Personal RF Exposure Assessment - WHO · Public information needs also personal RF exposure...

Geneva June FT RD Joe Wiart

Personal Personal RF Exposure AssessmentRF Exposure Assessment

J. Wiart, A. Gati, E larcheveque and M.F Wong,FranceTelecom R&D

[email protected]


OutlineOutline

• Specificity of the RF personal exposure assessment

• Personal dosimeter design description • Some measurements using PDM• Conclusion


Personal dosimetryPersonal dosimetryStudies have been done to develop protocols and to assess the

compliance to limits at a given location. (e.g. COST 244 bis & COST 281 Short Term Mission; CENELEC & IEC. Working Group; EUREKA BASEXPO and French ADONIS project)

Base Station epidemiological studies require personal RF exposure assessment.

Public information needs also personal RF exposure assessment

The "in situ" measurement systems and protocol have been developed for compliance testing but they are not adapted.

A specific measurement system and approaches were needed


traffic variation

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

1,00

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:0

0

11:0

0

12:0

0

13:0

0

14:0

0

15:0

0

16:0

0

17:0

0

18:0

0

19:0

0

20:0

0

21:0

0

22:0

0

23:0

0

Heure

Traf

ic n

orm

alis

é au

max

imum

dB

meters

Anatomy of RF exposureAnatomy of RF exposureThe main parameters influencing the personal exposure are

- Location- Traffic, fading and power variation of signal- Frequency

- Polarization and direction of arrival of incident field

Prior to analyze what should be a personal dosimeter it is of interest to characterize the quantity to assess.


Spectrum analysis of General Spectrum analysis of General Public exposurePublic exposure

Using compliance measurement protocols the spectrum of the General Pubic exposure has been analyzed .

Where General Public leaves and works the exposure is mainly linked to FM, TV, cellular network and wireless systems


FrequencyFrequency bandsbands of interest for the of interest for the general public personal exposure general public personal exposure

assessment assessment

–FM

–TV

–GSM 900 Tx & Rx

–GSM1800 Tx & Rx

–UMTS Tx & Rx

–WIFI

In case of epi study or public information the exposure assessment can be limited to pre-determine service such as


In RF domain the received power is In RF domain the received power is composed of many contributionscomposed of many contributions

At a given location a received signal is composed of many signals affected by reflections or

diffractions and coming from different sources. Therefore these contributions have different

amplitudes, phases and directions.

Locally a narrow band signal is affected by

spatial fading

This is a constraint for in situ exposure assessment but should be considered as an advantage for personal exposure assessment

∑= itotal EEρρ


"in situ" measurements "in situ" measurements

Studies have been done* to analyze the accuracy of the mean value of the E field strength

- The fading law cannot be linked to the environment characteristic. The usual way to assess the uncertainty of the estimation versus the number of sample cannot be used.

- The uncertainty linked to the mean value estimation can be linked to a fading severity factor ( standard deviation/mean value).

- The distribution of the fading severity factor can be determine in area such as a town ( eg Paris). Therefore a mean uncertainty vs the number of sample can be estimated ( eg with 3 pt the mean uncertainty is 3 dB)

The minimum uncertainty of " in situ" exposure assessment is about 3 dB

The accuracy of any comparison of in situ exposure is there limited by such uncertainty.

* "Analysis of Electric Field Averaging for In Situ. Radiofrequency Exposure Assessment" Emmanuel Larchevêque, Christian Dale, Man-Faï Wong and Joe Wiart IEEE VT 2005


Isotropy and multiIsotropy and multi--sources / multisources / multi--path RF propagationpath RF propagation

E

H

In a frequency band of interest the exposure is induced by

Different antennas

Waves coming from different directions

The isotropy can be seen as a mean isotropy.


