Abstract
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.
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.
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.
Witricity In History
Wireless power transmission is not a new idea. Nickola Tesla
demonstrated transmission of electrical energy without wires in early 19th
century. Tesla used electromagnetic induction systems. William C Brown
demonstrated a micro wave powered model helicopter in 1964. This receives all
the power needed for flight from a micro wave beam. In 1975 Bill Brown
transmitted 30kW power over a distance of 1 mile at 84% efficiency without
using cables. Researchers developed several technique for moving electricity
over long distance without wires.
Witricity At Present
In 2006 MIT researchers discovered a new method to provide
electricity to remote objects without wires. Wiricity is based on coupled
resonant objects. In 2007 researchers implemented a prototype using self
resonant coils. In this first experiment they demonstrated efficient
non-radiative power transfer over distance up to eight times the radius of the
coils. This experiment was done using two copper coils. Each coil act as self
resonant system. One of the coils is attached to the electricity source.
Instead of irradiating the environment with electromagnetic waves, it fills the
space with a non-radiative magnetic field oscillating at MHz frequencies. The
non-radiative field mediates the power exchange with the other coil, which is
specially designed to resonate with the field.
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.
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