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Abstract
A Crawford cell exposure
chamber (main section 30 cm
square) was used for electromagnetic dosimetry in
the 225 to 500 MHz frequency range. Electric field patterns were measured
within the cell. No higher-order modes were observed at any of the frequencies
studied below 500 MHz, but significant field perturbations were seen at 2450
MHz. Energy absorption in a prolate spheroidal hamster phantom and in saline-filled spheres
of various sizes was measured. The normalized whole body specific absorption
rate (SAR) in watts//kg per mW/cm² increased from 0.11 (at 25 MHz) to 0.42
(at 450 MHz) for the hamster phantom in E polarization, from 0.06 (at 325
MHz) to 0.20 (at 500 MHz) for K
polarization, and from 0.03) (at 325 MHz) to 0.12 (at 50O MHz) for H polarization.
Although these values exceed predictions from the long wave-length far-field
approximation for power absorption, the measured SARs
were corroborated directly using calorimetry. In
addition, calorimetric data obtained using saline-filled spheres suggests
that absorbed power in a Crawford cell converges to the far-field plane wave
theoretical values only for objects occupying less than 20% of the vertical
dimension from the septum to the outer wall.
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