Does Your Mobile Phone Radiate? Measuring Cell Phone Electromagnetic Radiation
AbstractEvery day, no matter where you are, you will see people using their cell phones. People use their cell phones for more than just making calls though. They use them for texting and searching the Internet, too. But some health groups are concerned that using your cell phone too much can be hazardous to your health as it exposes your body to electromagnetic radiation. In this electricity and electronics science project, you will investigate how much radiation your cell phone emits when used for calling and texting.
Michelle Maranowski, PhD, Science Buddies
Sabine De Brabandere, 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.
ObjectiveTo investigate if your cell phone emits electromagnetic radiation when making a phone call or sending a text message, and to determine the level of radiation at varying distances.
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.
Diagram of the electromagnetic spectrum with reference objects to demonstrate the relative scale of waves. Radiowaves (on the left) have the longest wavelengths in the spectrum (larger than a baseball). X-rays (on the right right of the spectrum) have the shortest wavelength (smaller than a water molecule).
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 frequency signal, 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. Scientists know radiation levels decreases rapidly with distance but since the cell phone is held very 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 cell phone while it is in calling mode and texting mode and determine the amount of microwave radiation coming from the phone using a radio frequency meter at three different distances (2 centimeters [cm], 5 cm, and 15 cm) and from different sides of the cell phone. Some governments have set a maximum exposure to microwave radiation expressed in milliwatts [mW] (or .001 Watt [W]) per square centimeter at specific distances from the device. Other exposure guidelines specify limits for human exposure to radio frequency emissions in terms of Specific Absorption Rate (SAR), a measure of the rate of absorption of radio frequency energy by the body. In this science project, you will measure how much energy is send out by your phone in different directions and how it changes with increasing distance. Only part of this energy will be absorbed by the body—so your measurements can not directly be compared to SAR limits. Would the radiation send out by a cell phone be different 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 and Concepts
- Electromagnetic spectrum
- Radio wave
- Non-ionizing radiation
- Ionizing radiation
- Average power
- 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?
- Brain, T., Tyson, J., and Layton, J. (2000, November 14). How Cell Phones Work. Retrieved September 25, 2010.
- Office of Engineering and Technology, Federal Communications Commission. (2010, August 4). Radio Frequency Safety. Retrieved September 25, 2010.
- National Consumer Advocacy Commission. (n.d.). Health Hazards of Cell Phone Use. Retrieved September 25, 2010.
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
- Radio frequency meter - available for rent from magneticsciences.com
- Volunteer with phone
- Lab notebook
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Building the Jig
- 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 to radio frequency (RF) meter. 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. Refer to the Science Buddies resource on the Engineering Design Process for more information.
- Define a Need: You need to test the cell phone from the front, back, and all four sides with a RF meter. You will also check the microwave radiation at different distances.
- 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.
- Prepare Preliminary Designs: On a piece of paper, work out what your jig should look like. Here are some things to think about:
- The jig should be designed so that the cell phone is on one end while the RF meter is on the other end.
- There should be a way to securely hold the cell phone without blocking it.
- There should be a way to securely hold the RF meter without blocking the top and front of the meter.
- The cell phone part of the jig should be able to freely rotate so that all sides can be measured.
- The RF meter should be mounted at the same level or height as the phone.
- The top side of the RF meter should point towards the cell phone as the receiving antenna of the meter is mounted inside this side of the meter. See also Figure 2 below.
- Since you need to measure the power at different distances, you will need to make the meter slide back and forth.
- Build the Jig: Remember to wear safety goggles if you use tools to build your jig.
- Test and redesign, as necessary.
Figure 2. The receiving antenna is mounted inside the meter, near the top of the meter. Distances to the cell phone should be measured with respect to this side of the meter.
Testing Your Cell Phone in Call Mode
- Create a data table like Table 1 below in your notebook. Add the title "Measured Average Power - Call Mode [μW/ m2]" . A table will help you record your measurements neatly.
|Front||Back||Top||Bottom||Right Side||Left Side|
|2 cm||Trial 1|
|5 cm||Trial 1|
|15 cm||Trial 1|
- Familiarize yourself with the RF meter. The RF meter displays several measured values as shown in Figure 3 below. Most values are likely to vary quickly during measurements. You will use the light indicator expressing the average power send out from the phone as the measurement in this science project.
A photo of an acoustimeter shows multiple readings that are labeled on the photo. The RF meter displays several measurements: the instant peak energy (a - top-right of the device screen), the hold peak energy (b - left of the device screen), average power (μW/ m2) (c - bottom-right of the device screen), light indication of peak energy V/m (d - left of the device body) and light indication of average power ( μW/ m2) (e - right of the device body).
Figure 3. The RF meter displays several measurements: the instant peak energy send out [V/m] (a), the highest peak energy send out since you turned on the meter [V/m] (b), average power send out [μW/ m2] (c), light indication of peak energy send out [V/m] (d) and light indication of average power send out [μW/ m2] (e).
