evaluation of human exposure levels around radio base stations … · 2012-04-25 · radio...

::: ETRI, The Future Wave :::

Technical Session of ITUTechnical Session of ITU--T SG5 Meeting in Geneva T SG5 Meeting in Geneva

April 16, 2012

Byung Chan Kim, Ph.D.

[email protected]

Evaluation of Human Exposure Levels around Radio Base Stations in Korea

::: ETRI, The Future Wave :::2

ContentsContentsContents

Background

Motivation

Research Issues in Korea

Spatial Averaging

Time Averaging

Predicting Formula

Evaluating Method

Uncertainty


Induced

current

Near field

Far

field

EMF

SAR

EMF Detection Technique Computational Technique

Computation

Visual model

ProtectionApplicationguidelineEvaluation Procedure

Background: Study on EMF & Health EffectBackground: Study on EMF & Health EffectBackground: Study on EMF & Health Effect

EMF: ElectroMagnetic Field


Background: Frequency RangeBackground: Frequency RangeBackground: Frequency Range

102 104 106 108 1010 1012 1014 1016 1018 1020

RadioMicrowave

InfraredUltraviolet

X-ray

Frequency, Hz

PowerLine

AMradio

TV

FMradio Microwave

oven

Cell phones

Heating Lamp Tanning

booth MedicalX-rays

Low inducedcurrents

��No proven effect

High inducedcurrents

��Heating

Electronicexcitation

��Photochemical effects

Broken bonds

��DNA damage

Non-ionizing Ionizing


100 kHz 10 MHz 10 GHz 300 GHz

current densitySAR power density

100 kHz 10 MHz 300 GHz

induced currentthermal effect,

excitationthermal effect

Background: Basis for Limiting ExposureBackground: Basis for Limiting ExposureBackground: Basis for Limiting Exposure

Dosimetry: Measurement or determination by calculation of internal electric field strength or induced current density or SAR in humans or animals

exposed to EMFs

Dosimetric Quantity

Limiting Basis


Reference Level

• Alternative means for determining

compliance: Electric field strength (E),

Magnetic field strength (H), Equivalent

plane power density (S)

• It applies to a situation where the

electromagnetic field is not influenced by

the presence of a body

Basic Restriction

• The fundamental quantities that

determine the physiological response of

the human body to EMFs: Current density

(J), Specific absorption ratio (SAR),

Power density(S)

• It applies to a situation with the body

present in the field

Background: Safety Limits-1Background: Safety LimitsBackground: Safety Limits--11


Background: Safety Limits-2Background: Safety LimitsBackground: Safety Limits--22

ICNIRP: International Committee on Non-Ionizing Radiation Protection

Frequency range E-field (V/m)* H-field (A/m)*

- 1 Hz - 3.2×104

1 Hz ～～～～ 8 Hz 10,000 3.2×104/f2

8 Hz ～～～～ 25 Hz 10,000 4,000/f

0.025 kHz ～～～～ 0.8 KHz 250/f 4/f

0.8 kHz ～～～～ 3 kHz 250/f 5

3 kHz ～～～～ 150 kHz 87 5

0.15 MHz ～～～～ 1 MHz 87 0.73/f

1 MHz ～～～～ 10 MHz 87/f1/2 0.73/f

10 MHz ～～～～ 400 MHz 28 0.073

400 MHz ～～～～ 2000 MHz 1.375f1/2 0.0037f1/2

2 GHz ～～～～ 300 GHz 61 0.16

Note 1. Field value is rms and unit of frequency is same with leftmost column

2. The field strength are to averaged over any 6-min period

<Reference levels for GP>


E ⊥ H No Locally Yes

Z = E/H ≠ Z0 ≒ Z0 ≒ Z0

Measured

quantity SAR E or H E or H

2D2/λλ/4

Distance from the source

Reacttivenear-field

Radiatingnear-field

Radiatingfar-field

0

Background: Field RegionBackground: Field RegionBackground: Field Region

Source: ITU-T Recommendation K.61, 2008


Background: Determine the Compliance-1Background: Determine the ComplianceBackground: Determine the Compliance--11

Dosimetry in near field

< Setups >

ρ

σ2

iE

SAR = iE σ ρ: rms [V/m], : conductivity [S/m], : density [kg/m3]


Background: Determine the Compliance-2Background: Determine the ComplianceBackground: Determine the Compliance--22

Spectrum [subcenter]Spectrum [subcenter]Spectrum [subcenter]Spectrum [subcenter]

0.0001

0.001

0.01

0.1

1

1830 1835 1840 1845 1850 1855 1860

Freq.[MHz]

Ele

ctri field

[V/m

]

Spectrum [subcenter]Spectrum [subcenter]Spectrum [subcenter]Spectrum [subcenter]

0

20

40

60

80

100

120

850 860 870 880 890 900 910

Freq. [MHz]

Ele

ctric

field

[dB

uV/m

]

Evaluation of maximum permissible exposure in far field


How can we evaluate reasonably the impact of EMF on the human body

in far field ?

