# Calculation of absorbed electromagnetic energy in human head radiated by mobile phones.

1 INTRODUCTION

It is well known that electromagnetic radiation produces undesirable effects on biological object. These effects are usually divided into thermal and non-thermal. Thermal effects are investigated to a greater extent than non-thermal effects, because investigation of non-thermal effects is based on previously known distribution of electromagnetic fields in tissues.

The aim of this paper is to present the distribution of electrical and magnetic field in the human head, as main a absorber of electromagnetic energy radiated by mobile phones.

2 ELECTROMAGNETIC MODEL OF BIOLOGICAL TISSUE

In the electromagnetic sense biological tissues are described as a dispersive domain characterized by complex dielectric constant which is frequency dependent.

[[??].sub.r] ([omega]) = [[epsilon]'.sub.r] - j[[epsilon]".sub.r] [??] [[??].sub.r] ([omega]) = [[epsilon]'.sub.r] - j ([sigma] / [omega][[epsilon].sub.0]) (1)

where [[epsilon]'.sub.r] and [[epsilon]".sub.r] are real and imaginary part of permeability, respectively, [omega] is angular frequency, and [sigma] stands for electrical conductivity.

For this purpose, characteristics of biological tissues, ([[epsilon].sub.r] and [sigma][S/m]), at 900MHz, which is most frequently used in GSM mobile communication, are presented in Table 1. Mass density, [rho](kg/[m.sub.3]) is frequency independent but is different for each tissue considered.

3 THE MODEL OF HUMAN HEAD

The human head is anatomically modeled with average anthropometric dimensions h = 256mm, w = 166mm and d = 260mm.The model of the human head consists of three layers and two domains. The skin, the fat, and the muscle are layers, the thickness of which is constant and equals 2 mm. Domains are the bone tissue and the brain, both of which are modeled as the rest of the total volume of human head. The model of human brain is inscribed in a parallelepiped the dimensions of which are 174x145x 170 mm. Every outer layer or domain contains the inner layers or domains. We assume that ear canal is 25 mm long and the constant diameter of cross section is 7 mm. We expect to prove that the small hole inside the head becomes the new source point of electromagnetic radiation [7], very similarly to the Huygens principle. Cross section of human head model is presented in Fig. 1. of the paper.

[FIGURE 1 OMITTED]

Two types of cellular phones are considered. The first type has a [lambda]/4 monopole antenna, Fig. 2, and the second type has a PIF antenna (Compact inverted-F antenna), Fig.2 In numerical modeling these are two separate cases, numbered as Case 1 and Case 2.

[FIGURE 2 OMITTED]

4 OUTLINE OF THE METHOD

Calculation of the components of electromagnetic field in non-homogenous media is very complex and it is impossible to get any of the results in a closed form. Obviously, numerical techniques are unnecessary. Numerical methods require more computation than other methods but they are very powerful simulation tools.

The Finite Integration Technique (FIT), first proposed by Weiland in 1977 [2, 3], is a consistent geometric discretization method turning Maxwell's equations into a set of algebraic matrix equations, the so-called Maxwell-Grid-Equations (MGE). The dualism of the discrete Maxwell's Equations has to be guaranteed, if the numerical systems are supposed to have numerically stable solutions.

5 NUMERICAL RESULT AND CONCLUSION

The numerical models for two types of mobile phones are formed using FIT methods [2,3,4,5]. For the both models of phones the characteristic are as follows: f = 900MHz, P = 0.5W, and Z = 50[ohm].

The method used to model mobile phones and human head in their real shape and electromagnetic characteristics, avoiding approximations, has been presented in this paper. An anatomical model of human head and real models for mobile phones have been used to compute the SAR[1g], SAR[10g], E, H, J, [w.sub.e], [w.sub.m], flux density, and power loss density.

Correct modeling of mobile phone is important because of that the new models of phones involved quite different type of antennas named PIF. This type of mobile phone is designed in such manner that the source of electromagnetic radiation is displaced from the ear canal.

A comparison between the calculated electromagnetic values computed for two models (Case 1 and Case 2) has been obtained and remarkable difference has been found. It is evident that in Case 2 we have power loss density that is significantly lower than in the Case 1.

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In the paper, we have shown some of the obtained results in Fig 4 to Fig 12.

In further investigation the mouth hole has to be considered when the mobile phone of type 2 is under consideration.

