A

Project Report On

WIRELESS ELECTRICAL POWER SYSTEM

Submitted

In partial fulfillment

For the award of the Degree of

Bachelor of Technology (B.TECH)

In Department of Electrical Engineering

2009-2013

Submitted To Submitted By Mr. Neeraj Garg Radhey Shyam Meena (09EEJEE037) H.O.D. Electrical Engineering B.Tech Final Year (2009-2013)

DEPT. OF ELECTRICAL ENGINEERING

GOVT ENGINEERING COLLEGE JHALAWAR

RAJASTAN TECHNICAL UNIVERSITY KOTA (RAJASTHAN)

PREFACE OF PROJECT

Today large number of new technologies depends on electrical supply system, so complexity of

wires is very high. In this project, as requirement of wireless electrical power system, project

team present an analysis the concept of cable less transmission i.e. Power without the usage of

any kind of the electrical conductor or wires. Transmission or distribution of 50 or 60 Hz

electrical energy from the generation point to the consumers end without any physical wire has

yet to mature as a familiar and viable technology.

Our team chose to project the feasibility of wireless power transmission through

inductive coupling. This consists of using a transmission and receiving coils as the coupling

antennas. Although the coils do not have to be solenoid they must be in the form of closed loops

to both transmit and receive power. To transmit power an alternating current must be passed

through a closed loop coil. The alternating current will create a time varying magnetic field. The

flux generated by the time varying magnetic field will then induce a voltage on a receiving coil

closed loop system. This seemingly simple system outlines the major principle that our research

investigated. The primary benefits to using inductive coupling are the simplicity of the

transmission and receiving antennas, additionally for small power transmission this is a much

safer means of conveyance. To demonstrate the success of our the teams we created a receiving

circuit to maximize the amount of received power and light an LED at a distance up to two feet.

We were able to create both transmission and receiving circuits capable of transmitting the

necessary power to light an LED in a pulsed mode. On average with transmitting one watt of

power the receiving circuit was able to receive 100 micro-watts of power. While the efficiency of

the system is extremely low, approximately 0.01% with some improvements we feel certain the

efficiency could be greatly improved. Furthermore, as the transmission distance is decreased the

efficiency of any system using inductive coupling improves exponentially.

ACKNOWLEDGEMENT

“Every good work requires the guidance of some experts.”

Many lives & destinies are destroyed due to the lack of proper guidance, directions &

opportunities. It is in this respect we feel that we are in much better condition today

due to continuous process of motivation & focus provided by our parents & teachers in

general. The process of completion of this project was a tedious job & requires care &

support at all stages. We would like to highlight the role played by individuals towards

this.

We oblige to acknowledge my heartiest gratitude to all honorable people who

helped us during our project on

“WIRELESS ELECTRICAL POWER SYSTEM.”

We want to express our thanks to Mr. Neeraj Garg (H.O.D., EE) for

granting us the permission for doing this project and to give their valuable time and

kind co-operation.

We would like to thanks Mr. Raju sir (TCS Ltd.), & Mr. Raman sir

(Operation Engineer ,BGR Energy System) for providing us the knowledge about

the wireless work and giving their valuable guidance during our project period.

We would like to thanks Mr. Sunil Kumar (Electronics Lab Technician)

for providing us knowledge and guidance about our project.

We Would Co-Heartedly Thank and Use This Opportunity to Express

Gratitude and Debtness to Mr.M.M.Sharma (Principal), Govt Engineering College

Jhalawar

We are also thanks a lot to other staff members of Electronics and

Electrical Dept. and also staff of labs for their further co-operation to gain the better

knowledge about the project.

Radhey Shyam Meena & Rakesh Kumar

Deepa Sharma & Samta Meena

Kanwar Lal & Teena Garg

B.Tech 4th Year

Electrical Engineering

TABLE OF CONTENTS

Table of Contents.....................................................................................................................................i

List of Figures........................................................................................................................................ii

Chapter-01 Basic of Wireless Electrical Power System 1.1 Executive Summary........................................................................................................................02

1.2 Introduction.....................................................................................................................................03

1.3 Problem Statement..........................................................................................................................04

1.4 Research..........................................................................................................................................05

1.5 Possible Solutions...........................................................................................................................06

Chapter-02 Operating Frequency and Design 2.1 Operating Frequency......................................................................................................................07

2.2 Design Choice................................................................................................................................09

2.3 Theoretical Background.................................................................................................................10

2.4 Safety and FCC regulations............................................................................................................11

2.5 Division of Work............................................................................................................................12

Chapter-03 Wireless System Design 3.1 System Design................................................................................................................................14

3.2 Power Supply..................................................................................................................................14

3.3 Oscillator.........................................................................................................................................16

3.4 Power Amplifier.............................................................................................................................19

3.5 Transmitter and Receiver Design...................................................................................................23

3.6 Booster/rectifier..............................................................................................................................28

3.7 LED Flasher....................................................................................................................................31

Chapter-04 Hard Ware Design …………………………………………………………...…...32

Chapter-05 Future Use 5.1Feasibility........................................................................................................................................35

5.2 Future Improvements.....................................................................................................................36

Chapter-06 Reference References..................................................................................................37

Appendices

Appendix A.Detailed specifications…………………………………………………………………38

Appendix B.fcc regulations……………………………………………………………………….. 40

LIST OF FIGURES

Figure 1: An Ideal Transformer............................................................................................................10

Figure 2: Entire System Block Diagram...............................................................................................14

Figure 3: Power Supply Schematic.......................................................................................................15

Figure 4: Colpitts oscillator schematic.................................................................................................16

Figure 5: Oscillator system schematic..................................................................................................17

Figure 6: Output of oscillator system...................................................................................................17

Figure 7: Class B Amplifier..................................................................................................................19

Figure 8: Preamplifier and Power Amp................................................................................................20

Figure 9: Power Amplifier Final Design..............................................................................................21

Figure 10: Power Amplifier FFT.........................................................................................................22

Figure 11: Flux density in a solenoid...................................................................................................23

Figure 12: Bigger Transmitter and Smaller Receiver Coil..................................................................24

