1. Wireless power transmission using electromagnetic
induction
Saumya George, Sidharth Goyal and Raj
Fr C Rrodrigues Institute of Technology
Abstract— Wireless transfer of electricity uses the phenomenon
of resonant magnetic coupling. In today’s scenario this method is
used to charge batteries, lighting bulb, and powering a small tv.
Further development will lead to its wider applications in the
field of transmission and distribution of power .The losses in the
wired systems can be successfully eliminated using wireless
means .thus a higher efficiency can be achieved. This paper deals
with the concepts behind the wireless transmission of power
popularly known as `witricity`.
Keywords— Witricity, Tesla coil, LC resonance.
I. INTRODUCTION
The phenomenon of wireless energy transfer was proposed
by Nikola Tesla [1]. He had a grand scheme to transmit
electricity wirelessly, around the world. In an effort to
transmit electric energy wirelessly, he aimed to build a 57m
tall tower which could transmit power kilometres away. Tesla
was successful to some extend but, his efforts received a
setback due to lack of funds. Moreover, the idea of airbone
power did not appeal to the industrial and commercial sectors
as they were too busy stringing electrical cables to worry very
much of how to do away with them.
As the wireless art developed during the turn of the 20th
century, the industry was looking toward a method of wireless
energy transfer. In 2007, Prof Marlin Solacic`s team described
a hardware that could light up a 60W incandescent lamp
wirelessly [2]. The bulb continued to glow even when
obstacles were placed in its path.
This paper gives an insight to the wireless transmission of
electric energy. Section II deals with the various methods of
wireless energy transfer .The further sections deal exclusively
with the use of electromagnetic induction principle for the
transfer of electricity .Section III-VI deals with the basic
concepts associated with witricity.
II. METHODS OF WIRELESS ELECTRIC TRANSFER
There are various methods for transmission of electric
energy which are[2]-
1. lasers: Lasers are widely used for the wireless power
transmission, propulsion and space exploration.
2. Microwaves: Microwaves and radio waves can also be
used. However the bulk transmission results in higher losses
and thus reduces efficiency.
3. Induction: The use of electromagnetic induction
principle for the transmission of power. The scope of this
paper is limited to the transmission of power through this
method.
III. BASIC PRINCIPLE OF WIRELESS TRANSMISSION USING
ELECTROMAGNETIC INDUCTION
Electromagnetic induction is a phenomenon that has
been well known since Michael Faraday first described it
in 19th century [3]. The law states that “whenever there is
a change in magnetic field associated with a conductor, an
emf is induced in it.”. The direction current due to the
induced emf is such that it opposes the cause producing it
(Lenses law).
The transmission of electricity wirelessly adopts the
same principle. Its working is same as that of a
transformer.
Fig1. Normal Transformer
A transformer consists of two windings - a primary
winding and a secondary winding and a magnetic core.
When AC voltage is applied to the primary winding,
an emf is induced in it [4]which is given by :
1 1 E = 4.44f f N
(1)

2. where , E1- emf induced in the primary winding
f -flux developed in the core
f- frequency of the supply
N1- Number of turns in primary winding
This field, when linked with the secondary, induces an emf
(E2) in the secondary and is given by:
2 2 E = 4.44f f N (2)
Where, N2- Number of turns in secondary winding
When a suitable load is connected to the secondary , a
proportional current flows. Thus the transformer transfers
energy from the primary to the secondary wirelessly through
the core. Though the same working would explain the
phenomenon of witricity, a marked difference is the absence
of core .
IV. A LC RESONANT CIRCUIT
In an LC circuit an inductor and a capacitor are connected
in series
Fig2. LC Circuit when capacitor discharges
An inductor stores energy in the magnetic field whereas a
capacitor stores energy in the electrostatic field.
The energy stored in a completely charged capacitor is
given as
E=0.5CV2. When this capacitor is connected to an inductor,
energy stored in the capacitor discharges. This results in a
current through the circuit. This current flowing through the
inductor produces a magnetic field. The stored energy in the
magnetic field is given as E=0.5LI2.
When the capacitor has completely discharged, the energy
a stored in the inductor discharges. The inductor, now, acts as
a current source and circulates a current I as shown in Fig3.
This current charges the capacitor in the direction opposite
to the original. This oscillation of energy will take place as
long as the inductor and the capacitor are connected together.
The rate at which the system oscillates is called as the
frequency of oscillation given as f=(1/2P LC ).
Fig3.LCcircuit during capacitor charging
V. TESLA COIL
A basic Tesla coil consists of two LC oscillators.
Fig4.Tesla coil
COIL DETAILS.
The primary and the secondary coil are located close to
each other so as to facilitate maximum flux linkage.
The number of turns in the secondary is more than that in
the primary. The secondary is tightly wound.
While the switch is opened, the voltage source drives a
current that charges the capacitor. When the switch is closed,
the capacitor discharges through the inductor. The resulting
magnetic field induces a corresponding voltage in the
secondary. As the number of the secondary windings is more,
the electric field in the secondary capacitor is more.
The output of this system is maximum when the primary
and the secondary oscillate at the same frequency.

