WIRELESS CHARGING OF MOBILE PHONES USING MICROWAVES document.docx

WIRELESS CHARGING OF MOBILE PHONES USING MICROWAVES

ABSTRACT

With mobile phones becoming a basic part of life, the recharging of mobile phone batteries has always been a problem. The mobile phones vary in their talk time and battery standby according to their manufacture and batteries. All these phones irrespective of their manufacturer and batteries have to be put to recharge after the battery has drained out. The main objective of this current proposal is to make the recharging of the mobile phones independent of their manufacturer and battery make. In this paper a new proposal has been made so as to make the recharging of the mobile phones is done automatically as you talk in your mobile phone! This is done by use of microwaves. The microwave signal is transmitted from the transmitter along with the message signal using special kind of antennas called slotted wave guide antenna at a frequency is 2.45 GHz. There are minimal additions, which have to be made in the mobile handsets, which are the addition of a sensor, a Rectenna, and a filter. With the above setup, the need for separate chargers for mobile phones is eliminated and makes charging universal. Thus the more you talk, the more is your mobile phone charged! With this proposal the manufacturers would be able to remove the talk time and battery standby from their phone specifications.

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1. INTRODUCTION

Smartphones are changing the way we live our lives, both online and off. With each new model, we are used to getting more processor speed, new features and programs, and entire new ways of using them. Despite increased capabilities, battery life simply hasn’t kept up. For most users, phones are sending out sad bleeps by lunchtime, signaling a low battery.

Wireless charging is set to change this. We want to eradicate the problem of the dead battery. 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. When white light is shone through a prism it is separated out into all the colors of the rainbow, this is the visible spectrum. So white light is a mixture of all colors. Black is not a color, it is what you get when all the light is taken away. Some physicists pretend that light consists of tiny particles which they call photons.

They travel at the speed of light The speed of light is about 300,000,000 m/s. The visible spectrum is just one small part of the electromagnetic spectrum. These electromagnetic waves are made up of to two parts. The first part is an electric field and the second part is a magnetic field. So that is why they are called electromagnetic waves. The two fields are at right angles to each other. The "electromagnetic spectrum" of an object has a different meaning, and is 2

instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object. The electromagnetic spectrum extends from below the low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometres down to a fraction of the size of an atom.

Microwaves are radio waves (a form of electromagnetic radiation) with wavelengths ranging from as long as one meter to as short as one millimeter. The prefix "micro-" in "microwave" is not meant to suggest a wavelength in the micrometer range. It indicates that microwaves are "small" compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. Microwave technology is extensively used for point-to-point telecommunications (i.e., non-broadcast uses).

Microwaves are especially suitable for this use since they are more easily focused into narrow beams than radio waves, allowing frequency reuse; their comparatively higher frequencies allow broad bandwidth and high data transmission rates, and antenna sizes are smaller than at lower frequencies because antenna size is inversely proportional to transmitted frequency. Microwaves are used in spacecraft communication, and much of the world's data, TV, and telephone communications are transmitted long distances by microwaves between ground stations and communications satellites.

Microwaves are also employed in microwave ovens and in radar technology.With mobile phones becoming a basic part of life, the recharging of mobile phone batteries has always been a problem. The mobile phones vary in their talk time and battery standby according to their manufacturer and batteries. All these phones irrespective of their manufacturer and batteries have to be put to recharge after the battery has drained out. The main objective of this current proposal is to make the recharging of the mobile phones independent of their manufacturer and battery make. In this paper a new proposal has been made so as to make the recharging of the mobile phones is done automatically as you talk in your mobile phone! This is done by use of microwaves. The microwave signal is transmitted from the transmitter along with the message

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signal using special kind of antennas called slotted wave guide antenna at a frequency is 2.45 GHz.

The basic addition to the mobile phone is going to be the rectenna. A rectenna is a rectifying antenna, a special type 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. Rectenna 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 rectenna, 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.

A rectenna comprises of a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power. 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 as shown in Fig... The diode rectifies the current induced in the antenna by the microwaves. Rectenna are highly efficient at converting microwave energy to electricity.of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arrangedin 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.

