Wireless power transmission

Wireless Power Transmission

Project 5

Design Team:
Neha Bagga
Joshua Gruntmeir
Samuel Lewis
Fifonsi Lidwine Senou

Senior Design II

ECEN 4023

December 13, 2004

i

Table of Contents
Table of Contents............................................................................................................................. i
List of Figures ................................................................................................................................ iii
List of Tables ................................................................................................................................. iii
Executive Summary ........................................................................................................................ 1
Introduction..................................................................................................................................... 2
Problem Statement .......................................................................................................................... 3
Research.......................................................................................................................................... 4
Nikolai Tesla............................................................................................................................... 4
Space Satellite System ................................................................................................................ 4
Microsystem and Microsensor Power Supply ............................................................................ 4
Possible Solutions ........................................................................................................................... 5
Antenna ................................................................................................................................... 5
Inductive Coupling.................................................................................................................. 5
Laser Power Transmission...................................................................................................... 5
Operating Frequency................................................................................................................... 5
Very High and Greater Frequency Ranges ............................................................................. 5
Very Low to Extremely Low Frequency Ranges ................................................................... 6
Low, Medium, and High Frequency Ranges .......................................................................... 6
Design Choice................................................................................................................................. 7
Theoretical Background.................................................................................................................. 8
Safety and FCC regulations ............................................................................................................ 9
Division of Work .......................................................................................................................... 10
System Design .............................................................................................................................. 11
Power Supply ............................................................................................................................ 11
Oscillator................................................................................................................................... 12
Design ................................................................................................................................... 13
Advantages and Disadvantages............................................................................................. 13
Design challenges ................................................................................................................. 13
Power Amplifier........................................................................................................................ 15
Design ................................................................................................................................... 15
Design Challenges ................................................................................................................ 19
Transmitter and Receiver Design.............................................................................................. 20
Solenoid Design .................................................................................................................... 20
Initial Experimentation ......................................................................................................... 21
Impedance Matching............................................................................................................. 25
FemLab Simulations ............................................................................................................. 25
Coupling Coefficient............................................................................................................. 28
Booster/rectifier ........................................................................................................................ 29
Design ................................................................................................................................... 29
Design challenges ................................................................................................................. 30
LED Flasher .............................................................................................................................. 31
Design ................................................................................................................................... 31

ii

Enclosures ................................................................................................................................. 32
Design ................................................................................................................................... 32
Feasibility...................................................................................................................................... 34
Future Improvements .................................................................................................................... 35
Cost analysis ................................................................................................................................. 36
References..................................................................................................................................... 38
Appendices.................................................................................................................................... 40
Appendix A........................................................................................................................... 40
Appendix B ........................................................................................................................... 41
Appendix C ........................................................................................................................... 42
Appendix D........................................................................................................................... 43
Appendix E ........................................................................................................................... 46
Appendix F............................................................................................................................ 49
Appendix G........................................................................................................................... 50
Appendix H........................................................................................................................... 51
Appendix I ............................................................................................................................ 52
Appendix J ............................................................................................................................ 53
Appendix K........................................................................................................................... 54

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List of Figures
Figure 1: An Ideal Transformer ...................................................................................................... 8
Figure 2: Entire System Block Diagram....................................................................................... 11
Figure 3: Power Supply Schematic............................................................................................... 12
Figure 4: Colpitts oscillator schematic ......................................................................................... 13
Figure 5: Oscillator system schematic .......................................................................................... 14
Figure 6: Output of oscillator system............................................................................................ 14
Figure 7: Class B Amplifier.......................................................................................................... 15
Figure 8: Preamplifier and Power Amp ........................................................................................ 16
Figure 9A: Power Amplifier Output............................................................................................. 17
Figure 9B: Power Amplifier Harmonics....................................................................................... 17
Figure 10: Power Amplifier Final Design .................................................................................... 18
Figure 11: Power Amplifier FFT .................................................................................................. 19
Figure 12: Flux density in a solenoid............................................................................................ 20
Figure 13: Bigger Transmitter and Smaller Receiver Coil ........................................................... 21
Figure 14: Transmitter and Receiver Coil sharing the same axis ................................................. 22
Figure 15: Best configuration for orientation of the Coils............................................................ 23
Figure 16: Femlab simulation of the Transmitter Coil ................................................................. 26
Figure 17: Magnetic Flux density plot at a distance above the coil.............................................. 27
Figure 18: Magnetic Flux Density plotted at a distance side of the coil....................................... 28
Figure 19: Schematic Diagram of the Coupling Circuit ............................................................... 29
Figure 20: Output of the Pspice Simulation for Received power ................................................ 29
Figure 21: Schematic of the Voltage Booster ............................................................................... 30
Figure 22: Schematic of the LED Flasher circuit ......................................................................... 31
Figure 23: Picture of the Transmitter System Enclosure .............................................................. 32
Figure 24: Picture of the Receiver System ................................................................................... 33
Figure 25: Power Received as Distance Increases........................................................................ 34
Figure 26: Alternate design for the Transmitter coil .................................................................... 35

