International Journal for Research and Development in Engineering (IJRDE)
www.ijrde.com
ISSN: 2279-0500
Special Issue: pp- 113-119
Wireless Electrical Energy Transfer
Nanda Kumar K1, N. Naha Renjini2 and Rasmi Rajan3
1,2,3
Assistant professor, EEE Department, Hindustan University, Chennai
ABSTRACT
The paper will detail the need and usefulness of
wireless power transmission and furthermore
the feasibility of using inductive coupling as the
means for wireless power transmission.
Nowadays usage of smart phones, laptops and
other portable electronic devices has been
increased. The users of these portable devices
need to recharge their devices in order to get an
uninterrupted service. The main problem faced
by them while recharging those devices is a need
of charging device. These problems can be
overcome by using a wireless connection
between the device and the output port. The
wireless connection can be made possible by
using the electromagnetic waves.
1. INTRODUCTION
The subject matter of the report will be directed
towards the knowledge level of an electrical
engineer. Thus some points about general circuits
may not be explicitly stated as they have been
taken as common knowledge for the intended
audience [1-8]. However, it is intended that anyone
with an interest in electrical circuits and more
importantly transformer theory or electromagnetic
fields would be able to understand and follow the
subject matter outlined in the following document.
The first section of the document will explicitly
illustrate the problem and what the group intended
to accomplish. With the complexity of the problem
in mind and what we must accomplish our team
then began research on the available means to
transmit power without a physical connection.
Once the initial background research was
accomplished it was necessary to layout the
advantages and disadvantages of all the available
means for wireless power transmission [5-10].
Once all the necessary criteria for each system were
known we chose the best solution for the problem.
After our team had chosen upon using inductive
coupling us all began to review the major theories
that would determine the constraints of the system
and what pieces of hardware must be designed to
achieve the transmission of wireless power.
Furthermore because we are transmitting power
through the surrounding area we had to be sure that
our system would not endanger others and be FCC
(Federal Communication Commission) compliant.
Once the basic system components were known our
team divided up the work load, set the necessary
deadlines, and began designing the following
circuits and hardware: power supply, oscillator,
transmission coil, receiving coil, and LED flashing
circuit. After the entire system was integrated into a
working unit it was time to determine how well the
system operated and the feasibility of wireless
power transfer through inductive coupling.
Additionally, future improvements that could
greatly improve the overall system will be
discussed.
1.1 Problem Statement
For the completion of this project, we had to
wirelessly transfer the power of an AC oscillating
waveform into a DC voltage on the receiving end
which will be used to light an LED to demonstrate
the instantaneous power transfer [11-15]. The
frequency of oscillation of the AC signal must not
exceed 100MHz. The power transfer needs to be
done over a two feet distance or greater. The
transferred AC power needs to be converted to DC
power and boosted up enough to drive a low power
display design, such as an LED in continuous
mode. The whole system must be FCC compliant.
1.2 Possible Solutions
In our research, as well as practical knowledge, we
knew of three possibilities to design a device [1617]. There are the use of antennas, inductive
coupling, and laser power transfer. In addition, we
had to be aware of how antennas and inductive
coupling would be affected by the frequency we
select.
1.2.1 Antenna
Antennas are the traditional means of signal
transmission and would likely work. In initial
research, it appears that system utilizing antennas
can receive power gains based upon the shape and
design of the antenna. This would allow more
power actually being sent and received while also
have a small input power. The difficulty comes in
the trade off of antenna size versus frequency. In
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International Journal for Research and Development in Engineering (IJRDE)
www.ijrde.com
ISSN: 2279-0500
Special Issue: pp- 113-119
attempting to stay in a lower frequency, one would
be require using antennas of very large size.
1.2.2 Inductive Coupling
Inductive coupling does not have the need for large
structures transfer power signals. Rather, inductive
coupling makes use of inductive coils to transfer
the power signals. Due to the use of coils rather
than the antenna, the size of the actual transmitter
and receiver can be made to fit the situation better.
The tradeoff is for the benefit of custom size, there
will be a poor gain on the solenoid transmitter and
receiver.
