## 2 Materials and Methods
For the purpose of further analysis, the exposure level for the upper band was applied in simulations (61 V/m) so that the results obtained for the two bands could be easily compared. The model of the human head presented in Figures 1 and 2 was used as the reference because it does not include any shielding. The improvised metallic shield (tinfoil hat) was modeled with an ellipsoidal shape structure surrounding the human head, forming a metal surface shield (see Figure 3). The electric conductivity of shield is assumed to be the same as for aluminum (\(\sigma=2.5\times 10^{7}\) S/m). In the literature, many structures are presented that were developed for the purpose of frequency selective shielding [10; 30; 31]. They are created with multiple conducting elements of complex shape that are tuned to absorb energy of the wave at a particular frequency. This concept can be applied to the head shields that in this case could be fabricated with textile technologies. They do not cover entire head with an electric conductor, such as aluminum foil, and could be potentially fabricated with conductive fibers integrated with clothing. In further research, I wanted to verify if a very simple structure that consists of a set of conducting elements can shield the head from electromagnetic fields in the comparable level to solid metal shields. I assumed that the frequency for this shield was 3600 MHz because this is the band for which higher data throughput is possible and the greater utilization is expected as well as power radiated by the equipment. Considering the limitations of textile technologies, in which long or complex conductive structures can be broken due to material flexibility [32], I was searching for the structure of the simplest possible geometry. The wire-based shield proposed here utilizes the concept of a receiving dipole antenna loaded with the resistor. It is presented in the Figure 4a. The dipole antenna couples to the electromagnetic wave and, if loaded, absorbs the energy of the electromagnetic wave. Since the textile technology of shield fabrication was assumed here, I did not utilize a perfectly conducting dipole loaded with a single resistor, but instead a wire element that  
Figure 3: Model of head with metal surface shield. is fabricated with an electric conductor of limited conductivity (lossy), as presented in Figure 4c. It acts similarly to an antenna fabricated with many resistors distributed along its length, presented in Figure 4b [33]. For this structure, it is difficult to predict the resonant length because the velocity of current propagation along the structure differs with element conductivity. If a set of wires is considered, the coupling between wires also depends on their distance, influencing the performance of the structure. To verify if the set of lossy wires can be used for shielding purposes, I used a sample configuration of a four-element array, which is presented in Figure 5. The limited number of elements was used to improve numerical efficiency of the experiment. To identify the length \(L\) and the conductivity \(\sigma\) of the wires, the simulations of power density behind the wires were performed. I used brute-force scan of element length and element conductivity to identify which combination gives promising results. I made the simulations for all combinations in the range of \(L\) from 30 to 60 mm, every 1 mm, and for values of \(\sigma\): 200, 500 and 1000 S/m. The distance between wires was set to \(D\) = 10 mm and the wire diameter was 1 mm, so the structure could be fabricated with embroidery technique as well as with ink-jet printing on textile substrate. The array was illuminated by a vertically polarized plane wave at 3600 MHz and electric field intensity \(Ez\) = 61 V/m. The test point was located at \(x\) = 5 mm, \(y\) = 0 and \(z\) = 0. The sample results obtained for different wire length and conductivity are presented in Table 1. For simplicity, only the data for the shortest, locally optimal length (\(L\) = 47 mm) and the longest wire are presented.