LowElectromagneticFieldExposure
WirelessDevices
FundamentalsandRecentAdvances
Editedby
MasoodUrRehman
UniversityofGlasgow,Glasgow,UK
MuhammadAliJamshed
UniversityofGlasgow,Glasgow,UK
Copyright©2023byTheInstituteofElectricalandElectronicsEngineers,Inc.Allrights reserved.
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Idedicatethisefforttomyparents,KhalilUrRehmanandIlfazBegum; mysiblings,Habib,Waheed,Tahera; mywife,Faiza; andmyson,Musaab.
MasoodUrRehman
Idedicatethisefforttomyparents,JamshedIqbalandNuzhutJamshed; mysiblings,Laiba,Maliha,Mariam; andmywife,AqsaTariq.
MuhammadAliJamshed
Contents
EditorBiography xii
ListofContributors xiii
Preface xv
1ElectromagneticFieldExposure:FundamentalsandKey Practices 1 MuhammadAliJamshed,FabienHéliot,TimW.C.Brown,and MasoodUrRehman
1.1Introduction 1
1.2EMFMetricandEvaluationFramework 3
1.2.1EMFExposureFactors 4
1.2.1.1TransmitAntennaRegions 4
1.2.1.2TransmitAntennaCharacteristics 5
1.2.1.3DurationofExposure 6
1.2.1.4ElectricalPropertiesofBiologicalTissues 6
1.2.2EMFExposureMetrics 6
1.2.2.1SpecificAbsorptionRate 7
1.2.2.2PowerDensity 8
1.2.2.3Exposure-Ratio 9
1.2.2.4Dose 10
1.2.2.5Composite/GenericMetricofEMFExposure 10
1.3ApplicationofMetricforSettingGuidelines/LimitsandReducing Exposure 10
1.3.1SARReduction 11
1.3.2PDReduction 12
1.3.3Exposure-RatioReduction 12
1.3.4DoseReduction 12
1.3.5CompositeEMFExposureReduction 13
1.4Conclusion 13 References 13
2ExposuretoElectromagneticFieldsEmittedfromWireless Devices:MechanismsandAssessmentMethods 19 YasirAlfadhl
2.1FundamentalsofEMFInteractionswiththeHumanBody 19
2.1.1ThermalEffect 21
2.1.2Non-thermalEffects 22
2.2PhysicalModelstoRepresenttheInteractionofEMFswithBiological Tissue 24
2.2.1InteractionMechanisms 24
2.2.1.1EffectsofBoundCharges 25
2.2.1.2EffectsofDipoleOrientations 25
2.2.1.3DriftofConductionCharges 25
2.2.2DielectricPropertiesofBiologicalMaterials 26
2.2.2.1RelaxationTheory 26
2.2.2.2Age-DependentDielectricProperties 28
2.2.3TheInteractionofEMFieldswithBiologicalMaterials 28
2.2.3.1InteractionsontheBodyScale 29
2.2.3.2InteractionsontheTissueScale 30
2.2.3.3InteractionontheCellularandSub-cellularScales 30
2.3DosimetryConcepts 30
2.3.1TheSpecificAbsorptionRate(SAR) 31
2.3.1.1SARMeasurementTechniquesovertheFrequencySpectrum 31
2.3.1.2SARSpatialAveraging 32
2.3.1.3TissueMassAveragingProcedures 32
2.3.1.4LocalizedandWhole-BodyAveragedSAR 34
2.3.2TheSpecificAbsorption(SA) 34
2.4DosimetryMethodology 35
2.4.1ExperimentalDosimetry 35
2.4.2NumericalDosimetry 36
2.4.2.1TheoreticalAnalysis 36
2.4.2.2NumericalModelling 37
2.5NumericalDosimetryattheRadiofrequencyandMicrowave Regions 38
2.5.1FormulationoftheScattered-FieldFDTDAlgorithm 39
2.5.2DiscretizationofAnatomicalModelsinFDTD 40
2.5.3ComparisonsofNumericalResultswithAnalyticalBenchmarks 42 References 46
3NumericalExposureAssessmentsofCommunication SystemsatHigherFrequencies 49
MuhammadRafaqatAliQureshi,YasirAlfadhl,andXiaodongChen
3.1Introduction 49
3.2ExposureConfiguration 50
3.3PlaneWaveExposureAssessmentofE-fieldAbsorptionWithinthe SkinUsingSARasaFunctionofFrequency 51
3.3.1ComparisonsofSARLevelsonDry-SkinandWet-Skin 52
3.4PlaneWaveExposureAssessmentofE-fieldAbsorptionWithin Multi-layerModelUsingSARasaFunctionofFrequency 58
3.4.1ComparisonsofSARLevelsonDry-SkinandMulti-layerModel 59
3.5PlaneWaveExposureAssessmentofE-fieldAbsorptionWithinthe EyeUsingSARasaFunctionofFrequency 63
3.5.1ComparisonsofSARLevelsonHEECMandMulti-layerModel 64
3.6ChapterSummary 68