Direction of arrival of in situ Direction of arrival of in situ contributionscontributions

The direction of arrival is important since they should have an impact on the design ( isotropy) of any "in situ" measurement system

The angles of arrival *(between waves and the horizontal) of contributions are mainly comprise between +40° and -30°

The polarization is mainly vertical (+-20°) in rural area and 40° (+-15°) in urban area

* "Angular Power Distribution and Mean Effective Gain of Mobile Antenna in Different Propagation Environments", K. Kalliola, K. Sulonen, H.Laitinen, O. Kivekäs, J. Krogerus, and P. Vainikainen, IEEE Sept. 2002.


Traffic and Time variations of RF Traffic and Time variations of RF exposure: Experimental approachesexposure: Experimental approaches

0 2 4 6 8 10 12 14 16 18 20 220.8

0.9

1

1.1

1.2

1.3

1.4

1.5time variation of FM services normalized to the mean value

FM/M

ean

valu

e

Hours0 2 4 6 8 10 12 14 16 18 20 22

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5time variation of GSM1800 services normalized to the mean value

GS

M18

00/M

ean

valu

e

Hours0 2 4 6 8 10 12 14 16 18 20 22

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5time variation of FM services normalized to the mean value

FM/M

ean

valu

e

Hours0 2 4 6 8 10 12 14 16 18 20 22

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5time variation of GSM1800 services normalized to the mean value

GS

M18

00/M

ean

valu

e

Hours

With GSM cellular

The ratio day / night is limited

night

Afternoon morning

With FM

There is no traffic


Theoretical analysis of cellular Theoretical analysis of cellular network traffic influence network traffic influence

The probability to have a saturated network is usually less than 2%

The probability to have all TRX emitted at the same time at fullpower during a significant time is also very small

0,00

0,20

0,40

0,60

0,80

1,00

1,200:

00

2:30

5:00

7:30

10:0

0

12:3

0

15:0

0

17:3

0

20:0

0

22:3

0

Time (hours)

perc

enta

ge o

f the

max

imum Traffic

Oupout power with4 TRXOupout power with6 TRXOupout power with8 TRX


Spatial DistributionSpatial Distribution

There is a real influence of the location


Personal dosimeter design and Personal dosimeter design and exposure characteristics exposure characteristics

The dosimeter has to take advantage of the RF human exposure specificity

– The main variations are linked to the location• Assess the personal exposure = assess the exposure where

the person is sleeping, working, walking….» Mean value?» Exposure distribution?

– The main Frequency of interest are those of FM, TV and wireless

– The main D.o.A are +40° -30° with vertical or Cross polar polarizations


The Personal DosimeterThe Personal Dosimeter


PPersonalersonal Dosimeter requirementsDosimeter requirements

From previous analysis the objectives of PDM are:

- Record over 24 h the RF exposure coming from main wireless systems and broadcast.

- Avoid interference with the person activity- Have a dynamic of 40 dB and a range [0.05v/m

5 v/m]

with reasonable cost to design and built it


Basic Basic technicaltechnical requirementrequirement• Isotropy has to take into account the D.o.A and

polarization of incident wave:– The electronic and power supply ( that will perturb

the isotropy) have to be located to minimize the X-Y isotropy

– The isotropy has be estimated in a statistic way

• Put on a table and the PDM shall be able to perform isotropic measurement of wave having DoA in the X-Y plane

• The PDM has to detect between 0.05 V/m and 5 V/m (@900MHz between ~ ICNIRP/1.000.000: and ICNIRP/100 )

• The PDM has to assess the exposure in FM, TV, GSM and UMTS + TETRA and Wifi

• The PDM has to be able to separate what is coming from handset and what is coming from base station

Z

XY


Design of the Personal dosimeter Design of the Personal dosimeter

www.antennessa.com

www.francetelecom.com

In 2001 FT RD and In 2001 FT RD and AntennessaAntennessa decided to decided to Combine their efforts to design and built a Combine their efforts to design and built a personal dosimeterpersonal dosimeter


DosimeterDosimeter PrinciplePrinciple

RF board

Power supply

CA

LC

UL

AT

OR

storage

MEASUREMENT

antenna

supe

rvis

or

+ post processing to take into account the type of signal ( e.g pulse in case of handset)


