Microwave power transmission (MPT) is the use of microwaves to transmit power through outer space or the atmosphere without the need for wires. It is a sub-type of the more general Wireless energy transfer methods, and is the most interesting because microwave devices offer the highest efficiency of conversion between DC-electicity and microwave radiative power. Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) frequencies, but relatively short for radio waves. ... Layers of Atmosphere - not to scale (NOAA)[1] Outer space, sometimes simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. ... Layers of Atmosphere - not to scale (NOAA)[3] Earths atmosphere is a layer of gases surrounding the planet Earth and retained by the Earths gravity. ... This article or section does not adequately cite its references or sources. ... It has been suggested that Power beaming be merged into this article or section. ...

Following World War II, which saw the development of high-power microwave emitters known as cavity magnetrons, the idea of using microwaves to transmit power was researched. In 1964, William C. Brown demonstrated a miniature helicopter equipped with a combination antenna and rectifier device called a rectenna. The rectenna converted microwave power into electricity, allowing the helicopter to fly^[1]. In principle, the rectenna is capable of very high conversion efficiencies - over 90% in optimal circumstances. Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... A cavity magnetron is a high-powered vacuum tube that generates coherent microwaves. ... 1964 (MCMLXIV) was a leap year starting on Wednesday (the link is to a full 1964 calendar). ... William C Brown pioneered microwave power transmission in the 1960s. ... Link title For other uses, see Helicopter (disambiguation). ... A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ... AC, half-wave and full wave rectified signals A rectifier is an electrical device, comprising one or more semiconductive devices (such as diodes) or vacuum tubes arranged for converting alternating current to direct current. ... A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. ...

Most proposed MPT systems now usually include a phased array microwave transmitter. While these have lower efficiency levels they have the advantage of being electrically steered using no moving parts, and are easier to scale to the necessary levels that a practical MPT system requires. A giant phased-array radar in Alaska In telecommunication, a phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and...

Using microwave power transmission to deliver electricity to communities without having to build cable-based infrastructure is being studied at Grand Bassin on Reunion Island in the Indian Ocean. Réunion is an island and overseas département (département doutre-mer, or DOM) of France, located in the Indian Ocean east of Madagascar, about 200 km southwest of Mauritius. ...

Common safety concerns

The common reaction to microwave transmission is one of concern, as microwaves are generally perceived by the public as dangerous forms of radiation - stemming from the fact that they are used in microwave ovens. While high power microwaves can be painful and dangerous as in the United States Military's Active Denial System, MPT systems are generally proposed to have only low intensity at the rectenna. Microwave oven A microwave oven is a kitchen appliance employing microwave radiation primarily to cook food. ... // Humvee with ADS mounted. ... A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. ...

Though this would be extremely safe as the power levels would be about equal to the leakage from a microwave oven, and only slightly more than a cell phone, the relatively diffuse microwave beam necessitates a large rectenna area for a significant amount of energy to be transmitted.

Research has involved exposing multiple generations of animals to microwave radiation of this or higher intensity, and no health issues have been found.^{[citation needed]}

Proposed uses

Main article: Solar power satellite

• MPT is the most commonly proposed method for transferring energy to the surface of the Earth from solar power satellites or other in-orbit power sources.

• MPT is occasionally proposed for the power source in beamed energy orbital space ships. Although lasers are more commonly proposed, their low efficiency in light generation and reception has led some designers to opt for microwave based systems.

An artists depiction of a solar satellite, which could send energy wirelessly to a space vessel or planetary surface. ...

Current Status

Wireless Power Transmission (using microwaves) is well proven. Experiments in the tens of kilowatts have been performed at Goldstone in California in 1975^[2][3][4] and more recently (1997) at Gand Bassin on Reunion Island^[5] The Goldstone Deep Space Communications Complex (GDSCC) —commonly called the Goldstone Observatory— is located in Californias Mojave Desert (USA). ... Réunion is an island and overseas département (département doutre-mer, or DOM) of France, located in the Indian Ocean east of Madagascar, about 200 km southwest of Mauritius. ...

References

1. ^ EXPERIMENTAL AIRBORNE MICROWAVE SUPPORTED PLATFORMDescriptive Note : Final rept. Jun 64-Apr 65
2. ^ NASA Video, date/author unknown
3. ^ Wireless Power Transmission for Solar Power Satellite (SPS) (Second Draft by N. Shinohara), Space Solar Power Workshop, Georgia Institute of Technology
4. ^ Brown., W. C. (September 1984). "The History of Power Transmission by Radio Waves". Microwave Theory and Techniques, IEEE Transactions on (Volume: 32, Issue: 9 On page(s): 1230- 1242 + ISSN: 0018-9480). 
5. ^ POINT-TO-POINT WIRELESS POWER TRANSPORTATION IN REUNION ISLAND 48th International Astronautical Congress, Turin, Italy, 6-10 October 1997 - IAF-97-R.4.08 J. D. Lan Sun Luk, A. Celeste, P. Romanacce, L. Chane Kuang Sang, J. C. Gatina - University of La Réunion - Faculty of Science and Technology.

See also

energy Portal

• Wireless energy transfer

Image File history File links Portal. ... It has been suggested that Power beaming be merged into this article or section. ...

External links

• http://www.kurasc.kyoto-u.ac.jp/plasma-group/sps/history2-e.html
• William C. Brown's Distinguished Career
• Mitsubishi proposed system to power low-power devices