## 4 Results and Discussion
Control measurements were carried out at the beginning and the end of each measuring campaign. Figures 5 and 6 show the measured electric field outside and inside the car at two locations (Location 1 and Location 2) for weekdays and weekends. The obtained mean values outside the car were 0.67 V/m and 0.83 V/m (at Location 1, weekend), 0.79 V/m and 0.83 V/m (at Location 1, weekday) and 0.21 V/m (at Location 2, weekday). These values were almost two times lower than the mean values for Scenarios 2 and 3. This comparison shows that the EMF generated by wireless cellular and local networks was attenuated by 25% in the vehicle due to the influence of the car cabin, interior, glass, etc. Comparing Figures 5 and 6, we can see that the mean values obtained during the control measurements in the car were about 25% lower than those outside the vehicle. It is also seen that the RF energy that accumulated in the car cabin during an outgoing voice call, video call or data transmission through 2G, 3G, 4G and 5G networks was sufficient to be captured and converted into usable electrical energy. Moreover, with the development of intelligent transport systems, connectivity between vehicles will increase. Hence, the number of wireless sources in the car will increase, and consequently, the application of RF energy-harvesting systems in cars will also increase. Our hypothesis is also confirmed by the results of other authors. [PERSON] and [PERSON] [53] demonstrated the possibility of harvesting electrical energy directly from an RF source. They powered a commercially available thermometer/hygrometer with LCD using only RF power harvested from a TV transmission tower with the help of a WISP (Wireless Identification and Sensing Platform). The authors thus demonstrated on a small scale that the existence of EMF can be captured and used to give enough energy for small devices to be operational [53]. Moreover, in another experiment conducted in 2013, [PERSON] et al. [20] demonstrated that ambient RF harvesting can be competitive with other technologies. The authors showed that the frequency of the RF sources is equivalent to DTV (digital television), GSM900, GSM1800 and 3G (mobile phones) bands that can be usual daily sources of energy, being operational in any urban or suburban area. Moreover, [PERSON] et al. 2020 [54] made measurements of RF-EMF exposure within urban public trans, showing a considerable amount of exposure in the case of 5G-type emitters, as the results in this study showed. A comparison of the results obtained in this study with the results of another similar study [20] reported in the literature is given in Figure 7,b to confirm our hypothesis. It can be seen that [PERSON] et al. obtained average values of the electric field across London Underground stations (calculated from RF power density) varied between 0.02 V/m and 0.56 V/m. The obtained results in this work also show that the average mean value of the measured electric field outside the car (in free space) was 0.50 V/m, which was close to that measured by [PERSON] et al. Furthermore, the mean values of the electric field in the car cabin during voice and video calls and data transmission via 2G, 3G, 4G and 5G cellular networks were comparable to or higher than those measured by [PERSON] et al. Moreover, the data show that the highest maximal values (see Figure 7b) in the car cabin during voice and video calls and data transmission via 2G, 3G, 4G and 5G cellular networks were three to four times higher than those measured by [PERSON] et al. [20] in the free space. Consequently, RF energy that accumulates in the car cabin during an outgoing voice call, video call or data transmission through 2G, 3G, 4G and 5G networks is sufficient to be captured and converted into usable electrical energy. Figure 5: Control measurements. E-field measured outside the car at two locations: Location 1 and Location 2 for weekdays and weekends: **(a,b)** Control 1, Location 1, weekend; **(c)** Control 1, Location 1, weekday; and **(d)** Control 1, Location 2, weekday.