With any new product that enhances the quality of our lives, we tend at first to ignore the possible risks associated with its use. But should we overlook a product that we must hold next to our head to use that radiates energy? Is the cell phone safe? What possible harm might it do to an adult or a child? We need to know the answers.
Cell-Phone Operation
In the United States, cell phones operate in the portion of the RF spectrum between 800 and 900 MHz and personal communications service (PCS) systems use the frequency band between 1,850 and 1,900 MHz. In some other nations, the frequency bands are different. Typically, the cell phone generates relatively low RF power, probably an average level of 0.6 W for an analog unit and less for a digital unit. The newer code division multiple access (CDMA) models have adaptive level control, so they send the minimum signal necessary to satisfy the base station. The power level is likely to be even lower in future designs to extend battery life, a high priority with most users.
There is a high concentration of radiated energy at the tip of the antenna. In most phones, the tip can be extended, and the user can hold it away from the head to minimize absorption as well as increase the range of operation. There isn’t much you can do to reduce absorption from other parts of the phone that have high RF levels, although the manufacturer can minimize the radiation at specific locations by shielding.
When a cell phone is held up to your ear and mouth while transmitting, up to 60% of the RF energy penetrates your head. This energy is absorbed by body tissue and generates heat that penetrates the brain to a depth of an inch or more. Studies indicate that the temperature rise is probably <0.2°F.
Possible Risks From Absorption of RF Energy
Is absorption of RF energy by the human head a hazard? It depends on several factors, beginning with the radiated level and the size of the person’s head. If the energy is moderately intense, the heart rate will decrease and electrical impulses produced by the brain will be affected. Both of these conditions generally are within the range of normal fluctuation. Extremely high levels of RF are another story. They can cause cataracts, skin and internal burns, heat exhaustion, and heat stroke.
Where does the cell phone fit into this picture? Is the radiation level extreme, moderately high, or below the level of concern? Radiation levels from a cell phone may or may not be high enough to cause problems. Studies are under way to determine the answer.
One significant activity is a partnership between the U.S. Food and Drug Administration (FDA) and the Cellular Telecommunications Industry Association (CTIA), where phone manufacturers have committed about $1 million for safety-related studies. The FDA will gather a panel of international experts to choose the study topics, find scientists to perform the studies, and oversee the process. Results are expected in about two years. This is a follow-on to the five-year $25-million study funded by the CTIA and completed in 1998.
In December 2000, the American Medical Association published the results of a study on cell-phone radiation and put the details of a second one on the Journal of the American Medical Association’s (JAMA) website. Both studies dealt with the examination of 1,250 patients with brain tumors and an equal number of healthy individuals. It found no increased risk of cancer among those who use cell phones regularly. According to Russell Owen, chief of the FDA radiation biology branch, “In all of the available scientific literature, there is nothing that indicates any adverse health effects from using cell phones.”
However, two questions remain. First, can an individual use a cell phone safely for 20 or 30 years? Secondly, can children use it safely and even into adulthood for 50 or 60 years?
The British government is aggressively searching for answers to these questions. In December 2000, it allocated $10 million for research on the matter. In the meantime, it requires that the radiation level on each model be disclosed to the consumer.
The United Kingdom also has prepared leaflets to summarize safety research to date. There is no evidence now that using the cell phone causes brain tumors or other ill effects, but the health risk can’t be ruled out, especially for children. In fact, the British government recommends that children not use cell phones at all.
Other nations have made similar studies, and their findings correlate with those of the United States, Canada, and the United Kingdom. Indeed, the subject has attracted a great deal of attention and very few answers. The largest, best-funded study currently is under way in Europe, but the results will not be available until 2003 at the earliest.
Incidentally, scientists are in virtually unanimous agreement that the radiation from a cell phone cannot ionize chemicals and therefore cannot cause genetic damage or cell mutations that could lead to cancer.
