A 20-kilowatt inductive charger built with stress-treated iron nanocrystalline cores transferred alternating-current power at 98.51 percent efficiency, researchers report in Nature Communications. The prototype pairs a new magnetic material process with the coil design, addressing losses and heat that limit compact wireless charging systems.
Inductive charging sends energy across an air gap through a magnetic field between a ground-side coil and a receiving coil. Magnetic cores guide that field; permeability describes how readily the core carries magnetic flux. The researchers' simulations showed the field concentrating near the edges of a high-permeability alloy core, where thermal images also showed hot spots. The design therefore had to consider where the field concentrated and heat built up, alongside the core's ability to guide the field.
The team stress-annealed an iron-based nanocrystalline alloy, heating it while applying mechanical stress to set a controlled magnetic direction. This allowed the researchers to tune its permeability. They then laminated the alloy into bars aligned with the charging coil, combining the material treatment with the geometry of the power-transfer system.
The system delivered 9.55 kilowatts per litre when volume was counted only for the coils and magnetic cores, and remained thermally stable during high-power operation. The 98.51 percent figure is an alternating-current-to-alternating-current measurement of the inductive link. It should not be read as wall-to-battery efficiency, which would also include power-conversion and battery losses.
The measurements apply to this research coupler, with the stated boundaries for efficiency and volume. They do not establish the performance of a complete charger in everyday vehicle use.