## 2 Materials and Methods
### Magnetic Field and RF-EMF Data Acquisition  
In this study, magnetic field measurements were taken using the SMP2 field strength meter [33]. The SMP2 is a sophisticated instrument designed for measuring EMF across a wide range of frequencies. It offers 3 functionalities: broadband measurements (DC to 60 GHz), frequency spectrum analysis (DC to 400 kHz), and static field measurements. The SMP2 is capable of measuring E, H, and B fields. It allows users to view real-time data and analyze results directly on the device. The SMP2 includes internal memory for data logging (log time is configurable from 0.5 s to 6 min. ), enabling users to store measurement data (instantaneous, max., min., and average) for later analysis. The device also supports accessories such as GPS modules for geolocated measurements. Furthermore, the SMP2 is designed to comply with international standards for EMF measurements, such as those set by the ICNIRP and the Institute of Electrical and Electronics Engineers (IEEE). This study measured the B using an SMP2 field strength meter with a WP400 probe, covering a frequency range of 1 Hz to 400 kHz. The measurement range of the WP400 probe is 50 nT to 10 mT, with a resolution of less than 0.01 nT and a noise level below 50 nT. The graphical display shows root mean square (RMS) values, axis values, and average, maximum, minimum, and peak levels. The log time was set to 0.5 s, and both RMS and peak values were recorded. An example of a measurement taken with SPM2 inside the bus is shown in Figure 4.  
The RF-EMF measurements were conducted using the EME SPY Evolution EMF meter, a device designed to continuously monitor human exposure to EMF across user-defined frequency bands ranging from 80 MHz to 6 GHz [34]. This range covers most of the RF spectrum, including frequencies used by mobile phones, Wi-Fi, Bluetooth, radio and television broadcasting, and other communication devices. The device measures the E field, providing information about the intensity of RF exposure in the environment. The EME SPY Evolution is a compact, lightweight device that is easy to carry and use in various settings. Figure 4: An example image of a measurement taken with the SMP2 inside the electric bus. One of the key features of the EME SPY Evolution is its ability to monitor multiple frequency bands simultaneously. This capability is particularly useful in environments where various RF sources are present, as it allows users to assess the contribution of each source to the overall RF exposure. The device has internal memory for data logging, allowing users to store measurement data for later analysis. The EME SPY Evolution is designed to comply with international standards for RF exposure assessment, such as those set by the ICNIRP and other relevant regulatory bodies. Equipped with a tri-axial E-field probe within the frequency band of 80 MHz to 6 GHz, the EME SPY offers high sensitivity, with readings of 0.05 V/m in the 80 MHz to 0.7 GHz and 3 GHz to 6 GHz ranges and 0.02 V/m in the 0.7 GHz to 3 GHz range. The EME SPY Evolution can record up to 166,000 samples in a 20-band scenario, with a customizable recording period ranging from 2 to 255 s, depending on the desired scenario. This study adjusted the measurement intervals to 6 s to effectively capture the time-based RF-EMF characteristics. For detailed technical specifications of the EME SPY, please refer to [32]. An example of a measurement taken with the EMS SPY in the bus is shown in Figure 5. The measured frequency bands of the EME Spy Evolution are summarized in Table 2.