Over the last several decades, innumerable investigations have been conducted to define the bioeffects of microwave (MW) fields on cells, tissue and whole animals, not only stemming from concerns of public safety from exposure to wireless communication systems, but also for the purpose of developing beneficial applications in therapeutic and diagnostic procedures. Studies with cells have indicated that certain exposure parameters related to MW fields may influence particular functions of cells by the interactions between specific cellular constituents in cells and the applied MW fields.

The goal of this research is to identify specific MW parameters in the frequency range 1 to 6 GHz that can induce possible nonthermal effects on catecholamine release from chromaffin cells. For the study, a free-space broadband in vitro MW exposure system consisting of a cell perfusion apparatus (CPA), which allows for on-line monitoring of catecholamine release, placed in the far field of a horn antenna, has been designed, constructed and tested. The system was characterized by measurements performed in an anechoic chamber as well as numerically using the Finite-Difference Time-Domain (FDTD) method, which computes detailed distributions of the electric field and specific absorption rate (SAR). All aspects of the experiments were computer controlled hence minimizing the possibility of human error during experiments.

Computations and experiments performed using an early design of the free-space exposure system led us to conclude that the system had certain limitations, which were (1) unsatisfactory homogeneity of the electric field, SAR and temperature distribution; and (2) insufficiently high magnitude of the electric field at the location of the cells. In order to overcome these limitations, modifications were made to the free-space exposure system including placing the CPA in the near field, rather than in the far field of the horn antenna and replacing the original CPA with one having smaller dimensions. These modifications significantly improved the homogeneity of the electric field, SAR and temperature distribution in the region containing the cells, and also increased the magnitude of the electric field to the maximum possible level achievable with the existing MW equipment. A series of carefully controlled experiments were carried out with this modified free space exposure system to quantify changes in catecholamine release under various parameters of MW field exposure. These experiments indicated that MW induced effects on catecholamine release occurs most often when a pulsed frequency sweep (PFS) with a 100 ms pulse width in the frequency range 5-6 GHz is used. However, not all experiments carried out using these MW exposure parameters showed an effect, indicating a lack of reproductivity. This could be because the maximum electric field magnitude capable of being produced by our exposure system is close to a threshold value for causing the effect on catecholamine release.

In an effect to increase the probability of inducing reproducible robust changes in catecholamine release, a second exposure system was designed that can produce much larger electric fields. The new system is based on a planar exposure chamber embedded in a low loss, high dielectric constant substrate material. Initial computations using the FDTD method have shown that the newly designed exposure system will be capable of producing an electric field that is 20–40 fold greater in magnitude than our original exposure system, while at the same time maintaining acceptable homogeneity of the electric field over the region containing the cells for the entire frequency range of interest.