Studies of the electric-field distribution in biological bodies - experimental dosimetry at radiofrequencies. Final report, December 1981-September 1985

The objective of the project was to develop and evaluate a computer-controlled system for measurements of the spatial distribution of the specific absorption rate (SAR) in biological bodies and to perform measurements on a model of the human body, with particular emphasis on exposures in the near-field of antennas. Far-Field Exposures. At frequencies above 160 MHz, in spite of large gradieints, local values of the SAR are only about 20 times higher than the whole-body average SAR for homogeneous models of human body. However, an additional increase by a factor of 4-5 can be anticipated at interfaces of high water content tissues with air (gas) pockets and low-water-content tissues. The existence of large gradients and high local SARs, as confirmed by the results, further supports an accepted view that biological effects at relatively low average SARs are due to thermal interactions. For humans, high SARs occur in the neck, and the ratio of the SAR in the neck to the whole-body average increases with frequency. Near-field Exposures. Based on the experimental findings the authors believe that, because of the spatial pattern of energy deposition, the whole-body average SAR is not an adequate dosimetric measure for near-field exposures.