protons for breakfast are mobile phones safe? week 5
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Protons for Breakfast Are Mobile Phones Safe? Week 5. November 2011. In the event of an alarm sounding…. This evening…. 0. The Media! How do mobile phones work? What is the hazard? How do electromagnetic waves interact with matter? SAR Microwave Ovens Mobile Phone - PowerPoint PPT PresentationTRANSCRIPT
Protons for Breakfast
Are Mobile Phones Safe?
Week 5
November 2011
In the event of an alarm sounding…
This evening…
0. The Media!1. How do mobile phones work?
What is the hazard?2. How do electromagnetic waves interact
with matter?3. SAR
• Microwave Ovens• Mobile Phone
4. Are mobile phones safe?
The word ‘radiation’
• The word ‘radiation’ meansAnything which ‘radiates’ on ray-like paths
• Could be SoundRadioLightInfra-red lightParticles or waves emitted from the nuclei of atoms
Nuclear Radiation
Media
Media
Sunday, 20 January 2008
It also complements other recent research. A massive study, following 1,656 Belgian teenagers for a year, found most of them used their phones after going to bed. It concluded that those who did this once a week were more than three times – and those who used them more often more than five times – as likely to be "very tired".
1. How do mobile phones work?
Magic?
Any sufficiently advanced technology is indistinguishable from magic
Arthur C. Clarke
Not magic
• Mobile Phones are ‘radio’ phones
• Operating at microwave frequencies
• Handset power minimised by having a network of local transmitters and receivers
• 50,000 base stations in UK
Roughly hexagonal cells
Mast
• Each colour represents a base station operating at a slightly different frequency
Mobile Phones (3)Recognise the masts?
• Each cell has a transmitter and receiver mast • Notice the typical three way structure
3G Masts
Photo Credit Brighton and Hove Green Party
Linking to base stations
• Mast power between 60 watts and 120 watts
• Handset power less than 1 watt
• Handset sends signals every few minutes to establish which is the nearest mast
• A central computer• keeps track of all the telephones that are switched on • remembers which cell they are in
Making a mobile-to-mobile call
Its complicated!
Network Control
Knows in which cell every telephone is
Originating Telephone
Receiving Telephone
2G or GSM phone
Hello! How are you?Sound
217 pulses of encoded sound every second No sound: No signal
Encoding to Radio Signal Hello! How are you?
Peak Power 2 W Maximum
Average power is 0.25 W Maximum
Global System for Mobile Communications
2G or GSM phone
Base station Transmitter Frequencies
(MHz)
Handset Transmitter Frequencies
(MHz)
Peak Handset Power(Watts)
Originally licensed to
GSM900 935 - 960 890-915 2O2 (Tesco)
Vodafone (Asda)
GSM1800 1805-1880 1710-1785 1 Orange T Mobile (Virgin)
Anatomy of a GSM Signal
2G or GSM phone
217 Pulses per second per telephone call
217 Pulses per second
Each frequency channel can carry 7 calls
Safety
• The safety issues surrounding mobile phones concern…
• the interactions of the microwaves emitted by mobile phones base stations
with human tissue
6 degrees
50 m to 200 m
And its not just mobile phones!
• ‘WiFi’ Wireless Networking• Bluetooth devices• Wireless keyboards and mice• DECT cordless phones• Baby Monitors• ‘Walkie Talkie’
• All involve electromagnetic waves in the radio and microwave part of the spectrum
2. How do electromagnetic waves interact with matter?
?
Electromagnetic spectrum
1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022
Radio & TVInfra Red
Microwaves
Gamma-Rays
X-Rays
Ultra Violet
Microwaves0.8 GHz
to 1000 GHz
Non-ionising Radiation
(generally not so bad)
Ionising Radiation
(generally bad)
Frequency (Hertz)
Waves & Matter
• When an electromagnetic wave interacts with matter…Some absorption Some reflectionSome transmission
Summary
• Electromagnetic waves interacting with matter can beReflected, absorbed or transmitted
• What happens depends onthe frequency of the electric fieldthe natural frequencies of the atoms and molecules
• Microwaves emitted by mobile phone systemsAre absorbed by human tissue
1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022
Radio & TV
Frequency (Hertz)
Microwaves
Infra Red Ultra Violet
X-rays
Gamma Rays
Electrons in Atoms
Protons in nucleus
Atoms in solids or
molecules
Entire molecules or parts of molecules
Lighter particles
Stronger forces
Waves
What vibrates?
Absorption demo
Frequency
•Well below the natural frequency•Not much absorption
•Well above the natural frequency•Not much absorption
•Near the natural frequency•Absorption
Waves & Matter
• When electromagnetic waves are ‘absorbed’ …• Atoms jiggle faster:
i.e. increase their temperature.
