Advancing Wireless Charging

Engineers at Aalto University have revolutionized wireless power transmission by developing a novel system that significantly improves efficiency over longer distances. While traditional wireless power-transfer devices excel in short-range charging using magnetic near fields, they suffer from a dramatic drop in transfer efficiency at larger distances, limiting their practicality in certain scenarios.

The Aalto team’s breakthrough lies in optimizing the interaction between antennas responsible for transmitting and receiving power, harnessing the phenomenon of “radiation suppression.” By suppressing the radiation resistance of the loop antennas involved in power exchange, they sustain the high efficiency of wireless charging devices over extended distances.

The researchers formulated a dynamic theory of wireless charging, meticulously examining both near (non-radiative) and far (radiative) distances and conditions. With the optimal frequency in the hundred-megahertz range, their system achieved remarkable transfer efficiency at distances approximately five times the size of the antenna.

To validate their concept, the team conducted experiments using two small loop antennas specifically designed for the target frequency range. Placed at a center-to-center distance of 18 cm for both coaxial and coplanar arrangements, the receiving and transmitting loops shared a radius of 3.6 cm. The results were astonishing, as radiation suppression played a pivotal role in boosting transfer efficiency by over 80%.

Lead author Nam Ha-Van, a postdoctoral researcher at Aalto University, explains the essence of their discovery: “By ensuring equal amplitudes and opposite phases in the currents of the loop antennas, we can effectively cancel out radiation loss, resulting in heightened efficiency.”

The newfound technique not only empowers the comprehensive analysis of any wireless power transfer system in theory and practice but also paves the way for assessing power transfer efficiency at both short and long distances, a previously unexplored territory. Moreover, the developed theory can be extended to explore coupling between antennas of various types and energy transfer between nano-objects, broadening its applications significantly.