Publishing their results in Nature Letter under the title “Robust wireless power transfer using a nonlinear parity–time-symmetric circuit”, the researchers demonstrated both theoretically and experimentally robust wireless power transfer through the use of a parity–time-symmetric circuit incorporating a nonlinear gain saturation element.
Compared to conventional methods where high transfer efficiency can only be maintained by constantly tuning the frequency or the internal coupling parameters of the coils as the transfer distance or the relative orientation of the source and receiver units varies, here transfer efficiency remained near unity over a distance variation of approximately one metre, without the need for any tuning.
To achieve this, the researchers eliminated the radio-frequency source in the transmitter and replaced it with a voltage amplifier and feedback resistor that would automatically figure out the right frequency for different distances without the need for human intervention and tuning.
That approach was tested with a LED bulb placed on the receiving coil. In a conventional setup without active tuning, LED brightness would diminish with distance but in the new setup, the brightness remained constant as the receiver moved away from the source by a distance of about three feet. As reported on Stanford University’s news pages, Fan’s team recently filed a patent application for their solution and hope to improve overall efficiency by using custom-made amplifiers with efficiencies over 90% compared to the low efficiency (under 10%) off-the-shelf general-purpose amplifier they used for their demonstration.
That demonstration only involved a 1-milliwatt charge but the researchers are hoping to be able to increase the system’s capabilities so it could be considered as an alternative for cars, providing there would be built-in infrastructure (coils embedded into the pavement).
“We still need to significantly increase the amount of electricity being transferred to charge electric cars, but we may not need to push the distance too much more”, explained Shanhui Fan, professor of electrical engineering and senior author of the study.
As described in a short video, in theory a coil in the bottom of the vehicle could receive electricity from a series of coils connected to an electric current embedded in the road, which would allow a moving car to recharge as it drives down the highway, in effect providing an unlimited ride.
Such a wireless charging solution would address the major drawback of plug-in electric cars, limited driving range and long charging times. Ideally, the wirelessly powered cars could rely on energy-harvesting-capable road infrastructures. This research could potentially be applicable to many wireless devices, including wearables and implantable electronics.
Stanford University – www.stanford.edu