SAR assessment on three layered spherical human head model irradiated by mobile phone antenna
© Rajasekaran and Rajagopal; licensee Springer 2014
Received: 19 March 2014
Accepted: 9 April 2014
Published: 13 August 2014
With the increasing application of wireless communication devices, mobile phone handsets are used by peoples of various age groups. This paper make an effort to asses the mobile phone radiation exposure effect on 4 years old, 8 years old children and an adult head model. Here, human head is modeled as a three layered sphere composed of skin, skull and brain. Hand held device model (with and without resistive sheet) having dipole antenna enclosed by plastic cover is used for human interaction. The software simulation performed by General Electro Magnetic Simulator, based on Finite Difference Time Domain technique yields Specific Absorption Rate and 3D-thermal distribution on spherical human head. Comparison of 1 g SAR, 10 g SAR values for adult and children head show that, children head absorbs more power than adult. Further, the application of resistive sheet on handset shows effective decrement in coupled power.
KeywordsFinite Difference Time Domain (FDTD) Specific Absorption Rate (SAR) Thermal effect Electro Magnetic (EM) radiation
With the rapid increase in technology, the world without communication is un-imaginable. So, mobile phone handset devices act like another hand to human society. Every product has its own advantages as well as disadvantages. However, we never thought of biological ill effects due to mobile phones a wireless communication device used by various age groups . The abundant usage of handsets has kindled some interest in few scientist and researchers regarding the ill effects due to Electro Magnetic radiation emitted by mobile phone antenna. Some research studies shows that, while placing mobile phone nearer to head, the emitted EM radiation gets coupled to human head tissues, which might alter the basic biological function of cells. Even, we can sense the temperature increment in outer case of handset as well as ear, where handsets are pressed while talking for longer hours.
The temperature increment in human tissue is due to power coupled and it may vary with interacting environment. However, the sensed heat gets eventually decreased to equilibrium due to blood circulation. The consequences of excessive heating in the body vary from temporary disturbances in cell functions to permanent destruction of tissues. Areas with less efficient cooling by the circulation, e.g. the lens of the eye, brain cells are more susceptible to electromagnetic radiation. Since, the usage of mobile phones is inevitable in this modern technological world, and the radiation exposure from mobile phone is non uniform, limits can be précised in terms of Specific Absorption Rate (SAR) with an averaging mass of 1 g and 10 g of tissue in the shape of cube. Further, heat induced in tissues signifies the well known adverse health effect at microwave frequencies ,. The analysis of power absorbed by the human head and the antenna performance are necessary for the compliance testing of mobile phones performance. This coupled field can be efficiently calculated by numerical method based on finite difference time domain technique .
This paper endeavor to assess the health hazards, particularly the power absorbed by tissues and thermal effects due to exploitation of mobile phones. Further, a simple and comprehend method of SAR decrement due to usage of resistive sheet on user-front side of handset case is also introduced and performance is analyzed. The work includes evaluation of specific absorption rate for children and adult with same electromagnetic environment. Results might enlighten the mobile phone users regarding radiation exposure effect from mobile phones and, ultimately results in the minimization of an individual’s risks.
Section Model development includes development of mobile phone antenna model, human head model and hand held device model. Section Measurement of power absorbed gives description about measurement of SAR and heat induced when mobile phone is in proximity with the human head model. Section Numerical results and discussions comprises of numerical results and discussions. Finally, section Conclusion covers the conclusion of the work.
User head model
Properties of tissues in human head
Brain diameter (mm)
Skull thickness (mm)
Skin thickness (mm)
4 year child
8 year child
Hand held device model
A handheld device model (shown in Figure 1b) used for human interaction was modeled by GEMS. Figure 2b shows the interaction of handheld geometric model which has a maximum dimension of 167 mm × 23 mm × 83 mm with spherical human head. Components considered for simulation are feeding port (dipole antenna), plastic cover (εr = 4.4) and plastic cover was modeled as dielectric materials .
