A New Theory of Wireless Power Transfer Delivers a Big Gain in Efficiency Over Long Distances
Delivering 80 percent efficiency over a distance five times greater than their size, these loops antennas prove the value of the new model.
Researchers at Aalto University in Finland have found a way to boost the efficiency of wireless power transfer (WPT) systems over longer distances — suppressing unwanted radiation losses to reach 80 percent efficiency at distances up to five times the length of the antenna.
"We wanted to balance effectively transferring power with the radiation loss that always happens over longer distances," explains lead author Nam Ha-Van of the team's work. "It turns out that when the currents in the loop antennas have equal amplitudes and opposite phases, we can cancel the radiation loss, thus boosting efficiency."
The team's work started very much in the realm of the theoretical, developing a new dynamic theory of wireless charging applicable to both close-range non-radiative and long-range radiative systems. This theory underpins a new system of analysis, including both mathematical and experimental proofs, delivering a more detailed power transfer efficiency evaluation than has previous been possible.
"This is all about figuring out the optimal setup for wireless power transfer, whether near or far," explains Ha-Van. "With our approach, we can now extend the transfer distance beyond that of conventional wireless charging systems, while maintaining high efficiency."
That extension is impressive, when compared with rival systems which can only operate near peak efficiency when effectively touching: in experimentation, the tweaked wireless power transfer system was able to maintain 80 percent efficiency even when the transmitting and receiving antennas were separated by an air gap five times the antenna's length.
"We believe the regime of the radiation suppression is very important," the team concludes in its paper, "not only because it grants high PTE [Power Transfer Efficiency] for substantial transfer distances but also because it prevents parasitic heating of the ambient around the WPT system."
The team's work is published in the journal Applied Physics under closed-access terms, with an open-access preprint available on Cornell's arXiv server.