Are mobile phones safe?

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Are mobile phones safe?

• Protons for Breakfast
• Week 5

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In the event of an alarm sounding
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How it all fits together

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What this evening is about

• What do we mean by safe?
• How do mobile phones work?
• What is the hazard?
• How do electromagnetic waves interact with
  matter?
• SAR
• Microwave Ovens SAR
• Mobile Phone SAR
• Are mobile phones safe?

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WarningThe word radiation

• The word radiation means
• Anything which radiates on ray-like paths
• Could be
• Sound
• Radio
• Light
• Infra-red light
• Particles or waves emitted from the nuclei of
  atoms
• Nuclear Radiation

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Safe?

• 1. What do we mean by safe?

Picture Credit Lessemf http//www.lessemf.com/mw
-oven.html
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Mobile Phones

• 2. How do mobile phones work?

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Mobile Phones (1) Magic?

• Any sufficiently advanced technology is
  indistinguishable from magic
• Arthur C. Clarke

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Mobile Phones (2)Not magic

• Each colour represents a base station operating
  at a slightly different frequency

• Mobile Phones are radio phones
• Operating frequency is in the microwave region of
  the spectrum
• Handset power is kept to a minimum by having a
  network of local transmitters and receivers
• 20,000 base stations in UK

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Mobile Phones (3)Recognise the masts?

• Each cell has a transmitter and receiver mast
• Notice the typical three way structure

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Mobile Phones (4)New 3G Masts

• Photo Credit Brighton and Hove Green Party

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Mobile Phones (4)Linking to base stations

• Masts broadcast with a power of between 60 watts
  to 120 watts
• Handsets broadcast with a power of about 1 watt
• Handsets send 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

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Mobile Phones (5)Making a mobile-to-mobile call

• Its complicated!

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Mobile Phones (6)Digital encoding
Sound

• Hello! How are you?

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Mobile phone Safety

• The safety issues surrounding mobile phones
  concern
• the interactions of the microwaves emitted by
• mobile phones
• base stations
• with human tissue

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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

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Mobile Phones

• 3. How do electromagnetic waves interact with
  matter?

?
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Electromagnetic spectrum
Radio TV
Infra Red
Gamma-Rays
Ultra Violet
Microwaves
X-Rays
Microwaves 0.8 GHzto 1000 GHz
Non-ionising Radiation (generally not so bad)
Ionising Radiation (generally bad)
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Frequency (Hertz)
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What absorbs the energy?Natural
FrequencyResonance

• If electrons (very light) jiggle
• natural frequency is in the visible or ultra
  violet range
• If atoms (10000 times heavier) jiggle
• natural frequency is in the infra-red/microwave
  range
• If whole molecules (Many times heavier) jiggle
• natural frequency is in the RF/Microwave range

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Waves Matter (6)Summary

• Electromagnetic waves interacting with matter can
  be
• Reflected
• Absorbed
• Transmitted
• Exactly what happens depends on
• the frequency of the electric field
• the natural frequencies of the atoms and
  molecules
• Microwaves emitted by mobile phone systems
• Are absorbed by human tissue

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Atoms, Molecules MaterialsNatural
FrequencyResonance
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Waves Matter (3)

• When electromagnetic waves are absorbed by
  matter

Atoms jiggle faster i.e. increase their
temperature.
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Waves Matter (5)

• When an electromagnetic wave interacts with
  matter
• Some absorption
• Some reflection
• Some transmission

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How much energy gets absorbed?
4. How much energy is absorbed?

• S.A.R.

