Application Of Feko Prqgram To The Analysis Of Sar On

APPLICATION OF FEKO PRQGRAM TO THE ANALYSIS OF SAR ON HUMAN HEAD MODELING AT 900 AND 1800 MHZ FROM A HANDSET ANTENNA 0.S. DAUTOV',RUSSIA, ADELZETNE. M., EGYPT^

' b a n State Technical University, Kazan, Russia, [email protected] Higher Institute of Energy, Aswan, Egypt, azeinm200 1 @hotmail.com Abstract. In this paper, a human head with a monopole handset antenna is simulated by using FEKO program for the analysis of Specific Absorption Rates (SAR) in the human head at 900 and I8OOMWz. The human head model is homogeneous and simulated with the brain equivalent material. The applied antenna is consisted of a quarter-wavelength monopole mounted on a mobile handset (treated as a metat box), operated at 900 and lSOOMHz frequencies and radiated power of 0.32 watt. The purpose of this simulation is for calculation of I g average SAR on the above systems, which is recommended its limit value 1.6Wkg in FCC and IC". In addition to this result, log average SAR is calculated, and the comparison between the results of 9OOMHz and that of 18OOMHz is done. 1-Introduction

With the expansion of current use and anticipated further increases in the use of mobile phones and other personal communication services, there have been cansiderable research efforts devoted to interactions between antennas an the human body. These activities are important from both human health and antenna performance points of view [l]. For absorption of energy, electromagnetic (EM) fields can be divided into four frequency ranges: Frequencies from about 100 lrHz to less than about 20 MHz, at which absorption in the trunk decreases rapidly with decreasing frequency, and significant absorption may occur in the neck and legs; Frequencies in the range from about 20 Mwz to 300 MHz, at which relatively high absorption can occur in the whole body, and to even higher values if partial body (e.g., head) resonances are considered; Frequencies in the range from about 300 M H z to several GHz, at which significant local, non-uniform absorption occurs; Frequencies above about 10 GHz, at which energy absorption occurs primarily at the body surface. Low-level effects that may be experienced by some people but are not based on tissue heating (a thermal effect), are still controversial and disputed, and are not covered by S A R limits [2],

I Averaging time I I

2- S A R limits

3- Numerical Modeling and simulation 3-1 Modeling Background

The Specific Absorption Rate (SAR) is the most

appropriate metric for determining EM effect exposure in the very near field of a Radio Frequency (RF) source [3]. The SAR (Wkg) at any point in the model can be determined from the calculated electric field (V/m)at that point by f4]:

Since experiments with real human bodies are strictly limited and animal experiments suffer from the same poor approximation of real humans another way of investigation was chosen. It is decided to investigate the possible impacts with numerical field calculations using several numerical models of the human body. A numerical model has the following advantages as compared to saline phantoms:

4EI2 SAR = P where; 274 0-7803-9374-0/05/$20.00 0 2005 IEEE

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1. The setup of the computational model can be chosen almost freely in a broad range, like location of the electrodes, placement of the body in the imagingsystem, modification to the design of the devices and so on. 2. Many different parameters can be changed in the computing domain, like the RI: which is not easy to perform with a commercial magnetic resonance (MR)scanner. 3. The geometric and physiologic parameters of the computationaI model are often more precise compared to a phantom. 4. Computational needs may be large but many calculationscan run on the machine in the background. However a numerical model is limited in size and resolution and needs to be implemented with several simplifications regarding the environmental or geametrical setup. Nevertheless they can deliver valuable clues for better understanding the experimental investigations and can be used to understand the experimental results [7].

3-2Dielectric Properties of Human Tissues For simulation of the electromagnetic fields in the human body the appropriate parameters for the conductivity q (S/m) and the relative permittivity E, of all different materials used for the calculation must be known. Additionally the fkequency dependence of these parameters must be considered and chosen appropriately. A recent compilation of Gabriel et al. [8] covers a wide range of different body tissues and offers equations to determine the appropriate dielectric values at each desired frequency [6]. Table 2. shows the real part of the dielectric permittivity (EJ, conductivity (0) . (S/m), and mass density (p) kg/m3 of tissues used in the simulations at 900 and 1800 MQz. Table 2. Properties of tissues used in the simulations at 900 and 1800 MI32 Properties of tissues I 900MHz I 18OOMHz dielectric uermittivitv (EI 45.8 I 43.5 I conductivitv( 0 1 Wm) I 0.77 I 1.15 I I massdensitvIolkdm’ I 1030 I 1030 I

3-3 FEKO Simulation and Validation The FEKO program is based on the Method of Moments (MOM). Electromagnetic fields are obtained by first calculating the electric surface currents on conducting surfaces and equivalent electric and magnetic surface currents on the surface of a dielectric solid. The currents are calculated using a linear combination of basis functions, where the coefficients are obtained by solving a system of linear equations. Once the current distribution is known, further parameters can be obrained e.g. the near field, the far field, radar cross sections, directivity or the input impedance of antennas [SI. The simulation procedure is as follows: 1 -Create the homogeneous human head model 2 -Defme the frequency, human parameters and meshing parmeters,

FEKO Program The total computation surface wire seernents

1

9ooMHz 9

18OOMHz 9

Total number o f i s

rows * coIumns disc Total time (hours)

