Updated at 23 Jun 2026
Electromagnetic fields span low to high frequencies, with electric and magnetic components considered separately at low frequencies and coupled at higher ones. In radiofrequency ranges, fields can transmit over long distances, used in broadcasting and wireless communication. SAR quantifies tissue energy absorption, mainly as heat.
Electromagnetic fields consist of electric and magnetic components, which are considered separately in the low-frequency range. As frequency increases, these components increasingly merge and are regarded as a single electromagnetic field. At frequencies of approximately 30 kHz and above, electromagnetic fields can detach from their source, such as an antenna, and propagate over long distances at the speed of light (approx. 300,000 km/s). This property is utilized technically for the transmission of information in applications such as radio, television, mobile communications, and wireless data transmission. The power flux density S of such a field describes the amount of energy per unit area (watts per square meter, W/m²), which is composed of the electric and magnetic field components. The field strength decreases with increasing distance from the source. To quantify the amount of energy absorbed by biological tissue in a frequency range of approximately 100 kHz to 10 GHz and converted primarily into heat, the specific absorption rate (SAR) is used. It is measured in watts per kilogram of tissue (W/kg) and averaged over a period of 6 minutes to establish a thermal equilibrium between energy input and heat distribution in the tissue. By averaging the SAR across different body masses, exposures for the entire body or individual body regions, such as the eye, can be distinguished. This scientific methodology is fundamental to the assessment of electromagnetic field exposure and its potential biological effects.
