Hybrid ray-tracing/numerical methods for human exposure evaluation for wireless power transfer wearable devices.

Wearable Wireless Power Transfer devices are becoming more and more widespread as remote health control systems, which allow patients for home monitoring, enable better life and more sustainable health care systems. Specifically, in this work the far-field radiative coupling mechanisms for WPT in the millimeter (mm)-wave range has been considered, which has not been intensively studied so far for WPT applications, due to the inherent high free space loss, but it is currently under vast investigation as the future EM spectrum for the development of 5G communications. In this framework the evaluation of human exposure to has become an important issue. As a matter of fact, these devices usually operate in indoor, in a rather complex environment where scattering objects are present, which can influence the received power level by means of reflections, diffractions and scattering. In these situations, accurate investigations are needed to assess if human exposure can give rise to health risks and to verify compliance with the existing protection standards. In this work, the exposure of a subject, a realistic human phantom, to the field received by the wearable WPT device in an indoor environment has been studied. The exposure has been analysed coupling the FDTD method, which is able to evaluate the SAR – Specific Absorption Ratio value inside the human body, with a ray-tracing algorithm, suitable to assess field propagation in furnished indoor environment and accounting for all the possible interactions with the objects in the environment. The obtained results show the possibility of highlighting possible non uniformity of the field distribution due to the presence of different objects in the environment.