Why are both W/m2 and W/kg used as measurement units?
The general public’s exposure to electromagnetic fields is quantified using SAR (the Specific Absorption Rate), which is expressed in W/kg (the power absorbed by living tissue per unit of mass). These limits constitute the basic restrictions for local exposure (head and upper body, members) and average full-body exposure. However, SAR is difficult to measure, particularly in the case of full-body exposure. This is why reference levels for the intensity of electrical field (V/m), the intensity of magnetic field (A/m) and power density (W/m²) have been defined. In practice, their measurement is much easier to carry out and guarantees the fact that if these levels aren’t exceeded, the basic restrictions won’t be exceeded either. In the case of mobile phones, we’re dealing with local exposure in the field near to the aerial, and reference levels are unusable. This is why basic restrictions must be used (W/kg).