Measurement of power absorbed
Specific absorption rate
Where, E is the effective value of the electric field intensity (V/m), dT/dt is the time derivative of the temperature (K/s), σ is the electrical conductivity (S/m), ρ is the mass density (kg/m3) and c is the specific heat (J/kg K). The unit of SAR is W/kg. Due to evolution in wireless technologies, dosimetric evaluation of handheld device is highly desirable for safety environment . For radio frequency signals, SAR value is calculated for either 1 g (Australia, United States) or 10 g (Europe, Japan) of simulated biological tissue in the shape of a cube. Partial (localized) non occupational exposure is limited to a spatial peak value not exceeding 1.6 W/kg (Australia, United States) and 2.0 W/kg (Japan). The partial exposure SAR limit recommended by the Council of the European Union and adopted by India is also 1.6 W/kg .
Tissues are made up of water, different salts and organic compounds and they can be considered as a mixture of insulators and conductors. Brain tissue is rich in water along with fat content and cerebrospinal fluid along the ventricles and extends to flow along spinal cord. When a portable cellular telephone is in the typical use position, the nearest brain tissue is in matter of relatively uniform dielectric characteristics with macroscopic values of dielectric constant and conductivity ε r = 52.7 and σ = 0.94 S/m in the frequency band of interest.
Studies  indicate that, the lens of eye may experience a temperature increase of 1°C at SAR level of 10 W/kg. At cell level the heating cause damage by disturbing the functioning of proteins. Cells begin to die when the temperature rises more than 5°C, but the tissues can endure momentary increases of tens of degrees.
Numerical results and discussions
From this the x, y, z component of electric and magnetic field values are calculated at each time by updating the values from the previous time step by the curl of the complementary field. The computational starting point is defined by the initial condition, achieved by applying a sinusoidal or impulsive propagating wave beginning at n = 0. At each increment of n, the solution for E and H evolve as wave propagates ,. In this section, first the performance evaluation of antenna in free space is considered. Further, the interaction of six layered spherical human head with mobile phone is evaluated for measurement of SAR and heat induced.
Evaluation of antenna in free space
Current distribution and S- parameters
Radiation pattern and efficiency
Mobile phone interaction with head model
The spherical human head composed of three inner layers (as in Table 1) is simulated and is allowed to interact with the mobile phone placed very near to ear (pressing the ear).
SAR averaged over 1 g and 10 g tissue when phone (without resistive sheet) placed near head
1-g SAR (W/Kg)
10-g SAR (W/Kg)
Max SAR (W/Kg)
Average SAR (W/Kg)
SAR values averaged over tissues when phone with resistive sheet placed near user head model
1-g SAR (W/Kg)
10-g SAR (W/Kg)
Max SAR (W/Kg)
Average SAR (W/Kg)
In this work, application of resistive sheet of 50 ohm is placed on the user front side of mobile phone handset case. And the comparative result shows, considerable decrement in power coupled. This introduced method shows maximum of 50% decrement in power coupled.
From the studies and above simulation results, it is concluded that, the power absorbed by children head is higher than adult. It might be due to variation in the head tissue layer thickness, which is lower in case of children. Since, the skull bone of adult is very thick comparatively; the intensity of power coupled to the brain is lesser. Further, the inclusion of 50 ohm resistive sheet in handset decreases the power coupled with the human head.
Balamurugan Rajagopal was born in Tamil Nadu, India in 1981. He received the Bachelor’s degree in EIE from NIT Jalandar, Punjab, India and Master’s in Electrical Engineering from Anna University, TN, India. Since 2007, he is working as an Assistant Professor in Department of Electrical Engineering in Anna University Regional Centre, Coimbatore, TN, India. He’s been granted for staff mobility program through Heritage program and India for you. His research interest includes Intellectual Property Rights, Power electronic converters for renewable energy systems, Bio-electromagnetics.
Lalithambika Rajasekaran was born in Tamil Nadu, India in 1987. She received the Bachelor degree in Electronics and Communication Engineering and Master’s in Electrical Engineering in 2009 and 2013 respectively from Anna University, Tamil Nadu, India. She was awarded with Gold medal in her Masters degree. Her research interest includes Bio- Electromagnetics, power electronic converters for renewable energy systems.
I wish to thank Doctors of various hospitals by giving their valuable explanations regarding Human anatomy and the difference between adult and child head.
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