Researchers find a way to double transfer efficiency of wireless charging

Researchers from North Carolina State University and Carnegie Mellon University have found that adding a magnetic resonance field enhancer (MRFE) – which can be as simple as a copper loop – to a wireless charging system can boost transfer efficiency by at least 100 percent, and possibly as much as 5,000 percent.

“Our experimental results show double the efficiency using the MRFE in comparison to air alone,” says NC State Associate Professor David Ricketts.

By placing the MRFE between the transmitter and the receiver (without touching either) as an intermediate material, the researchers were able to significantly enhance the magnetic field, increasing its efficiency.

“We realized that any enhancement needs to not only increase the magnetic field the receiver ‘sees,’ but also not siphon off any of the power being put out by the transmitter,” Ricketts says. “The MRFE amplifies the magnetic field while removing very little power from the system.”

Ricketts MRFE 3

The researchers conducted an experiment that transmitted power through air alone (figure 3), through a metamaterial (figure 2), and through an MRFE made of the same quality material as the metamaterial (figure 3). The MRFE significantly outperformed both of the others. Also, the MRFE is less than one-tenth the volume of metamaterial enhancers.

A pre-proof draft of the paper, “Magnetic field enhancement in wireless power with metamaterials and magnetic resonant couplers,” has been published in the journal IEEE Antennas and Wireless Propagation Letters.


Source: NC State University via Green Car Congress

  • Zephyr

    I’m sure I won’t be the last, but let me be the first to quibble over terminology. Efficiency has a ceiling of 100%, and wireless charging is already somewhere over 70%. It’s not even theoretically possible to improve it by the percentages given. Please check the math.

    • dogphlap dogphlap


    • Lance Pickup

      The only thing I can think is that this is referring to efficiency over a great distance, far greater than that achieved in current systems (which actually is over 90%–search on Qualcomm Halo efficiency). Not sure what the 1% in the bottom picture is referring to unless the gap is really huge. But clearly the 5000% they allude to is the difference between that 1% and the 49% in the top picture. Yeah, this article is not very meaningful with this scant information.

  • Michael B

    I don’t understand the appeal, except in very limited circumstances, but I guess it’s still worth researching.

    • vike

      I’ve dismissed the idea myself in the past, especially for home charging, but I think the main advantages are for public charging infrastructure. It would be very appealing if you could just pull into a space and start charging, without hauling around and re-stowing a heavy cable, or opening an access port to expose your car’s vulnerable charging interface to potential vandalism. We just accept all this now as part of the public charging experience, but wireless charging may be an important part of the feature set that attracts a wider audience of potential EV buyers.

    • Lance Pickup

      Definitely not practical for home charging or even most current public charging setups. But consider the future when cars may be able to self park. They will need a way to charge without human intervention.

      • Electric Bill

        Lance, you obviously have not heard of the very interesting device Tesla has developed that looks and behaves very much like a snake:.. there is no way to cut-and-paste the YouTube video of it, but it’s a real shocker– no pun intended. Do a search for “Tesla snake charger” on YouTube. This thing literally searches out the Tesla’s charge port, and plugs itself in like some kind of otherworldly cross between a length of electrical conduit and a vampire! Yup, this is one toy I would not mind having around the garage… especially if it could be trained to guard my EV from prowlers!

        • Lance Pickup

          No, I’ve seen that device. That’s another alternative to the self-parking cars needing to charge dilemma, and one that does not require additional hardware (or perhaps minimal hardware) on the vehicle itself.

    • DisqussingThought

      The biggest application, in my opinion, would be to enable EV lanes on highways and freeways that would not only provide the energy to propel the vehicle but also some extra to recharge the batteries as you drive.

      These lanes could be modified HOV lanes, installing the magnetic charging under the surface, which only activate when an electric vehicle is driving over them. Fossil burner vehicles would be able to use the lanes as regular HOV lanes but the magnetic chargers would not turn on when an ICE vehicle is over them. The other alternative is to do away with HOV lanes (since they’re hardly ever used as intended to reduce the number of cars during commuting times), then they would be EV-Only lanes.

  • Edward

    I think the aliens should share some of their technology. This is getting ridiculous that they won’t share one thing with us except the computer chip and the internet. Someone needs to speak up and say something to these things/aliens.

  • Electric Bill

    It appears the copper coil is just a passive restraint somewhat like an old-fashioned corset that uses no energy itself to function, and condenses the inductive field, perhaps forcing it to extend upward (or outward, as the case may be), which reminds me quite a bit of how a Tokamak fusion reactor works.

    Even if such a system would be less efficient than a direct physical J-plug or other conventional EV charger, if installed ubiquitously throughout a city it could have the huge advantage of providing charge to EVs with much smaller battery packs making those vehicles lighter, less expensive, and nimbler. Without huge battery packs like are needed today to give an EV comfortable range for a day’s driving, it could instead have greater cargo/ luggage space.

    Just as turnpikes today have special WiFi or other systems that can register the identity of moving vehicles on toll roads and automatically bill the driver for road usage, EV drivers could drive throughout the day “sipping” a little bit of charge here, a little bit there, never having to ever stop to stock up on a few gallons of high- test electrons.

    Another advantage of such a system would be to reduce the amount of lithium, rare earth minerals or other materials needed to make the batteries and other components– the smaller the battery pack, the smaller the motor, motor controller and other components for each vehicle, and therefore the overall production cost could drop significantly.

    I suspect the maturation of inductive charging technology and its broad implementation in urban and suburban environments may have an even greater effect eventually than improvements in battery energy density and other battery improvements.