University of Nairobi

School of Engineering

DEPARTMENT OF

ELECTRICAL AND INFORMATION ENGINEERING

PROJECT NO. 72

WIRELESS POWER TRANSMISSION

BY

Wamalwa Paul Wamboka

F17/36466/2010

SUPERVISOR : DR. DHARMADHIKARY VASANT

EXAMINER : DR. AKUON

A final year project report submitted to the University of Nairobi senate in partial fulfillment of

the requirements for the award of Bachelor of Science degree in Electrical and Electronic

Engineering.

Date of Submission: 16TH

MAY 2016

ii

Declaration

I, Paul Wamalwa hereby declare that this report is my original work. To the best of my

knowledge, the work presented here has not been presented for a degree in any other Institution

of Higher Learning.

………………………………………… …………………

Name of student Date

This report has been submitted for examination with our approval as university supervisor(s).

………………………………………… …………………

Name of supervisor Date

………………………………………… …………………

Name of supervisor Date

iii

Declaration of Originality

NAME OF STUDENT : Wamalwa Paul Wamboka

REGISTRATION NUMBER : F17/36466/2010

COLLEGE : Architecture and Engineering

FACULTY/SCHOOL/INSTITUTE : Engineering

DEPARTMENT : Electrical and Information Engineering

COURSE NAME : Bachelor of Science in Electrical and Electronic Engineering

TITLE OF WORK: WIRELESS POWER TRANSMISSION

1) I understand what plagiarism is and I am aware of the university policy in this regard.

2) I declare that this final year project report is my original work and has not been submitted

elsewhere for examination, award of a degree or publication. Where other people’s work or my

own work has been used, this has properly been acknowledged and referenced in accordance

with the University of Nairobi’s requirements.

3) I have not sought or used the services of any professional agencies to produce this work.

4) I have not allowed, and shall not allow anyone to copy my work with the intention of passing

it off as his/her own work.

5) I understand that any false claim in respect of this work shall result in disciplinary action, in

accordance with University anti-plagiarism policy

iv

Dedication

I dedicate this project to my family who have always been there for me through this journey and my late

brother Timothy who was a great inspiration to me.

v

Acknowledgement

First and foremost, I thank the Almighty God for His continual guidance throughout my

academic work to the accomplishment of this project. The psychological and financial support

and encouragement from my family greatly aided the accomplishment of this project and to them

I am very grateful. Special thanks to my father and mother for their sacrifices and guidance.

I am very grateful to my supervisor, Dr. Dharmadhikary Vasant and his assistant Mr. Gevira

Omondi for their useful guidance and incites throughout the project, it has been a great pleasure

for me to get an opportunity to work under the tutelage of both of you.

My appreciation goes to all my lecturers, lab technologists in the department of Electrical and

Electronics Engineering at the University of Nairobi who impacted knowledge in me and

accorded me help. Lastly to my classmates and friends in the department thank you.

vi

Contents

Declaration...................................................................................................................................... ii

Declaration of Originality .............................................................................................................. iii

Dedication ...................................................................................................................................... iv

Acknowledgement .......................................................................................................................... v

LIST OF TABLES....................................................................................................................... viii

LIST OF FIGURES ....................................................................................................................... ix

Abstract .......................................................................................................................................... xi

List of Abbreviations .................................................................................................................... xii

CHAPTER 1: INTRODUCTION................................................................................................... 1

1.1Background ............................................................................................................................ 1

1.2 Problem Statement ................................................................................................................ 1

1.3 Objectives.............................................................................................................................. 2

1.3.1 Overall objective............................................................................................................. 2

1.3.2 Specific objectives .......................................................................................................... 2

1.4 Justification for the Study ..................................................................................................... 2

1.5 Scope of work........................................................................................................................ 3

1.6 Project Paper Organization.................................................................................................... 3

CHAPTER 2: LITERATURE REVIEW ........................................................................................ 5

2.1 Outline of the Chapter ........................................................................................................... 5

2.2 History of Wireless Power Transfer...................................................................................... 5

2.3 Main concepts of wireless transmission of electric energy................................................... 6

2.4 Health and safety considerations........................................................................................... 9

2.5 WPT Standards and Alliances............................................................................................. 10

Qi by the Wireless Power Consortium (WPC)...................................................................... 10

Rezence by the Alliance for Wireless Power (A4WP).......................................................... 10

Power Matters Alliance (PMA)............................................................................................. 10

CHAPTER 3: THEORETICAL FRAMEWORK......................................................................... 12

CHAPTER 4: METHODS AND MATERIALS .......................................................................... 17

4.1 General Principle of Design ................................................................................................ 17

4.2Hardware and Software Components................................................................................... 20

vii

4.2.1.1Power Supply.............................................................................................................. 21

4.2.1.2DC - DC Boost Converter .......................................................................................... 21

4.2.1.3 Royer Oscillator......................................................................................................... 22

4.2.1.4 Full Wave Bridge Rectifier........................................................................................ 23

4.2.1.5 The Microcontroller Unit........................................................................................... 25

4.2.1.6 The LCD Screen ........................................................................................................ 28

4.2.1.7 Switching Circuit ....................................................................................................... 30

4.2.2 Software ........................................................................................................................... 31

4.2.2.1USBasp ....................................................................................................................... 31

4.2.2.2 Programming Language ............................................................................................ 32

CHAPTER 5: RESULTS AND DISCUSSIONS ......................................................................... 34

5.1 Results ................................................................................................................................. 34

5.2 Analysis and Discussion ..................................................................................................... 37

CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS................................................ 40

6.1 Conclusions ......................................................................................................................... 40

6.2. Recommendations .............................................................................................................. 41

REFERENCES ............................................................................................................................. 42

APPENDICES .............................................................................................................................. 43

viii

LIST OF TABLES

Table 2.1: Summary of main WPT Interface 1............................................................................. 11

ix

LIST OF FIGURES

Fig 2.1: Wardenclyffe Tower 1....................................................................................................... 6

Fig 2.2: Classification of WPT 1 .................................................................................................... 7

Fig: 2.3 Microwave Power Transfers 1........................................................................................... 8

Fig 3.2: Magnitude of B 1............................................................................................................. 13

Fig 3.3: Magnitude of A1.............................................................................................................. 14

Fig: 4.1 Design 1........................................................................................................................... 17

Fig: 4.2 Transmitter section circuit 1 ............................................................................................ 18

Fig: 4.2 transmitter section circuit 2 ............................................................................................. 18

Fig: 4.3 Receiver Circuit 1............................................................................................................ 19

Fig 4.4: Power Supply 1................................................................................................................ 21

Fig 4.5: switching regulator1 ........................................................................................................ 22

Fig 4.6: Oscillator 1 ...................................................................................................................... 23

Fig 4.7: Flow of Current 1 ............................................................................................................ 24

Fig 4.8: Flow of Current 1 ............................................................................................................ 25

