Wireless charging in mobile phones management system.pdf

AN
INTERNSHIP REPORT
ON
WIRELESS CHARGING IN MOBILE PHONE
PROJECT REPORT
BY
KAMAL ACHARYA
(Tribhuvan University)
Date: 2022/04/07

ABSTRACT
Mobile Phones are part of our life. It is the fastest and the easiest medium of communication. Battery life
of mobile phone is always been a problem for manufacturers. People are complaining about their
mobile’s battery life, that they don’t have long battery life and they have to charge their phone several
times. In this paper a new idea is shown to charge your mobile phone anywhere you want without
connecting its charger. This is done using microwaves. Microwaves are the radio waves which provide
communication between two mobile phones. The microwave is sent with the message by the transmitter
using antenna at the frequency of 2.45GHz. Here we are using Microwaves as the source of energy to
charge the phone. We have to add a sensor, a rectenna circuit and a filer in our mobile phone to do the
job. By adding these things we can charge our phone using microwave when we talk. So, as we talk more
we can charge more!!

CONTENTS
1. INTRODUCTION.................................................................................................1
1.1 ELECTROMAGNETIC SPECTRUM… ..................................................... 2
1.2 MICROWAVE REGION ...............................................................................2
2. WIRELESS POWER TRANSMISSION.............................................................3
2.1 WIRELESS POWER TRANSMISSION SYSTEM… .................................. 3
2.2 COMPONENTS OF WIRELESS POWER TRANSMISSION SYSTEM... 4
2.2.1 MICROWAVE GENERATOR..............................................................4
2.2.2 TRANSMITTING ANTENNA...............................................................4
2.2.3 RECTENNA............................................................................................4
3. DESIGN OVERVIEW… .......................................................................................5
3.1 TRANSMITTER ............................................................................................. 6
3.2 ANTENNA....................................................................................................... 7
3.3 RECEIVER & RECEIVER DESIGN .........................................................8-9
3.4 THE PROCESS OF RECTIFICATION ........................................................9
3.5 SENSOR CIRCUITRY ...................................................................................9
4. ADVANTAGES….................................................................................................11
5. DISADVANTAGES….......................................................................................... 11
6. CONCLUSION......................................................................................................12
7. REFERENCE ....................................................................................................... 13

INTRODUCTION
Portable electronic devices are very popular nowadays. As the usage of these portable electronic
devices is increasing, the demands for longer battery life are also increasing. These batteries need to be
recharged or replaced periodically. It is a hassle to charge or change the battery after a while, especially when
there is no power outlet around. Therefore, our team is inspired to design a wireless battery charger. This
wireless battery charger is expected to eliminate all the hassles with today’s battery technology.
As for now, there are no known companies that are developing the wireless battery charger. This
means that there might be a good opportunity in the market for this type of product. Moreover, people tend
to spend more money for convenience that meets the price. The outlook of this device is supported by the
above predictions.
It would be convenient not having to worry about charging or changing the batteries and still have a
working device. The advantage of this device is that it can wirelessly charge up the batteries which can save
time and money in a long run for the general public. Base on this concept, the design team has come up with
a new way to charge the batteries wirelessly. The project is to make a prototype device that converts
microwave signals to DC power. Once the prototype has been proved to be working, it is possible to
implement this prototype into other applications such as in television remote control, fire alarm, clock, and
places that are far to reach to change battery.