List of Tables
Table 1.1 ....................................................................................................................................... 22
Table 2.1 ....................................................................................................................................... 22
Table 3.1 ....................................................................................................................................... 23
Table 4.1 ....................................................................................................................................... 24
Table 5.1 ....................................................................................................................................... 24
Table 6.1 ....................................................................................................................................... 30

1

Executive Summary
Joshua Gruntmeir

Wireless power transmission is the means to power devices without a built in power source such
as a generator or 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 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 research 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 research 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.

2

Introduction
Joshua Gruntmeir

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.

3

Problem Statement
Fifonsi Senou

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.
The whole system must be FCC compliant. The detailed specifications are listed in Appendix A.

4

Research
Samuel Lewis

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 [1]. 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 [2].

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 [2]. 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, [3], 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, [4], 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.

5

Possible Solutions
Samuel Lewis

In our research, 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.

Operating Frequency
Very High and Greater Frequency Ranges
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 research.

6

Very Low to Extremely Low Frequency Ranges
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 [5]. 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 Ranges
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 [5]. 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 [5]. 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.

7

Design Choice
Neha Bagga

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.

8

Theoretical Background
Neha Bagga

Our power transmission system utilizes the concepts of transformer theory. In a basic single
phase transformer as shown in figure 1, 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 1.1. where N is the number of turns of the secondary coil and φ
is the flux generated [6]. Furthermore if a load is connected across the terminals of the coil,
current flows across the load.

V = -N (∂φ/∂t) [1.1]

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.

9

Safety and FCC regulations
Samuel Lewis

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 [7].
The FCC defines radio frequency energy as:
Electromagnetic energy at any frequency in the radio spectrum between 9 kHz and
3,000,000 MHz [7].

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.

10

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.

• Neha Bagga – Transmitter and Receiver Coil, Power Supply, Power Amplifier
• Joshua Gruntmeir - Transmitter and Receiver Coil, Power Supply, Power Amplifier
• Samuel Lewis – FCC Regulations and Safety, Oscillator, Voltage Booster/Rectifier
• Lidwine Senou – Oscillator, Voltage Booster/Rectifier, LED Flashing Circuit

A Gantt chart is available in Appendix C that shows the individual component deadlines and
who was assigned to the particular design component. Additionally, 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. Neha Bagga was chosen as the team leader to orchestrate
all meetings and facilitate any special needs a team member may have during the design process.
Lidwine Senou was tasked with recording meeting minutes so an accurate account of decisions
and research could be given to Dr. Zhang, the team’s senior advisor. These minutes can be seen
in Appendix D. Samuel Lewis was placed in charge of collecting all digital data our team may
record and any documents produced for keeping them in a consolidated collection for safety
purposes. Finally, Joshua Gruntmeir was tasked with having a forward knowledge of all
requirements to be fulfilled by the team as outlined by the Senior Design II website and council.
Furthermore, during the design and creation stages Joshua Gruntmeir was in charge of acquiring
any equipment necessary for testing purposes. Samuel Lewis was in charge of researching any
products to be ordered to ensure they will be applicable to the project. Neha Bagga was tasked
with ordering any needed components for the design. The team’s progress can be seen through
the status reports shown in Appendix E.

11

System Design
Joshua Gruntmeir

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 2.

Figure 2: Entire System Block Diagram

Power Supply
Joshua Gruntmeir

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 3.

12

Figure 3: Power Supply Schematic

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.

Oscillator
Fifonsi Senou
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 [8] . The
schematic of such oscillator is shown in figure 4.

