Wireless devices, such as smartphones, tablets, and laptops, are intended to be used in the vicinity of the human body. When an antenna is placed close to a lossy medium, near-field interactions may modify the electromagnetic field distribution. Here, we analyze analytically and numerically the impact of antenna/human body interactions on the transmitted power density (TPD) at 60 GHz using a skin-equivalent model. To this end, several scenarios of increasing complexity are considered: plane-wave illumination, equivalent source, and patch antenna arrays. Our results demonstrate that, for all considered scenarios, the presence of the body in the vicinity of a source results in an increase in the average TPD. The local TPD enhancement due to the body presence close to a patch antenna array reaches 95.5% for an adult (dry skin). The variations are higher for wet skin (up to 98.25%) and for children (up to 103.3%). Both absolute value and spatial distribution of TPD are altered by the antenna/body coupling. These results suggest that the exact distribution of TPD cannot be retrieved from measurements of the incident power density in free-space in absence of the body. Therefore, for accurate measurements of the absorbed and epithelial power density (metrics used as the main dosimetric quantities at frequencies > 6 GHz), it is important to perform measurements under conditions where the wireless device under test is perturbed in the same way as by the presence of the human body in realistic use case scenarios.
This letter introduces a technique for the power density (PD) pattern measurement in the near field taking into account the antenna/body coupling at millimeter waves (mmW). The proposed method employs a specifically designed structure reproducing the reflection coefficient from human skin. This structure is optimized to convert the absorbed PD into an infrared (IR) pattern, remotely recorded using a high-resolution IR camera for reconstruction of the PD distribution. As a validation example, numerical and experimental distributions are presented for a 4element patch antenna array and a conical horn antenna at 60 GHz. A very good agreement is demonstrated between simulations and measurements (correlation > 98%). The results suggest a strong potential of this technique for fast remote high-resolution PD measurements applied to characterization of wireless devices in vicinity of the human body.
This letter introduces a method for power density (PD) measurement of low-power millimeter-wave (mmWave) devices, accounting for antenna/body coupling. This technique employs a thin solid absorbing structure with equivalent scattering properties used to convert the absorbed power into a heat pattern measured by an infrared (IR) camera. The measured IR pattern is then used to reconstruct the PD distribution. The lock-in technique is used to enhance the signal-to-noise ratio (SNR). It consists in filtering the ambient IR noise as well as removing the parasitic heat conduction effect. The reduction of noise enables achieving a measurement sensitivity of the order of 1 mW/cm 2 , substantially overcoming the sensitivity without lock-in (> 10 dB). The proposed approach is experimentally validated for a conical horn antenna at 60 GHz. For the first time, this study demonstrates the sensitivity of IR-based measurements sufficient enough to assess the compliance of medium-and lowpower wireless devices above 6 GHz.
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