How Cell Phone Radiation Works
Just by their basic operation, cell phones have to emit
a small amount of electromagnetic radiation. If you've
read How Cell Phones Work, then you know that cell phones
emit signals via radio waves, which are comprised of radio-frequency
(RF) energy, a form of electromagnetic radiation.
There's a lot of talk in the news recently about whether
or not cell phones emit enough radiation to cause adverse
health effects. The concern is that cell phones are often
placed close to or against the head during use, which
puts the radiation in direct contact with the tissue in
the head. There's evidence supporting both sides of the
Source of Radiation
When talking on a cell phone, a transmitter takes the
sound of your voice and encodes it onto a continuous sine
wave (see How Radio Works to learn more about how sound
is transmitted). A sine wave is just a type of continuously
varying wave that radiates out from the antenna and fluctuates
evenly through space. Sine waves are measured in terms
of frequency, which is the number of times a wave oscillates
up and down per second. Once the encoded sound has been
placed on the sine wave, the transmitter sends the signal
to the antenna, which then sends the signal out.
Radiation in cell phones is generated in the transmitter
and emitted through the antenna.
Cell phones have low-power transmitters in them. Most
car phones have a transmitter power of 3 watts. A handheld
cell phone operates on about 0.75 to 1 watt of power.
The position of a transmitter inside a phone varies
depending on the manufacturer, but it is usually in
close proximity to the phone's antenna. The radio waves
that send the encoded signal are made up of electromagnetic
radiation propagated by the antenna. The function of
an antenna in any radio transmitter is to launch the
radio waves into space; in the case of cell phones,
these waves are picked up by a receiver in the cell-phone
Electromagnetic radiation is made up of waves of electric
and magnetic energy moving at the speed of light, according
to the Federal Communications Commission (FCC). All
electromagnetic energy falls somewhere on the electromagnetic
spectrum, which ranges from extremely low frequency
(ELF) radiation to X-rays and gamma rays. Later, you
will learn how these levels of radiation affect biological
When talking on a cell phone, most users place the phone
against the head. In this position, there is a good
chance that some of the radiation will be absorbed by
human tissue. In the next section, we will look at why
some scientists believe that cell phones are harmful,
and you'll find out what effects these ubiquitous devices
Potential Health Risks
In the late 1970s, concerns were raised that magnetic
fields from power lines were causing leukemia in children.
Subsequent epidemiological studies found no connection
between cancer and power lines. Around the same time,
similar cancer fears arose about computer monitors.
While there is some radiation emitted from computer
monitors, studies have shown that they don't raise cancer
rates. The latest health scare related to everyday technology
is the potential for radiation damage caused by cell
phones. Studies on the issue continue to contradict
All cell phones emit some amount of electromagnetic
radiation. Given the close proximity of the phone to
the head, it is possible for the radiation to cause
some sort of harm to the 118 million cell-phone users
in the United States. What is being debated in the scientific
and political arenas is just how much radiation is considered
unsafe, and if there are any potential long-term effects
of cell-phone radiation exposure.
There are two types of electromagnetic radiation:
Ionizing radiation - This type of radiation contains
enough electromagnetic energy to strip atoms and molecules
from the tissue and alter chemical reactions in the
body. Gamma rays and X-rays are two forms of ionizing
radiation. We know they cause damage, which is why we
wear a lead vest when X-rays are taken of our bodies.
Non-ionizing radiation - Non-ionizing radiation is typically
safe. It causes some heating effect, but usually not
enough to cause any type of long-term damage to tissue.
Radio-frequency energy, visible light and microwave
radiation are considered non-ionizing.
On its Web site, the FDA states that "the available
scientific evidence does not demonstrate any adverse
health effects associated with the use of mobile phones."
However, that doesn't mean that the potential for harm
doesn't exist. Radiation can damage human tissue if
it is exposed to high levels of RF radiation, according
to the FCC. RF radiation has the ability to heat human
tissue, much like the way microwave ovens heat food.
Damage to tissue can be caused by exposure to RF radiation
because the body is not equipped to dissipate excessive
amounts of heat. The eyes are particularly vulnerable
due to the lack of blood flow in that area.
