Reduction of radiated emission from resonance coil in GaN wireless power transmission circuit by using Nd–Fe–N magnetic material

In this study, the Nd–Fe–N materials are employed as an electromagnetic shield, for the first time, for the resonance coil in the 13.56-MHz-GaN wireless power transmission circuit. The Nd–Fe–N materials are introduced into the air-core resonance coil as the cap of the edges or the core. By using Nd–Fe–N, the radiated emission from the resonance coil is reduced because the electromagnetic field distribution is shrunk due to the effect of not the imaginary part but the real part of the permeability. When the spectrum of the magnetic field of the resonance coil is measured at the frequency from 30 MHz to 800 MHz, the intensity of the higher harmonics radiated emission is restricted by Nd–Fe–N in all of the frequency ranges. In particular, the Nd–Fe–N capped air-core coil shows the superior characteristics in both the shielding effect and the power loss. In addition, by numerical calculation, it is found that the effect of the electromagnetic shield will be enhanced by increasing the real part of the permeability by optimizing the Nd–Fe–N material fabrication.