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    Wiart Wiart Presentation Transcript

    • Numerical Dosimetry dedicated to Children RF ExposureJ. Wiart Whist lab.Orange Labshttp://whist.institut-telecom.fr/ NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • Summary  Context  Child exposure to mobile phone  Child exposure to plane wave(s)  Fetus exposure  Stochastic dosimetryNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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.NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • Numerical dosimetry is today able to handle complex configurations  Twenty years ago : simplistic models have to be used  Today: realistic models can be usedNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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. recherche & développementNIRCH Ljubjana 18 20 May 2011
    • 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 foradult valid for children? recherche & développement
    • 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%NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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 aMobile 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 NIRCH Ljubjana 18 20 May 2011 recherche & développement thickness
    • Head vs age (1) SHAPE CHANGES WITH AGE MORPHING TECHNIQUES HELPS Non Uniform transformation But have some limitation… 4 y.o 12 y.o AdultNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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 neededNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • International effort to develop realistic 3D numerical models Adult female body models Adult male body modelsChild body models Child head modelsNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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 MonopolNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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 2010NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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. 2010NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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 stationNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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 ageNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • Influence of morphology on WBSARNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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 NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • WBSAR for plane wave exposure at the reference levels Whole body SAR vs Incident fieldReference levels were established Adultswith simple model to guaranty thatbasic restriction will never been exceed.Several studies using morphedmodels report that exposed to the same childrenincident field strength children can havehigher exposureRecent study using MRI based childmodels has shown that exposed toreference level the ICNIRP basicrestrictions on the WBSAR areexceeded for small children bymaximum 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 2010NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • International effort to develop deformation toolsPhantoms based on MRI images do not represent human is day to day activitiesLarge effort have been done to develop deformation tools able to create realistic postureNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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)NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • Fetus exposureNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • Fœtus modelsFew simplistic models were developed forIRThese models have limitations for RF andnear field studiesImproved 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 2005Cech 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) NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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 09NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • Deformation tools dedicated to fetus exposure analysisNIRCH Ljubjana 18 20 May 2011 recherche & développement
    • Fetus exposureInfluence of the incident angleFetus 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 NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • 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= SARΩi FDTD X(Ωi) Y    k  k (X) kSAR over 1g in brain SAR over 10g Distribution of the maximum location NIRCH Ljubjana 18 20 May 2011 recherche & développement
    • As conclusionDans la confusion trouver la simplicitéDe la discorde faire jaillir lharmonieAu milieu de la difficulté se trouve lopportunité Albert Einstein, Trois règles de travail recherche & développement