Fig 4.9: Port Diagram of the AT mega 328P 1 ............................................................................. 28

x

Fig 4.10: 16X2 LCD 1 .................................................................................................................. 29

Fig 4.11: LCD &AT mega 328 connection 1 ............................................................................... 29

Fig 4.12: Multiplexer switch 1...................................................................................................... 30

Fig 4.13: USBasp Connection 1.................................................................................................... 31

Fig 4.14: Code flowchart 1 ........................................................................................................... 33

Fig 5.1: Components on the Veroboard 1 .................................................................................... 34

Fig 5.2: Imbedded Coils 1............................................................................................................ 35

Fig 5.3: Fabrication 1.................................................................................................................... 36

Fig 5.4: LED 1 .............................................................................................................................. 37

Fig 5.5: LED 2 1 ........................................................................................................................... 37

xi

Abstract

Wireless charging of gadgets is one of the new emerging technologies in the world at the

moment. The most common method used at the moment is wireless power transfer by inductive

coupling. . Wireless power transfer is one of the simplest and inexpensive ways of charging as it

eliminate the use of conventional copper cables and current carrying wires. In this project write

up, a methodology and principle of operation are devised for wireless power transfer through

inductive coupling, and a feasible design is modeled accordingly. The inductive coupling

technique is used since currently it’s the easiest method of wireless power transfer because of

high efficiency and large amount of the energy transferred. In the report paper, results of

experiments done to check wireless working will be shown. Also to further show its versatility

and range of applications the power transferred will be used to charge a battery with the aid of

additional circuitry. We will also study the effect of placing hurdles between the transmitter and

receiver so as to establish if it is an alternative in the medical industry for charging pace makers

etc. This research work focuses on the study of wireless power transfer for the purpose of

transferring energy at maximum efficiency within a small range or in the near field region

xii

List of Abbreviations

EMF Electromotive force

LCD Liquid Crystal Display

LED Light Emitting Diode

MOSFET Metal–Oxide–Semiconductor Field-Effect Transistor

Q Factor Quality factor

RF Radio frequency

RFID Radio frequency identification

RX Receiver

SAR Specific absorption rate

TX Transmitter

USB Universal serial bus

WPT Wireless power transfer

1

CHAPTER 1: INTRODUCTION

1.1Background

If you are using an electronic device perhaps a mobile phone and you need to recharge the

battery then you will probably have to get a charger and connect the phone to the wire. But what

if you could charge it without having to connect it to wire? Meaning power will be transferred

wirelessly. This is possible through a concept called Wireless Power Transmission. Research and

studies have been done ever since the 19th century but it is only recently that this concept has

begun to be implemented.

Currently engineers are trying to discover how to increase the efficiency of power transmitted

wirelessly and also methods that that are safe to human beings and the environment and

notwithstanding, methods that are cheaper and hence can be commercially viable. Though still in

the early stages, several electronic companies are beginning to roll out devices that can

wirelessly transmit power.

Wireless power transmission (WPT) is based on the principle of electromagnetic induction.

Electromagnetic induction works on the concept of a primary coil generating a predominantly

magnetic field and a secondary coil being within that field so a current is induced within its coils.

This causes the relatively short range due to the amount of power required to produce an

electromagnetic field.

1.2 Problem Statement

The project seeks to eliminate the use of wires in the transmission of power from the source to

the device to be powered. Although WPT is based on electromagnetic induction, there are

various methods that are used. Some are less efficient than others and costly while others don’t

allow for a longer range of transmission. In this project, it is required to design and construct an

electronic device that shall transmit power within a small range. The device can then be used to

charge batteries for devices like pace makers.

In the project a suitable method will be used to ensure that enough power is transmitted

wirelessly so that it can then charge batteries. The major challenge will be in the coupling circuit

which comprises of the coils where electromagnetic induction occurs. The number of turns of the

coil, inductance

2

1.3 Objectives

The project has a main objective whose achievement is aided by breaking it further down into

other smaller specific objectives. This helps in showing comprehensively how the final objective

of the project is achieved in a clear and concise manner.

1.3.1 Overall objectiveThe main objective of the project is to develop a device for wireless power transfer

1.3.2 Specific objectivesThe project will be divided into the following specific objectives that will aid in achieving the

main objective

Design and assemble a power supply unit.

Step up the dc supply.

Design and assemble an appropriate oscillator.

Develop transmitter and receiver coils.

Design the receiver module and rectify the ac voltage received on the receiver

coil.

Designing a battery charging circuit.

1.4 Justification for the Study

The need for devices that can wirelessly transmit power has over the years increased. Currently a

lot of research is being conducted in order to obtain suitable methods that can be used in the

development of such devices. The following are reasons why it is important

a) Flexibility: WPT will eliminate the use of conductors and wires. Rather than have

many wires running from a power source to power devices, the power can be

transmitted wirelessly hence the mess caused by cables can be avoided and also more

devices can be powered without having them all placed next to the power source

b) Safety: With the increase in electrification in areas, cases of electrical shocks have

been rampant as people and even animals end up touching the conductors. WPT will

eliminate these conductors hence preventing the electrical shocks.

c) Convenience: The application of WPT will enable the convenient use of devices. For

example, in the medical field pacemakers which use batteries can be recharged rather

3

than having a surgery every time the battery life is over. This will save on costs for

surgery and also is a more convenient option.

d) Reliability: Many times people are using a device and it runs out of power yet one

doesn’t have a cord to charge the device or perhaps there is no source of power

around. However with WPT the devices can be charged wirelessly hence the risk of

low battery power will be eliminated.

1.5 Scope of work

This project covers the hardware and software design and implementation of a device that will be

able to transfer power wirelessly. The study will look into the methods that are currently in use

and seek to improve on the areas where the performance is low. The hardware system will

involve the design and construction of a transmitter and receiver modules. Once there is proof

that power has been transmitted, a battery charging circuit will be designed and developed to

charge a 9V battery so as to show the application of a wireless power transfer device. The

software system will include code that will control ensure the system is intelligent enough to

determine the battery capacity and also to display the various parameters that are important.

1.6 Project Paper OrganizationThis project paper comprises five chapters namely:

Chapter 1:Introduction

This gives the project definition, project overview, objectives, project justification and

scope of work.

Chapter 2: Literature Review

This chapter presents information on the evolution and present state of theory, practice

and research of wireless power transmission.

Chapter 3: Theoretical Framework

In this chapter the theory behind the design of the project is given.

Chapter 4: Methodology and Materials

This chapter gives a detailed explanation on how the device once assembled operates. It

also explains the components used and their role in the design of each part of the device.

Chapter 5: Results and Analysis

4

This chapter, the results obtained are explained and discussed. The modifications that

were carried out are also explained in this section.

Chapter 6: Conclusion and Recommendations

This chapter gives the conclusion and recommendations after completion of the final year

project. It covers assessment of whether project objectives and scope were achieved, a

highlight of areas for future development, bibliography and appendices.

