Bio Effects of Mobile Phones

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    Introduction on MobilePhone SimulationsBiological Models

    SAR SimulationsHearing Aid Compatibility

    www.cst.com

    Tilmann Wittig

    Bio-Effects of Mobile PhonesUGM 2009 Darmstadt

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    Simulation at various levels ofcomplexity

    SonyEricsson M600

    Antenna level Phone level Body effects, head (SAM) and hand

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    Antenna level simulationReturn loss (S11)

    (farfield pattern)Radiation efficiency

    accurate modelling of losses important

    Simulation accuracy -40dB (careful with AR-filter)

    Simulation time: 11 Minutes

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    Antenna level simulation

    900 MHz 1800 MHz

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    Full phone level simulation

    STEP Import of complete phone

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    Full phone level simulation

    Simulation time: 19 Minutes

    As well: Return loss (S11) and radiation efficiencyHearing Aid Compatibility (HAC)Total Radiated Power (TRP)Total Isotropic Sensitivity (TIS)

    Agreement still good, but some uncertainties for materials, simplifications, …

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    Full phone level simulation, HACHAC: nearfield interacting with other devices,

    such as hearing aids

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    Full phone level sim., Matching

    Phone + PCB + antenna matching network simulated in CST DESIGN

    STUDIO to calculate total radiated power (TRP)

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    Phone + human simulation

    900 MHz 1800 MHz

    erad phone Phone head Phone headhand

    897,4 MHz 100 % 23 % (-6,3 dB) 6 % (-12.2 dB)

    1747,6 MHz 100 % 48 % (-3.2 dB) 7 % (-11.5 dB)

    Radiation efficiency

    SAR

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    Phone + human simulation

    Farfield for antena in thepresence of human model

    900 MHz 1800 MHz

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    Specific Absorbtion Rate (SAR)

    900 MHz 1800 MHz

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    Biological ModelsThe right choice of the biological model is essential for the reliabilityof a SAR or EMI simulation.

    Visible Humanvoxel data

    SAM Phantom

    other voxel data

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    SAM - Standard Anthropomorphic Model

    www.sam-phantom.com

    Frequency dependent materialproperties (according to

    standard) can be modelled bydispersive materials via

    tabulated input.

    Only one simulation run forbroadband results!!

    tissuesimulant

    liquid(TSL)

    plastic shellOriginally created for measurementsShape specified in IEEE/CENELEC/IEC standardsFilled with homogeneous glycol-containing tissue-simulant liquid, only two materials for simulation

    Virtual prototyping through simulation

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    Homogeneous Hand/Body Models

    Posable homogeneous hand/body models are available for CSTFor most high frequency applications fully sufficientSimulate much faster then voxel models

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    Homogeneous Full Body Models

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    Visible Human (HUGO)

    Available indifferent

    resolutions

    Materials ofinterest can be

    chosen

    Much more accurate and detailled modelling of the biological tissue

    Visible Human Projectproduced by the National Library ofMedicine (NLM), Marylandhttp://www.vr-laboratory.com/

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    General Voxel ModelsAny voxel model can be imported in CST MICROWAVE STUDIO®

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    Dispersive Broadband Simulation

    Re( r) Im( r)

    0.9 GHz 41.5 17.98 (= 0.9 S/m)

    1.8 GHz 40.0 13.98 (= 1.4 S/m)

    Typical requirement for dual band phones:

    Frequency dependentmaterial definition:

    Second order dispersivefit for tabulated values,only one simulation run

    required

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    Dispersive Broadband SimulationCompared material settings:

    Constant settings for 0.9 GHzsim. time 45 min.

    Constant settings for 1.8 GHzsim. time 45 min.

    Dispersive broadband fittotal sim. time: 57 min.

    Dispersive fit agrees very well for S-Parameter and SARvalues in both bands for only 25% extra simulation time

    0.9 GHz, 1g 1.35 1.31 1.74

    0.9 GHz, 10g 0.96 0.93 1.13

    1.8 GHz, 1g 0.69 1.32 1.32

    1.8 GHz, 10g 0.99 0.83 0.83

    S-Parameter comparison:

    SAR value comparison:

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    Cole-Cole-Materials

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    SAR

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    Overview and Background

    SAR – Specific Absorbtion Rate

    Unit of SAR: W/kg

    P : Power loss densityE : Electric field strength

    J : Current densitys: Conductivityr : DensityTypically averaged over pre-defined mass

    A measure for electromagnetic energy absorbed by biologicaltissue mass when exposed to radiating device (e.g. mobile phone)

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    22 J E P SAR

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    Definitions

    Point SAR : Local SAR without mass or volume averagingTotal SAR : Total power loss in the whole lossy structure divided byits total mass

    Mass Averaged SAR (typically 1g or 10g):

    For each point a cube with a defined mass is foundThe power loss density is integrated over this cubeThe integral power loss is divided by the cube‘s mass

    Volume Averaged SAR: Procedure as above, but on fixed volume.

