rectenna

The invention of the rectenna in the 1960s made long distance wireless power transmission feasible. The rectenna was invented in 1964 and patented in 1969{{patent|US|3434678}} [https://patents.google.com/patent/US3434678 Microwave to DC Converter] William C. Brown, et al, filed 5 May 1965, granted 25 March 1969 by US electrical engineer William C. Brown, who demonstrated it with a model helicopter powered by microwaves transmitted from the ground, received by an attached rectenna.{{cite web |title=William C. Brown |work=Project #07-1726: Cutting the Cord |publisher=2007–2008 Internet Science & Technology Fair, Mainland High School |date=2012 |url=http://mainland.cctt.org/istf2008/brown.asp |access-date=2012-03-30}} Since the 1970s, one of the major motivations for rectenna research has been to develop a receiving antenna for proposed solar power satellites, which would harvest energy from sunlight in space with solar cells and beam it down to Earth as microwaves to huge rectenna arrays.{{cite journal |author-last=Torrey |author-first=Lee |title=A trap to harness the sun |journal=New Scientist |volume=87 |issue=1209 |pages=124–127 |date=1980-07-10 |url=https://books.google.com/books?id=vfQxekunC3QC&q=rectenna&pg=PA125 |issn=0262-4079 |access-date=2012-03-30}} A proposed military application is to power drone reconnaissance aircraft with microwaves beamed from the ground, allowing them to stay aloft for long periods.

File:Millimeter wave textile rectenna.jpg

In recent years, interest has turned to using rectennas as power sources for small wireless microelectronic devices. The largest current use of rectennas is in RFID tags, proximity cards and contactless smart cards, which contain an integrated circuit (IC) which is powered by a small rectenna element. When the device is brought near an electronic reader unit, radio waves from the reader are received by the rectenna, powering up the IC, which transmits its data back to the reader.

The simplest crystal radio receiver, employing an antenna and a demodulating diode (rectifier), is actually a rectenna, although it discards the DC component before sending the signal to the headphones. People living near strong radio transmitters would occasionally discover that with a long receiving antenna, they could get enough electric power to light a light bulb.{{cite web |url=http://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/76.09.html |title=76.09 — Radio transmitter lights antenna bulb}}

However, this example uses only one antenna having a limited capture area. A rectenna array uses multiple antennas spread over a wide area to capture more energy.

Researchers are experimenting with the use of rectennas to power sensors in remote areas and distributed networks of sensors, especially for IoT applications.{{cite news |title=Over to you: Mythical electricity? |url=https://www.telegraph.co.uk/scienceandtechnology/technology/3336114/Over-to-you-Mythical-electricity.html |archive-url=https://web.archive.org/web/20090628191010/http://www.telegraph.co.uk/scienceandtechnology/technology/3336114/Over-to-you-Mythical-electricity.html |url-status=dead |archive-date=2009-06-28 |date=2004-11-24 |access-date=2009-06-25 |publisher=The Daily Telegraph}}

RF rectennas are used for several forms of wireless power transfer. In the microwave range, experimental devices have reached a power conversion efficiency of 85–90%.{{cite thesis |type=PhD Thesis |author-last=Zhang |author-first=J. |date=2000 |title=Rectennas for RF wireless energy harvesting |publisher=University of Liverpool |url=https://livrepository.liverpool.ac.uk/18537/}} The record conversion efficiency for a rectenna is 90.6% for 2.45 GHz,McSpadden, J. O., Fan, L., and Kai Chang, "Design and Experiments of a High-Conversion-Efficiency 5.8-GHz Rectenna," IEEE Trans. Microwave Theory and Technique, Vol. 46, No. 12, December 1998, pp. 2053–2060. https://ieeexplore.ieee.org/document/739282 with lower efficiency of about 82% achieved at 5.82 GHz.

{{main|Optical rectenna}}

In principle, similar devices, scaled down to the proportions used in nanotechnology, can be used to convert light directly into electricity. This type of device is called an optical rectenna (or "nantenna").{{cite journal |author-first1=Asha |author-last1=Sharma |author-first2=Virendra |author-last2=Singh |author-first3=Thomas L. |author-last3=Bougher |author-first4=Baratunde A. |author-last4=Cola |date=2015-10-09 |url=https://zenodo.org/record/851685 |journal=Nature Nanotechnology |volume=10 |issue=12 |pages=1027–1032 |title=A carbon nanotube optical rectenna |doi=10.1038/nnano.2015.220 |pmid=26414198 |bibcode=2015NatNa..10.1027S}}