5

CHAPTER 2: LITERATURE REVIEW

2.1 Outline of the Chapter

This chapter contains an evaluation of the current work with respect to the existing works. It is

devoted to a critical review of the technical and academic literature on previous works done on

wireless power transfer

Approach adopted: The following approach is adopted for this chapter;

History of Wireless Power Transfer

Main concepts of wireless transmission of electric energy

Health and safety considerations

WPT Standards and Alliances

2.2 History of Wireless Power Transfer

What exactly is wireless power transfer? This is the transmission of electrical energy from a

power source to an electrical load, such as an electrical power grid or a consuming device,

without the use of discrete man-made conductors.

The word wireless from a basic description means without wires.

Wireless power transmission (WPT) is one of the fields of engineering that has in the past few

years received a lot of attention. A lot of companies are spending millions of dollars trying to

research and develop ways of transferring power wirelessly. However the concept of WPT has

been in existence for over a century.

This concept was first discussed in the late 19th century. Nikola Tesla was the brains behind this

concept. He together with Heinrich Hertz theorized the possibility of power being transmitted

wirelessly. Tesla’s main idea was to use the planet as the conductor to transmit power to any

point on the earth. In 1899 Tesla successfully managed to illustrate the concept by powering

fluorescent lamps 25 miles away from the source of power. In 1901 Tesla built the Wardenclyffe

Tower.

6

His intentions were to use it to transmit messages and also to incorporate his WPT ideas. This

however wasn’t fruitful as his financier refused to invest in the project. Tesla’s ideas were then

dismissed as being impractical and unsafe.

Later on William .C. Brown came up with the theory of microwaves. His ideas majored on

beaming electric power from one point to another without wires, to vacuum tubes and solar-

power satellites using microwaves. Around 1960, he invented the rectenna which converts

microwave to dc power. This was a major breakthrough in WPT. This contributed much to the

modern development of microwave power transmission which forms a major basis of the

research and development of WPT currently.

The next step towards WPT was development of the RFID system.

2.3 Main concepts of wireless transmission of electric energy

As a result of the extensive research in WPT, various categories have arisen. WPT can be

categorized in terms of efficiency, distance of transmission, power level and size. Classification

based on distance of transmission however is more relevant.

Fig 2.1: Wardenclyffe Tower 1

7

For any electromagnetic source both electric (E-fields) and magnetic (H-fields) fields are

generated around it. These fields are characterized by the radiative and non-radiative

components. Depending on the distance from the source they can either be near field, transition

zone or far field. The transition zone possesses characteristics of both the near and far field

transfers.

The near field region can be said to be the found within the radius of a wavelength while far field

region is the area outside a radius of two wavelengths. This however is for transmitters and

receivers that have diameters shorter than the wavelength being used. The near field transfers

have all the polarization types i.e. vertical, horizontal, elliptical and circular while the far field

transfer only has one type.

This far in research the near field transfer has been found to have a higher efficiency during

transfer of power. This can be attributed to the decrease in both electric and magnetic fields

proportionally to the distance from the source. In addition, the near-field region allows higher

diffraction of the wave, resulting in stronger penetrability and weak directivity on a short range.

In light of all these, more research is being focused on development of the near field transfers as

compared to far field transfer.

Both near field transfer and far field are further categorized based on the method of operation of

the transfer. Some of the methods are as follows:

Fig 2.2: Classification of WPT 1

8

Far Field Transfer

a) Microwave Power transfer

In this method, dc is fed to the microwave generator which converts it to microwaves. This

radiation is passed through the coaxial-waveguide adaptor, and then through the waveguide

circulator, which reduces the radiation to exposure from outside power. Finally the radiation

passes through the tuner and directional coupler device, which separates the signal according to

signal propagation direction. The radiation is then transmitted over the air through antennae,

where it is received by the antenna at the rectenna, at which the microwave radiation passes

through a low pass filter, then a matching network, and then a rectifier as it is converted to DC

power

The other methods in far field transfer are:

b) Photo electricity

c) Propagating electromagnetic waves

Fig: 2.3 Microwave Power Transfer

Fig: 2.3 Microwave Power Transfers 1

1

9

Near Field Transfer

a) Inductive Coupling

This will be further elaborated in chapter 3 as it is the method of near field transfer that

will be used in the implementation of the project.

2.4 Health and safety considerations

Wireless power transmission is largely based on the radiation of electromagnetic fields.

However, there are safety limits that determine the levels of human exposure to electromagnetic

fields. Currently two world bodies give directives on the human exposure guidelines. These are

the Institute of Electrical and Electronic Engineers (IEEE) and the International Commission on

Non-Ionizing Radiation Protection (ICNIRP).

The main standards are: “IEEE Standard for Safety Levels with Respect to Human Exposure to

Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz” (IEEE C95.1-2005) and “ICNIRP

Guidelines For Limiting Exposure To Time-Varying Electric, Magnetic and Electromagnetic

Fields (up to 300 GHz).

The purposes of the IEEE [10] and ICNIRP [11] guidelines are similar:

“The purpose of this standard is to provide exposure limits to protect against established

adverse health effects to human health induced by exposure to RF (radio frequency) electric,

magnetic, and electromagnetic fields over the frequency range of 3 kHz to 300 GHz.”[IEEE]

“The main objective of this publication is to establish guidelines for limiting EMF

(electromagnetic field) exposure that will provide protection against known adverse health

effects. An adverse health effect causes a detectable impairment of the health of the exposed

individual or of his or her offspring; a biological effect on the other hand, may or may not result

in an adverse health effect”. [ICNIRP]

Both the IEEE and ICNIRP groups in their recent publications claim that there is no justified

evidence to show that human exposure to radio frequency (RF) electromagnetic fields causes

cancer, however evidence shows that RF electromagnetic fields could actually raise the

temperature of a human, cause heating up of body tissues and may stimulate nerve and muscle

10

tissues. It is in that respect that both bodies recommend limiting human exposure to

electromagnetic field strengths to levels safely below those that cause harm to human beings. In

the case of tissue heating, the IEEE and ICNIRP recommend limiting the specific absorption rate

or SAR, a measure of the amount of electromagnetic energy absorbed by the human body and

turned into heat. In the case of electro-stimulation of nerve and muscle tissues they groups

recommend limiting the internal electric field.

2.5 WPT Standards and Alliances

Qi by the Wireless Power Consortium (WPC)The Qi standard is an inductive coupling power transfer interface standard developed by the

Wireless Power Consortium (WPC). The Consortium was founded in 2008 as cooperation

between European, American and Asian companies in different industries in order to develop a

global standard for the inductive charging technology. The most prominent members include, for

example, Motorola Mobility Inc., Microsoft Corporation, Nokia, ASUSTek Computer Inc., LG

Electronics, Sony Corporation, HTC Corporation, TDK Corporation and Texas Instruments

Rezence by the Alliance for Wireless Power (A4WP)Rezence is a magnetic resonance power transfer standard developed by the Alliance for Wireless

Power (A4WP). A single transmitter can power up to eight receiver devices on mid-range

distances. Communication between transmitter and receiver is “out-of-band” and implemented

via Bluetooth. The A4WP was founded in early 2012 in order to develop a ubiquitous WPT

ecosystem. The most prominent members include Broad-com, Panasonic, Microsoft Corporation,

LG Electronics, Samsung, Logitech, WiTricity, Qualcomm, Incorporated, Gill Electronics,

Hewlett Packard, Integrated Device Technology, Inc., Intel and others.