1.2.3 Laser Power Transmission
The concept of laser power transmission is
addressed in the research of NASA and NASDA
solar programs. Lasers would allow for a very
concentrated stream of power to be transferred
from one point to another. Based upon available
research material, it appears that this solution
would be more practical for space to upper
atmosphere or terrestrial power transmission. This
option would not be valid to accomplish our tasks
because light wavelengths are higher than the
allowable operational frequencies.
2. BLOCK DIAGRAM & DESCRIPTION
the maximum amount of flux which will induce the
largest voltage on a receiving coil, a large amount
of current must be transferred into the transmitting
coil. The oscillator is not capable of supplying the
necessary current, thus the output signal from the
oscillator will then be passed through a power
amplifier (Power MOSFET) to produce the
necessary current.
A loop antenna is a radio antenna consisting of a
loop (or loops) of wire, tubing, or other electrical
conductor with its ends connected to a balanced
transmission line. Within this physical description
there are two very distinct antenna designs: the
small loop (or magnetic loop) with a size much
smaller than a wavelength, and the resonant loop
antenna with a circumference approximately equal
to the wavelength. Small loops have a poor
efficiency and are mainly used as receiving
antennas at low frequencies. Self-resonant loop
antennas are larger. They are typically used at
higher frequencies, especially VHF and UHF,
where their size is manageable.
One of the major improvements made to the
coupling circuit was accomplished by impedance
matching. When a capacitor is put in series with the
transmitter coil and it is tuned to its resonant
frequency, then the phase differences of the
capacitor and inductor are equal and opposite.
jwL =-1/jwC
Figure 2.1 Block Diagram
2.1 Block Diagram Description
A transformer is a static electrical device that
transfers energy by inductive coupling between its
winding circuits. A bridge rectifier is used for
conversion of an alternating current (AC) input into
a direct current (DC) output. A crystal oscillator is
an electronic oscillator circuit that uses the
mechanical resonance of a vibrating crystal of
piezoelectric material to create an electrical signal
with a very precise frequency. This frequency is
commonly used to provide a stable clock signal for
the driver circuit. The most common type of
piezoelectric resonator used is the quartz crystal, so
oscillator circuits incorporating them became
known as crystal oscillators. In order to generate
When this occurs the load will appear purely
resistive and the maximum amount of real power
will be transferred into the transmission coil as
voltage and current are in phase. This maximum
power transfer to the transmitter will ensure the
maximum amount of current which will produce
the most magnetic flux.
At the receiver circuit we utilized the same
concepts of impedance matching to tune the
receiver circuit to the same resonant frequency as
of the transmitter. This ensures that the maximum
power is transmitted to the receiver coil.
A parallel resonance circuit was used to maximize
voltage output to the load at the receiving end. A
LED is used in our circuit to indicate the power is
received by the receiver.
2.2 Circuit Diagram & Description
Methods Enriching Power and Energy Development (MEPED) 2014
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International Journal for Research and Development in Engineering (IJRDE)
www.ijrde.com
ISSN: 2279-0500
Special Issue: pp- 113-119
be called the coupling circuit. It is the heart of the
entire system as the actual wireless power transfer
is carried out here. The efficiency of the coupling
circuit determines the amount of power available
for the receiver system as well as how far the LED
can be from its actual power source.
Figure 2.2 Circuit Diagram
2.3 Power MOSFET, Transmission & Receiving
Circuit
Solenoid Design
A solenoid configuration was used for the design of
the transmitter and receiver. A solenoid is a long
cylinder upon which wire is wound in helical
geometry as shown in figure 2. The magnetic field
at the center of the solenoid is very uniform.
Usually, the length of a solenoid is several times of
its diameter. The longer the solenoid the more
uniform the magnetic field at the middle. In this
way a solenoid is a very practical way to generate a
uniform controlled magnetic field .
