Protons for Breakfast Are Mobile Phones Safe? Week 5 March 2013 In the event of of… a new ice age… 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’ 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". 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 • Each colour represents a base station operating at a slightly different frequency Roughly hexagonal cells • 52,500 base stations in UK Mast 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 Network Control Its complicated! Originating Telephone Knows in which cell every telephone is Receiving Telephone 2G or GSM phone Global System for Mobile Communications Sound Hello! How are you? Encoding to Radio Signal Hello! How are you? Peak Power 2 W Maximum Average power is 0.25 W Maximum No sound: No signal 217 pulses of encoded sound every second 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 2 O2 (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 Each frequency channel can carry 7 calls 217 Pulses per second 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 Infra Red Radio & TV Microwaves Microwaves 0.8 GHz to 1000 GHz Non-ionising Radiation (generally not so bad) Ultra Violet GammaRays X-Rays Ionising Radiation (generally bad) 1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 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 Waves Radio & TV Infra Red Ultra Violet Microwaves Gamma Rays X-rays What vibrates? Atoms in solids or molecules Electrons in Atoms Entire molecules or parts of molecules Protons in nucleus Lighter particles Stronger forces 1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 Frequency (Hertz) Absorption demo •Well below the natural frequency •Not much absorption •Near the natural frequency •Absorption •Well above the natural frequency •Not much absorption Frequency Waves & Matter • When electromagnetic waves are ‘absorbed’ … • Atoms jiggle faster: i.e. increase their temperature. Electricity Atoms Heat Electromagnetic waves 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 Example using light • 1 cm SAR: from 20 W source 20 W absorbed in hand rather than microwaves 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 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 Infra Red Radio & TV Ultra Violet GammaRays Microwaves X-Rays Microwave Oven 2.45 GHz Conventional Oven 200 °C 1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 Absorption of microwaves by liquid water 0.4 • 0.35 • • Near the natural frequency Absorption • Absorbtion 0.3 Well above the natural frequency Not much absorption 0.25 0.2 0.15 • • Well below the natural frequency Not much absorption 0.1 2.45 GHz 0.05 0 0.01 0.1 1 Frequency 10 100 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 0.4 0.35 0.3 0.25 Microwave ovens operate at 2.45 GHz 0.2 0.15 0.1 0.05 0 0.01 0.1 1 Frequency (GHz) 10 100 Absorption (2) Too weak • If power were absorbed too weakly, Microwaves would go right through No cooking 0.4 0.35 0.3 0.25 Microwave ovens operate at 2.45 GHz 0.2 0.15 0.1 0.05 0 0.01 0.1 1 Frequency (GHz) 10 100 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 0.4 0.35 0.3 0.25 Microwave ovens operate at 2.45 GHz 0.2 0.15 0.1 0.05 0 0.01 0.1 1 Frequency (GHz) 10 100 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 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 Oven SAR 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 Comparison with handsets SAR Watts per kilogram Temperature Rise in 1 kg of ‘Brain Fluid’ Microwave 700 8 ºC (ish) Mobile Phone 1 Can’t be measured directly 0.01 °C (ish) Expect 1/700 of microwave temperature rise The effects of blood flow reduce this further Back to Mobile Phones 3b. Mobile Phone SAR Mobile Phones (14) SAR and Safety Old Style New Style Mobile Phones (8) Your telephone • Look in the small print! Typical SAR with phone near the head • Typical figures Power Intensity Maximum SAR Watts Watts per square metre Watts per kilogram 1 200 1 • SAR Averaged over 10 grams • By law must be less than 2 watts per kilogram Base Station SAR Base Stations • Power 6 degrees 50 m to 200 m Base Station Information http://www.sitefinder.ofcom.org.uk/ EIRO How this is specified Equivalent isotropic Radiated Output 60 W Actual Pattern of Emitted Radiation Mast near my children’s old school 1000 W EiRO Power • 30 dBW • 1000 W • Equivalent isotropic Radiated Output • 60 W to 120 W in actual power Actual Pattern of Emitted Radiation SAR 0.001 Watts per kilogram 0.3 0.01 Watts per square metre Watts per square metre Comparison of handsets and base stations Power Intensity Maximum SAR Watts Watts per square metre Watts per kilogram Handset 1 200 About 1 Base Station 60 0.01 About 0.001 • Base station SAR is extremely low but you can’t choose whether you want it or not! 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 Watts per kilogram 0.1 Less than 0.01 About 0.0001 Comparison of handsets and base stations and wi-fi Power Intensity Maximum SAR Watts Watts per square metre Watts per 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 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’ Children Precautionary Approach: More research please 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 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? You decide! In smaller groups • Please come up with some questions, and suggestions • We will gather these together and then ask the experts 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 Goodnight See you next week to discuss Nuclear Power Mobile Phones Unused Slides More willing Perception of risk to take risk Benefits Less willing to take risk Direct Indirect Example Base Stations/ Mobile Phones Risk is expressed mathematically, Cars/ but our judgement of risk is not mathematical Technology Familiar Unfamiliar Mobile Phones Exposure Voluntary Involuntary Exposure Fair Unfair Exposure Consequence No Personal Personal Control Control Not Dreaded Dreaded Base Stations/ Mobile Phones Poverty/ Wealth Driver/ Pedestrian Cancer/ Broken bone How it all fits together… Electricity Atoms Heat Electromagnetic waves 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 Don’t try this at home! 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? Possibility#1 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) No Match Click with Left Hand Match Click with Right Hand Task Completed with Phone On LEFT On RIGHT OFF RESULTS 1 hour 1100 1 hour 1100 950 900 850 800 700 RIGHT HAND RESPONSE 1050 'No Match' RESPONSE 1000 750 Response Time: milliseconds Response Time: milliseconds LEFT HAND RESPONSE 1050 SHAM LEFT EXPOSURE RIGHT EXPOSURE Match RESPONSE 1000 950 900 850 800 750 700 1 2 3 4 5 6 7 8 9 10 11 12 Block SHAM LEFT EXPOSURE RIGHT EXPOSURE 1 2 3 4 5 6 7 Block 8 9 10 11 12 RESULTS With Uncertainty Only these two points have statistical significance 1100 1100 950 900 850 800 700 RIGHT HAND RESPONSE 1050 'Match' RESPONSE 'No Match' RESPONSE 1000 750 Response Time: milliseconds Response Time: milliseconds LEFT HAND RESPONSE 1050 SHAM LEFT EXPOSURE RIGHT EXPOSURE 1000 950 900 850 800 750 700 1 2 3 4 5 6 7 8 9 10 11 12 Block SHAM LEFT EXPOSURE RIGHT EXPOSURE 1 2 3 4 5 6 7 Block 8 9 10 11 12 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 ?