Appendix3.A 69 References 74
4AgeDependentExposureEstimationUsingNumerical Methods 77
MuhammadRafaqatAliQureshi,YasirAlfadhl,XiaodongChen,and MasoodUrRehman
4.1Introduction 77
4.2NumericalHumanModels 78
4.2.1AdultVoxelModels 78
4.2.2ChildVoxelModel 79
4.3Age-DependentTissueProperties 81
4.3.1MeasuredTissueProperties 82
4.3.2Age-dependentHumanDielectricPropertiesExtractionfrom MeasuredData 83
4.3.3NovelCalculationMethodsofAge-dependentDielectric Properties 83
4.3.3.1SingleFrequencyAge-DependentMethod 84
4.3.3.2DispersiveAge-DependentMethod 86
4.3.3.3ImplementationoftheCole–ColeModelonAge-Dependent Properties 90
4.3.3.4AccuracyAmongtheAge-dependentMethods 91
4.4NumericalValidation 95
4.4.1ComparisonwithanAnalyticalBenchmark 95
4.5ChapterSummary 97
Appendix4.A 97 References 111
5AntennaDesignConsiderationsforLowSARMobile Terminals 115
MuhammadAliJamshed,TimW.C.Brown,andFabienHéliot
5.1Introduction 115
5.2SARReductionandDualCouplingofAntenna 117
5.3CouplingManipulationSimulationCampaign 118
5.4SARAnalysisandSurfaceCurrent 123
5.5ResiliencetoDifferentHeadUseCases 127
5.6AnalysisofMIMOPerformanceinDataMode 130
5.7Conclusion 132 References 132
6MIMOAntennaswithCouplingManipulationforLowSAR Devices 135
MuhammadAliJamshed,TimW.C.Brown,andFabienHéliot
6.1Introduction 135
6.2WorkingPrincipleandAntennaGeometry 136
6.2.1AntennaDimensions 136
6.2.2SurfaceCurrentDistribution 138
6.2.3FrequencyRegionAnalysis 139
6.3AntennaMeasurements 141
6.3.1MIMOPerformance 141
6.4EfficiencyandSARAnalysis 143
6.5Conclusion 148 References 148
7ReinforcementLearningandDevice-to-Device CommunicationforLowEMFExposure 151 AliNauman,MuhammadAliJamshed,andSungWonKim
7.1Introduction 151
7.1.1ContributionofChapter 153
7.1.2ChapterOrganization 154
7.2Background 154
7.2.1NarrowbandInternetofThings(NB-IoT) 155
7.2.1.1FrameStructure 155
7.2.2Device-to-Device(D2D)Communication 157
7.2.3MachineLearning 160
7.2.3.1ReinforcementLearning 160
7.2.3.2Q-Learning 162
7.3RelatedWorks 163
7.4SystemModel,ProblemFormulation,andProposedRL-ID2D 164
x Contents
7.4.1NetworkModel 164
7.4.1.1ChannelModel 164
7.4.1.2MobilityModel 164
7.4.1.3Signal-to-Interference-Noise-Ratio(SINR) 166
7.4.2Definitions 166
7.4.2.1PacketDeliveryRatio 166
7.4.2.2PotentialRelaySet 167
7.4.2.3End-to-EndDeliveryRatio 167
7.4.3ProblemFormulation 167
7.4.4ReinforcementLearningEnabledRelaySelection 168
7.4.4.1Q-LearningFramework 168
7.4.5ProposedIntelligentD2DMechanism 171
7.5PerformanceEvaluation 174
7.5.1SimulationDeploymentScenarioandAnalysis 174
7.5.1.1AnalysisofQ-LearningBehaviorinNB-IoTUE 174
7.5.1.2AnalysisofEDRUnderVariousParameters 178
7.5.1.3AnalysisofE2EDelayUnderVariousParameters 179
7.5.1.4ComparativeAnalysisofRL-ID2DwithOpportunisticand DeterministicModel 180
7.6Conclusion 183 References 183
8UnsupervisedLearningBasedResourceAllocationforLow EMFNOMASystems 187 MuhammadAliJamshed,FabienHéliot,andTimW.C.Brown
8.1Introduction 187
8.1.1ExistingWork 188
8.1.2MotivationandContributions 189
8.1.3StructureoftheChapter 190
8.2EMF-AwarePD-NOMAFramework 192
8.2.1SystemModel 192
8.2.2ProblemFormulation 195
8.3MachineLearningBasedUserGrouping/SubcarrierAllocation 196
8.4PowerAssignment 198
8.5NumericalAnalysis 201
8.5.1SimulationResults 202
8.5.2SchemeValidityforRealApplications 206
8.6Conclusion 208 References 208
9Emission-AwareResourceOptimizationfor Backscatter-EnabledNOMANetworks 213 MuhammadAliJamshed,WaliUllahKhan,HarisPervaiz, MuhammadAliImran,andMasoodUrRehman