- Mount the RF meter and the cell phone onto the jig.
- Inform you volunteer you will call his/her number frequently in the coming hour. He/she is not expected to answer the phone.
- Measure the average power coming from the front of the cell phone at a distance of 2 cm, as follows.
- Move the top of the RF meter until it is 2 cm from the front of the cell phone.
- Make a call on the cell phone to your volunteer. Put your phone on speaker so you hear the ringing tone.
- While you hear the ringing, take an average power measurement as displayed by the light indicator labeled e on Figure 3 above.
- Record the value in your lab notebook.
- End the call
- Measure the average power coming from the back of the phone with the RF meter located 2 cm away, as follows.
- Rotate your cell phone so the back is facing the RF meter.
- Repeat steps 5.b–5.e .
- Measure the average power coming from the bottom of the cell phone with the meter located 2 cm away.
- Rotate your cell phone so the bottom is facing the RF meter and check if the distance to the top of the meter is still 2 cm.
- Repeat steps 5.b–5.e .
- In a similar way, measure the average power coming from the top of the cell phone with the meter located 2 cm away
- Measure the average power coming from each side of the cell phone with the RF meter located 2 cm away. This completes 1 trial. One row in your data table should be completely filled in.
- Repeat steps 5–9 with the RF meter located 5 cm away from the cell phone.
- Repeat steps 5–9 with the RF meter located 15 cm away from the cell phone.
- Repeat steps 5–11 two more for a total of 3 trials. 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.
Testing Your Cell Phone in SMS Texting Mode
- Now measure the average power emitted by the cell phone while it is in text mode. Create a new table like Table 1 above to record the measurements for texting.
- Mount the cell phone and RF meter in the jig.
- Inform you volunteer you will text his/her number frequently in the coming hour. He/she is not expected to respond.
- Measure the average power at 2 cm from the front of the cell phone, as follows.
- Move the RF meter 2 cm from the front side of the cell phone.
- Start a text conversation.
- As soon as you send a text, take a measurement.
- Record the average power in your lab notebook.
- In a similar way, measure the average power at 2 cm from from the back of the phone.
- Make a measurement at 2 cm from from the bottom of the cell phone.
- Make a measurement at 2 cm from from the top of the cell phone.
- Make a measurement at 2 cm from from each side of the cell phone.
- Repeat steps 4–8 with the RF meter located 5 cm away from the cell phone.
- Repeat steps 4–8 with the RF meter located 15 cm away from the cell phone.
- Repeat steps 4–10 two more times.
- Stop texting.
Analyzing Your Data
- Review your data. Start working with the data from when the cell phone was in call mode.
- Average the data over all three trials for when the RF meter was 2 cm from the cell phone
and the cell phone in call mode. Average the data measured from:
- The front of the phone.
- The back of the phone.
- The bottom of the phone.
- The top of the phone.
- The right side of the phone.
- The left side of the phone.
- Repeat step 2 and average the data over all three trials for when the RF meter was 5 cm from the cell phone.
- Repeat step 2 and average the data over all three trials for when the RF meter was 15 cm from the cell phone.
- Now repeat steps 2–4 with the data from when the cell phone was in text mode.
- Visualize the data. Make a plot for the cell phone in call mode. Label the x-axis Distance Between Cell Phone and RF Meter [cm]. Label the y-axis Average power [μW/m2]. Plot the average values for the measurements from the front for each distance. Add the average values for measurements with respect to the back, bottom, top, and each side of the phone choosing a different color for each direction.
- Repeat step 6 using the data collected with the phone in texting mode.
- What kind of information do you get from your plots?
- Is the average power send out by the phone the same in each direction (front, back, top, bottom, right side, left side)?
- Does the average power send out vary with distance from the phone?
- Does the data confirm your expectations?
- Does texting result in less power emitted than calling?
- How will this science project affect your cell phone usage behavior, if at all?
Ask an Expert
- Repeat this project using different cell phones. Do different cell phones emit different amounts of microwave radiation?
- The Introduction mentions radiation levels decrease rapidly with increasing distance from the emitting source. Theoretically, the decrease is inversely proportional to the distance squared. You can use your meter to study this decrease in more detail by measuring the radiation level (average power) at various distances like 2 cm, 5 cm, 15 cm and 30 cm. Can you create a best fit to your data points following the 1/r2 rule?
- Study how radio frequency signals change with distance around a radio or cell phone tower. Would you say there are possibly health risks associated with living in a vicinity of one of those towers? Or is it unlikely?
- Study the power emitted at different distances by a Bluetooth device. How does the power emitted by a Bluetooth device compare to the power emitted by your cell phone?
- Wi-Fi signals allow wireless devices to connect to the a wireless network. These are radio frequency electromagnetic signals as well. You can use the RF meter listed in the Materials section of this project or a phone app as advised in the two projects listed below to measure the strength of Wi-Fi signals. Be sure to check out following projects if you are interested in Wi-Fi Signals:
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