Stanford scientists have created a device that wirelessly transmits electricity to a movable disc. The technology could some day be used to charge moving electric vehicles and personal devices. Credit: Sid Assawaworrarit/Stanford University
If electric cars could recharge while driving down a highway, it would virtually eliminate concerns about their range and lower their cost, perhaps making electricity the standard fuel for vehicles.
Now Stanford University scientists have overcome a major hurdle to such a future by wirelessly transmitting electricity to a nearby moving object. Their results are published in the June 15 edition of Nature.
"In addition to advancing the wireless charging of vehicles and personal devices like cellphones, our new technology may untether robotics in manufacturing, which also are on the move," said Shanhui Fan, a professor of electrical engineering and senior author of the study. "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."
The group built on existing technology developed in 2007 at MIT for transmitting electricity wirelessly over a distance of a few feet to a stationary object. In the new work, the team transmitted electricity wirelessly to a moving LED lightbulb. That demonstration only involved a 1-milliwatt charge, whereas electric cars often require tens of kilowatts to operate. The team is now working on greatly increasing the amount of electricity that can be transferred, and tweaking the system to extend the transfer distance and improve efficiency.
Wireless charging would address a major drawback of plug-in electric cars - their limited driving range. Tesla Motors expects its upcoming Model 3 to go more than 200 miles on a single charge and the Chevy Bolt, which is already on the market, has an advertised range of 238 miles. But electric vehicle batteries generally take several hours to fully recharge. A charge-as-you-drive system would overcome these limitations.
"In theory, one could drive for an unlimited amount of time without having to stop to recharge," Fan explained. "The hope is that you'll be able to charge your electric car while you're driving down the highway. 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."
Some transportation experts envision an automated highway system where driverless electric vehicles are wirelessly charged by solar power or other renewable energy sources. The goal would be to reduce accidents and dramatically improve the flow of traffic while lowering greenhouse gas emissions.
Wireless technology could also assist GPS navigation of driverless cars. GPS is accurate up to about 35 feet. For safety, autonomous cars need to be in the center of the lane where the transmitter coils would be embedded, providing very precise positioning for GPS satellites.