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Researchers show use of MFRE can at least double wireless power transfer efficiency; more efficient than metamaterials

Researchers at North Carolina State University and Carnegie Mellon University have shown that passing wireless power transfer through a magnetic resonance field enhancer (MR-FE)—which could be as simple as a copper loop—can at least double transfer efficiency as compared to transferring through air alone. MR-FE use could potentially boost transfer efficiency by as much as 5,000% in some systems, the researchers said.

Wireless power transfer works via magnetic coupling or inductive coupling, and can achieve very high efficiency when the distances between the transmitter and receiver are small—less than a few centimeters. In such a case, the transmitter and receiver are strongly coupled, with a high coupling coefficient (usually greater that 0.9). As distance increases, the strength of the coupling decreases. Enhancing wireless power transfer efficiency over greater distances—to support, for example, the wireless charging of electric vehicles—has thus been a major goal of many research groups.

One of the leading candidates proposed for enhancing efficiency has been the use of metamaterials (MM)—artificial structures with particular electromagnetic properties—between transmitter and receiver.

The NCSU/CMU analysis, however, shows that the MR-FE approach can have up to a 4 times higher efficiency over the MM approach due to the lower loss of its field enhancement mechanism, said David Ricketts, an associate professor of electrical and computer engineering at NC State and corresponding author of a paper describing the work.

From left to right: performance of wireless power transfer using an MR-FE, a metamaterial (MM), and through air alone. Click to enlarge.

By placing the MR-FE 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. The MRFE amplifies the magnetic field while removing very little power from the system.

—David Ricketts

The researchers conducted an experiment that transmitted power through air alone, through a metamaterial, and through an MR-FE made of the same quality material as the metamaterial. The MR-FE significantly outperformed both of the others. In addition, the MRFE is less than one-tenth the volume of metamaterial enhancers.

This could help advance efforts to develop wireless power transfer technologies for use with electric vehicles, in buildings, or in any other application where enhanced efficiency or greater distances are important considerations.

—David Ricketts

Lead author of the paper is Matthew J. Chabalko, who worked on the project as a postdoctoral researcher at Carnegie Mellon and now works at Disney Research. Jordan Besnoff, a postdoctoral researcher at NC State, is a co-author of the paper.


  • Chabalko, M.; Besnoff, J.; Ricketts, D. (2015) “Magnetic field enhancement in wireless power using metamaterials magnetic resonant couplers.,” Antennas and Wireless Propagation Letters, IEEE vol. PP, no.99, pp. 1 doi: 10.1109/LAWP.2015.2452216doi:

  • Guy Lipworth, Joshua Ensworth, Kushal Seetharam, Da Huang, Jae Seung Lee, Paul Schmalenberg, Tsuyoshi Nomura, Matthew S. Reynolds, David R. Smith & Yaroslav Urzhumov (2014) “Magnetic Metamaterial Superlens for Increased Range Wireless Power Transfer” Scientific Reports 4, Article number: 3642 doi: 10.1038/srep03642

  • Wang, B.; Teo, K.H.; Nishino, T.; Yerazunis, W.; Barnwell, J.; Zhang, J. (2011) “Wireless Power Transfer with Metamaterials” TR2011-052



Oh Nikola, if only you hadn't been so crazy then we could have had time for you to share all the fruits of your genius.


I had a discussion recently on the boards with a representative of Plugless Power, and after consulting his engineers he specified their power loss in excess of that through wired charging at 7% for Level 1 and 12% for level 2.

In my view because of the convenience it offers this is a perfectly acceptable level of loss, comparable to the use of an automatic transmission over manual.

It would enable much more opportunity charging at stores etc when people would not bother to plug in.

Better efficiency always helps though, and this could do so.

I am not quite sure of the mechanics of interposing a field enhancer between the transmitter and receiver, so we will have to wait to see how it works out.

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