Figure 2.4 Flux density in a solenoid
The magnetic flux density in a solenoid can be
approximated by the following equation:
B = µ0nI
Figure 2.3 Transmission & Receiving Circuit
In order to generate the maximum amount of flux
which will induce the largest voltage on a receiving
coil, a large amount of current must be transferred
into the transmitting coil.
The oscillator is not capable of supplying the
necessary current, thus the output signal from the
oscillator will then be passed through a power
amplifier to produce the necessary current. The key
design aspects of the power amplifier are
generating enough current while producing a clean
output signal without large harmonic distortions. If
the output from the amplifier was not clean with
harmonic distortions the system would cease to be
FCC compliant.
Transmitter and Receiver Design
The transmitter and receiver circuit combined can
Where B is the magnetic flux density, µ0 is the
permeability of free space, n is number of turns of
wire per unit length and I is the current flowing
through the wire. To maximize the flux linked to
the receiver coil, it is imperative to increase the
magnetic flux density as much as possible.
The equation shows that one of the ways to
increase B is to increase the current (I) going into
the wire. Since all wires have some resistance, this
process requires increase in the voltage put across
the wires which can result in more heating in the
coil. B can also be increased by increasing n. This
can be accomplished by decreasing the wire size or
winding wires closely. Winding wires closely can
increase the overall resistance of the coil and thus
increase the heating in the coil. Another way of
increasing n is by winding several layers of wire
which can cause insulations problems as well as
decrease the diameter to length ratio. It is apparent
that there are several parameters that we have to
Methods Enriching Power and Energy Development (MEPED) 2014
115 | P a g e
International Journal for Research and Development in Engineering (IJRDE)
www.ijrde.com
ISSN: 2279-0500
Special Issue: pp- 113-119
manipulate to select the appropriate tradeoff that
might fit our system’s needs.
As the input power to our transmitter is limited to
1W, it certainly limits the amount of current that
can be pushed through the transmitter coil. Thus
one of the design goals of the team was to keep the
resistance low to maximize the current. In addition
to that, we also strived to increase the number of
turns per unit length without drastically
increasing the resistance. Initially our team
was using shielded wire for the coils. A major
advancement was made in decreasing wire size
by replacing it with magnetic wires. This wire
is common copper wire but rather than having
a thick insulation over the copper, it is simply
coated in enamel which keeps the overall
diameter of the wire much thinner compared to
shielded wire. Magnetic wires also have low
resistance and therefore can carry much higher
current.
We also utilized two complete layers of wires for
the transmitter coil to increase the number of turns
even more.
BIG LOOPS
transmitter
Separation distance
3inches
tried supplying the large diameter coil with a 7 volt
21 kHz sine waveform to act as the transmitter and
the small diameter coil was placed next to it at
various distances and the resulting voltage received
was measured.
Figure 2.5 Bigger Transmitter and Smaller Receiver Coil
Next we conducted the same experiment however
this time the coils were oriented in such a way
where they were along the same axis as shown
below.
SMALL
LOOPS
receiver
MEASURED VOLTAGE
7V
30mV
Figure 2.6 Transmitter and Receiver Coil sharing the
same axis
The following data was collected with this
arrangement.
These steps improved the performance of our
system to a great extent.
Initial Experimentation
In addition to the solenoid parameters, it was also
necessary to determine certain parameters such as
relative size of the transmitter and receiver coil, the
orientation of the coils, the turns ratio as well as the
operating frequency. To establish these parameters,
we conducted few experiments. For our
experiments we made two handmade inductive
coils of different diameters (approximately 1.5 ft
and 6 inches), but with equal turns (N=10). First we
BIG LOOPS FOR
TRANCEIVER
Separat
ion
distance
SMALL LOOPS
FOR RECEIVER
MEASURED VOLTAGES
0inch
7V
43mV
2inches
7V
18mV
5inches
7V
8mV
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International Journal for Research and Development in Engineering (IJRDE)
www.ijrde.com
ISSN: 2279-0500
Special Issue: pp- 113-119
Higher frequency is preferred for greater power
transmission over all distances. This agrees with
Faraday’s Law as the induced voltage is dependent
on the frequency. The large number of turns at the
transmitter would create more magnetic flux
density which can result in high flux linkage. The
major concern at the receiver was to find the
optimum number of turns while keeping the
resistance of the receiver coil minimal. Further
experimentation showed that the turn’s ratio of
transmitter and receiver coil had no effect on the
system whatsoever due to the large distance
between the coils.
