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21 November 2009

Answer to Question #2579 Submitted to "Ask the Experts"

Category: Cell Phones

The following question was answered by an expert in the appropriate field:

First of all, thanks for designing a wonderful site. My question is: how do you calculate EME (electromagnetic emissions) around the transmitter (antenna) at any given point and what are measures to keep it under the safety code?

Conceptually it is straightforward to predict the radiofrequency (RF) exposure intensity at any point in the vicinity of a cellular radio base station antenna. Simply multiply the effective radiation power times the inverse square of the distance times the relative gain of the antenna in the direction of the interest. The relative gain in different directions is know as the antenna radiation pattern and is usually available from the antenna manufacturer in graphical or tabular form.

Unfortunately, in real life the calculations involved in base station antenna evaluations are quite complex and require expert knowledge and experience to deal with the many parameters that are involved. An excellent reference summarizing this process is the Federal Communications Commission OET Bulletin No. 65 titled "Evaluating Compliance With FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields," available on the Federal Communications Commission (FCC) Web site.

To assess the RF hazards associated with handheld cell phones it is necessary to predict the rate of absorption in the body of radiofrequency energy, a parameter called the specific absorption rate (SAR). This is a very complex calculation, and cell phone manufacturers often rely on measurements of SAR in fluid-filled cylinders or plastic containers in the shape of a head. The FCC requires cell phone manufacturers to provide this data to FCC. You can obtain the data for your model phone on the the FCC's Web site. Unfortunately only cell phones manufactured in the last couple years are listed here.

As to your question about keeping RF exposures within the safety code, please read the other questions posted on this Web site this matter. Cellular radio products that meet FCC requirements will be within the guidelines established by safety standards organizations for users' and public exposure to RF radiation fields.

Gary H. Zeman, ScD, CHP

Answer posted on 9 April 2003. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.