Wireless system charges vehicles on the move

6 February 2012

The computer model feasibility study at Stanford University is based on commercial technology from a spin-out company of the Massachusetts Institute of Technology (MIT).

Wireless charging is based on the principle of magnetic resonance coupling, where two copper coils are tuned to resonate at the same natural frequency. One coil is connected to an electric current, which generates a magnetic field that causes the second coil to resonate. This magnetic resonance results in the invisible transfer of electric energy through the air from the first coil to the receiving coil.

MIT spin-out WiTricity has a device capable of wirelessly transferring about three kilowatts of electric power to a stationary vehicle parked in a garage or on the street.

In theory, a series of coils connected to an electric current could be embedded into the motorway to create an on-the-move charging system. Receiving coils attached to the bottom of the car would resonate as the vehicle speeds along, creating magnetic fields that continuously transfer electricity to charge the battery.

To determine the most efficient way to transmit 10KW of power to a real car, the Stanford team created computer models of systems with metal plates added to the basic coil design.

Using mathematical simulations, the researchers found that a coil bent at a 90-degree angle and attached to a metal plate can transfer 10KW of electrical energy to an identical coil 6.5 feet away.

‘That’s fast enough to maintain a constant speed,’ said project lead Shanhui Fan of Stanford.‘To actually charge the car battery would require arrays of coils embedded in the road. This wireless transfer scheme has an efficiency of 97 per cent.’