Rectenna 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 rectenna, 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. A rectenna comprises of a mesh of dipoles and diodes for absorbing microwave energy from a

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transmitter and converting it into electric power. 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 as shown in Fig... The diode rectifies the current induced in the antenna by the microwaves. Rectenna are highly efficient at converting microwave energy to electricity. 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. The Mobile Handset should additionally have a device, ―Rectenna‖ which would make it bulky and hence device size up to molecular level is essential. The main disadvantages of wireless charging are its lower efficiency and increased resistive heating in comparison to direct contact. Implementations using lower frequencies or older drive, Technologies charge more slowly and generate heat within most portable electronics. Due to the lower efficiency, devices can take longer to charge when supplied power is equal.

Although wireless charging might sound like the stuff of science fiction, this is not a farfetched vision of the future. The technology and theory behind wireless charging have been around for a long time – the idea was initially suggested by Nikola Tesla, who demonstrated the principle of wireless charging at the turn of the century. The technology is also closer to you than you may think: it is already a reality in such devices as electric toothbrushes and surgically implanted devices, like artificial hearts.Wireless charging, also known as inductive charging, is based on a few simple principles. The technology requires two coils: a transmitter and a receiver. An alternating current is passed through the transmitter coil, generating a magnetic field. This in turn induces a voltage in the receiver coil; this can be used to power a mobile device or charge a battery.

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2. TYPES OF WIRELESS CHARGING

There are three types of wireless charging.

1. Inductive charging 2. Radio charging 3. Resonance charging

2.1 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. Lower efficiency, waste heat - The main disadvantages of inductive charging are its lower efficiency and increased resistive heating in comparison to direct contact. Implementations using lower frequencies or older drive technologies charge more slowly and generate heat within most portable electronics.Slower charging - due to the lower efficiency, devices can take longer to charge when supplied power is equal.

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More expensive - Inductive charging also requires drive electronics and coils in both device and charger, increasing the complexity and cost of manufacturing.Inconvenience - When a mobile device is connected to a cable, it can be moved around within the limits of the cable and freely operated while charging. In current implementations of inductive charging (such as the Qi standard), the mobile device must be left on a pad, and thus can't be moved around or easily operated while charging.

Newer approaches reduce transfer losses through the use of ultra thin coils, higher frequencies, and optimized drive electronics. This results in more efficient and compact chargers and receivers, facilitating their integration into mobile devices or batteries with minimal changes required.[3][4] These technologies provide charging times comparable to wired approaches, and they are rapidly finding their way into mobile devices.

For example, the Magne Charge vehicle recharger system employs high-frequency induction to deliver high power at an efficiency of 86% (6.6 kW power delivery from a 7.68 kW power draw).

2.2 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.

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2.3 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. Wireless

charging provides an easier and more convenient means to powering a range of Consumer Electronic and Industrial devices. It provides a reliable and low maintenance solution for power transfer compared with traditional cable based contact methods. From smartphones and small electronic devices to mission critical equipment, wireless charging maintains safe, reliable transfer of power to ensure all forms of device and equipment are always charged and ready to go.

3. ELECTRICALENERGY TRANSFER An electric current flowing through a conductor, such as a wire, carries electrical energy. When an electric current passes through a circuit there is an electric field in the dielectric surrounding the conductor; magnetic field lines around the conductor and lines of electric force radially about the conductor. In a direct current circuit, if the current is continuous, the fields are constant; there is a condition of stress in the space surrounding the conductor, which represents stored electric and magnetic energy, just as a compressed spring or a moving mass represents stored energy. In an alternating current circuit, however, the fields also alternate; that is, with every half wave of current and of voltage, the magnetic and the electric field start at the conductor and run outwards into space with the speed of light. Where these alternating fields impinge on another conductor a voltage and a current are induced respectively in any dielectric substance, a field

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of charges is enforced, with a current in relaxation. Any change in the electrical conditions of the circuit, whether internal or external involves a readjustment of the stored magnetic and electric field energy of the circuit, that is, a so-called transient. A transient is of the general character of a condenser discharge through an inductive circuit. The phenomenon of the condenser discharge through an inductive circuit therefore is of the greatest importance to the engineer, as the foremost cause of high-voltage andhigh-frequency troubles in electric circuits.

