=Paper=
{{Paper
|id=Vol-1538/paper-02
|storemode=property
|title=Specific Absorption Rate (SAR) in the head of Tablet user's
|pdfUrl=https://ceur-ws.org/Vol-1538/paper-02.pdf
|volume=Vol-1538
|authors=Juliana Ferreira,Álvaro Augusto Almeida de Salles
|dblpUrl=https://dblp.org/rec/conf/latincom/FerreiraS15
}}
==Specific Absorption Rate (SAR) in the head of Tablet user's==
https://ceur-ws.org/Vol-1538/paper-02.pdf
7th Latin American Workshop On Communications - 2015
Specific Absorption Rate (SAR) in the head of Tablet user's
Juliana Borges Ferreira Álvaro Augusto Almeida de Salles,
Post-graduation program in Electrical Engineering Electrical Engineering Department
Federal University of Rio Grande do Sul, UFRGS Federal University of Rio Grande do Sul, UFRGS
Porto Alegre, RS, Brazil Porto Alegre, RS, Brazil
ju.borges@ufrgs.br aasalles@ufrgs.br
Abstract—Wireless communication devices such as tablets are The exposure limit recommended by ICNIRP and FCC are
increasing and developing rapidly. The effects of the psSAR lower than 2 W/Kg for any 10 g of tissue or psSAR
electromagnetic (EM) waves in the human body from the wireless lower than 1.6 W/Kg for any 1 g of tissue respectively.
communication devices have been paid attention. It is well known
that the absorption of electromagnetic waves on the human head This paper will focus on the impact of the radiation on the
for a certain period of time may lead to health problems such as SAR values produced by Tablet devices in realistic adults and
headaches, or even worse, significantly increased risk of brain children head models and in the SAM Phantom. The
cancer. In this paper, the Specific Absorption Rate (SAR) in the simulations are based on the Finite Difference Time Domain
head of tablet user’s is simulated for three different head models (FDTD) method. The commercial software SEMCAD-X [6]
and compared with available international recommendations. was used for the SAR simulations.
The models used are the Specific Anthropomorphic Mannequin
(SAM) and two realistic models of human head (a 34 years old The paper is organized as follows. Section II shows the
adult and a 6 years old child). The simulations were performed modeling and the device used. In section III the relevant
using the finite difference time domain (FDTD) method and the international recommendations limits for the SAR are
frequency used to feed the antenna was 2.45 GHz. All the results described. Section IV shows the computational resources.
are below the safety recommendations set up by the International Simulated results are discussed in section V and the in section
Commission Non-Ionizing Radiation Protection (ICNIRP) and VI the conclusions are presented.
the Federal Communications Committee (FCC). Among the
heterogeneous models, the highest peak spatial Specific II. MODELING
Absorption Rate (psSAR) values are estimated for the children.
For 1 g psSAR the child heterogeneous model shows highest
A. Tablet case model
value in comparison to the SAM model. Fig. 1 shows the tablet model with 134.7 × 200.1 ×
9.34 mm³ size. A popular tablet shape model was selected from
Keywords—Tablets; Specific absorption rate; Specific Grabcad database [7] and then imported into the SEMCAD X
anthropomorphic mannequin; Finite-difference time-domain software where it was adapted and the antenna was included.
method The relevant case parameters are included in Table I.
I. INTRODUCTION B. Antenna model
SAR evaluations in the human body from a tablet computer Fig. 2 shows some details of the Planar Inverted F antenna
is increasing in recent year. A substantial concern has risen (PIFA). A suitable antenna from the Antenna Magus Software
regarding the possible adverse effects on human health [1]-[2] database [8] was selected and imported into the SEMCAD X
due to the user’s electromagnetic (EM) energy absorption for software. After this, its dimensions and shape were adjusted to
long periods of time. Several safety standards have been fit the requirements of this project. The antenna was designed
defined [3]–[5] in order to prevent harmful effects in human to operate in the 2.45 GHz Wi-Fi communication band and
beings exposed to non-ionizing radiation (NIR). The Specific tested, showing good performance in the mid-band (see
Absorption Rate (SAR) is a unit to indicate the amount of Table II). It was positioned in the upper right side of the tablet.
