Introduction

I first became interested in a similar topic when I came to Canada. At that time we did not have a phone at home so me and my brother asked our mom to buy us a cell phone, but she said that a cell phone can be a threat to one's health. That's why I became interested in finding out if using a cell phone is dangerous to one's health and what can we do to prevent the effects if it was dangerous. I did a lot of research and found out that some experiments on this topic have already been done before, exposing rats to radiation, surveying the effect of mobile phones on humans etc. Some researchers said that it was in fact dangerous to use a cell phone and that there is a relationship between mobile phones and brain cancer, brain tumors, loss of memory etc., but others said completely the opposite. They said that using a cell phone does not relate to brain cancers etc., so everyone could go ahead and use their mobile phones whenever they want and how long they want without being afraid that their cell phone will have bad effects on their brain. But even as they stated that mobile phones are not dangerous, various reports of brain cancers, brain tumors etc. came in. Nothing was proven and still is not, and little answers were given. So I came up with another project idea. I decided to find out how cell phone radiation changes over distance (I was interested to find out how radiation changed in an enclosed space with walls that do not absorb radiation) and after I have, to research if there are any effective means to reduce the possible danger. Also I wanted to see if using a cell phone in a public place is similar to second-hand smoke. I did some research and found out that nothing like this was ever done before and even if it was, the results were not made public, perhaps because if the public found out, it would not be profitable for mobile phone companies or because research costs a lot and people just didn't want to spend a lot of money.

All cities that have mobile phone service consist of cells (hence the name cellular phone). Inside each cell is a base station that "serves" all mobile phone users in that cell. Different cells have different frequencies (although some use the same since the number of frequencies available is limited) to prevent interference, and power levels are kept to a minimum to ensure there is no interference between cells that use the same frequency. The power of a mobile phone automatically adjusts depending on how close/far the user is from the closest base station. The use of a large number of base stations to service a densely populated area does not necessarily link with greater RF (Radiation Frequency) exposure. The number of frequencies available within a cell varies from one to twelve with each frequency able to hold up to eight different users. Maximum power will be transmitted only when a frequency has all eight users operating at the same time. When a user is using his/her mobile phone, the signal first goes to the closest base station and in turn, that base station relies the signal to the receiver. However, a mobile phone's signal does not always go to the same base station. Say that a mobile phone user is in a car, he is going to work and calling someone at the same time (this is a bad example because most cities now have laws against using mobile phones while driving), and his office building and where the user is now are in different cells. As the user enters another cell, his/her service is automatically shifted to the base station of the cell that he/she is currently in (see Figure1, where B = Base station and U = mobile phone user).

Figure 1. As the mobile phone users moves from one cell to another, his/her service also shifts from one base station to another.

Another interesting fact is that relating to the antennas of mobile phones. All mobile phones have magnetic fields around them, but the magnetic fields look nothing like each other for long and short antennas. For long antennas the magnetic field looks like a stretched out doughnut with a small (stretched out of course) doughnut on top and bottom. However for short antennas the magnetic field looks like a very large, compressed doughnut. Since the magnetic field is compressed inwards and expanded outwards (towards the brain), that makes the mobile phones with small antennas more dangerous than those with long ones.

Figure 2. Magnetic field of a short antenna.

Figure 3. Magnetic field of long antenna.

The purpose of this experiment is to find out how cell phone radiation decreases over short and long distances and if using a cell phone in a public place is similar to second-hand smoke.

I think that the cell phone radiation will reduce double the distance in centimeters.

1. Spectrum Analyzer

2. Analogue cell phone or digital cell phone (does not matter which)

or

3.Microwave Signal Generator and antenna (to transmit the signal)

4.Antenna (to catch the signal)

Manipulated Variable:
The distance that the source of signal is away from the antennae

Responding Variable:

How much the cell phone signal changes over distance

Constant Variable:

Equipment (although it does not matter if you switch between the cell phone and the signal generator), room with signal absorbing walls or without and frequency.

1. Gather the materials.

2. Hook up the Spectrum Analyzer to the antennae.

3. Turn on the cell phone and call someone that knows you will be calling, keep the phone on until the experiment is done for the day.

