Smart Inventory Management System

(SIMS)

Masaki Negishi

Anthony Fai

Project 37

May 3, 2005

Instructor: Richard Cantzler

Final Report

1

ABSTRACT

The SIMS project is a cost effective solution for inventory management using RFID

technology. With a software and hardware component, SIMS allows multiple

antennae to be connected to one RFID reader to offer a wide coverage for the tracking

of inventory.

SIMS uses high frequency RFID standards at 13.56 MHz and corresponding passive

transponders to guarantee small packaging as well as eliminating the need for

replacing batteries. The system allows user interface through a computer in order to

selectively search for transponders.

SIMS only requires one time installation, and is very modular in its design.

Expansions to the system can be made by the addition of antennae or workstations

that have SIMS installed onto them. SIMS is also compatible with all RFID standards

such as low frequency and ultra high frequency ranges.

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TABLE OF CONTENTS

1. INTRODUCTION....................................................................................................................3

1.1 Purpose...............................................................................................................................4

1.2 Specifications......................................................................................................................4

1.3 Subprojects.........................................................................................................................4

1.3.1 RFID Reader..............................................................................................................4

1.3.2 Transponders.............................................................................................................5

1.3.3 Antennae....................................................................................................................5

1.3.4 PCIPU........................................................................................................................5

1.3.5 Power Supply............................................................................................................5

1.3.6 RF Switching Unit.....................................................................................................5

1.3.7 Software.....................................................................................................................5

2. DESIGN PROCEDURE & DETAILS.....................................................................................7

2.1 Antennae.............................................................................................................................7

2.2 PCIPU...............................................................................................................................10

2.3 Power Supply....................................................................................................................11

2.4 RF Switching Unit............................................................................................................11

2.5 Software............................................................................................................................13

3. DESIGN VERIFICATION.....................................................................................................15

3.1 Testing..............................................................................................................................15

3.1.1 Antennae..................................................................................................................15

3.1.2 Power Supply..........................................................................................................17

3.1.3 RF Switching Unit...................................................................................................18

3.1.4 Overall System........................................................................................................19

3.2 Conclusions.......................................................................................................................19

4. COST......................................................................................................................................20

4.1 Parts..................................................................................................................................20

4.2 Labor.................................................................................................................................20

5. CONCLUSIONS....................................................................................................................21

5.1 Successes and Challenges.................................................................................................21

5.2 Future Hardware Developments.......................................................................................21

5.3 Future Software Developments........................................................................................22

5.4 SWOT Analysis................................................................................................................23

5.5 Other RFID Frequencies...................................................................................................23

5.6 Credits...............................................................................................................................24

6. REFERENCES.......................................................................................................................25

APPENDIX A –SCHEMATICS..........................................................................................A.1

APPENDIX B –PARTS AND COST...................................................................................A.2

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1. INTRODUCTION

The overall system that we ended up with differs a bit from what we proposed during

the Design Review. We originally designed a system which requires matching

network components between components where impedance mismatch is very large.

This idea was originally in our mind since we assumed that we would not be able to

make antennae and RF switching unit to be 50-ohm components. Note that in our

original design (Fig1), we have matching networks between RF switching unit and

antennae, and between RFID reader and RF switching unit. The matching network

between antennae and RF switching unit could be omitted since an antenna itself

consists of a T-matching network, which will be discussed later in the antenna

section. Also, taking advantage of relays as switches enabled us not to worry about

the matching network between them and readers since the short paths created by

relays are electrically very small compared to the corresponding wavelength of

13.56MHz, which is roughly 22 meters. Also note that PC interface processing unit is

added to our final design as a control unit for the relays (Fig2). Moreover, the timing

hardware unit in the original design is replaced to a software unit since timer in a

computer is more accurate and timing can be easily changed.

Figure 1

4

Figure 2

1.1 Purpose:

Our goal is to create a functioning model for an inventory management system that

will use RFID technology as its backbone. It will allow users to track, search, and

label inventory wirelessly. This system will be able to locate inventory and report its

status (present or absent). It will provide a PC interface such that a user can go to the

system and search for the inventory desired.

