Editing Rectenna (section)

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

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 [[Internet of things|IoT]] applications.<ref>{{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]]}}</ref>

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%.<ref>{{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/}}</ref> The record conversion efficiency for a rectenna is 90.6% for 2.45&nbsp;GHz,<ref name="McSpadden1998">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</ref> with lower efficiency of about 82% achieved at 5.82&nbsp;GHz.<ref name="McSpadden1998"/>