Talk:Rectenna

Optical rectennae

Please explain this in more detail. Schottky diodes and p-n junctions used in solar cells are kind of the same thing. I assume the optical rectennas would be more than just a metal-semiconductor version of the solar cell... - Omegatron 00:11, Jan 9, 2005 (UTC)

Try this paper entitled Optical Rectenna For Direct Conversion Of Sunlight To Electricity:
http://www.nrel.gov/ncpv_prm/pdfs/papers/54.pdf

This paper now seems to have been replaced by Photovoltaic Technologies Beyond the Horizon: Optical Rectenna Solar Cell:
http://www.nrel.gov/docs/fy03osti/33263.pdf OlavN 07:17, 11 July 2007 (UTC)[reply]

The direct conversion of sunlight to electricity via this antenna-diode device would violate the second law of thermodynamics. If such a device could work one could use it to transfer energy via infrared from one body to another even if both started at the same temperature and were both in an insulated box. This can not happen in our universe.

The system might work with low entropy coherent radiation like radio, microwave, or laser transmissions but not with black body radiation. —Preceding unsigned comment added by Model E (talk • contribs) 03:27, 24 August 2008 (UTC)[reply]

It would work with sunlight. Just like a solar cell, it works as long as the radiant energy striking it is greater than the thermal black body radiation it emits. Sunlight has a far higher "color temperature" than room temperature infrared black body radiation. It just wouldn't work as a "free energy" device to convert ambient black body radiation to electricity, because the "Johnson noise" (thermal noise currents) in the load circuit would drive the antenna as a transmitter, causing it to radiate as much energy as it receives, resulting in no net electrical energy delivered to the load. --Chetvorno^TALK 23:06, 1 April 2012 (UTC)[reply]

Size of rectenna

What will be the size of rectenna if we use it to provide energy for an aeroplane or a car.--ZainAliK 20:55, 9 February 2008 (UTC)

Through the Rectum?

It seems we could lose the last paragraph under 'Optical' : "This device is used to perform the delicate corneal inversion procedure, Multi-Opti-Pupil-Optomy. In order to keep from damaging the eye sockets, they've got to go in through the rectum."

Theft of Electricity

WTF? Citation or can we bail on this?

I would also like to see where and why this is "prohibited." --Newton21989 (talk) 07:00, 17 March 2010 (UTC)[reply]

Sources

Please add more reliable sources to the article in order to keep it on Wikipedia. As of now no sources are being cited. Coaster7 (talk) 02:08, 19 March 2009 (UTC)[reply]

source

this source may be of use for this article: the history of wireless power transmission by william c brown. —Preceding unsigned comment added by Daiv (talk • contribs) 05:17, 13 July 2009 (UTC)[reply]

Better explanation of Whys and Wherefores

I hesitate to simply replace the existing explanation. Interested parties, please discuss! YodaWhat (talk) 03:09, 25 March 2012 (UTC)[reply]

To receive usable Energy via radio waves requires rather high Power levels, and a very different approach from merely receiving a Signal, which only requires a tiny sample of the wave. In the case of Space-Based Energy, we usually talk about beam Power in the gigawatts -- billions of watts, and we want to receive *all* of it. To prevent this high Power level from being dangerous (in the air or on the ground), the beam is made to spread out significantly, and the receiving antenna must be at least as big as the 'spot size' of the radio beam -- often several miles across. Since it is impractical to keep such a large antenna pointed directly at the transmitter, it is laid out as an array of numerous small antennas a little above the ground. But this means that the radio wave will reach different part of the antenna at different times -- out of phase. In turn, this means that the cables from each antenna can't simply be wired together, as the out-of-phase signals will act like a short-circuit and waste Energy. Instead, the signal from each of the antennas is individually Rectified -- turned into Direct Current (DC), as DC has no phase to get wrong. Then and only then can the wires all be joined together, combining a few Watts from each of myriads of antennas into one big Rectenna with one huge Power output.

Also, I scratch my head over this, as it seems irrelevant, and partly nonsensical: "Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional." — Preceding unsigned comment added by YodaWhat (talk • contribs) 03:43, 25 March 2012 (UTC)[reply]

Good point. I changed it from phased array to array. --Chetvorno^TALK 23:09, 1 April 2012 (UTC)[reply]