From these simple tests we realized four major
points of emphasis that would be crucial in
designing an efficient inductive coupling system:
•
•
•
The coils should be oriented such that they
share the same axis
The receiver should be larger than the
transmitter
The higher the frequency the more power
can be transferred over a given distance
After conducting several experiments with
longer solenoids and different number of
turns, we arrived at the final parameters
that seem to provide the maximum power
transfer between the transmitter and
receiver coils.
3. HARDWARE DESCRIPTION
3.1 System Design
With all the necessary background research
completed it became clear what basic design
components the entire system would require. First
we needed a method to power the transmission side
of the system. The power supply would then power
an oscillator which would provide the carrier signal
with which to transmit the power. Oscillators are
not generally designed to deliver power, thus it was
necessary to create a power amplifier to amplify the
oscillating signal. The power amplifier would then
transfer the output power to the transmission coil.
Next, a receiver coil would be constructed to
receive the transmitted power. However, the
received power would have an alternating current
which is undesirable for lighting a LED. The entire
system can be seen in the figure.
Figure 3.1 Project hardware
3.2 Power Supply Enclosure
Figure 3.2 Power Supply Enclosures
The main design aspects our team wanted to
incorporate in the power supply was that it could
use the 230 V AC voltage found in any basic wall
outlet, and use that voltage to power any necessary
circuits to the system. Initially, 230volts is too large
for our small circuits so we incorporated a small
transformer to step down the voltage. Furthermore
for any basic electrical components it would be
necessary to have a DC power supply available,
thus the stepped down AC voltage converted to DC
by a full-wave bridge rectifier. The full-wave
bridge rectifier is the KBU4D. Large capacitors
were then connected to the output of the full-wave
bridge rectifier to ensure that a steady DC voltage
could be maintained.
3.3 Crystal oscillator, Driver Circuit & MOSFET
Enclosure
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International Journal for Research and Development in Engineering (IJRDE)
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ISSN: 2279-0500
Special Issue: pp- 113-119
Figure 3.3 Crystal oscillator & Driver Hardware
During the operation, the oscillation is being
sustained by the crystal oscillator by taking a
voltage signal from a quartz resonator. The signal
is fed back to the resonator after being amplified. In
this circuit, the frequency is being micro tuned by
the presence of 47 µF capacitor. The 1 6Hz
converted frequency can be obtained from the pin
12 of IC as it serves as its output. Based on the
components used in the circuit, it will no longer
require additional adjustments for the circuit to
function well.
3.4 Transmitting and Receiving antenna
Figure 3.4 Transmitting antenna
to the system to increase its overall performance.
The oscillator output wasn’t a very clean sine wave
signal which increased the harmonic distortion of
the signal. A pure sine wave can be generated by
using better filters at the output. Currently our
system is powered by a transformer that provides
+18V/-18V volt rails. Our system can work with
lower power. Thus one of the future improvements
could be an implementation of a solar cell array to
make our system more mobile. The coupling circuit
can be made more efficient by altering the design
in several ways. Increasing the input current to the
transmitter coil would definitely enhance its
performance. We can also make the signals more
directional in the z direction by using a conical coil
as a transmitter instead of the solenoid coil.
5. CONCLUSION
Large number of institutions such as medical,
industrial, educational etc. need wireless electricity
transmission mechanism for its products to work
efficiently, effectively and at potentially reduced
costs. Plus it reduces the hassle of wires, nonrechargeable batteries and power cords at small
scale. On the other hand transmission
of power using wireless electricity mechanism
helps to reduce the cost of power
being supplied. Plus the source of power is clean
and environmental friendly. The proposed research
would attain following goals:
1. Development
of
wireless
electric
transmission mechanism for small scale
(private sector) which is efficient and
effective
2. Development
of
wireless
electric
transmission mechanism for large scale
(public sector) which is efficient, effective
and aimed at lower electricity production
cost.
