WiTricity

WiTricity, a portmanteau for wireless electricity, is a term coined initially by Dave Gerding in 2005 and used by an MIT research team led by Prof. Marin Soljačić in 2007,cite web | url = http://web.mit.edu/newsoffice/2006/wireless.html | title = Wireless electricity could power consumer, industrial electronics | publisher = MIT News | date = 2006-11-14] cite web | url = http://web.mit.edu/newsoffice/2007/wireless-0607.html | title = Goodbye wires… | publisher = MIT News | date = 2007-06-07] 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 (which is a few meters at the frequency used by the example system). In their first paper, the group also simulated GHz dielectric resonators.

History

Early developments: Pre-WWI

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Starting in 1901, Tesla intended to use his relating patents for wirelessly sending industrial amounts of energy internationally by his large-scale Wardenclyffe Tower project, making use [Also see more detailed discussion at .] of what is known today as waves in plasmas, magnetohydrodynamics, telluric current, Schumann resonances, as well as Zenneck waves rather than common electromagnetic radiation back then known as "Hertzian radiation". The construction of Wardenclyffe Tower was halted and then abandoned in 1905-7 due to his investors, specifically J. P. Morgan, leaving Tesla when they found out Tesla's intended main use for the technology was to provide free electricity as a public service around the world, not just the world's first radio station with regular entertainment broadcasts. The unfinished plant at Wardenclyffe was destroyed in 1917 amidst property and ownership disputes. During the 1930s, Tesla mused to use the same technology to facilitate a "macroscopic particle beam weapon", the so-called "Teleforce" for which he found no investors in spite of moderate press coverage up to WWII.

The "Tesla effect" (named in honor of Tesla) is the archaic term for an application of the wireless movement of energy through space and matter; not just the production of voltage across a conductor.

Since the 1960s

William C. Brown demonstrated in 1964 on the CBS Evening News with Walter Cronkite 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.

Technical background

Overview

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.

Applications

The MIT researchers successfully demonstrated the ability to power a 60-watt light bulb from a power source that was 2 meters (7 feet) 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 are quoted in this paper saying it should be possible to develop the system for commercial use in three to five years. [cite web | url = http://www.theaustralian.news.com.au/story/0,20867,21871209-2703,00.html | title = Wireless power pulls plug on cables | publisher = The Australian | date = 2007-06-08] The researchers suggest that the radiated power densities will be below the threshold for FCC safety regulations.

The Discovery Channel Show Project Earth aired an episode where power was wirelessly transmitted 12 feet to charge a cell phone.

Further applications for this technology include transmission of information — 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.

ee also

*List of emerging technologies
*Wireless energy transfer
*Evanescent wave coupling
* WREL technology

Notes

References

*cite journal
author = Aristeidis Karalis
coauthors = J.D. Joannopoulos, Marin Soljačić
title = Efficient wireless non-radiative mid-range energy transfer
id = arxiv|archive=physics|id=0611063v2
year = 2007
month = February .
* cite journal
author = Aristeidis Karalis
coauthors = J.D. Joannopoulos, Marin Soljačić
title = Efficient wireless non-radiative mid-range energy transfer
journal = Annals of Physics
doi = 10.1016/j.aop.2007.04.017
year = 2007
month = April
quote = (Subscription required)
volume = 323
pages = 34
* cite journal
author = Andre Kurs
coauthors = Aristeidis Karalis, Robert Moffatt, J.D. Joannopoulos, Peter Fisher, Marin Soljačić
title = Wireless power transfer via strongly coupled magnetic resonances
journal = Science Express
doi = 10.1126/science.1143254
year = 2007
month = June
quote = (Subscription required)
volume = 323
pages = 34
pmid = 17556549

External links

*cite news | url = http://www.electricitybid.com/electricity/index.php/category/witricity/ | title = Witricity News | author = Jim Smithies | publisher = Electricity Bid News
*cite news | url = http://plooms.com/?p=50 | title = WiTricity (Wireless Electricity) | author = Keith Davis | publisher = Plooms
*cite news | url = http://www.mit.edu/%7Esoljacic/wireless_power.html | title = Marin Soljačić (researcher team leader) home page on MIT
*cite news | url = http://news.bbc.co.uk/2/hi/technology/6725955.stm | title = Wireless energy promise powers up | author = Jonathan Fildes | publisher = BBC News | date = 2007-06-07
*cite news | url = http://www.sciam.com/article.cfm?articleid=07511C52-E7F2-99DF-3FA6ED2D7DC9AA20&chanId=sa025 | title = Wireless Energy Lights Bulb from Seven Feet Away | author = JR Minkel | publisher = Scientific American | date = 2007-06-07
*cite news | url = http://www.breitbart.com/article.php?id=paWirelessThur19Wirelesspower&show_article=1&catnum=0 | title = Breakthrough to a wireless (electricity) future (WiTricity) | publisher = The Press Association | date = 2007-06-07
*cite news | url = http://www.technewsworld.com/story/57757.html | title = MIT Wizards Zap Electricity Through the Air | author = Katherine Noyes | publisher = TechNewsWorld | date = 2007-06-08
*cite news | url = http://www.dailytech.com/MIT+Engineers+Unveil+Wireless+Power+System/article7632.htm | title = MIT Engineers Unveil Wireless Power System | author = Chris Peredun, Kristopher Kubichi | publisher = DailyTech | date = 2007-06-11
*cite news | url = http://www.sciencemag.org/cgi/data/1143254/DC1/1 | title = Supporting Online Material for Wireless Power Transfer via Strongly Coupled Magnetic Resonances | publisher = Science Magazine
* [http://www.mtt.org/awards/WCB's%20distinguished%20career.htm William C. Brown biography on the IEEE MTT-S website]