The Specific Absorption Rate
In the absence of specific knowledge of the human body’s RF tolerance level, some interim RF absorption limits were developed by ANSI, IEEE, and National Council on Radiation Protection and Measurements (NCRP). The limits have been imposed by the FCC. Other nations have adopted similar requirements.
The basic unit for measurement of RF energy from a cell phone is the specific absorption rate (SAR), defined by the IEEE as “…the time derivative of the incremental energy (dW) absorbed by (dissipated in) an incremental mass (dm) contained in a volume element (dV) of a given density.”
With the cell phone, the SAR is the rate at which RF energy is absorbed in the tissue of the user. The limit in the United States and Canada is 1.6 W of RF power in any kilogram of body tissue. It is measured in any 1-gram section, and the effective limit is 1 mW/g. European limits are somewhat less restrictive because most nations allow up to 10 mW averaged over 10 grams.
Starting August 1, 2001, the CTIA will require members to submit the SAR rating on each cell phone model. Will they meet the government’s limit? Probably so, based on evaluation of several types of cell phones by the Swiss Federal Institute of Technology. They found that generally the SAR of a commercial phone is no greater than the 1-mW/g limit. The highest absorption is in the ear, with the energy level in the brain generally no greater than 0.3 mW/g.
Measuring the SAR
In theory, the SAR measurement is simple. Just turn the phone on, hold it near your mouth and ear, and measure the resultant temperature increase in your brain tissue. However, people don’t want calorimetric probes inserted into their heads, and it is difficult to teach a laboratory rat to use the phone. As a viable alternative, body tissues can be simulated for the cell phone test.
Human body parts can be classified according to their water content. Muscle and skin can absorb more RF energy than fat or bone. Furthermore, properties of tissues are temperature-sensitive, so SAR measurements should be made at a consistent body temperature of about 37°C.
A special formulation for simulating brain and muscle, consisting of water, sugar, salt, and a viscosity-adjusting compound, is used as a standard simulator for the human head. It is contained in a phantom, a thin shell of head-shaped, low-absorption plastic.
Aprel Laboratories and the Dosimetry Research Board of the Spectrum Sciences Institute, both in Ottawa, have established a procedure for SAR measurement. The equipment consists of a PC, an isotropic probe, a positioner, and a data collection system, as shown in Figure 1. Typically, the probe is 3 to 5 mm in diameter and 25 to 30 cm long and deposited on and bonded to a substrate that offers minimum perturbation to the incident RF field.
The probe has three miniature dipoles, each loaded with a diode sensor at the tip. RF energy is sensed in three orthogonal directions and sent to the PC.
During a test, the phantom head is placed on its side over the operating cell phone, simulating actual use. The probe is inserted into the liquid in the phantom, and the computer drives the probe in 1- to 2-cm steps. When coarse evaluation is complete and the high-radiation spots are identified, each is scanned with a resolution of perhaps 1 to 5 mm. All the data points are stored in the PC, analyzed, and plotted. With this equipment and measurement technique, the RF field strength in any 1-gram volume can be quantized and compared with the SAR limit.
The Bottom Line on Safety
The jury is still out on the effect that the SAR of a cell phone has on an adult’s or a child’s physical condition. There is a proven danger, however, for those who choose to use the phone while driving a car—they may not live long enough to be affected by the absorption of RF energy.
For more information, visit these websites:
- American National Standards Institute (ANSI)
- Cellular Telecommunications Industry Association (CTIA)
- Federal Communications Commission (FCC)
- International Commission on Non-Ionizing Radiation Protection (ICNIRP)
- Institute of Electrical and Electronics Engineers (IEEE)
- Journal of the American Medical Association (JAMA)
- National Council on Radiation Protection and Measurements (NCRP)
Acknowledgement
The SAR measurement equipment and technique are excerpted from a draft copy of SSI/DRB-TP-D01-030, SAR Measurements Requirements, March 1998, with permission from Aprel Laboratories, 51 Spectrum Way, Nepean, Canada, 613-820-2730, www.aprel.com.
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May 2001