I 341.383MB I 1.307GB I 6.48 hours 1 12.67 hours

3-5 Calculation Position

As it cannot be expected that the user will hold the mobile phone exactly in one well defined position, therefore there are different operational conditions. As shown in Figure (l), a reference line describing the phone is defined as a line which connects the center of the ear piece with the center of the bottom of the case. The human head position is given by means of a reference plane defined by the following three points: auditory canal opening of both ears and the center of the closed mouth [lo]. With these definitions the calculation position is given by; the telephone line shall lie in the reference plane (40 degrees around x-axis). The angle between the phone line and the line connecting both auditory canal openings shall be reduced (10 degrees around y-axis) until the device touch the human head. A FEKO simulation of the human head and the handset antenna interaction is pictured in Figure (2). 4-Results Figure (3) shows the SAR variation along x-axis, that is “from one ear to the other” of the human head model at 900 MHz and 1800 MHz, it is noticed that for 18OOMHz the S A R decreases more rapidly with in-

275

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creasing depth from the phone head side than that for 900 MHz . Figures (4-5-6-7) show the distributions of the intemal electric fields, and the local SAR, at the y=O ptane for 900 and 1800 MNz respectively. It can be easily observed that high SAR regions produced by 900MHz monopole antenna are more extended as compared to those induced by 1800 MHz monopole antenna. This is due to the fact that the higher rate of energy absorption for a high frequency does not allow much energy to penetrate to a region that is located towards the back of the body. Results for average SAR and spatial-peak specific absorption rate in W k g for (1 gram and 10 grams) tissue in the shape of a cube for 900MHz and 1800 MHz are presented in Table 4.

Specific Absorption Rate

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Fig. (3) Penetration curves of SAR along x-axis

Fig. (4) Internal Electric Field (v/m) at 900 MHz Fig. (1): Geometrical definitions for the description of the calculation position.

Fig. ( 5 ) Internal Electric Field ( v h ) at 1800MHz

Fig. (2) The FEKO model

Fig. ( 6 ) SAR distribution at 900MHz 276

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tional J. of Electronics and Commun., Vo1.52, No.2, pp.65-75, March 1998. 2. David Riley, “Standards for the Management of Potential Health Risks of EM Fields” indexsar.com. 3. Allen S G, “Radiofrequency field measurements and hazard assessment’’, Joumal of Radiological Protection, Vol11-1, 1996. 4. FCC, OET Bulletin 65, “Evatuating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields,” Edition 9701, released December, 1997. 5 . IEEE C95.1-1991, IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 lcHz to 300 GHz (Institute of Bleckical and Electronics Engineers, Inc., New York, 1992). 6. European Commettee for Electrotechnical Standardization (CENELEC) Prestandard ENV 501662, Human exposure to electromagnetic fields. High frequency (10 lrHz to 300 GIfi) (January 1995). 7. Marc-Andrt Golombeck, OIaf Dtissel “Numerical Models of the Human Body applied to EMCProblems in the Surgery Rooms of the Future “ Institute of Biomedical Engineering University of Karlsruhe, Germany. 8. C.Gabriel et al., ,,Compilation of the Dielectric Properties of Body Tissues at RF and Microwave Frequencies“, http://www.brooks.aEmiUAFFU/HED/ hedr/reports/dielectric/TTitle/Title.html,1999. 9. FEKO program http://www.feko.info/contact.htm and http://www.emss.de. 10. EUROPEAN STANDAR EN 50361, Basic standard for the measurement of Specific Absorption Rate related to human exposure to electromagnetic fields from mobile phones (300 MHZ-3 GHz), CENELEC European Committee for Electrotechnical Standardization, rue de Stassart 35, B-1050 Brussels, July 200 1.

Fig. (7) SAR distribution at 18OOMfIz 5- Conclusion

The obtained results show that the spatial-peak

S A R values as averaged over 1 gram on the human head obtained with a radiated power of 320 mW for both simulations are well below the limit of 1.6 W k g . Where the spatial-peak SAR values for (lgram and 10 grams fiom table 4) tissue in the shape of a cube for 1800MWz are higher than those for 900MHz, the S A R regions produced by 900MHz monopole antenna are more extended as compared to those induced by 1800 M k monopole antenna, that explain why the average SAR, over human head, at 1S O O M H Z is less than that at 900MHz. The results have shown that it is possible to support experimental findings of phantom studies with numerical computer models. So there are possibilities to validate both - the experimental results and the calculations. Finally the FEKO simulation package used in this study has been proved to be adequate in evaluating the interaction between a handset antenna and the human body.

References 1. L. Sevgi & S. Paker, ”FDTD Based RCS Calculations and Antenna Simulations”, AEU, Intema-

THE COMBINED INFLUENCE OF THE STATIC MAGNETIC FIELD AND MICROWAVE RADIATION ON CONFORMATION OF NUCLEOID IN LIVING CELLS A. Y. MATRONCHIK, RUSSIA Moscow State Engineering Physics Institute, e-mail: [email protected] Abstract. The physical reasons of conformation change of nucleoid in living cells under action of microwave radiation are investigated. The mechanism based on cooperative influence of a constant magnetic field and a high-fkequency electric field on own fluctuations of nucleoid with a variable specific charge is offered. In conditions of resonances on frequency of an electric field and Larmor frequency of a magnetic field the maximum probabilities for the fixed values of angular coordinate of the center of mass of nucleoid is obtained. In h i s case values of a constant magnetic field are multiple to the relation of frequency of change of a specific charge to average value of a specific charge. Dependence of biological effect both on parameters of microwave radiation, and on a static magnetic field is proved. 277 0-7803-9374-0/05/$20.00 0 2005 IEEE

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