13

Figure 4: Colpitts oscillator schematic

Design
In designing the Colpitts oscillator shown in figure 4, a general purpose 2N2222A type bipolar
junction transistor was used [9]. 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 4 not mentioned above (L1, C1, C4
and C5) are frequency dependent. They are found using the following equation:
F osc= 1/ (2π√(L Ceq))

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 figure 4 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.

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 [10]. 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

14

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 5. The output of the
oscillator system is shown is figure 6. Its PCB layout is displayed in Appendix G.

Figure 5: Oscillator system schematic

Figure 6: Output of oscillator system

15

Power Amplifier
Joshua Gruntmeir

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 [11].

Figure 7: 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 8.

16

Figure 8: 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 [12]. 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 [13] [14]. 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.

17

8.0V

4.0V

0V

-4.0V

-8.0V
0s 5us 10us 15us 20us 25us 30us 35us 40us 45us 50us
V(R4:2) V(V5:+)
Time

Figure 9A: Power Amplifier Output

In the figure 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.
6.0V

4.0V

2.0V

0V
0Hz 1.0MHz 2.0MHz 3.0MHz 4.0MHz 5.0MHz 6.0MHz
V(R4:2) V(V5:+)
Frequency

Figure 9B: 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.

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

18

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 10: Power Amplifier Final Design

The printed circuit board layout of the power amplifier is shown in Appendix H.

19

Figure 11: 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.

20

Transmitter and Receiver Design
Neha Bagga

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 2. 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
[15].

Figure 12: 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 [16]. 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

21

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 13: Bigger Transmitter and Smaller Receiver Coil

22

BIG LOOPS FOR SMALL LOOPS
TRANCEIVER FOR RECEIVER
Separation MEASURED VOLTAGES
distance
0inch 7V 43mV

2inches 7V 18mV

5inches 7V 8mV

Table 1.1

Next we conducted the same experiment however this time the coils were oriented in such a way
where they were along the same axis as shown below.

Figure 14: Transmitter and Receiver Coil sharing the same axis
The following data was collected with this arrangement.
BIG LOOPS SMALL LOOPS
= transmitter = receiver
distance
3inches 7V 30mV
Table 2.1
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.

23

Figure 15: Best configuration for orientation of the Coils

Under this arrangement the following data was collected.

= receiver = transmitter
distance
3 inches 40mV 7V

Table 3.1

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.


Nature/ N observations Nature/N observations
value(turn) value(turn)
Receiver V=400mV at 3inches Transmitter 7V amplitude AC signal at
N=10turns Signal completely dies N=10turns 210kHz
out at 2 feet

Transmitter 7V amplitude AC signal Receiver V= 150mV at 3inches
N= 10 at 210kHz N=10 turns The wave dies out at 2feets
turns
Transmitter 7V amplitude AC signal receiver V=300mV at 3in
N=10 turns at 210kHz N=5turns
Receiver V > 400mV at 3in Transmitter 7V amplitude AC signal at
N=10turns N=5turns 210kHz

24

Receiver V= 200mVat 3in Transmitter 7V amplitude AC signal at
N= 5turns N=5 turns 210kHz
Receiver V< 150 mV Transmitter 7V amplitude AC signal at
N=10 turns N= 5turns 210kHz
Receiver V=200mV Transmitter 7V amplitude AC signal at
N= 5turns N=10turns 210kHz
Table 4.1

Higher frequency is preferred for greater power transmission over all distances. This agrees with
Faraday’s Law as the induced voltage is dependent on the frequency. The large number of turns
at the transmitter would create more magnetic flux density which can result in high flux linkage.
The major concern at the receiver was to find the optimum number of turns while keeping the
resistance of the receiver coil minimal. More number of turns at the receiver would induce more
voltage according to the equation 1.1, but it can also increase the resistance which wouldn’t be
desirable as it would lower the output current. Further experimentation showed that the turns
ratio of transmitter and receiver coil had no effect on the system whatsoever due to the large
distance between the coils.

