Wireless energy transfer

From Free net encyclopedia

(Redirected from Wireless power transmission)

Template:Cleanup-date Template:Wikify-date

Wireless energy transfer is the transfer of electromagnetic energy for power to do work via conduction, induction, or transmission without a physical connection.

Contents

[edit]

Description

Wireless energy transfer, by definition, does not require a direct electrical connection — no wires! Anyone can demonstrate that energy can be "sent" without a direct connection by simply touching the ends of a wire, briefly, to the ends of a small battery. Hold the wire near a compass needle while you do this and you'll see the compass needle twitch. It takes energy to make something move, so you've transmitted energy wirelessly. Well, at least without touching the compass with the wire!

Another, more dramatic demonstration of wireless energy begins with a radio transmitter generating more than a few watts, such as an amateur radio transmitter. A Fluorescent lamp with no wires attached to it, held near the antenna, will glow when the transmitter is activated. Send "SOS" and the light blinks "SOS". The transmitted energy causes the gas inside the lamp to glow, like the northern lights.

Once the basic principle is seen, then the problem is to concentrate the energy of the transmission so that most of it is received where it can be converted into useful power. Think of a flashlight that lets you focus the light beam or spread it out so that it's very wide. If you wanted to shine the flashlight on a solar cell, you'd want the flashlight's beam to be focussed.

Early systems (such as Tesla proposed) were incapable of such "focusing" of transmitted energy, because the necessary antenna size is impractical at low frequencies. Without focusing, much of the energy would be lost.

The advent of technology for much higher transmission frequencies (such as those used by microwave transmitters) created the possibility of "beaming" the energy through the use of directional antennas, such as the one invented by Hidetsugu Yagi. Lasers, which create a coherent and tightly "beamed" form of light energy, are even more appropriate.

In most cases the cost of such solutions is much higher than simply using copper wire. Wireless energy transfer, then, is most interesting for applications where the energy receiver can't be copper-tethered to the energy source — sending energy to an airplane or spacecraft, or another planet, for example.

[edit]

History


As the wireless art developed during the turn of the 20th century, industry was looking toward a method of wireless energy transfer. At the St. Louis World's Fair (1904) a prize was offered for a successful attempt to drive an 0.1 Horsepower air-ship motor by energy transmitted through space at a distance of least 100ft. (The Electrician (London), September 1902, pages 814-815)

[edit]

Hertz

A precursor of this technology can be found in the works of Heinrich Rudolf Hertz in the late nineteenth century. In 1888, Hertz experimented with pulsed power transmission at 500 megacycles per second.

[edit]

Tesla

The development of wireless energy transfer began in earnest with the lectures and patents of the electrical engineer Nikola Tesla (and is described in his 1916 deposition on the history of wireless and radio technology). In experiments around 1899, Tesla was able to light lamps filled with gas (similar to neon) from over 25 miles away without using wires. Tesla used a high frequency current (Prodigal Genius, O'Neill; pg 193). During his experiments in Colorado, he lit ordinary incandescent lamps at full candle-power by currents induced in a local loop consisting of a single wire forming a square of fifty feet each side, which includes the lamps, and which was at a distance of one hundred feet from the primary circuit energized by the oscillator (Century Magazine, June 1900).

The building of a global wireless energy distribution system called the Wardenclyffe Tower was started almost a century ago by Tesla but was abandoned because of lack of funds. The Wardenclyffe facility was meant to be the start of a national (and later global) system of towers broadcasting power to users as electromagnetic waves. There is some evidence that Wardenclyffe might have used extremely low frequency signals combined with a higher frequency signals. In practice, the transmitter electrically influences both the earth and the space above it. He made a point of describing the process as being essentially the same as passing electricity through a wire by conduction. Tesla believed that energy could be efficiently transmitted from the facility via longitudinal "non-Hertzian" (or maxwellian) waves (ed. see waves in plasmas for examples). Powered by an industrial alternator, the tower was apparently intended to inject large amounts of energy into a natural Earth circuit, using the Earth-Ionosphere network as the transmission circuit. Tesla called his wireless technique the "disturbed charge of ground and air method."

