[LINK] Some shocking news about wireless electricity

[stephen at melbpc.org.au]

Thanks Adam, Glen and all.  Here's more info on this interesting thread:

Quote; "An Apple patent submitted in 2005 and published in February 
describes technology for charging an iPhone or an iPod using zero-contact 
induction, for not only charging, but data transfer .."

<http://www.infoworld.com/article/07/06/07/Wireless-charging-here-at-
last_1.html?source=NLC-TB&cgd=2007-06-08>  (snip)

When you put (your) toothbrush in its charging cradle, you'll notice that 
no metal contacts are exposed for the electricity to charge the 
batteries. The toothbrush charges magically, right through the plastic. 

Don't look now, but that very same technology is coming soon to your cell 
phone, your iPod, even your laptop. 

2007 is the year that truly mainstream wirelessly charging products 
finally go on sale. 

How it works

There are three basic technologies for wireless charging: radio, 
resonance, and induction.

Radio charging is well suited for charging low-power devices at long 
distances -- some 30 feet away. This technology is ideal for trickle-
charging advance RFID chips affixed to, say, palettes loaded with 
products in a warehouse. 

Resonance charging makes sense for robots, cars, vacuum cleaners, and 
other applications that require massive power over minute distances -- 
essentially making contact with plastic, but not metal. 

Toothbrushes now, and random gadgets will very soon, use inductive 
charging. This technology uses a coil to create an electromagnetic field 
across a charging station surface. The device then converts power from 
the field back into usable electricity, which is put to work charging the 
battery. 

(Meanwhile, researchers at MIT said this week that they have come up with 
a way to wirelessly supply power that could lead to the development of 
gadgets that don't require batteries at all.) 

Where wireless charging gadgets come from

Wireless charging gadgets will come from some well-known companies, 
including Apple and just about every cell phone handset maker, as well as 
small startups you may not have heard of. 

An Apple patent submitted in 2005 and published in February describes 
technology for charging an iPhone or an iPod using zero-contact induction 
for not only charging but data transfer -- an arrangement that requires 
inductive coils in both base station and device. 

Apple's patent covers both single coil (charging only) and two-coil (both 
data and charging) approaches. (snip)

At 06:46 PM 10/06/2007, Glen Turner wrote:

In fact, inductive coupling is efficient. Plugpack rectification and
DC current over thin wires has its own losses and I feel comfortable
that you could build an inductive charging system with less
loss. Particularly since the source is a medium voltage AC.

The problem is that the size and weight required for the inductive
coils to be efficient is incompatible with the desired handheld form
for phones, iPods, etc.

It is possible that some very clever engineering might see possibilities
where others have not. But more likely this is a classic situation where
a prototype will have excellent performance (being able to be any size
and shape) but the result will never be suitable for a product.

> Yes well, as I said, 5 Watts to power a 300 mW transmitter :)

A poor example because you are trying to modulate the outgoing signal,
so the amplifying transistors need to be constrained to their linear
regions rather than their more efficient but non-linear regions
[simplifying hugely here but the point holds for the more detailed
explanation].

What it comes down to is the coupling between the input and output
coils. Have these people come up with a physical design that will
allow a small device to have an transformer-grade coupling between
the charger and the device.

If they have, the mechanism will be so novel and so, in retrospect,
obvious that having seen it you will be able to explain it to people.
Those people will then whack their forehead for not having thought of
it themselves.

But such ideas are scarce. I can count on the fingers of one hand
people I know that have had such insights to engineering problems
and I can count on my fingers and toes the people living that have
had such insights in their careers.

And such ideas being so scarce, you are perfectly entitled to be
skeptical. I just ask that you get the engineering rationale for
your skepticism correct.

> Then the idea of turning the TV of instead of Standby no longer is 
> relevant because it's charging the phone, laptop, shaver, watch, pace 
> maker, and other devices :)

That's likely to happen, but with a computer with Powered USB
in place of the TV in your example. Unfortunately, there is a
lot of argument that the standard for Powered USB has been
stuffed with too many compromises to work in the real world
and we'll probably need a Powered-2 USB before equipment is
likely to be acceptable to consumers.

Powered USB will lead to efficiencies because one large power supply is,
in practice, more efficient than multiple small power supplies.
This isn't so much an electrical argument, as one of the economics
of consumer sales (manufacturers care about cents in a $30 product
but in a $700 product will allow more expensive engineering, and
thus sophistication, and thus efficiency).

Best wishes, Glen
_______________________________________________

Cheers all ..
Stephen Loosley
Victoria, Australia