From these simple tests we realized four major points of emphasis that would be crucial in
designing an efficient inductive coupling system:
• The coils should be oriented such that they share the same axis
• The receiver should be larger than the transmitter
• The higher the frequency the more power can be transferred over a given distance

After conducting several experiments with longer solenoids and different number of turns, we
arrived at the final parameters that seem to provide the maximum power transfer between the
transmitter and receiver coils. They are shown in the table 5.1:

Number of Turns (N1) 130
Diameter (D1) 2.12 inches
Transmitter Inductance ( L1) 800 uH
Resistance (R1) 1.3 ohms
Length (l1) 1.825 inches
Number of Turns (N2) 60
Diameter (D2) 6.75 inches
Receiver Inductance ( L2) 926 uH
Resistance (R2) 1.2 ohms
Length (l2) 1.5 inches
Table 5.1

25

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 [17].

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.

FemLab Simulations
During experimentation with the coupling circuit, we noticed that certain alignments of the coils
result in more power transfers than the others. This essentially means that at certain points at the
2 feet distance flux lines concentrate. To make the best use of such points, we conducted femlab
simulations to monitor the flux density.

In femlab, the transmitter coil can be modeled as a single turn current carrying loop as shown in
figure 3. The rectangle represents the area for which magnetic flux density is calculated. The
left boundary of the rectangle represents the central axis of the coil and is set for axial symmetry.
The small circle is the cross section of the wire that loops around the axis. Constants such as
diameter of the wire, the current, surface current density, conductivity of the wire, frequency of
operation are defined in the simulation. The radius of the wire loop is modeled over the radius of
our transmitter coil. The streamline plot shown in the figure 16 shows that the flux lines are
similar to the solenoid.

26

Figure 16: Femlab simulation of the Transmitter Coil

To monitor the flux density at when the orientation is in the z direction, a horizontal line was
drawn above the coil. The resulting plot is shown in figure 17. The x variable in this plot is just
a reference parameter where 0 refers to the axis and 0.1 refers to the right edge of the rectangle
area. We can see that the maximum flux density occurs at 0.03 which is the coordinate for the
wire. Thus we can conclude that the maximum flux density in z direction would occur when the
receiver is aligned to the transmitter coil circumference.

27

Figure 17: Magnetic Flux density plot at a distance above the coil

We also plotted the magnetic flux density in at the side of the coils to verify our initial
assumption about the orientation. This was accomplished by drawing a vertical line from the top
of the rectangle area to the bottom. The magnetic flux density plot is shown in
figure 18. We can see that the magnetic flux density peaks when the receiver is aligned in plane
with the wire loop. Yet the value of flux density is still comparatively lower than the one
achieved when oriented in the z direction. Also with longer solenoids, the flux density in the z
direction can be increased even more. In this way, this experiment confirms our initial
assumption that the coils should be oriented in the z direction to maximize the flux density as
well as power received.

28

Figure 18: Magnetic Flux Density plotted at a distance side of the coil

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[6]. 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. The detailed calculations of the
coupling coefficient are in Appendix I.

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.

29

Figure 19: Schematic Diagram of the 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.

Figure 20: Output of the Pspice Simulation for Received power

Booster/rectifier
Samuel Lewis

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.

30

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 [18].

Figure 21: 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.

Data was gathered by using the full system. Vin and Iin were measured between the receiver coil
and the input to the voltage booster. The output was measured between the connections of the
voltage booster and the LED flasher.

Distance Vin Vout Iin Iout Time to light
2 Feet .480 2.40 99.1 uA .5uA 4 sec
Table 6.1
For information on the proto board design, go to Appendix J.

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.

31

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.

LED Flasher
Fifonsi Senou

Design

Figure 22: Schematic of the LED Flasher circuit

The LED flasher operates as a voltage control switch. The switching of the transistors is
controlled by the capacitor C1 in figure 22 above. It uses general purpose pnp and npn bipolar
junction transistors [19]. 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. The PCB layout of this
system is shown in Appendix K.

32

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

Enclosures
Samuel Lewis

Design
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

Figure 23: Picture of the Transmitter System Enclosure

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.

33

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.

Figure 24: Picture of the Receiver System

34

Feasibility
Joshua Gruntmeir

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.

Distance vs. Power

4000
Power (micro-watts)

3000

2000

1000

0
0 5 10 15 20 25 30
Distance (Inches)

Distance vs. Power
Figure 25: Power Received as Distance Increases

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 body.

35

Future Improvements
Neha Bagga
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 26.

Figure 26: 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.

