Among the concepts put forth for decreasing the range anxiety associated with electric cars, one is to embed electrical coils within the asphalt. This would allow vehicles to wirelessly draw power from the road as they traveled, although it would also involve having to tear up existing roads to install those coils. An alternative could be on its way, however. Scientists at North Carolina State University are developing a system in which power could be transmitted from stationary roadside stations to mobile receiver coils in cars passing by.

Previous attempts at doing the same sort of thing have had their drawbacks.

In one case, transmitting coils that were larger than the receiving coils were used, in order to deliver a high amount of power. Unfortunately, as the university explains, "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." This means that the system wasn't very efficient, plus all the electromagnetic radiation being flung around raised safety concerns.

In another case, a larger number of smaller coils were used. While this increased efficiency and decreased the danger, putting it into roadside use could be complex and expensive, as many carefully-positioned coils would be required.

Instead, the North Carolina researchers are using transmitting and receiving coils that are the same size as one another – the best arrangement for efficient transfer of energy. When no receivers are around, the transmitter emits a safe, low-level electromagnetic field. As a receiver comes into range, however, it triggers the transmitter to temporarily increase its output by 400 percent. Once the receiver has passed out of range, the output drops back to its previous level.

Out on the road, that could translate into a system that only fully fires itself up when an electric vehicle is going by. The current proof-of-concept model puts out a maximum of 0.5 kilowatts, although lead scientist Dr. Srdjan Lukic states that his team is working towards a scaled-up 50 kW version.

A paper on the research was recently published in the journal IEEE Transactions on Power Electronics.