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Received September 9, 2015, accepted October 29, 2015, date of publication November 23, 2015,
date of current version December 10, 2015.
Digital Object Identifier 10.1109/ACCESS.2015.2502900
Dosimetric Simulations of Brain Absorption of
Mobile Phone Radiation—The Relationship
Between psSAR and Age
CLAUDIO ENRIQUE FERNÁNDEZ-RODRÍGUEZ1, ALVARO AUGUSTO ALMEIDA DE SALLES2,
AND DEVRA LEE DAVIS3
1Federal Institute of Education, Science and Technology of Rio Grande do Sul, Canoas 92412-240, Brazil
2Electrical Engineering Department, Universidade Federal do Rio Grande do Sul, Porto Alegre 90040-060, Brazil
3Environmental Health Trust, Teton Village, WY 83025, USA
Corresponding author: C. E. Fernández-Rodríguez (claudio.fernandez@canoas.ifrs.edu.br)
This work was supported by Environmental Health Trust.
ABSTRACT As children develop, they differ from adults in a number of important ways, including anatomy,
metabolism, immune system, and the extent of myelination of the nervous system. As a consequence,
equivalent exposures to radiation from mobile phones result in different doses to specific tissues in children
compared with adults. Higher doses are likely to have more severe implications in the young. A young child’s
skull is not only smaller and thinner than an adult’s, but also has dielectric characteristics closer to those of
soft tissues, probably due to a higher water content. The young skull better matches the electromagnetic
characteristics of the skin and brain. As a result, finite-difference time-domain (FDTD) simulations confirm
field penetration and higher specific absorption rate (SAR) in deeper structures in the young brain. If the peak
spatial SAR (psSAR) is modeled in the entire head, as current testing standards recommend, the results for
adults and children are equivalent. Our anatomically based evaluations rely on FDTD simulations of different
tissues within the brain and confirm that the psSAR in a child’s brain is higher than in an adult’s brain.
INDEX TERMS Specific absorption rate, mobile phone certification, dosimetry, finite-difference
time-domain simulation.
I. INTRODUCTION
A growing literature indicates that dynamic changes in
neurochemistry, fiber architecture and tissue composition
occur during development of the young brain [1], [2].
Advances in neuroimaging show that during development
grey matter volume shrinks, while white matter that supports
complex cognition and behavior expands. Asynchronous
maturation of prefrontal and limbic systems may render youth
more susceptible to a number of potential developmental
toxicants [3].
As a result of these and other physiological and anatomical
differences between the young and older brain, biological
effects that are potentially related to the use of mobile phones
can be expected to differ with age. Nevertheless, inconsistent
arguments and results on this subject have been published
over the last two decades. Wiart showed that twice as much
radiation passes through the smaller, softer skull and into
the brain of a child, compared with an adult [4], con-
sistent with earlier work by Gandhi and Kang, 2002 [5].
Modern modeling demonstrates clear differences between
doses absorbed by children and adults exposed to EMFs
(electromagnetic fields) [4]–[7]. In contrast with that work,
in a recent report Foster and Chou [8] reviewed studies
of the intracranial dose rates of absorbed radio-frequency
electromagnetic radiation (RFEMR) in adults and children
and claimed that radio-frequency radiation exposures from
mobile phones to the head of a child and an adult do not
result in differences in absorption. Morris [9] identified
serious systematic errors and inconsistencies in that paper
and concluded that the data support the opposite conclusion
from that drawn by the authors. They note that, even if the
exposures to the young and the old brain were identical –
and they are not – the ways that the young brain responds
to microwave radiation indicate that it is clearly more
vulnerable.
In an effort to improve the understanding of RF exposures
from mobile phones, we provide anatomically-based model-
ing of the tissues of the brain using adult and child models
VOLUME 3, 2015
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2425
C. E. Fernández-Rodríguez et al.: Dosimetric Simulations of Brain Absorption of Mobile Phone Radiation
that have been developed in Porto Alegre, Brazil, with the
Environmental Health Trust (PAEHT). To illustrate and to
clarify absorption by brain tissues of children in comparison
with adults, we present simple FDTD SAR simulations using
SEMCAD X software [10] and Virtual Family [11] head
models of different ages.
Cell phone compliance test procedures are based on a
homogeneous physical model – a liquid-filled plastic head –
with dimensions of a large adult man (Specific Anthropomor-
phic Mannequin or SAM). Depending upon whether these
tests are extrapolated, or if analogous tests are carried out
in child and adolescent models, the results may indicate a
trend for increasing peak spatial SAR (psSAR) in the younger
models [4]–[6], [12]–[17], or psSAR may be ambiguous [18].