Electromagnetic induction is proportional to the intensity of the current and voltage in the conductor which produces the fields and to the frequency. The higher the frequency the more intense the inductive effect. Energy is transferred from a conductor that produces the fields (the primary) to any conductor on which the fields impinge (the secondary). Part of the energy of the primary conductor passes inductively across space into secondary conductor and the energy decreases rapidly along the primary conductor. A high frequency current does not pass for long distances along a conductor but rapidly transfers its energy by induction to adjacent conductors.

Higher induction resulting from the higher frequency is the explanation of the apparent difference in the propagation of high frequency disturbances from the propagation of the low frequency power of alternating current systems. The higher the frequency the more preponderant become the inductive effects that transfer energy from circuit to circuit across space. The more rapidly the energy decreases and the current dies out along the circuit, the more local is the phenomenon.

The flow of electric energy thus comprises phenomena inside the conductor[8] and phenomena in the space outside the conductor—the electric field—which, in a continuous current circuit, is a condition of steady magnetic and dielectric stress, and in an alternating current circuit is alternating, that is, an electric wave launched by the conductor to become far-field electromagnetic radiation traveling through space with the speed of light.

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In electric power transmission and distribution, the phenomena inside the conductor are of main importance, and the electric field of the conductor is usually observed only incidentally. Inversely, in the use of electric power for radio telecommunications it is only the electric and magnetic fields outside of the conductor, that is far-field electromagnetic radiation, which is of importance in transmitting the message. The phenomenon in the conductor, the current in the launching structure, is not used.

The electric charge displacement in the conductor produces a magnetic field and resultant lines of electric force. The magnetic field is a maximum in the direction concentric, or approximately so, to the conductor. That is, a ferromagnetic body tends to set itself in a direction at right angles to the conductor. The electric field has a maximum in a direction radial, or approximately so, to the conductor. The electric field component tends in a direction radial to the conductor and dielectric bodies may be attracted or repelled radially to the conductor.

The electric field of a circuit over which energy flows has three main axes at right angles with each other: 1. The magnetic field, concentric with the conductor. 2. The lines of electric force, radial to the conductor. 3. The power gradient, parallel to the conductor.

Where the electric circuit consists of several conductors, the electric fields of the conductors superimpose upon each other, and the resultant magnetic field lines and lines of electric force are not concentric and radial respectively, except approximately in the immediate neighborhood of the conductor. Between parallel conductors they are conjugate of circles. Neither the power consumption in the conductor, nor the magnetic field, nor the electric field, are proportional to the flow of energy through the circuit.

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However, the product of the intensity of the magnetic field and the intensity of the electric field is proportional to the flow of energy or the power, and the power is therefore resolved into a product of the two components i and e, which are chosen proportional respectively to the intensity of the magnetic field and of the electric field. The component called the current is defined as that factor of the electric power which is proportional to the magnetic field, and the other component, called the voltage, is defined as that factor of the electric power which is proportional to the electric field. In radio telecommunications the electric field of the transmit antenna propagates through space as a radio wave and impinges upon the receive antenna where it is observed by its magnetic and electric effect. Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays and gamma rays are shown to be the same electromagnetic radiation phenomenon, differing one from the other only in frequency of vibration.

4. ELECTROMAGNETIC SPECTRUM

Most parts of the electromagnetic spectrum are used in science for spectroscopic and other probing interactions, as ways to study and characterize matter. The types of electromagnetic radiation are broadly classified into the following classes: 1. Gamma radiation , 2. X-ray radiation , 3. Ultraviolet radiation , 4. Visible radiation , 5. Infrared radiation , 6. Microwave radiation and 7. Radio waves

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4.0 FIGURE OF ELECTROMAGNETIC SPECTRUM

The electromagnetic spectrum 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.

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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

4.1 MICROWAVE REGION Microwaves 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. Here we are going to use the S band of the Microwave Spectrum.

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4.1.1 FREQUENCY BANDS TABULAR FORM

Designation

Frequencyrange

L

Band

1

to

2

GHz

S

Band

2

to

4

GHz

C

Band

4

to

8

GHz

X

Band

8

to

12

GHz

to

18

GHz

18

to

26

GHz

26

to

40

GHz

Ku

Band

K

12

Band

Ka

Band

Q

Band

30

to

50

GHz

U

Band

40

to

60

GHz

The frequency selection is another important aspect in transmission. Here 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.

