Out at Stanford University a research team may have solved the problem of range anxiety with wireless charging technology that one day could create an electric highway.

Wireless Dynamic Car Charging Graphic from Stanford. Click image for the largest view.

The team follows research work from 2007 at the Massachusetts Institute of Technology getting magnetic resonance to light a 60-watt bulb.  That experiment demonstrated that power could be transferred between two stationary coils about six feet apart, even when people and other obstacles are placed in between.

The MIT team researchers even created a spin-off company named WiTricity that is developing a stationary charging system capable of wirelessly transferring about 3 kW of electric power to a vehicle parked in a garage or on the street.

But Stanford has proposed a design published in the journal Applied Physics Letters that would transfer up to 10 kW of electrical energy to a coil 6.5 feet away with an efficiency of up to 97%.  One can imagine the groans in Massachusetts.

Both the new company WiTricity and the Stanford team are building high-efficiency wireless charging systems using magnetic resonance coupling that wirelessly transmit large electric currents between metal coils positioned a little less than or about 2 meters apart. The long-term goal of this type of research is to develop an “all-electric” highway that wirelessly charges the cars and trucks as they cruise down the road.

Magnetic resonance coupling transfers power with two copper coils tuned to resonate at the same natural frequency. The coils are placed a couple meters apart with one coil connected to an electric current that generates a magnetic field, which causes the second coil to resonate. This magnetic resonance results in the transfer of electric energy through the space between the first coil and the receiving coil.

The WiTricity design for power transfer efficiency depends on the relative sizes of the power source, capture devices, and on the distance between the devices.  Maximum efficiency of the WiTricity design is achieved when the devices are relatively close to one another, going past 95%.  WiTricity has secured partnerships with automobile manufacturer Toyota and electrical component manufacturer Delphi.

Across the country at Stanford, (Isn’t competition great?) Shanhui Fan, an associate professor of electrical engineering, and his colleagues wondered if the MIT system could be modified to transfer 10 kW of electric power over a distance of 6.5 feet enough to charge a car moving at highway speeds.

Working with computer models the team set out to determine the most efficient way to transmit 10 kilowatts of power to a real car.

Shanhui Fan explains the problem, “Asphalt in the road would probably have little effect, but metallic elements in the body of the car can drastically disturb electromagnetic fields. That’s why we did the APL (computer model) study – to figure out the optimum transfer scheme if large metal objects are present.”

The Stanford team created computer models of systems with metal plates added to the basic coil design.  Using mathematical simulations, postdoctoral scholars Xiaofang Yu and Sunil Sandhu found that a coil bent at a 90-degree angle and attached to a metallic plane can transfer 10 kW of electrical energy to an identical coil 6.5 feet away.

Fan and team members Xiaofang Yu, Sunil Sandhu, Sven Beiker, and Richard Sassoon recently filed a patent application for their wireless system.

Next up are plans to test it in the laboratory and eventually try it out in real driving conditions. The researchers also want to make sure that the system won’t harm, interfere with, or affect drivers, passengers or the dozens of microcomputers that control steering, navigation, air conditioning and other vehicle operations.

The team has started discussions with Michael Lepech, an assistant professor of civil and environmental engineering, to study the optimal layout of roadbed transmitters and determine if rebar and other metals in the pavement will reduce efficiency.  Sven Beiker, executive director of the Center for Automotive Research at Stanford (CARS) and his group are involved to be sure that the remaining 3% is lost as heat and not as potentially harmful radiation.

Both the MIT firm WiTricity and the Stanford team are way out in front of the technology.  The SAE (Society of Automotive Engineers) taskforce on wireless charging and positioning of electric vehicles isn’t yet working up an on-road dynamic charging specification, even though a wireless charging and positioning of electric vehicles standard is expected to come with a final draft later this year.

Before everyone gets excited these technologies have quite a way to go.  The level of efficiency now looks very good.  The concept seems feasible.  But these kinds of ideas are going to be road-building projects and consume large amounts of copper.   Then one wonders how to bill the user.  Dynamic charging is a grand idea, and looks like it will work, but we’re quite a way from rolling on the highway and driving unlimited distances.   But it sure is appealing idea for the future.


3 Comments so far

  1. Matt Musson on February 6, 2012 7:21 AM


    It’s too easy being green. Living high on the Prius falacy and pretending that ‘benign’ consumption is good for the environment.

    “A new car, a solar-powered swimming-pool heater, a 200-mile-an-hour train that makes intercity travel more pleasant and less expensive, better-tasting tomatoes —these are the sacrifices we’re prepared to make for the future of the planet.”

  2. Benjamin Cole on February 6, 2012 6:49 PM

    I like this idea of being able to charge a car without plugging it in. It seems to me the first use of this will be in parking lots and garages. Perhaps you will park your car for shopping and purchase a 15 minute charge up from your space. In your home garage, another system. At work, you could buy two hours of charging etc.

    Charging while on the run seems not do-able, commercially speaking. In addition, it would make the least sense to wire up roads precisely in the areas where you would run out of power—the rural hinterlands.

    In urbanized areas, I suspect there will be plenty of places to charge up, especially if people can make money doing so. That is, you park at the mall, and you can buy $2 of power with a credit card swipe at the point of parking. They give you$1 of power, and they are happy and you are too.

    My guess is that within 10 years we will be able to get 80 miles on a charged battery and perhaps have a small onboard motor, gasoline powered, for additional range. If you really want to go into the outback then you rent an old-fashioned ICE.

  3. modesto heating and air conditioning on November 20, 2013 11:38 AM

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