Several researchers have reported conflicting results, evaluat-
ing the psSAR either in a homogeneous model of the head, or
with consideration of specific tissues (e.g., grey matter, white
matter, pineal gland, hippocampus, etc.) [4]–[6], [12]–[18].
In previous work [13], using dielectric constants scaled from
adult human parameters with values from young and old rat
tissues [19], FDTD simulations yielded brain psSAR 60%
higher for an average-weight 10 year old boy, compared with
an overweight adult man [20].
The length of the cell phone antenna is typically 3 cm or
less. When talking on the phone the antenna may be operated
very close to the user’s head. A child’s head can have a
diameter around 15 cm or less and an adult head can have
a diameter around 20 cm or more, both substantially greater
than the antenna dimensions.
The cell phone compliance tests are performed with
a 0.6 cm thick plastic pinna to represent the outer part
of the human ear when compressed by the cell phone in
use [21]. This introduces another matter of controversy.
The FCC recently declared that the auricle or the outer
ear is to be treated as an extremity, like the hand or foot,
and not as part of the head in accordance with revision
IEEE Std C95.1-2005 [22]. This standard expands the defini-
tion of extremity to include the pinna, which makes the pinna
subject to a higher psSAR, see Table 1. The present work
excludes pinna tissue from the head tissue SAR averaging.
TABLE 1. SAR limits in three standards, for extremities and for other
tissues (e.g. brain). These limits are for exposure of the
general public in an uncontrolled environment.
When comparing published results it is often difficult, or
impossible, to determine whether head tissue SAR values are
based on averaging volumes that include or exclude the pinna.
In fact, some papers make no mention of how the pinna
was treated. Although head tissue SAR is the major focus
of attention, papers that consider the pinna as an extremity
cannot simply ignore its existence, the pinna must still meet
the higher peak spatial SAR for extremities.
No matter how the ear is treated mathematically and in
exposure guidance, in reality the antenna is held very close
to the head. As a first approximation, with this geometry, the
estimated psSAR and total EMF absorption for both adult
and child heads can be close to the psSAR and to the total
EMF absorption for a semi-space with similar characteristics.
Therefore, the extrapolations in the compliance tests in which
the psSAR is estimated throughout the entire head can result
in similar values for adults and for children. Of greater rele-
vance for health, are doses absorbed by the brain.
SAR is based solely on the average value estimated over
a period of six or thirty minutes. In fact, there are reports
from a number of authors indicating that pulsed signals are
more bioactive than continuous waves. These reports include
Belyaev et al. [25] who found greater DNA damage and
possibly greater health risks from UMTS in contrast to GSM,
both of which involve pulsed signals. At this point, SAR
determinations using the SAM-based system cannot take into
account pulse intensities, duration and repetition rate tied
with information transfer. SAR calculations reflect only
average power.
II. HEAD AND BRAIN SAR IN ADULTS AND CHILDREN
A. SIMPLIFIED MODEL TO ESTIMATE THE EFFECT OF
VARIATION I N DIELECTRIC PARAMETE RS
The permittivity and conductivity of mammalian head and
brain tissues are higher for samples obtained from younger
than from older animals. One of the most significant dif-
ferences is for the bones, which in the young resemble the
parameters for soft tissues. This can be due to differences
in the tissues’ water content. In [26] it is reported that some
tissue dielectric parameters of piglets are higher than for adult
pigs. For 10 kg piglets, which can be correlated with
a 4 year old child, the dielectric constants for skin, fat, bones
and brain respectively are 24%, 151%, 119% and 4% higher,
in comparison with a 250 kg (adult) pig.
Although a plane wave on a flat phantom is not an accurate
model for the interaction between the cell phone electro-
magnetic field and the head, it can be useful to understand
the relationship between tissue specific doses and values
of the dielectric parameters [27]. It is relatively easy to model
the head as three or four coaxial cylindrical slabs (skin, bone
and brain, adding or not a subcutaneous fat fourth slab) flat
phantom. In addition to this, for the FDTD simulations, both
homogeneous and more realistic models are available. These
models are illustrated in Figure 1.
