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How to Calculate Power Flux Density

Power flux density provides a measure of the energy that flows through a unit area each second. Large flux densities typically indicate large energy transfers. Power flux density (PFD) calculations for energy radiators like the antenna of a radio transmitter or the surface of a heat source provide valuable information about how quickly the intensity of the emitted radiation is diminished during energy propagation. PFD is usually measured in watts per square linear unit, but may be expressed in other units that are more descriptive of the strength of the radiation field.

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Instructions

- 1
  Obtain the power output (P), measured in watts, of the isotropic radiation emitter. Isotropic emitters radiate uniformly in all directions.
- 2
  Obtain the distance (d) in meters or feet from the isotropic emitter at which the power flux density is to be calculated.
- 3
  Calculate the spherical area over which the radiation is distributed at a distance (d) from the emitter, using this formula: Area (A) = 12.57 x (d) x (d). Area may be expressed in square meters or square feet.
- 4
  Calculate the power flux density by dividing the power output of the emitter by the area over which the radiation is spread at a distance (d) from the emitter. Substitute the calculated area and the power output into the following formula: Power flux density (PFD) = power output (P) / area (A). PFD is measured in W/(m^2) or W/(ft)^2.

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