Wireless power transfer in the radiating near-field region

Many works on near-field wireless power transfer (WPT) have been carried out in the coupled-mode resonance region. In this region, very high power transfer efficiency (PTE) above 80% can be attained. However, such a region is very short when measured in terms of wavelength and it is rather difficult to design antennas that extend the distance over which such coupled mode phenomenon can be maintained. Furthermore, optimal impedance matching is distance-dependent and challenging to implement in practice.