# Low-Frequency Magnetic Field Exposure System for Cells Electromagnetic Biocompatibility Studies
## 2 Design of Exposure System  
The exposure system design assumes the use of two identical applicators of MF. Using two applicators will ensure the same cultivation conditions for exposed and control samples. One applicator serves as a source of MF; the second one represents a state without intervention/negative control. Furthermore, the design assumes the use of an incubator maintaining a constant temperature, Erlenmeyer flasks with liquid yeast-cell culture, shielding, and a system for additional temperature monitoring. The applicator of the exposure system suitable for LF MF irradiation should meet the following demands:  
* The area of interest (AOI) with uniform exposure--the homogeneity of the MF represented by magnetic flux density field (B-field) at a minimum level of 98%;* Identical cultivation conditions for exposed and control samples;
* The possibility to perform at least five experiments in parallel--five exposed and five control samples, to enhance the number of results for statistical evaluation and thus reduce the time required for experiments;
* The applicator geometries optimized for an inner dimension of the incubator Q-Cell 240;
* Sufficient airflow in the incubator for both control and exposed samples;
* Safe handling with samples.  
Due to the above-defined requirements, a simple long cylindrical coil seems to be the most suitable choice for the applicator. Other groups reported the employment of Helmholtz coil for in vitro [25] or in vivo experiments [26], two flattened orthogonal coils [27], exposure system sXc-ELF composed of a set of square Helmholtz coils [28], also solenoid coil for in vitro experiments [29; 30], a system of coupling coils with adjustable transfer distance [31], tetra-coil [32], and many more setups presented in [33; 34; 35; 36; 37]. Most of the mentioned systems are designed for irradiation of only one sample or multiple samples with a minimal volume using a microplate and do not consider the inhomogeneity of the B-field.  
To enhance the identical cultivation conditions for exposed and control samples, the laboratory incubator Q-cell 240 is chosen. The incubator maintains a stable temperature with an accuracy of 0.5 \({}^{\circ}\)C via forced air circulation in the chamber. The inner dimensions of the incubator \(1315\times 504\times 320\) mm\({}^{3}\) (height \(\times\) width \(\times\) depth), determine the maximal size of the coils. Therefore, to ensure sufficient air circulation in the coil cavity, the maximal possible length of the coil is 1000 mm.  
The inner diameter of the coil is determined by the pursuit to reach a high level of the magnetic field homogeneity--the smaller the diameter of the coil, the higher the homogeneity--and concerning the sample size (Erlenmeyer bank) and safe handling of them. The experiment used flasks with a volume of 100 mL, a height of 105 mm, and a diameter of 64 mm. Therefore, the inner diameter of the coil is set to 135 mm. The conceptual drawing of the cylindrical coil design is shown in Figure 1.  
Figure 1: Technical drawing of the proposed coil.  
The coil should cover the entire space of the samples to achieve the necessary uniformity of B-field within the cell culture samples; therefore, the edge samples should be located 100 mm from the respective edge of the coil. The level height of the culture medium placed in the bank is also considered to determine the position from the edge of the coil.  
The exposure coil is proposed to be driven by sinusoidal electric current to produce a high enough B-field within the irradiated volume but not affecting thermal conditions. For this purpose, tightly wound wire with a thickness of 1 mm and sufficient current load capacity is chosen, resulting in coils with 2000 turns each.