Human Exposure to RF-EMF From Active RIS in Outdoor Environments: A Vehicular Communication Case Study

This study assesses the impact of reconfigurable intelligent surface (RIS) on the radio frequency electromagnetic field dose absorbed by a pedestrian in a vehicle-to-vehicle (V2V) communication scenario in urban settings. The exposure scenario consists of a two-lane road surrounded by buildings, with a transmitting vehicle (Tx – V2V antenna) and a target receiver (Rx) in non-line-of-sight condition due to the presence of a blocking vehicle. An active RIS is placed in the opposite lane to aid direct communication between the Tx and Rx. The absorbed dose induced by the environmental electric field -generated by the Tx and reradiated by the RIS -is assessed in pedestrians of different ages (adult and child human models) by computing the whole-body specific absorption rate (SARwb W/kg). The analysis considers (i) different pedestrian positions, (ii) two V2V frequencies (5.9 GHz and 28 GHz), (iii) two RIS set-ups (vehicle-mounted, infrastructure-mounted), (iv) three V2V antenna positions, and (v) three RIS locations relative to the V2V antenna. At 28 GHz we also analyzed the absorbed power density (Sab W/m2). The presence of the RIS induced a maximum SARwb of 0.13 mW/kg and Sab of 5.8 mW/m2 in the child at 28 GHz and a maximum relative increase of dose absorbed-compared to the case without the RIS -that is +1.60 times greater. Results highlight how V2V antenna position significantly impact (p < 0.05) the increase of the dose absorbed. Nevertheless, all the exposure levels found are well below the limits recommended by the ICNIRP guidelines.