**1. Introduction**

Due to the increasing environmental concerns, renewable energy sources have recently attracted a great deal of attention from both industry and academia [1]. A key technology following this trend is the usage of electric vehicles (EVs), whose widespread diffusion is still limited by the charging infrastructure and their on-board energy storage systems, mainly batteries [2]. To overcome so-called "range anxiety", static or dynamic wireless power transfer (WPT) systems have been proposed to recharge EVs either while they are parked or in movement [3]. However, one of the main issues related to EV-WPT systems is the large electromagnetic field (EMF) emissions during recharging operations. Indeed, the demand for fast charging has increased the power level of WPT systems from 3.3 up to 22 kW [4], yielding an EMF leakage larger than in conventional wireless systems used to recharge consumer devices. This leakage in the neighborhood environment of the car (outside and inside) has increased the need to determine the compliance of WPT systems with international safety standards and guidelines [5,6].

The exposure assessment of static and dynamic EV-WPT systems has been widely investigated [7–15]. However, while the influence of the car chassis material has been investigated in [14,15], the effect of the human posture and related positions against the WPT coils has not rigorously been addressed. Such an influence is therefore investigated in this work for a large variation of anatomical models, postures and WPT coil position/configurations. Specifically, the magnetic field emitted by a static WPT system operating at the intermediate frequency (IF) of 85 kHz and engaged in recharging the battery of a compact car, namely a FIAT 500, has been considered.

The compliance assessment of EV-WPT systems is not straightforward. Indeed, while the standalone design of the recharging system could be easily performed with classical numerical approaches, the presence of the car body, which is more difficult to take into account, has been shown to play an important role [14,15]. However, the presence of

**Citation:** De Santis, V.; Giaccone, L.; Freschi, F. Influence of Posture and Coil Position on the Safety of a WPT System While Recharging a Compact EV. *Energies* **2021**, *14*, 7248. https:// doi.org/10.3390/en14217248

Academic Editor: Adel El-Shahat

Received: 8 October 2021 Accepted: 1 November 2021 Published: 3 November 2021

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the human body does not affect the source field up to some megahertz [16,17], making it possible to separate the overall compliance procedure into two steps: (1) the simulation of the magnetic field source (WPT system and car body) and (2) numerical dosimetry (human body subject to the previously evaluated IF field). Step (1) is solved with an ad-hoc hybrid scheme coupling the boundary element method (BEM) with the surface impedance boundary conditions (SIBCs) in order to fit both the multiscale open-boundary (WPT system) and thin-sheet (car body) characteristics of the problem [18]. Step (2) is instead performed with the commercial software Sim4Life (https://zmt.swiss/sim4life, accessed on 26 October 2021), which relies on a Virtual Population (ViP). This allowed us to achieve the non-trivial task of assessing the numerical dosimetry on realistic anatomical models with different postures resembling those of a driver, of a person lying on the ground floor or in the rear-seats and of bystanders near to the car, while the WPT coils (both aligned and misaligned) were placed either in the rear or front position of the car floor due to the presence of the battery pack between the wheels.