Heat
Electricity
Electromagnetic waves
Atoms
3. How much energy gets absorbed?
S.A.R.Specific Energy Absorption Rate
Terminology
• Powerwatts
• Intensitywatts per square metre
• Specific energy Absorption Rate (SAR)watts per kilogram
• 1 cm from 20 W source 20 W absorbed in hand Intensity 8000 watts per square metreSAR 200 watts per kilogram
• 10 cm from 20 W source 2 W absorbed in hand Intensity 200 watts per square metreSAR 20 watts per kilogram
• 1 metre from 20 W source 0.02 W absorbed in hand Intensity 5 watts per square metreSAR 0.2 watts per kilogram
SAR: Example using lightrather than microwaves
Microwave Hazard
The potential hazard from mobile phones and other wireless devices arises from
the absorption of microwave radiationMobile phones
• only emit a watt or two• so little power it makes
experiments difficult
Microwave ovens• emit a few hundred watts• makes experiments easy
Microwave Ovens
3a. Microwave ovens
Electromagnetic spectrum
1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022
Radio & TVInfra Red
Microwaves
Gamma-Rays
X-Rays
Ultra Violet
Microwaves
Conventional Oven200 °C
Microwave Oven 2.45 GHz
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.01 0.1 1 10 100
Abs
orbt
ion
Frequency
Absorption of microwaves by liquid water
• Well below the natural frequency
• Not much absorption
• Well above the natural frequency
• Not much absorption
• Near the natural frequency
• Absorption
2.45 GHz
Absorption (1)Too strong
• If power were absorbed too strongly,Microwaves would only penetrate a short distanceSurface would be heatedInside would remain uncooked
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.01 0.1 1 10 100
Loss
of e
nerg
y in
wat
er a
t 0
C
Frequency (GHz)
Microwave ovens operate at 2.45 GHz
Absorption (2) Too weak
• If power were absorbed too weakly,Microwaves would go right through No cooking
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.01 0.1 1 10 100
Loss
of e
nerg
y in
wat
er a
t 0
C
Frequency (GHz)
Microwave ovens operate at 2.45 GHz
Absorption (3)
• If power is absorbed just right,Microwaves penetrate about 5 cm (2 inches) Cooks the outer 5 cm of the foodGood enough for most cases
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.01 0.1 1 10 100
Loss
of e
nerg
y in
wat
er a
t 0
C
Frequency (GHz)
Microwave ovens operate at 2.45 GHz
Microwave OvensSummary
• A microwave oven cooks food by heating it
• The heating comes from• intense waves at 2.45 GHz • (Instead of a wide spectrum of waves at infra red frequencies)
Frequency chosen because of absorption properties of water molecules at that frequency.
Microwave Ovens
Inside a microwave oven
Microwave Power
• Power– This is a 700 watt oven– Think of 7 x 100 watt light bulbs
Microwave Electric field
• 700 watts – Around 140 000 volts per metre– Look what happens to a CD
Microwave Intensity
– Between 104 to 105 watts per square metre– (Most intense sunlight around 103 watts per square metre)
– Very Dangerous
Could I have a stupid volunteer
please?
Microwave OvenSAR inside oven
• 700 watts absorbed in 1 kg of water: – SAR = 700 watts per kg
• Question: After 1 minute, how hot would your brain become if subject to an SAR of 700 watts per kg?
Experiment
Microwave OvensComparison with handsets
SAR Wattsper kilogram
Temperature Rise in 1 kg of ‘Brain Fluid’
Microwave 700 8 ºC (ish)
Mobile Phone 1 Can’t be measured directly
Expect 1/700 of microwave temperature riseThe effects of blood flow reduce this further
0.01 °C (ish)
Back to Mobile Phones 3b. Mobile Phone SAR
New StyleOld StyleMobile Phones (14) SAR and Safety
Mobile Phones (8) Your telephone
• Look in the small print!
Typical SAR with phone near the head
• SAR Averaged over 10 grams• By law must be less than 2 watts per kilogram
Power Intensity MaximumSAR
Watts Watts per square metre
Wattsper kilogram
1 200 1
• Typical figures
Base Station SAR
Base Stations
• Power
6 degrees
50 m to 200 m
Base Station Informationhttp://www.sitefinder.ofcom.org.uk/
EIRO
Equivalent isotropic RadiatedOutput
Actual Pattern of Emitted Radiation
60 W
How this is specified
Mast near my children’s old schoolPower• 30 dBW • 1000 W • Equivalent isotropic
Radiated Output• 60 W to 120 W in
actual power
1000 W EiRO
Actual Pattern of Emitted Radiation
0.3Watts per square metre
0.01Watts per square metre
SAR 0.001Watts per kilogram
Comparison of handsetsand base stations
• Base station SAR is extremely lowbut you can’t choose whether you want it or not!
Power Intensity MaximumSAR
Watts Watts per square metre
Wattsper kilogram
Handset 1 200 About 1
Base Station 60 0.01 About 0.001
Wireless Networking
• WiFi802.11(b), 802.11(g), 802.11(n)
• Operates at 2.4 GHz
Power Intensity(at 1 metre)
SAR(at 1 metre)
Watts Watts per square metre
Wattsper kilogram
0.1 Less than 0.01 About 0.0001
Comparison of handsetsand base stations and wi-fi
Power Intensity MaximumSAR
Watts Watts per square metre
Wattsper kilogram
Handset 1 200 About 1
Base Station 60 0.01 About 0.001
Wi Fi 0.1 < 0.01 About 0.0001
4. Are Mobile Phones Safe?
SAR and Safety
Health Protection Agency• Based on ICNIRP guidelines
http://www.icnirp.de/documents/emfgdl.pdf International Commission on Non-Ionising Radiation Protectiondetermines what we believe is safe
• How do they do that?• They determine a borderline safe level• Divide by 10 for occupational exposure• Divide by another factor 5 for general public exposure
What are the risks?
