Fast In-Phantom Absorbed Power Density Evaluation at mmWaves Based on Infrared Measurements

This article introduces a novel method for fast measurement of the absorbed power density (APD) induced by an electromagnetic field (EMF) emmitting device operating near the human body at frequencies above 6 GHz, taking into account antenna/body interaction. The method employs an infrared (IR) thermography to remotely monitor the heat induced in a reflectivity-based skin equivalent phantom designed to reproduce the EMF scattering properties of human skin and the APD inside the human body. Such a phantom, implemented in the form of a thin planar solid dielectric structure, perturbs the device under test in a similar way as it would be perturbed by the presence of the human body, allowing the absorbed microwave energy to be effectively converted into an IR signal. The heat dynamics and the spatial temperature distribution on the phantom surface are measured by an IR camera and then converted to APD by postprocessing. To enhance the sensitivity of the method and to minimize the effect of heat conduction, spectral filtering is used. The proposed method is validated at 60 GHz using reference antennas (i.e. a cavity-fed dipole array and a pyramidal horn loaded with a slot array). The measured APD is compared with the reference APD simulated in human skin. The high accuracy and significant measurement time reduction, compared to conventional RF-based APD evaluation techniques, demonstrate a promising potential of the proposed IR-based method for fast EMF dosimetry and user exposure compliance testing of millimeter-wave (mmWave) 5 G and 6 G wireless devices.