dosimetry in the human head for two types of mobile phone antennas at gsm frequencies

Cent. Eur. J. Eng.DOI: 10.2478/s13531-013-0140-7

Central European Journal of Engineering

Dosimetry in the Human Head for Two Types ofMobile Phone Antennas at GSM Frequencies

Research Article

Radouane Karli1∗,Hassan Ammor1, Jaouad Terhzaz2

1 Electronic and Communication Laboratory EMI, Mohammed V University-Agdal, Rabat, Morocco

2 Centre régional des métiers de l’éducation et de la formation (CRMEF), Casablanca, Morocco

Received 03 July 2013; accepted 28 October 2013

Abstract: In this paper, a comparative study of dipole and patch antennas commonly used in portable telephones isinvestigated. The two models antennas are considered working at 900, 1800 and 2450 MHz bands. Thus, wehave included different distances between the mobile phone and the human head model. This study shows theeffects of electromagnetic waves on the human head model. The objective is to evaluate the SAR in simulationanatomic based model of the human head for different antenna-head distances and in many frequencies. Allnumerical simulations results are performed using Ansoft HFSS software.

Keywords: SAR • Human head • Dipole antenna • Patch antenna© Versita sp. z o.o.

1. Introduction

In the last ten years, mobile phone usage has beenrapidly spread globally. It is broadly accepted that mobilephones cause heating of the human organ exposed to theirradiation and specifically the human head.The extraordinary worldwide growth of wirelesscommunications and the consequent increase of user’sexposure to microwaves have induced increasing concernsabout possible health effects from the public opinion,media, electronic industry, health organizations andscientific community [1, 2].The diffusion of mobile phones has brought about anincreased concern for the possible consequences ofelectromagnetic radiation on human health, in particular∗E-mail: [email protected]

for children. As a matter of fact, when a cellular phoneis in use, the transmitting antenna is placed very close tothe user’s head where a substantial part of the radiatedpower is absorbed.Several research projects have been conducted in orderto evaluate the possible biological effects resultingfrom human exposure to such an electromagneticradiation [3, 4]. Safety limits for electromagneticexposures have been proposed by national andinternational organizations [5, 6].In the frequency range between 100 KHz-10 GHz, theprimary dosimetric parameter for the exposure is thespecific absorption rate. It is generally accepted thatSAR is the most appropriate metric for determiningelectromagnetic energy (EME) exposure in the verynear field of a RF source [7, 8]. The advantages ofanalyzing specific absorption rate generated by cellularphones inside a human head are among others [9], asfollows; verification of the compliance of phones with

Dosimetry in the Human Head for Two Types of Mobile Phone Antennas at GSM Frequencies

standards [10], electromagnetic solver, experimentallyvalidated, gives not only reliable values of specificabsorption rate but also locations inside a head [11, 12],high resolution in field evaluation could be of interest, asinput data for the analysis of athermal effects [13].Several methods have been used to study the effect of anantenna radiator on a human head such as homogenous ormultilayered concentric spheres [14], multilayered planarmodel [15].This research is a pioneer work that simulates the SARdistribution using the software ansoft HFSS through ananatomically based human head under electromagneticradiation. In this paper a seven dimensional realistichuman head model was used to simulate the SARdistribution over the realistic human head at differentfrequencies and gap distances. The effects of operatingfrequencies and gap distances between the mobile phoneand the human head on distributions of SAR withinthe human head are systematically investigated. Thefrequencies of 900 MHz, 1800 MHz and 2450 MHzwere chosen for simulations in this study, as theyhave wavelengths in the microwave band and are usedfrequently in area of mobile phone usage. We usetwo model antennas for simulation, dipole antenna andpatch antenna operating in three frequencies (900, 1800,2450 MHz) separately to simulate the mobile phone andto comparing the specific absorption rate between the twoantennas.2. Specific absorption rateWhen electromagnetic waves propagate through thehuman tissues, the energy of electromagnetic waves isabsorbed by the tissues. Interaction of electromagneticfields with biological tissues can be defined in term ofspecific absorption rate (SAR).The specific absorption rate (SAR) is an index thatmeasures the level of radio frequency electromagneticfield in the human head, as emitted by the mobile phonewhen operating at full power, in the worst conditions. Itsunit is watts per kilogram (W/kg). Governments haveput standards for the maximum SAR that should not beexceeded to avoid health hazards. This maximum is set to1.6 W/kg averaged over 1 g of tissue, or 2 W/kg averagedover 10 g of tissue, in USA and Europe, respectively [16].The specific absorption rate is described by the followingequation:

SAR = σ2ρ |E |2 (1)where σ is electric conductivity (S/m) and ρ is the tissuedensity (kg/m3). SAR is calculated as a function ofposition from the estimates of local fields and tissues

properties. An integral of SAR over a volume of tissuecontaining a given mass gives the absorbed power. Thisis typically expressed in units of mW/g, or mW/cm3 (fora given tissue density) averaged over 1 g of tissue [17].The SAR value averaged was subsequently calculatedconsidering the contribution of the smaller cube and thecontribution of the cubical shell around it:SAR = ∑

