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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: 2) by frojack on Monday August 03 2015, @04:03PM

    by frojack (1554) on Monday August 03 2015, @04:03PM (#217436) Journal

    The Summary is so vague its not clear this even was an antenna.
    Sounds like it was just a loop of wire (hula hoop) not connected to anything.

    To answer your question, apparently NOBODY thought of this before. So what you seem to suggest should be plainly obvious to the most casual observer, somehow escaped the attentions of electrical engineers the world over until these guys came along.

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  • (Score: 0) by Anonymous Coward on Monday August 03 2015, @04:13PM

    by Anonymous Coward on Monday August 03 2015, @04:13PM (#217444)

    It would seem a bit obvious; the efficiency drops approximately proportional to the square of the distance, and with this resonant loop, that is basically a receiver and transmitter at the same time, they have reduced the distance between the original coils to two lengths of half the original distance (assuming zero thinkness of the new coil), and therefor twice the efficiency, minus the losses in the new coil itself.

    This WAS obvious to many electrical engineers, but the point is that this doesn't really change anything. If you can put a resonant coil halfway, you could also have places the receiver or transmitter coils in the same place, in most application, which would give you another factor of 2 improvement.

    I can't think of any application where you could place an extra resonant coil in the gap between the transmitter and receiver coils, where you couldn't move one of those in the first place.

    • (Score: 2) by jcross on Monday August 03 2015, @04:25PM

      by jcross (4009) on Monday August 03 2015, @04:25PM (#217449)

      Add to this the fact that if TFS is accurate, that is some really fat wire! Given the size of that coil of 4.25 cm diameter wire, where are you going to put that, period? Wherever you do put it, don't let the crackheads know where, or it's going straight to the closest sketchy scrap yard.

    • (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.
      "