Or

Use the Microwave Signal Generator and put it to operate on the frequency of the cell phone (usually 900 MHz), hook it up to the transmitting antennae

4. Make sure there are no obstacles between the source of signal and the antennae.

5. Measure how the signal decreases over short (2-30 cm) and long (1-5 m) distance.

6. Convert the results from dBm to mW using the formula:
1 dBm = 10 log(x) / 1mW.

7. Plot results on line graphs.

8. Draw conclusions of how the cell phone signal changes over distance.

Figure 4.Spectrum Analyzer

Figure 5. Antenna to capture the signal

Figure 6. Microwave Signal Generator

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FirstTrial

In this trial the following equipment was used:

Spectrum Analyzer, Hewlett Packard

Antennae, 300 - 1000 mHz

Cellular Telephone, Nokia, 890 - 915 mHz

Figure 7. Radiation (dBm) measured over distance of 2 cm

Figure 8. Radiation (dBm) measured over distance of 10 cm

Figure 9. Radiation (dBm) measured over distance of 20 cm

Figure 10. Radiation (dBm) measured over distance of 30 cm

Results in dBm (First Trial)


Results in mW (First Trial)


By how much the radiation was reduced from the 1st measurement (first trial)

Figure 11. Decreasing of the radiation level over short distances

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In this trial the following equipment was used:

Agulant - e4437B Microwave Signal Generator

Antennae with a gane of 8 dBm, Transmitting at +10 dBm

Spectrum Analyzer - HP-MSIB Hewlett Packard

ETS Systems, Model 3147 Log Periodic Antennae with a gane of 4.4 dBm at 900 mH

Figure 12. Radiation (dBm) measured over distance of 1.7m

Figure 13. Radiation (dBm) measured over distance of 4.2m

Figure 14. Radiation (dBm) measured over distance of 5.7m

Results in dBm (Second Trial)

Results in mW (First Trial)

By how much the radiation was reduced from the 1st measurement (Second Trial)

Figure 15. Decreasing of the radiation level over long distances

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Third Trial

In this trial the following equipment was used:

Spectrum Analyzer, Hewlett Packard

Antennae, 300 - 1000 mHz

Cellular Telephone, Nokia, 890 - 915 mHz

Graphs for this trial are missing because the Spectrum Analyzer's memory for printing went down.

Results In dBm (third trial)

Results In mW (third trial)

By how much the radiation was reduced from the 1st measurement (third trial)

Figure 16. Decreasing of the radiation level over short and long distances

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Analysis of Results

In this experiment I did three trials. First trial was done on the distance of 2cm, 10cm, 20cm and 30cm. Second trial was done on the distance of 1.7m, 4.2m and 5.7 m. The third trial was done on the distance of 0.3m, 1m, 2m, 3m, 4m and 5m. The results for the trials are shown below.

In trial one, over the distance of 8 centimeters the radiation has reduced by almost 48 times, over the distance of 18 centimeters it has reduced by about 119 times and over the distance of 28 centimeters it has reduced by nearly 290 times.

In trial two, over the distance of 2.5 meters the radiation has reduced double and over the distance of 4 meters the radiation has reduced by almost 4 times.

In trial three, over the distance of 70 cm the radiation has reduced by about 5 times, over the distance of 170 cm by almost 28 times, over the distance of 270 cm by nearly 92 times, over the distance of 370 cm by 171 times, and over the distance of 470 cm by about 482 times.

The results above suggest that over short distances the signal decreases rapidly and over long distances it decreases quite slowly. Also after taking a look at the results, one could say that using your cell phone in a public place is not similar to secondhand smoke.

After doing a lot of literature analysis, I have found many interesting facts. There are many kinds of different antennas, for example ones that are very long (old models), ones that come out a bit. Ones that stick out of the cell phone but do not come out and ones that have an internal antenna. As strange as it may seem, the old models of cell phones are the safer ones. Each antenna has a magnetic field around it. For short antennas the magnetic field resembles a doughnut, which is compressed and therefore stretched outwards (towards the brain). As for long antennas, the magnetic field looks similar to a stretched out (vertically) doughnut with a small (and stretched out) doughnut on the top and bottom. Since the magnetic field of a short antenna is closer to the brain than that of an old cell phone, that makes the short antenna mo re dangerous. The new models of mobile phones fool many people, everyone thinks that the current models of mobile phone in production are way safer than the old ones because they are new. However it is completely opposite.