Specific Energy Absorption Rate
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Terminology (6)Summary

• Power
• watts
• Intensity
• watts per square metre
• Specific energy Absorption Rate (SAR)
• watts per kilogram

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Powerwatts

• Power is measure of
• the total amount of energy emitted per second

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Intensity watts per square metre

• Intensity is measure of
• the amount of energy flowing across per unit area
  per second
• It is like brightness
• A light looks less bright as one moves further
  away from it, because the same power is spread
  over a larger area

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Specific energy Absorption Rate (SAR) watts per
kilogram

• Measures energy absorbed per kilogram per second
• A high SAR means
• a substance heats up quickly
• A low SAR means
• a substance heats up slowly
• SAR is a property of
• an emitting device
• in a particular position with respect to
• an absorbing substance

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Specific energy Absorption Rate (SAR) watts per
kilogram

• SAR is a property of
• an emitting device
• in a particular position with respect to
• an absorbing substance

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Terminology (5)Specific energy Absorption Rate
(SAR) watts per kilogram

• SARExample using light
• rather than microwaves

• 1 cm from 20 W source
• 20 W absorbed in hand
• Intensity 8000 watts per square metre
• SAR 200 watts per kilogram

• 10 cm from 20 W source
• 2 W absorbed in hand
• Intensity 200 watts per square metre
• SAR 20 watts per kilogram

• 1 metre from 20 W source
• 0.02 W absorbed in hand
• Intensity 5 watts per square metre
• SAR 0.2 watts per kilogram

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Terminology (6)Summary

• Power
• watts
• Intensity
• watts per square metre
• Specific energy Absorption Rate (SAR)
• watts per kilogram

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Microwave Hazard
The potential hazard from mobile phones and other
wireless devices arises from the absorption of
microwave radiation

• Mobile phones
• only emit a watt or two
• so little power it makes experiments difficult

• Microwave ovens
• emit a few hundred watts
• makes experiments easy

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Microwave Ovens
5. Microwave ovens
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Electromagnetic spectrum
Gamma-Rays
Radio TV
Infra Red
Ultra Violet
Microwaves
X-Rays
Microwaves

• Microwaves
• From
• 0.8 GHzto
• 1000 GHz

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Microwave Ovens The absorption of microwave
energy by liquid water
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Absorption (1)Too strong

• If power were absorbed too strongly,
• Microwaves would only penetrate a short distance
• Surface would be heated
• Inside would remain uncooked

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Absorption (2) Too weak

• If power were absorbed too weakly,
• Microwaves would go right through
• No cooking

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Absorption (3)

• If power is absorbed just right,
• Microwaves penetrate about 5 cm (2 inches)
• Cooks the outer 5 cm of the food
• Good enough for most cases

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Microwave OvensSummary

• A microwave oven cooks food by heating it
• The heating comes from
• intense waves at 2.45 GHz
• rather than
• a wide spectrum of waves at infra red
  frequencies.
• Frequency chosen because of absorption properties
  of water molecules at that frequency.

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Microwave GenerationCavity Magnetron Valve
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Microwave Ovens
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Microwave Ovens
Inside a microwave oven
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Microwave Power

• Power
• This is a 700 watt oven
• Think of 7 x 100 watt light bulbs

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MicrowaveElectric field

• 700 watts
• Around 140 000 volts per metre
• Look what happens to a CD

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Microwave Intensity

• 700 watts
• transmitted into an area of around 1/25th square
  metre
• 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?

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A Cautionary Tale
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 -
Dont try this at home!
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Microwave OvenSAR inside oven

• Inside
• 700 watts
• Absorbed in 1 kg of water SAR 700 watts per kg
• Your brain weighs about a kilogram!
• QUESTION After 1 minute, what temperature rise
  results from an SAR of 700 watts per kg?

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Microwave Ovens (13) SAR
SAR Wattsper kilogram Temperature Rise in 1 kg of Brain Fluid
Microwave 700 8 ºC (ish)
Mobile Phone 1 Cant be measured directly
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Mobile Phones

• Back to Mobile Phones
• 6. Mobile Phone SAR

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Mobile Phones (6) Typical SAR with phone near
the head

• Typical figures

Power Intensity Maximum SAR
Watts Watts per square metre Wattsper kilogram
1 200 1

• SAR Averaged over 10 grams
• By law must be less than 2 watts per kilogram

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Mobile Phones (7) Is this SAR very big?

