Those challenges include the use of ferrite, a fragile and expensive material; concerns about exposing passengers to electromagnetic fields; and the risk of the charging pad accidentally heating up nearby metal objects.
Afridi, however, believes a more practical and affordable system might use electrical fields instead. Recent cost-reduction and technical breakthroughs in power electronics, near-field coupler designs and semiconductor materials such as exotic gallium nitride could make it easier to pull off. Afridi's promising work with electrical fields at Cornell has hit its targets and attracted funding from the Advanced Research Projects Agency – Energy and the National Science Foundation.
Today, automakers such as Renault and BMW are starting to roll out stationary commercial EV charging stations that are wireless; charging a battery to 80 percent takes 30 to 40 minutes.
But Afridi says that charging moving vehicles is more complicated and involves vastly higher and faster power transfers. He estimates commercial electrical-field EV charging might be 10 or even 15 years away. But he feels that now is the time for discussion and development as the U.S. government plans massive infrastructure investments, world EV markets surge and auto companies announce multibillion-dollar EV investment plans.
With dynamic wireless power transfer, either capacitive or inductive, the vehicle's receiving unit quickly moves past the sending unit embedded in the road. A vehicle might be on a half-mile-long charging grid for 30 seconds or less. So, both types require sophisticated power electronics, such as a high-frequency inverter and rectifier.
So far, only experimental roadways for wireless magnetic-field power transfer have been built. And these prototypes have consistently proved to be complicated, fragile and expensive.
Estimates by different experts and companies range from $600,000 to $2.5 million a kilometer, depending on individual configurations and requirements.
"It may be possible that the magnetic field system's economics will not work out," Afridi says. "The capacitive system is a lot cheaper in principle. If nobody deploys the magnetic-field system in the next three to five years, we may just skip the magnetic-field systems all together and go directly to the electric-field system."