�A small prototype serves as a proof of concept for the new technology

New mobile wireless vehicle charging technique

Wireless charging for electric vehicles on the move is a step closer after researchers successfully tested a new prototype.

The new technique, developed by engineers at North Carolina State University (NC State), improves the efficiency of power transfer is the first step towards the goal of creating highway "stations" that can recharge electric vehicles wirelessly as the vehicles drive by.

Lukic and his team have developed a small prototype of their system, which can transmit energy at a rate of 0.5kW at peak efficiency, and they are now working to both scale it up and increase the power of the system.

"We've made changes to both the receiver and the transmitter in order to make wireless energy transfer safer and more efficient," said Dr Srdjan Lukic, an assistant professor of electrical engineering at NC State and senior author of a paper on the research.

"Our goal is to move from 0.5kW into the 50kW range," he added. "That would make it more practical."

The researchers developed a series of segmented transmitter coils, each of which broadcasts a low-level electromagnetic field as well as a receiver coil that is the same size as each of the transmitter coils, which can be placed in a car or other mobile platform. The size of the coils is important, because coils of the same size transfer energy more efficiently.

The researchers then modified the receiver so that when it comes into range and couples with a transmitter coil, that specific transmitter coil automatically increases its current – boosting its magnetic field strength and the related transfer of energy by 400 per cent.

The transmitter coil's current then returns to normal levels when the receiver passes out of the range of the transmitter.

The technique combined lessons learned from two previous approaches to mobile, wireless charging. The first used large transmitter coils, but this approach created a powerful and imprecise field that could couple to the frame of a car or other metal objects passing through the field.

Because of the magnetic field's strength, which is required to transfer sufficient power to the receiver, these electromagnetic field "leaks" raised safety concerns and reduced system efficiency.

The other approach used smaller transmitter coils, which addressed safety and efficiency concerns, but this approach would require a very large number of transmitters to effectively "cover" a section of the roadway, adding substantial cost and complexity to the system, and requiring very precise vehicle position detection technology.

"We tried to take the best from both of those approaches," Lukic said.

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