Stavros Koulouridis, Dipl. Eng., Ph.D. Lecturer

Transcription

1 Electromagnetic Compatibility for Wireless Networks Stavros Koulouridis, Dipl. Eng., Ph.D. Lecturer Laboratory of Electrotechnics Electrical and Computer Engineering (E.C.E.) Dept University of Patras

2 Purpose Analyze biological effects of EM radiation from two different viewpoints Microscopically (Biophysical interaction mechanisms) Ionizing radiation Planck s equation and ionization energy Cutoff between non-ionizing and ionizing radiation Non-ionizing radiation Low frequencies Radio frequencies Low-power fields High-power fields Macroscopically (Dosimetry) Wave incidence Parameters of medium Penetration depth and frequency dependence Human body resonance Tissue heating Guidelines for limiting exposure to RF EM fields Radiation from mobile communications equipment Studies on potential health effects Mobile phone handsets

3 EM Spectrum

4 Microscopic approach NON-IONIZING RADIATION IONIZING RADIATION VLF LF RF 30kHz 300kHz 300GHz 1THz Hz Hz Hz mm IR UV X-ray -ray We will consider two kinds of electromagnetic radiation separately because their effects on the human body are vastly different: Non-ionizing Radiation Frequency range: - 3x10 14 Hz Designations: VLF, LF, RF, millimeter, submillimeter, IR, visible Sources: Power lines, radio / TV broadcasting, radar, cellular phones Ionizing Radiation Frequency range: > 3x10 14 Hz Designations: UV, X-rays, gamma rays Sources: cosmic radiation, medical applications

5 Ionizing radiation: Energy Electromagnetic waves are composed of discrete units of energy called quanta or photons The energy of these photons can be found from Planck s equation and is a direct function of the frequency of the EM wave (h is Planck s constant and it is equivalent to x J s): E=h*f When these photons are incident id on the molecules l of cells in biological i l tissue at high energies (>10 ev), they can break bonds and ionize the molecules For example, the energy required to ionize H 2 O is approximately 33 ev Using Planck s equation: the lowest frequency wave that can ionize water molecules is approximately 8 x Hz

6 Ionizing radiation effects Ionizing radiation has many biological effects which are potentially lethal Effects of ionizing radiation have been studied most extensively in two areas: DNA damage and transcription / multiplicative dysfunction Membrane permeability changes leading to loss of barrier function Health effects of hazardous doses of ionizing radiation include: Marrow stem cell damage Impairment of immune function Neurological syndrome Neuronal / capillary damage

7 Non-ionizing radiation Non-Ionizing radiation does not generate chemical mutation to the radiated biological systems Microscopic effects of non-ionizing EM energy have been studied extensively over the past few decades because we are exposed to these waves more often than ever before However, many mechanisms of interaction are still not well known nor are relevant results consistent In contrast, effects and health/safety standards are widely accepted in the science community These effects of non-ionizing radiation should be considered in two separate frequency bands, distinguished by the relative size of wavelength through the medium (human body) Low frequency radiation: >> D Radio frequency radiation: ~ D, << D

8 Radio frequencies AM Broadcasting Microwave Oven Satellite Comm. 300kHz 3 00GHz RF TV Broadcasting, FM Radio Cellular Phone

9 Microwaves (Non ionizingi i radiation) Biological Effects of EM fields Do not destroy inter-molecular structure Increase of H 2 O molecules mobility in biological tissues (Basic Mechanism) Temperature Increase Heat effects (Cataractogenesis, Effect on Blood Brain Barrier, Microwave Auditory Effect, Microwave Syndrome -dizziness, concentration disorders ) Non N Verified DNA effects. Medical applications Treatment applications Hyperthermia Applied on cancer tumors Diathermy Surgery, Muscle Pain relief Diagnostic Applications Diffraction Tomography (Dispersion of EM waves through tissues reflected waves are used to reconstruct structures based on their dielectric properties) Radiometry (Thermal Noise measurements Structure reconstruction, non Invasive Temperature measurements) Thermo acoustic Tomography (Acoustic waves created by heating with EM pulses Structure Reconstruction) 9

