Table of Content Environmental Exposures to RF · Environmental Exposures to RF /Neubauer Mobile...
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128.3.2008 – 4th EBEA Course
Environmental Exposures to RF /Neubauer
Environmental Exposures to RF
Georg Neubauer
228.3.2008 – 4th EBEA Course
Environmental Exposures to RF /Neubauer
Table of Content
� Environmental exposures to RF
sources
� Mobile communication standards
� Measurement methods
� Conclusions
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Environmental exposure to RF sources
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Natural Sources
� Sun
� Cosmic Microwave
Radiation
� Lightning
� Earth
Source:
www.magnetfeld.de
www.alterlaa.net
www.rasputin.de
www.space-odyssey.de
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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
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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
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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
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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
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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
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Mobile Communication Technologies
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LAN
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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
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Wireless Communication
For the household and office
DECT, WLAN, Bluetooth
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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)
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DECT Digital Enhanced Cordless Telecommunication (2)
� 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
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DECT Digital Enhanced Cordless Telecommunication (3)
� 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
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DECT Digital Enhanced Cordless Telecommunication (4)
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
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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
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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
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WLAN Wireless Local Area Network (3)
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)
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WLAN Wireless Local Area Network (4)
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)
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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
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Base stations
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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
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Exposure assessment in Salzburg
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
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Exposure Assessment in Salzburg
Example for simulation (OFCOM)
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Exposure assessment in Salzburg
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
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Exposure Assessment
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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
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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)
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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
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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
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Thank you for your attention!