1. Numerical Dosimetry dedicated to
Children RF Exposure
J. Wiart
Whist lab.
Orange Labs
http://whist.institut-telecom.fr/
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2. Summary
 Context
 Child exposure to mobile phone
 Child exposure to plane wave(s)
 Fetus exposure
 Stochastic dosimetry
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3. unprecedented increase in the use by
children of wireless communication systems
 The last decade has seen
an unprecedented
increase in the use by
children of wireless
communication systems.
This strong growth has
highlighted the need to
assess the exposure of
children induced by these
radio-frequency (RF)
wireless systems.
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4. Numerical dosimetry is today
able to handle complex configurations
 Twenty years ago : simplistic models have to be used
 Today: realistic models can be used
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5. Exposure depends on morphology
 The exposure induced by a system
emitting EMF depends on many
parameters such as frequency,
location and type of the sources but
also on dielectric properties of
biological tissues, morphology and T. Wu et al Phys. Med. Biol. (2011)
posture of the person exposed.
 Exposed to the same incident field
strength smallest person seems to be
higher exposed
 The child exposure analysis is an
important question since the power
absorbed depends on parameters (e.g. E. Conil et al 2008 Phys. Med. Biol. (2008)
morphology, usage) that are age
dependent.
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6. Child exposure.
 What is the child exposure and in
particular the head and organ still in
development?
Are ICNIRP Limit valid for Children?
Are methods and phantoms developed for
adult valid for children?
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7. SAR and Children: a long story..
- From 1992 to 2005 more than 10 studies have been done but often with adult
head down sized.
- The model of head, the phone model, the position of the handset relative to the
head are sensitive parameters
- A children head is not a small adult head and the homogeneous down scaling
induces anatomical errors.
80%
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8. Correct Anatomical model is fundamental
to assess child exposure to mobile phone:
 Since children MRI are difficult to obtain. Homogeneous
down scaling of adult model has been the first approach. But
a child is not a small adult. Proportion changes with age. 80%
Homogeneous down scaling induces anatomical errors.
 Erroneous SAR results have been obtained with this uniform
down scaling approach.
 Non uniform downscaling (morphing) has been developed
 Useful for global analysis but to be used carefully : from 5 to 20 the
brain volume increase of about 10% but skull thickness is increase of
more than 70% while from 3 to 20 the skin thickness is increase of 60%
Study of Specific Absorption Rate (SAR) Induced in the Two Child Head Models and Adult Heads Using a
Mobile Phones Abdelhamid Hadjem, David Lautru, Christian Dale, Man Faï Wong, Victor Fouad Hanna,
Joe Wiart IEEE Trans. MTT ; Vol.°53 ; N° 1 ; janvier 2005 ; pp. 4-11.
Modeling of RF exposure in children J. Wiart, A. Hadjem, N. Gadi, I Bloch, M F Wong,, A Pradier,
D Lautru; V.F Hanna and C. Dale. Bioelectromagnetics Vol 26 Issue S7 pp 45-50 2005 Brain vol vs
Skull
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9. Head vs age (1)
SHAPE CHANGES WITH AGE
MORPHING TECHNIQUES HELPS
Non Uniform transformation
But have some limitation… 4 y.o 12 y.o Adult
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10. Head vs age (2)
Organs have specific growth Skull thickness vs age Brain weight vs age
2,5
Skin Thickness vs age
2
1,5
1
0,5
0
2 - 3 y.o 11- 13 y.o Adult
MRI Based Models are needed
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11. International effort to develop
realistic 3D numerical models
Adult female body models Adult male body models
Child body models
Child head models
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12. Child brain exposure to mobile phone
 Based on realistic head models,
comparison between adult and
child head models exposure have
been conducted
 Over10g no difference has been
observed
Wiart et .al 2008 Children 5-8
2,00 chidren 8-15
 Locally the exposure can differ 1,75
1,50
Adult
SAR (w/kg)
1,25
(eg brain peripheral tissues)
1,00
0,75
0,50
0,25
 Wiart et al 2008 0,00
2400 2100 1800 900 2400 2100 1800 900 2400 2100 1800 900
MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz
 Christ et al PMB 2010 DMP CMP GMP
Dipole Patch Monopol
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13. Influence of new usages
 Compared to exposure
induced by a phone close
to the ear
• @ 10 cm in front of the
head the exposure is
below 10%
• @ 40 cm the exposure is
close to 1%
• A Hadjem IEEE EMC 2010
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14. Influence of EM dielectric
properties.
 Dielectric properties evolve with age
Gabriel Bioelectromagnetism 2005
 Improvement of dielectric properties variation with age
A Peyman et al Phy. Med. biol. 2010
 The impact of variation of dielectric data on dosimetry is not simple
Hurt et al 2000, Mason et al 2000, Gajšek et al 2001
 Dependences of dielectric tissue properties do not lead to
systematic changes of the SAR. The exposure of the bone marrow
of children can exceed that of adults due to the strong decrease in
electric conductivity of this tissue with age.
