The transmission of wireless-aware energy is a technique allowing the distribution of electrical energy without using hardware support. This technique is intended to be used to feed from the difficult places of access.
Contrary to the data transmission, the output is the criterion to be maximized, it will determine the differences of principal technologies.

### History

In 1825, William Sturgeon invents the electromagnet, an main idea rolled up around an iron core. The principle of electromagnetic induction a fluctuating magnetic field induced an electric current in an electric wire is discovered by Michael Faraday in 1831.
Combining these two discovered, Nicholas Joseph Callan is the first in 1836 to make the demonstration of a transmission of a wireless-aware electrical energy. The apparatus with induction coil of Callan consists of 2 reels isolated called windings primary and secondary placed around an iron core. A battery connected intermittently to the primary "induces" a tension in the secondary, causing a spark.
In an induction coil or an electric transformer, which can have a ferrous heart or air, the transmission of energy is done by simple electromagnetic coupling also known by mutual the induction term. With this method, it is possible to transmit energy at long distances. However, to direct energy in the right direction, the two reels must be placed sufficiently close.
In the case of resonant coupling, where the reels are regulated on the same frequency, a significant power can be transmitted on several meters.
In 1864, James Clerk Maxwell carries out a mathematical modeling of the behavior of electromagnetic radiations. In 1888, Heinrich Hertz produces a wireless transmission of radio waves, validating the mathematical models of Maxwell. The apparatus of Hertz is regarded as the first radio operator transmitter. A few years later, Gugliemo Marconi improves the transmitter, by adding to it a high conductor and a connection to the ground. These two elements can be found in work of Benjamin Franklin in 1749 and Mahlon Loomas in 1864.
Nikola Tesla investigue also in the radio transmission but contrary in Marconi, Tesla designs its own transmitter, of an instantaneous power five times higher than that of its predecessors. All these systems at least use 4 resonant circuits, 2 for the transmitter and 2 for the receiver.
Whereas the wireless-aware techniques develop with the beginning of the XX e century, of search are carried out on alternative methods of transmission. The goal was to generate an effect locally and to detect it remotely. Tests are carried out on more consequent loads, replacing the receivers slightly resistive used hitherto to detect a received signal. To St Louis World S Fair (1904), a price is offered for the feeding to a distance of 30 meters of an engine of 0.1 horse (75 W).

### Ratio cuts ⁄ power

The size of the components is determined by:
the distance from transmission
the longueur onde used
laws of physics, in particular the criterion of Rayleigh or limit of diffraction, used in the design of antennas RF, like in the design of the laser. These laws describe the behavior of radii (micro ondes or laser) which will weaken and diffuse with the distance. More the transmitter will be large (diameter of an antenna, opening of a laser), more the radius will be concentrated, and less it will be spread out according to the distance (and vice versa). The small antennas also will support the loss of energy by the secondary lobes.
The levels of power are then calculated according to all these parameters, as well as the sum of the profits and the losses characteristic of the antennas, and the taking into account of the transparency of the medium in which the wave is transported. This stage is known as being the calculation of the assessment of connection.

