Electromagnetic exposure effects on human organs
In recent years, there has been growing public concern about the influence of electromagnetic waves on the human body. At the moment, humans are exposed to various sources of electromagnetic fields in many situations that occur in everyday life. The use of EM waves in various applications has increased rapidly and includes the use of mobile phones, tablets, and mobile phone base stations. Near and far-field EM sources have several power levels and exposure distances that cause differences in EMF distribution patterns and absorption of electromagnetic power by the human body. Although the standards of security, in terms of SAR values limits, are regulated, are not explicitly expressed in terms of maximum temperature rise in the tissue caused by the absorption of EM energy.
The main effect is known as a short-term biological result from exposure to EM radiation, is the rise in temperature in the human body and its sensory organs, given by the absorption of electromagnetic energy. The thermal damage can occur in the human tissues under the exposure condition body part with intense EM waves. In realistic situations, the rise in temperature cannot be measured directly in the body. Instead, it must be estimated indirectly through numerical techniques. Therefore, the numerical analysis of heat transfers in the organs of the human body.
SAR is defined as the amount of EM energy that is absorbed in the unit of time by a unit mass element in a biological system W / Kg.
It is exposed to EM fields provides useful information on the absorption of EM energy in a variety of exposure conditions. Thermal modeling of human tissue is important as a tool to study the effect of external heat sources and to predict abnormalities in tissues. There modeling of heat transport in human tissue was initially introduced by Pennes based on the heat diffusion equation. Due to the simplifications of the model bio thermal plant, other researchers have extended and modified it. Although many have been proposed advanced models of heat transport in biological tissue, Pennes' biothermal model is still a good approximation and is still widely used to model the heating of the biological tissue due to its easy implementation and minimal data requirement.
The field electrical induced, SAR, and temperature rise become more complex to determine how much the human body is non-uniform in shape and contains several organs. The characteristics of EM absorption and temperature distributions in the body resulting from different radiation patterns of the field from the near field and far-field sources are not well established. The biological effects associated with the absorption of EMF energy (electromagnetic field absorption), a systematic study of different distribution models is required EMF that interacts with body tissues.
The computational determination of the SAR is presented (specific absorption rate), and temperature increases in a human trunk exposed to radiation EM in the near and far-field. A heterogeneous human torso model was developed by Wessapan and group 3 to determine the SAR, and the temperature increases induced by the EM energy. Model heterogeneous human includes eleven types of tissue, skin, fat, muscle, bone, testicles, the large intestine, small intestine, bladder, blood, stomach, and liver. The electric field, the SAR, and the temperature assume different distributions in the various organs during exposure to the fields electromagnetic and are obtained through the numerical simulation of the propagation of EM waves and a non-stationary bio thermal model.
The effect of the exposure distance on the SAR and the increase of the temperature in each tissue organ are systematically studied. In particular, the SAR maximum and the increase in temperature in the internal organs are compared for exposure in the near and far-field. The frequencies of 900 and 1800 MHz have been chosen since these frequencies are used globally in a wide range of applications. Attention is turned to the maximum SAR and the increase in temperature in the organs of a body compared to the safety guidelines to consider the possible consequences of EM exposure and their implications for the thresholds.
Interaction between electromagnetic fields and human tissues
When electromagnetic waves propagate through tissue, the energy of EM waves comes absorbed by the tissue. The SAR is given by:
SAR = σ / p ∣ E ∣ 2
Where E is the intensity of the electric field (V / m), p is the density of the tissue (kgm3 ⁄), and σ is the conductivity electric (S / m).
Equation for heat transfer analysis by Pennes
The coupled effects of propagation are studied EM waves and heat transfer in transient conditions to analyze heat transfer and temperature rise due to field exposures near and far-field due to EM. The distribution of temperature also corresponds to the distribution of the SAR. This is because the SAR, in the tissue, is distributed due to energy absorption. Subsequently, the absorbed electromagnetic energy is converted into thermal energy, which increases the temperature of the tissue.
There is no phase change for any substance in the tissue. There are no reactions chemicals in the tissue. The heat transfer is modeled in two dimensions. The rise of temperature in the organs of the body is obtained by solving the Pennes bio thermal equation.
The transient bio thermal equation effectively describes how the transfer of
The heat inside the tissue and the equation can be written as follows:
pC dT dt = (kVT) + pbCb(Tb − T) + Qmet + Qext
Where C is the specific heat capacity of the tissues (J / kg K), k is the thermal conductivity of the tissue.
(W⁄m K), T is the temperature of the tissue, Tb is the temperature of the blood, pb is the density of the blood, Cb is the heat capacity of the blood, wb is the blood perfusion rate (1 / s), Qmet is the source of metabolic heat (W m3 ⁄) and Qext is the external heat source (due to external mechanisms, for example, those of an electromagnetic nature) (W m3 ⁄).
In this analysis, the transmission of heat between the tissue and blood flow is approximated by the term of blood perfusion, pbCbwb (Tb - T).
The term external heat source is equal to the resistive heat generated by an electromagnetic field (the electromagnetic power absorbed) and is defined as:
Qext = 1 2 σtissue ∣ E ∣ 2= p 2 SAR
The analysis of heat transfer excludes the surrounding space and is considered only in the model human. The surface of the skin is considered a convective boundary condition, where the convective heat transfer coefficient between the skin and the air is 20 W m2 ⁄ K
−n (−kVT) = ℎam (T - Tam)
Where Tam is the ambient temperature and ℎam is the convection coefficient (W m2 ⁄ K). It's supposed that no contact resistance occurs between the internal organs of the human body; therefore, internal limits are assumed as continuous:
−n (kuVTu - kdVTd) = 0
Tu = Td
At the initial stage, the distribution of temperature within the human being is considered uniform.
Electric field, SAR
, and temperature distributions in various organs during field exposure electromagnetic are obtained through the numerical simulation of the wave propagation of the electromagnetic waves and a bio-stationary heat transfer model. The condition of exposure considered refers to the ICNIRP (International Commission of Non-Ionizing) standard Radiation Protection) for safety levels at the maximum SAR value of 2 W / kg (general exposure audience) and 10 W / kg.
Author: Vicki Lezama