> One of the things they must be doing is very precise load
> characterization to prevent house fires (put a non-compatible device
> on top and it might not only get cooked, but overheat enough to start
> a fire).

To get the sort of near field power transfer that they mention the
system has to be sharply resonant - and they do in fact mention that
it is resonant. As Q increases achievable range increases - but
efficiency also tends to be lower. The MIT 'discovery' that was in the
news a few years back lit a 60 Watt bulb at around 10 feet. Tesla
managed to wirelessly light the "Crystal Palace" for the Great
Exhbition in 1851? - maybe later. Regarless of the year, Sony seem to
have missed that piece of prior art.

In 1973 (that dates me) I rode Professor Don Ottos' electric "buggy"
(slowly) down the halls of the Auckland University Engineering School
- using inductive power transfer at 400 Hz. Electronic devices that
switched power at 'useful' frequencies were not readily available (or
at all available) and they used the available 400 Hz supply. Since
then the ease of producing HF energy has opened up the field. Otto
died young and his work and patents were forgotten for a decade or two
to be rediscovered by the University as "new developments" and sold to
the Japanese and Germans for IPT work. Along the way they all patented
parallel and series resonance several times over. The long dead Tesla
could probably have been tapped as a rotary power source in his own
right.

Sony seem to be re re discovering it all, as do a raft of other hardy
pioneers who are vending inductive charging pads and the like. I did a
demonstration warehouse picking system, that powered the picking bins
by IPT, about 10+ years ago. There's a long expired US patent out
there somewhere.

> So they not only test to make sure that a valid load is
> present before turning on the high power coils, but they probably also
> test to make sure that _only_ the correct load is present.

They could do. It's likely that if there was =A0a valid load present
then a parasite load that was suitably tuned could also take power.
The resonance peak will be narrow and may even have to track. They
could even make it need to track by dithering the transmit frequency.

> However, it will likely always be a "people with pacemakers and other
> medical devices or implants (insulin pumps, metal plates or pins, etc)
> should not come near to the device."

Odds are that it won't be too too bad - as above.

> The kicker is that I don't see a great need for this. =A0It looks cool,
> and there's a certain high end market for this sort of device, but
> moving power a distance shorter than 6 feet (length of a power cord)
> isn't terribly useful.

Indeed.

> I can see it for recharging portable devices
> which are cumbersome to plug/unplug (palm pre has this, for instance)
> but for items which are typically put in place and never moved there
> are far cheaper and more efficient ways to get electricity and signals
> to them in a hidden manner.

One target is vehicles - either those in a "service loop" or overnight
charging of cars or, in a large enough system, vehicles as they stop
at lights etc.

A friend made a charging system for a tourist shuttle in Whakarewarewa
Maori village in this country. Entirely successful. Probably similar
range to Sony's system. He was one of=A0Otto's previous students :-).


=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Russell McMahon.

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