he  Finite-Difference  Time-Domain  (FDTD)  is the     most     often     used     method     for     evaluating     of electromagnetic   fields   in   human   tissue. The   ever-rising diffusion  of  cellular  phones  has  brought  about  an  increased concern  for  the  possible  consequences  of  electromagnetic radiation  on  human  health. This  paper  presents  a  study  of electric  ,magnetic  fields distribution  in  human  prostate tissue . Concerning    numerical    modeling,    the    power absorption and specific absorption rate (SAR) in a prostatearegenerally  computedusing FDTD  methods  in  one and two   dimension.   Results   show   that   mobile   radiation  penetrate  the  prostate  tissues  and  attenuate  fast  to  reach zero  at  the  inner  of  tissue. The  absorbent  power  and  SAR show maximum at the interface .he  Finite-Difference  Time-Domain  (FDTD)  is the     most     often     used     method     for     evaluating     of electromagnetic   fields   in   human   tissue. The   ever-rising diffusion  of  cellular  phones  has  brought  about  an  increased concern  for  the  possible  consequences  of  electromagnetic radiation  on  human  health. This  paper  presents  a  study  of electric  ,magnetic  fields distribution  in  human  prostate tissue . Concerning    numerical    modeling,    the    power absorption and specific absorption rate (SAR) in a prostatearegenerally  computedusing FDTD  methods  in  one and two   dimension.   Results   show   that   mobile   radiation  penetrate  the  prostate  tissues  and  attenuate  fast  to  reach zero  at  the  inner  of  tissue. The  absorbent  power  and  SAR show maximum at the interface 