Figure 13: Transmitter and bigger Receiver Coil …………………………………………….……...25

Figure 14: coupling circuit …………………………………………………………………..……….27

Figure 15: Output of the Pspice Simulation for Received power.........................................................27

Figure 16: Schematic of the Voltage Booster.......................................................................................28

Figure 17: Schematic of the LED Flasher circuit.................................................................................30

Figure 18: Picture of the Transmitter System Enclosure......................................................................33

Figure 19: Picture of the Receiver System...........................................................................................34

Figure 20: Alternate design for the Transmitter coil............................................................................36

CHAPTER-01

BASIC OF WIRELESS ELECTRICAL POWER SYSTEM

1.1 EXECUTIVE SUMMARY

Wireless power transmission is the means to power devices without a built in power source such

as a battery. There are multiple needs and uses for such technology. One initial use of such

technology is found in powering small devices where much of the size of the device is in the

battery itself. By eliminating the battery in a small device it would be possible to compact the

device even further. Furthermore, on a larger scale as consumable energy sources on the planet

are dwindling in number it remains an important task to look to the future. If it was possible to

transmit power wirelessly it would be economical to retrieve power from outer space and simply

transmit it back to the planet’s surface as an endless power source. In our initial research about

this project we discovered many have looked into the feasibility of wireless power transmission

and there are many solutions that all offer promise. Our team chose to project the feasibility of

wireless power transmission through inductive coupling. This consists of using a transmission

and receiving coils as the coupling antennas. Although the coils do not have to be solenoid they

must be in the form of closed loops to both transmit and receive power. To transmit power an

alternating current must be passed through a closed loop coil. The alternating current will create

a time varying magnetic field. The flux generated by the time varying magnetic field will then

induce a voltage on a receiving coil closed loop system. This seemingly simple system outlines

the major principle that our research investigated. The primary benefits to using inductive

coupling are the simplicity of the transmission and receiving antennas, additionally for small

power transmission this is a much safer means of conveyance. To demonstrate the success of our

the teams we created a receiving circuit to maximize the amount of received power and light an

LED at a distance up to two feet. Within a few months of research as part time workers we were

able to create both transmission and receiving circuits capable of transmitting the necessary

power to light an LED in a pulsed mode. On average with transmitting one watt of power the

receiving circuit was able to receive 100 micro-watts of power. While the efficiency of the

system is extremely low, approximately 0.01% with some improvements we feel certain the

efficiency could be greatly improved. Furthermore, as the transmission distance is decreased the

efficiency of any system using inductive coupling improves exponentially.

1.2 INTRODUCTION

This document will detail the need and usefulness of wireless power transmission and

furthermore the feasibility of using inductive coupling as the means for wireless power

transmission. The subject matter of the report will be directed towards the knowledge level of an

electrical engineer. Thus some points about general circuits may not be explicitly stated as they

have been taken as common knowledge for the intended audience. However, it is intended that

anyone with an interest in electrical circuits and more importantantly transformer theory or

electromagnetic fields would be able to understand and follow the subject matter outlined in the

following document. The report will outline our teams design process and the logical steps we

took in our experimentation and design of the final unit. The first section of the document will

explicitly illustrate the problem and what the group intended to accomplish. With the complexity

of the problem in mind and what we must accomplish our team then began research on the

available means to transmit power without a physical connection. Once the initial background

research was accomplished it was necessary to layout the advantages and disadvantages of all the

available means for wireless power transmission. Once all the necessary criteria for each system

were known we chose the best solution for the problem. After our team had chosen upon using

inductive coupling we all began to review the major theories that would determine the

constraints of the system and what pieces of hardware must be designed to achieve the

transmission of wireless power. Furthermore because we are transmitting power through the

surrounding area we had to be sure that our system would not endanger others and be FCC

compliant. Once the basic system components were known our team divided up the work load,

set the necessary deadlines, and began designing the following circuits and hardware: power

supply, oscillator, transmission coil, receiving coil, voltage booster/rectifier, and LED flashing

circuit. After the entire system was integrated into a working unit it was time to determine how

well the system operated and the feasibility of wireless power transfer through inductive

coupling. Additionally, future improvements that could greatly improve the overall system will

be discussed. Finally, the cost of producing the system, any references our team used, and extra

calculations will be presented in the appendices.

1.3 PROBLEM STATEMENT

For the completion of this project, we were asked to wirelessly transfer the power of an AC

oscillating waveform into a DC voltage on the receiving end which will be used to light an LED

to demonstrate the instantaneous power transfer. The frequency of oscillation of the AC signal

must not exceed 100MHz. The power transfer needs to be done over a two feet distance or

greater. The transferred AC power needs to be converted to DC power and boosted up enough to

drive a low power display design, such as an LED in continuous or pulsed mode.

1.4 RESEARCH

Nikolai Tesla

Nikolai Tesla was the first to develop the designs for wireless power transmission. Tesla was

famed for his work in the research and work with alternating current. His wireless research began

with his original transformer design and though a series of experiments that separated the

primary and the secondary coils of a transformer. Tesla performed many wireless power

transmission experiments near Colorado Springs. In Tesla’s experimentation, Tesla was able to

light a filament with only a single connection to earth. Tesla’s findings lead him to design the

Wardenclyffe plant as a giant mushroom shaped wireless power transmitter. Tesla was never

able to complete construction of this project.

Space Satellite System

The concept of wireless power transmission has been an area of research that the U.S.

Department of Energy (D.O.E.) and the National Aeronautical Space Administration (NASA)

have been working to develop. NASA has been looking into research to develop a collection of

satellites with the capability to collect solar energy and transmit the power to earth. The current

design for project by NASA and DOE is to use microwaves to transfer power to rectifying

antennas on earths.

Similar to this system, NASA and DOE have put research into using laser technology to beam

power to earth. Japan’s National Space Development Agency (NASDA) has also been

performing this variety of research to use satellite and laser technology to beam power to earth.

Japan is expected to have the laser technology developed by 2025. The use of laser technology

would theoretically eliminate many of the problems that could occur with the use of microwaves.

This laser satellite system is unlikely to be devolved by the United States due to current treaties

with Russia preventing either nation from having satellites with high power laser technology.