{{cite press release |date=2015-09-28 |title=First optical rectenna -- combined rectifier and antenna -- converts light to DC current |website=EurekAlert! |url=http://www.eurekalert.org/pub_releases/2015-09/giot-for092315.php}}Patent application {{patent|WO|2014063149}} relates. Theoretically, high efficiencies can be maintained as the device shrinks, but to date efficiency has been limited, and so far there has not been convincing evidence that rectification has been achieved at optical frequencies. The University of Missouri previously reported on work to develop low-cost, high-efficiency optical-frequency rectennas.{{cite press release |url=http://munews.missouri.edu/news-releases/2011/0516-new-solar-technology-could-break-photovoltaic-limits/ |title=New solar technology could break photovoltaic limits |publisher=University of Missouri |date=2011-05-16}} Other prototype devices were investigated in a collaboration between the University of Connecticut and Penn State Altoona using a grant from the National Science Foundation.{{cite press release |url=http://today.uconn.edu/blog/2013/02/uconn-professors-patented-technique-key-to-new-solar-power-technology/ |title=UConn Professor's Patented Technique Key to New Solar Power Technology |date=2013-02-04 |author-first=Colin |author-last=Poitras}} With the use of atomic layer deposition it has been suggested that conversion efficiencies of solar energy to electricity higher than 70% could eventually be achieved.

The creation of successful optical rectenna technology has two major complicating factors:

1. Fabricating an antenna small enough to couple optical wavelengths.
2. Creating an ultra-fast diode capable of rectifying the high frequency oscillations, at frequency of ~500 THz.

Below are a few examples of potential paths to creating diodes that would be fast enough to rectify optical and near-optical radiation.

A promising path towards creating these ultrafast diodes has been in the form of "geometric diodes".{{Cite book |author-last=Zhu |author-first=Z. |title=Rectenna Solar Cells |publisher=Springer |date=2013 |location=New York, USA |pages=209–227}} Graphene geometric diodes have been reported to rectify terahertz radiation.{{Cite journal |author-last1=Zhu |author-first1=Zixu |author-last2=Joshi |author-first2=Saumil |author-last3=Grover |author-first3=Sachit |author-last4=Moddel |author-first4=Garret |date=2013-04-15 |title=Graphene geometric diodes for terahertz rectennas |journal=Journal of Physics D: Applied Physics |volume=46 |issue=18 |pages=185101 |doi=10.1088/0022-3727/46/18/185101 |bibcode=2013JPhD...46r5101Z |s2cid=9573157 |issn=0022-3727}} In April 2020, geometric diodes were reported in silicon nanowires.{{Cite journal |author-last1=Custer |author-first1=James P. |author-last2=Low |author-first2=Jeremy D. |author-last3=Hill |author-first3=David J. |author-last4=Teitsworth |author-first4=Taylor S. |author-last5=Christesen |author-first5=Joseph D. |author-last6=McKinney |author-first6=Collin J. |author-last7=McBride |author-first7=James R. |author-last8=Brooke |author-first8=Martin A. |author-last9=Warren |author-first9=Scott C. |author-last10=Cahoon |author-first10=James F. |date=2020-04-10 |title=Ratcheting quasi-ballistic electrons in silicon geometric diodes at room temperature |url=https://www.science.org/doi/10.1126/science.aay8663 |journal=Science |language=en |volume=368 |issue=6487 |pages=177–180 |doi=10.1126/science.aay8663 |issn=0036-8075 |pmid=32273466 |bibcode=2020Sci...368..177C |s2cid=215550903|url-access=subscription }} The wires were shown experimentally to rectify up to 40 GHz, that result was the limit of the instrument used, and the wires theoretically may be able to rectify signals in the terahertz region as well.

• Microstrip antenna
• Wireless power transfer

{{reflist}}

• [https://web.archive.org/web/20090802101748/http://www.mtt.org/awards/WCB%27s%20distinguished%20career.htm William C. Brown's Distinguished Career]
• {{cite journal |doi=10.1038/s41586-019-0892-1 |pmid=30692651 |title=Two-dimensional MoS2-enabled flexible rectenna for Wi-Fi-band wireless energy harvesting |journal=Nature |date=2019 |author-last1=Zhang |author-first1=Xu |author-last2=Grajal |author-first2=Jesús |author-last3=Vazquez-Roy |author-first3=Jose Luis |author-last4=Radhakrishna |author-first4=Ujwal |author-last5=Wang |author-first5=Xiaoxue |author-last6=Chern |author-first6=Winston |author-last7=Zhou |author-first7=Lin |author-last8=Lin |author-first8=Yuxuan |author-last9=Shen |author-first9=Pin-Chun |author-last10=Ji |author-first10=Xiang |author-last11=Ling |author-first11=Xi |author-last12=Zubair |author-first12=Ahmad |author-last13=Zhang |author-first13=Yuhao |author-last14=Wang |author-first14=Han |author-last15=Dubey |author-first15=Madan |author-last16=Kong |author-first16=Jing |author-last17=Dresselhaus |author-first17=Mildred |author-link17=Mildred Dresselhaus |author-last18=Palacios |author-first18=Tomás |volume=566 |issue=7744 |pages=368–372 |bibcode=2019Natur.566..368Z |s2cid=59307657|url=https://oa.upm.es/79152/ }}
• {{cite press release |date=2019-01-28 |title=Converting Wi-Fi signals to electricity with new 2D materials |website=ScienceDaily |url=https://www.sciencedaily.com/releases/2019/01/190128111718.htm}}

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