3. VI. SCHEMATIC DIAGRAM OF WIRELESS
TRANSMISSION
Fig5. Schematic representation of wireless transmission
A Tesla coil is used at the transmitter end as well as the
receiver end. At the transmitter end, when the primary is
powered, high frequency electromagnetic waves are produced.
The secondary has a torroid attached to it which causes a
corona discharge when provided with a high frequency
supply.
The receiver is similar to the transmitter and is tuned with
the transmitter frequency. The power level can be boosted
with the help of power amplifiers.
VII. ADVANTAGE OF WIRELESS POWER TRANSMISSION
The advantages of wireless transmission of electricity over
wired systems are-
1. Wireless transmission would completely eliminate
the hazards of the already existing transmission
line cables and towers.
2. It facilitates the power connection on a global
scale.
3. The amount of electronic waste produced will
reduce considerably.
4. The cost of transmission and distribution of
overall power will reduce considerably.
5. Power will be effectively transmitted over
inaccessible areas.
6. Loss of power will be reduced.
7. Fault due to short circuit condition, insulation
failure will not exist.
V.DISADVANTAGE
The disadvantages of the wireless systems are stated below-
1. Tesla coil work on the principle of electromagnetic
induction. The electromagnetic field in the Tesla coil
may induce a voltage in the nearby conductors.
Hence the coil cannot be placed in the vicinity of
electronic equipments.
2. The system must be built with proper protective
devices like fuses and must be earthed.
3. Any contact with the coil under working condition
can be hazardous. Moreover, touching the tank
circuit immediately after disconnecting the supply
can prove dangerous. This is because of the residual
charges in the tank circuit.
4. A very high current flows through the secondary.
Thus heating it. Care should be taken that the coil is
not placed near flammable substances.
5. Electric discharges through the air ionise it and
produce toxic gases. Exposure to these gases causes
irritation in the eye and affect the lungs.
6. Peacemakers are also affected when subjected to
prolonged electromagnetic field.
7. These devices are loud.
8. Today the application are short range.
VIII. APPLICATION
Wirless transmission is still in the primitive stages.Further
research and study will further widen its area of
application.The main implimentation of witricity,today is in
charging of electronic devices.
Fig7. Induction chargers.
The gadget to be charged are placed in close proximity with
the source of wireless transfer. Over a period of time, the
device battery gets charged. Hence there is no need to plug in
the device and devoid of wires.
Moreover only one charging pad can be used to charge an
entire range of devices.
Cellphones, electric toothbrushes, electric buses etc can be
charged wirelessly.
Wireless charging pads are becoming widely available for
consumer electronics, including the Dell Lattitude Zlaptop,
the Palm Pre smartphone.
VII. CONCLUSIONS
Wireless transmission of electricity is still in its developing
stage .The actual potential of witricity has not yet been
tapped .However, today there are quite a number of electric
cars that are charged wirelessly. A big step in that direction is
taken by Berlin based Bombardier Transportation, which is
gearing up to offer an electric streetcar that is inductively
powered through the roadway. If this approach for powering
streetcars catches on, a wider range of buses will be next.
Transmitter Receiver
Load

4. With rapid progress in this field soon your room could be lit
up by means of wirelessly powered lighting system.
REFERENCES
[1] Witricity-a project report (FCRIT)
[2] Ieee spectrum 5.10 Electrons unplugged pg 31Verlag, 1998.
[3] Electrical machineries M G Say
[4] Wikwpedia.
[5] The IEEE website. [Online]. Available: http://www.ieee.org/