power absorbed per unit mass of human biological tissue when The relevant antenna parameters are included in Table II.
exposed to electromagnetic radiation. The SAR is defined
C. SAM phantom
using the following equation (1):
The SAM phantom is an available [9] adult human head
( ) | ( )|² model made of plastic shell, with ear spacers in two sides of
= ( )
( ) (1)
the head and a homogeneous liquid inside the shell, elaborated
with electrical parameters close to the average head tissues
dielectric parameters. Table III contains the dielectric
where σ is the electrical equivalent conductivity of the sample properties of the SAM phantom [9]. The SAM phantom with
(S/m), ρ is the density of the sample (Kg/m³), and E is the RMS the Tablet is shown on Fig. 3.
electric-field (V/m).
Copyright © 2015 for the individual papers by the papers’ authors. Copying permitted for private and academic purposes. This volume is published and
copyrighted by its editors. Latin American Workshop On Communications' 2015 Arequipa, Peru Published on CEUR-WS: http://ceur-ws.org/Vol-1538/
D. Adult and children head models TABLE II. Dielectric Properties and Measured Characteristics
of the Antenna PIFA @ 2.45GHz.
Two available [10] realistic head models were used in these Dielectric Properties Measured Characteristics
simulations. They are heterogeneous and reproduce S11 [dB] for
approximately the human head tissue morphology. These σ [S/m] εr 2.45 GHz
Zo [Ω]
models were obtained from magnetic resonance imaging (MRI) 0.0001 2 -36.8 50
and are available at the Virtual Family [10].
These models are shown on Fig. 4. The first one is a 34
years old adult man (DUKE) and the second is a 6 years old
boy (THELONIOUS). The different tissue dielectric
parameters used in these simulations were obtained from [11]
and are included in Table IV.
Fig 3. SAM phantom (homogeneous model) with Tablet.
TABLE III. Dielectric Properties of the SAM Phantom following
the IEEE 1528 Recommended Practice @ 2.45 GHz
Material σ [S/m] εr
SAM shell 0.0016 5
SAM liquid 1.8 39.2
(a) (b)
Fig. 1. Tablet configurations: (a) Tablet (front view);
(b) Tablet (side view).
TABLE I. Dielectric Properties of the Tablet @ 2.45GHz.
σ [S/m] εr
Screen 0.0001 2.3
Case 0.0001 2.3
(a) 34 years old adult man (b) 6 years old child
(DUKE) (THELONIOUS)
Fig. 4. Heterogeneous models with Tablet.
TABLE IV. Dielectric Properties of the Heterogeneous
Models Tissues @ 2.45 GHz.
Tissue εr σ [S/m]
Fat 0.104 5.280
Bone 0.394 11.381
Grey matter 1.807 48.911
(a)
White matter 1.215 36.167
Liquid Brain 66.243 3.457
Muscle 52.729 1.738
Aqueous Humor 68.208 2.478
Skin 38.007 1.464
Crystalline 44.625 1.504
Sclera 52.628 2.033
Vitreous Humor 68.208 2.478
(b) (c)
Cerebellum 30.145 1.088
Fig 2. Antenna (PIFA) configurations: (a) Antenna PIFA (structure); Nerve 30.145 1.088
(b) Antenna PIFA (front view); (c) Antenna PIFA (side view).
III. INTERNATIONAL RECOMMENDATIONS The 10 g and 1 g psSAR were estimated and are shown in
Some international organizations recommend the Table VII and Fig. 5-6. All the results simulated are below the
evaluations and exposure limits to electromagnetic fields FCC psSAR limit [13] of 1.6 W/Kg in each 1 g of tissue and
generated by wireless devices near the human body (e.g., [3- the ICNIRP psSAR limit of 2 W/Kg in each 10 g of tissue.
