High-Efficiency Applicator Based on Printed Circuit Board in Millimeter-Wave Region

The purpose of this study is to develop a novel in vitro millimeter-wave (MMW) applicator for an exposure apparatus that allows high power efficiency with reasonably good homogeneity over a sufficient exposure area, as well as the capability of temperature control in biological samples. The applicator is made of a printed circuit board and has a large and circular (90-mm diameter) exposure area that is fed with MMWs using post-wall waveguide technology. The applicator is designed for the exposure of cells to MMWs at 60 GHz. The proposed applicator has an absorption efficiency of 54%, where the absorption efficiency is defined as the ratio of the total power absorbed in the culture medium to the input power. Its efficiency is higher than those of other apparatuses operating at 60 GHz reported in the literature. Most of the cells (89%) are located within the ±5-dB region relative to the average specific absorption rate, which shows reasonably good homogeneity compared with previously reported literature data. The applicator enables efficient temperature control for in vitro experiments to explore unknown and possible nonthermal effects of MMW exposures.