MIT unveils wireless-power device
Published: 11 Jun 2007 09:54 BST
US researchers have produced a system which delivers power to devices without the need for wires.
A team from the Massachusetts Institute of Technology (MIT) lit a 60-watt light bulb from a power source two metres away and with no physical connections between the source and the appliance.
The "WiTricity" device — the term coined by the MIT team to describe the wireless-power phenomenon — uses magnetic fields to deliver power to the gadgets remotely.
The charger sends power to the gadget using magnetic induction, which is the ability to change a magnetic field to produce an electrical current.
Various methods of transmitting power wirelessly have been known for some time — such as radio waves or Wi-Fi.
But, while such examples are excellent for the wireless transmission of information, they are not feasible for substantial power transmissions because radio waves and Wi-Fi radiation spread in all directions and vast amounts of power end up being wasted into free space.
In contrast, WiTricity synchronises the charger and gadget to exchange energy efficiently without leaking much power to other objects.
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WiTricity does this by getting the charger and power-hungry device to connect using magnetic fields at "coupled resonant frequencies".
Imagine a room with 100 identical wine glasses, each filled with wine up to a different level. If an opera singer sings a sufficiently loud single note inside the room, a glass of a corresponding frequency to the singer's warbles might accumulate sufficient energy to explode, while not influencing the other glasses.
The singer and the exploding glass are "coupled resonators" — and the WiTricity charger is synonymous to the singer, the gadget to the exploding glass.
While the singer uses sound waves to transmit energy to the glass, WiTricity chargers use coupled magnetic fields to charge gadgets remotely.
The MIT team's design consists of two copper coils — one attached to the power source and the other to the gadget — which respectively produce and pick up the magnetic fields.
Speaking in November 2006, Marin Soljacic, assistant professor of physics at MIT, said the device has a three- to five-metre range.
Soljacic added that any power-hungry device would need to be fitted with a card, similar to a Wi-Fi card in a laptop, to receive the signal and start charging.
The coils currently have a radius of around 10 inches. Soljacic said simpler and smaller designs will be created in the future.
The MIT physicists devised the WiTricity system last year and this is the first time a working example has been unveiled.
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