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How to Convert EIRP to Flux

Prolonged exposure to high-power radio-frequency waves has the same effect on the human body as a microwave has on food. The Federal Communications Commission safeguards the public by limiting the maximum permissible exposure to emissions from transmitters of all types, including handheld portable telephones. Power density, also known as flux and expressed in milliwatts per square centimeter or watts per square meter, is a common measure for defining maximum permissible exposure and is related to the effective isotropic radiated power (EIRP) of a transmitter. Flux is dependent on EIRP and on distance from the transmitter.

Things You'll Need

Calculator

Instructions

- 1
  Consult the manufacturer̵7;s data sheet and note the EIRP of the transmitter or device that you are evaluating. Check whether this is given in watts or milliwatts.
- 2
  Check the distance from the transmitter for which you intend to calculate the power flux density. If the EIRP is in watts, note the distance in meters; if it is in milliwatts, note the distance in centimeters.
- 3
  Multiply the distance by itself and multiply this figure by 12.57, the value of 4 times pi. Note the answer. For example, if the distance is 5 meters, the answer is 314.25, since 5 x 5 x 12.57 = 314.25.
- 4
  Divide the EIRP by the answer and note the result, which is the power flux density in milliwatts per square centimeter or watts per square meter, depending on the units you used.
- 5
  Check your math. For example, if the distance is 5 meters and the EIRP is 100 watts, the flux is 0.31 watts per square meter. If the distance is 5 centimeters and the EIRP is 100 milliwatts, the flux is 0.31 milliwatts per square centimeter.

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