Elwasife, khitam

English

Institutional Repository of the Islamic University of Gaza

 International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) 120  FDTD Computation of Prostate Tissue Exposure to Cellular Phones Radiation Khitam  Y. Elwasife Department of Physics, College of Science, Islamic University, Gaza, Palestinian Territory  kelwasife@iugaza.edu.ps  abstract - The Finite-Difference Time-Domain (FDTD) is the most often used method for evaluating of electromagnetic fields in human tissue. The ever-rising diffusion of cellular phones has brought about an increased concern for the possible consequences of electromagnetic radiation on human health. This paper presents a study of electric , magnetic fields  distribution in human prostate tissue . Concerning numerical modeling, the power absorption  and specific absorption rate (SAR) in a prostate are generally computed using FDTD methods in one and two dimension . Results show that mobile radiation  penetrate the prostate tissues and attenuate fast to reach zero at the inner of tissue. The absorbent power and SAR show maximum at the interface . Key words- FDTD method, life tissue, cellular phone radiation . I. INTRODUCTION Computation of electromagnetic field inside a tissue at mobile communication has been studied, which presents a new approach to calculate the electromagnetic field inside a tissue, composed of electrically excitable cell by means of the FDTD (finite difference time domain method) [1-2]. the simulation results of the absorption of RF energy in the biological tissue in the case of the cell phones has been evaluated . The Ansoft HFSS method with boundary conditions and assigned excitations by an antenna dipole, an antenna monopole and patch antenna are used as the cell phone. The human head is simulated by HFSS at GSM frequencies 900 MHz and 1800 MHz. In order to evaluate the ability of the HFSS code, we use the FDTD computations and the measurement results of the SAR distribution obtained from the spherical glass bowl filled with different liquids and either a wired dipole antenna[3].  The classical FDTD was modified by using an unsplitting field formulation which can combine the simulated physical domain and an artificial absorbing layer as a single computational domain [4].  the simulation of electromagnetic interaction in the human head model using the FDTD with a modified PML investigated .    The simulated physical domain contains a dipole antenna, a high-resolution human head model and a metal wall. In the simulation, a dipole antenna acts as a mobile phone operated at 900 MHz and 1.8 GHz[5].  In general, IEEE standard required that the SAR 1-g of handheld wireless phones not exceed 1.6 watts/kg, averaged over 1-g mass of tissues [6]. Although the SAR 1-g is determined at the highest power level, the actual SAR 1-g value while operating depends on factors such as the proximity of the antenna to the human head while in use.  M, Burkhardt et al has been modeled The ear, including skin- and cartilage-layer, by using two layers in the multi layered superquadric ellipsoid[7]. The skin-layer (of the ear) is modeled by thickness of one FDTD cell. SAR simulation in wireless communication and safety discussions in the society discussed [8], numerical simulation in cellular phone study by powerful time techniques(TD) and the transmission line matrix(TLM).A finite element thermal model of the head has been developed to calculate temperature rises generated in the brain by radiation from cellular telephones and similar electromagnetic devises. Martinez-Burdalo et al. further analyzed SAR depositions in different-aged human heads exposed to electromagnetic radiation resulted from a mobile phone [9]. electromagnetic  waves  interactions  with human   bodies has been studied by M. F. Wong[10].  The Changes in the dielectric properties of rat prostate ex vivo at 915 MHz during heating has been evaluated[11].  It found that the temperature coefficients can be utilized in microwave treatment planning programmers to provide insight into the effects of dielectric changes that arise during microwave thermal therapy of prostate cancer. In this work we studied the effect of electromagnetic waves produce from mobile phone on human prostate tissue, computation FDTD  Simulations were run for  mobile phone radiation  of  the human prostate which frequency was 0.9 GHz continuous wave form source . FDTD method implemented in MATLAB program was used to compute the distribution of electric , magnetic fields, specific absorption rate and power density  in the prostate  tissue.   International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) 121  II. MODELLING AND COMPUTATIONAL METHOD It assumed that electromagnetic radiation from mobile phone  is incident vertically upon the interface prostate  tissue with dielectric properties  shown in table(1).  TABLE I DIELECTRIC PROPERTIES OF PROSTATE TISSUE AT FREQUENCY 900MHz    The dielectric properties of  a life tissue are different  according changing frequency. The function of the prostate is to secrete a slightly alkaline fluid, milky or white in appearance[12], that usually constitutes 20–30% of the volume of the semen along with spermatozoa and seminal vesicle fluid the electric field and the magnetic field are found to satisfy the equations 2 2( ) 0,2 2( ) 0,EandH                              (1)  The electric field is assumed to propagate in the z direction with polarization at the x direction. Now  we  present  the  Maxwell’s  equations  in  one dimensions. We suppose the absence of  magnetic or electric current sources, and the  existence of absorbing materials in the space  under study .The finite difference time domain (FDTD) method is powerful solution for solving Maxwell’s equations, introduced by K.S. Yee [13]. The algorithm involves direct discriminations of Maxwell’s equations by writing the spatial and time derivatives in a central finite difference form.  