Specific absorption rate (SAR) is defined by the National Council on Radiation Protection and Measurements as "...the time derivative of the incremental energy absorbed by (dissipated in) an incremental mass contained in a volume of a given density" (NRCP, 1981). The whole-body and partial-body SAR form the basis of permissible exposure limits for radio frequency radiation (RFR). The whole-body SAR provides very useful information regarding the influence of frequency, polarization, and orientation on RFR absorption. However, RFR is not absorbed uniformly throughout a biological system. Numerous factors contribute to the heterogeneity of SAR values in biological system, including differences in electrical properties of different tissues, impedance mismatches at tissue boundaries, and the complex geometry of individual organs and structures. Due to these factors, local SAR must be used to reveal the distribution of RFR absorption within the animal. Without this information, bioeffects data obtained from one species cannot be meaningfully extrapolated to another.
展开▼
