>>>wireless charging<<<

Wireless charging is any of
several methods of
charging batteries without
... the use of cables or device-
specific AC adaptors.
Wireless charging can be used for a wide variety of
devices including cell
phones, laptop computers and MP3 players as well as
larger objects, such as robots and electric cars. There are three methods of
wireless charging:
>inductive charging
>radio charging and
>resonance charging.

Inductive charging is used
for charging mid-sized
items such as cell phones,
MP3 players and PDAs. In inductive charging, an
adapter equipped with
contact points is attached to the device's back plate.
When the device requires a
charge, it is placed on a
conductive charging pad,
which is plugged into a
socket.

Radio charging is used for
charging items with small
batteries and low power
requirements, such as
watches, hearing aids,
medical implants, cell phones, MP3 players and
wireless keyboard and
mice. Radio waves are
already in use to transmit
and receive cellular telephone, television, radio
and Wi-Fi signals. Wireless radio charging works
similarly. A transmitter,
plugged into a socket,
generates radio waves.
When the receiver attached
to the device is set to the same frequency as the transmitter, it will charge
the device's battery.

Resonance charging is used
for items that require large
amounts of power, such as
an electric car, robot,
vacuum cleaner or laptop
computer. In resonance charging, a copper coil
attached to a power source
is the sending unit.
Another coil, attached to
the device to be charged, is
the receiver. Both coils are tuned to the same
electromagnetic frequency,
which makes it possible for
energy to be transferred
from one to the other.The
method works over short distances (3-5 meters).

The idea of wireless power
transmission is not new. In
1899, Nikola Tesla wirelessly transmitted 100
million volts of electricity 26 miles to light 200 bulbs
and run an electric motor.
However, at that time
direct current ( DC, which is the wired method) and
alternating current (AC)
were competing
technologies. DC, backed
strenuously by Thomas
Edison, emerged the winner.