## 4 Discussion  
The results of computer simulations presented above make it possible to estimate the effectiveness of head shields made of conductive materials. Their shielding properties can be verified by comparing the exposure parameters of the body obtained with the uncovered head model and the head surrounded by a shielding structure. In the case of the power density analysis for the head area, no major differences were found between the model with the shield and the model uncovered. For the angle of exposure \(\varphi=0^{\circ}\) and \(\theta=90^{\circ}\) (front illumination) and for the frequency of 750 MHz, the effect of EM wave attenuation in the human head is visible even without additional cover. For the case of the head without cover (Figure 5), the power density has the greatest values for the face region; that is, the side illuminated directly by the wave. In the region of the left eye, the maximum power density varies from 3 to 1 W/m\({}^{2}\). The power density in the back of the head is lower due to the attenuation in tissues. In the region of the cerebral cortex at the back of the brain, the power density is approximately 0.3 W/m\({}^{2}\). In the model of the tinfoil hat (Figure 6), a similar effect is visible; however, power density in the back of the head was additionally decreased. This effect applies to the very low power density range, which is more than 10 dB smaller than the levels on the side exposed to radiation. Therefore, it has no significant influence on limiting the maximum radiation level in the head area. In the region of the left eye, the maximum power density varies at a similar level to the uncovered case: from 3.1 to 0.7 W/m\({}^{2}\). In the region of the cerebral cortex at the back of the brain, the power density is smaller than in the uncovered case, approximately 0.01 W/m\({}^{2}\). The differences between the shielded and unshielded case are also not very spectacular in terms of power density for 3600 MHz. Here, for the uncovered case (see Figure 7), in the region of the left eye, the maximum power density varies from 0.3 to 16 W/m\({}^{2}\), while for the metallic shield it varies from 0.2 W/m\({}^{2}\) to 12 W/m\({}^{2}\). The presence of the conductive shield changes the power density distribution in the proximity of the face. In the region of the eye lens, in the uncovered case the maximum power density is approximately 6 W/m\({}^{2}\). For the shielded model, it has greater value and is equal to 7.3 W/m\({}^{2}\) in the left side of the eye lens. This means that the conductive screen caused a local increase in the power density in the human body, which is an undesirable effect. Additionally, for 3600 MHz, the metal shield decreases the power density in the region of the cerebral cortex at the back of the brain, from 0.12 to 0.04 W/m\({}^{2}\). A very simple shielding structure designed with conducting wires (presented in Figure 4) has similar performance to the metal surface shield. The results of the power density simulation obtained for this case, presented in Figure 9, are similar to the results for the metallic surface shield (presented in Figure 8). For the shielding structure made with wires in the region of the left eye, the maximum power density varies from 0.45 to 14 W/m\({}^{2}\), while for the region of the cerebral cortex at the back of the brain it is 0.06 W/m\({}^{2}\). The results of \(SAR\) simulations were gathered to verify the performance of the shield for different angles of wave incidence. \(SAR\) averaged in 10 g and in 1 g of tissue was simulated for unshielded and shielded head. The results obtained for 750 MHz are presented in Tables 2 and 2. For this frequency, the maximum value of \(SAR\) averaged in tissue mass is greater for the shielded case compared to the unshielded case for all angles that were considered. The average value of \(SAR\) averaged in tissue mass for entire head (both for 1 and 10 g) is slightly lower for the shielded case, depending on the angle of exposure \(\varphi\).