Cross-Validation of Near-Field Energy Deposition on 5G Metasurfaces Using Transient Infrared Thermography and Electric-Field Mapping

The advancement of 5G/6G infrastructure requires specifications that are challenging from an engineering point of view. Some of the advanced field-manipulation techniques rely on High Impedance Surfaces (HISs), including modulated appearances. However, their intense near-field energy localization for some frequencies poses challenges for bioelectromagnetic safety. Measurements of such hot spots require special attention; traditional metallic probes are often invasive and locally distort fields. This paper proposes and validates a non-invasive methodology using Transient Infrared (IR) Thermography for high-resolution mapping of a substantial area (in terms of wavelength). By capturing the initial thermal gradient (dT/dt) on a HIS built on an Arlon AD430 substrate, we estimate the local specific absorption rate (SAR) of energy deposition before heat diffusion occurs. Cross-validation with electric (E)-field measurements at two different distances from the HIS in the sub-6 GHz 5G frequency spectrum, namely at 2 mm and at 22 mm, reveals a remarkable spatial correlation between thermal hot-spots and peak intensities, which decrease by ~83% across these distances. This study demonstrates that transient IR thermography is a rapid, non-perturbing tool for auditing electromagnetic safety compliance, providing a robust framework for determining SAR in human tissues exposed to radiation from future 5G devices.