Power Matters Alliance (PMA)Power Matters Alliance (PMA) is a non-profit organization, which develops inductive and

resonant power transfer standards. PMA was founded in 2012 in order to technically harmonize

and advance multiple inductive WPT standards, promote WPT within the automobiles industry

and popular public infrastructure venues. The most prominent members include Duracell

Powermat, LG Innotek, Panasonic Corporation, Samsung Electronics, Toshiba Corporation,

Sony Corporation, Energous Corporation, Freescale Semiconductor Inc., Integrated Device

Technology (IDT) and Microsoft Corporation.

11

A summary of the main WPT Interface Standards and Alliances as of January 2015.

Organization WPC PMA A4WPEstablished 2008 2012 2012Number of members 203+ 80+ 140+Transfer type Inductive coupling Inductive coupling Magnetic resonanceMax. transfer power 5W (10-15W

soon)

5W (10-15W soon) up to 50WRange Short range Short range Mid-rangeTransfer frequency 100 to 205 kHz 277 to 357 kHz 6.78 MHzLatest version 1.1.2 PMA1.1 A4WP-S-0001 v1.2Certified Products 684 24 -Authorized test labs 10 3 2

Table 2.1: Summary of main WPT Interface 1

12

CHAPTER 3: THEORETICAL FRAMEWORK

3.1 Wireless transfer by Inductive Coupling

This chapter elaborates on the method of wireless power transfer that was selected which is

inductive coupling.

The concept of transmitting power wirelessly is based on electromagnetic fields, precisely due to

electromagnetic induction. Biot-Savart's law, which is similar to Coulomb's law, states that the

magnetic field intensity dH at r due to current element / d\ at r' is dR. It gives the relation

between the magnetic field and magnitude, direction, proximity and length of the electric current

by which it has been generated.

(1)

Where R is the full displacement vector from the current source to the field point, Idl is the

infinitesimal current source point in the wire. A magnetic field of B(r) is produced by the copper

coil. The magnitude of the magnetic field is affected by r which is the distance from the center of

the coil to the field point. The strength of magnetic field B is proportional to the current I in the

coil. Supposing two copper laminated coils are placed within the near the field region while

aligned together side by side a magnetic field is generated. This however only occurs provided

the transmitter coil is powered and the current flowing through it alternating current. This

magnetic field that has been generated by the TX coil at the point x which is on the RX coil is

thus going to be given by

Fig: 3.1Magneticfield1

13

= ( ) (2)

Where N is the number of turns of the coil, I is the transmitter inductor current, a is the radius of

the TX coil while d is the distance of separation between the TX and RX coil. The magnetic flux

that will pass through the Rx coil will be given by:Φ = ∬ (3)

B is the magnetic flux density generated by the transmitter and S is the area of the receiver coil

surface. In the transmitter coil the current flowing is time dependent thus produces magnetic flux

variation in the receiver coil. An electromotive force (emf) will then be induced in the RX coil,

which is obtained by applying Faraday’s law of induction which states that “The induced emf ε

in a coil is proportional to the negative of the rate of change of magnetic flux”. The equation for

emf is as below.= − (4)

For a coil that consists of N loops, the total induced emf would be N times as large:= − Φ(5)

Where Φ is the magnetic flux. The EMF is driving the current in the secondary coil whose

magnetic field is opposing the time variation in the magnetic flux according to Lenz’s law.

Hence, the power is transferred from TX coil to RX coil. An emf may be induced in the

following ways:

(i) by varying the magnitude of B with time as in the figure below

Fig 3.2: Magnitude of B 1

14

(ii) by varying the magnitude of A, i.e., the area enclosed by the loop with time

Self-inductance is the property of the circuit when its own magnetic field is opposing the current

change in the circuit. Self-inductance of the coil can be defined as:= Φ(6)

Where N is the number of turns Φis magnetic flux and I is the current of the coil. By combining

(4) and (6) we obtain:= − (7)

Or= − (8)

Where L is self-inductance of the coil, M is mutual inductance of two coils, I is the current of the

coil. Thus the EMF induced on the coil is directly proportional to the mutual inductance of the

coils and rate at which the current is oscillating. Mutual inductance can also be given by= (9)

Where k is the coupling factor, L1andL2 are TX and RX inductances. The coupling factor

determines the grade of the coupling, i.e. how much flux of the total flux actually penetrated the

receiver coil. It can have a value from 0 to According to (2) and (3) and if the current is

alternating, get:

Φ = ( )( ) (10)

Combining it with (4) gives:

ℰ = − ( ( ) )(11)

Fig 3.3: Magnitude of A1

15

This clearly shows that the voltage induced to the secondary coil depends on the current and

voltage in the primary coil, the frequency of the current and voltage in the primary coil, the

separation distance between the coils and the surface area of the coils. The resulting two coil

coupling system is depicted below.

Here C1 and C2 are tuning capacitors, L1 and L2 are coupled inductors with mutual inductance

M, R1 and R2 represent parasitic resistances (loss resistances in the inductors), d is the distance

between the coils and V1 and V2 are input and output voltages. The output power of the second

coil can be defined as:

( ) (12)

Where the operating frequency of the system, RL is load resistance. Thus the overall efficiency

of the system depends only on the transmission frequency, mutual inductance, coils’ parasitic

resistances and load resistance.

Quality factor (Q factor) which is defined as the ratio of the inductance to the resistance of the

coil determines the energy transmitted and overall efficiency of the system. A higher Q factor

means a lower energy loss and so better transmission efficiency. Usually Q factor has values

from 0 up to 1000 for WPT coils. It is define as

Q= (13)

Fig: 3.4 the two coil coupling system1

16

Where L is the inductance of the coil, R is its resistance and is the operating frequency of the

system. Obviously, Q factor increases when the operating frequency increases. However, when it

reaches its peak values, it will decrease as the operating frequency continues to rise. A higher Q

factor means a narrower band-width, which results in dropped coupling efficiency and the need

of a tuning circuit. The maximum transfer efficiency is defined by:

= (14)

Where k is the coupling factor between two coils, Q1and Q2are the quality factors of the

transmitter and receiver coils. Consequently, in order to reach the maximum efficiency,

developers should optimize the coupling and quality factors of their systems.

17

CHAPTER 4: METHODS AND MATERIALS

4.1 General Principle of Design

From the theory in chapter 4 the general principle of operation was designed using inductive

coupling and ensuring that the power transfer was as efficient as possible and the transfer within

the near field. The design also ensured for purposes of versatility and optimization the battery

charging circuit was energy efficient and prevented losses.

