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.
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 hasnt
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 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 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 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 far-fetched 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.
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.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
theQi 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, theMagne Chargevehicle recharger system employs
high-frequency induction to deliver high power at an efficiency of
86% (6.6kW power delivery from a 7.68kW 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.
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
chargingprovides 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 TRANSFERAn electric current flowing through
a conductor, such as awire, carries electrical energy. When an
electric current passes through a circuit there is an electric
field in thedielectricsurrounding the conductor; magnetic field
lines around the conductor and lines of electric force radially
about the conductor. In adirect currentcircuit, 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 analternating
currentcircuit, 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 inducedrespectively
in any dielectric substance, a field 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-calledtransient. 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 ofhigh-voltageandhigh-frequencytroubles in
electric circuits.
Electromagnetic induction is proportional to the intensity of
the current and voltage in the conductor which produces the fields
and to thefrequency. 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 conductorthe
electric fieldwhich, 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.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 forradio 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. Themagnetic
field,concentricwith the conductor.2. Thelines of electric
force,radialto the conductor.3. Thepower gradient, parallelto 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, exceptapproximately in the
immediate neighborhoodof the conductor. Between parallel conductors
they are conjugateof 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. 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 componentsiande, 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. Inradiotelecommunications the electric field of the
transmit antenna propagates through space as aradio waveand
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 radiationphenomenon,
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
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.
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.
4.1.1 FREQUENCY BANDS TABULAR FORM
Designation FrequencyrangeL Band 1 to 2 GHzS Band 2 to 4 GHzC
Band 4 to 8 GHzX Band 8 to 12 GHzKu Band 12 to 18 GHzK Band 18 to
26 GHzKa Band 26 to 40 GHzQ Band 30 to 50 GHzU 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
error-tolerant communications applications such as wireless LANs
and Bluetooth: 900 MHz band (33.3 cm) (also GSM communication in
India) 2.45 GHz band (12.2 cm) IEEE 802.11b wireless Ethernet also
operates on the 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.
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.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!
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 thelinear-beam tubes, such as the TWT and
the klystron. View (B) is a simplified drawing of themagnetron.
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.
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 spacebetween the plate (anode) and
the cathode serves as a grid. The plate of a magnetron does not
have thesame physical appearanceasthe plateof anordinary 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. Theplate structure isa 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 centralportion ofthe
tube dividing the innerstructure into asmany segments asthereare
cavities. Alternate segments arestrapped together toput the
cavities inparallelwith 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 highpower, 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
ofelectrons that are emitted whenhigh-velocity electrons return to
strike the cathode.
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 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%.
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.
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 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.
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.
4.4 SENSOR CIRCUIT DESIGN
4.5 LM2907/ LM2917 TACHOMETER
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 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.
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.
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 beginningWireless 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.
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 AddisonWesley 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.
BIBILOGRAPHY http://www.seminarsonly.com
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