The dielectric parameters (900 MHz) for adult human [28],
for adult 250 kg pigs, for 10 kg piglets [26] and the correlated
values for a 4 year old child are presented in Table 2, where
εris the relative permittivity and σis the conductivity. It is
immediately evident that the different tissue parameters of
2426 VOLUME 3, 2015
C. E. Fernández-Rodríguez et al.: Dosimetric Simulations of Brain Absorption of Mobile Phone Radiation
FIGURE 1. A homogeneous phantom (IEEE 1528 [21]), a 4-slabs flat
phantom and a heterogeneous model (Eartha, from Virtual Family)
used in the FDTD simulations.
TABLE 2. Permittivity and conductivity for some tissues exposed
at 900 MHz.
the young vary over smaller ranges. With closer impedance
matching between the young tissues, higher electric field and
SAR values would occur in the young brain.
These higher values affect the transmission coefficient τ.
For a plane wave leaving a medium with intrinsic
impedance η1and entering a medium with η2, at a 90◦to
the surface, the transmission coefficient τcan be reduced to
τ=2η1
η1+η2
,(1)
where
η=sjωµ
jωε +σ
,(2)
is the intrinsic impedance of each medium, where j is the
imaginary unit, ωis the angular frequency and µis the
magnetic permeability.
We modeled the head as a four slab (skin, fat, bone, brain)
flat phantom with adult human electromagnetic parameters.
If we disregard multiple reflections, which can be a good
approximation since the interfaces are irregular and may
scatter the incident wave, the resultant transmission coeffi-
cient for the multilayer phantom can be approximated by
the product of the transmission coefficients in each interface.
The magnitude of the resultant electric field transmission
coefficient air-brain |τ|is 0.1989. In order to model a child
we adjusted the adult electromagnetic parameters with the
same proportional increase observed for pigs [26]. The total
transmission coefficient magnitude |τ|for this 4-slab child
model is 0.2114, an increase of 6.3% compared with the adult
4-slab model. Since the SAR is proportional to the square
value of the electric field intensity |E|, this increase in |E|
leads to a 13% higher brain SAR in the young, merely due to
the dielectric constant variations associated with age.
It can be more appropriate to model the child as
a 3-slab flat phantom, with no subcutaneous fat. Then the total
transmission coefficient magnitude |τ|is 0.2345, an increase
of 18% in τ, which translates into an increase of 39% in the
brain SAR due to the dielectric constant variations and the
absence of a significant subcutaneous fat layer. This is shown
in Table 3.
TABLE 3. Transmission coefficient in adult and children flat phantom
models.
The higher dielectric constants of the young skull (and fat)
better match the skin and brain impedances, resulting in a
deeper field penetration and higher SAR in the young brain.
The absorption in the outer tissues depend also on their
thickness. The young skull can be very thin (e.g. 3 mm thick,
depending upon the age and the skull region considered)
and the subcutaneous fat can be absent. In the adult, the
average skull is around 7 mm and can easily reach 9 mm
thick [27], [29]–[31]. The attenuation coefficient αfor the
bones is 3.04 Np/m (nepers per meter) for the adult param-
eters and the resultant attenuation for a 9 mm slab is 2.7%,
while for a 3 mm slab it is 0.9 %.
α=2πfv
u
u
tµε
2s1+σ
2πfε2
−1.(3)
Using the fitted parameters, the attenuation coefficient of
the young bones increases to 3.98 Np/m and the resultant
attenuation over 3 mm of bone is 1.2%. The adult bone
thickness causes a higher attenuation, with consequently
a 3% higher brain SAR in the young. Moreover, the attenua-
tion of RF radiation by a 1 cm subcutaneous fat layer results
in a 3% lower brain SAR.
A thinner skull and a probable absence of subcutaneous
fat results in a deeper field penetration and higher SAR in
the young brain. In the plane wave or 4-slabs flat phantom
model, the variation of the dielectric parameters can result in
a 50% higher psSAR in the young brain.
We also simulated in SEMCAD-X the 3 slabs flat phantom,
and the results are shown in Table 4. The simulated frequency
was 900 MHz using a half wavelength dipole antenna with
250 mW input power, 6 mm away. The flat phantom’s mesh
was approximately 200 ×200 ×100 voxels.
Significantly greater psSARs are calculated when using
child parameters for the whole head (105% and 135% greater)
and for the brain (50% and 60% greater) psSAR.
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C. E. Fernández-Rodríguez et al.: Dosimetric Simulations of Brain Absorption of Mobile Phone Radiation
TABLE 4. psSAR (W/kg) in the head and brain of the flat phantoms.
