Much rubbish is written about IPT (Inductive Power Transfer) and many
patents seem to be trying to endlessly reinvent things that Tesla
played with. Or Prof Don Otto ** :-).

BUT it seems like Stanford may have found a way of increasing the
range over which very high efficiency transfer can be achieved
Their examples show transfer of around 97% efficiency at ranges of
about 1 metre and somewhat more than 80% at 3 metres. See figure 4 in
the free access paper below.

Their "enabling technology" appears to be "metallic planes" behind the
coils relative to an axis running between the coils. I've only glanced
at the paper so far but it looks promising - with the best efficiency
topology also being the most convenient one for many applications.

           http://www.stanford.edu/group/fan/publication/Yu_APL_99_214102_2=
011.pdf

It does appear at first glance * as if they may be reinventing a
near-field version of the Yagi-Uda antenna, in which case their
patents may be somewhat shaky.

             http://en.wikipedia.org/wiki/Yagi-Uda_antenna

Automotive on-highway recharging using this technique

               http://www.gizmag.com/stanford-wireless-ev-charging/21321/?u=
tm_source=3DGizmag+Subscribers&utm_campaign=3D4686329cac-UA-2235360-4&utm_m=
edium=3Demail

____________________

** 1971 IPT work - the late Don Otto, Auckalnd University.

            http://en.wikipedia.org/wiki/Wireless_energy_transfer

Says:

    ** 1971: Prof. Don Otto develops a small trolley powered by
induction at The University of Auckland, in New Zealand.[citation
needed]

I "drove"  it at one stage :-)



   Russell McMahon
   Applied Technology ltd

___________________________

* proper reading may show this impression to be wrong.
--=20
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