TELECOM Digest OnLine - Sorted: Physicist Moots Wireless Electricity

Physicist Moots Wireless Electricity

Australian Broadcasting Company (
Wed, 15 Nov 2006 17:05:29 -0600

You may one day be able to recharge your laptop or mobile phone
without having to plug it into the wall, says a US physicist.

But others say there are many hurdles before such transfer of energy
means we can say goodbye to wires.

Assistant Professor Marin Soljacic, of Massachusetts Institute of
Technology, will present his team's work at the American Institute of
Physics forum in San Francisco this week.

Today's wireless transfer of energy, such as the transfer of light
energy from the Sun for solar power or the transfer of microwaves from
transmitters for communication, involve relatively low levels of

But recharging devices like laptops requires a much higher level of
energy. And if this was routinely zapped through the air it could
'fry' any living organisms that get in the way.

But Prof Soljacic says he has found a way of transmitting energy so
that only the devices that it is recharging will pick it up, so it
will not affect humans.

Instead of using traditional radiation, he wants to use the part of
the electromagnetic field that is 'non-radiative'.

He says devices can be tuned to the frequency of this field and thus
act as a sink for all the energy the transmitter gives out.

Prof Soljacic says this would prevent energy radiating out to areas it
does not need to go to, providing an efficient and safe method of
wireless energy transfer.

"The team calculates that an object the size of a laptop could be
recharged within a few metres of the power source," he says. "Placing
one source in each room could provide coverage throughout your home."

Prof Soljacic also thinks the technology could be used to power freely
roaming robots in a factory.

Finding a 'magic' frequency --

But Australian physicists, yet to see the full details of Prof
Soljacic's work, are sceptical of his claims.

They say the challenge is finding a 'magic' frequency that does not
also affect living organisms and thus pose possible health risks.

"You would be reintroducing all the problems that we went through with
mobile phones," says Dr Geoff Anstis of the University of Technology,
Sydney, referring to the uncertainty surrounding any long-term health
effects of using mobiles.

"And it wouldn't be until a couple of decades that you may be happy
that there isn't a significant problem."

His colleague Professor Geoff Smith agrees and says there are also
technical challenges to keeping the devices tuned with the
transmitters, thus preventing the general release of stray energy.

"I think this is nice physics but there's a way to go before it would
be possible," says Prof Smith.

He says any changes in the surrounding environment could "de-tune" the
system and stop the safe and efficient transfer of power.

Electrical engineer Dr Trevor Bird of CSIRO's ICT Centre says attempts
so far to develop wireless power transfer have not been very

He agrees that safety and technical barriers to wireless power systems
are huge and would like further details on Prof Soljacic's proposal.

Dr Bird also says that, depending on the frequency of the field, the
antenna on the device being recharged may have to be very large.

Source: ABC
Copyright 2006 ABC

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[TELECOM Digest Editor's Note: If I understand this correctly, they
are saying solar power could be used, but not in sufficient voltage
to keep the phone fully charged, etc. Why not provide both types of
power inputs to the units; both *wired* electricity (as at present)
and solar power. The solar power would provide a nice, slow -- but
constant -- source of additional power all day long while the phone
was in use or sitting idle. PAT]

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