The time-dependent Maxwell's curl equations in general form, which will allow us to simulate propagation in media that have conductivity 0HEt                                                             (2)                                                                                DH Et                                                         (3) Where the displacement vector D is related to the electric field through the complex permittivity . In 1-D, we consider only Ex and Hy are not equal to zero and traveling in the z-direction [14] . In addition, we assume that the fields do not vary in the x-y plane, i.e. 0xand 0y. However, the dielectric properties of prostate are donated with the complex permittivity as ( )0jr r                                                      (4)                                                                                Where ω is the angular frequency, and r  is the real relative part of the permittivity, σ is the conductivity and ω is the radial frequency of the signal. The quantity σ /ωε0 is called the loss tangent. It describes the looseness of the medium. Since the human tissues are nonmagnetic, it has been assumed that µ1= µ0. The free space is assumed for the exterior of the model with wave number0 0 0k    . Then Equations (2,3) can be reduced  to [ ( )( ) 1( )0 0H tE t yx E txztr r                      (5)                                               ( ) ( )10H t E ty xt z                                    (6)                                                           In the FDTD formulation, the central difference approximations for both the temporal and spatial derivatives are obtained at z k z  and t n t   for the first equation  1/2 1/2 ( 1/2) ( 1/2)( ) ( ) 101/2 1/2( ) ( )20n nn n H k H kE k E k y yx xt zrn nE k E kx xr                                                                                                (7) Tissue name Conductivity σ[S/m]by  900MHz Relative permittivity by 900MHz Penetration depth [m] Density ρ[kg/m3] Air 0 1 1 1.229 Prostate  1.2096 60.553 0.034802 1100  International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) 122  and  1 1/2 1/2( 1 / 2) ( 1 / 2) ( 1) ( )10n n n nH k H k E k E ky y x xt z                                                                                              (8)   Where   n is the time index and k is the spatial index, which indexes times t = n t   and positions z k z  . The time index is written as a superscript, and the spatial index is within brackets. Equations (7 and 8) can be rearranged as a pair of ‘computer update equations’, which can be repeatedly updated in loop, to obtain the next time values of Exn+1/2 (k) and Hyn+1 (k + 1/2), corresponding the Ex(t +∆t/2, z) and Hy(t +∆t, z + ∆z/2). As a result, Ex and Hy will differ by several orders of magnitude.  the changing of variables, equations (7and 8) become     0001/ 2 1/ 2.12( ) ( ).121 / 2[ ( 1 / 2) ( 1 / 2)].12n ntrE k E kx xtrn nH k H ky ytrr             (9)   1( 1 / 2) ( 1 / 2)1/ 2 1/ 21[ ( 1) ( )]0n nH k H ky yn ntE k E kx xz                        (10)      Stability and the FDTD method: For stability purposes, we need to choose the cell size z  to allow 10 to 15 points per wave length. We used in all our simulations a time step 02ztc  where c0 is the speed of light in free space.  The most important points in FDTD calculations are the stability and numerical dispersion [15].  III. NUMERICAL RESULTS AND DISSCUSION   A one dimensional finite difference model for predicting electric and magnetic fields  in living tissues such as prostate tissue undergoing microwave heating is presented. .  For cell   phone  radiation  studies, the  simulated  radiation source  is a continuous  waveform (CW) of  .9GHz, The values of  electrical parameters, relative permittivity and  electric conductivity for this frequency,  are adopted from [16]. The  SAR  IS  a  measurement  used  to  quantify  and  the  localized  deposition  of  microwave  energy.  The  SAR  units  are  watts  per  kilogram  (W /kg).  As  a  dosimetric  quantity,  the  SAR denotes the time rate of  electromagnetic  energy absorption at  a given  location in the tissue. The expression for the SAR is as follows: 22ESAR                                                   (11) Where E is the electrical field (V/m), σ  is the electrical conductivity (S/m) of  the  tissue and   is  the mass density of  the tissue (kg/m),and the power density is 22Ep                                             (12) Simulations were run for  mobile phone radiation  of  the  human prostate which frequency was 0.9 GHz continuous wave form source . In equation (9)  the appropriate mesh sides Δx = .01and time steps Δt = .04 are considered for calculations H, E . FDTD method implemented in MATLAB program was used to compute the distribution of electric , magnetic fields, specific absorption rate and power density  in the prostate  tissue.  Figure (1) represent the electric field in prostate tissue vs time steps, the electric field is maximum and decrease  exponentially towards the inner tissue.  