10 Study of interaction between biological tissues and sources Study and analysis of interaction is carried out by both computational and experimental methods Development of models (laboratory, numerical, etc) of body In vitro, in vivo, in silico. Computational Studies for: EM dosimetry problems Operation and Development of EM sources Design of Biomedical Systems EM dosimetry: Calculation of power absorption in tissues Studies on harmful effects International Dose Limits Minimize Heating Effects Computational Studies by: Analytical Methods (Mathematical closed solutions, simple geometries, canonical problems) Numerical Methods (Complex Geometries) Specific Absorption Rate (SAR), Power Density, Electric or Magnetic field 2 SAR ( W / kg ) SAR quantifies ΕΜ fields thermal effects E S ( W / m or mw / cm ) Z 0 H Z 0 Power density (S) only at far field 10 2

11 Experience from the use of RF fields Use of electromagnetic fields mainly after the 2 nd World War Radar Telecommunication systems Use of electromagnetic fields for diagnostic purposes MRI Use of electromagnetic fields for therapeutic purposes Hyperthermia

12 Radio frequency EMF effects (100 khz-300 GHz) Mechanisms of interaction for RF radiation on the body are very different at lowlevels of radiation as compared to higher levels Low-level RF radiation causes predominantly non-thermal effects because the intensity is not high enough to significantly change tissue temperature Non-thermal effects are direct interactions of EMF with biological cells Very important because most common exposure is at low-levels levels Not as well understood: mechanisms are not fully explored nor consistently documented High-level RF radiation causes thermal effects Thermal effects are indirect interactions: EMF -> heat -> biological effect Hazards are well established, safety levels are well documented

13 Non-thermal effects of RF EMF RF fields induce torque on molecular dipoles which can result in ion displacement, vibrations in bound charges, and precession This effect is characterized by the Bloch Equation dm M B dt With an applied magnetic field, the nuclear spins will precess in a left-hand direction around the field with angular frequency proportional to its amplitude No observable biological hazards have been noted as a result of these mechanisms because they are outweighed by random thermal agitation ti in lowlevel fields This phenomenon is exploited in Magnetic Resonance Imaging

14 Non-thermal effects of RF EMF In vitro research reports show that membrane structure and functionality may be altered in RF fields No mechanism that can be experimentally verified has been found to describe these effects, although h some researchers have proposed possible ways of interaction

15 Amplitude Modulated Fields Changes in calcium efflux VHF fields with amplitude modulation at extremely low frequencies increase in calcium ions release from brain cells Resonance phenomenon envelope frequency 6-20 Hz (16 Hz) ~ frequencies of brain electrical activity power density 1 mw/cm 2

16 Pulsed Fields Microwave auditory effect ec First reported by persons working in the vicinity of radar transponders. Microwave auditory effect consists of audible clicks produced by microwave pulses (200 MHz-6.5 GHz) and perceived directly by the recipient without the aid of any receiving equipment. This effect occurs as a result of the thermal gradient which generates a thermoelastic pressure wave in the brain tissues. This wave propagates up to the cochlea where it is detected by the cells of the inner ear A very fast but weak temperature increase

17 Genotoxicity studies Experimental Studies no increase in DNA damage during non-thermal in vitro experiments for high frequency pulsed fields increase in DNA breaks in rat brain cells, following exposure to RF EMF at 2450 MHz in the form of short intense pulses

18 Experimental Studies Induction of cataracts (formation of lens opacity in the human eye) Induction of cataracts to rabbits exposed to high levels of electromagnetic power density Significant temperature increase due to eye s low blood flow

19 Thermal effects of RF EMF Period, T = 1 / f Biological Tissue Electric field alternations, at a frequency f, of a RF electromagnetic wave that is incident id on biological i l tissue Remember: For RF and microwave fields, this frequency is generally between 30 khz and 300 GHz