3. Determine whether the radiations from the
wireless electric transmission system have
biological impact.
REFERENCES
Figure 3.5 Receiving antenna
4. FUTURE IMPROVEMENTS
There are several improvements that can be made
[1] G.
L.
Peterson,
“THE
WIRELESS
TRANSMISSION
OF
ELECTRICAL
ENERGY,” IEEE[online document], 2004,
[cited
12/10/04],
http://www.tfcbooks.com/articles/tws8c.htm
[2] [U.S. Department of Energy, “Energy Savers:
Solar Power Satellites,” [online document] rev
2004
June
17,
[cited
12/10/04],
http://www.eere.energy.gov/consumerinfo/fact
sheets/l123.html
[3] S. Kopparthi, Pratul K. Ajmera, "Power
delivery for remotely located Microsystems,"
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ISSN: 2279-0500
Special Issue: pp- 113-119
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
Proc. of IEEE Region 5, 2004 Annual Tech.
Conference, 2004 April 2, pp. 31-39.
Tomohiro Yamada, Hirotaka Sugawara,
Kenichi Okada, Kazuya Masu, Akio Oki and
Yasuhiro
Horiike,"Battery-less
Wireless
Communication System through Human Body
for in- vivo Healthcare Chip,"IEEE Topical
Meeting on Silicon Monolithic Integrated
Circuits in RF Systems, pp. 322-325, Sept.
2004.
“Category:Radio spectrum -Wikipedia, the free
encyclopedia,” [online document], 2004 Aug
26
[cited
12/11/04],
http://en.wikipedia.org/wiki/Category:Radio_s
pectrum.
Zia A. Yamayee and Juan L. Bala, Jr.,
Electromechanical Energy Devices and Power
Systems, John Wiley and Sons, 1947, p. 78.
Code of Federal Regulations, Title 47, Volume
1,Revised as of October 1, 2003 ,From the U.S.
Government Printing Office via GPO Access,
CITE: 47CFR15.3, Page 686-689
”Oscillator
Basics”,
October
2004,
http://www.electronicstutorials.com/oscillators/oscillator- basics.html
DiscreteSemiconductors, “2N2222”, November
2004,
http://www.semiconductors.philips.com/acroba
t_download/datasheets/2N2222_CNV_2.pdf.
All Data Sheets, “AD711JN Operational
Amplifier”,
November
2004,
http://www.alldatasheet.com/datasheetpdf/view/AD/AD711JN.html.
”2.3 Class B” September 2004, http://www.standrews.ac.uk/~www_pa/Scots_Guide/audio/p
art2/page2.html.
Texas Insturments, “OPA13442 Operational
Amplifier”,
September
2004,
http://focus.ti.com/lit/ds/sbos058/sbos058.pdf.
Digikey,
“TIP31
BJT”,
http://rocky.digikey.com/WebLib/OnSemi/Web%20Data/TIP31_A_B_C,%20TIP32
_A_B_C.pdf.
Digikey,“TIP42,BJT”,http://rocky.digikey.com
/WebLib/ST%20Micro/Web%20Data/TIP41A,
B,C_42A,C.pdf.
Barry.“Solenoid Physics” (Barry’s CoilGun
Design
Site)
[online]
2004,
http://www.oz.net/~coilgun/theory/solenoidphy
sics.htm (Accessed: September 27, 2004).
Fawwaz T. Ulaby, Fundamentals of Applied
Electromagnetics 2001 Media Edition, Prentice
Hall, 2001.
“The Spark Transmitter. 2. Maximising Power,
part
1.
“
November
2004,
http://home.freeuk.net/dunckx/wireless/maxpo
wer1/maxpower1.html
R. Victor Jones, “Diode Applications,” [Online
Document], 2001 Oct 25, [cited 2004 Dec 11],
http://people.deas.harvard.edu/~jones/es154/lec
tures/lecture_2/diode_circuits/diode_appl.html
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