## 2 Materials and Methods
### Electromagnetic Field Measurement  
In the present experiment, a typical cell culture was performed, in which fibroblast cells were exposed to radio frequency radiation emitted by a cell phone for approx. 1-2 h. The results of the obtained electrical measurements will allow for the estimation of the cell culture response to the appearance of the electromagnetic field and to it switching off. The main problem was that a regular mobile phone could not be used, as inserting it into the incubator by opening it during culture would affect the environmental conditions. Additionally, leaving the phone in the chamber from the beginning of the experiment  
Figure 1: The expected nature of changes in the measured resistance for 4 kHz and capacitance for 64 kHz. Impedance measurement results at 16 kHz are usually very similar to the resistance graph. As the measured value of the resistance and the impedance increases, the value of the measured capacitance value decreases. In the first phase, cells are placed in the well with the medium (arrows indicate cell movement) (I). Then, cells migrate along the surface of the bottom of the container at a dynamic pace, multiplying (II). After this stage, cell growth (III) slows down, after which the cells occupy the entire bottom of the container, reaching full confluence and forming a monolayer (IV). The last stage of the life cycle of cells is their death and loss of contact with the substrate (V) [16]. would cause cells to grow in the constant presence of an electromagnetic field resulting from the phone connecting to the base station. Therefore, a device based on an open-source electronics platform (Arduino UNO) with a SIM800L GSM/GPRS module attached was prepared, which had a switch mounted outside the climate chamber. The selected GSM module supports frequencies in the 900 MHz range, and the microcontroller was programmed in such a way as to automatically answer incoming calls. This made it possible to turn on the power at any time and connect to the device after a short while. A GSM antenna with a U.FL connector was attached to the telephone module, which was attached at the edge of the test substrate at approx. 1 cm from wells 4 and 8, and for the remaining pairs (3 and 7, 2 and 6, 1 and 5) by another about one centimeter away. The intensity of the electromagnetic field generated by a mobile phone usually depends on the location of base stations in the vicinity, traffic in the mobile network, and the distance of the mobile phone from the base stations [21]. Therefore, before starting the cell culture, measurements of the electromagnetic field strength of the manufactured device were carried out. Measurements were made using the EMI Test Receiver R&S ESCI3 and a dedicated RS E02 near-field probe, which was placed at the following distances: 0 cm, 2.5 cm, and 5 cm from the antenna. The probe measures frequencies from 30 MHz to 3 GHz. It is a passive element connected to the 50 \(\Omega\) input of the receiver via a 20 dB amplifier. An R&S(r) HZ-16 amplifier was used to obtain the most accurate measurement results. It was placed between the spectrum analyzer and the measurement probe when studying weak high-frequency fields. Due to the specifications of the preamplifier, the use of which results in results being increased by 20 dB, the user is forced to subtract this value when analyzing measurements. The obtained results were compared with the measurements of the mobile phone: Samsung, operating in the GSM900 system, measured with the same instruments, under identical conditions. A SIM card from the same mobile network operator on which the phones operated was inserted into the GSM module. From the graphs shown (Figures 2-6), it can be observed that the repeatability of the measurements was slightly better for the mobile phone, while it was worse for the developed device. However, the field strength in the prepared device had a value slightly higher than that of a mobile phone, but the measurements were relatively repeatable.