    Typical Standards, maximum of mass averaged SAR:US and Canada: 1.6 W/kg averaged over 10g of tissueEU, Japan, Brazil: 2.0 W/kg averaged over 1g of tissue

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    Averaging Procedure

    1. Point of avg. SAR calculation2. Search for 10 g cube (iteratively)3. Integrate losses in cube

    At boundary treatment dependson chosen averaging standard:IEEE C95.3 / CST C95.3CST legacy

    The „constant volume“ assumption uses an averaged cube size:- Faster (no iterative search for cube with correct mass)

    - Only approximative (not according to official SAR standard)

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    SAR Standards under Development

    Several guidelines and standards specify SAR safety limits (i.e. ICNIRP).

    Standards like IEEE 1528 regulate measurement methods for practicalassessment of compliance.

    A simulation standard IEEE 1528.X is in development1528.1 requirements for hexahedral time domain codes (end of 2008)1528.2 application to cars with passenger/bystander (~2009)1528.3 application to mobile phones near head (~2009)1528.4 requirements for tetrahedral frequency domain codesCST participates in standards committee .

    IEEE C95.3 Annex E specifies SAR averaging scheme for simulation.CST MICROWAVE STUDIO® has already been approved by the FCC (USA)to comply with hex td standard drafts.

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    SAR Handling inCST MICROWAVE STUDIO®

    Pre-conditions before start of simulation:A power-loss monitor needs to be defined at frequencies of interest .All materials used for mass averaging need to have mass density ρ .

    Choose the Powerloss monitor

    Definition of averaging massor Point SAR

    Define labeling

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    SAR Special Settings

    Define reference power,Port input or accepted power

    Restrict volume for:- maximum search and statistics

    - reduced computational effort

    Choose averaging method

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    Template Based Postprocessing

    Alternatively: Postprocessing Templates can be defined

    Available as 1D and 0Dresult template

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    SAR Results

    Generalinformation

    Statistics fortotal volume(e.g.head + hand)

    Statistics forSubvolume(e.g. just head)

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    Visualization of SAR 2D or 3D plot including information about position of the maximum

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    Visualization of Max. SAR Cube

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    PBA®, TST™ and Subgridding

    1mm voxel

    resolutionnear ear

    0.3mm gridat helix

    with PBA®

    30mm grid

    at openboundary

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    Visible Human SAR

    SAR 10g [W/kg]SAR 1g [W/kg]

    Subgridding allows high resolution SARevaluation in critical regions

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    Performance Summary

    SAMNo Subgrid

    SAMSubgrid

    VoxelNo Subgrid

    VoxelSubgrid

    Mesh cells 2.1 M 163k 2.9 M 288k

    Solver time 5,486 s 568 s 7,281 s 1,867 sSAR time 1g 209 s 39 s 781 s 140 s

    SAR time 10g 1,080 s 51 s 4,292 s 185 s

    Acceleration Factor 10 Factor 5.6

    Software performance on Intel Xeon 3 GHz, 2 GB RAM(Hardware acceleration will increase performance by additional factor)

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    Bioheat Simulation

    See last presentation in this session

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    Hearing Aid Compatibility (HAC)Requirements for HAC evaluation:

    Define E- AND H-fieldmonitors for all frequenciesof interest

    Define and store a WorkingCoordinate System (WCS) at thespeaker point, aligned with thephone

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    Hearing Aid Compatibility (HAC)Pick HAC as 0D result template:

    Specify speaker point WCS

    Choose ArticulationWeighting Factor(AWF) according totransmission protocol

    Choose evaluation resolution

    Choose frequency and port

    Specify accepted orStimulated power

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    Hearing Aid Compatibility (HAC)After Evaluation check log-file:

    Logfile contains initial field values,scaled field values, field exclusionscheme and final HAC categoryaccording ANSI C63.19

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    Hearing Aid Compatibility (HAC)Field plots andHAC segments:

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    Summary

    All advantages of CST MWS (PBA®, TST™, MSS™, ...)apply to SAR simulations

    Frequency dependent materials: Broadband SAR in onesimulation run

    One tool for both antenna design and SAR verification

    Support of various standards, participation in IEEEstandard committees

    Simplified and more flexible handling of voxel models

    SAR simulations with CST MICROWAVE STUDIO®