20 Thermal effects: Heat generation Ionic conduction and vibration of dipole molecules following alternations of the field lead to an increase of kinetic energy which is converted to heat The simplistic model below elucidates this phenomenon by first demonstrating induction of dipole moments by an applied electric field (electronic polarization) No field Field applied E Electron Orbit No induced moment Induced moment These dipole moments are internally induced electric fields that oppose the externally applied field They try to (unsuccessfully) follow the alternations of the electric field at RF and microwave frequencies but instead lag behind the transmitted wave, thus energy is gained

21 Thermoregulation Whenever heat is generated within the body, thermoregulatory control mechanisms take effect Body has both passive and active thermoregulatory mechanisms: Passive: Heat radiation Evaporation cooling Conduction / convection Active Internal fluids (such as blood) transfer heat to external parts of the body In humans, heat is transferred to skin where it can be radiated or convected away (cutaneous vasodilation) To maintain homeostasis, these control mechanisms respond to the stimuli or stressors from the outside environment

22 Thermoregulation Sense and Thermoregulate RF Field Induced Heat Tissue T If T exceeds a certain threshold value, the thermoregulation feedback system will break down and the tissue temperature will rise beyond control Bi l i l d d ibl ti d th ill lt if th RF fi ld Biological damage and, possibly, tissue death will result if the RF field continues to be applied

23 At risk? Tissues which are at highest risk are those with lower blood perfusion: Eyes Gall bladder Testes These tissues are least able to dissipate heat through the active These tissues are least able to dissipate heat through the active thermoregulatory mechanism of blood flow

24 What happens macroscopically? Problem of electromagnetic wave incidence on a lossy medium (tissue) Incident EM energy is reflected and refracted at the interface of air and tissue Fundamental constants defining how much is reflected and refracted are parameters of the medium Air Biological Tissue E r E t E i r Interfa acesr Hr H t S t H i S i

25 Parameters of biological media Permittivity,, defines the polarizability of a material Applied E-field gives rise to dipole moment distribution in atoms or molecules Secondary fields are set up, thus net E-field is different If dipole moment distribution is denoted by vector P, the relationship between applied electric field and P is: P ( ) E Conductivity,, summarizes the microscopic behavior of conductors Applied E-field gives rise to electron drift This drift results in a current density in the direction of the E-field Conductivity is the factor which relates the E-field to the drift current J E 0

26 Parameters of biological media Permeability,, is analogous to the permittivity in that it describes the relationship between the magnetic dipole vector and the magnetic field Most of the cells and tissues are non-magnetic For these types of materials, is considered to be equivalent to 0, the permeability of free space It is, therefore, much less critical to our analysis of EM interaction with biological tissue than permittivity and conductivity B H These three parameters fundamentally characterize any medium macroscopically Parameters can be used to determine depth of penetration and absorbed power of an incident electromagnetic wave on the medium

27 Electrical Properties of Biological Tissue Properties: - ε r, σ, mass density - μ r = 1.0 for biological tissues Depend on Tissue Bone, fat, cartilage have low σ Muscle, blood, brain, etc. (water-based tissues) have large σ Depend on Frequency Low Frequency: ε r large, σ small High Frequency: ε r small, σ large

28 Permittivity of tissues Dispersion for high-water content tissues α (ELF <10kHz, 80Hz) β (RF, 10kHz 100MHz, 50kHz) γ (MW, >100MHz, 20GHz)

29 Permittivity of tissues

30 Conductivity of tissues

31 Tissue Properties 900 MHz 1800 MHz Tissue r (S/m) r (S/m) bone muscle fat cartilage brain & glands skin

32 Tissue Properties 900 MHz 1800 MHz Tissue r (S/m) r (S/m) nerve blood CSF eye humour sclera lens

33 Penetration of EM waves in biological i l tissue Time dependence of the fields (exp+ jωt) Use of vector phasors J r r E r Dr 0rEr H r jd r J r Conductivity current: Electric flux density: Ampere-Maxwell Law: r Hr j0 r j Er 0 r r r j r j r 0 '' Complex dielectric i permittivity Loss tangent of the tissue: tanδ= '