The ISM bands are defined by the ITU-T in S5.138 and S5.150 of the Radio Due to variations in national radio regulations. In recent years they have also been used for license-free errortolerant communications applications such as wireless LANs and Bluetooth: 900 MHz band (33.3

cm)

2.45 IEEE

(also

GSM

GHz 802.11b

wireless

communication

band Ethernet

also

in

India)

(12.2 operates

on

the

cm) 2.45

GHz

band.

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.

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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 noncommercial 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

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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.

4.2 GENERAL 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! 16

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

1. Magnetron

2. Slotted waveguide antenna

The MAGNETRON (A), is a self-contained microwave oscillator that operates differently from thel i n e a r - b e a m t u b e s , s u c h a s t h e T W T a n d t h e k l y s t r o n . V i e w ( B ) i s a s i m p l i f i e d d r a w i n g o f t h e magnetron. CROSSED-ELECTRON and MAGNETIC fields are used in the magnetron to produce the high-power output required in radar and communications equipment. Magnetron is the combination of a simple diode vacuum tube with built in cavity resonators and an extremely powerful permanent magnet.

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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 magnetron is classed as a diode because it has no grid. A magnetic field located in the space between the plate (anode) and the cathode serves as a grid. The plate of a magnetron does not have thesame physical appearance as the plate of an ordinary electron

tube. Since

conventional

inductive-capacitive (LC) networks become

impractical at microwave frequencies, the plate is fabricated into acylindrical copper block containing resonant cavities that serve as tuned circuits.

The magnetron basediffers considerably from the conventional tube base. The magnetron base is short in length and haslarge diameter leads that are carefully sealed into the tube and shielded. The cathode and filament areat the center of the tube and are supported by the filament leads. The filament leads are large and rigidenough to keep the cathode and filament structure fixed in position. The output lead is usually a probeor loops extending into one of the tuned cavities and coupled into a waveguide or coaxial line. The plate structure is a solid block of copper.

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. The cylindrical holes around its circumference are resonant cavities.

A narrow slot runs from eachcavity into the central portion of the tube dividing the inner structure into as many segments as thereare cavities. Alternate segments are strapped 18

together to put the cavities in parallel with regard to theoutput. The cavities control the output frequency. The straps are circular, metal bands that are placedacross the top of the block at the entrance slots to the cavities. Since the cathode must operate at high power, it must be fairly large and must also be able to withstand high operating temperatures. It mustalso have good emission characteristics, particularly under return bombardment by the electrons. This is because most of the output power is provided by the large number of electrons that are emitted whenhigh-velocity electrons return to strike the cathode.

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The cathode is indirectly heated and is constructedof a high-emission material. The open space between the plate and the cathode is called the INTERACTION SPACE. In this space the electric and magnetic fields interact to exert force upon the electrons.

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.

4.2.2 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

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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.

4.2.2 Slotted waveguide antenna

4.2.3 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%.

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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.

4.2.4 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.

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BLOCK DIAGRAM OF RECTENNA

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).

4.3 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

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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. 24

4.4 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.

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4.4 SENSOR CIRCUIT DESIGN

4.5 LM2907/ LM2917 TACHOMETER

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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.

4.5.1 Applications of LM2907 circuit are 1. Frequency to voltage conversion (tachometer) 2. Speedometers 3. Speed governors 27

4. Automotive door lock control 5. Clutch control 6. Horn control

4.6 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.

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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%.

4.7 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.

4.8 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

4.9 APPLICATIONS 1. As the topics name itself this technology is used for ―Wireless charging of mobile phones‖.

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5.

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.

This is just the beginning Wireless charging is already available for low-power applications (up to 5 Watts), suitable for mobile phones and other devices. However, medium- and high-power applications are also being developed, and in the future your kitchen appliances may very well be wireless.

Since wireless charging is set to become so ubiquitous with applications ranging from cell phones to home appliances, there is a real need to ensure that charging is standardized. This is why the Wireless Power Consortium developed Qi – the standard for interoperable wireless charging. With Qi, we want to ensure that your device can be charged wirelessly, no matter where you go, and no matter what brand charger you are using.

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6. 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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BIBILOGRAPHY 

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