### Output

Systems with close field
These techniques allow the transmission of energy at a distance comparable with the diameter of the transmitting elements. It generally goes from a few cm to a few meters.
Inductive coupling
The principle of an electric transformer is the example more the current of transmission of wireless-aware energy. The reels of the primary and the secondary are electrically isolated one from the other. The transfer of energy is done by known electromagnetic coupling under the name of induced current. The principal disadvantage is the necessary proximity of the receiver to allow the coupling.
The applications are varied:
Certain electric chargers of portable objects use this principle to avoid the contacts: brush with electric tooth, portables
Hotplates to induction. One can advance the fact that the metal ustensil does not constitute a secondary winding strictly speaking. One can regard it as a core not rolled of an alternate electromagnet, in which the induced currents cause the heating effect.
Transfer transcutané (SMALL FIRECLAY CUP or Transcutaneous Energy Transfer) in the systems of piles cardiac (ex AbioCor), and established different systems.
Inductive coupling by resonance
In 2006, Marine Soljacic as of other researchers of Massachusetts Institute off Technology (MIT) propose a new application of transfer of wireless-aware energy, while being based on the theory of electromagnetism with close field, and the use of coupled resonators. In their short theoretical analysis they show that during the emission of electromagnetic waves with a guide of wave to great angle, fleeting waves are produced without transporting energy. If a resonant guide of wave is placed close to the transmitter, the waves évanescentes can transmit energy by an similar effect to the tunnel effect, the coupling of the fleeting waves.
Channeled energy can thus be transformed into electrical energy continues on the level of the receiver, and it would not be dissipated or is not absorbed by the environment of the system. June 7th, 2007 a prototype is constructed by MIT WiTricité makes it possible to supply a bulb of 60 Watts at a distance of 2 meters, with an output of 40%.
The inductive coupling by resonance is a promising answer to the defects related on the traditional inductive coupling and the electromagnetic radiations: outdistance and effectiveness. Resonance increases the output by concentrating the magnetic field on the receiver which has the same frequency of resonance. The receiver is a solenoid with a rolling up on simple layer, contrary to the secondary of the traditional transformers, as well as capacitive plates at each end, which grant the reel to the frequency of the transmitter, thus eliminating the loss from energy of problem of wave.
As of the beginning of the year 1960, the transfer of energy by resonant inductive coupling was used successfully in the medical implants such as the cardiac pacemaker or the artificial heart. Whereas the first systems used a receiver with resonant reel the last systems also use transmitters with resonant reel. These medical systems are conceived to have an optimal output with electronics low power, by managing the losses of adaptability and dynamic variations of the reels.
The distance from transmission of these systems is generally lower than 20 cm. Today the transfer of energy by resonant inductive coupling is frequently used in many marketed implants.
The transfer of energy for the power supply of the electric cars and the buses is an experimental application of great power (10kW) of this technology. Important levels of power are necessary for the fast refill of the vehicles, and a good output allows a saving energy and the reduction in the environmental impacts. An experimental highway using this principle was carried out to reload the batteries of a bus protoype
The bus could be equipped with a retractable reel to decrease the distance from transmission, the prototype system having been conceived for a distance of 10 cm. Search is also made to reload the cars on points of parking and in the garages.
The refill of its batteries thanks to the radio waves and marketing are announced imminent.
Systems with far field
These systems allow the routing of energy at distances much larger than the diameter of the transmitters, for example on several kilometers. Until the beginning of the XXI esiècle, the transmission of wireless-aware energy at short and average distances will be exploited little (RFID chips low power). The fear of possible health hazards concerning the air transmission of energy is a cause of the abandonment of the project.
The use of radiations directional microwaves makes it possible to limit the risks concerning health and the security. The control of the precision of alignment between the transmitter and the receiver is a decisive criterion for the security of the system. In 2007, search starts to lead to concrete solutions, the such Witricité system.
Recently, of new technologies of high-output converters of energy microwave in electrical energy continues were born thus allowing to recover a maximum of energy of the beam microwave incident. These technologies are based on a filtration system and a rectifier, based on the original association of a passive system of adaptation of impedance optimized and of a specific converter. This type of device has a great potential of application for the feeding of wandering systems in the context of the development of the ambient intelligence.
This technological advance gives the possibility of recovering energy enough to feed a great number of small devices labelling, identification, repatriation of data of a given up sensor, small microprocessors, and could thus be used like source of supply in electrical energy of a multitude of micro systems low fuel consumption located until several meters of the source with an output of conversion ever reached hitherto. These microsystems will have one unlimited lifespan compared to those equipped with elements of local storage of energy per electrochemical way (pile). It is also possible to use this technology to remotely reload accumulators embarked on a wandering system or not connected to an energy source.
While making converge the electromagnetic field thanks to a giant antenna, NASA realized in 1975 a transfer of approximately 34kW on a distance from 1,5km. The output obtained was, according to NASA superior to 82%. The use of such a system is obviously not without health risk, within sight of the very powerful electromagnetic fields.

### Systems of transmission of D.C. current to ultra high voltage

The new system of transmission of power in D.C. current of 1.100 kilovolts developed by ABB rises with 26 meters above the ground, that is to say the equivalent of a building of seven floors.
Many utilities would jump on the occasion to acquire a system able to transport billion volts of electricity. More the tension is high minus necessary amperage to deliver the same power is important, and the reduction in amperage involving a reduction of the losses, more power can arrive to the final customer. ABB currently endeavors to develop all the necessary components to build a system of transmission of power CCUHT (D.C. current with ultra high voltage) of 1.100 kilovolts (kV) or 1,1 million volts, which has represented the greatest progression in terms of capacity and effectiveness for more than two decades. Such a system could deliver approximately 10.000 MW on several thousands of kilometers with tiny losses. To develop the system, of many technical challenges had to be raised and these exploits followed closely the advertisement by ABB of its first transformer converter of D.C. current to ultra high voltage (CCUHT) of 1.100 Kv, a key component of the system. Today, other components are also available, in particular the disconnecting switches of derivation to ultra high voltage, the low-voltage surge limiters, the condensers of coupling and the filters. These components are as essential as the transformer converter in networks CCUHT because they contribute to the safety of the transport of energy CCUHT. The disconnecting switches of derivation are necessary to derive or reinstate quickly converters CCHT in the network after a maintenance or an operation to reduced tension. The condensers of coupling are used as pesticidal filters, the low-voltage surge limiters constitute a key component ensuring the protection of the system against overpressures, and the filters guarantee the quality of energy by attenuating the electric harmonics and the other disturbances. To develop networks CCUHT, the system must be able to support constraints high voltage and to preserve an electric high degree of insulation. For example, all the components with ultra high voltage presented above were designed and tested to guarantee a level of behavior to overpressures of operations >2,1 megavolts (MV) or 2,1 million volts, and a level of behavior to the shocks of the lightning >2,5 MV, unequalled levels for products of this category. The levels of protection of the low-voltage surge limiters were optimized to offer a sufficient operating margin. With this intention, ABB looked after the systems design in order to guarantee exceptional thermal performances and used ZnO varistors of high-quality.
By increasing the distance between the ground and the parts under tension, the properties of insulation of the air can be used to improve the performances of insulation of products CCUHT 1.100 Kv. Thus, the majority of the systems is located at an important distance from the ground: the filters 26 meters, the disconnecting switches of derivation to 14 ⁄ 16 m, the low-voltage surge limiters to 16 m and the condensers of coupling to 18 Mr. These constraints physical involved new requirements for the design of the products CCUHT, which must be able to face the seismic activities and with the combinations of associated mechanical loads. Transport CCHT is an evolution of technology CCHT, development by ABB there is more than 50 years. ABB is a world leader of technologies of transport CCHT which counts with its credit several avant-gardists achievements and more than 70 projects throughout the world representing a total transport capacity of approximately 60.000 MW.

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