## 4 Results and Discussion  
The results of the experiment are capable of sustaining our main hypothesis that an electromagnetic field is generated during mobile phone usage inside a vehicle, and the intensity of the field allows future experiments to be conducted to effectively harvest usable electrical energy from this field. In the following section, we explain the results that sustain this hypothesis of the research. Figure 2 shows the measured electric field in the car during ongoing voice calls (Scenario 1 from Table 1) in each sub-scenario at two locations (Location 1 and Location 2) for weekdays and weekends. Comparing the results depicted in Figure 2, we can see that the highest measured value of the electric field appeared during the voice calls via the GSM network (Sub-Scenario 1a from Table 1). The results show that, regardless of the location and the day of the week (weekend or weekday) for Sub-Scenario 1a (see Figure 2a), the maximum measured value of the electric field remained almost unchanged, ranging from 18.39 V/m to 21.85 V/m. As seen in Figure 2b, 18.39 V/m (Location 1, Weekday) and 21.85 V/m (Location 1, Weekend) were measured for 2-5 s, after which the measured \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Scenario** & **Sub-Scenario** & **Description** & **User Terminal Network Mode** \\ \hline \multirow{3}{*}{Scenario 1: voice call} & Sub-Scenario 1a & voice call set up via GSM network & 2G only \\  & Sub-Scenario 1b & voice call set up via UMTS network & 3G only \\  & Sub-Scenario 1c & voice call set up via LTE/5G network & 5G/LTE/3G/2G (auto connect) \\ \hline \multirow{3}{*}{Scenario 2: video call} & Sub-Scenario 2a & video call set up via GSM network & 2G only \\  & Sub-Scenario 2b & video call set up via UMTS network & 3G only \\  & Sub-Scenario 2c & video call set up via LTE network & LTE/3G/2G (auto connect) \\  & Sub-Scenario 2d & video call set up via 5G network & 5G/LTE/3G/2G (auto connect) \\ \hline \multirow{3}{*}{Scenario 3: data usage (Mobile Hot Spot) *} & Sub-Scenario 3a & data transmission via UMTS network & 3G only \\  & Sub-Scenario 3b & data transmission via LTE network & LTE/3G/2G (auto connect) \\ \cline{1-1}  & Sub-Scenario 3c & data transmission via 5G network & 5G/LTE/3G/2G (auto connect) \\ \hline \hline \end{tabular}  
* UT is configured as a Mobile Hot Spot, and a laptop is connected to it.  
\end{table} 
Table 1: Wireless communication scenarios. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Control Measurements** & **Conditions** & **Descriptions** \\ \hline Control 1 & outside the car & LSProbe is outside the car. UT is switched off. \\ \hline Control 2 & inside the car & LSProbe is inside the car. UT is switched off. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Conditions for control measurements of EMFs. values decreased. These results were obtained because, in GSM mode during a voice call in the first 5 s, the output power level of the mobile phone was 33 dBm at GSM900 and 30 dBm at GSM1800, the maximum level. In the first several seconds, the user equipment occupied the control channel, called the random-access channel [49]. After that, the mobile phone decreased the power level in correspondence with the APC algorithm to achieve the lowest possible transmit power [49; 50]. It can also be seen in Figure 2b that, at Location 2, the measured electric field throughout the 6-minute period remained high--about 15 V/m. The main reason for these results is that the phone was located in an underground car park, where the signal level from the base station was low. Therefore, the user equipment transmitted for all 6 min periods with a higher power compared to that of Location 1. Moreover, in Figure 2b, it can be seen that the mobile phone use in the circuit-switching mode in the GSM network [52] was transmitted in time slots. The maximum measured values of the electric field during a UMTS, LTE and 5G voice call are five to six times lower than those in the GSM network, between 3.46 V/m and 4.93 V/m.