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SAR REPORT-25.13021908.pdf

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Progress In Electromagnetics Research, Vol. 138, 367–388, 2013 EFFECTS OF ELECTROMAGNETIC ABSORPTION TOWARDS HUMAN HEAD DUE TO VARIATION OF ITS DIELECTRIC PROPERTIES AT 900, 1800 AND 1900 MHz WITH DIFFERENT ANTENNA SUBSTRATES Nur A. Husni1, 2 , Mohammad T. Islam1, * , Mohammad R. I. Faruque1 , and Norbahiah Misran1, 2 1 Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, UKM, Bangi, Selangor 43600, Malaysia 2 Dept. of Electrical, Electronic and Systems Engineering, Faculty o
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  Progress In Electromagnetics Research, Vol. 138, 367–388, 2013  EFFECTS OF ELECTROMAGNETIC ABSORPTION TO-WARDS HUMAN HEAD DUE TO VARIATION OF ITSDIELECTRIC PROPERTIES AT 900, 1800 AND 1900MHzWITH DIFFERENT ANTENNA SUBSTRATESNur A. Husni 1, 2 , Mohammad T. Islam 1, * ,Mohammad R. I. Faruque 1 , and Norbahiah Misran 1, 2 1 Institute of Space Science (ANGKASA), Universiti KebangsaanMalaysia, UKM, Bangi, Selangor 43600, Malaysia 2 Dept. of Electrical, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia,UKM, Bangi, Selangor 43600, Malaysia Abstract —This paper analyzes and discusses the effect of theelectromagnetic absorption by human head against variation of headdielectric properties at 900, 1800 and 1900MHz. The characteristicsof helical antenna and its substrates with variation in human headdielectric properties are simulated by implementing finite-differencetime-domain (FDTD) method using CST Microwave studio. Thevariations in human head dielectric properties were manipulatedby increasing and decreasing 10% and 20% of each of the humanhead dielectric properties. In this paper, SAR values increase withincrement of head conductivity, and increment of head permittivityand head density lead to decrement of SAR values. Helical antennawith substrate of FR4 results in higher SAR values in all frequencyexposures. The head SAR values are higher with higher frequencyexposures. The helical antenna with substrate of Rogers RO3006(loss free) is found to be better over FR4 and Rogers RO4003 (lossfree), which contributes towards much lower SAR values in all GSMfrequency bands exposure. Received 19 February 2013, Accepted 19 March 2013, Scheduled 28 March 2013  * Corresponding author: Mohammad Tariqul Islam (titareq@yahoo.com).  368 Husni et al. 1. INTRODUCTION Mobile phone technology was introduced in the early twentieth century.Now the technology has rapidly evolved and been utilized across theglobe. Though this technological front is important, we need to beaware of some inherent dangers that it presents. Microwave radiationhave been discussed and debated among researchers in this field. Thisradiation affects human health which disrupts the biological systemof human body by electromagnetic waves emitted from the mobilephone towards its user [1–9]. There was also a claim from previousresearch that with over 10 years of using this technology, radiationfrom mobile phone potentially doubles the risk of brain tumor atthe side of the head where the mobile phone has been used over aperiod of time [10]. Research found that the risk of brain cancerdoubled in adults with overuse of mobile phone and five times amongyoungsters [11]. Recently, the World Health Organization (WHO) havestated that the mobile phone potentially leads to brain cancer [12–17].The International Agency of Research Cancer (IARC) has groupedelectromagnetic fields into Group 2B which is carcinogenic towardshuman. A lot of concerns regarding wireless devices safety have beendiscussed due to abundance application of wireless communication inthese days. Microwaves radiated from mobile phone interacted withbody tissues which produce internal electric and magnetic fields andcause thermal effect with close proximity of handset towards the bodyin particular time duration [18,19]. Investigations have been donepertaining the effects of radio frequency (RF) radiation upon humanbody using various models and scenarios [20].Several international authoritative bodies are responsible forregulating safe SAR limit in exposed onto human tissues [21], includingInternational Commission on Non-Ionizing Radiation Protection(ICNIRP) in Europe. The ICNIRP regulates safe limit of SAR of 2W/kg over 10g sample of body tissue. Japan, Brazil and NewZealand are the other countries following this regulation. In the UnitedStates, Federal Communications Commission (FCC) set SAR limit of 1.6W/kg over 1g of body tissues [21–23]. Other countries abidingto this standard are Canada, Australia and Taiwan. In Malaysia,the authoritative body of Malaysian Communication & MultimediaCommission (MCMC) regulates safe SAR limit of a mobile phone thatfollows the standard of ICNIRP.RF radiations that penetrate through human body from mobilephone are measured in terms of SAR. SAR denotes power absorbed byhuman from handset over certain volume of body tissue [24–27]. SAR isdirectly proportional to body conductivity and inversely proportional  Progress In Electromagnetics Research, Vol. 138, 2013 369 to body permittivity [28]. SAR is influenced by dielectric valuesof human body, and these values are very much dependent on theorientation, human-body and frequency exposure. The conductivity, σ , and relative permittivity,  ε , of human tissues are the determiningfactors for both optimal RF communication and dosimetry [29–32].Human body tissue with higher water content is more susceptibleto absorbing radiation or so called power radiated from handset.Higher water content shows that the particular body tissue is greaterin conductivity which increases SAR values. The permittivity andconductivity are frequency dependent [2,33]. The peak of spatialSAR in a child and adult head models is exposed to 900MHz mobiletelephone using the finite-difference time-domain (FDTD) method,and it is found that variation of the 1g or 10g average spatial SARpeak with different dielectric properties is within 10% [33,34]. Theaverage SAR values are always inversely proportional with variationsof body permittivity. There is also some estimation of the dependenceof SAR values on the variability in dielectric values which should bedetermined.The specific absorption rate has been adopted as the reliableparameter for RF power safety for performing magnetic resonanceimaging experiments proposed by Rojas et al. [35]. They havecalculated SAR using numerical method based on finite elementmethod and 3D model of a rat’s brain modeled using the softwareAUTODESK 3DS MAX. This brain model has adopted the tissueproperties including the tissue’s conductivity and permittivity froma database of Gabriel et al. 1996 [36]. The authors have developeda parametric model to describe the variation of dielectric propertiesincluding the permittivity and conductivity of body tissues as afunction of frequency. The body tissues’ conductivity and permittivityare frequency dependent. Therefore, at each frequency exposure,the body tissues have specific dielectric properties. In Gabriel etal.’s experiment the frequency spectrum was from 10Hz to 100GHz.Since Rojas et al. calculated SAR at frequencies of 10, 50, 100, and300MHz, the tissues’ conductivity and permittivity are included in thementioned database prepared by Gabriel et al.This paper focuses on analysis of the effect of electromagneticabsorption towards human head with variations of dielectric propertieswith frequency exposure of 900, 1800 and 1900MHz together withdifferent antenna substrates.  370 Husni et al. 2. MODELS AND METHOD2.1. Models The model used for the head was the Specific AnthropomorphicMannequin (SAM) Phantom with mobile phone model attachedtogether with helical antenna. The head model consists of innerand outer layers having specific dielectric properties similar to anactual human head. The dielectric properties were constant at alltimes at a particular frequency exposure, and its properties werechanged due to particular changes towards the head. The helicalantenna attached onto the handset was the radiation source, andelectromagnetic absorption upon the head was measured. Operationalfrequencies used in this work were 900, 1800 and 1900MHz. The effectsof SAR values were also analyzed using three different substrates of the antenna which were FR4, Rogers RO3006 (loss free) and RogersRO4003 (loss free). Variations of 10% and 20% of each of the head’sdielectric properties were made, and SAR values were evaluated.Dielectric properties of substrates for helical antenna are shownin Table 1. Table 1.  Dielectric properties of substrates for helical antenna.Type of Substrate Permittivity,  ε r Conductivity, σ  [S/m]Rogers RO3006 (loss free) 6.15 0.61Rogers RO4003 (loss free) 3.38 0.71FR4 4.30 0.27Homogeneous human head dielectric properties at 900, 1800 and1900MHz are listed in Table 2. Table 2.  Homogeneous human head dielectric properties.Frequency[MHz]Permittivity, ε r Conductivity, σ  [S/m]Density, ρ  [kg/m 3 ]900 41.5 0.97 10301800 40.0 1.40 10301900 40.0 1.40 1030
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