Sar Explained

WHAT IS SAR?

Specific Absorption Rate (SAR) is a measure of the RF energy absorbed by the human body when exposed to a radio frequency (RF) emitter. Unlike measurements of the incident fields that cause the exposure, SAR provides an accurate indication of the potential harm that could result from exposure.

WHEN IS SAR USED?

Whenever there is potential for people to be exposed to complex electromagnetic fields that may exceed allowed limits, SAR is an appropriate metric. This usually occurs close to the source of RF energy or in situations where passive objects can resonate or re-radiate energy. Standards require SAR assessments in some situations.

SAR STANDARDS

Australian and international RF exposure standards (such as ARPANSA RPS3 and C95.1) are based on SAR limits. The field limits given in these standards are derived from typical SAR levels for people in simple far-field exposure situations and can be misleading in near-field scenarios. Existing standards allow SAR assessments to be done by measurement or simulation. New IEC/IEEE standards specifically for computational assessment of SAR are due for release soon.

SAR ASSESSMENTS

For many years Specific Absorption Rate (SAR) has been measured using robotic probes and liquid phantoms that approximate average human tissue. While this approach is widely accepted, it is time-consuming and requires significant investment in specialised equipment. In addition, SAR measurement has inherent accuracy limitations and can only be used to assess very simple exposure scenarios.

Recent advances in Computational Electromagnetics (CEM) have made it possible to assess SAR with greater accuracy and fidelity using high resolution computer models of the human body. Unlike phantom measurements, Computational SAR techniques can be used to accurately assess virtually any real-world RF exposure scenario. In addition to exposure from body-worn or hand-held devices, SAR assessments can be done for in-situ personnel exposed to complex near-field hazards, such as in vehicles, aircraft, ships and confined spaces.