wireless charging of mobile phones using microwave full seminar report

WIRELESS CHARGING OF MOBILE USING MICROWAVE

CHAPTER 1

INTRODUCTION
The principle of wireless charging has been around for over a century but only now
are we beginning to recognize its true potential. First, we need to be careful about how
liberal we use "wireless" as a term; such a word implies that you can just walk around the
house or office and be greeted by waves of energy beamed straight to your phone. We're
referring, largely, to inductive charging the ability to manipulate an electromagnetic field
in order to transfer energy a very short distance between two objects (a transmitter and
receiver). It's limited to distances of just a few millimeters for the moment, but even with
this limitation, such a concept will allow us to power up phones, laptops, keyboards,
kitchen appliances, and power tools from a large number of places: in our homes, our
cars, and even the mall.
There are three types of wireless charging.
1. Inductive charging
2. Radio charging
3. Resonance charging

1.1 INDUCTIVE CHARGING
Inductive charging charges electrical batteries using electromagnetic induction. A
charging station sends energy through inductive coupling to an electrical device, which
stores the energy in the batteries. Because there is a small gap between the two coils,
inductive charging is one kind of short distance wireless energy transfer.
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.

Dept. of ECE SDMIT Ujire

Page 1


1.2 RADIO CHARGING
Radio charging is only effective for small devices. The battery of a laptop computer,
for example, requires more power than radio waves can deliver. The range also limits the
effectiveness of radio charging, which works on the same principle as an AM/FM radio
does: The closer the receiver is to the transmitter, the better reception will be. In the case
of wireless radio charging, better reception translates to a stronger charge for the item.

1.3 RESONANCE CHARGING
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.
A new method is developed in order to charge mobile phones, by using microwaves.


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CHAPTER 2

ELECTROMAGNETIC SPECTRUM

Fig.2.1 electromagnetic spectrum
The electromagnetic spectrum[4] is the range of all possible frequencies of
electromagnetic radiation. The electromagnetic spectrum extends from below the low
frequencies used for modern radio communication to gamma radiation at the shortwavelength (high-frequency) end.
Electromagnetic radiation is the means for many of our interactions with the world:
light allows us to see; radio waves give us TV and radio; microwaves are used in radar
communications; X-rays allow glimpses of our internal organs; and gamma rays let us
eavesdrop on exploding stars thousands of light-years away. Electromagnetic radiation is
the messenger, or the signal from sender to receiver. The sender could be a TV station, a
star, or the burner on a stove. The receiver could be a TV set, an eye, or an X-ray film. In
each case, the sender gives off or reflects some kind of electromagnetic radiation.
All these different kinds of electromagnetic radiation actually differ only in a single
property — their wavelength. When electromagnetic radiation is spread out according to

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its wavelength, the result is a spectrum, as seen in Fig. The visible spectrum, as seen in a
rainbow, is only a small part of the whole electromagnetic spectrum.
The electromagnetic spectrum is divided into following classes,
1. Gamma radiation
2. X-ray radiation
3. Ultraviolet radiation
4. Visible radiation
5. Infrared radiation
6. Microwave radiation
7. Radio waves

2.1 MICROWAVE REGION
Microwaves[5] are the Radio wave which has the wave length range of 1 mm to 1
meter and the frequency is 300MHz to 300GHz. Each and every object on the earth
absorb different amount of microwave energy.
Microwaves are good for transmitting information from one place to another because
microwave energy can penetrate haze, light rain and snow, clouds, and smoke. Shorter
microwaves are used in remote sensing. These microwaves are used for clouds and
smoke, these waves are good for viewing the Earth from space. Microwave waves are
used in the communication industry and in the kitchen as a way to cook foods.
Microwave radiation is still associated with energy levels that are usually considered
harmless except for people with pace makers.
The frequency selection is another important aspect in transmission. Here we are
going to use the S band of the Microwave Spectrum, which lies between 2-4GHz.We
have selected the license free 2.45 GHz ISM band for our purpose. The Industrial,
Scientific and Medical (ISM) radio bands were originally reserved internationally for
non-commercial use of RF electromagnetic fields for industrial, scientific and medical
purposes.