34 Penetration of EM waves in biological i l tissue Semi-infinite homogeneous medium Region 0 Region 1 Air Biological Tissue ε 0 μ 0 Ε x inc ε μ 0 σ z z=0 E inc ˆ k jk0z xe e Maxwell-Faraday Law: H j 1 E

35 Air Penetration of EM waves in biological i l tissue jk 0 z jk 0 z E z E e Re x0 0 k H z E e Re 0 jk 0 z jk 0 y0 0 0 Biological tissue E z E Te x1 0 jkz k Hy1 z E 0 Te 0 jkz Propagation constant 1/2 1/2 k k0 j k0 j j 0

36 Boundary conditions on the interface z=0 E E 1 R T x0 x1 H H k 1 R kt y0 y1 0 Transmission coefficient: T 2 1 j 0 1/2 Reflection coefficient: R 1 j 1 j 0 0 1/2 1/2

37 Penetration of EM waves in biological i l tissue 2 Wavelength inside tissue: In high water content tissues (high permittivity values) Absorbed power density: P z Ex1 z 2 In high water content tissues (high conductivity values) 2 Any wave that enters a lossy medium will be attenuated after some distance Depth of penetration (D.O.P.) characterizes the distance after which the field intensity is 1 / e of its incident value (8.7 db) x1 Ex1 z E z e e, z : e e E z 0 E z 0 x1 j j z z 1 x1

38 Penetration of EM waves in biological i l tissue Depth of Penetration: 1/ In high water content tissues (high dielectric parameters) Highly lossy medium : 1/2 1 j j k j 1 j D.O.P. dependence upon frequency 0

39 Two-layered biological tissue model Air 0 ε 0 z=-d z=0 1 2 ε 1 ε 2 σ 1 σ 2 Muscle μ 0 μ 0 μ 0 z Ε x inc Fat k jk 0z jk0z 0 jk 0 z jk0z H C x0 0 0 y0 z C 0e 0 e 0 k jk0z jk1z 1 jk1z jk1z 1 Hy1 z C0e C 1e x1 1 1 E z Ce Ce E z C e C e 0 2 E z C e jk z 2 2 Hy2 z C2e x2 2 k 0 jk z

40 E E Boundary conditions on the interface z=0 H H x0 x1 y0 y k1 k2 k k C C RC, jkz jkz 0 E z E e Re R re * * 1 2 j * * 1 2 In a tissue layer with width smaller than the D.O.P. : R j re k j Stationary wave High reflection coefficient on the fat-muscle interface Absorbed power density 2 z 2 E 0 2z 2 2z P z e r e 2rcos 2 z 2 2

41 Absorbed power density vs. depth

42 Resonance Phenomena When the long axis of the body is parallel to the electric field vector and under plane wave exposure conditions, whole body SAR reaches maximal values. The amount of energy absorbed depends on a number of factors including the size of the human body. Electrically ll grounded d individuals For non-grounded individuals resonant frequencies are higher h by a factor of about 2.

43 Schematic Diagram of Interaction Incident field parameters Frequency, intensity, polarization, source-object configuration (near- or far-field) Coupling geometry Electromagnetic ti properties of near objects Influence of the ground, reflecting surfaces, or other objects in the field near the exposed body Characteristics of the exposed body Size, internal and external geometry, dielectric properties of the various tissues Biological Tissues Thermal properties Blood flow Absorbed b power distribution ib ti Thermoregulatory mechanisms Temperature distribution Biological response

44 Thermal Effects Power absorption by the human body Absorbed power per unit of tissue mass SAR (Specific Absorption Rate) SAR E σ: tissue conductivity (Si/m) 2 (W/ Kg) Ε: effective value of electric field (V/m) ρ: tissue mass density (kg/m 3 ) Thermal response of biological tissues Blood flow Thermoregulatory mechanisms

45 Guidelines for Limiting EMF Exposure Well-documented d research results Only short-term immediate health effects (thermal effects) are considered Insufficient available data on long-term and non-thermal effects Potential long-term effects, such as an increased risk of cancer, are not considered