FIGURE 2. SAR (50 dB modeled over a full color scale) for the two 3 slab
flat phantoms: with 9 mm skull (left) and 3 mm skull (right).
The SAR in the two models is shown in Figure 2.
In the two models, the SAR behaves similarly with the dis-
tance from the skin surface – i.e. similar values are observed
at a given distance from the antenna in both models. Impacts
may be very different; 1 cm depth is in the skull of the adult,
but in the brain of the child.
B. SAR IN THE HEAD AND BRAI N OF REALISTIC MODELS
Despite the relevance of simpler models to analyze the
interaction between the electromagnetic field and biologi-
cal tissues, this does not preclude the use of more accu-
rate models. SAR simulations at 900 MHz were performed
using SEMCAD-X (FDTD) [10] and realistic models from
MRI (e.g. Virtual Family [11]). A cell phone model in
the touch position with a planar inverted F-type microstrip
antenna (PIFA) with 250 mW delivered power, in the ear
position (top, center) was used. A mesh of approximately
280 ×220 ×150 voxels was used for each head model.
To account for gender dimorphism and population differ-
ences four European females were modelled (girls aged 5, 8
and 11 y and a young woman). Current recommendations
consider 10 g and 1 g averaging masses [22]–[24]. We also
conducted simulations for an averaging volume containing
100 mg of tissue. In brain tissues, this would contain hundreds
of thousands of neurons, since neurons have an average mass
of approximately 10−6g. Figure 3 shows the psSAR values
for different averaging volumes in the head (excluding the
pinna, as recommended in the IEEE 1528 practice [21]).
For the entire head, including the skull, psSAR is
higher for the IEEE SAM, which was claimed to be
‘‘conservative’’ [21]. Across the 4 mathematical models the
psSAR values for 5 years old Roberta are lower than for other
models, for all averaging masses, while there is no clear trend
for the 8 years and older models.
FIGURE 3. psSAR (W/kg) in the head (excluding the pinna) of four Virtual
Family girl and woman models and in the IEEE 1528 SAM, for averaging
masses of 0.1 g to 10 g.
Figure 4 summarizes the psSAR in brain tissues for the
three girls and a woman.
FIGURE 4. psSAR (W/kg) in the brains of four Virtual Family girls and
a woman models.
FIGURE 5. psSAR (W/kg) in the brains of one PAEHT boy model,
two Virtual Family boys and a Virtual Family man models.
The psSAR estimated for the 5 year old female brain is
approximately twice that estimated for older individuals.
Other models were also simulated. Figure 5 shows the
psSAR in the brain for three boys and a man.
The psSAR decreases to less than half that in the 3 years
old boy across models up to 34 years.
III. DISCUSSION AND CONCLUSIONS
There are important differences in modeled absorption of
mobile phone radiation by the brain of children versus adults.
2428 VOLUME 3, 2015
C. E. Fernández-Rodríguez et al.: Dosimetric Simulations of Brain Absorption of Mobile Phone Radiation
A young child has a smaller skull, with dielectric parameters
approximating those of soft tissue, resulting in higher psSAR
values (e.g. over double) in young children’s brains compared
with adults’. In addition, the young brain is not fully myeli-
nated, and has a different tissue architecture, which could
increase the health risks.
It is misleading to assume that compliance with the
recommended standard exposure limits [22]–[24] guarantees
the absence of health effects or risks, or even that the health
hazards and risks are equivalent for children and adults.
Children are developing, and have a higher rate of
metabolism, an immature immune system and different tissue
characteristics, that render them more vulnerable.
The brain tissues in the young absorb higher doses than
the adults’, as shown in Figures 4 and 5, and as previously
reported [4]–[7], [11]–[18]. This is due in part to morphologic
differences such as different skull thicknesses, and also to
the differences in the dielectric characteristics of the younger
head tissues, such as the permittivity εand the equivalent
conductivity σ.
Whereas the real skull is not homogeneous, several avail-
able head models consider the skull as a uniform structure
(some consider also the bone marrow). In the future, more
accurate models of the skull (mainly for the young) would
be helpful for SAR assessments. A precise description of the
region close to the cell phone, including the pterion, the stylo-
mastoid foramen and the antero lateral fontanel, the cortical
layers (tables of the skull), the diploe cancellous tissue and
bone marrow, as well as the cartilaginous or ossified joints
and fibrous sutures (such as the sphenosquamosal suture)
may result in significant differences in SAR calculated in the
brain.