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Conclusion

After taking a look at the results above one could notice that over short distances the radiation decreases more rapidly (approximately 6-10 times distance), and over long distances it decreases quite slowly (between 0.07 and 1.02 times distance). Also, after looking at the results, one could safely say that using a mobile phone in a public place is not similar to secondhand smoke and is actually pretty safe for those around you (but not yourself). However I have to emphasize that these results can't be treated 100% correct, because all trials were made in an enclosed space without radiation absorbing walls. And where the cell phone signal might increase or decrease due to multiple reflections from walls and different objects in the room.

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Recommendations

- The reduction of the cell size, and the increase of base stations, which would dramatically lessen the minimum power needed for communication without interferences.

- When using a mobile phone, the antennae should always be pulled out and away from the head.

- A new type of mobile phone could be made with a longer antennae pointing downwards, and away from the head, instead of a short antennae pointing upwards.

- If buying a mobile phone, one should buy the cell phone with a big antenna instead of small.

- One could use a hands-free device, such as headphones and a microphone so that there will be minimum RF exposure to the head.

If one does not want to use a microphone and headphones, then I would recommend to use the cell phone as on one of the diagrams below:

Figure 17. Best: New kind of cell phone with the antenna pointed downward.

Good: Antenna pulled out and away from the head. Bad: Antenna not pointed away from the head or not pulled out.

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Acknowledgements

I would like to express my thanks to Dr. Garth Wells, (TRLabs, Saskatoon) and Dr. V. Khachikyan (Institute of Power and Communications) for helping me to operate the Spectrum Analyzer and Microwave Signal Generator, and for the useful discussions.

I am very thankful to Mr. Don Field, (CellCheck, Saskatoon) and Dr. K. Mitchell and Mr. H. Olivier (University of Saskatchewan) for giving me several cell phones for my project.

I am also grateful to my mom, Svetlana Petelina for her support, useful advices and helping me do some calculations in IDL, and to my older brother Alex for allowing me to use his computer as much as I need for this project.

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References

Scientific papers:

K. R. Foster & J. E. Moulder, Are mobile phones safe?, Public Health, pp. 23-28, August, 2000

Don Maisch. Mobile phone use: It's time to take precautions. ACNEM Journal, V 20, No. 1, pp.3-10. 2001

Books:

Constantine A. Balanis. Antenna Theory: Analysis and Design, 1997

Websites:

http://www.academon.com/lib/paper/4764.html

www.cancer-health.org

www.globalchange.com/radiationnews.htm

www.arpansa.gov.au/mph_sys.htm

More pages from www.arpansa.gov.au

news.bbc.co.uk/hi/english/health/newsid_351000/351048.stm

news.zdnet.co.uk/story/0,,t269-s2103167,00.html

www.studiosra.it/news/acnem.pdf

www.doh.gov.uk/mobile.htm

web.mit.edu/newsoffice/nr/2002/bio-radio.html

www.cellularbazaar.com/mobile_health.htm

www.tassie.net.au/emfacts/mobiles/cellphones.html

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Project Info

Grade grouping: 7-9

Team size: 1or2

Subject area: Phy/Ast

Project type: Experimental

Project level: Standard

Project format: Traditional

Summary: I collected information and studied the published results on the influence of mobile phone radiation on human health. I came to realize that in spite of many governmental and commercial research conducted, no specific numbers are released for the public. Because of this I decided to measure the decrease of mobile phone radiation at different distances. I found that over short distances (2-30 cm) the radiation decreases quite rapidly: approximately 6-10 times distance. However, over long distances (1-5 m) the radiation decreases quite slowly: between 0.07 and 1.02 times distance. Over the distance of 28 centimeters (the difference between 30cm and 2cm) the radiation decreased by 290 times, therefore I concluded that using a mobile phone in a public place probably is not similar to secondhand smoke. Since the radiation from the mobile phone is mainly determined by the lenght and position of the phone's antenna, I proposed several ways to ease it's influence on the head.

Webpage software used: None

Hardware tools used: Scanner, camera

Source of the idea for project: see Introduction

Special Skills: HTML

Awards:

Junior Award in Physical Sciences (First Place)

The most proffesional presentation in Physical Sciences

Provincial Showcase Special Award

Virtual Science Fair home page

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I am looking forward to any feedback:

o_d_petelin@hotmail.com