How is radio frequency radiation measured?
RF waves and RF fields have both electrical and magnetic components. It is often convenient to express the strength of the RF field in terms of each component. For example, the unit “volts per meter” (V/m) is used to measure the electric field strength, and the unit “amperes per meter” (A/m) is used to express the magnetic field strength. Another common way to characterize an RF field is by means of the power density. Power density is defined as power per unit area. For example, power density can be expressed in terms of milliwatts (one thousandth of a watt) per square centimeter (mW/cm2 or microwatts (one millionth of a watt) per square centimeter (W/cm2). Note the use of the quantity power density, which is the rate of flow of electromagnetic energy per unit surface area. This quantity is particularly meaningful in the “far field” region of an antenna, a region where the radiation field has a plane-wave character, with the electric and magnetic field vectors perpendicular to each oth