A Peyman et al pmb 2010
Christ et al Phy. Med. biol. 2010
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15. Brain exposure to far field. Comparison
with exposure induced by mobile
1 v/m
At 0.1 v/ few 10s of gsm == 1 month of base station
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16. Children exposure to mobile phone.
 Current compliance tests are conservative.
 The exposure of tissues or regions having similar distance to the phone
for adults and children have comparable exposure
 Brain peripheral tissues close to the surface can have higher exposure in
child than in adult, these possible differences depend also on the current
distribution of the phone
 Usage should have a large influence on the exposure
 Exposure from access point is weak compare to exposure from mobile
 The exposure of the bone marrow of children can exceed that of adults
due to the strong decrease in electric conductivity of this tissue with age
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17. Influence of morphology on WBSAR
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18. Exposure to plane vs BSA and BMI
Morphing based
 Several studies have shown that @ 2.1 GHz
EM absorption in the resonance
-3
x 10
14
VH Familiy
frequency region greatly depends
JM Family
12
JF Family
Norman Family
10 Korean Family
on the electric properties of tissue,
WBSAR (W/Kg)
Zubal Family
8
WBSAR vs 1/BMI
while in the GHz region it is 6
affected mainly by the surface 4
area of the model or the body
2
0.03 0.04 0.05 0.06 0.07 0.08
(-1)
BMI
mass index.
-3
x 10
14
Norm an fam ily
Korean fam ily
• Hirata et al Bioelectromagnetics, 2007
12 Zubal fam ily
VH fam ily
WBSAR vs BSA
Japanese m ale fam ily
Japanese fem ale fam ily
10
• El habachi et al pmb 2010
WBSAR
8
• Hirata et al ieee emc 2010
6
• Conil et al CRAS 2010
4
2
0.02 0.025 0.03 0.035 0.04 0.045 0.05
Pi*BSA/weight
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19. WBSAR for plane wave exposure at
the reference levels Whole body SAR vs Incident field
Reference levels were established Adults
with simple model to guaranty that
basic restriction will never been exceed.
Several studies using morphed
models report that exposed to the same children
incident field strength children can have
higher exposure
Recent study using MRI based child
models has shown that exposed to
reference level the ICNIRP basic
restrictions on the WBSAR are
exceeded for small children by
maximum 45%
• Wang et al 2006, Conil et al 2008,Hirata et
al 2007, 2009, Nagaoka et al 2008,Findlay et
al 2005,Dimbylow 2002, 2005, Sandrini et al
2004. Kuln et al 2009 Bakker et al 2010
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20. International effort to develop
deformation tools
Phantoms based on MRI images do not represent
human is day to day activities
Large effort have been done to develop
deformation tools able to create realistic posture
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21. Exposure to multiple random plane
wave.
• WBSAR in a complex environment complies with the
ICNIRP basic restriction when the averaged field over the
human body is equal to the ICNIRP reference level
• G Vermeeren heath phy 2008
• In case of multiple coherent signals ( ie multiple coherent
plane waves) 95% of the exposure are below the plane
exposure
• Th Kientega Annals of telecom 2011 (tbp)
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22. Fetus exposure
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23. Fœtus models
Few simplistic models were developed for
IR
These models have limitations for RF and
near field studies
Improved models have been developed.
Dimbylow . Phy in Medicine and Biology, 2006.
Shi Medical Physics, 2004.
T. Nagaoka, et al . Phy in Medicine and Biology,, 2007.
Kainz et al , BEMS and EBEA 2005
Cech et al. Physics in Medicine and Biology, 2007.
 Improvement of the fetus dielectric
properties
 Dielectric properties of human placenta, umbilical cord
and amniotic fluid A Peyman et al Phys. Med. Biol. 56
(2011)
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24. International effort to develop realistic
3D Fetus numerical models
Dimbylow . Phy in Medicine and Biology, 2006.
Shi Medical Physics, 2004.
T. Nagaoka, et al . Phy in Medicine and Biology,, 2007.
Kainz et al , BEMS and EBEA 2005
Cech et al. Physics in Medicine and Biology, 2007.
Anquez et al ESPR 2008.
Anquez et al IEEE Int’l Symp on Biomedical Imaging 2008.
Bibin et al WC 09
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25. Deformation tools dedicated to
fetus exposure analysis
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26. Fetus exposure
Influence of the incident angle
Fetus exposure to mobile phone
In this case SAR over 10g in Fetus exposure is less than 10% of the SAR over 10g in Mother
In both case it is important to have deformable models
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27. Stochastic Dosimetry to manage
variable configuration
 Influence of the position of the phone using
chaos polynomial.
• J. Silly-Carette et al IEEE MWCL 2009
• Ghamni et al BEMS 2011
SAR statistical distribution ?
Input Y= SAR
Ωi FDTD
X(Ωi)
Y    k  k (X)
k
SAR over 1g in brain SAR over 10g
Distribution of the maximum location
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28. As conclusion
Dans la confusion trouver la simplicité
De la discorde faire jaillir l'harmonie
Au milieu de la difficulté se trouve l'opportunité
Albert Einstein,
Trois règles de travail
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