Novel Technique for In-Body Absorbed Power Density Assessment Based on Free-Space E-Field Measurement

We introduce a novel method for measurement of the absorbed power density (APD) above 6 GHz, accounting for antenna/body interaction. A reflectivity-based thin planar solid phantom is used to mimic the scattering characteristics of human skin. This allows to perturb the antenna under test (AUT) in a similar way as it would be perturbed by the presence of the human body. The lower electromagnetic losses in the phantom medium result in an enhanced transmission through the phantom facilitating free-space
E
-field vector measurement on the opposite to the AUT side of the phantom. The measured
E
-field is backpropagated in space to retrieve APD using a plane-wave spectrum (PWS) technique. The proposed method is validated at 60 GHz using reference antennas, namely, a cavity-fed dipole array and pyramidal horn with a slot array. A very good agreement is demonstrated between the target APD at the air/skin interface (peak, averaged, and spatial distribution) and the one reconstructed from the simulated and measured
E
-field. The maximum relative deviations between the computed and measured peak (
$p\text{APD}$
), 1 cm
$^2$
peak spatial average (
$ps\text{APD}_{1\,\text{cm}^2}$
), and 4 cm
$^2$
peak spatial average (
$ps\text{APD}_{4\,\text{cm}^2}$
) are 13.2% (0.55 dB), 14.9% (0.6 dB), and 15.7% (0.63 dB), respectively. The results demonstrate that the proposed technique is promising for experimental dosimetry and compliance testing of wireless devices operating above 6 GHz.