Cell-phone use continues to rise, which is why scientists
and lawmakers are so concerned about the potential risks
associated with the devices.
The added concern with non-ionizing radiation, the type
of radiation associated with cell phones, is that it
could have long-term effects. Although it may not immediately
cause damage to tissue, scientists are still unsure
about whether prolonged exposure could create problems.
This is an especially sensitive issue today, because
more people are using cell phones than ever before.
In 1994, there were 16 million cell-phone users in the
United States alone. As of July 17, 2001, there were
more than 118 million.
Here are a few illnesses and ailments that have potential
links to cell-phone radiation:
Studies have only muddled the issue. As with most controversial
topics, different studies have different results. Some
say that cell phones are linked to higher occurrences
of cancer and other ailments, while other studies report
that cell-phone users have no higher rate of cancer
than the population as a whole. No study to date has
provided conclusive evidence that cell phones can cause
any of these illnesses. However, there are ongoing studies
that are examining the issue more closely. See the links
page at the end of this article for more information
on these studies.
At high levels, radio-frequency energy can rapidly
heat biological tissue and cause damage such as burns,
according to a recent report from the U.S. General Accounting
Office (GAO), a nonpartisan congressional agency that
audits federal programs. The report went on to state
that mobile phones operate at power levels well below
the point at which such heating effects would take place.
The amount of radiation emitted from the devices is
actually minute, and the U.S. federal government places
limits on how much radiation a cell phone can emit.
In the next section, we'll look into how cell-phone
radiation levels are tested.
Testing for Radiation
Every cell-phone model has to be tested and meet FCC
standards before it is allowed to be sold in the United
States. Testing is primarily done by the manufacturers
themselves, which creates some uncertainty about the
testing procedures, according to a GAO report.
The exposure limit set by the FCC for cell phones is
based on the overall heating effects of radio-frequency
energy. The exposure limit was established by the FCC
in 1996. A year later, the FCC published non-mandatory
testing guidelines that helped manufacturers comply
with exposure limits. The FCC still allows other testing
techniques once an FCC review of the procedures is completed.
Radiation levels are tested based on the specific absorption
rate (SAR), which is a way of measuring the amount of
radio-frequency energy that is absorbed by the human
body. In order to gain an FCC license, a phone's maximum
SAR level must be less than 1.6 watts per kilogram (W/kg).
In 2000, the Cellular Telecommunications Industry Association
(CTIA) ordered cell-phone manufacturers to place labels
on phones disclosing radiation levels.
Photo courtesy U.S. General Accounting Office
A probe attached to a mechanical arm is directed to
take SAR measurements throughout a human-shaped mold.
The mold is filled with a liquid mixture that simulates
the electrical properties of human tissue.
Testing techniques vary somewhat, but are generally
pretty standard. The GAO report "Research and Regulatory
Efforts on Mobile Phone Health Issues," published
in May 2001, describes how SAR levels are checked. Here
is what the report described:
A mold shaped like a human head and torso is filled
with a fluid mixture that is designed to simulate the
electrical properties of human tissue.
The cell phone under review is placed on the outside
of the mold.
A probe attached to a computer-controlled mechanical
arm is inserted into the mixture at various locations.
The phone is made to transmit a signal at full power
while the probe is moved through the mixture.
During the test, the phone's antenna is extended and
retracted in order to check for any fluctuations in
radiation that the phone might demonstrate in different
configurations. The manufacturer is supposed to submit
the highest SAR level measured during these tests to
the FCC. Phones are required to test below 1.6 W/kg
averaged over 1 cubic gram of fluid.
To find the specific absorption rate of your phone,
you can visit this FCC Web site. Your phone should have
an FCC identification code. Type that code in the correct
field and the site should offer information on your
Due to the lack of any industry-wide testing standard,
the FCC must evaluate the individual procedures used
by each manufacturer in certifying the SAR level of
each new phone, according to the GAO report.
It's still unclear as to whether cell phones actually
cause any significant damage to the human body. Studies
continue to contradict one another on the issue. Additional
studies may shed some light on the true effects of cell-phone
radiation, but will likely only confuse consumers even
further. In the meantime, millions of cell-phone users
take whatever risk may be involved in using the devices.
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