Exposure to high density microwaves can cause detrimental effects on the central nervous system, testis, cardiovascular system, hematopoetic system, uteroplacental function [8]. Various nonthermal effects of MWs from mobile phones on the central nervous system, including permeability of the blood-brain barrier (BBB), neuronal electrical activity and increase in calcium ion efflux, neurotransmitter balance, cognitive function, and sleep have recently been reviewed [9,10]. It has been reported that increased incidence of brain tumors and acoustic neurinoma is correlated with exposure to mobile phone MWs depending on duration of mobile phone use [11]. Formation of reactive oxygen species (ROS) and increased oxidative stress may be involved in the action of microwave radiation on the biological system [12].

Based on Fig. 9-12, it can be assumed that the highest degree of brain tissue compromised the radiation level in pineal gland and structures around it. It is proven that chronic exposure to electromagnetic radiation leads to a reduction of secretion of neuro-hormone melatonin from the pineal gland [13]. The fall of melatonin concentration is a consequence of its increased takeover by the tissue is exposed to oxidative stress conditions, exposure to microwave radiation [14].

It is proven that mobile phone caused oxidative damage biochemically by increasing the levels of malondialdehyde (MDA), carbonyl groups, xanthine oxidase (XO) activity and decreasing catalase (CAT) activity. Treatment with the melatonin significantly prevented oxidative damage in the brain [15-19].

REFERENCES

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[8.] Krstic. D, Zigar. D, Petkovic. D, "Modeling electromagnetic absorption from mobile phone in human head", Biological Effect of Electromagnetic Fields - First Conference with International participation, No 21.1, pp. 5, Novi Sad, 29-30.05.2009, (on Serbian).

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[11.] Michaelson. SM, "Health implications of exposure to radiofrequency/microwave energies", Br J. Ind. Med. 39(2):105-119, 1982.

[12.] Paulraj. R, Behari. J, "Single strand DNA breaks in rat brain cells exposed to microwave radiation", Mutat. Res. 596 (1-2):76-80, 2006.

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[14.] Hardell. L, Mild. KH, Carlberg. M, "Further aspects on cellular and cordless telephones and brain tumours", Int. J. Oncol. 22(2):399-407, 2003.

[15.] Koylu. H, Mollaoglu. H, Ozguner. F, Naziroglu. M, Delibas. N, "Melatonin modulates 900 Mhz microwave-induced lipid peroxidation changes in rat brain", Toxicol. Ind. Health. 22(5):211-216, 2006.

[16.] Burch. JB, Reif. JS, Noonan. CW, Ichinose. T, Bachand. AM, Koleber. TL, Yost. MG, "Melatonin metabolite excretion among cellular telephone users", Int J Radiat Biol. 78(11):1029-36, 2002.

[17.] Oktem. F, Ozguner. F, Mollaoglu. H, Koyu. A, "Oxidative Damage in the Kidney Induced by 900-MHz- Emitted Mobile Phone: Protection by Melatonin". Arch Med Res. 36:350-55, 2005.

[18.] Sokolovic. D, Djindjic. B, Nikolic. J, Bjelakovic. G, Pavlovic. D, Kocic. G, Krstic. D, Cvetkovic. T, Pavlovic. V, "Melatonin reduces oxidative stress induced by chronic exposure of microwave radiation from mobile phones in rat brain", J Radiat Res (Tokyo), 49(6):579-86, 2008.

[19.] Sokolvic. D, "Melatonin as modulator of efect microwave radiation on metabolisam Arginine and Polyamine", Doctoral dissertations, Nis, 2008, (on Serbian).

Dejan Krstic (1), Darko Zigar (1), Dejan Petkovic (1), Dusan Sokolovic (2)

(1) Faculty of Occupational Safety in Nis, Carnojevica 10a, Nis, Serbia,

(2) Medical faculty in Nis, Bulevar Zorana Dindica 81, Nis,

dejank@znrfak.ni.ac.rs, darko.zigar@znrfak.ni.ac.rs, dejan.petkovic@znrfak.ni.ac.rs, soko@medfak.ni.ac.rs
```Table 1. Characteristics of tissues at 900MHz

Tissue  [[epsilon].sub.r]  [sigma][S/m]  [rho]
(kg/[m.sup.3])

skin    41.4053            0.8667         1100
fat     5.4619             0.0510         1100
muscle  56.8790            0.9953         1040
bone    12.4537            0.1433         1850
brain   45,8000            0,1766         1030
```