9.1Introduction 213
9.1.1MotivationandContributions 214
9.2SystemModel 215
9.2.1ProblemFormulation 217
9.3ProposedSolution 218
9.3.1Sub-carrierAllocation 218
9.3.2PowerAllocation 218
9.4PerformanceEvaluation 221
9.5Conclusion 223
References 223
10RoadAheadforLowEMFUserProximityDevices 225
MuhammadAliJamshed,FabienHéliot,TimW.C.Brown,and MasoodUrRehman
10.1Introduction 225
10.2PerceptionandPhysiologicalImpactofEMF 226
10.2.1Public’sPerceptionofExposureandRiskAssessment 226
10.2.2PhysiologicalImpact 227
10.2.2.1AgeRangeandExposure 227
10.2.2.2mmWaveandExposure 227
10.2.2.3BrainTumourandExposure 228
10.3EMFExposureEvaluationMetricandRegulations:AFuture Perspective 229
10.3.1ExpectedExposureContributionofFutureWirelessCommunication Technologies 229
10.3.1.1ExposureandmmWave 229
10.3.1.2ExposureandMassiveMIMO 229
10.3.1.3ExposureandDensification 230
10.3.2OpenIssuesandFutureResearchTracks 231
10.3.2.1NewEMFLimitsandGuidelines 231
10.3.2.2EMFMitigationTechniquesandNewMetrics 231
10.3.2.3OtherOpenIssues 232
10.4Conclusion 232 References 233
Index 237
EditorBiography
MasoodUrRehman receivedaB.Sc.degreeinelectronicsandtelecommunication engineeringfromtheUniversityofEngineeringandTechnology,Lahore,Pakistan, in2004andaM.Sc.andPh.D.degreesinelectronicengineeringfromQueenMary UniversityofLondon,London,UK,in2006and2010,respectively.Heworkedat QueenMaryUniversityofLondonasaPostdoctoralResearchAssistantuntil2012 beforejoiningtheCentreforWirelessResearchattheUniversityofBedfordshireas aLecturer.HeservedbrieflyattheUniversityofEssex,UKandthenmovedtothe JamesWattSchoolofEngineeringattheUniversityofGlasgow,UKinthecapacity ofanAssistantProfessor.Hisresearchinterestsincludecompactantennadesign, radiowavepropagationandchannelcharacterization,satellitenavigationsystem antennasinclutteredenvironment,electromagneticwaveinteractionwithhuman body,body-centricwirelessnetworksandsensors,remotehealthcaretechnology, mmWaveandnano-communicationsforbody-centricnetworks,andD2D/H2Hcommunications.Hehasworkedonanumberofprojectssupportedbyindustrialpartners andresearchcouncils.Hehascontributedtoapatentandauthored/co-authored 4books,7bookchapters,andmorethan120technicalarticlesinleadingjournals andpeerreviewedconferences.Dr.UrRehmanisafellowoftheHigherEducation Academy,UK,amemberoftheIETandpartofthetechnicalprogramcommitteesand organizingcommitteesofseveralinternationalconferences,workshops,andspecial sessions.HeisactingasanAssociateEditoroftheIEEEAccessandIETElectronics LettersandLeadGuestEditorofnumerousspecialissuesofrenownedjournals.He alsoservesasareviewerforbookpublishers,IEEEconferences,andleadingjournals.
MuhammadAliJamshed receivedaPh.D.degreefromtheUniversityofSurrey, Guildford,UK,in2021.HeisendorsedbyRoyalAcademyofEngineeringunder exceptionaltalentcategory.HewasnominatedforDepartmentalPrizeforExcellenceinResearchin2019attheUniversityofSurrey.HeservedbrieflyasWireless ResearchEngineeratBriteYellowLtd.,UK,andthenmovedtoJamesWattSchoolof Engineering,UniversityofGlasgow,asaPost-DoctoralResearchAssistant.Hehas authored/co-authored2bookchaptersandmorethan37technicalarticlesinleading journalsandpeerreviewedconferences.HismainresearchinterestsincludeEMF exposurereduction,lowSARantennasformobilehandsets,machinelearningfor wirelesscommunication,Backscattercommunication,andwirelesssensornetworks. HeservedasaReviewer,TPC,andtheSessionChair,atmanywell-knownconferences, i.e.ICC,WCNC,VTC,GlobeCometc.,andotherscientificworkshops.
