[AI] Unplugged: Goodbye cables, hello energy beams

Sanjay ilovecold at gmail.com
Thu Jun 17 03:17:50 EDT 2010

          Your gadgets are finally about to become truly wireless - as long
          as you don't mind lasers criss-crossing your living room

by David Robson

LET'S face it: power cables are unsightly dust-traps. PCs, TVs and
music players are becoming slicker every year, but the nest of vipers
in the corner of every room remains an ugly impediment to true

Then there is the inconvenience of charging phones, MP3 players and
PDAs. A minor hassle, admittedly, but it is easy to forget to top up
the batteries and before you know it you have left the house with a
dead gadget. Wouldn't life be simpler if power was invisibly beamed to
your devices whenever you walked into a building with an electricity
supply? Wireless communication is ubiquitous, after all, so why can't
we permanently unshackle our electronics from power cables too?

Poor transmission efficiencies and safety concerns have plagued
attempts at wireless power transfer, but a handful of start-ups - and
some big names, like Sony and Intel - are having another go at making
it work. The last few years have seen promising demonstrations of
cellphones, laptops and TVs being powered wirelessly. Are we on our
way to waving goodbye to wires once and for all?

The idea of wireless power transfer is almost as old as electricity
generation itself. At the beginning of the 20th century, Nikola Tesla
proposed using huge coils to transmit electricity through the
troposphere to power homes. He even started building Wardenclyffe
Tower on Long Island, New York, an enormous telecommunications tower
that would also test his idea for wireless power transmission. The
story goes that his backers pulled the funding when they realised
there would be no feasible way to ensure people paid for the
electricity they were using, and the wired power grid sprang up

Wireless transmission emerged again in the 1960s, with a demonstration
of a miniature helicopter powered using microwaves beamed from the
ground. Some have even suggested that one day we might power
spaceships by beaming power to them with lasers (New Scientist, 17
February 1996, p 28). As well as this, much theoretical work has gone
into exploring the possibility of beaming power down to Earth from
satellites that harvest solar energy (New Scientist, 24 November
2007, p 42).

Long-distance ground-to-ground wireless power transmission would
require expensive infrastructure, however, and with concerns over the
safety of transmitting it via high-power microwaves, the idea has been
met with trepidation.

While we won't be seeing a wireless power grid any time soon, the idea
of beaming power on a smaller scale is rapidly gaining momentum. That
is largely because, with wireless communication, like Wi-Fi and
Bluetooth, and ever-shrinking circuits, power cables are now the only
limit to becoming truly portable. "The move was inevitable once
wireless communication became popular," says David Graham, a
co-founder of Powerbeam in San Jose, California.

With this new impetus, engineers and start-up companies have jumped at
the challenge, and while beamed power is still in its infancy, three
viable options seem to be emerging. The use of radio waves to transmit
electricity is perhaps the most obvious solution, since you can in
principle use the same kinds of transmitters and receivers used in
Wi-Fi communication. Powercast, based in Pittsburgh, Pennsylvania,
has recently used this technology to transmit microwatts and
milliwatts of power over at least 15 metres to industrial sensors.
They believe a similar approach could one day be used to recharge
small devices like remote controls, alarm clocks and even cellphones.

A second possibility, for more power-hungry devices, is to fire a
finely focused infrared laser beam at a photovoltaic cell, which
converts the beam back to electrical energy. It's an approach
PowerBeam has adopted, but so far its efficiency is only between 15
and 30 per cent. While that could serve more power-hungry appliances,
it would in practice be too wasteful.

The technology has been used to power wireless lamps, speakers and
electronic photo frames that require less than 10 watts to function.
Over time, as both the lasers and photovoltaic cells improve, the
company hopes efficiencies of up to 50 per cent will be possible.
"There's no reason we couldn't power a laptop eventually," says
Graham. Unlike some other possible techniques, a sharply focused beam
loses minimal energy over large distances, preserving its efficiency:
"A hundred metres is no big deal."

Inconvenient beams
Others are sceptical that this technique would be practical for truly
portable devices, which are constantly moving around and between
rooms. "An infrared beam would not be convenient to charge a mobile
phone - it's too directional," says Menno Treffers, chairman of
the Wireless Power Consortium in the Netherlands. Powerbeam's solution
is to fit a small fluorescent bulb to the receiving device so that a
camera on the transmitter can track the light and steer the laser beam
accordingly. Another problem is that a separate beam is needed for
each device you want to power, which would be tricky to engineer, says
Aristeidis Karalis at the Massachusetts Institute of Technology,
who is developing an alternative wireless power transmission system.

