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Georgia Institute of Technology

ECE 4007

Senior Design

L01

Project Proposal

Wireless Power

Daniel Deller, Skip Dew, Justin Freeman,Curtis Jordan, Ray Lecture, Malik Little

Monday, September 15, 2008



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TABLE OF CONTENTS

Executive Summary ……………………………………………………………………… ii

1. Introduction ………………………………………………………………………….. 1

1.1 Objective ………………………………………………………………… 11.2 Motivation ………………………………………………………………. 21.3 Background ……………………………………………………………... 2

2. Project Description and Goals ………………………………………………………. 3

3. Technical Specification …………………………………………………………..…. 5

4. Design Approach and Details ……………………………………………………….. 6

4.1 Design Approach ………………………………………………………… 74.2 Codes and Standards …………………………………………………….. 84.3 Constraints, Alternatives, and Tradeoffs ………………………………… 9

5. Schedule, Tasks, and Milestones…………………………………………………….. 10

6. Project Demonstration ………………………………………………………………. 11

7. Marketing and Cost Analysis ……………………………………………………….. 12

7.1 Marketing Analysis ……………………………………………………… 12

7.2 Cost Analysis ……………………………………………………………. 12

8. Summary …………………………………………………………………………….. 13

9. References …………………………………………………………………………… 14



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EXECUTIVE SUMMARY

Wireless power transmission (WPT) devices are on the forefront of electronics

technology making them potentially marketable products. WPT devices have been thought to

be possible since Nikola Tesla’s transmission model in 1897. The newest way relies on inductive

coupling techniques to transmit power between transmitting and receiving coils. The frequency

at which the device relays power between the transmitter and receiver is dependent on the size of

the coils. The higher the frequency at which the device is transmitting, the smaller the coils must

be.

Current wireless power transmitters are capable of transmitting current at distances of

less than one inch up to one foot. These distances allow for use in small consumer electronic

devices such as electric toothbrushes and razors. While these applications have proven to be

very profitable, the market still remains open for use in larger electronic devices. An aspect of

WPT that has been largely unexplored is the ability to charge a battery. Grids can also be

integrated into new construction designs to provide large scale wireless power coverage to all

electronic devices buildings.

The design team is proposing that, implementing an oscillator at using high frequencies

(10MHz) producing inductive coupling between two small inductive coils, WPT can be

achieved. The illuminating of a light bulb and charging of a battery will be accomplished using a

rectifying circuit that will attempt to cancel harmonics and transfer the maximum amount of

power. This method of can propagate power over a distance of two meters providing

functionality that is not readily available in the consumer market.



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1. INTRODUCTION

In 1897, Nikola Tesla discovered that he could transmit up to 20 MV or more [1]. This

was done by sending a signal into the upper stratosphere at a frequency of 925 Hz to distances

thousands of miles away from the transmitter, as stated in his “System of Transmitting Electrical

Energy” patent [2]. Wireless power transfer (WPT) receivers are devices that can wirelessly

transmit power to illuminate a light bulb or charge a battery. This is a proof of concept

technology that paves the way for charging cell phones, laptop, and PDA batteries wirelessly.

Wireless power technology is in high demand because of its convenience to consumer and

industrial marketplaces. This device prototype is to cost less than $100.00 and will be a fully

operational and completely independent of any other device.

1.1 Objective

Wireless power transfer will be achieved via resonant inductive coupling between the

transmitting and receiving coils in the near field. The purpose of wireless power is to

successfully demonstrate the transfer of power by illuminating a light bulb. The device will be

able to transmit 60 W of power over a distance of two meters. The charging of a battery will be

accomplished using a rectifying circuit that will attempt to cancel harmonics and transfer the

maximum amount of power.



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1.2 Motivation

While wireless power devices have already been created by other companies and

institutions, they are still very basic and not practical. Charging a battery wirelessly has also

been done before by small home appliance companies. The difference in this WPT technique

and the new proposed wireless power system is its ability to send power wirelessly two meters.