The circuit was divided into two sections:

1. Transmitter Circuit

2. Receiver Circuit

The transmitter circuit comprised of the power supply, boost converter, royer oscillator and the

copper laminated coils. The receiver side had the receiver coil, rectifier, LCD, Atmega 328

microcontroller and the switching circuit that used the CD4066. The figure below shows the

block diagram of the design.

AC power is supplied from the mains and fed to the power supply. It is stepped down and then

rectified to give dc power. The dc voltage is then passed through the voltage regulator LM7805

so as to give a constant 5V dc. This DC signal is however not enough to cause a significant to

create a large emf that will cause the induction. The 5V is then fed to the dc boost converter to

raise the voltage to 30V. The 30V now becomes the input to the royer oscillator circuit. The

oscillator then converts the received DC voltage to AC power with a high frequency.

Fig: 4.1 Design 1

18

The MOSFETS cause a large current which is then supplied to the transmitting copper coil. The

diagram below shows the circuit of the transmitter section.

The transmitter circuit section has two power MOSFETs (IRF540) which are biased using the

resistors R1, R2, R3, R4.There is also a choke made up of inductors L1 & L2.The 8 capacitors C

operate as resonating capacitors to ensure the coils are at resonant frequencies. Oscillators have

feedback, in the case of the royer oscillator negative feedback. The two diodes D1 & D2 thus

provide the cross coupled feedback required. The transmitter coil L which is basically an

inductor is where the electromagnetic induction occurs. The coil used in this case is gauge 26.

When power is given to the oscillator circuit, the DC current starts flowing through the two sides

of the coil (L1&L2) and also to the Drain terminals of the MOSFET. During the same instant,

voltage appears on gate terminal of both the transistors and tries to turn ON the transistors. Any

one of the transistor will be faster than the other and it will turn ON first.

When Q1 turns on first, its drain voltage will be clamped to near ground. Meanwhile Q2 will be

in the off state. Once Q2 is in the conduction state its drain voltage begins rising steadily to peak

and then immediately begins to drops due to the tank circuit formed by the capacitor C and the

primary coil of oscillator through one half cycle. The operating frequency of the oscillator is

determined by the resonance formula given below

Fig: 4.2 Transmitter section circuit 1

Fig: 4.2 transmitter section circuit 2

19

F = ½ × π × √ (LC)

In the receiver side the circuit was as below

When the receiver coil is placed within the near field range from the transmitter coil, the

magnetic field in the transmitter coil extends and it induces an AC voltage which generates a

current flow in the receiver coil of the wireless charger. The transmitted AC voltage is then fed

to the rectifier which converts it to DC. A capacitive filter is used to eliminate any ripples. The

rectified voltage is fed to the voltage regulator LM7805 to ensure that the voltage is regulated

and constant. The output is regulated 5V dc. This power then goes to the power the

microcontroller, LCD and the CD4066 switch.

Fig: 4.3 Receiver Circuit 1

20

Cost Analysis of Components

ITEMS UNIT COST

Microcontroller Atmega 328 1 350

16 X 2 LCD 1 400

Power MOSFETS IR540 2 60

Coil 26 gauge 3 meters 60

Diodes 7 21

Resistors 10 55

Capacitors 20 84

LM7805 Voltage Regulator 1 30

16 MHz Crystal 1 30

LM 2621 1 200

IC Socket 1 20

Inductors 4 24

Veroboard 1 100

1444

21

4.2 Hardware and Software Components

4.2.1Hardware

4.2.1.1Power Supply

The oscillator needed 30V dc supplied. The power supply unit used however gave an output of

5V dc. The power supply contained a transformer that stepped down the 230V ac supplied from

the mains to 9V ac. A full-wave bridge rectifier then rectified the 9V ac. Full wave bridge

rectifier is preferred over the half wave bridge rectifier since, for the half wave rectifier, a large

capacitor will be required to hold up the voltage during the gap whereby an AC cycle is skipped.

The bridge rectifier has an efficiency of 80% hence the rectified output was less than the input.

The output received was 7.2V dc. This voltage however is still erratic and pulsating thus a

smoothening capacitor is required. The smoothening capacitor supplies charge when as the

rectifier voltage falls thus evening out any fluctuations by the signal. The smoothened dc voltage

is then fed to the voltage stabilizer LM7805 which ensures a stable output voltage of 5v.

4.2.1.2 DC - DC Boost Converter

This is required since the voltage required to be fed into the oscillator is 30V yet from the power

supply unit only 5V is being achieved. To step up to 30V we used the switching regulator below.

Fig 4.4: Power Supply 1

22

This switching regulator can operate in the continuous or the discontinuous mode so that the

output voltage is higher. It consists of the following components: an inductor, capacitor,

switching device, diode, and the input voltage source. The switch is usually controlled by a pulse

width modulator. A potentiometer is also available that regulates the output voltage. In the

continuous mode, the switch conducts and thus the current through the inductor is ramped up.

When the switch is turned off, the voltage at point 4 in the above circuit rises rapidly. This is

because the inductor is attempting to maintain the current at a constant. The diode in turn goes on

and thus the inductor dumps the current into capacitor C3 resulting in more energy being

generated and thus a higher output voltage than the input voltage.

4.2.1.3 Royer Oscillator

Oscillators are systems that consist of both passive and active components of a circuit which then

generate sinusoidal waveforms or repetitive waveforms. Oscillator circuits generate waveforms

without the aid external inputs. They convert the dc supply power source to ac power which is

supplied to a load. For this design I used a royer oscillator. This oscillator belongs to the

relaxation oscillators classification since its output is non sinusoidal.

Fig 4.5: switching regulator1

23

The capacitors turn the oscillator into a harmonic oscillator that outputs sine waves. This

oscillator has two parts. The first part is a relaxation oscillator. It is connected as an astable multi

vibrator which converts the dc power fed into it. It then converts the received dc power to a high

frequency ac power. This part generates square waves which are the input of the second part

which is the power amplifier. These waves are the input at the gate terminal of the power

MOSFET.

The second part is the power amplifier. The gate of the first MOSFET is driven by the signal

generated at the oscillator part. This MOSFET provides the voltage and the current needed to

drive the gate of the second MOSFET. When the second MOSFET turns on it allows a large

current from the dc signal to flow to the transmitting coil. The large current generates a large flux

which then induces a high voltage to the receiving coil.

4.2.1.4 Full Wave Bridge Rectifier

The transmitted current received on the receiver side is ac. However for purposes of charging the

battery, dc is needed hence the need for rectification. In the design, a full wave bridge rectifier

instead of a half wave rectifier. It’s basically a full wave rectifier but uses four diodes instead of

two which then form arms that are the bridge rectifier. It was used because of the following

reasons:

Fig 4.6: Oscillator 1

24

i. It doesn’t require a center tap on the secondary winding thus ac voltage can be fed

directly to the bridge circuit.

ii. For its construction, crystal diodes can be used. The diodes are easily available in the

market and cheap. The circuit is also more compact.

iii. The transformer utilization power is higher

There are four diagonal arms. When ac voltage is applied to one arm, the rectified dc voltage is

obtained from the opposite arm. The bridge rectifier operates in positive and negative half cycles.

