Simplified model and measurement of specific absorption rate distribution in a culture flask within a transverse electromagnetic mode exposure system

In vitro experiments in bioelectromagnetics frequently require the determin ation of specific absorption rate (SAR) within a layer of cells on the bott om of a culture flask when the SAR has rapid spatial variation both horizon tally within the cell layer and vertically in the medium bathing the cells. This problem has only recently been treated in the literature; and it is h ere approached differently for another irradiation system. It is shown that a simple two-dimensional frequency-domain guided-wave treatment yields res ults qualitatively comparable to those of more computationally intensive th ree-dimensional time-domain free-field scattering treatments. The problem o f inferring local SARs from temperature-vs.-time curves is shown to be seri ously confounded by thermal diffusion; and specific analytic and numerical results are presented to aid in understanding this effect. A novel experime ntal technique is introduced for measuring millikelvin temperature offsets with subsecond resolution, and illustrative experimental data are presented . Finally, present experimental and theoretical uncertainties are considere d; and it is pessimistically asserted that, in a culture flask where spatia l SAR variation is rapid, point SAR measurements by thermal methods may be in error by as much as +/-3 dB. More reliable thermal determinations will r equire extreme care, challenging technological innovations, or both. Bioele ctromagnetics 20:183-193, 1999. (C) 1999 Wiley-Liss, Inc.