Using infrared thermography for addressing the spatial variability of electromagnetic field in the proximity of emitting antennas

The spatial variability of electromagnetic field (EMF) in the proximity of two patch antennas operating at 3,5 GHz and 5,17 GHz was investigated by measuring the temperature of a thin liquid film placed near the transmitting antenna using an infrared camera. Measurements were performed for two types of signals: 1) continuous wave; 2) Long Term Evolution (LTE) signals of different bandwidths (5/10 MHz). An algorithm was designed to extract the maximum heating rate of the liquid, obtained when the effect of the thermal diffusion mechanism is minimal. This maximum heating rate is proportional to the internal electric field strength and thus the Specific Absorption Rate (SAR) value. A simulation was also performed to obtain the SAR distribution with comparative analysis of experimental and computational results. Our findings demonstrate the applicability of infrared thermography for EMF spatial mapping, highlighting the limitations of this measurement technique and providing preliminary insights on the difference between continuous wave and broadband signals like those emitted in modern communication standards.