HOW IS RADIOFREQUENCY 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). The quantity used to measure how much RF energy is actually absorbed by the body is called the Specific Absorption Rate or SAR. The SAR is a measure of the rate of absorption of RF energy. It is usually expressed in units of watts per kilogram (W/kg) or milliwatts per gram (mW/g).
An RF electromagnetic wave has both an electric and a magnetic component (electric field and magnetic field), and it is often convenient to express the intensity of the RF environment at a given location in terms of units specific to each component. For example, the unit “volts per meter” (V/m) is used to express the strength of the electric field (electric “field strength”), and the unit “amperes per meter” (A/m) is used to express the strength of the magnetic field (magnetic “field strength”). Another commonly used unit for characterizing the total electromagnetic field is “power density.” Power density is most appropriately used when the point of measurement is far enough away from an antenna to be located in the “far-field” zone of the antenna. Power density is defined as power per unit area. For example, power density is commonly expressed in terms of watts per square meter (W/m2), milliwatts per square centimeter (mW/cm2), or microwatts per square centimeter (µW/cm2). One mW/cm2
The measurements used depend on whether the source of energy is remote from or near to the person exposed to the radiation. In situations where the person is more than several wavelengths from a RF source, power density is used. This is defined as the rate of energy flow through a given surface area, and it is measured in watts per square metre. When the person is close to the RF source, as when using a wireless phone held to the head, the Specific Absorption Rate is used.
An RF electromagnetic wave or RF “field” has both an electric and a magnetic component (electric field and magnetic field), and it is often convenient to express the intensity of the RF environment at a given location in terms of units specific for each component. For example, the unit “volts per meter” (V/m) is used to measure the strength of the electric field (electric “field strength”), and the unit “amperes per meter” (A/m) is used to express the strength of the magnetic field (magnetic “field strength”). Another commonly used unit for characterizing an RF electromagnetic field is “power density.” Power density is most accurately used when the point of measurement is far enough away from an antenna to be located in what is commonly referred to as the “far-field” zone of the antenna. Power density is defined as power per unit area. For example, power density can be expressed in terms of milliwatts per square centimeter (mW/cm2) or microwatts per square centimeter (W/cm2). One mW eq
