By Jonathan Fildes
Technology reporter, BBC News, Oxford

A system that can deliver power to devices without the need for wires has been shown off at a hi-tech conference.

The technique exploits simple physics and can be used to charge a range of electronic devices.

Eric Giler, chief executive of US firm Witricity, showed mobile phones and televisions charging wirelessly at the TED Global conference in Oxford.

He said the system could replace the miles of expensive power cables and billions of disposable batteries.

"There is something like 40 billion disposable batteries built every year for power that, generally speaking, is used within a few inches or feet of where there is very inexpensive power," he said.

Trillions of dollars, he said, had also been invested building an infrastructure of wires "to get power form where it is created to where it is used."

"We love this stuff [electricity] so much," he said.

Mr Giler showed off a Google G1 phone and an Apple iPhone that could be charged using the system.

Witricity, he said, had managed to pack all the necessary components into the body of the G1 phone, but Apple had made that process slightly harder.

"They don’t make it easy at Apple to get inside their phones so we put a little sleeve on the back," he said.

He also showed off a commercially available television using the system.

"Imagine you get one of these things and you want to hang it on the wall," he said. "Think about it, you don’t want those ugly cords hanging down."

Good vibrations

The system is based on work by physicist Marin Soljacic at the Massachusetts Institute of Technology (MIT).

It exploits "resonance", whereby energy transfer is markedly more efficient when a certain frequency is applied.

When two objects have the same resonant frequency, they exchange energy strongly without having an effect on other, surrounding objects.

For example, it is resonance that can cause a wine glass to explode when a singer hits exactly the right tone.

But instead of using acoustic resonance, Witricity’s approach exploits the resonance of low frequency electromagnetic waves.

HOW WIRELESS POWER WORKS

• 1. First magnetic coil (Antenna A) housed in a box and can be set in wall or ceiling
• 2. Antenna A, powered by mains, resonates at a specific frequency
• 3. Electromagnetic waves transmitted through the air
• 4. Second magnetic coil (Antenna B) fitted in laptop/TV etc resonates at same frequency as first coil and absorbs energy
• 5. Energy charges the device

The system uses two coils – one plugged into the mains and the other embedded or attached to the gadget.

Each coil is carefully engineered with the same resonant frequency. When the main coil is connected to an electricity supply, the magnetic field it produces is resonant with that of with the second coil, allowing "tails" of energy to flow between them.

As each "cycle" of energy arrives at the second coil, a voltage begins to build up that can be used to charge the gadget.

Mr Giler said the main coil could be embedded in the "ceiling, in the floor, or underneath your desktop".

Devices using the system would automatically begin to charge as soon as they were within range, he said.

"You’d never have to worry about plugging these things in again."

Safety concerns

Mr Giler was keen to stress the safety of the equipment during the demonstration.

"There’s nothing going on – I’m OK," he said walking around a television running on wireless power.

The system is able to operate safely because the energy is largely transferred through magnetic fields.

"Humans and the vast majority of objects around us are non-magnetic in nature," Professor Soljacic, one of the inventors of the system, told BBC News during a visit to Witricity earlier this year.

It is able to do this by exploiting an effect that occurs in a region known as the "far field", the region seen at a distance of more than one wavelength from the device.

In this field, a transmitter would emit mixture of magnetic and potentially dangerous electric fields.

But, crucially, at a distance of less than one wavelength – the "near field" – it is almost entirely magnetic.

Hence, Witricity uses low frequency electromagnetic waves, whose waves are about 30m (100ft) long. Shorter wavelengths would not work.

‘Ridiculous technology’

Witricity is not the first jump on the concept of wireless electricity.

For example, the nineteenth century American inventor Thomas Edison and physicist and engineer Nikola Tesla explored the concept.

"In the very early days of electricity before the electric grid was deployed [they] were very interested in developing a scheme to transmit electricity wirelessly over long distances," explained Professor Soljacic.

"They couldn’t imagine dragging this vast infrastructure of metallic wires across every continent."

Tesla even went so far as to build a 29m-high aerial known as Wardenclyffe Tower in New York.

"It ran into some financial troubles and that work was never completed," said Professor Soljacic.

Today, chip-giant Intel has seized on a similar idea to Witricity’s, whilst other companies work on highly directional mechanisms of energy transfer, such as lasers.

However, unlike Witricity’s work, lasers require an uninterrupted line of sight, and are therefore not good for powering objects around the home.

In contrast, Mr Giler said Witricity’s approach could be used for a range of applications from laptops and phones to implanted medical devices and electric cars.

"Imagine driving in the garage and the car charges itself," he said.

He even said he had had interest from a company who proposed to use the system for an "electrically-heated dog bowl".

"You go from the sublime to the ridiculous," he said.

Ted Global is a conference dedicated to "ideas worth spreading". It runs from the 21 to 24 July in Oxford, UK. </p

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