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posted by janrinok on Monday August 03 2015, @02:21PM   Printer-friendly
from the charge! dept.

Now researchers from North Carolina State University and Carnegie Mellon University say they have hit upon a way to boost the efficiency of the energy transfer in that [wireless transfer] situation. They reported, in a paper published in the online edition of the journal IEEE Antennas and Wireless Propagation Letters, that by placing a magnetic resonance field enhancer (MRFE)—a loop of copper wire resonating at the same frequency as the AC current feeding the transmitter coil—between the transmitter and receiver coil, they could boost the transmission efficiency by at least 100 percent. "Our experimental results show double the efficiency using the MRFE in comparison to air alone," David Ricketts of NC State, said in a press release. The MRFE increases the strength of the magnetic field that reaches the receiver coil, resulting in an increase of the transmission efficiency.
...
For their experimental setup, the team used two coils of 4.25-centimeter- diameter copper wire with six turns for the transmitter and receiver coils. The coils were separated by 12.2 cm and the transmitter coil was powered with a 2.94-megahertz signal. They measured the transmission efficiency by placing a metamaterial between the transmitter and receiver coil and comparing it with a setup where a single, 12-cm-diameter copper-wire loop replaced the metamaterial. They found that the copper wire version improved the efficiency by a factor of almost two.

Does wireless charging solve any problems that an industry-adopted connector standard wouldn't?


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  • (Score: 1, Informative) by Anonymous Coward on Monday August 03 2015, @04:28PM

    by Anonymous Coward on Monday August 03 2015, @04:28PM (#217451)

    The Friss link efficiency equation does not apply in this situation as the antenna operate in the reactive near field. Information about the performance of air cored wireless power transfer systems with respect to distance and misalignment can be found here:
    https://spiral.imperial.ac.uk/bitstream/10044/1/10025/12/IPTTPE%20Pinuela.pdf [imperial.ac.uk]
    As you can see the efficiency curve is flat with increasing distance before rapidly dropping off. I will also duplicate my comment in the IEEE spectrum piece that this is not new:

    "
    This is well known see from 2010:
    Fei Zhang; Hackworth, S.A.; Weinong Fu; Mingui Sun, "The relay effect on wireless power transfer using witricity," Electromagnetic Field Computation (CEFC), 2010 14th Biennial IEEE Conference on , vol., no., pp.1,1, 9-12 May 2010
    doi: 10.1109/CEFC.2010.5481512

    Or for something identical but not not applied directly to wireless power transfer from 2006:
    Syms, R.R.A.; Shamonina, E.; Solymar, L., "Magneto-inductive waveguide devices," Microwaves, Antennas and Propagation, IEE Proceedings , vol.153, no.2, pp.111,121, 3 April 2006
    doi: 10.1049/ip-map:20050119

    Analysis of the wireless power transfer case
    Chi Kwan Lee; Zhong, W.X.; Hui, S.Y.R., "Effects of Magnetic Coupling of
    Nonadjacent Resonators on Wireless Power Domino-Resonator Systems," Power Electronics, IEEE Transactions on , vol.27, no.4, pp.1905,1916, April 2012
    doi: 10.1109/TPEL.2011.2169460

    But in most applications the whole point of the wireless power transfer is to operate over an air gap where you do not want to place intermediate resonators. I can think of a few senarios where intermediate resonantors could be used (artifical arm, new containment vessel) but they are quite limited.
    "

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