1.1 Electromagnetic Spectrum
As we know that when light shone through the prism it is divided in all the colors which we called rainbow, and
technically it is called visible spectrum. So light is made of photons. Photons are bundle of energy. Light is
traveling at the speed of 3,00,000 km/hr So when light hit an object coming on its way it actually rebound from
its surface. And it comes in to our eyes and we can see the object. But color of the object is seen by us is depend
how much amount of energy is rebound as photons from the object. But some theory can’t be explained by taking
the light as the bunch of photos. So some physicians assume that it is some kind of wave. They define an
electromagnetic sanctum of different wave lengths which is divided in two parts. One is electric field and the
other is magnetic field.
1.2 Microwave Region
Microwaves are the Radio wave which has the wave length range of 1 cm to 1 meter. And the frequency is
300MHz to 300GHz.Each and every object on the earth absorb different amount of microwave energy.
Microwave oven converts this microwave energy in to the frequency which the food absorbs and gets energy
from it and get worm. But the bowl containing the food do not get worm because its capacity of absorbing
microwave frequency is different! Microwaves are good at carrying information from one place to other. As the
microwave penetrates the solid material and also it do not have and effect of weather and rain etc. So it is useful
to carry information. There are different frequency bands according to the range of frequencies shown:
Designation Frequency Range
L Band 1 to 2 GHz
S Band 2 to 4 GHz
C Band 4 to 8 GHz
X Band 8 to 12 GHz
Ku Band 12 to 18 GHz
K Band 18 to 26 GHz
Ka Band 26 to 40 GHz
Q Band 30 to 50 GHz
U Band 40 to 60 GHz
V Band 46 to 56 GHz
W Band 56 to 100 GHz
We will use S Band for our experiment. As Industrial, Scientific and Medical (ISM) some bands are reserve for
some specific purpose. So we can’t use it. Here S band is freely available band which we can use for experiment.

WIRELESS POWER TRASMISSION
Nikolas Tesla is the father of wireless electricity transmission. Who first transmitted electricity without wire.
Magnetic induction is the main principle behind the wireless power transmission. As we put one coil carrying
current through it, it creates a magnetic field near to it. And if we put other coil over there than it is induce by
the first coil and it carry current from it! This is the simple principle behind it.
2.1 Wireless Power Transmission System
William C. Brown demonstrated how power can be transfer through space using microwaves. The concept of
wireless power transmission is shown the block diagram.
Figure1
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 Recteena 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.

2.2 Components of wireless power transmission system
The important components of this system are Microwave generator, Transmitting antenna, and the receiving
antenna.
2.2.1. Microwave Generator
The Microwave Generator is the one which generates the microwave of preferred frequency. It generates the
Microwave by the interaction of steam of elections and the magnetic field.
2.2.2 Transmitting Antenna
There are many kind of slotted wave guide antenna available. Like parabolic dish antenna, microstrip patch
antenna are the popular type of transmitting antenna.
2.2.3 Rectenna
A rectenna is a rectifying antenna, a special type of antenna that is used to convert microwave energy into direct
current electricity. A simple rectenna element consists of a dipole antenna with an RF diode connected across the
dipole elements. The current included by the microwaves in the antenna is rectified by the diode. Which powers
a load connected across the diode. Schottky diodes are used because they have low voltage drop and high speed
so that they have low power loss.
Figure 2

SPECIFICATIONS
The design is separated into three subsystems: the transmitter, the antenna, and the charging circuit. This charger will
charge the battery by utilizing the microwave signal at 900 MHz frequency. It will convert the microwave signal to DC
signal, and then it will use the DC signal to charge the battery. Below are the design specifications of the charger circuit.
Design Specifications
Source frequencies: 900 MHz
Charging distance: 1 feet
Voltage output: 2.0V
Power output: 60 mW
Battery type: One AAA
DESIGN OVERVIEW
This wireless battery charger is designed to operate at 900 MHz. In this project, a power transmitter acts as the
power source. It will transmit power to the receiver side. And then, the rectifier circuit in the receiver will convert
the RF/ microwave signal into DC signal. After the DC signal is produced, the charging circuit will store the
power into the battery. Here is the block diagram of the overall design.
Figure: 3

