WITRICITY - Wireless Electricity Transmitting System

The technology used for wireless power transmission is known as witricity. Wireless power transmission is not a new idea, Nikola Tesla proposed theories of wireless power transmission in the late 1800s and early 1900s. Tesla's work was impressive, but it did not immediately lead to wide spread practical methods for wireless power transmission. Since then many researchers have developed several techniques for moving electricity over long distances without wires. Some exist only as theories or prototypes, but others are already in use. In 2006 researchers at Massachusetts Institute of Technology led by Marine Soijacic discovered an efficient way to transfer power between coils separated by a few meters. They have dubbed this technology as witricity. Witricity is based upon coupled resonant objects. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while not interchanging the surroundings. The researchers demonstrate the ability to transfer 60W with approximately 40% efficiency over distance in excess of 2 meters. Currently the project is looking for power transmission in the range of 100watts. As witricity is in the development stage, lots of work is to be done in improving the range of power transmission and efficiency.

INTRODUCTION

If we are particularly organized and good with tie wrap then also a few dusty power cord tangles around our home. We have even had to follow one particular cord through the seemingly impossible snarl to the outlet hoping that the plug pull will be the right one. This is one of the downfalls of electricity. While it can make people's lives easier, it can add a lot of clutter in the process. For these reasons, scientists have tried to develop methods of wireless power transmission that could cut the clutter or lead to clean sources of electricity. Wireless power transmission is not a new idea. Many researchers developed several methods for wireless power transmission. But witricity is a new technology used for wireless power transmission. By the use of this technology transmission of electrical energy to remote objects without wires can be possible. The inventors of witricity are the researchers from Massachusetts Institute of Technology (MIT). They developed a new technology for wireless electricity transmission and this is based upon the coupled resonant objects. In this resonant magnetic fields are used. So the wastage of power is reduced. The system consists of witricity transmitters and receivers. The transmitters and receivers contain magnetic loop antennas made of copper coils and they are tuned to the same frequency.

RADIO AND MICROWAVE

If resonance is incorporated or not, induction generally sends wireless power over relatively short distance. For very long distance power transmission radio and microwaves are used. Japanese researcher YAGI developed a directional array antenna known as YAGI antenna for wireless energy transmission. It is widely used for broadcasting and wireless telecommunications industries. While it did not prove to be particularly useful for 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 is a rectifying antenna, an antenna used to convert microwaves into DC power. Being that an antenna refers to any type of device that converts electromagnetic waves into electricity or vice versa. A rectenna is simply a microwave antenna. Inverse rectennas convert electricity into microwave beams, rectennas suitable for receiving energy beamed from solar panels in geocentric orbit would need to be several miles across. Although power densities of such an arrangement would be low enough to avoid any damage to people or the environment. Rectifying antennae are usually made an array of dipole antennae, which have positive and negative poles. These antennae connect to semiconductor diodes. Rectenna conversion has an efficiency of about 95%.

In the 1980s, Canada's Communications Research Centre created a small airplane that could run off power beamed from the Earth. The unmanned plane, called the Stationary High Altitude Relay Platform (SHARP), was designed as a communications relay. Rather flying from point to point, the SHARP could fly in circles two kilometers in diameter at an altitude of about 13 miles (21 kilometers). Most importantly, the aircraft could fly for months at a time.

The secret to the SHARP'S long flight time was a large, ground-based microwave transmitter. The SHARP'S circular flight path kept it in range of this transmitter. A large, disc-shaped rectifying antenna, or rectenna, just behind the plane's wings changed the microwave energy from the transmitter into direct-current (DC) electricity. Because of the microwaves interaction with the rectenna, the SHARP had a constant power supply as long as it was in range of a functioning microwave array. This arrangement functions according to the following procedure.

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.

Micro wave power transmission has some drawbacks:

» The solar power stations on the moon would require supervision and maintenance. In other words, the project would require sustainable, manned moon bases.

•       Only part of the earth has a direct line of sight to the moon at any given time. To make sure the whole planet had a steady power supply, a network of satellites would have to re-direct the microwave energy.

•       Many people would resist the idea of being constantly bathed in microwaves from space, even if the risk were relatively low.

ADVANTAGES OF WITRICITY

1.   No need of line of sight - In witricity power transmission there is any ;

need of line of sight between transmitter and receiver. That is power !

transmission can be possible if there is any obstructions like wood,

metal, or other devices were placed in between the transmitter and

receiver.

2.     No need of power cables and batteries - Witricity replaces the use of power cables and batteries.

3.    Does not interfere with radio waves

4.   Wastage of power is small - Electromagnetic waves would tunnel, they

would not propagate through air to be absorbed or dissipated. So the

wastage is small.

5.   Negative heaiih implications - By the use of resonant coupling wave

lengths produced are far lower and thus make it harmless.

6.     Highly efficient than electromagnetic induction - Electro magnetic induction system can be used for wireless energy transfer only if the primary and secondary are in very close proximity. Resonant induction system is one million times as efficient as electro magnetic induction system.

7.     Less costly - The components of transmitter and receivers are cheaper. So this system is less costly.

DISADVANTAGES

Wireless power transmission can be possible only in few meters.

Efficiency is only about 40%.

As witricity is in development stage, lot of work is done for improving the efficiency and distance between transmitter and receiver.

CONCLUSION

Witricity is in development stage, lots of work is to be done to use it for wireless power applications. Currently the project is looking for power transmission in the range of 100w. Before the establishment of this technology the detailed study must be done to check whether it cause any harm on any living beings.