During the positive cycle point A is positive and point B becomes negative. In this case diodes

D1 and D2 will be conducting while D3 and D4 will be off. D1 and D2 at this point are forward

biased and conducting in series with the load. The current flows in the direction as in the figure

below

During the negative half cycle, the polarity of the ac voltage being fed is reversed such that point

B now is the positive while point A becomes negative. Diodes D3 and D4 in this case will be on

meaning they are forward biased hence can conduct while D1 and D2 which are off will be

reverse biased. Similarly to the positive ac cycle, D3 and D4 will conduct in series with the load

and current will flow as in the figure below

Fig 4.7: Flow of Current 1

25

It is worth noting that current in the load flows in the same direction for both ac cycles. This

therefore means that the current in the full wave cycle is unidirectional. However the rectified dc

voltage had ripples. A capacitive filter was added instead of the inductive filter since the

reactance of the capacitor is much smaller than the resistor value.

4.2.1.5 The Microcontroller Unit

A simple definition of the microcontroller is a computer on a chip. The microcontroller enables

the project to be a standalone system which is able to produce varied reactions to various

situations according to preset controls. The microcontroller in this project is the AT mega 328

microcontroller.

The system is required to alert the user if a load is in place, calculate and display the level of

charge, start the charging if needed and finally cut the charging when the load is fully charged.

To do these actions on its own, the microcontroller needs to be loaded with a program to enable

it execute all these actions.

Types of Microcontrollers

There are several ways in which microcontrollers can be classified. The several aspects of

classification lead to several types of microcontrollers.

Classification based on internal bus width

This classification results into three sub groups. Considering the length of the internal bus, a

microcontroller can either be 8-bit, 16-bit or 32-bit.

8-bit microcontrollers

Fig 4.8: Flow of Current 1

26

8-bit microcontrollers, as the name suggests have a bus width of 8 bits. Examples of such

microcontrollers are Intel 8031/8051, PIC 1X and Motorola MC68HC11 families

16-bit microcontroller

Have greater precision than the 8-bit microcontroller. Has a range of 0X0000 – 0XFFFF (0-

65535) for every cycle. Examples of these microcontrollers are the extended 8051XA, PIC2X,

Intel 8096 and the Motorola MC68HC12 families.

32-bit microcontroller

Used in automated devices, engine control systems, office machines and other embedded

systems. From the name, the bus width is 32 bits and have even greater accuracy than the 16 bit

types. Examples are Intel/Atmel 251 family and PIC3X families

Application of Microcontrollers

Microcontrollers have many applications across the technological fields’ nowadays. Some of the

most common applications are;

In Day to day activities;

Light sensing & controlling devices

Temperature sensing and controlling devices

Fire detection & safety devices

Industrial instrumentation devices

Process control devices

In Industries;

Industrial instrumentation devices

Process control devices

In Metering and measurement devices

Volt Meter

Measuring revolving objects

Current meter

Hand-held metering systems

These are some of the situations and appliances which use microcontrollers to operate.

AT mega 328

This is a single chip microcontroller created by the Atmel cooperation and it belongs to the

megaAVR series. Typical features of this microcontroller are;

27

28 pins (23 are I/O)

32 Kbytes flash memory

1kbyte EEPROM Data memory

Two timers (one 8-bit and one 16-bit )

Supports USART functionalities

Works with an external oscillator of up to 20MHz

The I/O pins are responsible for connections of peripherals of the main system such as the LEDs

and the LCD screen. The crystal is also connected to the microcontroller because the IC will not

work properly without the crystal.

The microcontroller was used to control the charging of the battery. One of the challenges with

this microcontroller was that it has a voltage limit of 5V yet the battery being charged is a 9V

battery. This means it can’t measure the voltage of 9V. To solve this, a voltage divider circuit

was introduced. The range over which the microcontroller can measure voltage can be increased

by using two resistors to create a voltage divider. The voltage divider decreases the voltage being

measured to within the range of the microcontroller analog inputs. Code in the Arduino sketch is

then used to calculate the actual voltage being measured. The microcontroller also sends a signal

to the CD4066 switch to turn of the charging. The measured voltage is then displayed on the

LCD.

28

4.2.1.6 The LCD Screen

In this project, a display screen was used to show various aspects of the project. The LCD

displayed the name of the project and the battery status. Internally, the LCD is made up of a thin

layer of liquid crystals sandwiched between two layers of transparent electrode glass sheets. The

nature of the glass sheets determines the type of the LCD screen. If both glass sheets are

transparent then the LCD is transmissive and if one sheet has a reflective coat then the cell will

be reflective. The liquid crystal molecules are able to twist, therefore changing slightly the

amount of light penetration resulting in different characters being displayed on the screen.

The display unit for this project is a 16X2 LCD as shown below.

Fig 4.9: Port Diagram of the AT mega 328P 1

29

This means that the screen can display a maximum of 16 characters on one line and there are two

lines where the characters can be displayed. The LCD used was HITACHI 44780. It was

connected to the AT mega 328 microcontroller as below. A potentiometer was connected to

control the brightness of the LCD. The LCD model used has additional pins 15 and 16 that were

used to turn the backlight on.

Fig 4.10: 16X2 LCD 1

Fig 4.11: LCD &AT mega 328 connection 1

30

4.2.1.7 Switching Circuit

When the charging is complete, it is important to cut supply to the load so that power is

conserved. The switching off of the circuit is achieved by the IC Cd 4066. Conventional

switching circuit components such as the relay are not possible in this situation because of the

lower power produced after transmission. Had a relay been used in the circuit, there would not

have been enough power for the relay to work and therefore the switch will not work.

The CD 4066 is a low power multiplexing switch circuit which is an ideal replacement for

mechanical switches. The IC has a bandwidth of around 8MHz, current consumption of 1 mA

but it requires a high level power supply voltage since the input impedance of the circuit drops

with higher voltage levels. The circuit cuts supply to the load once the batteries are full so that

power is not lost unnecessarily.

The multiplexer switch diagram is shown below

Fig 4.12: Multiplexer switch 1

31

4.2.2 Software

4.2.2.1 USBasp

This is a USB based programmer for the microcontroller used for burning hex files into AVR

microcontroller. In order to program any microcontroller you need the .HEX file or the sketch

which is the machine code for the microcontroller. This file is generated by the corresponding

assembler software, which converts programming code into machine code. Programming code

can be produced by third party cross compiler software, we used arduino.