In recent years they have also been used for license-free error-tolerant

communications applications such as wireless LANs and Bluetooth.
According to the range of frequencies there are different frequency bands are
present. Specialized vacuum tubes are used to generate microwaves. These devices

Page 4

operate on different principles from low-frequency vacuum tubes, using the ballistic
motion of electrons in a vacuum under the influence of controlling electric or magnetic
fields, and include the magnetron (used in microwave ovens), klystron, traveling-wave
tube (TWT), and gyrotron. These devices work in the density modulated mode, rather
than the current modulated mode. This means that they work on the basis of clumps of
electrons flying ballistically through them, rather than using a continuous stream of
electrons. Cutaway view inside a cavity magnetron as used in a microwave oven.
Low-power microwave sources use solid-state devices such as the field-effect
transistor (at least at lower frequencies), tunnel diodes, Gunn diodes, and IMPATT
diodes. Low-power sources are available as benchtop instruments, rackmount
instruments, and embeddable modules and in card-level formats. A maser is a solid state
device which amplifies microwaves using similar principles to the laser, which amplifies
higher frequency light waves.
All warm objects emit low level microwave black body radiation, depending on
their temperature, so in meteorology and remote sensing microwave radiometers are used
to measure the temperature of objects or terrain. The sun and other astronomical radio
sources such as Cassiopeia, emit low level microwave radiation which carries information
about their makeup, which is studied by radio astronomers using receivers called radio
telescopes. The cosmic microwave background radiation (CMBR), for example, is a weak
microwave noise filling empty space which is a major source of information on
cosmology's Big Bang theory of the origin of the Universe.


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CHAPTER 3

GENERAL BLOCK DIAGRAM

Fig 3.1 Block diagram

Here as we can see there are two part. One is transmitting part and the other is the
Receiving part. At the transmitting end there is one microwave power source which is
actually producing microwaves. Which is attach to the Coax-Waveguide and here Tuner
is the one which match the impedance of the transmitting antenna and the microwave
source. Directional Coupler helps the signal to propagate in a particular direction. It
spread the Microwaves in a space and sent it to the receiver side. Receiver side
Impedance matching circuit receives the microwave signal through Rectena circuit. This
circuit is nothing but the combination of filter circuit and the schottky Diode. Which
actually convert our microwave in to the DC power!


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CHAPTER 4

TRANSMITTER SECTION
The transmitter section consists of two parts. They are:
1. Magnetron

2. Slotted waveguide antenna

4.1 MAGNETRON

Fig.4.1 Magnetron
Magnetron[4] is the combination of a simple diode vacuum tube with built in cavity
resonators and an extremely powerful permanent magnet. The typical magnet consists of
a circular anode into which has been machined with an even number of resonant cavities.
The diameter of each cavity is equal to a one-half wavelength at the desired operating
frequency. The anode is usually made of copper and is connected to a high-voltage
positive direct current. In the center of the anode, called the interaction chamber, is a
circular cathode.
The magnetic fields of the moving electrons interact with the strong field supplied
by the magnet. The result is that the path for the electron flow from the cathode is not
directly to the anode, but instead is curved. By properly adjusting the anode voltage and
the strength of the magnetic field, the electrons can be made to bend

that they rarely
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reach the anode and cause current flow. The path becomes circular loops. Eventually, the
electrons do reach the anode and cause current flow. By adjusting the dc anode voltage
and the strength of the magnetic field, the electron path is made circular. In making their
circular passes in the interaction chamber, electrons excite the resonant cavities into
oscillation. A magnetron, therefore, is an oscillator, not an amplifier. A takeoff loop in
one cavity provides the output.
Magnetrons are capable if developing extremely high levels of microwave power.
When operated in a pulse mode, magnetron can generate several megawatts of power in
the microwave region. Pulsed magnetrons are commonly used in radar systems.
Continuous-wave magnetrons are also used and can generate hundreds and even
thousands of watts of power.

4.2 SLOTTED WAVEGUIDED ANTENNA
The slotted waveguide is used in an omni-directional role. It is the simplest ways to
get a real 10dB gain over 360 degrees of beam width. The Slotted waveguide antenna is a
Horizontally Polarized type Antenna, light in weight and weather proof. 3 Tuning screws
are placed for tweaking the SWR and can be used to adjust the center frequency
downwards from 2320MHz nominal to about 2300MHz. This antenna is available for
different frequencies. This antenna, called a slotted waveguide, is a very low loss
transmission line. It allows propagating signals to a number of smaller antennas (slots).
The signal is coupled into the waveguide with a simple coaxial probe, and as it travels
along the guide, it traverses the slots. Each of these slots allows a little of the energy to
radiate. The slots are in a linear array pattern. The waveguide antenna transmits almost all
of its energy at the horizon, usually exactly where we want it to go.