What method should be used to measure the exposure practically ?

MotivationMotivationMotivation


Research Issues in KoreaResearch Issues in KoreaResearch Issues in Korea

Spatial averaging: Number of points

Time averaging: 6 min or others at each point

Prediction: Possible maximum field level location

Uncertainty: Probability function

reflection

direct

?


Multi-path reflections & Non uniform field distributions

Natural and Man-made structures

No global standard regarding number of points

Australia France Portugal Belgium Italy EN50383

Reference height[m] 1.5 0.75 1.1,1.5,1.7 - 1.1,1.5,1.9 -

No. of points 5 9 3 6 3 -

dimension

[height*width, m]1.0 1.0*0.5 - 1.2*0.4 - 0.7*0.4

Obtaining value Max. Ave. Ave. Ave. Ave. Ave.

Spatial Averaging: Previous StatusSpatial Averaging: Previous StatusSpatial Averaging: Previous Status

j

n

j

j

j

n

j

j

i

n

i

i

global

globaltemplate

n

E

n

E

n

E

E

EEDeviation

j

ji

∑

∑∑

=

== −

=−

=

1

11


By small scale fading: N points have to be independent

The correlation distance

• Theoretically 0.4 λ and empirically 0.8 λ

• Usually 0.5 λ

Spatial Averaging: Previous StudySpatial Averaging: Previous StudySpatial Averaging: Previous Study

( )∑∑−

=

−−

=

−

−

=

1

0

1

0 !

1

!

1)(

N

j

jN

jN

j

N

Nj

eN

jep γ

γγ γγ

+−

+= )2(,)2(,)(

2

2

2

2

2

2

2

2

b

aN

b

NaQ

b

aN

b

NaQp NN γ

γγ

� Rayleigh model

� Rician model ( :standard deviation),222

YXa µµ +=

Error estimation

Source: E. Larcheveque et al., “Analysis of electric field averaging for in-situ radiofrequency exposure assessment,” IEEET Trans. on VTC, vol.54, no.4, pp.1245-1250, 2005.

b


Assessed quantity

• Electric and magnetic field strength or equivalent plane wave power density

At a given location

• Diffraction and reflections

• Different phases and amplitudes

Spatial variations known as small-scale fading

• It does not allow a repeatable exposure level

• We should use an averaging scheme.

Spatial Averaging: RationaleSpatial Averaging: RationaleSpatial Averaging: Rationale


To determine the number of measurement points

• Imitate the space occupied by human

• Analysis the spatial variations of electric field strength

To consider the effect of environments

• Urban

• Suburbs

• Rural

Spatial Averaging: Approach for New MethodSpatial Averaging: Approach for New MethodSpatial Averaging: Approach for New Method

1.7 m

1.5 m

1.1 m

Isotropic Electric Probe

GPS Receiver 노트북

Spectrum Analyzer

RS2321.5 m Calibrated Cable

Tripode

Computer

1.1 m

1.5 m

1.7 m

0.2 m0.2 m


Spatial Averaging: AnalysisSpatial Averaging: AnalysisSpatial Averaging: Analysis

Unit : V/m

No. of points BS1 BS2 BS3 BS4 BS5 BS6

27 Ave. 0.2866 0.2713 0.2308 0.3514 0.0299 0.0457

9

Ave.(-) 0.2888 0.2714 0.2312 0.3616 0.0274 0.0477

Ave.( 0 ) 0.2835 0.2712 0.2313 0.3511 0.0331 0.0424

Ave.(+) 0.2874 0.2712 0.2312 0.3616 0.0274 0.0477

6

Ave.(-) 0.2867 0.2716 0.2301 0.3457 0.0300 0.0461

Ave.( 0 ) 0.2826 0.2709 0.2312 0.3590 0.0315 0.0440

Ave.(+) 0.2881 0.2711 0.2309 0.3835 0.0275 0.0473

Number of Max.

average point 9 6 9 6 9 9

Maximum mean value occur when 6 or 9 points are used in averaging process.

The more number of base stations we select, the better statistical meanings we can get.