46 Occupational vs General Public Exposure Limitations ti Occupationally exposed General public comprises population consists of adults who are generally exposed under known conditions are trained to be aware of potential risk and to take appropriate precautions individuals of all ages and of varying health status, and may include particularly susceptible groups or individuals. id In many cases, members of the general public are unaware of their exposure to EMF. Individual members of the general public cannot be expected to take precautions to minimize or avoid exposure More stringent exposure restrictions are adopted for the public than for the occupationally exposed population

47 Basic restrictions and reference levels l Restrictions on the effects of exposure are based on established health effects and are termed basic restrictions In the 100kHz-10GHz range, basic restrictions are provided on SAR to prevent whole body heat stress and localized tissue heating Protection against adverse health effects requires that these basic restrictions are not exceeded

48 Basic restrictions and reference levels l A whole-body SAR value of 4 W/kg has been identified as a threshold level of exposure at which harmful biological effects can occur. A safety factor of 10 is applied to provide adequate protection for occupational exposure. An additional safety factor of 5 is introduced for exposure of the public. The reference levels are obtained from the basic restrictions by mathematical modeling and extrapolation of laboratory results at specific frequencies.

49 EM Dosimetry Parameters Specific Absorption Rate SAR (W/kg) exposure conditions 2 E radiated tissue SAR Basic limitations Difficulty in determining-measuring SAR ( W/ Kgr ) Power density of equivalent plane wave (W/m 2 or mw/cm 2 ) characteristics of the EM source (far field) independence of the exposed body Reference value P E Z 2 0 ( W / m Ε : effective value of the incident electric field Ζ 0 =377 Ω: free space impedance 2 )

50 Basic restrictions (100 khz-10 GHz) ICNIRP/IEEE SAR (whole body average over a 6 min period) SAR (localized li 10g-head & trunk-over a 6 min period) SAR (localized li 10glimbs-over a 6 min period) General public exposure 0.08 W/kg 2 W/kg 4 W/kg Occupational exposure 0.4 W/kg 10 W/kg 20 W/kg

51 Reference Levels Average Power Density

52 Mobile Communication Systems The last years, public s interest has been focused on the effects of EMF emitted by mobile communication systems. Ongoing increase of mobile phone users 383 million mobile phone users in Europe 84% average usage in Europe Mobile usage spreading by children

53 Studies related to cancer Animal Studies Doubling of lymphoma incidence in a genetically-sensitive strain of mice after exposure to GSM-type pulsed microwaves for two 30-minute periods each day for 18 months (Australia) DNA damage in mice exposed to microwave radiation at mobile communication frequencies (University of Washington) Effect on the long term memory function (University of Washington) Effect on the Blood Brain Barrier (University of Lund) increase of the BBB permeability to proteins (albumen) possible correlation with diseases such as Alzheimer

54 Human Volunteer Studies Reduction in reaction time to external triggering: Tests on 35 volunteers exposed to continuous and pulsed microwave radiation (University of Bristol) Effects on sleep and cognitive function: Disturbance of normal sleeping EEG patterns due to exposure to GSM radiation for 30 min while awake (University of Zurich) Eye cancer: Analysis of the questionnaires given to 118 uveal melanoma patients, comparatively to those given to 475 healthy subjects (University of Essen)

55 Non-Thermal Effects Russian scientists observations Microwave Syndrome (refers to exposure to microwave radiation under the reference levels) irritability, fatigue, loss of appetite, reduced intellectual ability, inability to concentrate, emotional instability, depression and headache Studies in several countries Mobile phone users refer symptoms similar to those of the Microwave Syndrome.