This gives it an edge over what is currently available on the market. WPT is convenient for the

user because it is accessible and it is not confined to a single outlet location. This system is

marketable on many levels. For the individual consumer, this technology allows powering and

charging of portable devices such as cell phones and laptops. Building designers would integrate

WPT technology into the walls or floors of new construction to allow for the distribution of

wireless power.

1.3 Background

Currently there are very few wireless power transmitters on the market. MIT was the

first to demonstrate wireless power using resonant near field inductive coupling in the summer of

2007. In 2008, Intel also achieved wireless power though inductive coupling [3]. These

methods consist of two coils which are configured to have the same resonant frequency, with an

oscillator that sends a sinusoidal signal transmitting the power at the resonant frequency. These

designs are currently in the laboratory phase of development and are not ready for mainstream

use. They usually consist of exposed coils and transmit high frequency signals at levels not

desirable for prolonged human interaction.

The primary component in any WPT system is the antenna. The amount of power

transmitted and effectively received will depend on how well the antennas are designed. Whether



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for communications or WPT, the major factor in determining which antenna to use for any given

application will usually depend on polarization, gain, bandwidth, and impedance matching. This

paper has a twofold objective. The first goal is to explore previous research and the current state

of WPT antennas. The second goal is to view the underlying antenna technology to ascertain the

best antenna for use in near field WPT.

There are many different methods to transmit power wirelessly but the most well known

techniques include sending the signal by using the Tesla effect, microwaves, or by resonant

coupling. According to patents and technical literature, each of these methods has worked and

show promise to be used in mainstream applications but one problem arises. Is it safe for

humans to be in the vicinity of these devices while they are in operation? The researchers at

MIT successfully tested a method of transmitting power wirelessly by using the technique of

resonant coupling. Since this was done at midrange distances, this technique could be applied to

power hand held mobile electronics in the near future. Keeping this application in mind, MIT

researchers devised a more safety conscious design that will pass the IEEE standard for human

exposure to Radio Frequency.

2. PROJECT DESCRIPTION AND GOALS

The design team will develop a wireless power apparatus which will be used to power a light

bulb and eventually charge a battery. The wireless power system could be marketable to

electrical engineers who wish to power or charge electronics without wires. WPT will be

achieved using the following parts:



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• Power supply

• Oscillator driving the transmitting coil

• Copper coils for transmitting and receiving

• Load on receiving end (light bulb or rectifying circuit)

The wireless power apparatus will achieve the following goals:

• Transmit power two meters

• Light a 60 W light bulb

•

Charge a 1.5 V rechargeable battery

• Does not emit unacceptable levels of radiation due to RF wave propagation

The purpose of the project is to demonstrate a wireless power transmitter and receiver

system. The high frequencies produced by the wireless power transmitter need to be reasonably

measured and contained. Additionally, small changes in the size of the coils and distance of the

transmitter to the receiver will be accounted for by designing an oscillator capable of tuning the

system. The wireless power receiver will initially be designed to illuminate a small light bulb.

The receiver will then be redesigned in order to include the ability to charge a battery wirelessly.

Since this is a proof of concept design, the focus will be on efficiency, practicality, and safety.

The device must be able to provide a useful amount of power (1.5 V) in order to be marketable.

For the same reason, the device must also be practical enough to implement in common

household and commercial electronic devices such as cell phones and laptops. Lastly, the device

must be safe for everyday use and not emit unhealthy amounts of radiation due to RF wave

propagation.



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3. TECHNICAL SPECIFICAITONS

The technical specifications of the wireless power device are listed below in Table 1.

Table 1. Technical Specifications of the Wireless Power Device.

Component Specification Description

Coils 25 cm radius Helical antennas

Distance 2 m Distance between thecoils

Oscillation Frequency 100 MHz Resonant frequency ofthe coils

Power 60 W To power a light bulb

Rechargeable Battery 1.5 V AA rechargeable battery

The wireless power transmitter and receiver (TX\RX) will use coils with a radius of 25

cm as the helical antennas for transmitting power. These antennas provide for inductive

coupling between the TX\RX. The TX\RX will be a distance of two meters apart. This distance

is crucial to the success of the design. Next to the transmitter will be an oscillator built at an

oscillation frequency of 10 MHz, which is the resonant frequency of the coils. This TX/RX will

be tuned together and will have the ability to illuminate a 60 W light bulb or charge a 1.5V

battery.



