Abstract

Objective

Introduction

Just about everywhere you go, you can see someone using a cell phone. You can use a cell phone to call your mom to pick you up from the mall, text your best friends, check the Internet for movie times, and even play games. The cell phone is an important part of how we communicate with our friends and family.

But how does a cell phone do all of that? Cell phones are basically radios that depend on radio signals to receive and transmit information. When you talk into your cell phone, it converts your voice into a microwave frequency signal. Cell phones transmit and receive information at microwave frequencies, which are within the radio frequency (RF) spectrum. Radio waves and microwaves are all part of the electromagnetic spectrum. See Figure 1 to view the full electromagnetic spectrum.

Figure 1. The electromagnetic spectrum. (Image courtesy of Lawrence Berkeley National Laboratory, 2009.)

Each cell phone carrier (like Verizon, AT&T, etc.) is given a set of frequencies, which they use to transmit and receive information in a typical city. Each cell phone carrier then breaks the city up into cells (each cell is a few square miles). Each cell has a base station. When you turn on your cell phone, it communicates with its closest base station and shares information about you and where you are located. When you make or receive a call from a friend, many operations have occurred that identify where and who you and your friend are, determining which microwave frequencies your phones should use so that you can both talk. Once the connection has been made, having a conversation on the phone is like talking on a two-way radio.

When you use your cell phone to talk or text, your body absorbs some amount of the microwave frequencies, and there might be some health issues associated with this. The electromagnetic spectrum is classified into non-ionizing radiation and ionizing radiation. Non-ionizing radiation does not damage the genetic material in body's molecules, and might or might not cause illness (more on this in the next paragraph), but if the exposure to microwave radiation is sufficiently intense (which you can read more about in the Office of Engineering and Technology reference in the Bibliography, below), then it can cause biological damage, such as burns and cataracts. Ionizing radiation, on the other hand, is dangerous to our bodies, and in high doses can cause cancer and birth defects. Radio frequencies and microwave frequencies are classified as non-ionizing radiation, and x-rays and gamma rays are examples of ionizing radiation.

There is a lot of debate about whether or not the radiation (the microwave frequencies that the cell phone is receiving and sending) from cell phones is harmful to humans. Since the cell phone is held close to the head, many scientists are studying whether the rise in cell phone usage is creating a rise in brain tumors. There have been a lot of studies done, but the results have been inconclusive. In this electricity and electronics project, you will conduct your own study. You will look at a typical cell phone while it is in calling mode and texting mode and determine the amount of microwave radiation coming from the phone using a microwave leakage meter at three different distances (2 centimeters [cm], 5 cm, and 15 cm) and from different sides of the cell phone. The Federal government has set the maximum exposure to microwave radiation at 5 milliwatts (mW) per square centimeter 2 inches from the device. The maximum exposure is also called the specific absorption rate (SAR) and the unit of measure is in watts per kilogram (W/kg). Will your cell phone reach this limit? Does it matter if you are speaking or texting? Is it a good idea to always use a hands-free device when using your phone? Perform your own study and figure out how comfortable you are using a cell phone with the data you gather.

Terms, Concepts, and Questions to Start Background Research

• Frequency
• Electromagnetic spectrum
• Radio wave
• Microwave
• Absorb
• Non-ionizing radiation
• Ionizing radiation
• X-ray
• Gamma ray
• Watt
• Data

Questions

• Can you describe, in detail, how a cell phone sends and receives calls?
• What is the Federal Communications Commission (FCC)-mandated radiation limit for cell phones? Hint Read the sources in the Bibliography.
• What is the difference, in terms of frequency, between microwave frequencies and the more dangerous x-rays and gamma rays?
• Which is more dangerous, talking on a cell phone or driving and talking on a cell phone?

Bibliography

• Brain, T., Tyson, J., and Layton, J. (2000, November 14). How Cell Phones Work. Retrieved September 25, 2010, from www.howstuffworks.com/cell-phone.htm
• Office of Engineering and Technology, Federal Communications Commission. (2010, August 4). Radio Frequency Safety. Retrieved September 25, 2010, from www.fcc.gov/oet/rfsafety/rf-faqs.html
• National Consumer Advocacy Commission. (n.d.). Health Hazards of Cell Phone Use. Retrieved September 25, 2010, from www.cellphonesafety.org/health/

Materials and Equipment

• Cell phone
• Material to make a jig; this will require some creative problem-solving on your part, so read through the Experimental Procedure, below, to determine the materials you will need.
• Ruler, metric
• Tools to make the jig; this will require some creative problem-solving on your part, so read through the Experimental Procedure, below, to determine the kinds of tools you will need.
• Safety goggles
• Digital microwave oven leakage meter; available online at www.amazon.com
• Volunteer
• Lab notebook

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Experimental Procedure

Building the Jig

1. The first step is to build the jig so that you can easily measure microwave radiation emissions. The jig is a way to securely and accurately hold the phone a set distance from the microwave leakage detector. Making a jig will allow you to make measurements at the same distance for every trial. Follow the engineering process below to make the jig.
1. Define a Need: You need to test the cell phone from the front, back, and sides with a microwave leak detector. You will also check the microwave radiation at different distances.
2. Establish Design Criteria: From what material will you make the jig? This depends on many factors, such as the cost of the materials, whether the material absorbs microwaves, and how easy it is to work with.
3. Prepare Preliminary Designs: On a piece of paper, work out what your jig should look like. Here are some things to think about:
1. The jig should be designed so that the cell phone is on one end while the microwave detector is on the other end.
2. There should be a way to securely hold the cell phone without blocking it.
3. The cell phone part of the jig should be able to freely rotate so that all sides can be measured.
4. The microwave leakage meter should be mounted at the same level or height as the phone.
5. Since you need to measure the leakage at different distances, you will need to make the meter slide back and forth.
4. Build the Jig: Remember to wear safety goggles if you use tools to build your jig.
5. Test and redesign, as necessary.

