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128.3.2008 – 4th EBEA Course

Environmental Exposures to RF /Neubauer

Environmental Exposures to RF

Georg Neubauer



Table of Content

� Environmental exposures to RF

sources

� Mobile communication standards

� Measurement methods

� Conclusions



Environmental exposure to RF sources



Natural Sources

� Sun

� Cosmic Microwave

Radiation

� Lightning

� Earth

Source:

www.magnetfeld.de

www.alterlaa.net

www.rasputin.de

www.space-odyssey.de



The Sun

� Integrated part of radiation of the sun in the

microwave range is about 10 pW/cm² (100 nW/m²)

� During outbreaks the microwave irradiation can be

larger by orders of magnitude

� Outbreaks (larger one‘s are called prominences)

develop nearby sunspots of the sun – the

development of sunspots is associated

with changes of the magnetic field

Source: www.uni-sw.gwdg.de



Cosmic Radiation (Radioastronomy) 1

� 1937: First radio telescope from Grote Reber

(USA)

� 1944: Hendrik van de Hulst (University Leiden)

finds out, that interstellar hydrogen causes

emission at 21.2 cm (1.43 GHz)

� 1951 Edward Purcell (Harward) records this line

for the first time

� 1963 Barrett and Weinreb discover emissions of

OH at different spectral lines between 1612 and

1720 MHz

Source: www.alterego.arch.ethz.ch



Cosmic Radiation (Radioastronomy) 2

� 1968 Townes et al discovered the emission line of the ammonia molecule

at 1.25 cm (24 GHz) close to the constellation Sagittarius

� Townes discovered interstellar water molecules (1.35 cm; 22.2 GHz)

� Also discovered due to microwave emissions: Formaldehyde, CO, H2

� Interstellar magnetic field between 2 and 100 µG



Wireless Communication Technologies

� Very prominent examples of new communication technologies are mobile

communication applications, local area networks and broadcasting applications

� Some prominent technologies of these categories are compared in the frame of this

presentation

� The list of the discussed technologies is not complete



New Communication Technologies: Examples

DAB (Digital Audio Broadcasting), DVB-T (Digital

Video Broadcasting –Terrestrial), DRM (Digital

Radio Mondiale),..

IEEE 802.11x, Bluetooth, ZigBee, UWB

(Ultrawideband), Hiperlan(High Performance Local

Area Network), WiMax(Worldwide Interoperability for Microwave Access),….

GSM (Global System for Mobile Communication),

CDMA 2000 (Code Division Multiple Access), DECT

(Digital Enhanced Cordless Communication), UMTS (Universal Mobile

Telecommunication Systems),…

Broadcasting

Applications

Local Area NetworksMobile Communication

Technologies



Mobile Communication Technologies



LAN



Radio and BroadcastingFrequency Band Channel Bandwidth Data rate Range of application

(MHz) (kHz) Mbit/s

DRM < 30 QAM OFDM with FEC 4,5, 5, 9, 10, 18, 20 FM up to 0,13

AM up to 0,05 LW, MW, SW radio

DVB-T 174 - 230 and 582 - 790 16 or 64 QAM COFDM 8000 max 39,

typ 14 - 24 Broadcasting

Technology Modulation

type

Multiple Access



Wireless Communication

For the household and office

DECT, WLAN, Bluetooth



DECT Digital Enhanced Cordless Telecommunication (1)

� Wireless phone in the household (1 base station and 6 mobile units) or as wireless

extension system (cellular net with several base stations, up to some hundred mobiles)

� Frequency range from 1880-1900 MHz (10 channels, 1728 kHz channel separation)

� Maximum burst-power: 250 mW

� Automatic dynamic frequency selection (automatic selection of best suitable channel, also

possible during active speech)

� Mobile transmits not at all without active transmission!

