Exposure assessment of stray electromagnetic fields generated by a wireless power transfer system

The magnetic wireless power transfer (WPT) technology represents a promising application in contactless electric vehicle battery charging systems. In this framework, a bench prototype of resonant type, delivering a power of 560 W at 85 kHz, suitable for charging the batteries of a city car, was designed and realized. Identical transmitting and receiving resonant coils, equipped with ferrite cores, were realized in a spiral configuration. The single coil and the coupled system were experimentally characterized in terms of inductance and mutual inductance for dimensioning the resonance circuit. Measurements of the stray electromagnetic fields (EMFs) emitted by the prototype were performed, in order to assess the exposure levels at which operators, working in proximity of the bench prototype, will be subjected. Results evidenced that, for this prototype, both measured electric (E) and induction magnetic (B) fields are compliant with the European Directive 2013/35/EU, in which minimum health and safety requirements regarding the EMFs exposure of operators are established. Yet, it is worth noting that measured E field (maximum 127.8 ± 3.1 V/m) was not compliant with the exposure limit established by the European Recommendation (1999/519/CE) for the population (83 V/m). As consequence, it should be necessary to characterize the stray EMFs in the actual exposure scenario, with the system directly mounted on the city car. Moreover, the exposure assessment of wireless systems delivering higher powers (some kW) should be required, also foreseeing numerical dosimetry to assess the induced E field within the human body.