Are mobile phones safe?

Protons for Breakfast

Week 5

In the event of an alarm sounding…

How it all fits together…

Electromagnetic waves

Atoms

Heat

Electricity

What this evening is about…

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?

Warning…The 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

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".

Mobile Phones

1. How do mobile phones work?

Mobile Phones (1) Magic?

Any sufficiently advanced technology is indistinguishable from magic

Arthur C. Clarke

Mobile Phones (2)Not magic

• 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

• 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

Mobile Phones (4)New 3G Masts

Photo Credit Brighton and Hove Green Party

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 Maximum Power of 2 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

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

Its complicated!

Network Control

Knows in which cell every telephone is

Originating Telephone

Receiving Telephone

Mobile Phones (6)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

Mobile Phones (6)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 1Orange

T Mobile (Virgin)

Anatomy of a GSM Signal

Mobile phone 2G or GSM phone

217 Pulses per second per telephone call

217 Pulses per second

Each frequency channel can carry 7 calls

Mobile phone 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

• ‘WiFi’ Wireless Networking• Bluetooth devices• Wireless keyboards and mice• DECT cordless phones• Baby Monitors• ‘Walkie Talkie’

And its not just mobile phones!

• All involve electromagnetic waves in the radio and microwave part of the spectrum

Mobile Phones

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)

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

Waves & Matter (5)

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

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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Frequency

Atoms, Molecules & Materials‘Natural’ FrequencyResonance

• Well below the natural frequency

• Not much absorption

• Well above the natural frequency

• Not much absorption

• Near the natural frequency

• Absorption

Waves & Matter (3)

When electromagnetic waves are ‘absorbed’ by

matter …

Atoms jiggle faster:

i.e. increase their temperature.

Heat

Electricity

Electromagnetic waves

Atoms

How much energy gets absorbed?

S.A.R.Specific Energy Absorption Rate

3. How much energy is absorbed?

Terminology (6)Summary

• Power– watts

• Intensity– watts per square metre

• Specific energy Absorption Rate (SAR)– watts per kilogram

Terminology (5)Specific energy Absorption Rate (SAR) 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

SAR:Example 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

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

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 Oven

Microwave Oven

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Microwave Ovens The absorption of microwave energy by liquid water

• Well below the natural frequency

• Not much absorption

• Well above the natural frequency

• Not much absorption

• Near the natural frequency

• Absorption

2.4 GHz

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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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

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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 food– Good enough for most cases

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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 • rather than

– 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

MicrowaveElectric field

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

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?

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 -

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 Ovens (13) Comparison 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)

Mobile Phones

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!

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

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

Power Intensity Maximum

SAR

Watts Watts per square metre

Wattsper kilogram

1 200 1

• Typical figures

Mobile Phones

7. Base Station SAR

Mobile Phones (11) Base Stations

• Power

6 degrees

50 m to 200 m

Mobile Phones (12) http://www.sitefinder.ofcom.org.uk/

EIRO

Equivalent isotropic RadiatedOutput

Actual Pattern of Emitted Radiation

60 W

How this is specified

1000 W EiRO

Actual Pattern of Emitted Radiation

Mast near my children’s school Power• 30 dBW • 1000 W • Equivalent isotropic

Radiated Output• 60 W to 120 W in

actual power

0.3Watts per square metre

0.01Watts per square metre

SAR 0.001Watts per kilogram

Mobile Phones (13) Comparison of handsetsand base stations

• Base station SAR is extremely low– but you can’t choose whether you want it or not!

Power Intensity Maximum

SAR

Watts Watts per square metre

Wattsper kilogram

Handset 1 200 About 1

Base Station 60 0.01 About 0.001

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

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 < 0.01 About 0.0001

Mobile Phones

4. Are Mobile Phones Safe?

Mobile Phones (14) SAR and Safety

Health Protection Agency• Based on ICNIRP guidelines

http://www.icnirp.de/documents/emfgdl.pdf – International Commission on Non-Ionising Radiation Protection– determines 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

Is 2 watts per kilogram a safe value of SAR?

Is exposure to 10 watts per square metre safe?

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

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 50:50 government & industry

Mobile Phones (18) Are mobile phones safe? 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?

R Luria, I Eliyahu, R Hareuveny, M Margaliot, N, Meiran

Cognitive Effects of Radiation Emitted by Cellular Phones: The influence of exposure side and time

Biolectromagnetics 30: 198-204 (2009)

Possibility#1

No MatchClick with Left Hand

MatchClick with Right Hand

Task Completed with PhoneOn LEFTOn RIGHTOFF

RESULTS

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: mill

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Block

LEFT HAND RESPONSE

'No Match' RESPONSE

1 hour 1 hour

RESULTSWith Uncertainty

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SHAMLEFT EXPOSURERIGHT EXPOSURE

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LEFT HAND RESPONSE

'No Match' RESPONSE

Only these two points have statistical significance

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

Possibility#2

PET ScanThis device can see you think!

Glucose metabolism in this area appears to have been affected

Mobile Phones (22) 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 power– Increase the number of masts

• Ban mobile phone use while driving ?– Done: has it been effective?

• Nothing ?

Mobile Phones (23) What should we do?

What– if anything - should we do?

Go forth and DECIDE!

On-line Resources

• www.protonsforbreakfast.org –This PowerPoint ™ presentation.–Handouts as a pdf file

• protonsforbreakfast.wordpress.com–Me going on about things

• links.protonsforbreakfast.org –Links to other sites & resources

See you next week to discuss Nuclear Power

Goodnight

Mobile Phones

Unused Slides

Safe?

1. What do we mean by ‘safe’?

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

Risk is expressed mathematically,

but our judgement of risk is not mathematical

Perception of riskMore willing

to take risk

Less willing

to take risk

Example

Benefits Direct IndirectBase Stations/

Mobile Phones

Technology Familiar UnfamiliarCars/

Mobile Phones

Exposure Voluntary InvoluntaryBase Stations/

Mobile Phones

Exposure Fair UnfairPoverty/

Wealth

Exposure Personal ControlNo Personal Control

Driver/

Pedestrian

Consequence Not Dreaded DreadedCancer/

Broken bone