Non-invasive near-field characterization of Bloch mode dispersion in sinusoidally modulated metasurfaces via transient infrared thermography

: This study presents a disruptive, non-invasive diagnostic framework for the high-resolution electromagnetic characterization of sinusoidally modulated High Impedance Surfaces (HIS). Traditional near-field scanning techniques, while standardized, are inherently limited by probe-induced field perturbations and restricted spatial throughput. To overcome these constraints, we propose and validate the use of transient infrared (IR) thermography as a high-fidelity electromagnetic-to-thermal transducer. Operating within the 2.1-2.4 GHz spectrum, we demonstrate that the thermal signature captured on a high-emissivity Arlon substrate serves as a precise metrological proxy for Bloch mode propagation and energy localization. By synchronizing frequency-domain vector network analysis with spatial thermal mapping, we achieve a direct experimental extraction of the guided wavelength ([Formula: see text]) and the Slow-Wave Factor (SWF). Our quantitative assessment reveals a remarkable wavelength compression in the HIS prototype, reaching an SWF of 6.56 at 2.339 GHz, which correlates with a profound resonance dip of -21.09 dB. The temporal stability of the standing wave patterns observed during the transient heating phase (0-60 s) confirms the excitation of stable Bloch modes and validates the methodology's ability to decouple electromagnetic signatures from lateral heat diffusion. These results establish transient IR thermography as a robust, high-throughput alternative for validating complex periodic metasurfaces, providing a strategic pathway for the optimization of next-generation wearable shielding and electromagnetic compliance in augmented/virtual (AR/VR) technologies.