This treaty was created to prevent either nation from completing President Regan’s “Star Wars”

project.

Microsystem and Microsensor Power Supply

Currently, the use of inductive coupling is in development and research phases. There several

different projects that use inductive coupling to create alternatives for batteries. One developed at

the Tokyo Institute of Technology is to develop a power supply for a medical sensor while it is

left inside the human body. In this system, power was transmitted by both electromagnetic waves

when at close distance to the transmitter an also by magnetic flux when at farther distances. The

receiver portion utilizes a cascade voltage booster to charge capacitors within the device to

provide the necessary power to the system. Another similar project, done at Louisiana State

University in Baton Rouge, uses inductive coupling in a similar method recharge an internal

small battery in a small bio-implanted microsystem.

1.5 POSSIBLE SOLUTIONS

In this project, as well as practical knowledge, we knew of three possibilities to design a device.

There are the use of antennas, inductive coupling, and laser power transfer. In addition, we had

to be aware of how antennas and inductive coupling would be affected by the frequency we

select.

ANTENNA

Antennas are the traditional means of signal transmission and would likely work. In initial

research, it appears that system utilizing antennas can receive power gains based upon the shape

and design of the antenna. This would allow more power actually being sent and received while

also have a small input power. The difficulty comes in the trade off of antenna size versus

frequency. In attempting to stay in a lower frequency, one would be require using antennas of

very large size.

INDUCTIVE COUPLING

Inductive coupling does not have the need for large structures transfer power signals. Rather,

inductive coupling makes use of inductive coils to transfer the power signals. Due to the use of

coils rather than the antenna, the size of the actual transmitter and receiver can be made to fit the

situation better. The tradeoff is for the benefit of custom size, there will be a poor gain on the

solenoid transmitter and receiver.

LASER POWER TRANSMISSION

The concept of laser power transmission is addressed in the research of NASA and NASDA

solar programs. Lasers would allow for a very concentrated stream of power to be transferred

from one point to another. Based upon available research material, it appears that this solution

would be more practical for space to upper atmosphere or terrestrial power transmission. This

option would not be valid to accomplish our tasks because light wavelengths are higher than the

specified allowable operational frequencies.

CHAPTER-02

OPERATING FREQUENCY AND DESIGN

2.1-FREQUENCY

Very High And Greater Frequency Range-

High High frequency transmissions are common in several devices including cell phones and

other wireless communications. Higher frequencies can be made to transmit in very specific

directions. In addition, these antennas can be rather small. This set of frequency ranges includes

microwave frequency bands. Very High Frequencies to Extremely High frequencies are

described as being in the range of 30 MHz to 300 GHz and Microwave frequencies are described

as being the range of 3 GHz to 300 GHz. The safety issues of using the high end of the spectrum

are not completely known. There is currently research looking into the safety of microwave and

higher frequencies. However, many of the devices in this frequency range are not permissible

due to the frequency limitations placed,on our

Very Low to Extremely Low Frequency Range-

Antennas of these frequencies would need to be of sizes that are very impractical to build and

would be better suited for power transmission over wire. Several of these frequencies are

specifically used for submarine communication transmission. Extremely low frequencies and

possibly other frequencies in the band up to 3 KHz have the uncertain risk of being potentially

hazardous the humans and the environment. There is still on going research on the dangers on

very low to extremely low range frequencies.

Low, Medium, and High Frequency Range-

Radio Frequencies in these bands seem to have few hazardous concerns given by the FCC. In

addition, these frequencies are commonly used as the primary frequency bands of radio

transmission. The high frequency band is typically used in short range communications due to

the ease of the reflection of these waves off the ionosphere. This range is described as being from

3 MHz to 30 MHz. In addition, this frequency range includes two experimental frequency bands.

The major disadvantage of working in this frequency range is the inability to properly test in the

design phase due to effects parasitic capacitance in breadboards. Medium Frequency includes the

AM broadcast band. Medium frequencies are described as being from 300 KHz to 3 MHz. This

band includes one band used for testing purposes. The Low frequency band is primarily used for

aircraft, navigation, information and weather systems. In addition, this frequency includes a band

commonly used for testing purposes. The low frequency band is described as being from 30 KHz

to 300 KHz.

2.2 DESIGN CHOICE

After reviewing the possible solutions, inductive coupling was chosen as the best alternative. Our

team believes that inductive coupling based system will meet most of the design criteria in the

designated time given to us. We also felt that our background and knowledge of electromagnetic

fields and transformer theory would help us resolve any problems encountered during the design

process.

Inductive coupling also offers several advantages over other options that are as follows:

SIMPLE DESIGN –

The design is very simple in theory as well as the physical implementation. The circuits built are

not complex and the component count is very low too.

LOWER FREQUENCY OPERATION –

The operating frequency range is in the kilohertz range. This attribute makes it easy to

experiment and test in breadboard. Furthermore there is low risk of radiation in the LF band.

LOW COST –

The entire system is designed with discrete components that are readily available. No special

parts or custom order parts were necessary for the design. Thus we were able to keep the cost of

the entire system very low.

PRACTICAL FOR SHORT DISTANCE –

The designed system is very practical for short distance as long as the coupling coefficient is

optimumized. The design also offers the flexibility of making the receiver much smaller for

practical applications.

Inductive coupling also has some shortcomings that need to be addressed.

HIGH POWER LOSS –

Due its air core design the flux leakage is very high. This results in a high power loss and low

efficiency.

NON-DIRECTIONALITY –

The current design creates uniform flux density and isn’t very directional. Apart from the power

loss, it also could be dangerous where higher power transfers are necessary.

2.3 THEORETICAL BACKGROUND

Our power transmission system utilizes the concepts of transformer theory. In a basic single

phase transformer as shown in figure, when the primary coil is connected to an AC source, a

time varying flux is produced in the core. This flux is confined within the magnetic core. If

another coil is added on the same core, the flux links the second coil inducing voltage at its

terminals given by the equation . where N is the number of turns of the secondary coil and φ is

the flux generated. Furthermore if a load is connected across the terminals of the coil, current

flows across the load.

