## 2 Materials and Methods
### Physical Measurements Using Multi-Location On-Body RF EMF Measurements System  
The protocol of multi-location distributed RF EMF exposure evaluation was also self-tested using a physical model. Relevant measurements were performed in two real scenarios of exposure to RF EMF emitted by antennas of the public mobile communication system: (1) on the roof of a building with a height similar to the height of the antennas, where quasi-horizontal propagation of RF EMF may be assumed), (2) on a pedestrian bridge over a street, below the antennas, where quasi-vertical propagation of RF EMF may be assumed (Figure 5). The RF EMF frequency composition in the location of these tests was studied using a frequency spectrum analyser SRM-3006 (measurement range 0.2 mV/m-200 V/m in the frequency band 420-6000 MHz, manufacturer Narda, Pfullingen, Germany). The following components of recorded RF EMF, emitted from nearby base station antennas, were found: LTE800 (DL), LTE900 (DL), LTE1800 (DL), LTE2100 (DL), LTE2600 (DL & TDD) and LTE3600 (5G) (TDD)--frequency bands characterized in Table 1.  
Measurements covered the time-synchronised recordings of the root-mean-square (RMS) value of the E-field strength in frequency bands compliant with the above-mentioned RF EMF frequency components found in the location of the tests. The physical model of a multi-location on-body measurement system was developed using three frequency-selective, narrowband PEMs of a type EME SPY Evolution (characterized in Table 3). Measurements were performed using a sampling rate of three seconds.  
The sensitivity of each data logger was checked in the TEST-SAFE-BIO/CIOP-PIB calibration laboratory (accredited by the Polish Centre for Accreditation at EN ISO/IEC 17025 standard [34]/certificate No AP061)--in the continuous sinusoidal reference EMF produced inside the Gigahertz Transverse Electromagnetic Mode (GTEM) chamber, at frequencies relevant to the components of RF EMF in the location of the test measurements. The verification of the PEMS directional sensitivity was carried out using 3 orthogonal PEMs positions inside GTEM chamber. Individual correction factors \(\mathrm{C_{fb}}\) for each PEMs in the particular frequency band (fb) were determined as average values of correction factors (ratio of E-field applied to E-field measured), obtained during measurements for 3 orthogonal position of PEM). \(\mathrm{C_{fb}}\) factors were tested in each fb considered in this study: at center frequency from the bands used by public mobile communication and Internet access systems given in Table 1.  
The PEMs were carried by a researcher (co-author of this study taking measurements) fixed in the backpacks (front and back locations of PEMs on the body), and the third PEM was fixed on the top of a plastic helmet. During the 10-min tests, the researcher performed slow rotations to the right and left in a defined measuring location, with the body in a straight position.  
In the position where the vertical axis of the researcher's body was during the test measurements, a vertical distribution of the unperturbed E-field was also determined by spot measurements without a presence of a researcher there. This was done for each of the frequency components of RF EMF present there, using the SRM-3006 analyzer.