However, the purpose of these measurements does not determine the statistical

significance (p-value estimation) between “an exposure to EMF from base station antenna”

and “that’s impact on the human health” but check the levels of exposure.


Spatial Averaging: Korea’s MethodSpatial Averaging: KoreaSpatial Averaging: Korea’’s Methods Method

1.1 m

1.5 m

1.7 m

0.2 m

Location of the main organs of human and theoretical correlation distance

Reliable and repeatable exposure assessment

Source: Byung Chan Kim et al., “Methods of Evaluating Human Exposure to Electromagnetic Fields Radiated from Operating Base Stations in Korea,”

Bioelectromagnetics, vol. 29, no. 7, pp. 579-582, Oct. 2008.

N

S

S

orN

H

H

orN

E

E

N

N

N

∑

∑

∑

=

=

=

=

=

=

1i

i

1i

2i

1i

2i

ˆ

)ˆ(

)ˆ(

N : number of points

:ˆiE root mean square


Time Averaging: Previous StatusTime Averaging: Previous StatusTime Averaging: Previous Status

Number of points for spatial averaging: 3, 6, 9, 20 points (ITU-T K.61 and IEC62232)

Measurement time

• ICNIRP guidelines: Recommend averaged over any 6 min period

• Frequencies between 100 kHz and 10 GHz.

Source: ITU-T Recommendation K.61, 2008


Time Averaging: Previous StudyTime Averaging: Previous StudyTime Averaging: Previous Study

{ } )]/exp(1[)( τσ tLtTMax SAR −−=∆

Tissue

Mass

density

(kg/m3)

Thermal

conductivity

(W/m K)

Specific heat

capacity

(J/Kg K)

Volumetric

perfusion

(m3/m3s)

Equilibration

time

(min)

Conductivity

(K kg/W)

Skeletal muscle 1050 0.50 3465 0.9 17 300

Kidney 1050 0.54 3700 61 0.27 4.4

Liver 1060 0.52 3600 15 1.1 18

Adipose tissue 950 0.27 3100 0.5 25 480

Brain 1040 0.54 3640 7.3 2.2 36

Blood 1060 0.51 3720 - - -

Established biological and health effects

• Temperature (eyeball) rise of more than 1 degree

Heat transfer model

)810( rLSAR −= , r: exposed mass/total mass

),()),((),(),(

2

2

txqTtxTx

txT

t

txTa =−+

∂

∂−

∂

∂βα

Source: “Gunnar Brix, Martin Seebass, Gesine Hellwig, Jurgen Griebel, “Estimation of Heat Transfer and Temperature Rise in Partial-Body Regions

during MR Procedures: An analytical approach with respect to safety considerations,” Magnetic Resonance Imaging, vol. 20, pp. 65-76, 2002.


The averaging time

• means the appropriate time over which exposure is averaged

• is 6 min at each point

• increases as the number of points increases

• increasing means an increase in cost

• is related to the time constant for partial body heating: present of a human bodypresent of a human body

• therefore, is not always necessary in all far field assessments

Reference levels at any point

• are evaluated in the absence of a human bodyabsence of a human body

• are intended to be spatially averaged values body of the exposed individual

Time Averaging: Rationale of Time ReductionTime Averaging: Rationale of Time ReductionTime Averaging: Rationale of Time Reduction


Time Averaging: Approach and AnalysisTime Averaging: Approach and AnalysisTime Averaging: Approach and Analysis

Analyzed the eighteen periods of time from 180 to 10 sec: 10 sec interval

Time (sec)

Base station360 180 60 40 10

1 109.14 109.14 109.16 109.14 109.08

2 109.80 109.79 109.79 109.79 109.80

3 107.07 107.07 107.09 107.07 107.11

4 111.59 111.55 111.60 111.63 111.81

5 92.56 92.36 92.34 92.33 92.56

6 90.41 90.28 90.76 90.84 90.74

7 97.38 97.26 97.39 97.40 97.67

Unit : dBuV/m

Base station 1 2 3 4 5 6 7 8 9 10

Arithmetic average(dBuV/m) 110 117 106 109 114 100 93 107 110 99

Standard deviation (SD) 0.25 0.62 0.98 0.46 0.39 1.07 0.59 0.40 0.58 0.51

Tr/2(confidence level: 95%, DoF: 29) 2.05 2.05 2.05 2.05 2.05 2.05 2.05 2.05 2.05 2.05

Standard uncertainty 0.09 0.23 0.36 0.17 0.15 0.40 0.22 0.15 0.22 0.19

The estimated standard uncertainties: 0.09 ~ 0.40 dB (t-distribution; t.025=2.05, DoF=29)