V1 (SAR )imi + ∑V2−V1 (SAR )jmj∑

V1 mi + ∑V2−V1 mj

(2)where mi = ρ∆V and mj = ρj ·∆V 10−V1

V2−V1 . Index i refers tothe lattice cells inside the inner cube and index j to thosearound it.3. Methods and modelThe first step in evaluating the effects of a certain exposureto radiation in the human head is the determination ofthe induced internal electromagnetic field and its spatialdistribution. In this study, a dipole and patch antennasof a mobile phone located at the left side of a humanhead with various gap distances is considered as nearfield radiation source for human head models. Figure 1(a)shows the three-dimensional realistic human head modelwith the dipole and patch antenna used in this studyat various gap distances between the two antennas andthe human head. This model comprises seven types oftissue which are skin, fat, muscle, skull, dura, csf andbrain. These tissues have different dielectric and thermalproperties. Figure 1(b) gives the head dimensions usedin this study, which are directly taken from statisticalbody-size data [16]. On the numerical values taken forthe dielectric properties and density tissue layers of thehuman head, they are given in Table 1 for the threefrequencies Studies. We used the values found in theliterature to perform our simulation.4. Results and discussionWe have chosen the model of the human head as asphere filled with a dielectric layer akin to the humanhead shown in the Figure 2. The considered modelcomprised seven layers. In this simulation, the core wassurrounding by seven spherical shells representing theskin, the fat, muscle, skull, dura, csf and brain with theirrespective electromagnetic properties. The properties ofthe materials used in the simulations are presented inTable 1.The dimensions we have chosen are as follows: for thesphere, we took a radius of 90 mm for the first layer of

Radouane Karli,Hassan Ammor, Jaouad Terhzaz

Figure 1. The Model of a human head. (a) Cross section human head model with mobile phone. (b) Plane microwaves irradiating a cranial modelcomposed of seven layers.

Table 1. The properties of the materials used in the simulations.

Type of tissue 900 MHz 1800 MHz 2450 MHzεr σ (S/m) ρ(kg/m3) εr σ (S/m) ρ(kg/m3) εr σ (S/m) ρ(kg/m3)SKIN 43.8 0.86 1100 43.85 1.23 1100 42.85 1.59 1100FAT 11.3 0.11 1100 11.02 0.19 1100 10.82 0.26 1100MUSCLE 55.9 0.97 1040 54.44 1.38 1040 53.64 1.77 1040SKULL 20.8 0.34 1850 15.56 0.43 1850 15.01 0.57 1850DURA 44.4 0.96 1030 42.89 1.32 1030 42.03 1.66 1030CSF 68.6 2.41 1030 67.2 2.92 1030 66.24 3.45 1030BRAIN 45.8 0.77 1030 43.54 1.15 1030 42.61 1.48 1030

Figure 2. Model HFSS of Layered sphere irradiated by a dipoleantenna.

skin type, for the thickness 2 mm, for the fat a value of1 mm, 4 mm for the muscle and 10 mm for the skull, dura1 mm, csf 2 mm and the last layer is the brain as illustratedin Figure 1(b).In the first time, we use for the simulation of the mobile

phone a dipole antenna operating at 900 MHz frequency,1800 MHz and then at 2450 MHz frequency. Wecalculated the distribution of the local SAR in the headat three different distances from the antenna, which are5 mm, 10 mm and 20 mm. The results are presented inthe Figure 3 for a dipole antenna in three frequencies(900, 1800, 2450 MHz).In the second time, we use a patch antenna operatingat 900 MHz frequency at first, 1800 MHz in the secondand then 2450 MHz frequency as shown in Figure 4, theantenna patch consists of a ground plane, a FR4_epoxytype substrate permittivity εr = 4.4 and excited by amicrostrip line.As we did with the dipole antenna, we calculate thedistribution of average SAR in the head for patch antenna.The effect of gap distance between the mobile phoneand the human head has also investigated. Figure 5,Figure 6 and Figure 7 shows the comparison of theSAR distribution within the human head for differentdistances (5, 10 and 20 mm) respectively in 900, 1800and 2450 MHz.We note that the level of the SAR has significant values ifthe antenna is too close to the sphere (the head) andinsignificant when it is a bit far. If we increase the


Figure 3. Local SAR variation at different distances dipole antenna-head.


Figure 4. Model HFSS of Layered sphere irradiated by a patch antenna. (a) Return loss. (b) Model with SAR measurements.

Figure 5. Local SAR variation at different patch antenna-head distances at 900 MHz.

frequency of 900 MHz to 1800 MHz and to 2450 MHz,the SAR value tends to move in the same direction.Also, the highest level of SAR is in the skin. So, it absorbsmore radiation than the other layers. The fat absorbs thelowest amount. For the muscle, it generally absorbs a lot

of radiation, but since it is a bit far from the radiationsource and the wave is degraded through the skin, fatand muscle, it absorbs less. So these layers provide someprotection to the brain.The Figure 8(a) and Figure 8(b) bellows show the


Figure 8. The fields distribution in the head caused by: (a) Dipole antenna. (b) Patch antenna.

distribution of the electromagnetic fields for bothantennas. The magnitude of the waves is relatively largefor the dipole.The results obtained at the head model excited by thepatch antenna are too small compared with that to thedipole antenna, which justifies the importance of patchantennas and their use in telecommunication in recentscientific research.5. ConclusionThis paper presents the effect of electromagnetic fieldgenerated by the cell phone and its distribution in theexposed human body, especially in the head. We alsopresent the comparative study of a dipole antenna anda patch antenna at 900, 1800 and 2450 MHz. Thisstudy clarifies the numerical simulation of local SARin the human head exposed to mobile phone radiation

at the different frequencies with various gap distancesbetween the mobile phone and the human head. Thenumerical simulations in this study show several importantfeatures of the energy absorption in the human head andwhen comparison of both different types of mobile phone,has demonstrate that mobile phone with dipole antennaproduces more heat compared to mobile phone with patchantenna witch justifies the emergence of great use inrecent applications of mobile phone systems.References

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dosimetry in the human head for two types of mobile phone antennas at gsm frequencies

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