28 Aralık 2007 Cuma


MIT WiTricity
Goodbye wires…

WiTricity, a portmanteau for wireless electricity, is a term coined initially by Dave Gerding in 2005 and used by a MIT research team led by Prof. Marin Soljačić in 2007, to describe the ability to provide electrical energy to remote objects without wires. WiTricity is based on strong coupling between electromagnetic resonant objects to transfer energy wirelessly between them. The system consists of WiTricity transmitters and receivers that contain magnetic loop antennas critically tuned to the same frequency. As WiTricity operates in the electromagnetic near-field, the receiving devices must be no more than about a quarter wavelength from the transmitter, that is a few meters at the frequency of a few MHz used by the system. In their first paper, the group also simulated GHz dielectric resonators.

Wireless power transmission is not a new idea, William C. Brown demonstrated in 1964 on the CBS Walter Cronkite news a microwave-powered model helicopter that received all the power needed for flight from a microwave beam. Between 1969 and 1975 Bill Brown was technical director of a JPL Raytheon program that beamed 30 kW over a distance of 1 mile at 84% efficiency.

Unlike the far field wireless power transfer systems based on traveling EM waves, WiTricity employs near field inductive coupling through magnetic fields, which interact far more weakly with surrounding objects, including biological tissue. It is not known exactly why this technology had not been developed. Researchers attribute it to various reasons ranging from the limitations of well-known physical laws, to simply a lack of need. Only recently have modern consumers obtained a high number of portable electronic devices which currently require batteries and plug-in chargers.

The MIT researchers successfully demonstrated the ability to power a 60 watt light bulb from a power source that was 2 meters (7 ft) away at roughly 40% efficiency. They used two capacitively loaded copper coils, 60 centimeters (24 in) in diameter, oriented along the same axis, The coils were designed to resonate together at 10 MHz. One was connected inductively to a power source, the other to a bulb. The setup powered the bulb on, even when the direct line of sight was blocked using a wooden panel. Aristeidis Karalis says that "the usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system".

The researchers plan to miniaturize the setup enough for commercial use in three to five years. The researchers suggest that the radiated power densities will be below the threshold for FCC safety regulations.

Further applications for this technology include transmission of information — since the underlying technology is not electromagnetic waves, It would not interfere with radio waves and thus could be used as a cheap and efficient communication device without requiring a license or a government permit.

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