Fig.4.2 Slotted waveguide antenna


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CHAPTER 5

RECEIVER DESIGN
The basic addition to the mobile phone is going to be the rectenna. A rectenna is a
rectifying antenna, a special type of antenna that is used to directly convert microwave
energy into DC electricity. Its elements are usually arranged in a mesh pattern, giving it a
distinct appearance from most antennae.
A simple rectenna can be constructed from a Schottky diode placed between
antenna dipoles. The diode rectifies the current induced in the antenna by the
microwaves. Rectennae are highly efficient at converting microwave energy to electricity.
In laboratory environments, efficiencies above 90% have been observed with regularity.
Some experimentation has been done with inverse rectennae, converting electricity into
microwave energy, but efficiencies are much lower--only in the area of 1%. With the
advent of nanotechnology and MEMS the size of these devices can be brought down to
molecular level. It has been theorized that similar devices, scaled down to the proportions
used in nanotechnology, could be used to convert light into electricity at much greater
efficiencies than what is currently possible with solar cells. This type of device is called
an optical rectenna. Theoretically, high efficiencies can be maintained as the device
shrinks, but experiments funded by the United States National Renewable energy
Laboratory have so far only obtained roughly 1% efficiency while using infrared light.
Another important part of our receiver circuitry is a simple sensor. This is simply used to
identify when the mobile phone user is talking. As our main objective is to charge the
mobile phone with the transmitted microwave after rectifying it by the rectenna, the
sensor plays an important role.
Antenna design is important in the proposed rectenna. The antenna absorbs the
incident microwave power, and the rectifier converts it into a useful electric power. In this
paper, in order to reduce the size of the rectenna, we propose to combine the BPF and the
antenna into a single unit.


Page 9


5.1 RECTENNA
A rectifying antenna rectifies received microwaves into DC current. A rectenna
comprises of a mesh of dipoles and diodes for absorbing microwave energy from a
transmitter and converting it into electric power. A simple rectenna can be constructed
from a Schottky diode placed between antenna dipoles. The diode rectifies the current
induced in the antenna by the microwaves. Rectenna are highly efficient at converting
microwave energy to electricity. In laboratory environments, efficiencies above 90% have
been observed with regularity. In future rectennas will be used to generate large-scale
power from microwave beams delivered from orbiting GPS satellites.

FIG 5.1 Block diagram of a rectenna with a load
There are at least two advantages for rectennas:
1. The life time of the rectenna is almost unlimited and it does not need
replacement (unlike batteries).
2. It is "green" for the environment (unlike batteries, no deposition to pollute the
environment).

5.2 SCHOTTKY BARRIER DIODE
A Schottky barrier diode is different from a common P/N silicon diode. The
common diode is formed by connecting a P type semiconductor with an N type
semiconductor, this is connecting between a semiconductor and another semiconductor;
however, a Schottky barrier diode is formed by connecting a metal with a semiconductor.
When the metal contacts the semiconductor, there will be a layer of potential barrier
(Schottky barrier) formed on the contact surface of them, which shows a characteristic of
rectification. The material of the semiconductor usually is a semiconductor of n-type

Page 10

(occasionally p-type), and the material of metal generally is chosen from different metals
such as molybdenum, chromium, platinum and tungsten. Sputtering technique connects
the metal and the semiconductor.
A Schottky barrier diode is a majority carrier device, while a common diode is a
minority carrier device. When a common PN diode is turned from electric connecting to
circuit breakage, the redundant minority carrier on the contact surface should be removed
to result in time delay. The Schottky barrier diode itself has no minority carrier, it can
quickly turn from electric connecting to circuit breakage, its speed is much faster than a
common P/N diode, so its reverse recovery time Tr is very short and shorter than 10 ns.
And the forward voltage bias of the Schottky barrier diode is under 0.6V or so, lower than
that (about 1.1V) of the common PN diode. So, The Schottky barrier diode is a
comparatively ideal diode, such as for a 1 ampere limited current PN interface.

5.3 SENSOR CIRCUITRY
The sensor circuitry is a simple circuit, which detects if the mobile phone
receives any message signal. This is required, as the phone has to be charged as long as
the user is talking. Thus a simple F to V converter would serve our purpose. In India the
operating frequency of the mobile phone operators is generally 900MHz or 1800MHz for
the GSM system for mobile communication. Thus the usage of simple F to V converters
would act as switches to trigger the rectenna circuit to on. The sensor circuit is used to
find whether the mobile phone using the microwaves for message transferring or not! So
here we can use any Frequency to Voltage converter to do our job. We can use LM2907
for F to V conversion. So when our phone is receiving microwave signal it make the
rectenna circuit on and charge the battery.
A simple yet powerful F to V converter is LM2907. Using LM2907 would greatly
serve our purpose. It acts as a switch for triggering the rectenna circuitry. The general
block diagram for the LM2907 is given below.
Thus on the reception of the signal the sensor circuitry directs the rectenna circuit to
ON and the mobile phone begins to charge using the microwave power.


