Both waveguides (exposure and sham-exposure) of 4 m diameter and 17 cm vertical plate distance were placed within the same room and carried up to 24 cages measuring 425 mm Œ 265 mm Œ 160 mm (L Œ W Œ H) each of them housing 6-7 mice. The cage area was covered with trapezoidal lids (3 cages per opening) with wire mesh. At the outer boundaries of the units, absorbers were installed.
A modulated signal generator and an amplifier were connected to the cone antenna of one unit (and also the presence of the field was monitored continuously) via a "black box" so that it could not be seen which group of animals was exposed (blind design).
Because the plate distance of the radial waveguide had to be chosen larger than half the wavelength due to the regulated height of the cages, special modifications of the fundamental geometry had to be performed to obtain only the fundamental TEM-mode and avoid the propagation of the unwanted higher order modes.
Varying SARs in the mice moving freely inside their cages were analysed by numerical computations of the EMF distribution inside the radial waveguide for five different configurations of the animals, which were assumed to be uniformly distributed in time. It was considered sufficient to use simple homogeneous models (ellipsoids, 6 cm x 3 cm, appr. 32 g) filled with muscle tissue for the mice. The standard deviation of the whole body SAR turned out to be ± 40%. The assessment of maximum localized SAR was performed by use of an anatomical mice model which was placed into the group of ellipsoids.
Bundesamt für Strahlenschutz (BfS; Federal Office for Radiation Protection), Salzgitter, Germany
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