wireless charging of mobile phones using microwave full seminar report

WIRELESS CHARGING OF MOBILE USING MICROWAVE

Dept. of ECE SDMIT Ujire

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.



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.



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 short-

wavelength (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



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



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.



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!



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



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



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.



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



(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.



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.



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%.



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”.



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.



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: McGraw-

Hill. 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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