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".
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 52,500 base stations in UK 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 GSM900935 - 960890-9152 O 2 (Tesco) Vodafone (Asda) GSM18001805-18801710-17851 Orange T Mobile (Virgin)
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
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 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 910 10 11 10 12 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 21 10 22 Radio & TV Infra Red Microwaves Gamma- Rays X-Rays Ultra Violet Microwaves 0.8 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 reflection Some transmission
Summary Electromagnetic waves interacting with matter can be Reflected, absorbed or transmitted 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
1 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 910 10 11 10 12 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 21 10 22 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 Power watts Intensity watts 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 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 SAR: Example using light rather than microwaves
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
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 distance Surface would be heated Inside would remain uncooked
Absorption (2) Too weak If power were absorbed too weakly, Microwaves would go right through No cooking
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
Microwave Ovens Summary 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 Comparison with handsets SAR Watts per kilogram Temperature Rise in 1 kg of Brain Fluid Microwave7008 ºC (ish) Mobile Phone1 Cant be measured directly Expect 1/700 of microwave temperature rise The effects of blood flow reduce this further 0.01 °C (ish)
New Style Old Style Mobile 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 PowerIntensityMaximum SAR WattsWatts per square metre Watts per kilogram 12001 Typical figures
Base Station Information http://www.sitefinder.ofcom.org.uk /
EIRO Equivalent isotropic Radiated Output Actual Pattern of Emitted Radiation 60 W How this is specified
Mast near my childrens old school Power 30 dBW 1000 W Equivalent isotropic Radiated Output 60 W to 120 W in actual power 0.3 Watts per square metre 0.01 Watts per square metre SAR 0.001 Watts per kilogram
Comparison of handsets and base stations Base station SAR is extremely low but you cant choose whether you want it or not! PowerIntensityMaximum SAR WattsWatts per square metre Watts per kilogram Handset1200About 1 Base Station600.01About 0.001
Wireless Networking WiFi 802.11(b), 802.11(g), 802.11(n) Operates at 2.4 GHz PowerIntensity (at 1 metre) SAR (at 1 metre) WattsWatts per square metre Watts per kilogram 0.1Less than 0.01About 0.0001
Comparison of handsets and base stations and wi-fi PowerIntensityMaximum SAR WattsWatts per square metre Watts per kilogram Handset1200About 1 Base Station600.01About 0.001 Wi Fi0.1< 0.01About 0.0001
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
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
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
Stewart Report Mobile Phones and their networks are pretty safe There may be effects Precautionary Approach: More research please ChildrenDriving
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, 2011Vol 305, No. 8
PET Scan This 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 & resources Me going on about things
See you next week to discuss Nuclear Power Goodnight
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 DirectIndirect Base Stations/ Mobile Phones Technology FamiliarUnfamiliar Cars/ Mobile Phones Exposure VoluntaryInvoluntary Base Stations/ Mobile Phones Exposure FairUnfair Poverty/ Wealth Exposure Personal Control No Personal Control Driver/ Pedestrian Consequence Not DreadedDreaded Cancer/ Broken bone
Electromagnetic waves Electricity Heat How it all fits together… Atoms
A Cautionary Tale Dont 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, Meiran Cognitive Effects of Radiation Emitted by Cellular Phones: The influence of exposure side and time Biolectromagnetics 30: 198-204 (2009) Possibility#1
RESULTS With Uncertainty 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 power Increase the number of masts Ban mobile phone use while driving ? Done: has it been effective? Nothing ?
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