FDTD Assessment of Exposures to Far-Field mmWave Beams in Anatomical Head Model

In new fifth generation wireless communication systems, the radiation from a small cell base station antenna may form a beam. Unlike conventional wireless systems and local exposures from mobile phones, different body parts, including complex surfaces (e.g., nose and pinna), are exposed to an intense beam. This article adopts a hybrid spherical near-field transformation and finite-difference time-domain method to assess the power absorption and resultant temperature rise in a human head model exposed to a radiation beam from a patch array at 28 GHz in the far-field region. Unlike previous studies, the spherical near-field measurement can be used as an input and thus can combine nonreactive near-field measurement (computation) with dosimetry analysis. We then considered electrically larger antenna-body distances than local exposure scenarios, ranging from 0.25 to 2 m with various incident angles, corresponding to canonical beam exposure from a small-cell base station. For a single head model exposed to the antenna array, parameter variations create a total of 112 cases providing a diversity of exposure scenarios. Peak spatial-average absorbed power density and skin temperature rise were assessed for our computations of the selected scenarios. Higher temperature rises were observed around the nose or pinna due to the interference fringe effect. This effect is more pronounced when the beamwidth at the head surface is large, leading to slightly higher heating factors than those previously obtained using a planar body model with plane-wave approximation.