The Specific Absorption Rate (SAR) is defined as the rate at which energy is absorbed per unit of mass of body tissue.
The evaluation of the SAR of a device falls within the scope of EMF (ElectroMagnetic Field) measurements intended to measure the levels of the human body’s exposure to radiofrequency waves.
Considering the extent of the development of radiofrequency devices in our modern societies, most international legislations define limits for human exposure to electromagnetic fields (such as the essential requirements of the RED and Low Voltage Directives for the European regulations and the CE Marking scheme).
Among the different physical values that can be used to characterise exposure to electromagnetic fields, SAR is particularly appropriate for transmitters used close to the body (other methods are used to assess compliance with the public exposure limits for the electromagnetic fields emitted by base stations, e.g. GSM, FM, TV transmitters, etc. )
The whole-body SAR measurement is widely accepted as defining the relationship between thermal effects and exposure to radiofrequency waves.
The local SAR measurement enables the exposure of specific parts of the body to be taken into consideration (such as the head in relation to a mobile phone).
The SAR limits are defined to prevent generalised thermal stress of the body and excessive localised heating of body tissues.
SAR measurements are required by many regulations worldwide.
The SAR limit values may vary from one legislation to another:
SAR measurement standards apply to communication devices emitting electromagnetic fields and intended for use against the ear or near the body (< 200mm).
It should be noted that equipment equipped with several sub-assemblies whose SAR has been assessed separately must again be subject to a DAS measure.
The DAS measuring system consists of: