A quarter century of in vitro research: A new look at exposure methods

The specific absorption rate (SAR) distributions in radio frequency-exposed solutions containing suspended or plated cells in vessels used for in vitr o research were calculated by the finite-difference-time-domain method, gra phed in color, and statistically analyzed in terms of uniformity for applic ation to research on safety of wireless devices. The uniformity of SAR was quantified by visual inspection of colored plots, histograms, means, standa rd deviations, and maximums for the cell suspensions exposed in test tubes, Petri dishes, and rectangular flasks. Exposure sources included plane wave s, transverse electromagnetic (TEM) cells, and striplines used at frequenci es of 837, 2450, or 3,000 MHz. The results demonstrated that the most nonun iform SARs for plated or suspended cells in solution occurred for exposures of test tubes and rectangular flasks with plane waves, polarized for maxim al absorption. The most uniform SARs for a layer of cells occurred for expo sure of Petri dishes oriented for weakest coupling to the fields in a TEM c ell. Additional improvement in uniformity was found to be possible by restr icting the edge of the layer of cells from being too near the edges of the dish. It was not possible to achieve satisfactory uniformity in the SAR in cell suspensions exposed in standard vessels to any of the sources. The bes t but not satisfactory SAR uniformity was observed for cells suspended in t he lowest 1-ml volume of the liquid contained in a test tube exposed at the bottom in a TEM cell. Experimental measurements of average SAR by temperat ure change for this case varied from 18% higher to 26% lower than finite di fference time domain-derived values. The most uniform SAR distribution for cell suspensions in nonstandard containers was found for a rectangular slab configuration exposed in a stripline with the plates separated from the me dia by a thin layer of insulation. It is possible to experimentally impleme nt this model by placing a fluid-filled thin-wall rectangular container tig htly between the plates of a stripline. Bioelectromagnetics 20:21-39, 1999. (C) 1999 Wiley-Liss, Inc.