Anatomy of the PDM Anatomy of the PDM

RF analysis

Patent: EP-03300264.3

SUPERVISEUR/TRAITEMENT

USB

Analog to Digital

Converter

data storage

TV3FM

TV4&5GSM Tx

GSM Rx

DCS TxDCS Rx

UMTS TxUMTS Rx

Vbatterie

(temperature

power supply

real time clock

RF board power supply

RF board control

RF board

user’s interface

Numerical processing

Antenna(s)

Patent EP-04300371.4


Capability of present dosimeterCapability of present dosimeter

Sample from 3 to 255 seconds

Up to 7000 records able to be down loaded in txt as well as Excel format

Few days of autonomy

HMI to help users


TechnicalTechnical characteristicscharacteristicsIsotropyIsotropy

• Isotropy • Isotropy X-Y

- Vertical and horizontal fields • Vertical dosimeter

• In other configuration the isotropy is perturbed by the presence of the electronic and power supply but these configuration are not really relevant for the configuration.

• Rejection– In major cases up to -38 dB except special cases:

– Filter design is complex and a rejection should be limited in specific case such as DCS limit band (DCS Rx on UMTS Tx limit bands)

Z

XY

+- 2 dB at 95%


Manage Manage thethe Influence Influence ofof thethe body body throughthrough a a statisticalstatistical approachapproach

ϕθϕθϕθϕθ ddpGfEPi

iPWreceived ),(),(),,(∑ ∫∫=

On a table

-50-40

-30-20

-10

01

2

3

4

5

6

7

89

10

11

12

13

14

15

16

-50

-40

-30

-20

-10

01

2

3

4

5

6

7

89

10

11

12

13

14

15

16

Body worn

CalibrationFactor 1

CalibrationFactor 2

In each frequency band of interest the total exposure is the sum of different sources and reflections therefore the exposure is often coming from everywhere……

The main question is the calibration: in situ and using comparisons with reference method


Example of result: record over 10hExample of result: record over 10h

@ 900 MHz @ 1800 MHz


Influence of samplingInfluence of sampling

0 1 2 3 4 5 6 7 8 9 100

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Time (Hour)

Ele

ctric

fiel

d (V

/m)

Field induced by down link GSM 900 MHz

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

10

20

30

40

50

60

70

80

Exposure (V/m)

Per

cent

age

Exposure distribution with a sample of 5s

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

10

20

30

40

50

60

70

80

Exposure (V/m)

Per

cent

age

Exposure distribution with a sampling of 15s

Non frequent events are affected by the sampling. This frequent events correspond to high exposure during very short time (e.g exposure above 5V/m for one measurement over 7000).


Importance of the log bookImportance of the log bookExposure induced by GSM 900 down

0

1

2

3

4

5

0 500 1000 1500

x 3s (300=15min)

V/m GSMrx

Exposure induced by GSM down

0,01

0,1

1

10

0 500 1000 1500

x 3s (300=15min)

V/m GSMrx

Exposure induced by GSM 1800 Down

00,20,40,60,8

11,2

0 300 600 900 1200 1500

x 3s (300=15min)

V/m DCSRx

Linear representation and logarithmic representation

In this case the dosimeter was put close to the body and put on a table every 15 min…

Exposure induced by GSM 1800 Down

0,01

0,1

1

10

0 300 600 900 1200 1500

x 3s (300=15min)

V/m DCSRx


ThanksThanks

http://perso.rd.francetelecom.fr/joe.wiart/

"Il faut de l'imagination pour se "Il faut de l'imagination pour se représenter la réalité" représenter la réalité"

Giuseppe PontiggiaGiuseppe Pontiggia

[email protected]

Date post:	08-Aug-2020
Category:	Documents
Upload:	others
View:	0 times
Download:	0 times

Personal RF Exposure Assessment - WHO · Public information needs also personal RF exposure...

Documents