The magnetic field penetrate in prostate tissue from mobile radiation is illustrated in figure(2). It shows that the amplitude of the magnetic field is more than electric field amplitude  and decrease fast  by  much time steps through the tissue.in figure (3) we run  MATLAB program using one dimension FDTD method to plot the specific absorption rate (SAR) in prostate tissue. The SAR and power density is directly proportional according the  density of the tissue as in equation (11,12), so the minimum value in the case of SAR and power is at 35 time steps. In figure(4) the power density  was plotting with respect to time steps and   the  figure show  a maximum peak  is less than amplitude more  SAR curve  peaks. Two dimension FDTD method illustrated in figure (5,6). The  curves shows the electric field  sticking prostate tissue in tow dimension by using bone and lines shape.  This results  denote that the mobile phone radiation is effect on human tissue  and caused  specific absorption rate according the dielectric properties of tissue  which is changing by changing the frequency.  International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) 123   VI. CONCLUSION   prostate human tissue  representing simplified model life tissue irradiated by plane waves produced by mobile phone is investigated.. FDTD is used to study the distribution of the electromagnetic fields in the prostate  tissues, the absorbent power, and SAR distribution. It is found that the fields penetrates the interface of tissue and  attenuated rapidly till they reach zero at inner  layer. Absorbent power and SAR have maximum values at the interface of tissue .  According to the result from the graphs , notice that the there are   the effect of frequency 900MHz by mobile phone  Global System Mobile (GSM)  is more at the first time steps through the cell of tissue. The dielectric properties for tissue are different according the change in frequency. This model enabled us to make simulations with very small cell size, and thus, figuring out the effect of thin layers on the SAR distribution was possible in a small simulation time. 0 50 100 150 200 250-2-1.5-1-0.500.511.52time stepsElectric field  Figure(1) Eclectic field in prostate tissue by one dimensional FDTD method 0 50 100 150 200 250-6-4-20246Time stepsMagneticfield  magnetic field in space Figure (2) Magnetic field in prostate tissue by one dimensional FDTD method  30 35 40 45 50 5500.10.20.30.40.5Time stepsPower density  Figure(3) power  density  in prostate tissue by one dimensional FDTD method 30 35 40 45 50 55 60100200300400500600Time stepsSAR Figure(4) SAR  in prostate tissue by one dimensional FDTD method time stepsElectric field  20 40 60 80 100 120 140 160 180 20050100150200-0.3-0.2-0.100.10.20.3 Figure(5) 2D EM propagation -striking a prostate tissue  (bone color)  International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012) 124  time stepsElectric field  20 40 60 80 100 120 140 160 180 20050100150200-0.3-0.2-0.100.10.20.3 Figure(6) 2D EM propagation -striking a prostate tissue   (lines) REFERENCES [1] Gianluca Emili and Andrea Schiavoni. 2003. Computation of Electromagnetic Field Inside a Tissue at Mobile Communications Frequencies,Vol.51,No.1.  [2] A.Talflove.1995.Computational Electrodynamics. (Norwood, MA: Artech House.  [3] Seddik Bri. 2011. Specific Absorption Rate (SAR) Distribution in the Human Head at Global System Mobil (GSM) Frequencies. European Journal of Scientific Research ISSN 1450-216X Vol.49 No.4 ,  590-600. [4] L. Ling, L. Ronglin, X. Suming and N. Guangzheng, 2002. A New Generalized Perfectly Matched Layer for Terminating 3-D Lossy Media, IEEE Transactions on Magnetics, Vol. 38, No. 2, 713-716. [5] Nuttaka Homsup, Terapass Jariyanorawiss, 2009 FDTD Simulation of a Mobile Phone Operating near a Metal Wall, Journal of  Computers, Vol. 4, No. 2. [6] IEEE Standard, 2003 IEEE Recommended Practice for Determining the Peak Spatial-Average Specific Absorption Rate (SAR) in the Human Head from Wireless Communications Devices: Measurement Techniques, The Institute of Electrical and Electronics Engineers (IEEE), New York, USA, 18-19. [7] M, Burkhardt and N. Kuster, 2000. Appropriate Modeling of the Ear for Compliance Testing of Handheld MTE with SAR Safety Limits at 900/1800MHz," IEEE Transactions on Microwave Theory and Techniques, vol. 48, No. 11, 1927- 1934. [8] M.O.Ozyalcin, 2002 SAR Simulation In Wireless Communication And Safety Discussions In The Society" Turk J Elec. Engin.Vol.10,No.2. [9] M. Martinez-Burdalo, A. Martin, M. Anguiano, and R. Villar, , 2004 Comparison of FDTD-calculated speciﬁc absorption rate in adults and children when using a mobile phone at 900 and 1800 MHz,” Phys. Med. Bio., vol. 49, no. 2, 345–354. [10] M. F. Wong and J. Wiart, , 2005 Modelling of electromagnetic  waves  interactions  with human   bodies,   C.   R.   Académie   des Sciences, Physique, vol. 6,no. 6, 585- 594. [11] Chin L, Sherar M. 2004 Changes in the dielectric properties of rat prostate ex vivo at 915 MHz during heating. Int J Hyperthermia. Vol. 20,No.5,517-27. [12]Chemica Composition of  Human Semen and of the  Secretions            of the  Prostate and Seminal                  Vesicles". http://ajplegacy.physiology.org. Retrieved 2010-08-           10  [13] K. S. Yee, 1966 IEEE Trans. antennas and Propagat. AP-14, 302.  [14] khitam Y. Elwasife, 2011,Power Density and SAR in Multi-Layered Life     Tissue at Global System Mobile (GSM) Frequencies.  Journal of Electromagnetic Analysis and Applications,  3, 328-332    [15] K. K. Mei, X. Zhang, 1988 IEEE Trans. Microwave Theory Tech.   MTT-36, 1775 .  [16] S.Gabriel, R.W.Lau and C.Gabriel, 1996. The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues, Phys. Med. Biol. 41 , 2271-22   

FDTD Computation of Prostate Tissue Exposure to Cellular Phones Radiation

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FDTD Computation of Prostate Tissue Exposure to Cellular Phones Radiation

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