In what unit is SAR measured?

Specific Absorption Rate (SAR) is a measure used to quantify the amount of radiofrequency energy absorbed by the body when exposed to an electromagnetic field. The unit of SAR is Watts per kilogram (W/kg). This measurement indicates how much power (in watts) is absorbed by a mass (in kilograms) of biological tissue.

The choice of Watts per kilogram as the unit is significant because it allows for a comparison of absorption across different body masses. For instance, if two people are exposed to the same electromagnetic field, understanding SAR in terms of W/kg allows health and safety regulators to evaluate how effectively the energy is being absorbed relative to body weight, which is crucial for assessing potential health impacts.

Other units such as Joules/Kilogram or Calories/Kilogram do not adequately express the rate of energy absorption related to the effect of time, which is critical for understanding SAR in the context of exposure duration. Watts, being a measure of energy transfer per time, provides a direct correlation to how quickly energy is being absorbed by a specific weight of tissue, making it the most appropriate unit for SAR measurement.