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A nantenna (nano antenna) is a nanoscopic rectifying antenna, an experimental technology being developed to convert light to electric power. The concept is based on the rectenna (rectifying antenna), a device used in wireless power transmission. A rectenna is a specialized radio antenna which is used to convert radio waves into direct current electricity. Light is composed of electromagnetic waves like radio waves, but of much smaller wavelength. A nantenna is a very small rectenna the size of a light wave, fabricated using nanotechnology, which acts as an "antenna" for light, converting light into electricity. It is hoped that arrays of nantennas could be an efficient means of converting sunlight into electric power, producing solar power more efficiently than conventional solar cells. The idea was first proposed by Robert L. Bailey in 1972. As of 2012, only a few nantenna devices have been built, demonstrating only that energy conversion is possible.〔http://www.mat.ucsb.edu/~g.legrady/academic/courses/13f254/lexicon.html〕 It is unknown if they will ever be as cost-effective as photovoltaic cells. A nantenna is an electromagnetic collector designed to absorb specific wavelengths that are proportional to the size of the nantenna. Currently, Idaho National Laboratories has designed a nantenna to absorb wavelengths in the range of 3–15 μm.〔Novack, Steven D., et al. “Solar Nantenna Electromagnetic Collectors.” American Society of Mechanical Engineers (Aug. 2008): 1–7. Idaho National Laboratory. 15 Feb. 2009 ==History of nantennas== Robert Bailey, along with James C. Fletcher, received a patent in 1973 for an “electromagnetic wave converter”.〔http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=3760257.PN.&OS=PN/3760257&RS=PN/3760257〕 The patented device was similar to modern day nantenna devices. In 1974, T. Gustafson and coauthors demonstrated that these types of devices could rectify even visible light to DC current Alvin M. Marks received a patent in 1984 for a device explicitly stating the use of sub-micron antennas for the direct conversion of light power to electrical power.〔http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4445050.PN.&OS=PN/4445050&RS=PN/4445050〕 Marks’s device showed substantial improvements in efficiency over Bailey’s device. In 1996, Guang H. Lin reported resonant light absorption by a fabricated nanostructure and rectification of light with frequencies in the visible range.〔 In 2002, ITN Energy Systems, Inc. published a report on their work on optical antennas coupled with high frequency diodes. ITN set out to build a nantenna array with single digit efficiency. Although they were unsuccessful, the issues associated with building a high efficiency nantenna were better understood.〔 In 2015 researchers fabricated a solar energy collector that can convert optical light to DC current. Baratunde Cola, a professor at Georgia Institute of Technology, led the team that developed this optical rectenna using carbon nanotubes. The team grew vertical arrays of multiwall carbon nanotubes (MWCNTs) on a metal-coated substrate. The nanotubes were coated with insulating aluminum oxide and altogether capped with a metal electrode layer. The small dimensions of the nanotubes act as antennae, capable of capturing optical wavelengths. The MWCNT also doubles as one layer of a metal-insulator-metal (MIM) tunneling diode. Due to the small diameter of MWCNT tips, this combination forms an ultrafast diode that is capable of rectifying the high frequency optical radiation. The overall achieved conversion efficiency of this device is around 10^-5 %.〔 Nonetheless, nantenna research is ongoing. Future efforts have been undertaken to improve the device efficiency by investigating alternative materials, manipulating the MWCNTs to encourage conduction at the interface, and reduce resistances within the structure. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nantenna」の詳細全文を読む スポンサード リンク
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