Testing Your Cell Phone in Call Mode

1. Insert the cell phone into the jig.
2. Open the microwave leakage meter and read the instructions on how to use it.
3. Mount the microwave leakage meter onto the jig.
4. Measure the leakage coming from the front of the cell phone, as follows.
1. Move the microwave leakage meter 2 cm from the cell phone.
2. Make a call on the cell phone to your volunteer. When the call is answered, take a microwave leakage measurement. Record the leakage value in your lab notebook.
5. Measure the leakage coming from the back of the phone with the leakage meter located 2 cm away. Record the leakage value in your lab notebook.
6. Measure the leakage coming from the bottom of the cell phone with the leakage meter located 2 cm away. Record the leakage value in your lab notebook.
7. Measure the leakage coming from the top of the cell phone with the leakage located meter 2 cm away. Record the leakage value in your lab notebook.
8. Measure the leakage coming from the sides of the cell phone with the leakage meter located 2 cm away. Record the leakage value for each side in your lab notebook.
9. Repeat steps 4–8 with the microwave leakage meter located 5 cm away from the cell phone.
10. Repeat steps 4–8 with the microwave leakage meter located 15 cm away from the cell phone.
11. Repeat steps 4–10 two more times. When doing science experiments, it is important to perform the experiment at least three times to make sure that your results are repeatable and reproducible.
12. Stop the phone call.

Testing Your Cell Phone in SMS Texting Mode

1. Now measure the microwave leakage of your cell phone while it is in text mode.
2. Mount the cell phone and microwave leakage meter in the jig.
3. Measure the leakage coming from the front of the cell phone, as follows.
1. Move the microwave leakage meter 2 cm from the cell phone.
2. Text your volunteer and start a text conversation. As soon as you send a text, take a microwave leakage measurement. Record the leakage value in your lab notebook.
4. Measure the leakage coming from the back of the phone with the leakage meter located 2 cm away. As soon as you send a text, take a microwave leakage measurement. Record the microwave leakage value in your lab notebook.
5. Measure the leakage coming from the bottom of the cell phone with the leakage meter located 2 cm away. As soon as you send a text, take a microwave leakage measurement. Record the microwave leakage value in your lab notebook.
6. Measure the leakage coming from the top of the cell phone with the leakage meter located 2 cm away. As soon as you send a text, take a microwave leakage measurement. Record the microwave leakage value in your lab notebook.
7. Measure the leakage coming from the sides of the cell phone with the leakage meter located 2 cm away. As soon as you send a text, take a microwave leakage measurement. Record the leakage value for each side in your lab notebook.
8. Repeat steps 3–7 with the microwave leakage meter located 5 cm away from the cell phone.
9. Repeat steps 3–7 with the microwave leakage meter located 15 cm away from the cell phone.
10. Repeat steps 3–9 two more times.
11. Stop texting.

Analyzing Your Data

1. Review your data. Start working with the data from when the cell phone was in call mode.
2. Average the data over all three trials for when the microwave leakage meter was 2 cm from the cell phone and the cell phone in call mode. Average the data measured from:
1. The front of the phone.
2. The back of the phone.
3. The bottom of the phone.
4. The top of the phone.
5. The sides of the phone.
3. Repeat step 2 and average the data over all three trials for when the microwave leakage meter was 5 cm from the cell phone.
4. Repeat step 2 and average the data over all three trials for when the microwave leakage meter was 15 cm from the cell phone.
5. Now review the data from when the cell phone was in text mode.
6. Average the data over all three trials for when the microwave leakage meter was 2 cm from the cell phone and the cell phone in text mode. Average the data measured from:
1. The front of the phone.
2. The back of the phone.
3. The bottom of the phone.
4. The top of the phone.
5. The sides of the phone.
7. Repeat step 6 and average the data over all three trials for when the microwave leakage meter was 5 cm from the cell phone.
8. Repeat step 6 and average the data over all three trials for when the microwave leakage meter was 15 cm from the cell phone.
9. Now plot the data. Make a plot for the cell phone in call mode. Label the x-axis Distance Between Cell Phone and Microwave Leakage Meter. Label the y-axis Microwave Leakage (mW/cm²). Plot the average values for the measurements from the back, front, bottom, top, and sides for each distance.
10. Make a plot for the cell phone in text mode. Label the x-axis Distance Between Cell Phone and Microwave Leakage Meter. Label the y-axis Microwave Leakage (mW/cm²). Plot the average values for the measurements from the back, front, bottom, top, and sides for each distance.
11. What kind of information do you get from your plots? How does the leakage varying depending on the area of the cell phone? How does it vary with distance? Does texting result in less leakage than calling? How will this science project affect your cell phone usage behavior, if at all?

Variations

• Repeat this project using different cell phones. Do different cell phones emit different amounts of microwave radiation?

• For more science project ideas in this area of science, see Electricity & Electronics Project Ideas.

Credits

Michelle Maranowski, PhD, Science Buddies

This science project is based upon the following Science Buddies Clever Scientist Award winning project: Bose, Gautam. (2010). Microwave Emissions From Cellular Phones.

Last edit date: 2011-02-14 12:00:00