Picture an all-electric vehicle cruising down the highway, emitting little noise and no noxious fumes. It’s such an improvement that you have to wonder why only a handful of all-electric vehicles are now available on the mass market.
Here’s a big reason: Picture the driver of that same car getting a call from a relative living far away who needs immediate help. Suddenly, the driver’s eyes become riveted on the most important indicator on the dashboard: the estimated number of kilometers that the car can go on the remaining battery charge. Will he make it to his relative’s house? Even if he does, will he find a charging station so he can get back home?
Maybe there’s a way to relieve this fear forever and make drivers’ lives much easier as well. If we embed transmitting coils in roadways, electric cars carrying receiving coils could charge themselves as they zoom down the road. An e-car owner would never have to search for a charging station or plug in the car. That is the goal of the research team at the Korea Advanced Institute of Science and Technology (KAIST), in Daejeon, which has developed what we call the on-line electric vehicle (OLEV) system.
Wireless power transmission isn’t a new idea: Nikola Tesla built a 57-meter-tall tower behind his lab in Shoreham, N.Y., partly to beam power to remote equipment. But only in the past decade have researchers begun to make the breakthroughs that can allow for commercially practical wireless charging, not only for portable electronic products like smartphones but even for industrial robots and electric cars.
The technology depends on the same principle of electromagnetic induction that enables a transformer to change the voltage of an alternating current. The current flows through one coil of wire, creating a magnetic field whose polarity reverses with each cycle and inducing a corresponding alternating field in a secondary coil. The ratio of the number of turns in the two coils determines whether the transformer steps voltage up or down. Transformers usually include an iron-rich core, which links the coils and increases the field strength, but you don’t really need it. If the two coils are separated by air, current flowing through the first coil will still create a magnetic field, which will still be picked up by the second coil—it just won’t be picked up as well. The greater the air gap, the less efficient the transfer of power will be.
How, then, to increase the efficiency of the power transfer without having to make the low-slung receivers even more vulnerable? The answer that KAIST settled on is called magnetic resonance coupling. When a transmitting coil sends electro-magnetic waves tuned to a frequency matching the resonance of a circuit holding a receiving coil, it will transfer energy to it very efficiently.
In 2009, KAIST was given $25 million by the National Science and Technology to develop wirelessly powered vehicles. One year later, KAIST launched their first vehicle which was a passenger tram at the Seoul Grand Park Zoo. Today, the tram zips around the park on a 2.2 km loop of roadway, 370 meters of which has transmitting coils embedded in the asphalt. As the tram rolls along, magnetic sensors in the road detect its approach and activate the transmitters to send 62 kilowatts to the receiving coils on on the underside of the tram.
KAIST demonstrated an OLEV bus at the Expo 2012 in Yeosu, South Korea and plans to have it running by July. Next, KAIST plans to apply OLEV technology to a high-speed railway system. Another application in the works: OLEV technology in ports for vehicles used to move shipping containers.
The time has come to cut the cord—the power cord. There is no better way to realize the dream of the nonpolluting car.
Source (story): Seungyoung Ahn, Nam Pyo Suh & Dong-Ho Cho, IEEE Spectrum
Images: Korea Advanced Institute of Science and Technology and James Provost