36

Cost analysis
Fifonsi Senou

Part name Part reference Quantity Unit cost Total cost
number ($) ($)
General
purpose npn 2N2222A 2 1.25 2.50
transistor
General
purpose pnp 2N2907A 1 1.25 1.25
transistor
Variable 101/501 2 1 2
resistor
1/4W resistor 1kΩ 5 0.10 0.50
1/4W resistor 100Ω 1 0.10 0.10
1/4W resistor 20kΩ 2 0.10 0.20
1/4W resistor 10kΩ 1 0.10 0.10
1/4W resistor 4.7MΩ 1 0.10 0.10
1/4W resistor 4.7kΩ 1 0.10 0.10
1/4W resistor 47Ω 1 0.10 0.10
Tantalum 0.68uF 1 1.69 1.69
Pc mount 100uF 1 1.29 1.29
capacitor
Ceramic 10nF 1 0.30 0.30
Ceramic 3nF 1 0.30 0.30
Electrolic 33uF 1 1.29 1.29
Variable ARCO308 3 3.5 10.50
capacitor
Inductor 308uH 1 0.50 0.50
Op Amp AD711jn 1 1.25 1.25
LED Chicago mini 1 1.59 1.59
Vishay 6 0.13 0.78
Schottky diodes 1n5711
Tantalum 10 uF 6 1.59 9.54
capacitors

Transformer Heavy-Duty 1
Chassis-Mount
Transformer w/ 10.49 10.49
leads.
Full Wave KBU4D 1 1.99 1.99
Bridge rectifier
Large capacitor 470uF 2 5.29 10.58
Op amp Opa134 1 1.25 1.25
Power bjt Tip42 1 1.59 1.59
Power bjt Tip 31 1 1.59 1.59

37

wires Magnet wire set 2 4.89 9.78
enclosure box 1 5.00 5.00
enclosure Jack/ switches several 6/2 15.00
Manufacturing PCB board 2 10 20
board

Total cost $113.25

38

References
Joshua Gruntmeir

[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.

[5] “Category:Radio spectrum -Wikipedia, the free encyclopedia,” [online document], 2004 Aug
26 [cited 12/11/04], http://en.wikipedia.org/wiki/Category:Radio_spectrum.

[6] Zia A. Yamayee and Juan L. Bala, Jr., Electromechanical Energy Devices and Power
Systems, John Wiley and Sons, 1947, p. 78.

[7] Code of Federal Regulations, Title 47, Volume 1,Revised as of October 1, 2003 ,From the
U.S. Government Printing Office via GPO Access, CITE: 47CFR15.3, Page 686-689

[8]”Oscillator Basics”, October 2004, http://www.electronics-tutorials.com/oscillators/oscillator-
basics.htm

[9]Discrete Semiconductors, “2N2222”, November 2004,
http://www.semiconductors.philips.com/acrobat_download/datasheets/2N2222_CNV_2.pdf.

[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.

39

[14] Digikey, “TIP42 BJT”,
http://rocky.digikey.com/WebLib/ST%20Micro/Web%20Data/TIP41A,B,C_42A,C.pdf.

[15] Barry. “Solenoid Physics” (Barry’s CoilGun Design Site) [online] 2004,
http://www.oz.net/~coilgun/theory/solenoidphysics.htm (Accessed: September 27, 2004).

[16] Fawwaz T. Ulaby, Fundamentals of Applied Electromagnetics 2001 Media Edition, Prentice
Hall, 2001.

[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.

40

Appendices
Fifonsi Senou

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.

Caution: Students should be careful of the safety issues of high power radiation and FCC regulations.

41

Appendix B

FCC Regulation:

[Code of Federal Regulations]
[Title 47, Volume 1]
[Revised as of October 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 47CFR15.217]

[Page 743]

TITLE 47--TELECOMMUNICATION

CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION

PART 15--RADIO FREQUENCY DEVICES--Table of Contents

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
emissions.