To transfer program using it, one end is connected to the computer that has assembler software

and code. The other end is then connected to a6-pin or a 10-pin cable. From this cable, female to

female pins can be used which can then easily be hooked to a breadboard. Regardless of whether

the 6-pin cable or 10-pin cable is used, only 6 pins will be in use, these are the MISO, SCK,

RST, VTG, MOSI, and GND connections.

Fig 4.13: USBasp Connection 1

32

The pins function as follows:

a) MOSI- (Master Out Slave In) - it allows the master device to send data to slave or

target device.

b) MISO- (Master in Slave Out) - it allows slave device/target to send information to

master device.

c) SCK – (serial clock) - this mutual clock shared between master and slave device for

synchronized communication.

d) Reset- (target AVR MCU Reset) - The reset pin for the AVR chip being programmed

must be put in active low in order for programming to occur.

e) VCC- (Power) - The master and slave device both need power in order to operate.

f) GND- (Common Ground) - The master and slave device must share a common power

ground data to the target AVR which is being programmed.

The SCK pin is the clock. It is essential because in order for the master and slave device to

communicate, they need to have a time signal to communicate data in synchrony. The common

clock signal shared between the master and slave device allow for efficient communication.

The RST pin is an essential connection because it must be put to an active low connection in

order for programming to occur between the master and slave device. It is normally held high,

but for programming to occur, it must be put low. It is an active low pin. When the RST pin is

put low, the master slave can communicate on the SCK, MISO, and MOSI lines.

4.2.2.2 Programming Language

A programming language is a constructed language designed to communicate instructions to a

machine. They are used to create programs that control how a machine functions in different

circumstances. This project is done in assembler language. This is a low level programming

language for a microcontroller or other programmable device. The assembler language has a very

strong association with the architecture of the microcontroller hence a good understanding of the

microprocessor architecture is required when programming using assembler.

Programming in assembler language has the following advantages:

Requires less memory and execution time.

Allows hardware specific complex jobs easier

Suits time sensitive jobs

33

During the programming process the flowchart below was used to so that the code could be

developed in segments and then combined to function as one.

Fig 4.14: Code flowchart 1

34

CHAPTER 5: RESULTS AND DISCUSSIONS

5.1 Results

The main objective of the project was to develop a device for wireless power transfer. The

device had to be an electronic circuit. The achievement of this objective was further broken

down into specific objectives which all together aided the development of the device. The other

objectives were as follows:

I. Design and assemble a power supply unit. The power supply was to step down 230V

ac supplied by the mains to 12V ac high frequency. The 12V ac was then to be rectified

to give 5V dc.

II. Step up the dc supply. Using a boost converter, the dc voltage was raised to 30V dc

III. Design and assemble an appropriate oscillator. For the project, a royer oscillator was

found to be most suitable.

After assembling and fabricating the components on the veroboard. The above three objectives

formed the transmitter module. When assembled and fabricated it was as depicted in the figure

below.

Fig 5.1: Components on the Veroboard 1

35

IV. Develop transmitter and receiver coils. Electromagnetic induction occurs between

these two coils and an emf generated on the TX coil that induces a current on the RX

coil. The coils were embedded on the fabricated casing of the modules. However they are

as in the figure below.

V. Design the receiver module and rectify the ac voltage received on the receiver coil.

For A rectifier was needed to output dc power which would be used to power other

components.

Fig 5.2: Imbedded Coils 1

36

VI. Designing a battery charging circuit. The transmitted power was to be used to charge a

battery so as to further demonstrate the application of wireless power transmission in the

modern world. The figure below illustrates the fabrication of the device.

Fig 5.3: Fabrication 1

37

5.2 Analysis and Discussion

5.2.1 Coils

To test if power was transmitted we first soldered an LED to the receiver coil. The test was

successful with only 5V dc powering the oscillator. However the power was too to energize the

battery charging circuit that comprised of an LCD and microprocessor. The voltage was stepped

up using a boost converter to 30V dc. Two receiving coils were used and each had an LED lamp.

They both lit brightly. We then added a set of LEDs and the results were as in the figures below.

In the above figure, the receiving coils were not separated from the transmitter coil. However as

the distance of separation increased the brightness reduced. This proved that indeed the distance

of separation determines the current induced in the receiver coil. As distance increases, less

current is induced from the change of flux. The test LED bulbs lit brightest up to a separation

distance of 5cm between the two coils after which their brightness reduced significantly.

Also, different gauges of the coil were used to determine which was more effective. Currently in

the market the most common are gauge 26 and gauge 16. It was noted that for the coils of gauge

Fig 5.4: LED 1

Fig 5.5: LED 1

Fig 5.5: LED 2

38

16, the distance of separation between the coils had to be shorter and also the brightness of the

bulb was less than for the gauge 26.

Various objects were placed between the receiver and the transmitter coil to test if the shielding

would have an effect on the power being transmitted. It was observed that this didn’t have any

significant effect on the power that was transmitted. However when a magnetic material was

placed in between the coils it had an effect.

5.2.2 Oscillator

The royer oscillator was chosen because of its simplicity yet powerful design. It is capable of

generating very high oscillating current which is necessary to increase the strength of the

magnetic field. This is achieved by the semi-conductor used. In this case, the IR 540 power

mosfets. However due to the large current, heating occurred in the MOSFETs thus heat sinks

were attached to them.

When the voltage was stepped up to 30V dc, upon doing the initial test the transmitter circuit

didn’t oscillate yet the first MOSFET was rapidly heating up. It was discovered that due to

voltage being fed rising too slowly on power up a short circuit occurred. To solve this issue, a

reset switch was introduced between the power supply and the oscillator circuit. The switch also

enabled the circuit to be reset once the MOSFETs heated up.

It was also observed that as much as the voltage to the oscillator had been stepped up, the power

being received on the load coil wasn’t enough to power the battery charging circuit. This was

attributed to the receiver coil being slightly out of resonance thus it wasn’t able to receive the

power well. To solve this we ensured that the coils had the same number of turns and the

capacitors used were identical so that both the transmitter and receiver circuits had the same

resonant frequency.

39

5.2.3 Battery Charging Circuit

The battery charging circuit consisted of the rectifier which converted the ac power to dc, an

Atmega 328 microcontroller, a 16X2 LCD and a CD4066 switch. This part was largely

controlled by the microcontroller. Initially a relay was used as the switch once the battery is full.

However it was drawing more current and thus acted as load. The CD4066 became a better

alternative as it consumed less current and also was less bulky as compared to the single channel

relay.

One of the challenges with modern chargers is that once charging is complete; there is no

notification to the user to stop the charging. To solve this; a buzzer was used so that once the

charging is complete it sounds. However this meant the input signal had to be driven at the same

frequency as that of the buzzer and also it consumes more power. An RGB LED was instead

used. Its operation was coded and loaded to the microcontroller.

It was observed that, once the battery started charging it heavily loaded the rectifier voltage and

caused it to drop significantly. The battery internal resistance is suspected to be the major cause

of this.

40

CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusions

The objectives of the project were met. An electronic device that wirelessly transmits power and

then charges batteries was developed. We were able to design discrete components such as the

royer oscillator, coils and a full bridge voltage rectifier for the system design process.