1.2 Specifications :

SIMS requires a number of specifications in order to operate properly. The

specifications are listed below:

1. Operating frequency of 13.56 MHz for the RF components (reader, antenna,

transponders)

2. Power supply of 24 Vdc for the RFID reader

3. Power supply of 5 Vdc for TTL circuitry

4. Overall system impedance seen from RFID reader of 50 Ohms

5. Absence of metal, liquids, and noise from antenna and transponders

6. PERL installed on a workstation

7. 50 Ohm coaxial cables with BNC and SMA connectors

1.3 Subprojects :

The entire project can be broken down to seven subprojects. They are as follows:

1.3.1 RFID Reader:

Texas Instruments’ RFID Reader S6500 was used to transmit signals. It outputs

48V-peak-to-peak with frequency of 13.56 MHz. The corresponding wavelength

of it is roughly 22 meters, which made our switching scheme simpler because the

5

short paths created by the relays were much smaller electrically. Reader itself

has the impedance of 50 ohms. When the impedance of other components (or

input impedance looking from the reader) is not matched to 50 Ohms, the reader

will give the RF error. The reader is so selective that it does not allow other

components to have SWR of 1.5 or above. This made our antenna design very

difficult.

1.3.2 Transponders:

A transponder consists of a loop antenna and a microprocessor chip. There two

types of transponders: passive and active. A passive transponder only consists of

a loop antenna and a microprocessor chip. The magnetic field from the antenna

induces current on the passive transponders so that they have enough power to

trigger the microprocessor. Unlike passive transponders, active transponders

require batteries. We took advantage of passive transponders to lower the total

cost of our system and to make our system require only first-time installation

(i.e. no need for battery change on the transponders).

1.3.3 Antennae :

Antennae used are loop antennas. Their function is to propagate 13.56 MHz

signals between the reader and transponders. Many antennae can be used in our

system.

1.3.4 PC Interface Processing Unit:

The PC Interface Processing Unit (PCIPU) uses a PIC microprocessor as its core,

which is programmed to take inputs from a computer via a RS232 serial cable

and then send out that signal to RF Switching Unit to turn on the desired antenna.

1.3.5 Power Supply:

A power supply was made to supply 5 V and ground to relays and PIC. This

power supply can supply more stable and less ripple 5V than that of which the

universal AC/DC adaptor supplies. Also, including the power supply is

extremely useful and makes our system more like a commercial product.

1.3.6 RF Switching Unit:

The RF Switching Unit, as the name suggests, serves to switch between antennas

for RF input and output to and from the RFID reader. It should be able to handle

at least 13.56 MHz and high power.

1.3.7 Software:

A total of three programs were used for the demonstration, two of which were

created and one that was taken from Texas Instruments. A PERL program was

written to take user inputs from a keyboard and send them out through COM Port

2. A PIC program on the PCIPU was written to take inputs from the COM Port

and then output them to the RF Switching Unit. The S6 Reader Utility V1.32 is a

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windows based software program that interfaces to the S6500 Reader. It provides

a means to demonstrate the functional capabilities of the readers as the execution

of commands such as reading and writing information to and from transponders

and can be employed to assist in reader configuration or diagnosis. The software

can be found in the software section of Texas Instrument’s RFID page

http://www.ti.com/rfid.

7

2. DESIGN PROCEDURE & DETAILS

During the project, many we encountered many design issues and had to make

modifications to our design. Some of the changes involved drastic changes to entire

components, while others were not as severe.

2.1 Antenna:

As proposed in Design Review, we tried to make in-house antennae to lower the

cost of our system. Despite the fact that we spent more than half of our time on

an antenna, we could not accomplish to make one primarily because of its

instability in the environment.

1) In-House Antenna:

The antenna we tried to build consists of:

a. copper tapes to create a square loop and T-matching network

b. tuning capacitor to tune the antenna to 50 ohm

c. damping resistor to lower the Q of the antenna

d. wooden board to place the copper-tape antenna

Matching Network:

The original matching network for the antenna was to create a T-matching

network on the RF board using capacitors and inductors. The design equations

for the T-matching network are as follows:

Figure 3

Rv is a virtual resistance and can be specified by us. Note that Rv > Rload,

and Rv > R2.

8

Q factors:

Q1 = sqrt(Rv/Rload – 1)

Q2 = sqrt(Rv/R2 – 1)

We can set Q1 or Q2 to be 20, and determine Rv.

