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laterally shielded exposure cabin with the inner surface covered by pyramidal RF absorbing material
Test subjects wore a special head set consisting of a modified stereo head phone (all metallic parts removed) with small matched helical antennas mounted in a way to achieve an exposure distribution in the head similar to the case of mobile phone usage. Subjects were exposed only at the left side of the head, but they were not informed about this fact.
Each subject was tested on a single week day between 3:30 and 7:00 p.m. and underwent four tests used for assessing visual perception under three different exposure conditions (high exposure, low exposure, and sham exposure) that were controlled randomly and double-blinded by control software. Additionally, all tests except the Critical Flicker and Fusion Frequency Test were presented to the subjects under a positive control condition (flicker light applied from the back) at the end of the subject's session.
SAR values indicated resulted in the cortex of the left temporal lobe of the brain in the high exposure condition. Low exposure condition was defined to be one tenth of high exposure, and sham was at least 50 dB below low exposure. Background ambient field strength measured in the frequency range from DC up to 18 GHz was found to be negligible.
Mess- und Berechnungsdetails
A detailed dosimetric analysis of the exposure system was based on the power recordings (forward as well as reverse power measurements) obtained during the experiments and extensive numerical simulations using the SEMCAD simulation platform and the anatomical European male head model at a spatial resolution of 1.5-3 mm. The validity of the numerical model of the small helical antennas used was verified prior to the dosimetric analysis by comparisons of experimental and numerical results, showing deviations of less than ±5%. Furthermore, the SAR inside the homogeneous specific anthropomorphic mannequin (SAM) phantom measured using an automated SAR test facility (DASY 3) agreed within ±10% with corresponding SEMCAD calculations. The minimum and maximum values of SAR to be expected in the test subjects' temporal cortex were obtained by an uncertainty analysis, the main contribution (~85%) being due to the variations of the antenna's position with respect to the head, caused by different head sizes and shapes.