Page 11


Fig.5.2 LM2907
The LM2907 LM2917 series are monolithic frequency to voltage converters with a
high gain op amp Comparator designed to operate a relay, lamp, or other load when the
input frequency reaches or exceeds a selected rate. The tachometer uses a Charge Pump
technique and offers frequency doubling for low ripple, full input protection in two
versions (LM2907-8, LM2917-8) and its output swings to ground for a zero frequency
input.
The op amp Comparator is fully compatible with the tachometer and has a floating
Transistor as its output. This feature allows either a ground or supply referred load of up
to 50 mA. The collector may be taken above VCC up to a maximum VCE of 28V.
The two basic configurations offered include an 8-pin device with a ground
referenced tachometer input and an internal connection between the tachometer output
and the op amp non-inverting input. This version is well suited for single speed or
frequency switching or fully buffered frequency to voltage conversion applications.
The more versatile configurations provide differential tachometer input and
uncommitted op amp inputs. With this version the tachometer input may be floated and
the op amp becomes suitable for active Filter conditioning of the tachometer output.
Both of these configurations are available with an active Shunt Regulator
connected across the power leads. The Regulator clamps the supply such that stable
frequency to voltage and frequency to current operations are possible with any supply
voltage and a suitable resistor.


Page 12

Applications of LM2907 circuit are
1. Frequency to voltage conversion (tachometer)
2. Speedometers
3. Speed governors
4. Automotive door lock control
5. Clutch control
6. Horn control

5.4 PROCESS OF RECTIFICATION
Studies on various microwave power rectifier configurations show that a bridge
configuration is better than a single diode one. But the dimensions and the cost of that
kind of solution do not meet our objective. This study consists in designing and
simulating a single diode power rectifier in “hybrid technology” with improved
sensitivity at low power levels.
Microwave energy transmitted from space to earth apparently has the potential to
provide environmentally clean electric power on a very large scale. The key to improve
transmission efficiency is the rectifying circuit. The aim of this study is to make a low
cost power rectifier for low and high power levels at a frequency of 2.45GHz with good
efficiency of rectifying operation. The objective also is to increase the detection
sensitivity at low power levels of power.
Different configurations can be used to convert the electromagnetic waves into
DC signal. The study done showed that the use of a bridge is better than a single diode,
but the purpose of this study is to achieve a low cost microwave rectifier with single
Schottky diode for low and high power levels that has a good performance.
The goal of this investigation is the development of a hybrid microwave rectifier
with single Schottky diode. The first study of this circuit is based on the optimization of
the rectifier in order to have a good matching of the input impedance at the desired
frequency 2.45 GHz. Besides the aim of the second study is the increasing of the
detection sensitivity at low levels of power. The efficiency of Schottky diode microwave
rectifying circuit is found to be greater than 90%.


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CHAPTER 6

ADVANTAGES, DISADVANTAGES AND
APPLICATIONS

6.1 ADVANTAGES

1. Charging of mobile phone is done wirelessly
2. We can saving time for charging mobiles
3. Wastage of power is less
4. Mobile get charged as we make call even during long journey
5. Only one microwave transmitter can serve to all the service providers in that area.
6. The need of different types of chargers by different manufacturers is totally
eliminated.

6.2 DISADVANTAGES
1. Wireless transmission of the energy causes some effects to human body, because
of its radiation
2. Network traffic may cause problems in charging
3. Charging depends on network coverage
4. Rate of charging may be of minute range
5. Practical possibilities are not yet applicable as there is no much advancement in
this field.
6. Process is of high cost

6.3 APPLICATIONS
1. As the topics name itself this technology is used for “Wireless charging of mobile
phones”.

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CHAPTER 7

CONCLUSION
Thus this paper successfully demonstrates a novel method of using the power of the
microwave to charge the mobile phones without the use of wired chargers. Thus this
method provides great advantage to the mobile phone users to carry their phones
anywhere even if the place is devoid of facilities for charging. A novel use of the rectenna
and a sensor in a mobile phone could provide a new dimension in the revelation of mobile
phone.


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CHAPTER 8

REFERENCES
1.

Theodore.S.Rappaport, “Wireless Communications Principles and Practice”.

2. Wireless Power Transmission – A Next Generation Power Transmission System,
International Journal of Computer Applications Volume 1 – No. 13.
3. Lander, Cyril W. "2. Rectifying Circuits". Power electronics London: McGrawHill. 3rd edition, 1993.
4. Tae-Whan yoo and Kai Chang, "Theoreticaland Experimental Development of 10
and 35 GHz rectennas" IEEE Transaction on microwave Theory and Techniques,
vol. 40. NO.6. June.1992.
5. Pozar, David M. Microwave Engineering Addison–Wesley Publishing
Company,1993.
6. Hawkins, Joe, etal, "Wireless Space Power Experiment," in Proceedings of the 9th
summer Conference of NASA/USRA Advanced Design Program and
Advanced Space Design Program, June 14-18, 1993.


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