Conclusions that were drawn from the project study are as follows:

1. Based on the theory of wireless charging via inductive coupling, which was the method

used in the project, it was seen that various aspects i.e. distance, resonant frequency,

quality factor; coil turns ratio determine the efficiency of WPT. In addition there is an

exponential decay for power versus the distance of separation.

2. From the analysis it was seen that at 0cm separation distance, the power transfer was

most efficient as seen by the brightness of the test lamps.

3. From the project WPT for short range or near field occurred up to a distance of 5cm after

which the power transferred began to significantly drop.

4. It can also be concluded that WPT can be used in other applications. In the project we

were able to charge a 9V battery from power that was transmitted wirelessly.

5. Lastly, we can conclude that WPT is not affected by non-magnetic materials shielding the

two coils. This therefore means that it can be effectively used in the medical field to

charge pacemakers and other devices

41

6.2. Recommendations

From this project write up we were able to get a preliminary analysis of the design of a wireless

transfer system. However more research and improvement is required in order to realize a more

practical system. Based on the challenges faced during the design and observations, the

following are recommendations for future work:

Research on the variation of the Q factor and damping factor this can be done by

designing a receiver circuit which is in synchrony with the transmitter circuit. The

receiver circuit could have a feedback system which will change the load accordingly and

which can be detected by the oscillator so that it also adjusts accordingly to achieve

optimum power output.

Studying on the effect of using multiple receivers on the power output, a major

challenge in the design was obtaining a reasonable amount of power. This study can

investigate if the power obtained in the receiver will be higher.

Using an array of transmitter and receiver antennas and coils so as to establish which

is more efficient.

Oscillator load pull needs to be studied In this project the oscillator was designed

without much consideration of frequency pushing and the current design does not take

into account optimum power operating point for the oscillator. A study needs to be

conducted to establish these parameters.

Research on a better, efficient circuit the use of phased locked loops (PLL) and power

amplifier needs to be studied in order to achieve better frequency stability, more power

and efficiency.

42

REFERENCES

[1] D. Chattopadhyay, Electronics (fundamentals And Applications) 7th Ed. New Dehli, India:

New Age Pub., 2006.

[2] Paul Horowitz and Winfield Hill, The Art of Electronics, 2nd Ed. Cambridge, England:

Cambridge Univ. Press, 1989.

[3] U.A. Bakshi and A.P.Godse, Electronic Devices And Circuits I, 3rd Ed. Pune, India:

Technical Pub., 2008.

[4] A. F. J. Levi, Applied Quantum Mechanics, 2nd Ed. Cambridge, England: Cambridge Univ.

Press, 2006.

[5] Luciano Mescia et al, Innovative Materials and Systems for Energy Harvesting Applications,

Hershey PA: IGI Global, 2015.

[6] W. C. Brown (1996, January). The History of Wireless Power Transmission: Solar energy

[Online] Available: http://www.sciencedirect.com/science/article/pii/0038092X9500080B

[7] Mandip Jung Sibakoti and Joey Hambleton (2011, December) Wireless Power Transmission

Using Magnetic Resonance [Online] Available: http://www.cornellcollege.edu/physics-and-

engineering/pdfs/phy-312/mandip-sibakoti.pdf

[8] Dr. Morris Kesler (2013) Highly Resonant Wireless Power Transfer: Safe, Efficient, and over

Distance [Online] Available: http://www.witricity.com/assets/highly-resonant-power-transfer-

kesler-witricity-2013.pdf

[9] Daniel Teninty, P.E (2010, November 2) Wireless Power Consortium [Online] Available:

http://www.energy.ca.gov/appliances/battery_chargers/documents/2010-10-

11_workshop/comments/Wireless%20Power%20Consortium%20Comments_TN%2058928.pdf

[10]Vladislav Khayrudinov “Wireless Power Transfer system Development and

Implementation,” Thesis, Dept Electron Eng., Helsinki Metropolia University of Applied

Sciences, Helsinki, Finland, 2015.

43

APPENDICES

Microcontroller code

#include <LiquidCrystal.h>LiquidCrystal lcd(12, 11, 10, 9, 8, 7 );int ledr = A2;int ledg = A4;int ledb = A3;int analoginput=0;float vout=0.0;float vin=0.0;float R1=20000.0;float R2= 10000.0;int value =0;void count(void);int screenWidth = 16 ;int screenHeight= 2 ;String line1 = "THE WIRELESS POWER TRANSIMISSION PROJECT";String line2 = "VOLTAGE:";String line3 = "BATTERY CONNECTED CHARGING ";

int stringStart,stringStop = 0 ;int scrollCursor= screenWidth;

void setup() {pinMode(analoginput,INPUT);pinMode(A2, OUTPUT);digitalWrite(A2, LOW);pinMode(A4, OUTPUT);digitalWrite(A4, LOW);pinMode(A3, OUTPUT);digitalWrite(A3, HIGH);lcd.begin(screenWidth,screenHeight);

}void loop(){value = analogRead(analoginput);vout = (value*5.0)/1024.0;vin = vout/(R2/(R1+R2));if(vin<0.09){vin= 0.0;}

else if (vin<5.00){

digitalWrite(A2, LOW);digitalWrite(A4, LOW);

44

digitalWrite(A3, HIGH);lcd.setCursor(scrollCursor, 0);lcd.print(line1.substring(stringStart,stringStop));lcd.setCursor( 1 , 1 );lcd.print(line2);delay(300);lcd.clear();if (stringStart == 0 && scrollCursor > 0 ){scrollCursor-- ;stringStop ++ ;}else if (stringStart == stringStop){stringStart =stringStop = 0 ;scrollCursor = screenWidth;}else if(

stringStop== line1.length() && scrollCursor== 0){stringStart ++ ;} else {stringStart ++ ;stringStop ++ ;}

lcd.setCursor(1, 1);lcd.print("VOLTAGE:");lcd.setCursor(9, 1);lcd.print(vin);lcd.setCursor(14, 1);lcd.print("V");}else{

lcd.setCursor(scrollCursor, 0);lcd.print(line3.substring(stringStart,stringStop));lcd.setCursor( 0 , 1 );lcd.print(line2);delay(300);lcd.clear();if (stringStart == 0 && scrollCursor > 0 ){scrollCursor-- ;stringStop ++ ;}else if (stringStart == stringStop){stringStart =stringStop = 0 ;

45

scrollCursor = screenWidth;}else if(

stringStop== line1.length() && scrollCursor== 0){stringStart ++ ;} else {stringStart ++ ;stringStop ++ ;}

digitalWrite(A2, HIGH);digitalWrite(A4, LOW);digitalWrite(A3, LOW);lcd.setCursor(1, 1);lcd.print("VOLTAGE:");lcd.setCursor(9, 1);lcd.print(vin);lcd.setCursor(14, 1);lcd.print("V");}

}