Using Q factor = 20, we can determine values of X2, X’, X’’, and X1.

X2 = (- or +)Rsmall * Q,

X’ = (+ or - )Rbig / Q

Where Rsmall is smaller of Rv and R2

And

X1 = (- or +)Rsmall * Q

X’’ = (+ or -)Rbig/Q

Where Rsmall is smaller of Rv and Rload

Then use jX = j * (2 * pi * 13.56MHz) * L

or

X = 1/(j * (2 * pi * 13.56MHz) *C)

to solve for inductances and capacitances.

Note: Load reactance is included in X1.

This theory could not be used for the antenna impedance matching since the

antenna itself has to have the impedance very close to 50 ohm before connecting

the 50-Ohm coaxial cable. Otherwise, the mismatch at the antenna and coaxial

cable junction will result in reducing power transmitted to the antenna. For this

reason, we decided to make a T-matching network on the antenna itself by adding

two copper strips as shown in Fig3. To match the antenna to 50 ohm using this T-

matching network, we manually moved it and varied the capacitance of the

antenna using variable capacitor. To examine the impedance of the antenna, the

vector network analyzer was used. Using SOLT calibration technique, the

network analyzer was calibrated with reference plane being one of the coaxial

cable ends. However, we could not find any point on the antenna to make the

impedance of it 50 ohm, which implies the SWR of 1 in our system. (The closest

SWR we could obtain by this T-matching network was 2.2.)

9

Figure 4

2) Antenna from Texas Instruments:

An antenna from Texas Instruments (RI-ANT-T01A) was purchased in place of

the in-house antenna. By default, antenna was tuned at 13.56 MHz and has the

input impedance of 50 Ohm.

Figure 5

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2.2 PCIPU:

The PC Interface Processing Unit was later added on to the project. The Timing

Unit proposed in the Design Review was replaced to eliminate any potential

errors that may occur from the unit itself, or other issues with synchronization

with the reader.

To take inputs from a computer, which have logic high at 13 V and logic low at -

13V, a MAX232 chip is implemented to drop the voltage levels to that of TTL

chips. Once the input signal from the serial port is received and dropped down to

an acceptable voltage level from the MAX232 chip, the PIC microprocessor first

checks if the proper header is present. The inputs from the keyboard must have

the header “AF,” followed by two hexadecimals that indicate which antenna to

turn on. The header is used to prevent any accidental inputs from the user. If the

input is correct, the PIC then sends out the hexadecimals to the RF Switching

Unit, and also back to the computer through the serial cable to confirm that it

sent out the signal that it was instructed to.

The PIC microprocessor has 8 pins that are used as outputs to the RF Switching

Unit. They send either logic high or low to let to turn on the antenna of choice.

With 8 pins, and the implementation of a multiplexer, a maximum of 28 = 256

antennas can be controlled with one PCIPU.

For debugging purposes, LED’s are placed to check if the PIC is running through

the correct program loops and if the outputs to the RF Switching Unit are correct.

Shown below is the picture of the actual PCIPU.

Figure 6

11

The four LED’s on the lower left hand corner of the board are used to indicate

the program running through the loops, and the LED array on the upper right

hand corner indicates the outputs to the RF Switching Unit.

The schematic for the PCIPU is shown in the Appendix.

2.3 Power Supply:

The power supply we made really is nothing but a regulator (LM317T). This

three-terminal device takes the DC voltage from the universal adaptor, and

outputs the regulated voltage which is in the range of 1.5 volts and 37V. The

third terminal of LM317T (Adjust) is used to adjust the output voltage needed.

The design equation is:

Vout = 1.25(1 + (R2 +Radjust) / R1) + Iadjust(R2 + Radjust), where all the variables are

shown in figure below.

Figure 7

We used a 1K ohm potentiometer for Radjust to manually adjust the output voltage.

Also, note that two diodes are Dout and D2 are placed to protect against the

current dump from capacitors Cout and C2, respectively.

2.4 RF Switching Unit:

Although it serves the exact same function as the design mentioned in the Design

Review, the design has changed drastically. Instead of using the PIN diodes

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mentioned originally, the present design uses relay switches as the RF switch.

