17-09-2014, 09:55 AM
WITRICITY WIRELESS POWER TRANSMISSION
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ABSTRACT:
The aim of this paper is to introduce a new system of transmitting the power which is called wireless electricity or witricity. Witricity is based upon coupled resonant objects to transfer electrical energy between objects without wires. The system consists of a Witricity transmitter (power source), and devices which act as receivers (electrical load). It is based on the principle of resonant coupling and microwave energy transfers. The action of an electrical transformer is the simplest instance of wireless energy transfer. There are mainly two types of transfers i.e. short range and long range transmission. The short range are of 2-3metres where as the long range are of few kilometers.
Wireless transmission is ideal in cases where instantaneous or continuous energy transfer is needed, but interconnecting wires are inconvenient, hazardous, or impossible. The tangle of cables and plugs needed to recharge today's electronic gadgets could soon be a thing of the past. The concept exploits century-old physics and could work over distances of many metres. Consumers desire a simple universal solution that frees them from the hassles of plug-in chargers and adaptors. "Wireless power technology has the potential to deliver on all of these needs." However, transferring the power is the important part of the solution.
HOW IT WORKS-
Wireless light: Researchers used magnetic resonance coupling to power a 60-watt light bulb. Tuned to the same frequency, two 60-centimeter copper coils can transmit electricity over a distance of two meters, through the air and around an obstacle.
The researchers built two resonant copper coils and hung them from the ceiling, about two meters apart.
When they plugged one coil into the wall, alternating current flowed through it,
Creating a magnetic field.
The second coil, tuned to the same frequency and hooked to a light bulb, reso¬nated with the magnetic field, generating an electric current that lit up the bulb--even with a thin wall between the coils.
How wireless energy could work
Resonance", a phenomenon that causes an object to vibrate when energy of a certain frequency is applied. Two resonant objects of the same frequency tend to couple very strongly." Resonance can be seen in musical instruments for example. "When you play a tune on one, then another instrument with the same acoustic resonance will pick up that tune, it will visibly vibrate,"
Instead of using acoustic vibrations, system exploits the resonance of electromagnetic waves. Electromagnetic radiation includes radio waves, infrared and X-rays. Typically, systems that use electromagnetic radiation, such as
Short range power transmission and reception
Power supply for portable electronic devices is considered, which receives ambient radio frequency radiation (typically in an urban environment) and converts it to DC electricity that is stored in a battery for use by the portable device.
Long-distance Wireless Power-
Some plans for wireless power involve moving electricity over a span of miles. A few proposals even involve sending power to the Earth from space. The Stationary High Altitude Relay Platform (SHARP) unmanned plane could run off power beamed from the Earth. The secret to the SHARP's long flight time was a large, ground-based microwave transmitter. A large, disc-shaped rectifying antenna, or rectenna, near the system changed the microwave energy from the transmitter into direct-current (DC) electricity. Because of the microwaves' interaction with the rectenna, the system had a constant power supply as long as it was in range of a functioning microwave array.
Rectifying antennae are central to many wireless power transmission theories. They are usually made of an array of dipole antennae, which have positive and negative poles. These antennae connect to semiconductor diodes. Here's what happens:
1. Microwaves, which are part of the electromagnetic spectrum, reach the dipole antennae.
2. The antennae collect the microwave energy and transmit it to the diodes.
3. The diodes act like switches that are open or closed as well as turnstiles that let electrons flow in only one direction. They direct the electrons to the rectenna's circuitry.
4. The circuitry routes the electrons to the parts and systems that need them.
Resonant induction
By designing electromagnetic resonators that suffer minimal loss due to radiation and absorption and have a near field with mid-range extent (namely a few times the resonator size), mid-range efficient wireless energy-transfer is possible. The reasonment is that, if two such resonant objects are brought in mid-range proximity, their near fields (consisting of so-called 'evanescent waves') couple (evanescent wave coupling) and can allow the energy to transfer from one object to the other within times much shorter than all loss times, which were designed to be long, and thus with the maximum possible energy-transfer efficiency. Since the resonant wavelength is much larger than the resonators, the field can circumvent extraneous objects in the vicinity and thus this mid-range energy-transfer scheme does not require line-of-sight. By utilizing in particular the magnetic field to achieve the coupling, this method can be safe
Resonance and Wireless Power
Household devices produce relatively small magnetic fields. For this reason, chargers hold devices at the distance necessary to induce a current, which can only happen if the coils are close together. A larger, stronger field could induce current from farther away, but the process would be extremely inefficient. Since a magnetic field spreads in all directions, making a larger one would waste a lot of energy. The distance between the coils can be extended by adding resonance to the equation.
Radio and microwave
Microwave power transmission
Power transmission via radio waves can be made more directional, allowing longer distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in the microwave range. A rectenna may be used to convert the microwave energy back into electricity. Rectenna conversion efficiencies exceeding 95% have been realized. Power beaming using microwaves has been proposed for the transmission of energy from orbiting solar power satellites to Earth and the beaming of power to spacecraft leaving orbit has been considered.
Power beaming by microwaves has the difficulty that for most space applications the required aperture sizes are very large. These sizes can be somewhat decreased by using shorter wavelengths, although short wavelengths may have difficulties with atmospheric absorption and beam blockage by rain or water droplets.
For earthbound applications a large area 10 km diameter receiving array allows large total power levels to be used while operating at the low power density suggested for human electromagnetic exposure safety. A human safe power density of 1 mW/cm2 distributed across a 10 km diameter area corresponds to 750 megawatts total power level. This is the power level found in many modern electric power plants.
Electrical conduction
Electrical energy can also be transmitted by means of electrical currents made to flow through naturally existing conductors, specifically the earth, lakes and oceans, and through the atmosphere — a natural medium that can be made conducting if the breakdown voltage is exceeded and the gas becomes ionized. For example, when a high voltage is applied across a neon tube the gas becomes ionized and a current passes between the two internal electrodes. In a practical wireless energy transmission system using this principle, a high-power ultraviolet beam might be used to form a vertical ionized channel in the air directly above the transmitter-receiver stations. The same concept is used in virtual lightning rods, the electrolaser electroshock weapon and has been proposed for disabling vehicles.
CONCLUSION-
From these researches and discoveries it can be said that wireless power transmission is going to be a major field of interest for scientists and for people. The facts that the power can be transmitted from space to earth will revolutionize the field of satellites. Since the uses of wireless power transmission are many, from easy installation, neatness, easy maintenance to multi-equipment working are amazing, the area for researchers on this field seems very interesting.
Rather concentrating on the false beliefs, the concentration should be put on advantages of witricity for further increasing the efficiency of wireless power transmission with more safety measures. It is a rocking technology provided the researches continue to move in same speeding direction.