IEC TR 63040 — Electric Vehicle Wireless Power Transfer Systems: EMF Safety Guidelines

Wireless power transfer (WPT) systems for electric vehicles offer the convenience of cable-free charging, but they also introduce a critical engineering challenge: ensuring that the electromagnetic fields (EMF) generated during high-power energy transfer remain within safe exposure limits for both humans and living organisms. IEC TR 63040 provides comprehensive guidelines for the assessment and management of EMF safety in EV wireless charging systems, covering frequencies from a few kilohertz up to several megahertz. This technical report is essential reading for power electronics engineers, automotive EMC specialists, and public health professionals involved in the deployment of WPT infrastructure.

EMF Exposure Assessment Framework

IEC TR 63040 establishes a tiered approach to EMF safety assessment, aligned with the general framework of IEC 62311. The first tier involves basic screening using reference levels derived from international guidelines (ICNIRP 1998/2010 and IEEE C95.1). If the WPT system’s magnetic field strength at a distance of 30 cm from the charger surface exceeds the reference levels, a more detailed assessment is required. The second tier involves detailed numerical dosimetry using anatomically realistic human body models and finite-difference time-domain (FDTD) or finite-element method (FEM) simulations to compute induced electric field and specific absorption rate (SAR) in tissues.

The report identifies that the key dosimetric quantities for WPT systems are the induced electric field strength (E-field) in the central nervous system (CNS) for frequencies below 10 MHz, and the specific absorption rate (SAR) for frequencies above 100 kHz. Between these overlapping ranges, both quantities may need to be evaluated depending on the operating frequency of the WPT system. Most automotive WPT systems operate in the 80–90 kHz band (aligned with SAE J2954), placing them in the region where both induced E-field and SAR are relevant.

Mitigation Strategies and Coil Design Considerations

IEC TR 63040 goes beyond assessment and provides detailed guidance on EMF mitigation. The report describes several engineering strategies: geometric optimisation of the transmitter and receiver coils (e.g., using double-sided or flux-pipe configurations to reduce stray fields), active shielding using cancellation coils driven in anti-phase, and passive shielding with ferrite materials or conductive plates. The choice of shielding technique depends on the operating frequency, power level, and installation environment. For example, ferrite shielding is highly effective at 85 kHz but adds mass and cost, while active cancellation coils require additional drive electronics and introduce complexity.

The report also addresses the influence of coil misalignment — a common real-world condition where the vehicle is not perfectly positioned over the charging pad. Misalignment not only reduces power transfer efficiency but also alters the magnetic field distribution, potentially increasing exposure in certain directions. IEC TR 63040 recommends that EMF compliance assessments be performed at multiple alignment positions covering the expected range of parking variation, typically ±150 mm lateral and ±75 mm longitudinal.

Engineering Design Insights and System-Level Implications

From a system-level perspective, IEC TR 63040 emphasises that EMF safety cannot be treated as a standalone requirement — it must be integrated into the overall WPT system design from the earliest stages. Retrofitting EMF shielding after the coil geometry and power electronics have been finalised is significantly more expensive and less effective. The report provides a recommended workflow that begins with analytical estimation of the magnetic field based on coil geometry and current, followed by numerical simulation, and finally experimental validation using a calibrated field probe.

The report also discusses the interaction between WPT EMF and implantable medical devices such as pacemakers and neurostimulators. Although detailed patient-specific assessments are outside the scope of IEC TR 63040, the report provides guidance on establishing exclusion zones and warning signage, as well as referencing the applicable medical device immunity standards (ISO 14117 for pacemakers).