Reduction of Exposure Inhomogeneity for Millimeter-Wave Experiments on Cells In Vitro

An in vitro experiment of millimeter-wave effects requires a minimum exposure inhomogeneity for cells to receive the same exposure intensity. Two methods are studied to minimize the inhomogeneity for far-field exposures. The propagation and polarization directions of incident waves are optimized to reduce the standard deviation (SD) of the specific absorption rate (SAR) in cells cultivated in a 35-mm Petri dish. The SAR distributions are characterized and the SAR variance is interpreted. Choke rings are introduced and optimized to support the Petri dish and decrease the SAR SD by canceling the scattered waves. The numerical study is based on the finite-difference time-domain algorithm. A six-degree-of-freedom algorithm is developed to generate incident waves with various properties in the problem space enclosing the model made of 0.125-mm voxels. The exposure scenarios include the plane-wave exposure and antenna exposures with different half-power widths, incident waves of various propagation and polarization directions, and frequencies of 42.3, 53.6, 61.2, and 60.5 GHz. The exposure with the upward wave is confirmed for the lowest SAR SD, which is reduced to well below 10% by using choke rings. The choke ring approach is comparatively validated in the simulation of an experimental setup.