ListofContributors
YasirAlfadhl
SchoolofElectronicEngineeringand ComputerScience
QueenMaryUniversityofLondon
London UK
TimW.C.Brown
InstituteofCommunicationSystems (ICS)
Homeof5Gand6GInnovation Centre,UniversityofSurrey
Guildford UK
XiaodongChen
SchoolofElectronicEngineeringand ComputerScience
QueenMaryUniversityofLondon
London UK
FabienHéliot
InstituteofCommunicationSystems (ICS)
Homeof5Gand6GInnovation Centre,UniversityofSurrey Guildford UK
MuhammadAliImran JamesWattSchoolofEngineering UniversityofGlasgow
Glasgow
UK
MuhammadAliJamshed JamesWattSchoolofEngineering UniversityofGlasgow
Glasgow
UK
WaliUllahKhan InterdisciplinaryCenterforSecurity ReliabilityandTrust(SnT) UniversityofLuxembourg LuxembourgCity Luxembourg
SungWonKim DepartmentofInformationand CommunicationEngineering
YeungnamUniversity
Gyeongsan-si
SouthKorea
xiv ListofContributors
AliNauman
DepartmentofInformationand CommunicationEngineering
YeungnamUniversity
Gyeongsan-si
SouthKorea
HarisPervaiz
SchoolofComputingand Communications
LancasterUniversity
Lancaster
UK
MuhammadRafaqatAliQureshi SchoolofElectronicEngineeringand ComputerScience QueenMaryUniversityofLondon
London UK
MasoodUrRehman JamesWattSchoolofEngineering UniversityofGlasgow
Glasgow UK
Preface
Thepastdecadehasseenahugeupsurgeinthedemandofwirelessdevicesthat areexpectedtocrossthe29.4billionmarkby2030.Thisincreaseisfueledbythe advancesinwearables,portables,flexibleelectronics,andotherwirelesstechnologiesfacilitatingcommunication,transportation,andnavigationneedsofbillions ofusersaroundtheworldinthewakeofInternetofThingsand5G/6G.These risingnumbers,alongwithever-growingdatarequirements,necessitateagrowth inthecapacityofwirelesscommunicationnetworksbyalmost1000times.Part ofthiscapacityenhancementwillbemadepossiblebyincreasingthenumberof accesspoints(APs).Thesedevelopmentsareultimatelyresultinginaddedelectromagneticfield(EMF)exposuresourcesintheenvironment.
EMFexposurehasbeendeemedpronetoinflictadversehealthandsafety effectsontheusers.TheWorldHealthOrganization(WHO)hasclassified theseEMFradiationsaspossiblycarcinogenictohumansandhasanongoing projecttoassesspotentialhealtheffectsofexposuretoEMFinthegeneraland workingpopulation.TheFederalCommunicationsCommission(FCC)andthe InternationalCommissiononNon-IonizingRadiationProtection(ICNIRP)have, therefore,imposedstrictsafetystandardsfordeviceoperation.Consequently, EMFexposurecharacterizationwarrantingstrictadherencetothesesafety regulationsisavitaldesignparameterforwirelessdevicestoensurethesafetyof theusers.
Thecurrentdevelopmentsandexpectedfuturegrowthofthewireless systemsarealsomountingconcernsregardingusers’safetyandpossible healthconsequencesofEMFexposuretomodernwirelesstechnologies, suchasmillimeter-wave(mmWave)communications,massivemultiple-input multiple-output(MIMO),andbeamforming.Itnecessitatesdeeperinvestigations onhealthriskassessmentsandrequiresacomprehensivereferencedealingwith thisfundamentalandparamountissuesuggestingsomenoveldirectionsfor updatingtheEMFexposureevaluationframework.
Adedicatedbooktacklingthisimportantissueisseldomavailable.Therefore, thisvolumewillnotonlyfillthisgapbutalsoeducatethereaderonmostimportant aspectsofdesigningenergyefficientandlowEMFwirelessdeviceslayingfoundationforfutureadvancements.Amultidisciplinaryapproachbasedonartificial intelligence(AI)andnewmultiplexingtechnologieslikenon-orthogonalmultiple access(NOMA)isadoptedtodeviseefficientmechanismsandtechniquesrealizinglowEMFsolutionsthroughintegrationofantennadesign,systemmodeling, andsignalprocessing.