3.1. Transmitter
A magnetron is a diode vacuum tube. Filament in the tube act as the cathode. Magnetron is actually act as a
oscillator to produce microwaves. It can be done by putting magnet between the resonating chambers which is
the center of the oscillator. These resonating chambers are called the anode of the magnetron. When
electrons come out from the cathode it direct towards the Anode. As it pass through the magnetic field it start
circulating in the resonating cavity and start producing waves according to its frequency. And the generated RF
signal flow outside of the chamber.
Figure: 4 (a) Figure: 4 (b) - 900 MHz Video/Audio Transmitter
Since the group does not design the transmitter, therefore the design is mainly focus on the receiver side. A power
transmitter is bought from a commercial website. It is a 900 MHz video/audio transmitter. Here’s the specification
of the transmitter.
Power: 12V DC, 900 mA
Output Power: 3 Watts
Operating Frequency: 900 MHz
Connector Type: SMA – Female
Output Impedance: 50 Ω

3.2. Antenna
The antenna plays a very important role. To charge a battery, a high DC power signal is needed. The
wireless battery charger circuit must keep the power loss to the minimal. Therefore, there are many considerations
to choose the correct parts for the design. The considerations of choosing the appropriate antenna are:
1. Impedance of the antenna
2. Gain of the antenna
Taking the above design spec in consideration, the team found Yagi antennas that fit our spec. Below is a
picture of the Yagi antenna.
Figure 5: A picture of the 9 dBi gain Yagi antenna
The impedance of the antenna should match with the output impedance of the power transmitter and input
impedance of the rectifier circuit. Non-matching impedance between circuits can cause a tremendous power loss
due to signal distortion. Since the output impedance of the transmitter is 50 Ω, the antenna should also have 50
Ω impedance.
The higher of the antenna gain yields a better result of the design. However, higher gain will also
increase the cost and the size of the antenna. This becomes a major factor in choosing the antenna due to the
group’s limited financial resources. After consideration, a 9 dBi Yagi antenna is chosen for the design

3.3. Receiver
The receiver’s main purpose is to charge an AAA battery. A simple battery charging theory is to run
current through the battery, and apply a voltage difference between the terminals of the battery to reverse the
chemical process. By doing so, it recharges the battery. There are other efficient and faster ways to charge the
battery, but it requires a large amount of energy which the wireless battery charger cannot obtain, yet. Therefore,
in our design, we use a straight forward method to charge the battery.
Microwave signal is an AC signal with a frequency range of 1 GHz – 1000 GHz. 900 MHz is in between
the RF/ Microwave range. No matter how high the frequency is, AC signal is still AC signal. Therefore, the signal
can also be treated as a low frequency AC signal. In order to get a DC signal out of the AC signal, a rectifier
circuit is needed.
Figure 6: Full-wave Rectifier Circuit
A full-wave rectifier is chosen for the project due to its simplicity and efficiency in converting the AC
signal. The full-wave rectifier is consisted of four diodes. Since the power received by the receiver will be
relatively low and the signal frequency is high, the diodes are required to have a very low turn on voltage and
operating frequency at 900 MHz. For this reason, a Schottky diode by Skyworks is chosen for the design.
At the output of the rectifier, the signal is not a fully DC signal yet. Thus, by adding a capacitor and a
resistor can smooth out the output to become DC signal. However, the time constant produced by the capacitor
and the resistor should be calculated carefully to fit the desired time constant.
Figure 7: Full-Wave Rectifier with Capacitor and resistor.