V = -N (∂φ/∂t)

Figure 1: An Ideal Transformer

Our system follows the same concepts of Faraday’s law of electromagnetic induction, but with

two major differences. Our system is an air core transformer i.e. there is no solid magnetic core

that confines the flux produced at the primary. This means that there is high flux leakage and

only a portion of the flux generated induces an emf across the secondary coil. Moreover in our

system the primary and secondary coils are two feet apart, which results in low flux linkage, low

coupling, and even lower power transfer. Therefore the biggest challenge in this project is to

maximize the flux linkage between the primary and secondary coils to be able to transfer enough

power to light an LED at the given distance.

2.4 SAFETY AND FCC REGULATIONS

One of the key factors in our device was to be aware of FCC (Federal Communications

Commission) regulations. The FCC regulations are put in place first to limit the use of particular

frequency bandwidths. In doing so, the FCC prevents multiple users from occupying the same

frequency band and interfering with one another. In addition, the FCC also regulates power

emissions of a variety of different devices.

Due to the nature of our project, we will be affected by FCC regulations. Our project is an

intentional radiator as well as working with radio frequency (RF) energy.

The FCC defines an intentional radiator as:

A device that intentionally generates and emits radio frequency energy by radiation or induction.

The FCC defines radio frequency energy as:

Electromagnetic energy at any frequency in the radio spectrum between 9 kHz and 3,000,000

MHz

For this project, the frequency band of 160-190 KHz was selected. The frequency of 160-190

KHz is an open test band that does not require any special permission to work in the frequency

range. This frequency range contains three limiting factors. The limitations of this frequency are

the following:

• Total input power into the final radio frequency stage shall not exceed 1 watt.

• The total length of transmission line, antenna, and ground lead shall not exceed 15 meters.

• All emissions below 160 kHz and above 190 kHz shall be attenuated at least 20 dB below

the level of the unmodulated carrier.

For the complete FCC code, refer to Appendix B.

Radiation in the frequency band of 160 KHz to 190 KHz does not seem particularly hazardous at

such low power levels. In general, it is suggested to remain a distance radius of 6 inches away

from the transmitter and not standing in the direction of transmission. Additionally avoid

exposure to children under a body weight of 50 lbs.

During the testing procedure, radiation from the transmitter did not affect cell phones,

calculators, and digital watches. Direct effects of the radiation of the system on medical devices,

such as pace makers, are unknown. It is recommended that people with medical implants remain

a distance of 1 meter away from the transmitter as a precaution.

2.5 DIVISION OF WORK

In order for our team to be productive every team member was given very specific goals and

deadlines to meet. Furthermore for all design components everyone worked with another team

member to ensure success. We felt that because many did not possess a technical background in

certain necessary fields having the assistance of another engineer would prove to be an

invaluable resource. Every team member and their major responsibilities are listed below.

Samta Meena – Oscillator,

Deepa Sharma- Power Amplifier

Radhey Shyam Meena – FCC Regulations and Safety and Transmitte

Rakesh Kumar – Receiver Coil & power supply

Teena Garg –, Voltage Booster/Rectifier

Kanwar lal - LED Flashing Circuit

team members were tasked with other various responsibilities not directly related to the design

process, but to ensure the cooperation of all team members. These positions were designed to

create order in team meetings and the design environment.

CHAPTER-03

WIRELESS SYSTEM DESIGN

3.1 SYSTEM DESIGN

With all the necessary background research completed it became clear what basic design

components the entire system would require. First we needed a method to power the

transmission side of the system. The power supply would then power an oscillator which would

provide the carrier signal with which to transmit the power. Oscillators are not generally

designed to deliver power, thus it was necessary to create a power amplifier to amplify the

oscillating signal. The power amplifier would then transfer the output power to the transmission

coil. Next, a receiver coil would be constructed to receive the transmitted power. However, the

received power would have an alternating current which is undesirable for lighting a LED. Thus,

a voltage booster and rectifier would be needed to increase the received voltage while outputting

a clean DC voltage. Finally, a LED flasher circuit would be constructed to flash the LED when

enough power had been received to light the LED. The entire system can be seen in the figure.

Figure 2: Entire System Block Diagram

3.2 POWER SUPPLY

The main design aspects our team wanted to incorporate in the power supply was that it could

use the 120 V AC voltage found in any basic wall outlet, and use that voltage to power any

necessary circuits to the system. Initially, 120 volts is too large for our small circuits so we

incorporated a small transformer to step down the voltage. Furthermore for any basic electrical

components it would be necessary to have a DC power supply available, thus the stepped down

AC voltage converted to DC by a full-wave bridge rectifier. The full-wave bridge rectifier is the

KBU4D which can be easily found at any Radioshack store. Large capacitors were then

connected to the output of the full-wave bridge rectifier to ensure that a steady DC voltage could

be maintained. The power supply schematic can be seen in figure

Fig-03 Power Supply

The center tap on the secondary side of the transformer serves as the ground for the entire circuit.

Thus, all additional circuits connected to the power supply will use the center tap of the

transformer for the ground plane. The secondary on the transformer is rated at 25 volts but with

loading from additional circuits the steady state voltage reduces to 18 volts.

The design for the power supply is extremely compact and very simple to implement.

Furthermore, the voltage is more than sufficient for the necessary circuits that will be connected

to it. The layout of the power supply is shown in Appendix F. One of the major drawbacks of the

transformer is the two amp output, but due to FCC regulations the maximum power that could be

delivered to the transmission coil would be one watt. A two amp output is more than sufficient to

supply one watt of power.

As stated earlier the only real drawback to the power supply design would be the current output.

If it was possible to transmit more than one watt of power to the transmission coil a more robust

power supply capable of supplying more current would be better suited.

Although no tough design challenges were present in creating the power supply, it was necessary

that the system operate well because of a good design. The key points in creating a DC power

supply are the voltage, current, and removing ripple in the DC components. All three of these

key points were known and addressed in the design process.

