Numerical Calculation of Whole-Body Exposure to Beams From mmWave Base Stations Using Superposition of Spherical Waves

Whole-body exposure to beams from fifth-generation (5G) base stations is numerically studied. Since the base stations have the capability for beamforming, the assessment of exposure to all possible beams from such stations must be performed to find the worst-case value. However, numerical evaluations using anatomically realistic computational human models for various beams are computationally costly, and an exhaustive evaluation can be challenging. Therefore, a reduction in computational burden is required. In this paper, a computational method consisting of two stages is presented. This method is based on the principle that radiation from a source can be decomposed into a superposition of vector spherical harmonics. First, a computational human model is exposed to each decomposed wave, and the results for each wave are stored. Then, exposure to a beam is evaluated using the weighted sum of pre-exposure data with complex weights, which represent the beam. The whole-body-average (WBA) specific absorption rate (SAR) for various beams and antennas operating at 28 GHz was synthesized. The synthesized results were compared with the results of the conventional method. The comparisons for $8\times 8$ array antennas positioned at horizontal distances of 1.0, 2.0, 3.0, and 4.0 m and heights of 1.0 m and 2.5 m from a three-year-old pediatric model yielded less than 1.5% relative error. The worst-case WBA-SARs for exposure to $8\times 8$ and $4\times 4$ dipole arrays with various polarization angles and $8\times 8$ patch arrays were computed using the precalculation data.