56 Difficulties Long-term results Epidemiological Studies e.g. to observe increase in cancer incidents due to mobile phone usage (possible correlation study), at least 10 years are essential During the essential long time period the sample under study has changed its habits Requirements for study reliability Large sample with fixed characteristics Comparative sample for testing the study results Dosimetric information On going g large-scale epidemiological study coordinated by the WHO in order to investigate potential correlation between mobile phone usage and head/neck cancer

57 INTERPHONE study An international collaboration of 13 countries investigating mobile phone use and the risk of intracranial tumours. Cardis E, Kilkenny M. International case-control study of adult brain, head and neck tumours: results of the feasibility study, Radiat Prot Dosimetry 1999;83:179-83

58 Acoustic Neuroma Acoustic neuroma (benign tumour of the inner ear): Increase of acoustic neuroma risk for 10 or more years of mobile phone use. The risk increase is confined to the side of the head where the phone is usually held. (Karolinska Institute)

59 INTERPHONE study 1 Ongoing pooled population-based case-control epidemiological study (5 North European countries: Finland, Denmark, Sweden, Norway, UK) * p y ) Objective: Assessment of the risk of acoustic neuroma in relation to mobile phone use Participants: Patients of acoustic neuroma (male and female) aged years, observation period: , 678 patients, 3553 controls Results: - There was no increased risk of acoustic neuroma in relation to regular mobile phone use - No association of risk with duration of use, lifetime cumulative hours of use or number of calls, for analogue or digital phones separately was found - An increased risk after than 10 years of use could not be ruled out * Mobile phone use and risk of acoustic neuroma: results of the Interphone case-control study in five North European counties, British Journal of Cancer, 2005

60 INTERPHONE study 2 Objective: To investigate the risk of glioma in adults in relation to mobile phone use Design: Population based case-control control study with collection of personal interview data* Setting: Five areas of the United Kingdom Participants: 966 people (18-69 years) diagnosed with a glioma from 1 December 2000 to 29 February 2004 and 1716 controls randomly selected Main outcome measures: Odds ratios for risk of glioma in relation to mobile phone use Results: The overall odds ratio for regular phone use was 0.94 (95% confidence interval 0.78 to 1.13). There was no relation for risk of glioma and time since first use, lifetime years of use, and cumulative number of calls and hours of use. A significant excess risk for reported phone use ipsilateral to the tumour (1.24, 1.02 to 1.52) was paralleled by a significant reduction in risk (0.75, 0.61 to 0.93) for contralateral use. Conclusions: Use of a mobile phone, either in the short or medium term, is not associated with an increased risk of glioma. This is consistent with most but not all published studies. The complementary positive and negative risks associated with ipsilateral and contralateral use of the phone in relation to the side of the tumour might be due to recall bias. * Mobile phone use and risk of acoustic neuroma: results of the Interphone case-control study in five North European counties, British Journal of Cancer, 2005

61 INTERPHONE study 3 Population-based case-control study conducted in Germany * Objective: To examine whether the risk of glioma and meningioma in adults is related to mobile phone use Participants: i t Patients t (male and female) aged years, observation period: , glioma patients, 381 meningioma patients, 1535 controls Results: - No indication of an overall increased risk of glioma or meningioma among regular cellular telephone users - An elevated risk of glioma among gpersons who had used cellular phones for 10 or more years, but based on small numbers - No assosiation between cordless telephone use and the risks of glioma or meningioma - An increased risk of high-grade glioma for women, which can be a chance finding Note: The number of cellular phone users for 10 years or more was low and effects of recall bias cannot be ruled out * Cellular phones, cordless phones, and the risks of glioma and meningioma (Interphone Study Group, Germany), American Journal of Epidemiology, October 2006

62 Mobile Communication Systems- Base Stations ti They transport signal from mobile phone to mobile phone Radiation power ~ decades of W Radiation power in correlation with mobile base stations density Sparsely areas, fewer er base stations: higher power Densely populated areas, more base stations: lower power

63 Mobile Communication Systems- Base Stations ti Base Station Height: m Beam: directional slight down gradient high horizontal width (~120 ο ) low vertical width Power reduces drastically with the distance from the base station

64 Mobile Communication Systems- Mobile Phones Typical average radiation power of mobile phones GSM 250 mw (900 MHz) 125 mw (1800 MHz) Mobile phones radiate in the vicinity of sensitive tissues Estimation of human head exposure to microwave radiation Measurements in phantoms Computational simulation

