Signal-Level Models of Pointwise Electromagnetic Exposure for Millimeter Wave Communication

Electromagnetic exposure from wireless devices is strictly regulated around the world to ensure the safety of consumers. Recent studies have demonstrated that multi-antenna systems can leverage signal-level exposure models to jointly mitigate user radiation absorption and achieve high data rates. This is especially important for millimeter wave technologies, which are susceptible to power back-off techniques due to high propagation and blockage losses. However, prior models require significant overhead in the form of exposure measurements to compute model parameters and cannot be easily modified to predict electromagnetic absorption in different testing configurations. This article proposes methods to approximate the characteristic matrix of a quadratic model for two exposure measures in the millimeter wave band: incident power density and surface specific absorption rate (SAR). The presented models can be calculated with a small number of parameters and can be altered to account for mutual coupling, near-field effects, and changes in the exposure scenario. Spatial sampling schemes based on these models are derived to determine how many testing points are necessary to estimate exposure in a region within a specified margin of error. Software simulation results with half-wave dipoles validate the accuracy of the proposed models in a millimeter wave scenario.