BothsoftwareandhardwaresolutionstominimizeEMFexposurecovering state-of-the-artandadvancedtopicsarediscussed.EMFevaluationtoolsand numericalassessmentmethodsforconventionalaswellasfuturewirelesssystems’ enablerssuchasmmWavetechnologiesaredetailedasalsoisEMFreduction throughradioresourceallocation,energyconservation,EMF-awareantenna design,backscattercommunication,andMIMO.Moreover,acomprehensive accountofvalidationstudiesaswellasthemodelingandselectionofdielectric propertiesforalltheagegroupsareutilizedtoprovidesufficientbackgroundand highlightrecentadvancements.Thebookisconcludedbyhighlightingpotential futuredirectionsofresearchandimplementationforenergy-efficientandlow EMFuserproximitywirelessdevices.Thebookcoversawidevarietyofsubject categoriesandwould,therefore,benefitalargerreadershipinthescientific community.
UniversityofGlasgow Glasgow,UK
MasoodUrRehman MuhammadAliJamshed
ElectromagneticFieldExposure:Fundamentalsand KeyPractices
MuhammadAliJamshed 1 ,FabienHéliot 2 ,TimW.C.Brown 2 ,and MasoodUrRehman 1
1 JamesWattSchoolofEngineering,UniversityofGlasgow,Glasgow,UK
2 InstituteofCommunicationSystems(ICS),Homeof5Gand6GInnovationCentre,UniversityofSurrey, Guildford,UK
1.1Introduction
Inthepast,significantresearcheffortshavebeendevotedtofirstunderstanding howEMfield(EMF)exposureaffectshumans[1–3]and,then,tocreatetools formeasuringexposureanddefiningexposuremetrics[4–6];thesemeasuring techniquesandmetricscanbeusedtoestablishexposurerecommendations[7]. Indeed,thehealthimpactofEMF,magneticfield(MF),andelectricalfield(EF) iscurrentlybeingcontestedinstudiesandamongthegeneralpublic,particularly forchildren[8].Wirelesscommunication(e.g.thecellularsystem)hasgrown sorapidlyinrecentdecadesthatitisnowoneofthemostmajorsourcesof EMFexposureinthegeneralenvironment(seeFigure1.1).Similarlytoother sourcesofEMFexposure,measuresandrecommendationshavebeencreated inwirelesscommunicationthroughoutthelastdecades[10]torestrictexposure and,thereafter,enhanceapproachestominimizeit[11].Inthefuturegeneration ofcommunicationnetworks,theexponentialincreasesinbothmultimediatraffic andconnecteddeviceswillnecessitateariseinthenumberofaccesspoints (APs)(e.g.basestations)tomeetdemand.Asaresultoftherisingnumberof wirelessdevicesandAPs,thelevelofEMFexposurewillincrease.Similarly,the widespreaduseofmmWavespectrumin5G,whichwillhavecarrierfrequencies over24GHz,isanticipatedtohaveaneffectonexposuresinceitwouldnecessitate ahighdensityofAPs[12].Recentresearchin[13–16]hasrevealedthatexposure atthesefrequenciesmayposesomehealthrisks.
Figure1.1 CommonEMFexposuresourcesgenerallypresentintheenvironment[9].
Thechapter’sstructureandkeytopicsofdiscussionaresummarizedasfollows:
1.Section1.2coverstheexistingtechniquesforassessingEMFexposureinvariouscircumstances,i.e.theEMFassessmentframework,andincludesinformationonthemetricsmosttypicallyusedformeasuringEMFexposurein communication.First,researchprojectsrelatingtotheEMFexposureassessmentframeworksareprovided;themajorityofthesestudiesoutlinetheirEMF exposureevaluationmechanism,examinethereasonsofexposure,andthen recommendsolutionstominimizeit.Second,differentcategoriesofexposure metricsarereviewed,whereeachcategoryofmetricsisexplainedvis–á–visits targetscenario(s).Third,genericmetricsarepresented,whicharedeveloped byintegratingmeasurementsfromseveralcategories.
2.Section1.3explainsandillustrateshowthevariousavailableEMFmetricshave beenutilizedforrestricting(i.e.creatingstandards)orloweringexposure.
3.Finally,Section1.4concludesthechapter.