DoF: Degree of Freedom


0 20 40 60 80 100 120 140 160 180

Time period [sec]

0

0.2

0.4

0.6

Sta

nd

ard

devia

tio

n [d

B]

BS 1

BS 2

BS 3

BS 4

BS 5

BS 6

BS 7

Compare the SD with uncertainty of measurement drift

• Between the 360 sec average value and different time periods

• No overlapping time period: 1~60, 61~120, 121~180, 181~240, 241~300, 301~360 sec

• Maximum value of SD: 0.58 dB at 10 sec

• Uncertainty for repeated measurement: 0.4 dB

Time Averaging: Korea’s MethodTime Averaging: KoreaTime Averaging: Korea’’s Methods Method

uncertainty for measurement drift

−−

==

−−

=

=

∑

∑

∑

=

=

=

n

j

r

j

r

n

j

jj

n

j

j

qqnn

tn

qstqs

qqn

qs

qn

q

1

22/2/

1

2

1

)(1

11)()(

)(1

1)(

1• Average:

• Standard

deviations:

Source: Byung Chan Kim et al., “Reduction of averaging time for evaluation of human exposure to radiofrequency electromagnetic fields from cellular

base stations,” IEICE Trans. on Communications, vol. E93-B, no. 7, pp. 1862-1864, July 2010.


Predicting Formula: Korea’s MethodPredicting Formula: KoreaPredicting Formula: Korea’’s Methods Method

Need to predict the possible maximum exposure position

−

+∗=

−−′+−′

−−′+−′−=Γ

−

Γ+=

==

=×=

=

=

=×==

==

−

−

rt

rti

irir

irir

inrj

t

inin

rad

in

in

hh

hh

jj

jj

ll

GP

r

jeaE

GPIGP

I

IE

rU

r

IE

rEr

U

ErHErWrU

UGPP

UG

αθ

θλσεθλσε

θλσεθλσε

α

βα

β

π

η

η

π

π

η

π

η

ηφθ

πη

φθη

φθ

ηφθ

φθπφθ

π

β

θ

θ

θ

θ

sinsin

cos)60(sin)60(

cos)60(sin)60(

cos

)2

cos()sin2

cos(

2)1(ˆ

2,

2

82),(

4

),,(2

),(

2]Re[

2

1),(

),(4,),(

4

1

2

2

0

20

2

20

max

2

max

2

202

max2

22

2

2*22

r

r

rr

−

Γ+=

Γ+=+=

−

α

βα

β

πη

β

θcos

)2

cos()sin2

cos(

2)1(ˆ

)1(

0

ll

r

eIjaE

EEEE

rjt

drdt

r

rrrr

d-wave

r-wave

Receiver

Transmitter

Image transmitter

1rr

1rr

dr

2rr

gr

iθ

α

rh

th

th


Depending on the operation state,

• Put on the market: EN50383 (certification measurement)

• Put into service (EEM): RRL Notice 2010-64, EN50400

• Offer a service (In situ): TTAS.KO-06.0125, EN50492, IEC62232

Evaluating Methods: Protocols and StatusEvaluating Methods: Protocols and StatusEvaluating Methods: Protocols and Status

EEM: Electromagnetic Environment Measurement

1.1 m1.1 m

1.5 m1.5 m

1.7 m1.7 m

0.2 m0.2 m


1.7 m

1.5 m

1.1 m

: Position

: Point

1.7 m

1.5 m

1.1 m

0.2 m 0.2 m

: Position

: Point

Basic Precision

Focused on human beings: human-centric

Korean standard was established in December, 2006.

Assume spatially averaged value / Take total exposure ratio (TER) of same frequency

Only 1 point in any positions within space occupied by human body

Evaluating Methods: Korea’ method for In Situ Evaluating Methods: KoreaEvaluating Methods: Korea’’ method for In Situ method for In Situ


Evaluating Methods: Korea’ method for In Situ Evaluating Methods: KoreaEvaluating Methods: Korea’’ method for In Situ method for In Situ

Evaluation at place of concern

• Where the general public have voiced concerns about EMF

• Reference for the WHO in developing its anticipated Environmental Health Criteria (EHC)

on radiofrequency

Hospital

Commercial area

Residencial area

School

Apartment c

omplexTotal

1E-008

1E-007

1E-006

1E-005

0.0001

0.001

0.01

0.1

1

Fra

ctin o

f exposure

lim

it

1E-008 1E-007 1E-006 1E-005 0.0001 0.001 0.01 0.1 1

Fraction of exposure limit

0

10

20

30

40

50

Num

ber

of po

sitio

ns

Total

Hospital

Commercial area

Residencial area

School

Apatment complex

Source: Byung Chan Kim et al., “Methods of Evaluating Human Exposure to Electromagnetic Fields Radiated from Operating Base Stations in Korea,”

Bioelectromagnetics, vol. 29, no. 7, pp. 579-582, Oct. 2008.


