tissue. Typically, \(SAR\) is averaged in 10 g and in 1 g of tissue. The simulations of \(SAR\) were made for \(0^{\circ}\leq\varphi\leq 180^{\circ}\) and \(0^{\circ}\leq\theta\leq 90^{\circ}\) with steps of \(30^{\circ}\). The results of \(SAR\) parameter simulations for the unshielded and shielded head are presented in Table 2 for the frequency of 750 MHz and for the most probable case where the base station antenna is far from the user and the wave approaches from horizontal direction (\(\theta\) = 90\({}^{\circ}\)). To simplify the analysis, it was first simulated for three values of wave incidence angle (\(\varphi\) = 0\({}^{\circ}\), 90\({}^{\circ}\), 180\({}^{\circ}\)). Table 2 in Appendix B presents \(SAR\) for all the combinations of \(\varphi\) and \(\theta\) angles that were considered. Data presented in Tables 2 and 2 present the maximum and average values of \(SAR\) averaged in 10 and 1 g of tissues. Figure 13: Power density for wire shield, 3600 MHz (in the logarithmic scale with reference value equal to 10 W/m\({}^{2}\)). In the Table 3, \(SAR\) parameters are presented for the frequency of 3600 MHz for a limited number of wave incidence angles \(\varphi\) and for \(\theta=90^{\circ}\) that correspond with distant transmitter location. In this case, the data obtained for no shield and metal shield are presented together with the results obtained for the wire shield model presented in Figure 8. Table 10 gathers the results of \(SAR\) simulations for all angles of wave incidence that were considered. In Figure 14, \(SAR\) averaged in 1 g of tissue mass simulated for 750 MHz is presented for the unshielded case (a) and the metal surface shield (b). Figure 15 presents the same parameter for the 3600 MHz shielded and unshielded case. Results obtained for the wire shield that was designed for 3600 MHz are presented in Figure 16. The distribution of the \(SAR\) parameter presented in those figures was simulated in the \(x\)-\(y\) plane at eye level so the position of the plane is the same as for the power density data presented in Figures 8-12. Here, the mass-averaged \(SAR\) value is given on a linear scale in the range from 0.5 to 0.05 W/kg.