Conventional methods for WPT or wireless charging, such as induction pads, efficiently transfer power over short distances using magnetic near fields. However, as the distance increases, efficiency typically diminishes considerably.
Researchers at Aalto University, a public research institution situated in the Finnish city of Espoo, have demonstrated a method by which high efficiency can be maintained over extended distances.
According to a report in SciTechDaily, the research team achieved this by suppressing the radiation resistance of the loop antennas used in the power transfer process.
Previously, the same research laboratory introduced an omnidirectional wireless charging system that enabled devices to be charged regardless of their orientation.
This new development expands upon that achievement by introducing a dynamic theory of wireless charging, examining both near (non-radiative) and far (radiative) distances and conditions.
In the study, the researchers were able to achieve transfer efficiency exceeding 80 percent at distances roughly five times the size of the antenna, using the optimal frequency within the hundred-megahertz range.
Lead author Nam Ha-Van, a postdoctoral researcher at Aalto University, said: “We wanted to balance effectively transferring power with the radiation loss that always happens over longer distances. 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 breakthrough could have implications for the wireless charging of consumer electronics like smartphones but also for medical implants with limited battery capacity, say the research team.