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4. DESIGN APPROACH AND DETAILS

4.1 Design Approach

The wireless power device will be designed in at least two sections: the oscillator and

antennae coils. These sections are outlined below in Figure 1.

Figure 1. The wireless power device showing the transmitter and receiver.

The oscillator circuit is connected to the transmitting coil. A sign wave is generated and

transmitted two meters to the receiving coil which is attached directly to the 60 W light bulb or

1.5 V battery.

Oscillator

The oscillator being used to generate the 10 MHz frequency is a typical Colpitts

oscillator, shown in Figure 2 [4].



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Figure 2. Example circuit for a 50 MHz Colpitts oscillator.

Connected to the output of the Colpitts oscillator will be an antenna used to transmit the

power signal encapsulated in a 10 MHz sinusoidal waveform. This signal will encounter the

transmitting coil which is coupled to the receiving coil due to resonant inductive coupling.

Antennae

Transmitting signals over long distances requires that the transmission beam have a high

degree of directionality and a very large gain requiring a larger size antenna. In the near field

there is still the need for directionality and gain, but also the need for the beam not to be affected

by outside radiation as it is generally transmitted at lower power levels. For purposes of far field

or long distance WPT, wide angle dipole antennas are better suited for the task. While for near

field or short range WPT, helical antennas provide better gain and power transfer.



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Figure 3. Frequency range calculations for acceptable IEEE frequency levels.

4.3 Constraints, Alternatives, and Tradeoffs

Constraints

Cost arises as a major constraint in building a WPT system as a result of other

constraints. In particular is the use of antenna design and simulation software. There is great

software on the market specifically for the purpose of designing the antenna and modeling its

radiation pattern. However, the most applicable software usually costs thousands of dollars.

Another constraint related to the cost is the size of the helical antenna used. A larger antenna will

allow for a higher gain and thus higher efficiency, but it can cost up to $374.

Alternatives

Alternatively what can be done is to use free software that, while limited in scope, can

give a reasonably accurate description of the desired radiation pattern and the antenna specs

needed to achieve that result. By using the antenna design software, the helical antenna used can

be optimized and possibly tapered to get the same gain as a larger antenna, but with half the

amount of copper needed to fabricate the antenna. By increasing the frequency used to transmit

power, the size of the helical antenna can again be reduced further cutting costs.



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Tradeoffs

By implementing the aforementioned alternatives we reduce costs, but it comes with a

trade off of reducing the distance over which power can be transmitted. The limited scope of the

free software can also increase the time needed to design the antenna. However, if software

allows for an adequate tapered helical antenna model the gain and efficiency could prove to be a

more ideal than previously expected.

5. Schedule, Tasks, and Milestones

A Gantt chart containing the tasks and schedule for completing the project is shown

below in Figure 4.

Figure 4. Gantt chart for wireless power transmitter and receiver.

R. Lecture, M. Little, and S. Dew are currently working together to design the oscillator

required by the wireless power transmitter. C. Jordan is working to produce the helical antennas



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necessary to achieve inductive coupling between the transmitter and receiver. After the helical

antennas are built, J. Freeman, and D. Dellar will work with C. Jordan to improve on the tuning

of the antennas with respect to the entire system.

6. PROJECT DEMONSTRATION

In the final demonstration, safety will be of the highest concern. In December of 2008

the device will be tested in the Van Leer building under the supervision of the project advisor

with all members of the design section present for observation. M. Little, R. Lecture, and C.

Jordan will measure the potential across the antennae to ensure that they are at acceptable levels

and not prone to discharge. Once the safety of the system has been demonstrated, the transmitter

antennae will be connected to the oscillator circuit by J. Freeman and D. Dellar and the receiver

will be connected to the light bulb or battery by S. Dew. The demonstrators will operate the

system by connecting the power supply to the oscillator and adjusting the antennae until the light

bulb has been illuminated. Next, the light bulb will be disconnected and C. Jordan and M. Little

will connect the battery in order to demonstrate the wireless power charging capability of the

device.

