A novel waveguide-based radio frequency/microwave exposure system for studying nonthermal effects on neurotransmitter Release-finite-difference time-domain modeling

A research effort is underway to identify specific radio frequency/microwave parameters in the frequency range 0.75-1.12 GHz that can produce nonthermal effects on the release of catecholamines from cultured bovine adrenal medullary chromaffin cells, an established in vitro model of neural-type cells. A well-characterized exposure system is crucial for interpreting the biological outcomes of experiments. This paper describes a novel waveguide-based exposure system that permits perfusion of the cells with a temperature-controlled balanced salt solution for online monitoring of catecholamine release from the cells during radio frequency/microwave exposure. The finite-difference time-domain method was used to optimize the exposure conditions, the goal being to achieve the maximum possible homogeneity in the distribution of the specific absorption rate at the location of the cells in the waveguide. At a frequency of 1 GHz, optimal coupling of the radio frequency/microwave field into the region containing the cells was obtained only when the cells were placed at the location of the electric field maximum of the standing wave pattern, with the electric field parallel to the plane containing the cells. In this case, the specific absorption rate distribution was found to be the highest as well as homogeneous to within 30%.