3.2 OSCILLATOR

There are two popular types of oscillators: the Colpitts and the Hartley oscillator. The Colpitts is

somewhat similar to the shunt fed Hartley with the exception that instead of utilizing a tapped

inductor like the Hartley oscillator does, it uses two series capacitors in its LC circuit. The

connection between these two capacitors is used as the center tap for the circuit. The schematic

of such oscillator is shown in figure

Fig-04 .Colpitts Oscillator

DESIGN

In designing the Colpitts oscillator shown in figure, a general purpose 2N2222A type bipolar

junction transistor was used . The two biasing resistors connected to the base of the transistor are

used to limit the voltage and current going in the base of the transistor for proper operation. They

need to be in the tens of kilo ohms range for low base current. The capacitor connected to the

base of the transistor is used to keep the base voltage constant. The bias resistor at the emitter of

the transistor which can be replaced by a large inductor is used to prevent the capacitors C4 and

C5 to be short circuited. The other components in figure not mentioned above (L1, C1, C4 and

C5) are frequency dependent. They are found using the following equation:

F osc= 1/ (2π√(L C eq))

The capacitor C5 is tunable and is used to adjust the frequency of oscillation.

One oscillation cycle is produced by the charging and discharging of the capacitor and inductor

respectively. The oscillating frequency of the circuit shown in fig. is 175 kHz.

ADVANTAGES AND DISADVANTAGES

The advantage in using the Colpitts oscillator is that is does not require the use of a center tapped

inductor, a variable inductor. Such inductors are heavy, costly and hard to work with as they

generate electromagnetic waves that will alter the frequency of oscillation. Such an oscillator has

limited frequency range because so many fixed value components are used.

Figure 05: Oscillator system schematic

Figure 06: Output of oscillator system

DESIGN,CHALLENGES-

The designed oscillator worked as expected as a stand alone system but its output was very

sensitive to loading. To rectify that problem, a buffer that uses the high frequency power

amplifier, AD711jn was integrated. Also the output of the oscillator is directly fed to the power

amplifier. The power amplifier has a 0.7V input amplitude limitation. Due to the 2V DC input

supplied to the oscillator, its oscillation is done at 2V level instead of 0V. A DC bias offset

problem was then encountered. To correct that problem a difference amplifier to subtract the 2V

DC from the output signal of the oscillator was implemented. Finally in order to conform with

the higher harmonic distortion rule set by the FCC regulation, a low pass filter with cutoff

frequency at 190kHz was added to the output of the buffer. The higher harmonics are thus

filtered out. The complete schematic of the oscillator is shown is figure

3.4 POWER AMPLIFIER

DESIGN

In order to generate the maximum amount of flux which will induce the largest voltage on a

receiving coil, a large amount of current must be transferred into the transmitting coil. The

oscillator is not capable of supplying the necessary current, thus the output signal from the

oscillator will then be passed through a power amplifier to produce the necessary current. The

key design aspects of the power amplifier are generating enough current while producing a clean

output signal without large harmonic distortions. If the output from the amplifier was not clean

with harmonic distortions the system would cease to be FCC compliant. A simple amplifier

design capable of yielding high current for an alternating waveform is the class B amplifier. A

diagram of this amplifier can be seen below

Figure 07: Class B Amplifier

The main design challenge with class B amplifiers occurs when the signal alternates polarity and

more importantly rather quickly which is the case with our 175 kHz carrier frequency. The

problem arises when one BJT is turned off and the other on, this creates crossover distortions.

These crossover distortions would create higher order harmonics which are very undesirable. To

compensate for these distortions a feedback control loop is desirable. Furthermore this feedback

would offer control over the output voltage level. To create this feedback loop a preamplifier was

added to the design. An operational amplifier was used as the preamplifier and the feedback

control loop. This design can be seen in the figure

Figure 08: Preamplifier and Power Amp

It can be noted that the diodes connected the output of the operational amplifier and the BJT

bases have been removed as voltage biasing was not necessary. Furthermore, there are no

resistors connected to the emitters of each BJT because we are trying to deliver the most current

possible to the load. Thus limiting the current with resistors is not desirable. The input vs. output

file can be seen below. The OPA134 operational amplifier was chosen for this project because it

is an acoustic amplifier that is made for high switching frequencies with minimal distortions. The

OPA134 has a bandwidth up to 8 MHz which is more than sufficient for the carrier frequency of

175 kHz. Furthermore at 175 kHz the OPA134 offers up to 40 dB gain, but for our needs the

operational amplifier will only have a gain of 20 dB. For the npn transistor the TIP31 was chosen

and for the pnp transistor the TIP42 was chosen. Both transistors can operate up to 1 MHz which

is more than enough to operate at 175 kHz. Furthermore, they can both support a collector

current up to 3 amps, while the power supply can only output 2 amps maximum this will be

sufficient to supply the necessary current to the transmission coil.

POWER AMPLIFIER OUTPUT

In this the larger waveform represents the output signal while the input signal is the smaller

signal. It can easily be seen how the signal has been greatly amplified. Finally the harmonic

distortions may also be viewed according to the simulation.

POWER AMPLIFIER HARMONICS

Again it is possible to see the amplification however here one will notice the presence of the

harmonic distortions found in the larger waveform. Due to the presence of the feedback loop

connected to the emitters of the BJTs the harmonics are minimal.

ADVANTAGES AND DISADVANTAGES

The overall advantages to the amplifier are quite apparent, this system is capable of greatly

increasing the power transmitted to a given load. Furthermore, by using a variable resistor in

place of R5 the 5 KOhm resistor it would be possible to implement an amplifier with variable

Gain.

this would be extremely useful when the transmission coil resistance could vary upon future

design aspects. This would allow the gain of the amplifier to be adjusted as necessary, yet at the

same time always comply with the FCC regulations and transmit less than the one watt.

The power amplifier performs as it was designed too, if it was necessary to improve upon it

ideally more current output would be desired. Furthermore, to really ensure FCC regulations a

class AB amplifier could be designed which would further minimize the harmonic distortions.

Figure 11 is the output from the power amplifier using FFT (Fast Fourier Transfer).

The final production model of the power amplifier was improved by adding a variable resistor to

change the overall amplifier gain. Furthermore, it became apparent that a large variable capacitor

would be needed in series with the transmission coil. The need for this capacitor will be

discussed in the following section. Thus the system was modeled accordingly below.