Uncertainty: Previous studyUncertainty: Previous studyUncertainty: Previous study

Several kinds of uncertainty sources exist

The rationale of probability function is insufficient

Budget Uncertainty Source Probability Function

Measurement equipment

Calibration Normal

Isotropy Normal

Linearity Rectangular

Measurement device Normal

Noise Normal

Power chain Normal

Physical parameters

Drifts in output power of the EUT, probe, temperature and humanity Rectangular

Perturbation of the environment Rectangular

Influence of the body

Post processing

Spatial averaging Rectangular

Divisor of U-shape probability function: , Rectangular: , Triangular: , Normal: 2.0 2 3 6

Source: EN50492, 2008


Uncertainty: RationaleUncertainty: RationaleUncertainty: Rationale

A measured quantity is not measured directly, but is determined from other quantities

through a functional relationship

),,,(

),,,(

21

21

N

N

rrrfq

RRRfQ

LL

LL

=

= : measured quantity

: estimate

2σ

95%

Exposure limit

Assessment result

∑∑==

=−−

==n

j

j

n

j

jq

nqqq

nnn

qsqs

11

2 1,)(

1

11)()(

Uncertainty: The variance of the mean


Uncertainty: Approach & AnalysisUncertainty: Approach & AnalysisUncertainty: Approach & Analysis

Type Contribution components Uncertainty sources

A

Physical parameters Power drift (measurement drift), Body influence, noise

Mechanical constraintsTripod positioning, Mismatch between receiving antenna

(or probe) and base station’s antenna

Post-processing Spatial averaging

B Measurement equipmentCalibration, Power receiver, Isotropy /linearity of probe,

Cable, Power chain

Type A: Be obtained by repeated measurement

Type B: Be estimated by the data on the calibration or specification sheet

1 2 3 4 5 6 7 8 9 10 11121314151617 1819 20212223242526 2728 2930

Base Stations

0.001

0.01

0.1

1

10

De

via

tio

n b

etw

ee

n D

iffe

ren

t D

ista

nce

s (

dB

)| 1m-2m |

| 1m-3m |

| 2m-3m |

0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930

Number of Days

1

2

3

4

5

6

7

8

Da

ily I

np

ut

Po

we

r V

ari

atio

ns (

dB

)

Urban

Suburban

Rural

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 2526272829 30

Base Stations

0.01

0.1

1

10

Un

ce

rta

inty

fo

r P

ow

er

Dri

ft (

dB

)

Standard deviation

Standard uncertainty

Power drift Body influence Mismatches


Uncertainty: Krea’s MethodsUncertainty: KreaUncertainty: Krea’’s Methodss Methods

The estimated uncertainty satisfy the recommendation by international standard (under 6

dB )

Evaluation

type

Contribution

components

Uncertainty

sources

Probability

function

Uncertainty

value [dB]Divisor DoF Rationale of distribution

Standard

uncertainty [dB]

Physical parameter

Power drift Student-t 0.67 2.05 29Small sample, unknown

population mean & variance 0.33

A

Influence of body Student-t 0.22 2.05 29Small sample, unknown


Mechanical constraint Mismatches Student-t 1.29 2.05 29Small sample, unknown


Post-processing Spatial averaging Student-t 0.99 2.26 9Small sample, unknown


BMeasurement

equipment

Calibration Normal 3.00 2.00 ∞ Data sheet 1.50

Spectrum analyzer Normal 0.34 2.00 ∞ Calibration sheet 0.17

Isotropy Normal 1.50 2.00 ∞ Calibration sheet 0.75

Linearity Normal 0.89 2.00 ∞ Calibration sheet 0.45

Cable Normal 0.40 2.00 ∞ Calibration sheet 0.20

Combined uncertainty Root Sum Square of all standard uncertainty (√∑u2) 1.95

Expanded uncertainty Student-t 1.95 1.96 1,447 DoF and t-distribution table 3.82

Source: Byung Chan Kim et al., “Uncertainty Estimation for Evaluating of Human Exposure Levels to RF Electromagnetic Fields from Cellular Base

Stations,” Accepted in IEEE Trans. on EMC and will publish soon.


Thank you and Questions ?

evaluation of human exposure levels around radio base stations … · 2012-04-25 · radio...

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