PIN diodes, although good for RF switching for small AC signals, do not

perform well the signals from the RFID reader, which are of 48 volts peak to

peak. In addition, the use of PIN diodes also introduced impedance mismatch,

which would be bothersome to eliminate. Originally the overall design also

included an impedance matching network, but that was also scrapped for two

main reasons: a) the impedance matching network had to be made bidirectional

to account for the signal from the reader going towards the antenna and for the

signal coming back from the antenna to the reader; and b) the impedance seen

from the antenna keeps changing with respect to the antenna, whose impedance

is a function of position, environmental factors, and background noise. Using a

relay switch minimizes any impedance mismatch from the RF Switching Unit

since the switch is simply a thru between the reader and antenna when it is on,

and an open circuit when off.

The RF Switching Units takes two kinds of inputs, one from the reader and one

from the PC Interface Processing Unit (PCIPU). The inputs from the PCIPU are

connected to the magnets that turn the relays on and off. The RF signal from the

reader then goes through to the RF output that is connected to the input by the

armature of the relay switch. With a total of four RF outputs, up to four antennas

can be connected.

Before using the current design, an intermediate design was used that

implemented both PIN diodes and relay switches. The relays were used in that

design to ensure that the PIN diodes were completely turned off when desired.

This seemed redundant since the relays alone were enough, and the wavelength

of the RF signal used (22 meters) is long enough that the switch is electrically

small.

Of course, there is a drawback for using relay switches. A relay switch can only

operate for approximately 10,000 switches before the armature wears out. Hence

a better solution with longer lifetime is necessary for future design. One

suggestion is to use solid-state devices for switching.

An image of the circuit is shown below.

13

Figure 8

A schematic a single switch is given in the Appendix.

2.5 Software:

PERL Software:

The file “serial.pl” was the program written to take user inputs from a keyboard

and send them out through COM Port 2. Run in DOS, the program allows four

user inputs:

1. Q: Quit the program

2. H: Display the menu for help

3. I: Specify the time interval for data transmission

4. T: Transmit data through COM Port 2

To transmit data through the COM Port, which is the program’s main function, the

user must enter the header “AF” followed by two hexadecimals. This is done to

prevent accidental inputs. After is sends the data, is waits to get the data back

from the COM Port to check if what the PCIPU received is correct.

To run this program, PERL must be installed onto the computer, as well as the

correct libraries. PERL and the libraries can be found on

http://www.activestate.com/.

PIC Software:

14

The file “Switch0331.hex” was written to program the PIC microprocessor on

the PCIPU to take inputs from the COM Port and then output them to the RF

Switching Unit. It also sends back the signal that it takes in back to the computer

to confirm that a signal was sent and for verification.

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3. DESIGN VERIFICATION

Verification was done on the analog components of the project. Software was just

checked to see that it operated according to how we desired it to operate, and same

goes with the PCIPU. The parts that were testing extensively were the antenna, power

supply, and the overall system when everything was connected together.

3.1 Testing:

The following paragraphs are the compilation of tests done on the components

mentioned earlier.

3.1.1 Antenna:

Some measurements are taken to characterize the behavior of this antenna.

Once data is obtained from VNA, the data can be examined by transporting it to

ADS. The data includes s-parameters. What we obtained is simply S11, which is

simply the input reflection coefficient. SWR can be calculated using S11:

Let mag(S11) be magnitude of S11. Then,

SWR = (1 + mag(S11)) / (1-mag(S11))

a. Measurement Results

i) Antenna placed in free space (away from metal)

When antenna was placed away from the metal, it has the impedance

very close to 50 ohm (figure below). SWR is calculated using the

equation above: SWR = 1.004.

16

Figure 9

ii) Antenna placed on the lab station desk

When antenna was placed on the lab station desk, imaginary part of

the antenna impedance increased to 25.031, while the real part of it

kept almost unchanged. This increases both magnitude and phase of

the overall input impedance of the antenna. SWR is calculated to be:

1.636. Even though the SWR of 1.636 seems to be reasonable, the

RFID reader is very picky and gave us RF error.

17

iii) Antenna placed very close to the lab equipment

When the antenna is placed very close to the lab equipment, antenna

impedance changed to 16.720 + j40.707, which gives us the

magnitude of 44.007, and phase of 67.670 degrees. SWR of this is

calculated to be: SWR = 5.111. With this SWR, there is a great

mismatch, and reader could not recognize the signal coming back

from the antenna.