Figure 09: Power Amplifier Final Design

Fig -10 Power amplifier FFT

The input to the power amplifier was the oscillator and above is the harmonic components of the

output signal. It can easily be seen the largest point is at 175 kHz the carrier frequency, and the

next largest point is 21.2 dB below the main signal this ensures that the FCC regulations have

been met according to the harmonic content below 160 kHz and beyond 190 kHz.

DESIGN CHALLENGES

The major design challenges that occurred in creating the power amplifier was maximizing the

power transfer to the coil and minimizing the harmonic distortions. The impedance matching

network was the most substantial design upgrade in improving the current flow which will be

explained in detail in later sections. Initially we transferred 70 mA to the coil however with the

impedance matching we were easily transferring 200 mA while staying under the one watt power

limitation. Finally, the feedback control through the preamplifier allowed the class B amplifier to

work for our project even with the transition distortions.

3.5 TRANSMITTER AND RECEIVER DESIGN

The transmitter and receiver circuit combined can be called the coupling circuit. It is the heart of

the entire system as the actual wireless power transfer is carried out here. The efficiency of the

coupling circuit determines the amount of power available for the receiver system as well as how

far the LED can be from its actual power source.

SOLENOID DESIGN

A solenoid configuration was used for the design of the transmitter and receiver. A solenoid is a

long cylinder upon which wire is wound in helical geometry as shown in figure. The magnetic

field at the center of the solenoid is very uniform. Usually, the length of a solenoid is several

times of its diameter. The longer the solenoid the more uniform the magnetic field at the middle.

In this way a solenoid is a very practical way to generate a uniform controlled magnetic field.

Figure 11: Flux density in a solenoid

The magnetic flux density in a solenoid can be approximated by the following equation:

B = μ0nI

where B is the magnetic flux density, μ0

is the permeability of free space, n is number of turns of

wire per unit length and I is the current flowing through the wire. To maximize the flux linked to

the receiver coil, it is imperative to increase the magnetic flux density as much as possible.

The equation shows that one of the ways to increase B is to increase the current (I) going into the

wire. Since all wires have some resistance, this process requires increase in the voltage put

across the wires which can result in more heating in the coil. B can also be increased by

increasing n. This can be accomplished by decreasing the wire size or winding wires closely.

Winding wires closely can increase the overall resistance of the coil and thus increase the heating

in the coil. Another way of increasing n is by winding several layers of wire which can cause

insulations problems as well as decrease the diameter to length ratio. It is apparent that there are

several parameters that we have to manipulate to select the appropriate tradeoff that might fit our

system’s needs.

As the input power to our transmitter is limited to 1W, it certainly limits the

amount of current that can be pushed through the transmitter coil. Thus one of the design goals

of the team was to keep the resistance low to maximize the current. In addition to that, we also

strived to increase the number of turns per unit length without drastically increasing the

resistance. Initially our team was using shielded wire for the coils. A major advancement was

made in decreasing wire size by replacing it with magnetic wires. This wire is common copper

wire but rather than having a thick insulation over the copper, it is simply coated in enamel

which keeps the overall diameter of the wire much thinner compared to shielded wire. Magnetic

wires also has low resistance and therefore can carry much higher current. We also utilized two

complete layers of wires for the transmitter coil to increase the number of turns even more.

These steps improved the performance of our system to a great extent.

INITIAL EXPERIMENTATION

In addition to the solenoid parameters, it was also necessary to determine certain parameters such

as relative size of the transmitter and receiver coil, the orientation of the coils, the turns ratio as

well as the operating frequency. To establish these parameters, we conducted few experiments.

For our experiments we made two handmade inductive coils of different diameters

(approximately 1.5 ft and 6 inches), but with equal turns (N=10). First we tried supplying the

large diameter coil with a 7 volt 21 kHz sine waveform to act as the transmitter and the small

diameter coil was placed next to it at various distances and the resulting voltage received was

measured.

Figure 12: Bigger Transmitter and Smaller Receiver Coil

BIG LOOPS FOR TRANCEIVER SMALL LOOPS FOR RECEIVER

Separation distance MEASURED VOLTAGES

0inch 7V 43mV

2inches 7V 18mV

5inches 7V 8mV

Quickly we realized that it was best to orient the coils such that they were directed along the

same axis.

Next, we wanted to verify which was best to have has the receiver the larger diameter coils or the

smaller diameter coils while being oriented in the following manner.

Fig. 13 receiver coil bigger then transmitter coil

Under this arrangement the following data was collected.

BIG LOOPS

= receiver

SMALL LOOPS

= transmitter

Separation distance MEASURED VOLTAGES

3 inches 40mV 7V

This proved that it was better to have the receiver diameter larger than the transmitter.

Next, we varied the frequency and the

number of turns to determine how

these factors affected the received

power allowing for the following date

to be collected. BIG LOOPS

SMALL LOOPS

Nature/ N

value(turn)

observations Nature/N

value(turn)

observations

Receiver

N=10turns

V=400mV at

3inches

Transmitter

N=10turns

7V amplitude AC

signal at 210kHz

Signal completely

dies out at 2 feet

Transmitter

N= 10 turns

7V amplitude AC

signal at 210kHz

Receiver

N=10 turns

V= 150mV at

3inches

The wave dies out

at 2feets

Transmitter

N=10 turns

7V amplitude AC

signal at 210kHz

receiver

N=5turns

V=300mV at 3in

Receiver

N=10turns

V > 400mV at 3in Transmitter

N=5turns

7V amplitude AC

signal at 210kHz

IMPEDANCE MATCHING

One of the major improvements made to the coupling circuit was accomplished by impedance

matching. When a capacitor is put in series with the transmitter coil and it is tuned to its resonant

frequency, then the phase differences of the capacitor and inductor are equal and opposite.

jwL =-1/jwC

When this occurs the load will appear purely resistive and the maximum amount of real power

will be transferred into the transmission coil as voltage and current are in phase. This maximum

power transfer to the transmitter will ensure the maximum amount of current which will produce

the most magnetic flux.

At the receiver circuit we utilized the same concepts of impedance matching to tune the receiver

circuit to the same resonant frequency as of the transmitter. This ensures that the maximum

power is transmitted to the receiver coil. A parallel resonance circuit was used to maximize

voltage output to the load at the receiving end.