1.2EMFMetricandEvaluationFramework
AsignificantamountofworkhasbeencarriedoutinrecentyearsforevaluatingtheEMFexposureinvariousscenarios,usingdifferentmeasurementsystems andtools,toassessthepotentialrisksemanatingfromEMFradiationsinwireless communicationsandmitigatetheireffects(throughguidelinesandEMF-aware reductiontechniques).Asaresult,EMFmonitoringhasgainedrelevanceinwirelessnetworksoverthelastdecade[17],giventhatambientRF-EMFexposuredoes notremainconstantovertimeowingtoenvironmentalchangesandvariations inthenumberofactiveusers(aswellasthenatureoftheirdeviceusage).For example,themoniT(acronymforelectromagneticradiationexposureassessment inmobilecommunications)project,fundedbyOptimus,TMN,andVodafone[18], providedpublicinformationonpopulationexposuretoEMFfrommobilecommunicationsystemsinPortugalfrom2004to2012.Thisproject’smonitoringsystem wasbuiltonanetworkofautonomousremoteprobingstationsandacomprehensiveEMFsoundingprogram,bothofwhichwerecarriedoutinpublicspaces aroundthecountry.Accordingtotheprojectmonitoringdata,theEMFvalues ofmobilesystemswerebelowtherequiredthreshold.AnotherEMFassessment andmonitoringeffortwastheSEMONTproject,whichwasimplementedandutilizedforreal-timeEMFexposureevaluation.Monitoringfindingsindicatedthat possibleexposurewaswellbelowthepermissiblelevelsetbySerbianlegislation forthegeneralpopulation[19].Theirapproachwasthenutilizedtoquantifythe exposureproducedbyGSMwhenfluctuationsintrafficcircumstanceswereconsidered[20].AccordingtoRFexposureassessments,exposurelevelstendtogrow withrisingurbanization[21].Meanwhile,theexposuresurveyassessmentin[22] discoveredthatexposurelevelsinEuropearenotexceedingtherecommendedlevels,butexposurefromwirelesscommunicationdeviceshasincreasedsignificantly overthelastyears,accountingformorethan60%oftotalexposure.
Inadditiontothesemonitoringinitiatives,otherprojects,suchasthemonitoringandcontrolactivitiesrelatingtoelectromagneticfieldsintheRFrange (MONICEM)andlowEMFexposurefuturenetwork(LEXNET)projects,have establishednewEMFassessmentmetricsthatmaybeusedtoreducetheoverall levelofEMFexposure.Forexample,inMONICEM,whichwassupportedbyboth theinter-Universitycenterforthestudyofinteractionsbetweenelectromagnetic fieldsandbiosystems(ICEmB)andtheinstituteforenvironmentalprotection andresearch(ISPRA),itwasdiscoveredthatservicessuchascellularbase
1ElectromagneticFieldExposure:FundamentalsandKeyPractices
stations,wirelessnetworks,andsooncreatelargeamountsofEMFradiations, muchoverthenaturallimitations.Theprojectcreatedanenvironmentalimpact indicator(FIAE)basedontheEMFderivedfromagenericsource[23].Similarly, intheLEXNETproject,whichwasfundedbytheEuropeanCommission,a newrealisticmetricknownastheexposureindex(EI)[24]wasdevelopedto quantifythedegreeofEMFexposuretopeopleintheenvironment.Usingthis criterion,theresearchestablishedinnovativestrategiesforlowering(byatleast 50%)humanexposuretoelectromagnetic(EM)radiationgeneratedbywireless communicationwhilemaintainingqualityofservice(QoS)[25].Themetrics createdinMONICEMorLEXNETareintendedforassessingorrealistically modelingEMFexposureacrossvastgeographicalregionswhileaccounting forvariousformsofEMFradiations.Thesemoregeneralmeasurementsor assessmentframeworkssometimesrelyonorcombineexistingmeasurescreated formoreparticularcontexts.Forexample,considertheEIcreatedbyLEXNET, whichincludesinitsdefinitionthespecificabsorptionrate(SAR)andpower density(PD),bothofwhicharetypicalmetricsformeasuringtheEMFexposure ofwirelesscommunicationdevicesandequipment.Inthefollowingsections,we willfirstgothroughthemostoftenusedmetricsinwirelesscommunicationsfor analyzingEMFexposureinvariouscircumstances,andthendescribehowsome ofthemmaybecombinedtogeneratemoregeneralmetrics.
1.2.1EMFExposureFactors
Asabyproductofitstransmission,eachdevicedeliveringinformationtoanother devicecreatesEMFexposuretousersorpersonsinwirelesscommunications.In general,thetotalexposureatanylocationinagivenregionunderobservation isthesumoftheradiationsemittedbyalltransmittingdevicesinthevicinity (accountingforboththeactiveandpassiveexposures).Theseverityoftheexposureisdeterminedbyfourmajorcriteria,whicharediscussedinthefollowing.