3.1.2 Power Supply:

We obtained very clean 5 Vdc from the power supply output with maximum

voltage and minimum voltage being 5.023 V and 4.975V, respectively. The

image below was captured from an oscilloscope, which illustrates the amount

of ripple from the power supply.

18

Figure 10

3.1.3 RF Switching Unit:

We verified that the RF Switching Unit does work and that transponders can be

detected when the reader and antenna are connected to SIMS. The testing we

made was on the isolation of the signal. Since there are multiple antennae

attached to the RF Switching Unit and only one antenna will be on at a time, it is

necessary to see if the non-connected antennae will pick up any signal as to

check the isolation of the component. Hooking up an oscilloscope to a RF output

that is not transmitting and the relay is off while the reader is on, we obtained the

following image.

19

Figure 11

Although there is still some signal, its amplitude is only 481.3 mV, while is very

small according to the 48 V when an antenna is transmitting. Thus, the RF

Switching Unit has relatively good isolation.

3.1.4 Overall System:

After connecting the antenna to SIMS, measurements were taken. As shown in

the figure below, magnitude of the input impedance seems to too big for the

reader to recognize the signal coming back. However, phase of the impedance is

so small (5.012) that it could be recognized by the reader without any problem.

SWR was calculated to be: SWR = 1.349.

Figure 12

3.2 Conclusions:

From the tests done, all components operate as desired. The antenna needs to be

operating away from any metal and lab equipment, and in a vertical position

preferably in free space for optimal performance. The RF Switching Unit still can

improve in its signal isolation, but is acceptable for the time being. Overall the

system operates fine. The RFID reader acts as if the SIMS system did not add any

significant amount of impedance.

20

4. COST

The total cost for this project is divided into two parts, one for parts, and the other for

labor. A complete breakdown is given in the Appendix. This section will summarize

the total amounts.

4.1 Parts:

The total amount spent on parts was $287.31, which consists on mainly the parts

on the hardware we built. We left our cost on parts that we not used on the final

product, but were involved in the testing phases, in order to identify how much is

spent on one product.

If we were to include the RFID reader and the antenna that were acquired from

Texas Instruments, the total cost would sum up to be $1750.59

4.2 Labor:

The total amount of labor cost is $7200.00. This is acquired but multiplying $30

per hour by a total of 120 hours for two engineers.

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5. CONCLUSIONS

5.1 Successes and Challenges:

This project was a success in the sense that we had a functioning system at the

end that was able to do the basic features that we originally indicated. Although

we fell short of what we claimed to be able to do during the proposal and Design

Review, our product was created such that additions can be easily added to it.

The largest challenge was the RF components. The reader is extremely picky in

that the components added to it cannot have a SWR of more than 1.4. At such a

low frequency, everything is operating at near field for the antenna, making even

the slightest environmental conditions influential. The antenna design was

painstakingly difficult, as it was very hard to make a stable enough antenna with

sufficient reading range. PIN diodes also became a challenge that set back some

time.

5.2 Future Hardware Developments:

To improve the SIMS project, some future developments can be made for the

hardware. Due to time constraints, these changes could not be done within the

semester. Here are some suggested projects:

1. Improved RF Switching Unit: As mentioned in the section about the RF

Switching Unit, a better solution is necessary. The lifetime of the current solution

may become too short for long-term operation. A solid-state device can be

implemented to solve this issue. Further testing and investigation can also be

done on PIN diodes if time permits. More antenna outputs can be added to the

unit depending on the number needed. One thing to keep in mind is that

additional cable length to antennas that are further away from the unit must be

multiples of 11.06 meters, which is half of the wavelength of HF RFID readers. If

other frequencies are to be used, then the half wavelength rule must still be

followed.

2. Antenna Design: Further research can be done on the antenna purchased from

Texas Instruments to see why their product is functional while the one built

during the project has such poor performance. A better BALUN and matching

network is to be implemented for a more stable antenna. Larger antennas also

allow longer reading range.