COUPLING COEFFICIENT

The entire system was also modeled using coupling coefficient. A coupling coefficient is a

number that expresses the amount of electrical coupling that takes exists between two circuits.

The coupling coefficient is calculated as the ratio of the mutual inductance to the square root of

the product of the self-inductance of the coupled circuits as shown in the equation below

k = M/√(L1* L2)

where M is the mutual inductance and L1 and L2 self inductances of the transmitter and receiver

coils approximately. This number determines how much power is transfer between coupled

circuits and is the range between 0 and 1. The coupling coefficient is directly dependent on the

spatial relationship of the coils as well their sizes. We made some theoretical calculations as to

the estimated value of our coupling coefficient of our system.

We utilized this number to model the theoretical power that we should be receiving in Pspice.

The schematic diagram of our coupling circuit using coupling coefficient is shown in the figure

19 where R2 represents our effective load at the receiver.

Fig 14 .Coupling Circuit

The average power received at the load is around 400uW as shown in figure 20. Our system

outputs 100uW approximately. Thus we can see that our actual system follows the model

reasonably well.

Fig. 15: Output Simulation for Received power

3.6 BOOSTER/RECTIFIER

DESIGN

The booster/rectifier was based on the cascaded voltage booster circuit in [3]. Their design was

used to feed a capacitor which powered the control circuitry. Our original design was to use a

full wave rectifier and then feed the DC signal to a DC-DC converter to obtain the proper output

voltage. Using one circuit to accomplish both goals effectively reduces the complexity of the

design of the receiver circuit.

The voltage multiplier works by rectifying an AC signal and charging half of the capacitors

during the positive cycle. During the negative cycle, the capacitors charged during the positive

cycle are an effective “open circuit” while the other half of the capacitors are being charged.

When the circuit is viewed over the output of the voltage multiplier, the total voltage of all the

capacitors is added up.

Fig.16 : Schematic of the Voltage Booster

The finalized design utilizes 3 multiplication stages. The final design uses 6 Vishay 1n5711

schottky diodes and 6 10uf tantalum capacitors. These were selected due to their low current

leakage characteristics.

ADVANTAGES AND DISADVANTAGES

This circuit is simple to design, test, and build. The device does the duty of both rectifying an

AC voltage and multiplying it. It is easy to increase the number of multiplication stages in the

design. The design yields a large reduction of current on its output. This reduction makes the

circuit good for charging capacitors.

DESIGN CHALLENGES

This portion had three primary design challenges. The first was to increase voltage gain. The

next stage was to reduce any time constant of the booster to provide near instantaneous power on

the output. The next phase was to create an optimum voltage to current ratio to the next stage of

the receiver. And finally the last task was to reduce overall power dissipation in the circuit. All

aspects of these challenges are related to the selection of parts. In diodes, we need a low current

dissipation as well as low forward current and high speed switch capability. We need capacitors

that are low power dissipating and of the proper size. High value capacitors create a longer

charge time. In addition, higher value capacitors also seem to reduce the available voltage gain

as seen in on the output.

3.7-LED-FLASHER

DESIGN

The LED flasher operates as a voltage control switch. The switching of the transistors is

controlled by the capacitor C1 in figure above. It uses general purpose pnp and npn bipolar

junction transistors. The capacitor C1 controls the switching of the transistor as well as the flash

duration and frequency of the LED D1. The system generates negative pulses at the collector of

the npn transistor. Initially there is no voltage drop across the LED D1. That is because the

values selected for the resistors R4, R5 and R2 make the base voltage of the pnp transistor to be

almost 0V. Both transistors are turned off. At that time the capacitor C1 gets charged. When

fully charged, C1 starts discharging in the base of the pnp transistor and switches it on. The

pnp’s collector voltage switches on the npn transistor which drops its initial collector voltage. A

voltage drop is therefore generated across the LED D1 and current flowing through it that makes

it flash. The larger the value of C1, the lower the flashing frequency of the LED becomes,

additionally the LED is lit longer during its pulsed mode.

Figure 17 Schematic of the LED Flasher circuit

ADVANTAGE AND DISADVANTAGE

The flasher system is a low power system. It only requires 1.2uW for its operation.

CHAPTER-04

HARDWARE DESIGN

BASIC – The Enclosure designs are relatively simple. The transmitter was designed as a box

large enough to carry most components on the bottom of the box and screw them to the base. In

addition, there is sufficient room for additional circuits if necessary.

External Width = 8 ¼ inches Internal Width = 7 7/8 inches

External Length = 10 ¾ inches Internal Length = 10 1/8 inches

External Height = 6 ¼ inches internal Height = 5 1/8 inches

Base Height = ¾ inch

The construction of the box included space for an extension cord to exit the box and to be close

to the transformer and a switch to turn on the system. The side exiting to the receiver included

connection lines to the transmitter coil. On one of the long sides closest to the power amplifier

circuit, test point connections were made to measure voltage and current, with a switch to

activate current measurement. This side also included a connection point to tune the receiver coil

and an adjust the gain of the power amplifier.

The receiver enclosure was a radio shack 5x2.5x2 inch box. Initially, 4 holes were drilled for a

tunable capacitor on the receiver side, wire connections to the receiving coil, and for 2 LEDs to

be seen from the top. The capacitor was removed from the box to allow measurement connection

points outside of the box. Additional pieces of material were made and fitted into the receiver

box to hold the circuitry close enough to the top of the box and to hold the circuits steady. The

material is a non conducting,material.

fig. 18 transmitter circuit

Figure 19: Picture of the Receiver System

CHAPTER-05-FUTURE-

5.1-FEASIBILITY-

The feasibility of wireless power transfer is a definite reality as our project has demonstrated.

The major point of the research was to evaluate whether or not inductive coupling was a feasible

solution. While it is possible to transmit and receive power using inductive coupling it has some

definite drawbacks. For our team’s project the goal distance was two feet, at such a large

distance inductive coupling is far too inefficient in its current state. However the following graph

shows that the efficiency between power transmitted and power received increases exponentially

as the distance decreases, the data taken for the graph was compiled using the design project.