5]). Table V shows some recommended exposure limits. In the simulations for 1 g of tissue, the highest psSAR value
The IEEE 1528.2003 standard [9] uses a simplified human is in the children head model (Fig. 5).
head model to estimate the average peak spatial SAR value In the simulations for 10 g of tissue, the highest psSAR
generated by communication devices in the range from 300 value is in the SAM Phantom, and in the heterogeneous
MHz to 3 GHz. It is designed to provide a conservative models, the highest psSAR value is in the children head model
estimate of the maximum average values of SAR during (Fig. 6).
normal use of these devices. A model for the human anatomy
(SAM phantom) was developed to evaluate the exposure in the
TABLE VI. Absorbed Power Percentage
near field produced by wireless devices.
Adult Head Children Head
SAM Phantom
The IEC 62209-1 and IEC 62209-2 standards [12] deal with (DUKE) (THELONIOUS)
the assessment of exposure to electromagnetic fields generated 5.50 % 4.71% 3.97%
by wireless devices near the human body in the frequency
range 30 MHz to 6 GHz. These are applicable to any devices
operating at distances up to 200 mm away from the body, e.g., TABLE VII. psSAR OVER 1 g AND 10 g [W/kg]
when it is near the face or any other body region. Adult Head Children Head
SAM Phantom
(DUKE) (THELONIOUS)
SAR 10 g SAR 1 g SAR 10 g SAR 1 g SAR 10 g SAR 1 g
TABLE V. Standard and Recommendations. Limits for General
Population/Uncontrolled Exposure 0.0062 0.0122 0.0047 0.0114 0.0056 0.0132
ICNIRP [5] IEEE [3] IEEE [14] FCC [4]
Last
1998 2005 2004 2001
Revision
Head and psSAR X Distances X AGE (1g)
Trunk SAR 2 2 1.6 1.6
(W/kg) 0.014
Tissue mass
10 10 1 1 0.013
(g)
Exposure
6 6 30 30 0.012
time (min)
0.011
IV. COMPUTATIONAL RESOURCES 0.01
All the simulations in this work were performed using a 1g SAM 1g THEL (6 YEARS 1g DUKE (34 YEARS)
computer Intel Core i5 3470 at 3.4 GHz equipped with 32 GB
of RAM, NVidia Tesla C1060 GPU card, and Windows 7
Professional x64 operating system, available in the Fig. 5. psSAR 1 g
communications laboratory (LACOM) of the Federal
University of Rio Grande do Sul. The finite difference time
domain-FDTD method was used to simulate different scenarios
for the models and to estimate the SAR. psSAR X Distances X AGE (10g)
V. RESULTS AND DISCUSSION 0.008
A tablet, including the antenna and the box, was simulated 0.006
at 2.45 GHz assuming 30 mW normalized radiated power and
the distance between the eye lens of the head models and the 0.004
tablet was 150 mm. The SAR in the head models is estimated
in each situation of exposure. 0.002
In Table VI the absorbed power percentages are shown in
each case. The estimation with the SAM phantom shows that 0
5,5 % of the energy was absorbed by this model. For the Adult
Head model 4,71 % of the energy was absorbed and for the 10g SAM 10g THEL (6 YEARS) 10g DUKE (34 YEARS)
Children Head model 3,97 %. In the Fig. 7 the radiation pattern
as well as the SAR in a sagittal slice are shown. Fig. 6. psSAR 10 g
Fig. 7. Radiation pattern normalized to 0.0132 W/g = 0 dB, with a 30 dB color scale, and SAR averaged over 1g cube of tissue.
VI. CONCLUSION REFERENCES
The 1 g and 10 g of tissue psSAR produced in the head of
Tablet user’s was simulated when a PIFA antenna was [1] L. Hardell, M. Carlberg., F. Söderqvist, K. H. Mild, “Case-control study
of the association between malignant brain tumours diagnosed between
employed in three different head models. 2007 and 2009 and mobile and cordless phone use”, International
The homogeneous SAM phantom head model did not Journal of Oncology 43.6 (2013): 1833-1845.
present the higher levels of the 1g psSAR. Therefore, [2] Gandhi et al, “Exposure Limits: The underestimation of absorbed cell
phone radiation, especially in children”, Electromagnetic Biology and
according to these simulations, in 1g volume the SAM is not Medicine, Early Online, 1-18, 2011.
conservative. It is recommended that the existing mobile [3] Institute of Electrical and Electronics Engineers, IEEE, “Standard for
devices certification process should be complemented: Safety Levels with Respect to Human Exposure to Radio Frequency
Electromagnetic Fields, 3 kHz to 300 GHz”, IEEE Standard C95.1,
• … with an FDTD computer simulation process, 2005.