When SAR is averaged over larger volumes or masses
the psSAR falls off, approximately halving with every
ten-fold increase in averaging mass for head
models (Figure 4). Rather than moving to larger averaging
volumes to determine compliance, it would be more realistic
and informative to examine exposure in smaller volumes or
masses (e.g. 100 mg or 10 mg), and in specific tissues.
More generally, the diversity and modes of use of wireless
communications devices are escalating rapidly, and young
children may be exposed to associated radiation in many
ways, from playing with and chewing on parents’ phones and
devices marketed for the very young, to use of devices in a
wide variety of positions. A range of models permits calcula-
tion of radiation absorption from communications devices, as
well as from close proximity to other devices such as climbing
upon anti-theft detectors at store entrances, etc.
Research is increasingly demonstrating biological effects
and harms with ubiquitous exposures to RF radia-
tion, highlighting the need to ensure that exposures
of the young and unborn are As Low As Reasonably
Achievable (ALARA) [32].
IV. CONFLICT OF INTEREST STATMENT
The authors declare that there are no conflicts of interest.
ACKNOWLEDGMENTS
The authors thank Margaret E. Sears for assistance with
the preparation of the manuscript, Lloyd Morgan and
Robert D. Morris for constructive comments on this paper.
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CLAUDIO ENRIQUE FERNÁNDEZ-RODRÍGUEZ
received the B.Sc. degree in electrical engineering
from the State University of Campinas, Campinas,
Brazil, in 1996, and the M.Sc. degree in elec-
trical engineering from the Federal University of
Rio Grande do Sul, Porto Alegre, Brazil, in 2000.
He coordinates a UN Development Program for
the Strengthening of the Technological Education
in Brazil and in Uruguay through the creation of
binational schools and was the Founding Dean of
the Electrical Engineering School with the Federal Center of Technological
Education of Pelotas, Pelotas, Brazil. He served as the Director of Public
Outreach with the Federal Institute of Education, Science and Technology
of Rio Grande do Sul (IFRS), Canoas, Brazil, and as a Labor Union State
Secretary. He is currently an Associate Professor with IFRS. He has co-
authored over 50 technical publications and a book chapter and served as
a Reviewer of the Journal of Microwaves and Optoelectronics among other
international publications. His research interests include biological effects of
microwaves and RF, numerical methods in computational electromagnetism,
and engineering education.
ALVARO AUGUSTO ALMEIDA DE SALLES
was born in Bagé, Rio Grande do Sul, Brazil,
in 1946. He received the B.Sc. degree from the
Escola de Engenharia, Universidade Federal do
Rio Grande do Sul (UFRGS), Porto Alegre, Brazil,
in 1968, the M.Sc. degree from the Pontificia Uni-
versidade Católica do Rio de Janeiro (PUC/RJ),
Rio de Janeiro, in 1970, and the Ph.D. degree
from the University of London, London, in 1982,
all in electrical engineering. He was an Associate
Professor with PUC/RJ from 1970 to 1991. Since 1991, he has been a
Professor at UFRGS.
His main research interests are microwave semiconductor devices, opto-
electronic devices, mobile communications, antennas, and biological effects
of nonionizing radiation.
Dr. de Salles has authored over 80 papers in international conferences and
magazines.
DEVRA LEE DAVIS received the B.Sc., M.Sc.,
Ph.D., and M.P.H. degrees. She is the President
of Environmental Health Trust, a nonprofit trust
devoted to researching and controlling avoidable
environmental health threats. She has authored the
book entitled The Secret History of the War on
Cancer and other books, and is a fellow of the
American College of Epidemiology. She served as
the Founding Director of the Board on Environ-
mental Studies of the U.S. National Academy of
Sciences, and is internationally recognized for her work on environmental
health and disease prevention. She received bipartisan Senate confirmation
as a Presidential Appointee. She was the Founding Director of the world’s
first center for environmental oncology. She was the National Book Award
Finalist for When Smoke Ran Like Water in 2002. She lectures at universities
in the U.S. and Europe and was the winner of the Carnegie Science Medal
in 2010 and the Lifetime Achievement Award from Green America in 2012.
Her 2007 book entitled The Secret History of the War on Cancer, details the
ways that public relations strategies have undermined public health, and it
is being used at major schools of public health, including Harvard, Emory,
and Tulane University. She is a Visiting Professor at the Hebrew University
Hadassah Medical Center & OndokuzMayis University Medical School. Her
most recent book is Disconnect.
2430 VOLUME 3, 2015