Inductive coupling still has a definite future in the short range transmission distance. This

particularly has medical implementations to transmit a few inches to power a remote sensor

implanted in the human

5.2 FUTURE IMPROVEMENTS

There are several improvements that can be made to the system to increase its overall

performance. The oscillator output wasn’t a very clean sine wave signal which increased the

harmonic distortion of the signal. A pure sine wave can be generated by using better filters at the

output. Currently our system is powered by a transformer that provides +18V/-18V volt rails.

Our system can work with lower power. Thus one of the future improvements could be an

implementation of a solar cell array to make our system more mobile. The coupling circuit can

be made more efficient by altering the design in several ways. Increasing the input current to the

transmitter coil would definitely enhance its performance. We can also make the signals more

directional in the z direction by using a conical coil as a transmitter instead of the solenoid coil as

shown in figure

Figure20 : Alternate design for the Transmitter coil

Future design improvements in the booster/rectifier circuit would include additional testing on

different values of capacitance around 10 uF and seeing the effect of combining fast charging

capacitors (Ex. mica capacitors) along with slower voltage holding capacitors (Ex. tantalum

capacitors). Additional future improvements would utilize surface mount parts, particularly for

diodes. There are wider variety of surface mount schottky diodes available than compared to

available through hole components. Available surface mount components have lower current

losses as well as smaller forward currents.

CHAPTER-06

REFERENCES

[1] G. L. Peterson, “THE WIRELESS TRANSMISSION OF ELECTRICAL ENERGY,”

[online document], 2004, [cited 12/10/04], http://www.tfcbooks.com/articles/tws8c.htm

[2] U.S. Department of Energy, “Energy Savers: Solar Power Satellites,” [online document] rev

2004 June 17, [cited 12/10/04], http://www.eere.energy.gov/consumerinfo/factsheets/l123.html

[3] S. Kopparthi, Pratul K. Ajmera, "Power delivery for remotely located Microsystems," Proc.

of IEEE Region 5, 2004 Annual Tech. Conference, 2004 April 2, pp. 31-39.

[4] Tomohiro Yamada, Hirotaka Sugawara, Kenichi Okada, Kazuya Masu, Akio Oki and

Yasuhiro Horiike,"Battery-less Wireless Communication System through Human Body for in-

vivo Healthcare Chip,"IEEE Topical Meeting on Silicon Monolithic Integrated Circuits in RF

Systems, pp. 322-325, Sept. 2004.

[10] All Data Sheets, “AD711JN Operational Amplifier”, November 2004,

http://www.alldatasheet.com/datasheet-pdf/view/AD/AD711JN.html.

[11] ”2.3 Class B” September 2004, http://www.st-

andrews.ac.uk/~www_pa/Scots_Guide/audio/part2/page2.html.

[12] Texas Insturments, “OPA13442 Operational Amplifier”, September 2004,

http://focus.ti.com/lit/ds/sbos058/sbos058.pdf.

[13] Digikey, “TIP31 BJT”, http://rocky.digikey.com/WebLib/On-

Semi/Web%20Data/TIP31_A_B_C,%20TIP32_A_B_C.pdf.

[17] “The Spark Transmitter. 2. Maximising Power, part 1. “ November 2004,

http://home.freeuk.net/dunckx/wireless/maxpower1/maxpower1.html

[18] R. Victor Jones, “Diode Applications,” [Online Document], 2001 Oct 25, [cited 2004 Dec

11],

http://people.deas.harvard.edu/~jones/es154/lectures/lecture_2/diode_circuits/diode_appl.html

[19] Central Semiconductor Corp, “PNP Silicon Transistor”, November 2004,

http://www.semiconductors.philips.com/acrobat_download/datasheets/2N2222_CNV_2.pdf.

APPENDICES

APPENDIX A

Detailed specifications:

In many electronic devices the size is not limited by the electronic circuit, but by the battery;

such as pacemaker and many micro-sensors. The size of these devices can be reduced

significantly if the battery can be removed. However, the power must be supplied externally by

means of wireless transmission.

The basic principle of this project is to convert the energy of an AC oscillation into a DC

voltage, which can be used to charge a capacitor or battery. In order to avoid the complexity of

RF/MW circuit, the system will operate at a lower frequency (< 100 MHz range). This project is

consisted of the following components:

• Convert AC signal to DC signal

• DC-DC converter (increase the DC voltage)

• Oscillator design

• Coupling system design

• Low power display design

• Solar cell implementation

The project will be carried out in three phases:

Phase I: Convert an AC signal from a function generator into a DC signal, and raise the DC

voltage by a DC-DC converter so that it can charge a battery. The battery will be used to drive a

low power display.

Phase II: Design an oscillator and coupling circuit. The oscillator is used as a power transmitter,

and it is powered by a DC power supply. The coupled circuit can collects part of the power

transmitted, and output an AC signal. In this way, the wireless power transmission is achieved.

Phase III: Use a solar cell to replace the DC power supply in the transmitter circuit. In this way,

the whole system is battery free. At the same time, the system is optimized in order to increase

the distance between the transmitter and receiver, as well as higher power transfer.

Specification:

1) The power delivered in this way should be able to light up an LED, either in pulsed mode or

CW mode.

2) The distance between the transmitter and the receiver should be no less than 1 meter.

APPENDIX B

FCC Regulation:

[Code of Federal Regulations]

[Title 47, Volume 1]

[CITE: 47CFR15.217]

[Page 743]

TITLE 47--TELECOMMUNICATION

CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION

PART 15--RADIO FREQUENCY DEVICES--

Subpart C--Intentional Radiators

Sec. 15.217 Operation in the band 160-190 kHz.

(a) The total input power to the final radio frequency stage (exclusive of filament or heater

power) shall not exceed one watt.

(b) The total length of the transmission line, antenna, and ground lead (if used) shall not exceed

15 meters.

(c) All emissions below 160 kHz or above 190 kHz shall be attenuated at least 20 dB below the

level of the unmodulated carrier. Determination of compliance with the 20 dB attenuation

specification may be based on measurements at the intentional radiator's antenna output terminal

unless the intentional radiator uses a permanently attached antenna, in which case compliance

shall be demonstrated by measuring the radiated