42

Appendix C

Chart of Task Division:

Team Task
Members Description

Lidwine Oscillator
Sam Design
LED
Lidwine Flasher
Circuit

Neha Coupling
Josh Circuit

Neha Power
Josh Amplifier
Safety
Sam & FCC
Compliance
Voltage
Sam Booster &
Lidwine Rectifier

Neha Power
Josh Supply
Create
Entire Final
Team Report

43

Appendix D

Weekly Minute Report:

Weekly GOAL Advisor meeting Team meeting
minutes minutes
Week 1 - Research about - Discussion on the - research on
magnetic coupling probem coupling
- Look at IEEE - Discussion about - Meet professors
journals and the resonance for guidance and
proceedings about frequency advice
the subject - Choose the
- Topics discussion solution to
with Dr Zhang implement
- Find out power - Task division for
needed to light up a library research
LED
Time dedicated: Time dedicated:
45min 20 hrs
Week 2 - Inquire about - Discussion on the - basic experiment
FemLab software proposal with power transfer
- lab test &rearrangement of conversion rate
the Gantt chart. between transceiver
and receiver
- Discussion about
the implementation
of our chosen
solution

1hr 7 hrs

Week 3 - Transmission of - Experimental - Tested
~300mV at as close result’s discussion electromagnetic
to 1meter separation - Discussion on field transfer at a
distance as possible Improvements relatively small
- Improve the rate of separation distance
voltage transfer - Related power
transfer to diameters
of transceiver and
receiver.
- Determined which
diameter ,that of
transceiver or that of

44

receiver, needs to be
larger for better
power transfer

1hr 15 hrs

Week 4 - Design a Colpitts -Discussion on - oscillator designed
oscillator w/ an experimentations at 100kHz
oscillation results - impedance match
frequency no greater up was initiated
than 100kHz loss.
- Work on Time dedicated: Time dedicated:
frequency matching 45min 10hrs
on the transmitter
and receiver sides.

Week 5/6 - power transfer rate -Discussion on Experimental tests
vs. frequency of experimentations
oscillation results
- use of magnetic Time dedicated: Time dedicated:
wire for optimum 45min 12hrs
power transfer
Week 7/8 -Contact the FCC -Discussion on - FCC frequency
- improving experimentations range (160-190Khz)
coupling design results - oscillator designed
- redesign oscillator for Fosc= 175kHz
in FCC regulated - booster designed
frequency range Time dedicated: Time dedicated:
- design of 30min 15hrs
booster/rectifier
Week 9/10 - design the flasher -Discussion on - operational flasher
- research on power experimentations - research one
amplifier results power amplifier
40min 20hrs
Week 11 - oscillator redesign -Discussion on - operating
for operation at experimentations oscillator at desired
13.553MHz results frequency
- power amplifier - working power
design amplifier
1hr 10hrs
Week 12/13 - redesign of -advice to go back - 175kHz working
oscillator for to lower oscillation oscillator
operation at 175kHz frequency - optimized booster

45

- improvement of Time dedicated: Time dedicated:
the booster/rectifier 1hr 15hrs

Week 14/15 - whole system - results discussion - working system,
implementation ready for
- enclosure building demonstration
1hr 30hrs

Week 16/17 - Preparation for Time dedicated:
oral examination 50hrs
- writing final report

This table describes the team’s weekly goal, meeting with the advisor, team’s meetings as well
as time dedicated to the tasks.

46

Appendix E

Status Report 1:

49

Appendix F

Power supply Board:

50

Appendix G

Oscillator Board:

51

Appendix H

Power Amplifier Board:

52

Appendix I

Coupling Coefficient Calculations:

ur*uo u 1.26E-06 area2 0.02308686 meter^2
N1 130 turns
L1 0.046355 meter 1.825 inches L1 8.00E-04 H
L2 0.0381 meter 1.5 inches L2 9.26E-04 H
N2 60 turns
r1 0.0269875 meter 2.125 inches sqrt(l1*l2) 0.000860697
r2 0.085725 meter 6.75 inches
I1 0.2 amp
end2end z 0.6096 meter 24 inches
center2center Z 0.6518275 meter

B 1.13304E-06 ==> Φ 2.61584E-08
BZ 9.26795E-07 ==> || ΦZ 2.13968E-08
/
Λ 1.56951E-06
|| ΛZ 1.28381E-06
/
K 0.009117645 <== L12 7.84753E-06
KZ 0.007457951 <== L12Z 6.41904E-06

Yellow implies changeable
Blue imples values mostlikely
desired
z is measured from end to end of transmiter to closest end of
Reciever
Z is measured from the absolute center of the transciever to the absolute
of the reciever

53

Appendix J

Booster/Rectifier Board

54

Appendix K

LED flasher’s layout:

Wireless power transmission

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