Carole Leduc

Personal exposimeter for radiation assessment in real environments in the 60-GHz band

For the first time, a personal exposimeter (PEX) for 60 GHz radiation measurements is presented. The PEX is designed based on numerical simulations and both on-body and on-phantom calibration measurements to determine the antenna aperture and measurement uncertainty of the PEX. The measurement uncertainty of the PEX is quantified in terms of 50 and 95% prediction intervals of its response. A PEX consisting of three nodes (antennas) with VHH (vertical-horizontal-horizontal) polarization results in a 95% prediction interval of 6.6 dB. A 50% prediction interval of 1.3 dB (factor of 1.3) is obtained for measured power densities which is 3.1 dB lower than a single antenna experiment. The uncertainty is 19.7 dB smaller than that of existing commercial exposimeters at lower frequencies (≤6GHz).

Thermal Model of Electromagnetic Skin-Equivalent Phantom at Millimeter Waves

This paper reports the first thermal model and detailed analysis of the heating of an electromagnetic (EM) skin-equivalent phantom with a finite thickness at 60 GHz. The 1-D heat transfer equation is solved analytically for homogeneous phantoms with finite thicknesses. The temperature rise dynamics and heating distribution within the phantom are calculated for several phantom thicknesses (5, 10, and 15 mm) using measured thermal properties of the phantom. Analytical results are confirmed by numerical analysis based on EM-thermal cosimulations. Furthermore, the numerical model is validated by measurements using an experimental setup based on the high-resolution infrared thermometry. The impact of uncertainty of EM and the thermal parameters of the numerical model upon heat deposition is also studied. Our results reveal that, for short exposure durations (i.e., less than 1 min), the surface temperature is well described by the semi-infinite and finite-thickness phantom models, whereas, for longer exposures (more than 1 min), finite-thickness models must be used to properly account for heating accumulation close to the phantom boundaries. While the reported results cannot be directly used for predicting temperature increase in skin, they are of importance for temperature-based dosimetric assessment in the millimeter-wave band using currently available homogeneous phantoms.

Millington Effect and Propagation Enhancement in 60-GHz Body Area Networks

Millington effect for on-body propagation enhancement is presented in the 60-GHz band. Millingtons equations are developed to describe propagation above a flat inhomogeneous surface. This study focuses on mixed paths (human skin-metallic) for on-body scenarios. It is shown that adding metallic paths on the human skin can improve the power link budget between two nodes placed on the body. Two different schemes are studied experimentally to assess the analytical model using a flat phantom with electric properties of human skin and different lengths of metallic inserts. The first scheme considers a metallic plate between the transmitting and receiving antennas, while the second scheme proposes locating the metallic plates under the antennas. It is shown that the second scheme yields a better link budget than the first one for the same length of metal. Moreover, a numerical study is performed to assess the impact of the following different parameters: the location of the metal plate, size of the plate, and the height of the antennas. Excellent agreement between numerical and experimental results has been shown. In the best cases, the presented techniques allow to improve the path loss of 10-20 dB.

Impact of Antenna Topology and Feeding Technique on Coupling With Human Body: Application to 60-GHz Antenna Arrays

The 60-GHz band has been identified as an attractive solution for the next-generation mobile networks (5G) as well as for body-centric applications. This paper provides a quantitative comparative analysis of electromagnetic exposure and heating induced by 60-GHz body-mounted antennas. Near-field interaction between representative antenna arrays for off-body communications with three feeding topologies and human body is compared in terms of matching and radiation, as well as in terms of user exposure. The presence of a ground plane results in exposure reduction by more than 70 and 8 times in terms of peak and averaged levels, respectively. Designs allowing to avoid grating lobes allow further reduction of exposure. For considered antenna arrays operating at the maximum allowable power, International Commission on Non-Ionizing Radiation Protection occupational exposure limits are not exceeded. However, only the antennas with a ground plane comply with general public limits. Resulting heating is quantified for on-body millimeter-wave antennas. Detailed analysis is performed for acute and disperse exposures. Numerical results are validated by measurements. Effect of averaging is also investigated. For antennas with a ground plane, heating (typically of several tenths of °C) remains within environmental temperature fluctuations. However, the antennas without a ground plane can induce heating locally exceeding 10 °C.