# Sensitivity of Cell Cultures on Time-Varying Low-Frequency Magnetic Field Changes
## 1 Introduction  
Many organizations reject the evidence of the harmful non-thermal effects caused by low-frequency (LF) and radio frequency (RF) electromagnetic fields (EMF), arguing that there is no established mechanism whereby such low-energy EMF might cause reduced immunity, cancer, and other diseases. However, there is strong experimental evidence, that even weak EMF affects physiological processes in living organisms [1; 2; 3; 4; 5; 6]. The biological reaction on applied EMF is dependent on multiple parameters such as intensity, frequency range, exposure duration, or the dielectric properties of the organism tissues. The possible long-term evolution and adaptation of biological systems to conditions incorporating unnatural levels of EMF should not be neglected, as well [7]. Current research is focused on potential associations between EMF exposure and various health issues. Research groups over the world study possible physical mechanisms of EMF action onbiological structures and implement the knowledge to further beneficial investigations on the efficacy of anticancer drugs [8; 9; 10] related to EMF application. Furthermore, there are investigations concerning the risk of the growing appearance of childhood leukemia near the EMF sources [11; 12], and various types of malignancies. On the other hand, the therapeutic effects of EMF [13], drug delivery, and gene expression [14] are also a big part of current research. The question of whether the electric (EF) or magnetic field (MF) would play a dominant role in terms of the LF EMF-induced nonthermal biological effects, is yet to be clarified. Still, in some studies, there is a description of a threshold around \(10^{-4}\) V\(\cdot\)m\({}^{-1}\) for an external EF intensity to elicit a biological reaction at the cellular level [15]. At the cellular and subcellular levels, there are already several theories published describing the effects of weak LF MF, i.e., on proteins located on the surface of the cell membrane responsible for ion channels opening/closing: the ion cyclotron resonance (ICR) theory [16]; the ion parametric resonance (IPR) mechanism [17; 18]; the theory about reactive oxygen species and free radical pairs [19; 20]. The mentioned physical models are almost exclusively focused on the nonthermal effects of LF MF. The theories have been the target of scientific discussion and investigations for several decades, constantly producing new findings and knowledge in this research field, but despite all of the effort, the generally accepted theory or mechanism of LF EMF nonthermal action on cells is yet to be found. The IPR model proposed by [PERSON] is probably the most discussed model of the interaction of LF EMF and biological objects. This theory is an ion cyclotron resonance (ICR) theory interpreted in a new way--it considers the signal-to-noise ratio of EMF, which was neglected in ICR, and considers the effect of EMF on protein-bound ions. Both theories are based on the same physical conditions but have different interpretations. Although the experimental results [18; 21] confirm the validity of these theories, they still have not reached general acceptance. The basis of this theory is established on cyclotron resonance, described by [PERSON] [22], considering that the physiological activity of specific essential ions may change when the frequency of the applied time-varying MF equals the ion motion frequency in a static MF. The ion in the IPR theory is estimated as a harmonic oscillator, which is bound to a specific location on the cell membrane's surface and the application of parallelly combined MF should affect its oscillations [18]. However, this physical model was criticized by [PERSON] in [23; 24], pointing to the problem of thermal noise and signal-to-noise ratio. Work [25] by [PERSON] defended the IPR model, and these shortcomings were addressed by [PERSON] [26; 27]. [PERSON] et al. [28] state:  
_\"... the models based on electric interactions have difficulties obtaining a high enough signal-to-noise ratio at low field strengths.