Abstand zw. exponiertem Objekt und Expositionsquelle
The animals in the RF-field-exposed and sham-exposed groups were kept in identical chambers. The five chambers used for sham and RF exposure, respectively, were placed in two separate air-conditioned, adjacent rooms of the same dimensions. Exposure chambers (90 x 90 x 187 cm) were made from sheet steel and had a lining of absorbing material on the walls and the bottom. Each chamber contained in its bottom part a Plexiglas cage of 0.4 m² x 20 cm equipped with three stainless steel nipples for drinking and covered by a perforated Plexiglas lid. The top as well as the lower front and back sides of the chamber underneath the animal cage were kept open for ventilation but covered with wire netting to suppress leakage of the EMF.
Within the exposure chamber, the animal cage was located in the far field of a flat spiral antenna which was at a distance of 130 cm from the bottom of the cage and emitted a clockwise circularly polarized RF signal.
Exposure was interrupted once daily for about 10 to 20 min for feeding and inspection of animals, 3 to 4 h once weekly for tumour palpation, 1 to 2 h three times weekly for cleaning of cages, and 4 to 5 h once per month for servicing the exposure devices.
SAR values might have shown larger variations if instead of calculations for a standard rat model they had been based on actual phantom measurements of individual rats of different sizes and ages.
Mess- und Berechnungsdetails
The mean power flux density of the field at the bottom of the cage measured with a small isotropic electric probe exhibited a variation of ± 3 dB between the center and the corners of the cage. The SAR values were determined by means of computer simulations with MAFIA software using an anatomically correct model of the body of a rat. The varying dielectric properties of the animal tissues lead to an uncertainty of less than 20%. Because of a resonance effect due to the body length (excluding the tail) of young animals being approx. half the wavelength of the RF signal, the amount of energy absorbed by them is higher than that for older animals, and the SAR for the whole body was bound to decline continuously during the course of the experiment.
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