� Base station transmit regularly (also without call) a short (83 µs) synchronization signal(⇒ average power about 2 mW)




� Timing

Daten

(320 Bits Nutzdaten)

Hyperrahmen n Hyperrahmen n+1 … … … ..Hyperrahmen n-1

Zeit t

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

0 1 2 3 4 5 6 7 8 9 1 0 11 12 1 3 1 4 1 5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

1 Hyperrahmen =25 Multirahmen

1Multirahmen =16 Rahmen

1 Rahmen =

24 Zeitschlitze

Gesprächskanal 2

DownlinkGesprächskanal 3

DownlinkGesprächskanal 2

UplinkGesprächskanal 3

Uplink… … …… … …

HF-Bursts

Trennung vonUplink und Downlink

SynchronisationKanalqualitä ts-

prüfung

0,417 ms

10 m s

160 ms

4 s

0,417 ms

0,368 ms

Downlink Uplink




� Average transmission power:� Mobile with one active call: 250mW*0,368ms/10ms ≈ 10 mW

� Base station without active call: 250mW*0,083ms/10ms ≈ 2 mW

� Base station with 1 one active call: 250mW*0,368ms/10ms ≈ 10 mW

� Base station with 2 active calls: 250mW*2*0,368ms/10ms ≈ 20 mW

� Max. power of base stations ≈ 250 mW

� typical DECT-spectra:9 out of 10 channels active




Typical exposure

�Due to mobile close to headDue to small average power (about 10 mW), well below partial body limits

�Complete DECT installationStrongly dependent on actual traffic;

Without active speech very small, →e.g. in 2 m distance from base station 0.2 V/m, in 5 m distance about 0.08 V/m (limit about 58 V/m)

One active call (1 timeslot uplink, one timeslot downlink), →e.g. both 2 m distance to mobile and base station: about 0,6 V/m (limit about 58 V/m)

Office environment with DECT extension system (>250 MS), measurements at two typical work

places (5 respectively 10m distance to nearby base station), →Maximum average field strength

Working place 1: 0.15 V/m ; Working place 2: 0.1 V/m



WLAN Wireless Local Area Network (1)

� Different standards established IEEE 802.11a,b,g,h (Europe b,g,h)

� ISM-frequency range 2400-2483 MHz (IEEE 802.11 b,g), 5,2-5,83 GHz (IEEE 802.11 a,h),

� maximale burst-transmission power: 100 mW EIRP

� CSMA/CA access to media (no parallel transmission of devices on the same channel)

� Organization of net via Access Point: transmit always short Beacon signal (each 100 ms, about

0.5 ms length)

� Exposure strongly related to transmitted data



WLAN Wireless Local Area Network (2)IEEE 802.11b:

� Frequency range: 2400 MHz – 2483 MHz

� Transmission mode: Direct Sequence Spread Spectrum DSSS

IEEE 802.11g:

� Frequency range: 2400 MHz – 2483 MHz

� Transmission mode: Orthogonal Frequency Division Multiplex (OFDM) 52 carriers + 4 pilots

802.11b

802.11g

t

2402 2407 2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2462 2467 2472 2477 2482

Beispiel mit 3 parallelen WLANs nach IEEE 802.11g auf den Kanälen 1, 7, 13

Beispiel für Konfigurationen mit 2 parallelen WLANs auf Kanälen 3 und 10

16,56 MHz 22 MHz

OFDM (6, 9, 12, 18, 24, 36, 48 , 54 Mbps) DSSS (1, 2, 5,5, 11 Mbps)

OFDM (6, 9, 12, 18, 24, 36, 48 , 54 Mbps)DSSS (1, 2, 5,5, 11 Mbps)

WLAN Kanal Nr. 1 2 3 4 5 6 7 8 9 10 11 12 13




Typical exposure:

Channel Power MessungHöheMessposition

[cm] S *)

[mW/m2]rel. zum

Ref.wert [%]

185 0,363 0,0036

165 0,272 0,0027

145 0,307 0,0031

125 0,193 0,0019

105 0,325 0,0032

85 0,272 0,0027

räumlicher

Mittelwert0,289 0,0029

Access Point Antenne

Notebook (Client)

⇒⇒⇒⇒ Limited exposure (also due to transmitted power)




SAR due to devices operated close to the body:

⇒⇒⇒⇒ Exceeding of SAR limits very unlikely

Integrierte SMD-

Antennenelemente

vereinfachte Nachbildung

der integrierten SMD-Antennen(linkes Element ohne Gehäuse bzw. Substrat dargestellt)



