Wireless
electricity is the transmission of electrical energy from one object to another without the use of wires which will ensure that the
cellphones, laptops, iPods and other power devices will get charged on their
own and their will be no need of plugging them in. The principle behind this
technology of wireless electricity transmission is Magnetic coupled Resonance.
WiTricity,
a portmanteau for wireless electricity, is a term which describes wireless
energy transfer, the ability to provide electrical energy to remote objects
without wires. The term was coined initially in 2005 by Dave Gerding and later
used for the project of a MIT research team led by Prof. Marin Soljačić in
2007. Prof.
Marin Soljacic from
Massachusetts Institute of
Technology (MIT), has proved that
magnetic coupled resonance can be
utilized in order to transfer energy without wires. Marin Soljacic led a five
member team of researchers at MIT were able to light a
60W bulb from
a source placed
seven feet away,
with absolutely no physical
contact between the bulb
and the power source. Research
at MIT indicates that induction can take place little differently if the
electromagnetic fields around the coils resonate at the same frequency. The
theory uses a curved coil of wire as an inductor. A capacitance plate, which
can hold a charge, attaches to end of the coil. A electricity travels through
this coil, the coil begins to resonate. Its resonant frequency is a product of
inductance of the coil and the capacitance between the plates. Electricity,
trvelling along an electromagnetic wave, can tunnel for one coil to the other
as long as they both have the same resonant frequency. The effect is same as
one vibrating trumpet can cause the other to vibrate. As
long as both coils are out of range of another, nothing will happen, since the
fields around the coils aren’t strong enough to affect much around them.
Similarly. If the two coils resonate at different frequencies, nothing will
happen. But if two resonating coils with the same frequency get within a few
meters of each other, stream of energy move from the transmitting coil to the
receiving coil.According to this theory, one coil can send electricity to
several receiving coils, as long as they all resonate at the same frequency.
The researchers have named this non-radiative energy transfer since it involves
stationary fields around the coil rather than fields that spread in all
directions.
The MIT researchers
successfully demonstrated the ability to power a 60 watt light bulb
wirelessly, using two 5-turn copper coils of 60 cm (24 in) diameter, that
were 2 m (7 ft) away, at roughly 45% efficiency. The coils were
designed to resonate together at 9.9 MHz (≈
wavelength 30 m) and were oriented along the same axis. One was connected
inductively to a power source, and the other one to a bulb. The setup powered
the bulb on, even when the direct line of sight was blocked using a wooden
panel. Currently, researchers have been able to power a 60 watt light bulb at
roughly 90% efficiency at a distance of 3 feet. Unlike the far field
wireless power transmission systems based on traveling electro-magnetic
waves, WiTricity employs near field resonant inductive coupling through magnetic
fields similar to those found in transformers
except that the primary coil and secondary winding are physically separated,
and tuned to resonate
to increase their magnetic coupling. These tuned magnetic fields generated by
the primary coil can be arranged to interact vigorously with matched secondary
windings in distant equipment but far more weakly with any surrounding objects
or materials such as radio signals or biological tissue.The system worked with 40%
efficiency and the power
that wasn't
utilized remained in the vicinity
of the transmitter
itself,
and did
not radiate to
the surrounding environment.
The electric
power from the
power source causes
the copper coil connected to
it to start oscillating at
a particular (MHz)
frequency. Subsequently, the space around the copper coil gets filled
with nonmagnetic radiations. This generated magnetic field
further transfers the power to the
other copper coil connected
to the receiver. Since this coil is also of the same
frequency, it starts oscillating at the same frequency as the first coil. This
is known as 'coupled resonance' and is the principle behind Wireless
Electricity Tranmission.
The concept of
wireless electricity is not new. In fact it dates back to the
19th century, when Nikola
Tesla used conduction-
based systems instead of resonance magnetic
fields to transfer wireless power. In addition,
lasers have also
been used to
transmit energy without wires. However,
radio waves are
not feasible for power transmissions because the nature of
the radiation is such that it spreads across the place, resulting into a large
amount of radiations
being wasted.
And in
the case of
lasers, apart from
requirement of uninterrupted line
of sight (obstacles
hinders the transmission process), it is also very
dangerous.
But this new
technology differs from the rest of the old ones because the researchers have specifically tuned the transmitting unit to the receiving
device. The transmission is also not hindered by the presence of any object in
the line of sight. If the object to be charged is in the vicinity of the Wireless
Electricity source, then the energy transfer will undoubtedly take place.
The main advantage
of this system is that we can get electricity anywhere without wires. This will
enable us to use our portable electronic gadgets everywhere without bothering
about ending up in the charge of the batteries.
The nature of power
delivery is omni directional i.e. in every direction.
Magnetic resonances
are particularly suitable for everyday application because most of the common
materials do not interact with magnetic fields, so interactions with environmental
objects are suppressed even further.
ADVANTAGES
- Unaffected by day or night cycle, weather or seasons.
- This is a ecofriendly system.
- No need for electric rooms or meter closets.
- Reduction in E-waste
DISADVANTAGES
The resonance
condition should be satisfied or else an error exits and there is no
possibility of power transfer.
If there is a
possibility of strong ferromagnetic material presence causes low power transfer
due to radiation.
Replacing the old
goods with new ones is costly affair.
As witricity is in
the developmental stage, lots of work is still to be done in improving it as it
is disclosed that witricity power applications operate at only 40%
efficiency. However, Intel reproduced the MIT group's experiment by wirelessly
powering a light bulb with 75% efficiency at a shorter distance.
As shown in Figure: Wireless
Light
Marin Soljacic and
Colleagues 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 obtacle.
1.Resonant copper
coil attached to frequency converter and plugged into outlet
2.Wall outlet
3.Obstacle
4.Resonant copper
coil attached to light bulb
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