1.2.1.1TransmitAntennaRegions
Transmittingantennastypicallyhavetworadiatingregions:nearfieldandfarfield, withthenearfieldregionfurtherclassifiedasreactiveandradiatednearfield dependentonthedistanceandfrequencyoftheradiatingantenna.Thereactive nearfieldliesintheimmediateproximityoftheantenna,wheretheelectricand MFare90∘ outofphase,makingthereactiveeffectmoredominating.Theradiatingnearfield,alsoknownastheFresnelarea,isthespacebetweenthereactive nearandfarfields.Inthisarea,theradiatingimpactoftheantennabeginstooutweighthereactiveeffect.Thefarfieldarea,ontheotherhand,isfurtheraway fromtheantennaandhastheelectricandMFinphase.Itshouldbenotedthat eachzoneisdeterminedbyspecificboundarycriteria,whicharefurtherspecified
Figure1.2 Antennafieldareasaredepicted[26].
inFigure1.2.InFigure1.2, D denotesthediameteroftheantenna, R theradius ofeachzone,and λ thewavelengthofanEMwave.Theimpactofthenearfield onEMFexposureismoresignificantintheuplinkscenario,whentheantenna(s) ofausermobiledeviceradiate(s)tosenddatatoanaccesspoint(AP)andmost oftheantenna(s)dissipatedenergycaneasilybeabsorbedbytheuserbody/head (giventheuserbody/presencehead’sinthenearfieldregion)[27].Theinfluence oftheradiatedEMF,ontheotherhand,decreaseswithdistanceinthefarfield.It shouldbeemphasizedthatactiveexposurenormallyresultsfromnearfieldEMF waves,whereaspassiveexposuretypicallyresultsfromfarfieldradiations.
1.2.1.2TransmitAntennaCharacteristics
Thetransmittingantenna’sparameters,suchastransmittedpower,antennagain, directivity,effectiveaperture,polarization,beamwidth,andsoon,arecriticalin definingtheextentofexposure.TheintensityofexposureisgenerallyproportionaltotheintensityoftheEF,whichisproportionaltothetransmitpower.For example,in[28],theEMFradiationsfrommobilecommunicationantennaswere examinedbytakingintoconsiderationtherelevanceofantennacharacteristicsfor determiningexposure.
1.2.1.3DurationofExposure
Aswithanyothersortofexposure,suchaspollutionorcigarettesmoke,thelonger theexposure,thegreatertheexposuredosage.Forexample,[29]hasdemonstrated thatthedurationofexpositionisassociatedtoariseinbodytemperaturewhen humansareexposedtoRFradiation,whichcanbehazardousovertime.Similarly, [30]claimsthatgrowingmobilephoneusagemighthavenegativeimpactsonthe humanreproductivesystem.
1.2.1.4ElectricalPropertiesofBiologicalTissues
Variationsinthedielectriccharacteristicsoforganicmaterialsandtissuescanbe regardedasasignificantinfluenceinEMFexposure.Indeed,aspreviouslystated, childrenabsorbmoreradiationthanadultsduetodifferencesinthedielectric characteristicsoftheirtissues.Forexample,[31],whichexploredthechangesin dielectricconstantbetweenbonesandfattyregionsusingmicrowavetomography, foundarelativelylargedeviationindielectricconstantbetweensoftandhardtissues.Meanwhile,[32]providesathoroughexperimentalexaminationlinkedto thevariationindielectricconstantofdifferentbiologicaltissuesforfrequencies rangingfrom10Hzto20GHz.
1.2.2EMFExposureMetrics
Severalmetricshavebeendefinedthroughouttheyearsinordertoanalyze andpredicttheEMFexposureofwirelesscommunicationsystemsinvarious circumstances,dependingonthenumerousparametersindicatedinSection1.2.1. Tothebestofourknowledge,therearefourprimarycategoriesofEMFmetrics, namely,SAR,PD,exposure-ratio,anddosage,whichmaybegroupedasshownin Figure1.3.
Figure1.3 ThemostoftenusedmetricsforassessingEMFexposure[9].
1.2.2.1SpecificAbsorptionRate
TheSARisameasureofthegeneratedEMFinsidethehumanbodywhenexposed toatransmittingantenna’snearfield.WattsperkilogramaretheunitsofmeasurementofSAR.TheSARmeasureiswidelyusedbyregulatoryorganizations throughouttheworldtodetermineexposurestandardsandevaluatetheexposure producedbyvarioushandset[35].Indeed,toensurepublicsafety,eachhandset makershouldgivetheelectromagneticenergydepositionwithinsurrounding biologicaltissues,asmeasuredbytheSAR[36,37].TheSARinthenearfieldof anantennamountedonawirelessdevicecanbeexpressedas[38];
In(1.1), �� representstheconductivityoftheexposedtissue(s), E indicatesthe strengthoftheEFand md isthemassdensityofthesampleundertest.Figure1.4 depictsatypicalsetupformeasuringtheSARofahumanhead,inwhicharadio frequency(RF)radiatingdevice(withtwoantennacomponentsinourexample) ispositionedclosetoaphantomhead,andaprobe(receiver)isusedtomeasure thestrengthof E [33].TotestSARintheworstcasescenario,thephantomhead wouldbefilledwithasugarsolutionthatreplicatedthedielectricandconduction characteristicsofbraintissueonaverage.TheSARmaybefurtherclassified
Figure1.4 AtypicalSAR measuringsetupisdepicted.