Bluetooth� For small data rates and short distances (about 500 kbit/s, around 100m)

� ISM-frequency band 2400-2483 MHz (79 channels, 1 MHz separation)

� Frequency Hopping Spread Spectrum FHSS

� maximum burst-transmission power: 3 classes 1 mW, 10 mW, 100 mW EIRP

� Master slave approach (no parallel transmission)

� Exposure strongly dependent on data transfer, similar to WLAN for class 1 devices



Base stations





Exposure assessment in Salzburg

Selection criteria for base stations

� 1. class: Roof mounted stations in urban areas

� 2. class: Antennas on masts

� 3. class: Microcells

At least 1 base station/ class per provider




Methods

� Simulations used to find places of highest exposure in places of sensitive use in

an area of 200 m around the base stations

� Verification of simulations

� Broadband and frequency selective Prescan

� Final measurement according to Add3D procedure

� Determination of „extrapolation to reference operating mode“, inclusion of

uncertainty



Exposure Assessment in Salzburg

Example for simulation (OFCOM)




ResultsNummer desSendestandortes

Bezeichnung desSendestandortes

Max. Summenwert[mW/m²]

Max. Summenwert[V/m]

1 Liefering 0,356 0,3662 Grazer

Bundesstrasse2,092 0,888

3 Gaisberg 0,0036 0,03684 Vogelweider-

strasse2,654 1,00

5 Ernst - Greinstrasse 2,368 0,9456 Ginzkeyplatz 8,307 1,777 Gaswerkstrasse 39,618 3,8658 Friedhofstrasse 0,098 0,1929 Bachstrasse 1,048 0,62910 Hübnergasse 21,330 2,83611 Berchtesgardener-

strasse0,915 0,587

12 Maria -Cebotaristrasse

1,314 0,704

13 Makartplatz 0,164 0,248



Exposure Assessment



RF - Range

Assessment of undisturbed field strengths

(for comparison with reference values)

Minimum distance between source and body required

Broadband-

Measurementfrequsel.

Meas.

SAR Assessment

(to compare with basic restrictions)

coupling (very low distance)

Between source and body

Numerical

Calculation

Numerical

Calculation

Measurement only in simplified

homogeneous phantom

possible

Measurement

in Farfield

E or H

Measurement

in Nearfield

E and H

Broadband-

Measurement

frequencysel.

Measurement



Broadband Measurement Devices – Field Probes

� Show rms value (in some cases also peak value and average) of exposure within

sensitive range of probe

� Easy to handle

� No information of spectral content of exposure

� Usually not very sensitive Feldsonde mit

separater Verstärker/Anzeigeeinheit

Sondenkopf (enthält Dipol-/Spulentriple und Detektordioden)

Vorverstärker

Trag- und Schutzrohr (enthält hochohmige Zulietungen)

Verbindungskabel (Lichtwellenleiter)

Anzeigeeinheit (mit Messbereichs-

umschalter) Griff

Anzeigeeinheit mit integriertem Verstärker (dient gleichzeitig als Griff)

Feldsonde mit integrierter Verstärker/Anzeigeeinheit

(enthält hochohmige Zuleitungen)



Equipment for Frequency Selective Analysis

� Precision antennas and spectrum analyser

� Requires specific knowledge on equipment and signal to be measured

� Spectral content known

� Sensitive (small signals can be assessed)

� Handling requires more effort compared to broadband systems

Spektrum Analysator

Präzisions-

Messantenne

Messkabel



Conclusions

� Most of the typical environmental sources cause small exposure compared to limits

� Exposure assessment often sophisticated - for some types of technologies exposure assessment procedures are well advanced, e.g. GSM, DECT or UMTS, for others in the process of development, e.g. WiMax

� Some new and future technologies are challenging in respect of exposure assessment, e.g. UWB

� Selection of adequate equipment for the exposure assessment crucial

� Due to new developments exposure patterns will change in the future – more technologies will be operated, more devices will operate closer to the body, the nets might become denser

� Exposure assessment approaches of epidemiological studies should take these developments into account



Thank you for your attention!

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