## 4 Discussion  
The 5G technology for next-generation mobile communications is arousing a lot of interest since it permits greater channel capacity and higher data rates. The bands assigned to this emerging system includes the 28 GHz band, which is currently used in the USA for the 5G systems [3; 4], and the 26 GHz band, which was recently adopted by the European Commission [5]. This paper presents a numerical analysis of the human body exposure to a 5G generic mobile terminal operating at mmW, considering different users and different exposure scenarios. We presented a numerical analysis of the human body's exposure to a 5G  
Figure 7: SAR distribution in the browsing scenario in three different planes: axial, coronal, and sagittal. 2 \(\times\) 2-patch single-layer antenna array operating at mmW (@28 GHz, 30 mW), to be used in a commercial smartphone or tablet. Three representative realistic scenarios (phone call, message writing scenario, and browsing scenario) were considered and four different human virtual models were used in the numerical simulations. We numerically computed the local SAR and calculated the relative Sab, since it is the dosimetric quantity adopted by the relevant guidelines. Since very low values were obtained for Sab (<2.15% of ICNIRP basic restriction in the phone call scenario, <0.16% of ICNIRP basic restriction in the writing scenario, and <0.03% of ICNIRP basic restriction in the browsing scenario), we can conclude that all the considered exposure scenarios comply with the safety limits relative to RF exposure, both for adult and child models [4, 7, 8]. However, in specific and highly localized superficial points of the human models, the local SAR peak value was significant. This becomes important for some human tissues which are particularly vulnerable to electromagnetic radiation-induced heating: for example, the eyes that, in addition to be located on the body surface, are less perfused to blood so they cannot properly redistribute the generated heat [6]. From our calculations of the SAR depth of penetration, it was demonstrated that the RF power absorption decays very quickly in depth. Since the thickness of the human epidermis and dermis is about 0.1 and 2 mm, respectively, we can conclude that the mmW energy is rapidly absorbed within the epidermis and dermis and does not reach the deeper tissues in the body [36]. This shows again, in agreement with previous literature [18, 19, 21, 22, 37], that at this frequency and with the incident power values typical of the smartphone technology, it is highly unlikely that inner tissues absorb health-harmful power levels. From a comparison with a very similar exposure scenario including a 4G smartphone [10], we found that at 28 GHz, which is one of the frequencies intended for use in 5G technology, the reduction of SAR from the surface to the innermost tissues is much more sudden. As demonstrated in this study, in fact, the SAR value at a depth of 1 mm in the head is about 30% of the surface value in the adult male model and is about 2% of the surface value in adult female and children models. Moreover, in the present study, we did not find any particular hot spots, as were reported in the 4G study taken in comparison. Regarding the question about whether children absorb more RF energy than adults when using a smartphone, the debate is still heated in the literature and to date, there are no firm conclusions on this matter [23, 24, 25, 26, 27]. The differences in peak local SAR and Sab between adults and children also found in this work are not relevant for compliance assessment [18] but might be important for other purposes, including research on possible biological effects of RF energy. Anyway, assuming that there are any differences in power absorption distribution between adults and children, they could be relevant at lower frequencies (@4G and previous communication technologies) but would have minimal relevance at mmW frequencies since, as shown in this study, the absorption is exclusively localized on the skin for all the users.