65 2,0 1,8 1,6 1,4 12 1,2 1,0 0,8 0,6 0,4 0,2 0,0 Mobile phones SAR values (Sony Ericsson) Mobile phones SAR values Sony Ericsson SAR (W/kg) J100i J220i K310i K510i K600i K700i M600i S700i V800i W700i W810i W900i Z300i Z530i Z710i Models

66 Mobile phones SAR values (NOKIA) Mobile Phones SAR values NOKIA SAR (W/kg g) 2,0 18 1,8 1,6 1,4 1,2 1,0 0,8 0,6 04 0,4 0,2 0,0 N95 N93i N93 N92 N90 N80 N76 N73 N i Models

67 EM fields exposure evaluation Experimental methods Experimental models Head phantoms Canonical shapes (simple) (cube, sphere) Plastic cover, liquid material to simulate brain More detailed d models They are made from 5 or more tissues Robotic systems and sensors to carry out measurements Specific Anthropomorphic Mannequin (SAM) Phantom APREL SAR Assessment System ALSAS 10 Universal

68 EM fields exposure evaluation Computational simulations 3D models of head and mobile device Head models -Simple canonical models Απλά κανονικά μοντέλα (spheres, ellipsoids) - Accurate numerical models from CT, MRI cubical voxels of 1x1x1 or 2x2x2 mm 3 dielectric properties of measurements to similar tissues Mobile devices models - Helical or linear dipoles - Numerical CAD models Problems are solved from numerical methods, especially FDTD

69 Numerical example Mobile device Linear/Helical antenna Numerical head model Adult / Child 10 years FDTD analysis Realistic(13 tissues) User - Device distance Numerical results Maximum local, average 10g and 1g SAR Local SAR distributions Total absorbed power

70 Realistic model of head and mobile phone E E Plastic Cover f=1800 MHz 120 Πλαστικό Κάλυμμα Head model 13 different tissues Segmentation 1.25 mm Mobile device With helical or linear antenna In vertical position

71 Maximum local SAR 6 5 [W/k kg] Linear antenna/child Linear Antenna/Adult Helical Antenna/Child Helical Antenna/Adult 1 0 SAR max P in =125 mw P in

72 SAR Linear Antenna nna Child Adult ce ontal slic Horizo ertical slice Ve

73 SAR Helical antenna nna Child Adult e ntal slice Horizon Vert tical slice

74 Maximum 1g & 10g SAR Linear antenna/child a/c Linear Antenna/Adult Helical Antenna/Child Helical Antenna/Adult 3 ΙΕΕΕ: 1.6W/kg 1.6 CENELEC: 2 W/kg [W/k kg] [W/k kg] SARmax 1g P in =125 mw 0 SARmax 10g

75 Absorbed power [mw w] Pabs Linear antenna/child Linear Antenna/Adult Helical Antenna/Child Helical Antenna/Adult P in =125 mw P in

76 Maximum SAR Distance effect P in =125 mw 6 5,70 5 5,14 s (W//kgr) 4 local SAR (adult) local SAR (child) Max ximum SAR value 3 2 2,42 2,20 1,45 1,35 1,23 1,14 Average SAR 1g (adult) Average SAR 1g (child) Average SAR 10g (adult) Average SAR 10g (child) 1 0 0,56 0,62 0,37 0, distance (mm)

77 Absorbed power with distance P in =125 mw sorbed powe er (mw) Ab ,81 82,45 39,86 38, adult child distance (mm)

78 Conclusions Absorbed power around the limits High absorbed power from children Neural system is still developing Longer and higher exposure Considerable absorption decrease with increasing distance between head and antenna Helical antenna leads to higher SAR values as Helical antenna leads to higher SAR values as compared to linear

79 Measures. s. Need to do Design of novel devices with lower SAR values Nonstop evaluation of mobile devices against international limits Instructions on ways to decrease SAR exposure and maximum SAR value in mobile device manual Avoid to make frequent, long or unnecessary calls Do not allow children to use mobile phones Avoid to use mobile phone inside cars without the use of external antenna Keep mobile phone in distance hands-free