## 1 Introduction
\[\mathbf{k}=\omega\sqrt{\mu\overline{\epsilon}}=\sqrt{-\mathrm{j}\omega\mu( \sigma+\mathrm{j}\omega\varepsilon)}=\omega\sqrt{\varepsilon\mu}\sqrt{1-j \frac{\sigma}{\omega\varepsilon}}=\alpha-\mathrm{j}\beta, \tag{7}\]  
the real component \(\alpha\) (rad\(\cdot\)s\({}^{-1}\)) represents the relative phase shift of the EM wave, while the imaginary component \(\beta\) (m\({}^{-1}\)) represents the relative attenuation of the EM wave in the environment. We can conclude that the specific phase shift and attenuation of an EM 2021 wave are dependent on the field frequency and the magnetic and conductivity parameters of the environment through which the wave propagates. By utilizing the known wave vector value, it is possible to calculate the characteristic impedance of the environment, which is defined as the ratio of the electric and magnetic field intensity phasors, expressed as  
\[\hat{Z}=\frac{\mathbf{E}_{\mathrm{m}}}{\mathbf{H}_{\mathrm{m}}}=\frac{\omega \mu}{\mathbf{k}}=\frac{\omega\mu}{\sqrt{-\mathrm{j}\omega\mu(\sigma+\mathrm{ j}\omega\varepsilon)}}=\sqrt{\frac{\mathrm{j}\omega\mu}{\sigma+\mathrm{j}\omega \varepsilon}}. \tag{8}\]  
The ratio between the amplitudes of the electric and magnetic intensity is determined by the absolute value of the characteristic impedance, while the phase difference between the electric and magnetic components of the wave is determined by its argument. When a wave propagates in a medium with loss (like biological tissues), the amplitudes of its individual components decrease exponentially with an increasing attenuation coefficient \(\beta\). To quantify that decrease, we use the effective depth of penetration, which is the distance at which the electric and magnetic intensity drop to \(\mathrm{e}^{-1}\) of their original value upon entering the medium [10; 11]. \[\delta=\frac{1}{\beta}=\frac{1}{\sqrt{\frac{\omega^{2}\epsilon\mu}{2}}\sqrt{ \sqrt{1+\left(\frac{\sigma}{\omega\varepsilon}\right)^{2}}-1}}. \tag{9}\]  
Tissue is a heterogeneous material composed of water, dissolved organic molecules, macromolecules, ions, and insoluble substances. These components are highly organized into cellular and subcellular structures, forming macroscopic elements and both soft and hard tissues. The presence of ions plays a crucial role in interacting with the electric field, enabling ionic conductivity and polarization effects. The dielectric spectrum of biological tissue exhibits three main dispersion regions, known as alfa, beta, and gamma dispersions. Very high permittivity values characterize the low frequency alfa dispersion and can be at least partially attributed to the diffusion effects of counterions. beta dispersion occurs at medium frequencies and is primarily due to the capacitive charging of cell membranes and membranes of bound intracellular bodies (interfacial polarization). gamma dispersion is caused by the dipolar polarization of tissue water. At frequencies above a few hundred megahertz, where the tissue water response becomes the dominant mechanism, these values can be very high. However, tissues and other biological materials may exhibit more than the three principal dispersions. The parameters of dielectric properties for all biological tissues and their frequency-dependent variations are detailed in research studies, such as those based on [PERSON]'s dispersion relations [PERSON] (2016). The situation is even more difficult in the case of the presence of an implanted device in the human body e.g., devices for supporting cardiac activity. Cardio stimulation technology today encompasses a wide range of implantable medical devices that are increasingly used worldwide. According to valid national and European legislation, cardio stimulation technology is classified as active implantable medical devices (AIMD), which means they are subject to the strictest requirements in terms of reliability and safety. A modern cardio stimulation system is a medical device consisting of a device and one to three electrodes, depending on the patient's type of heart disorder.