The audience will know that the device is in working condition on two occasions. The

first instance will be when the light bulb illuminates. This demonstrates to the audience that the

device is visibly working and transmitting power wirelessly to the light bulb. The second

scenario will involve the battery. A voltmeter will be attached to the battery to demonstrate an



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initial voltage of 1.5V. After the device has been attached to the battery the voltmeter will again

be used to demonstrate the change in voltage.

7. MARKETING AND COST ANALYSIS

7.1 Marketing Analysis

This type of wireless power transmitter is not a product that is presently available on the

consumer market. There are several small electronic consumer devices that provide wireless

charging capabilities but none are of this scale and potential. Small electric toothbrushes and

razors implement an inductive charging technique however the effective charging distance is less

than six inches. This new cutting edge wireless power application will open up a new aspect of

wireless charging devices. This device increases the effective charging distance to two meters

and improves the voltage that is transmitted wirelessly.

The wireless power transmitter will be sold as a complete unit. It will be compatible with

several electronic devices that are inside the design specifications, be it a 60 Watt light bulb or a

1.5V battery.

7.2 Cost Analysis

Presuming the average electrical engineer’s salary is $65,000 dollars a year, the

individual hourly rate of the design team members would be $31 an hour. There are six

members on the wireless power team spending an average of 8 hours a week developing the

system. The cost of copper coil is expected to be $15 dollars a foot with six feet going into each

system. The power supply, resistors, inductors, and capacitors necessary to develop the



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oscillator are expected to cost an additional $15 dollars. The entire system will be built into an

electrical chasis expected to cost $10 dollars. This brings the total cost of development to

$25,336 dollars with the cost of each subsequent unit costing $30 should it go into production.

The suggested selling price is determined based on 1,000,000 units expected to be sold

over the course of 5 years . Based on the development of $25,336 and 1,000,000 units being sold

the suggested price is $33. At this price, the development costs would be regained after 844 units

were sold with the remaining balance going to profit and future developments.

8. SUMMARY

Currently the wireless power system is in the construction and testing phase. The

specific values necessary to build the oscillator are being precisely calculated using SPICE and

mathematical modeling techniques. The output values of the oscillator will be the dependant

factor of the design of the helical antennas.

The development phase of the rectifier circuit to charge the battery is underway. In this

phase, we are determining the best circuit necessary to reduce the amount of harmonics that are

generated due to the tuning mismatch between the rectifying circuit and oscillator.

After the design phase of the oscillator circuit is complete, it will be tested with the coils

and a 60 W light bulb to determine that it is functioning correctly.

Finally, the rectifying battery charging circuit will be added to the receiving coil of the

WTP system and testing will begin to charge a 1.5 V battery.



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9. REFERENCES

[1] E. Jones, “The Basics of Radio Wave Propagation,” [Organization Website],

[Cited 1 September 2008], Available HTTP: http://ecjones.org/propag.html

[2] N. Tesla, "System of Transmission of Electrical Energy," U.S. Patent 645 576,

Mar. 20, 1900

[3] M. Langer, “Wireless Power & “Sensitive” Robots”, [Organization Website],

[Cited 1 September 2008], Available HTTP:

http://news.yahoo.com/s/afp/20080821/ts_afp/usitinternetenergychipcompanyintel

[4] Tracking Advances in VCO Technology, Maxim Microchip Corp., Appl. 1768, pp 1-3.

[5] A. Bacon, ViaSat Antenna Engineer. Personal Interview. 29 August 2008.

[6] FCC Standard/regulation: Available HTTP:

http://www.fcc.gov/oet/info/rules/part15/part15-9-20-07.pdf

[7] Author unknown. (2007, June). Electromagnetic Fields and Public Health. WHO Fact

Sheet [online document]. No 322. Available HTTP:

http://www.who.int/mediacentre/factsheets/fs322/en/index.html

[8] A. Kuris et al., "Wireless Power Transfer via Strongly Coupled Magnetic

Resonances," Journal Science, vol. 317, pp 83-85, July 2007

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