Source:Jamshedetal.[9]/with permissionofIEEE.
Phantom head
Probe
Ground plane
Antenna elements
1ElectromagneticFieldExposure:FundamentalsandKeyPractices
basedontheEMFabsorbedbydifferentareasofthehumanbodyaswholebody averagedSAR,organ-specificSAR,andpeakspatialaverageSAR[39,40].
Inconfinedcontexts(i.e.rooms),thewhole-bodyaveragedSARorglobalSAR maybemeasuredbymeasuringthereverberationtimewithandwithouthumans withintheroom;thewhole-bodySARisthenapproximatedbasedonthedifferenceinreverberationtime[41].Theorgan-specificSARorlocalSARisusedto estimatetheradiationabsorptionofagivenorganinsidethehumanbody,andit isaveragedspatiallyoverthemassofacertainorganortissueinthebody[42].
LocalSARmedicinalconsequencesarelocalizedtoasinglebodilytissueaveragedover1gor10g.IncontrasttolocalSAR,globalSARconsidersthebiological impactsontheentirebody.InconjunctionwiththeprecedingSARdefinitions, thepeak-spatialaverageSARisusedtodeterminethelimitsofSARabsorption fordifferentareasofthehumanbody,aswellastoofferguidelinesforsafeguardinghumansfromRFnearfieldexposure[40].Meanwhile,forfrequenciesover 24GHz,theenergycontributionreceivedbybiologicaltissuesisquiteminimal inthereactivenearfield.Indeed,theaverageSARbecomesnullforfrequencies higherthan10GHzduetotheshallowpenetrationdepth[43];thus,thepoint-wise powerlossdensity(PLD)methodologyistypicallyusedtoestimatethecorrect radiationsabsorbedbythehumanbodyandobtainaccurateexposuremeasurementinthemmWavefrequencyband.ThefollowingequationillustratestherelationshipbetweenPLDandSAR[43];
where �� definesthemassdensityofthesampleundertest.
1.2.2.2PowerDensity
IncontrasttotheSAR,whichisbeneficialforassessingEMFexposureinthenear fieldofanantenna,thePDisthemetricofchoiceformeasuringEMFexposurein thefarradiatingfieldofanantenna,andismeasuredinWattspersquaremeter.In general,[26]givesthePDofanisotropicantennainitsfarfield,whichisuniform (powerperunitarea)inalldirections,andisasfollows;
= Pt 4�� R2 (W∕m2 ), (1.3) where Pt isthetransmittingpowerofthetransmitantennaand R isthedistanceat whichthePDismeasured.Whereasinthecontextofhumanbodyexposure,the PDofatransmittingantennainitsfarfieldregioncanbedefinedas[44]
= |E2 i | �� (W∕m2 ), (1.4)
where Ei (V/m)representstheroot-mean-squaredvalueoftheEFstrengthincidentonthetissuesurfaceofahumanbodyand �� (V/A)isthewaveimpedance.
Figure1.5 AnoverviewofPDmeasurement.Source:Jamshedetal.[9]/withpermission ofIEEE.
Furthermore,becauseEFandMFareinphaseinthisregion,MFstrengthmay beutilizedtoassessPDinthedistantfield.Figure1.5depictsanoverviewofPD measuring.
1.2.2.3Exposure-Ratio
Whenthereareseveralexposuresources,theexposure-ratiometricisusedtocalculateeachsource’scontributiontooverallexposure.Itmaybedefinedasthe averageormaximumcontributionofseveralsourcestotheoverallexposurevalue, suchthat
In(1.5), Ssignal representsthePDoftheRFsignalatageographicallocation v and Stotal isthetotalpowerdensityofallthesignalsatthesamelocation v.Because ofitsnature,thismetricisveryusefulfordeterminingthecontributionsofdifferentradioaccesstechnologies(RATs)tooverallexposureincellularsystems. Theexposurelevelsinnearandfarfieldswerecomputedin[45]using(1.5),and itwasestablishedthattheexposureleveldecreaseswithdistancefromthebase station.Furthermore,itwasdemonstratedinthe[46],usingtheexposure-ratio metric,thatLTE(incomparisonwiththecontributionsfromotherRATs)only accountsfor4%ofoverallexposureinStockholm.Meanwhile,inthe[47],the notionofexposure-ratioisutilizedtoquantifyRFexposureinvarioussituations, anditwasdiscoveredthattheaveragecontributiontototalexposureismorethan 60%forGSM,morethan3%forUMTS-HSPA,andlessthan1%forbothLTEand WiMAX.
