## 1 Introduction
It was shown that the use of new high-tech nanotextile materials for shielding layers around the human body can reduce the effects of EM fields; however, the material configuration should be chosen properly according to the area of application. In [5], the shielding of cellular phone radiation with thin metal plates is studied, showing that the thickness and orientation of the plate influences the amount of energy absorbed by the head. The shielding material properties were identified in [6] for a particular mobile phone antenna and in this way the amount of energy absorbed by the human head was reduced. In the papers that focus on shielding material development, composites with improved conductivity are considered for this application. In [7], the electrical conductivity and electromagnetic shielding effectiveness of two biocomposites are studied by experimental testing and numerical models, and in [8], it is for carbonless nanoplate composites. This shows the potential of fiber-based materials in the application to electromagnetic shielding. For frequency selective protection, various periodic structures are proposed in the literature. These arrangements do not require covering the entire area (in this case the head surface) with conductive material. These shields use dielectric base material and replicated elementary structures made of an electric conductor [9; 10]. To fabricate a wearable frequency selective shield, numerous technologies developed for realizing conductive structures of different shapes with textile materials can be applied [11]. The technologies of conductive ink printing or embroidery with conductive yarns used for textile antennas can be used [12]. Additionally, the physical vapor deposition of metals on textile substrates allows for fabrication of conducting structures for the complex shapes [13; 14], so it can be applied for this purpose as well. The frequency selective shielding structures that could be fabricated with textile technologies may result with products that are far more comfortable to the user compared to a tinfoil hat because they do not limit the transfer of heat and water, which is important for any material located close to the human body. This article focuses on the analysis of shielding properties of improvised head covers made of conductive materials (\"infoil hats\"). Those are developed and used by people who feel they are oversensitive to EM radiation and want to shield their heads from the waves emitted by 5G base stations [1; 2]. For this reason, in this research the source of radiation is plane EM wave since those who are afraid of EM fields are not likely to place their head in the proximity of a mobile phone. Moreover, the most probable scenario in this case is the head illumination by the wave propagating from the distant base station in the approximately horizontal direction. The analysis of the interaction of electromagnetic radiation and the tissues of the human body was carried out with the finite difference time domain method (FDTD), which is the preferred method for performing electromagnetic simulations for biological effects from wireless devices [15]. A heterogeneous numerical model of the head was used to simulate the effect of electromagnetic shielding at the frequencies of 5G systems. According to the regulations of the European Union, two frequency ranges are currently allocated for such systems. The 700 MHz band covers the range 694-790 MHz [16]. This band allows relatively large coverage of the wireless system to be achieved even in a complex urban environment. Owing to limited data throughput, it is dedicated mostly for Internet of Things applications where a large number of small-power transmitters are used. The next frequency range covers 3.4-3.8 GHz and provides the parameters required to support a large number of connected devices at the same time [17]. This band can be successfully used in the areas of large cities with a high density of buildings.