• … using anatomically based models, including those [4] Federal Communications Committee, FCC, Office of Engineering and
Technology, OET, Evaluating Compliance, “FCC Guidelines for Human
representatives of the children, Exposure to Radiofrequency Electromagnetic Fields”, Bulletin 65
(Edition 97-01), June 2001.
• … measuring the SAR, averaged over smaller volumes,
[5] International Commission on Non-Ionizing Radiation Protection,
• …and in different tissues. ICNIRP, “ICNIRP Statement on the Guidelines For Limiting Exposure
To Time-Varying Electric, Magnetic, And Electromagnetic Fields (Up
Then certification should be approved only if all tests result To 300 Ghz)”, ed: Health Physics Society, 1998.
in psSAR below the recommended limits. [6] Schmid & Partner Engineering AG (SPEAG), “SEMCAD X by SPEAG,
reference manual for the SEMCAD simulation platform for
The psSAR simulations in heterogeneous models (adult and electromagnetic compatibility, antenna design and dosimetriy”, Schmid
child) show higher levels in the children model. The possible & Partner Engineering AG (SPEAG), Tech. Rep., 2001,
reasons for the higher SAR estimated in the child head model http://www.speag.com.
compared with adult model can be due to different reasons (e.g. [7] GRABCAD. Available at: . Accessed Feb.
16, 2015.
thinner skull, higher dielectric parameters, smaller dimensions,
etc.). [8] ANTENA MAGUS. Available at:
. Accessed
It is very important to remark that the recommendations Mar. 02, 2015.
and the standards usually adopted in different countries only [9] Institute Of Electrical And Electronics Engineers, “IEEE 1528:
consider the health effects of short time of exposure. Adults, recommended practice for determining the peak spatial-average specific
absorption rate (SAR) in the human head from wireless communications
adolescents and children may use these devices for many hours devices”, 2003.
a day, many days a week and many weeks each year. Then [10] A. Christ, et al, “The Virtual Family – devolopment of surface-based
these exposures should be reduced in order to reduce the health anatomical models of two adults and two children for dosimetric
risks and the standards should be revised again since the last simulations”, Physics in Medicine and Biology, Zurich, v. 55, p. 23-28,
review was many years ago. Oct. 2010.
[11] Italian National Research Council - Institute of Applied Physics Nello [13] Federal Communications Commite, office of Engineering and
Carrara. Available at: technology, “Evaluating compilance with FCC Guidelines for Human
. Exposure to Radiofrequency Electromagnetic Fields, Additional
Accessed Aug. 15, 2013. Information for Evaluating Compliance of Mobile and Portable Devices
[12] International Electrotechnical Commission, IEC, “Human exposure to with FCC limits for Human Exposure to Radiofrequency Emissions”,
radio frequency fields from hand-held and body-mounted wireless Supplement C (Edition 01-01) to OET Bulletin 65 (Edition 97-01), June
communication devices -Human models, instrumentation, and 2001.
procedures - Part 2: Procedure to determine the specific absorption [14] Institute of Electrical and Electronics Engineers, IEEE ,”Standard for
rate (SAR) for wireless communication devices used in close Safety Levels with Respect to Human Exposure to Radio Frequency
proximity to the human body (frequency range of 30 MHz Electromagnetic Fields, 3 kHz to 300 GHz—Amendment 2: Specific
to 6 GHz)”, IEC62209-2. 2005. Absorption Rate (SAR) Limits for the Pinna”, C95.1b 2004.