• Microwave Oven heating
• SAR about 700 W per 1 kg
• 8 ºC rise after 1 minute?

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Mobile Phones (8) Your telephone

• Look in the small print!

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Mobile Phones

• 7. Base Station SAR

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Mobile Phones (11) Base Stations

• Power

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Mobile Phones (12) http//www.sitefinder.ofcom.or
g.uk/
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EIRO
How this is specified

• Equivalent
• isotropic
• Radiated
• Output

60 W
Actual Pattern of Emitted Radiation
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Mast near my childrens school

• Power
• 30 dBW
• 1000 W
• Equivalent isotropic Radiated Output
• 60 W to 120 W in actual power

SAR 0.001 Watts per kilogram
0.3 Watts per square metre
0.01 Watts per square metre
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Mobile Phones (13) Comparison of handsetsand
base stations
Power Intensity Maximum SAR
Watts Watts per square metre Wattsper kilogram
Handset 1 200 About 1
Base Station 60 0.01 About 0.001

• Base station SAR is extremely low
• but you cant choose whether you want it or not!

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WiFi (11) Wireless Networking

• WiFi
• 802.11(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
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Mobile Phones (13) Comparison of handsetsand
base stations
Power Intensity Maximum SAR
Watts Watts per square metre Wattsper kilogram
Handset 1 200 About 1
Base Station 60 0.01 About 0.001
Wi Fi 0.1 lt 0.01 About 0.0001
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Mobile Phones

• 7. Are Mobile Phones Safe?

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Mobile Phones (14) SAR and Safety

• NPL can estimate the SAR for a mobile phone in a
  standard position near a simulated head
• e.g. 1.2 watts per kilogram
• NPL cant advise on whether that dose is safe

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Mobile Phones (14) SAR and Safety

• Health Protection Agency
• Radiation Section
• formerly the National Radiological Protection
  Board
• Based on ICNIRP guidelines
• International Commission on Non-Ionising
  Radiation Protection
• determines what we believe is safe

Is 2 watts per kilogram a safe value of SAR? Is
exposure to 10 watts per square metre safe?
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Mobile Phones (15) 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 experiment
• Experiments are very hard

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Mobile Phones (17) Are mobile phones safe?

• Stewart Report
• A group of non-industry related experts
• Gave rise to MTHR
• Mobile Telecommunications and Health Research
• ONGOING Research Program
• Funded 5050 government industry

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Mobile Phones (18) Are mobile phones safe?
Stewart Report

• Mobile Phones are pretty safe
• There may be effects of Mobile Phones
• Precautionary Approach
• More research please
• Children
• Driving

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Mobile Phones

• What do we mean by safe?
• Our knowledge is not complete,
• There is some risk (or potential risk) that
  mobile phone technology could be associated with
  adverse health effects.
• As long as we use mobile phones, the risk will
  never be zero

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Mobile Phones (22) What could we do?

• Ban mobile phones ?
• The Precautionary principle
• How many deaths or cancers would be acceptable?
• 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 power
• Increase the number of masts
• Ban mobile phone use while driving ?
• Done has it been effective?
• Nothing ?

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Mobile Phones (23) What should we do?

• Go forth and DECIDE!
• Is current research enough?
• What else if anything - should we do?

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On-line Resources

• www.protonsforbreakfast.org
• This PowerPoint presentation.
• Handouts as a pdf file
• blog.protonsforbreakfast.org
• Me going on about things
• links.protonsforbreakfast.org
• Links to other sites resources

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Goodnight
See you next week to discuss Nuclear Power
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Perception of risk
More willing to take risk Less willing to take risk Example
Benefits Direct Indirect Base Stations/ Mobile Phones

• Risk is expressed mathematically,
• but our judgement of risk is not mathematical

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