Two radial waveguides each containing up to 28 samples were placed into an incubator and were used in turns as the exposure device or sham-exposure device. The samples in each waveguide were arranged symmetrically near the rim. The reflections were reduced by a 5-mm flat absorber along the waveguide perimeter.
The filters carrying the cell cultures were installed in cylindrical tubes between two discoid gold electrodes. Each sample holder was equipped with a two-electrode system for impedance monitoring. The leads of the electrodes were conducted upward through the metal caps that sealed the cartridges. Thus simultaneous RF-field exposure and LF impedance measurement was possible.
The barrier tightness was monitored continuously by TEER measurement using impedance spectroscopy described in detail by Wegener et al. in Brain Res. 853, 115-124 (2000). Impedance analysis was carried out in the frequency range from 1 Hz to 500 kHz applying a sinusoidal voltage of ~30 mV amplitude.
The electromagnetic field and the temperature of the medium were monitored constantly by a field antenna and a thermistor probe installed inside a cell culture vessel. The field distribution inside the exposure device was calculated based on the FDTD method.