Receiver Design
The basic addition to the mobile phone is going to be type of antenna that is used to directly con-vert
microwave energy into DC electricity. Actually the size of rectenna can be reducing using the Nano technology.
Fig 8: Whole set up for charging
We also have to add a sensor at receiver side. As we know we are going to charge the phone while a person
is talking. So here sensor is used to detect wither the phone is using microwaves or not.
3.4. The Process of Rectification
Microwave can easily travel through the media but it also loses some energy. So our key objec-tive is to
rectify the circuit and to rectify the waves at the low cost. And also we have to make the detection more sensitive. As
we know that bridge rectification is more efficient than the single diode we use this for the better performance. We
use the shottky diode to get the batter imped-ance. The Schottky barrier diode is a ideal diode, such as for a 1 ampere
limited current PN interface. Another advantage of the Schottky barrier diode is a very low noise index that is very
important for a communication receiver; its working scope may reach20GHz.
3.5. Sensor Circuitry
The sensor circuitry is a any message signal. This is very important as the phone has to be charged as long
as the user is talking. . Thus a simple frequency to voltage converter would serve our purpose. And this converter
would act as switches to trigger the retina circuit to on. Here in India the operating frequency of the GSM is 900 MHz
to 1800 MHz. We can use LM2907 for F to V conversion. The general block diagram for the LM2907 is given below
in fig.

Fig 9: Block diagram of LM2907
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.

VI. TESTING AND DATA
After building the complete final designed circuit,
we needed to know the output effectiveness in
respect to distance. The following data was taken
by using a multi-meter measuring voltage and
current values versus the distance between the
two antennas. Distance (ft)
Volts (V) Current (mA) Power (mW)
0.5 3.4 27 91.8
1 3.24 17.2 55.728
1.5 3.1 9.8 30.38
2 3 7.3 21.9
2.5 2.7 4 10.8
3 1.93 1.5 2.895
3.5 1.4 0.51 0.714
4 1.29 0.03 0.0387
Volts Vs. Distance00.511.522.533.5400.511.522.533.544.5Distance (ft)Voltage (V)Volts (V)
Figure 14a: Voltage versus distance chart
Current Vs Distance05101520253000.511.522.533.544.5Distance (ft)Current (mA)Current (mA)
Figure 14b: Current Vs. Distance Chart

ADVANTAGES
1. Charging of mobile phone is done wirelessly.
2. We can saving time for chageing mobiles.
3. Wastage of power is less.
4. Better than witricity as the distance the witricity can cover is about 20 meters whereas in this technology
we are using base station for transmission that can cover more area.
5. Mobile get charged as we make call even during long journey.
DISADVANTAGES
1. Radiation problems may occur.
2. Network traffic may cause problem in charging.
3. Charging depends on network coverage.
4. Rate of charging may be minute range.

Marketing Plan
The working prototype uses Yagi antennas for the design. The prototype may not seem like an attractive
design for today’s wireless devices; however it could be implemented into other applications. For
instance, it could be implemented onto devices in the tower and only charge up when needed. The team
strives to improve the wireless charger using the spiral patch antennas in the future. The spiral antenna
is able to pick up a wider range of frequencies instead of just tuned to one particular frequency. In
addition, the spiral antennas become smaller at higher frequency which is small enough to fit in a cell
phone or any wireless devices. The multiple rectifier design will also increase the received power.
Therefore, these improvements show that this project still holds valid market demands.

CONCLUSION
In conclusion, power loss and efficiency are the major problems for this design project. Our design
team has noticed the potential problem whether the converted DC power will be significant enough to charge up
the battery. Therefore, the characteristics of the diodes should be mounted directly onto the antenna for
minimum power dissipation. In addition to harmonics, the nonlinear diode creates a DC-bias in the resonant
circuit which can be extracted without affecting the RF/ microwave characteristics of the resonant circuit. The
time varying voltage and current relationship at the physical point of the diode in the cavity determines the loss
in the diode and, consequently, the RF/ microwave to DC efficiency.
As the wireless technology is getting popular nowadays, the demand of battery is also increasing. The
battery needs to be recharged or changed eventually. Therefore our team is inspired to design the wireless
battery charger. This wireless battery charger will eliminate all the hassle with the battery.
As for now, there are no known companies which develop the wireless battery charger. This means that the
opportunity is very big. Also, people tend to spend more money for convenience. It gives more reason that this
device will have a very good market.

References
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PROJECT. Authorea. August 01, 2024. DOI: https://doi.org/10.22541/au.172254872.26972790/v1
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