In various writings, Tesla explained that the Earth itself would behave as a resonant LC circuit that could be electrically excited at predescribed frequencies. However, Earth resonance would be of a very low frequency (about 7 Hz) which would utilize Schumann resonance. Alternatively, a surface or ground wave, similar to the Zenneck wave could have been utilized. Others believe that earth currents were to be utilized. According to Tesla, the planet's large cross-sectional area provides a low resistance path for the flow of earth currents. The greatest losses are apt to occur at the points where the transmitting and receiving stations are connected with the ground. This is why Tesla stated,

"You see the underground work is one of the most expensive parts of the tower. In this system that I have invented it is necessary for the machine to get a grip of the earth, otherwise it cannot shake the earth. It has to have a grip on the earth so that the whole of this globe can quiver, and to do that it is necessary to carry out a very expensive construction." ["Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony and Transmission of Power", p. 203]

To close the circuit, in theory, a second path would be established between the plants' elevated high-voltage terminals through rarified upper level atmospheric strata. The connection would be made by electrostatic induction or conduction through plasma. Tesla firmly believed that Wardenclyffe would permit wireless transmission and reception across large distances with negligible losses.

[edit]

Yagi

In Japan, Hidetsugu Yagi attempted wireless power transmission. In February 1926, Yagi and Uda published their first report on the wave projector directional antenna, later known as the yagi antenna. Yagi managed to demonstrate a proof of concept, but the engineering problems proved to be more onerous than conventional systems. [1]

[edit]

Modern Methods and Proposals

[edit]

Microwaves

Modern ideas are dominated by interest in microwave power transmission (MPT). It is the practice of using microwaves, radio waves with wavelengths of a few inches, to transmit power through outer space or the atmosphere wirelessly. Microwave technology wasn't sufficiently developed to allow significant power experiments until the 1960s.

The first microwave demonstration occurred in 1963 (with 13 percent efficiency). In 1964, William C. Brown (a pioneer in the use of microwaves) demonstrated a helicopter equipped with a device called a rectenna. The rectenna converted microwaves into electricity, allowing the helicopter to fly. By 1975, a 54 percent efficiency was attained by researchers.

On October 7, 1987, a SHARP (Stationary High Altitude Relay Platform) experiment was able to keep aloft a small airplane powered by an microwave beam converted with a rectenna. A small model (1.3 meter wingspan) flew for an hour. The full-scale proposed system was to use a 500kW signal at 5.8 GHz. [2]

A well-publicized proposal for MPT is called the Solar power satellite. It would be built in high Earth orbit to collect sunlight and convert that energy into microwaves. Beamed to a very large antenna on Earth, the microwaves would be converted into conventional electrical power. Problems with the idea include cost and the possible dangers of stray microwave energy.

German scientist Konstantin Meyl has stirred up some discussion with talk of Scalar field theory, but so far no actual wireless energy hardware, or scalar waves, have been detected.

[edit]

Lasers

Lasers emit energy at frequencies much higher than microwaves; otherwise the possibilities are similar. At present, though, high-power lasers are probably a more expensive solution.

One proposal is to use "highly efficient fiber lasers for wireless power transmission". [3]

Beam-powered propulsion is a class of spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant. At least one experiment has demonstrated the feasibility of using a pulsed high-power laser to push a highly-reflective object into the air. Some think it possible that a spacecraft could be accelerated to much higher speeds than is reasonable with chemical propulsion by using lasers to accelerate the craft. Of course, without a laser to decelerate it on the other end, this concept needs more work.

[edit]

Uses

The wireless transfer of energy is used in various devices, such as electric toothbrushes (to recharge their batteries) and the transcutaneous energy transfer (TET) systems in artificial hearts like AbioCor.

[edit]

See also

[edit]

Related patents

[edit]

External articles, references, and further reading

Nikola Tesla
Books, essays, and papers
Other history
  • Frank E. Little, James O. McSpadden, Kai Chang, and Nobuyuki Kaya, "Toward space solar power: Wireless energy transmission experiments past, present and future". AIP Conference Proceedings, January 15, 1998, Volume 420, Issue 1, pp. 1225-1233.
  • Lewis Coe, "Wireless Radio: A History". McFarland & Company, Jul 1, 1996. ISBN 0786402598
  • W. C. Brown,
    • "The history of wireless power transmission". Solar Energy, Vol. 56, No. 1, pp. 3-21, 1996.
    • "The History of Power Transmission by Radio Waves". IEEE Transactions on Microwave Theory and Techniques, 1984.
[edit]

External links

Retrieved from "http://www.netipedia.com/index.php/Wireless_energy_transfer"