[LINK] Some shocking news about wireless electricity

[Glen Turner]

On Sun, 2007-06-10 at 16:23 +1000, Adam Todd wrote:

> >Then there's the inherent inefficiencies in electronics, and in transforming
> >one form of energy to another.
> 
> Agree.  As I detailed in my own example.

Hi Adam,

Oh dear. A electromagnetic field in a wire versus in free space isn't
"transforming one form of energy to another". Both are electromagnetic.

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