The third possibility for wireless power is magnetic induction - the
most attractive option for beefy domestic applications. A fluctuating
magnetic field emanating from one coil can induce an electric current
in another coil close by, which is how many devices, like electric
toothbrushes and even some cellphones, recharge drained batteries. The
snag, however, has been that while efficiency is good at close
contact, it can drop to zero at even a few millimetres from the

Enter Karalis and his colleagues. It has long been known that such
mechanical energy transfer is improved enormously if two objects
resonate at the same frequency - it's how an opera singer can smash a
glass if she hits the right pitch. Karalis wondered whether the same
idea could improve the efficiency of magnetic induction at greater

The team's set-up consisted of an inducting coil connected to a
capacitor. The energy within this circuit oscillates rapidly between
an electric field in the capacitor and a magnetic field in the coil.
The frequency of this oscillation is controlled by the capacitor's
ability to store charge and the coil's ability to produce a magnetic
field. If the frequency in the energy-transmitter's circuit is
different from that of the receiver's circuit, they are non-resonant.
The result is that the magnetic field coming from the transmitter
interferes destructively with the field building up in the receiver,
constraining energy transfer. But if the transmitter and receiver are
resonant, the team reasoned, the oscillating fields of their two coils
would always be in sync, meaning the interference is constructive and
the amount of energy transferred is boosted.

They tested their theory in 2007 with great success, transmitting
60 watts across 2 metres, with 40 per cent efficiency (Science,
vol 317, p 83). The team has since founded a company called
WiTricity to develop the idea. Last year, the firm used two square
coils 30 centimetres across, one in the receiver and one in the
transmitter, to power a 50-watt TV 0.5 metres from the power supply,
with an impressive 70 per cent efficiency. "In some cases, the
improvement in the efficiency due to resonance can be more than
100,000 times that of non-resonant induction," says Karalis. Unlike
laser-based line-of-sight energy transmission, a magnetic field is not
focused and so can pass around or through obstacles between the
transmitter and receiver.

The big consumer electronics companies have also been keen to
investigate "resonant transfer". Sony, for example, has demonstrated a
wireless TV, and Intel is investigating the technology for a range of
devices. "Power transfer efficiency scales independently of power, so
the same efficiency can be achieved for laptops, consumer electronics
such as TVs, and smaller portable devices such as cellphones," says
Emily Cooper, a research engineer at Intel's labs in Seattle. In other
words, the same proportion of the total energy will be lost for a
power-hungry plasma TV as for a tiny PDA.
Sony has tested a wireless TV, and Intel is investigating the
technology for a range of devices

With such promising demonstrations, it seems likely that wireless
power will one day enter our homes in a big way. A technical standard,
dubbed Qi, is already being established for the non-resonant
magnetic-induction technique and compatible charging mats will soon be
available. It is early days for the other techniques, but similar
standards are likely to emerge.
With such promising demonstrations it seems likely wireless power will
enter our homes in a big way

Damage to the person
The technology is likely to meet some objections along the way,
however. For one thing, you would be forgiven for being a little
worried about zapping relatively high-power energy beams through the
atmosphere. Take laser transmission, for example. "High powers
concentrated in a narrow laser beam could cause serious damage to a
person," says Karalis. That shouldn't be a danger with PowerBeam's
products: if the small camera on the transmitter fails to see the
small light bulb of the receiver, it shuts down the laser within
milliseconds. And as a failsafe, the receiver also sends a message to
the transmitter via radio if it notices an unexplained interruption in
power reception.

Exposure to radio waves and fluctuating magnetic fields also have
their potential dangers. If they transmit heat to our cells, they can
damage tissue over a long period of time. "All the technologies pose a
potential risk for thermal interaction with the body, in the same way
that radiation from cellphones does," says Rudiger Matthes,
vice-chairman of the International Commission on Non-Ionizing
Radiation Protection in Oberschleioheim, Germany. But, provided the
exposure is below the thresholds put forward in guidelines from
ICNIRP, which companies like WiTricity are following closely, it
should not be a problem.

The fear remains that electromagnetic fields could damage tissue
through some other, non-thermal mechanism, a concern raised by many
biophysicists about cellphone signals. Without any available cohort
studies to test exposure over a long period of time, though, they have
had to rely on lab studies, which failed to find any clear or
reproducible biological effects. "The matter is still open to debate,"
says David de Pomerai at the University of Nottingham in the UK, who
studies the effect of microwaves on nematode worms. If the wireless
power transmission methods all fall within the ICNIRP's criteria, he
says that the exposure should be no more risky than that from

Perhaps more pressing, though, are environmental concerns. With global
warming an ever increasing issue, most people are looking for ways to
improve efficiency and save energy - and therefore reduce
power-station emissions of greenhouse gases. To some people, wireless
power transmission will seem like a distinctly profligate and
retrograde step.

"The fact that these appliances are only 10 to 60 per cent efficient
means that 90 to 40 per cent of the electricity the householder is
paying for is wasted," says Paula Owen, who heads the statistics group
at the Energy Saving Trust, based in London. "Consider these
products next to other typical household appliances. Boilers, for
example, are now over 90 per cent efficient. It seems we are going
back to the days of incandescent bulbs, which were only 5 per cent
efficient at creating light and are now being phased out."

Taking individual gadgets, the energy losses might seem small, but
scaling up to a truly wireless home would be a much bigger deal. The
question is, would you be prepared to throw away your green
credentials for wire-free, minimalist beauty?

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