• Basic safety assumption is that the main effect of exposure to microwaves is thermal
• Are there ‘non-thermal’ effects?If so are they harmful?Normal thermal vibrations are much larger than vibrations induced by microwaves emitted by mobile phones.
• Question of safety must be resolved by experimentExperiments are very hard
Are mobile phones safe?
Stewart Report • A group of non-industry related experts
Gave rise to MTHRMobile Telecommunications and Health Research
• ONGOING Research Program • Funded 50:50 government & industry
Stewart Report
Mobile Phones and their networks are ‘pretty’ safe
There may be ‘effects’
Precautionary Approach: More research
please
Children Driving
Mobile Phones
Suppose we discovered ‘an effect’:What might it look like?
Nora D. Volkow, Dardo Tomasi, Gene-Jack Wang, Paul Vaska, Joanna S. Fowler, Frank Telang, Dave Alexoff, Jean Logan, Christopher Wong,
Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Metabolism
Journal of the American Medical Association, February 23, 2011—Vol 305, No. 8
PET ScanThis device can see you think!
Glucose metabolism in this area appears to have been affected
What could we do?What should we do?
In smaller groups
• Please come up with some
questions, and suggestions
• We will gather these together and
then ask the experts
You decide!
On-line Resources
• www.protonsforbreakfast.org This PowerPoint ™ presentation.Handouts as a pdf file
• blog.protonsforbreakfast.org Links to other sites & resourcesMe going on about things
See you next week to discuss Nuclear Power
Goodnight
Mobile Phones
Unused Slides
Perception of risk
Risk is expressed mathematically, but our judgement of risk is not mathematical
More willing to take risk
Less willing to take risk
Example
Benefits Direct Indirect Base Stations/Mobile Phones
Technology Familiar Unfamiliar Cars/Mobile Phones
Exposure Voluntary Involuntary Base Stations/Mobile Phones
Exposure Fair Unfair Poverty/Wealth
Exposure Personal Control No Personal Control
Driver/Pedestrian
Consequence Not Dreaded Dreaded Cancer/ Broken bone
Electromagnetic waves
Electricity
Heat
How it all fits together…
Atoms
A Cautionary Tale
Don’t try this at home!
August 14, 2002 I don't want to sound like I know everything in the world or even like I know quite a lot. But you had a question regarding “If a microwave oven door were to open while it was still on, what would happen? Could it hurt you?- JP” Well ..Having the thought process that I have, kinda how should I put it? ...Stupid? or inventive or even in-between. Well, my microwave door did happen to come off. Magic Chef 900-watt microwave. Well, I did my best to try to fix it but the hinge on one side did not attach properly, therefore having a gap between the door and the appliance. Being me (stupid) I wondered if it would burn fast or would it gradually warm up. I slid my finger between...You probably dying to hear what happened... But it didn't gradually warm up at all. It was instant heat! It didn't scar me or anything like that, but sure scared the H*** out of me to find out it got so hot so quick. I didn't get any blisters either. But it just burned like touching something hot on the tip of my finger being that is the only thing I put in. Well you know the old adage, "You learn from your mistakes", stands true. lol -
Mobile Phones
Suppose we discovered ‘an effect’:What might it look like?
R Luria, I Eliyahu, R Hareuveny, M Margaliot, N, MeiranCognitive Effects of Radiation Emitted by Cellular Phones:
The influence of exposure side and timeBiolectromagnetics 30: 198-204 (2009)
Possibility#1
No MatchClick with Left Hand
MatchClick with Right Hand
Task Completed with PhoneOn LEFTOn RIGHTOFF
RESULTS
700
750
800
850
900
950
1000
1050
1100
1 2 3 4 5 6 7 8 9 10 11 12
SHAMLEFT EXPOSURERIGHT EXPOSURE
Res
pons
e Ti
me:
mill
isec
onds
Block
LEFT HAND RESPONSE
'No Match' RESPONSE
1 hour 1 hour
RESULTSWith Uncertainty
700
750
800
850
900
950
1000
1050
1100
1 2 3 4 5 6 7 8 9 10 11 12
SHAMLEFT EXPOSURERIGHT EXPOSURE
Res
pons
e Ti
me:
mill
isec
onds
Block
LEFT HAND RESPONSE
'No Match' RESPONSE
Only these two points have statistical significance
What could we do?
• Ban mobile phones ?The ‘Precautionary principle’Could there be some harm caused?How many lives are saved by mobile phones?
• Reduce mobile phone power ?Increase the number of mobile phone masts
• Reduce mast power ?Increase the mobile phone handset powerIncrease the number of masts
• Ban mobile phone use while driving ?Done: has it been effective?
• Nothing ?