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5.3 Future Software Developments

A user interface needs to be developed as a future project to make SIMS

complete. For the demonstration, the software used was a PERL code that allowed

users to type in hexadecimals to be sent to the PCIPU and the TI S6 Reader Utility

software that dealt with the PC to RFID reader interfacing.

The user-friendly interface should be web based so that users can log on any

connection, such as a remote desktop, laptop, or even handheld device such as a

PDA. On the backend of the software, a robust database is necessary to collect

inventory data. The inventory data should include:

1. Inventory name

2. Inventory ID

3. Inventory type (e.g. office supplies, electronics)

4. Quantity

5. Inventory description (explain its functions)

6. Inventory status (missing, present, borrowed out)

7. Inventory Location (or where last seen)

A suggested database structure is as follows:

A hierarchy must also be made to decide on who can make changes to the

system. The suggested hierarchy is:

1. Administrator

2. Instructor

3. Student

The system should also have code to communicate with the RFID reader and the

PCIPU. It should allow users to search for a single inventory, do a mass search,

or any other logical search. The searching algorithm, when scanning a room,

should be one that is optimal for the layout of the antennas and to avoid any

interference. A simple method would be a linear search through the antennas in a

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Type Name Description Quantity1 Furniture Office Furniture 52 Computers Dell Desktops 9ID Name Status Type Location001 Chair present 1 246EL002 Desk Missing 1 150EL*003 Dell Inspiron Borrowed 2 341EL*

room. Each antenna should be assigned to a location in a room. For example, in a

square room, an antenna layout can be as follows:

In this example, the location B-2 can correspond to a specified test bench in a

lab.

5.4 SWOT Analysis :

The following table gives a Strength, Weakness, Opportunity and Threat analysis

to our product. It gives a business perspective to the SIMS.

Strength Weakness

Modular design

Supports LF and UHF

Minimize number of readers

Cost effective

Short range

Susceptible to environmental factors

Relay power consumption and lifetime

Threat Opportunities

Smart Shelves

RTLS

Inventory Management

UHF implementation

Software Expansion

5.5 Other RFID Frequencies :

Another option to consider is other RFID frequencies. The table below gives a

summary of the advantages and disadvantages of the common frequencies.

24

Frequency Pros Cons

LF (100 – 140KHz; ~2.5 km)

Read Range: ~100 cm MAX

Magnetic

Inductive Transponders

Less susceptible to environment

Longer reading range than HF

Only usually one transponder can be read at

a time

Tags bulkier and more expensive than HF

ones and less memory capacity

HF (13.56MHz; ~22m)

Read Range: ~50 cm MAX

(current antenna ~25 cm)

Magnetic

Inductive Transponders

Anti-collision intelligence allows

multiple of tags to operate

concurrently

Well defined magnetic field

More susceptible to environment

Short reading range

UHF (860 – 960MHz; ~33 cm)

Read Range: ~9m MAX

Electric (but passive tags)

Capacitive Transponders

Anti-collision detection

Long reading range

Not well defined electric field

Field nulls near antenna requires complex

anti-collision intelligence

Tags have less memory capacity

5.6 Credits :

First and foremost, we would like to thank our TA Richard Martin Cantzler for

his great help. Without his constant help and support, we could not have

overcome many difficulties that we faced during the semester. He is a great TA

and friend.

We would also like to thank Professor Carney for his encouragement and

understanding our situation, especially for the antenna. He had faith in our

project and us.

Nicholas Soldner also helped us greatly for the RF components. His assistance is

greatly appreciated.

Many thanks go to Prof. Steven Franke and Prof. Bernhard for their advice and

help.

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6. REFERENCES

[1] Texas Instruments, Tag-it HF-I Transponder Inlays, Texas Instruments

Incorporated, 2005

[2] Texas Instruments, HF Antenna Design Notes Technical Application Report,

Texas Instruments Incorporated, 2003

[3] Texas Instruments, HF Antenna Cookbook, Technical Application Report, Texas

Instruments Incorporated, 2004

[4] Texas Instruments, Construction a 1000 x 600 HF Antenna Technical

Application Report, Texas Instruments Incorporated, 2003

[5] Texas Instruments, HF Reader System Series 6000 S6500/S6550 Program

Library FEISC Reference Guide, Texas Instruments Incorporated, 2001

[6] Texas Instruments, HF Reader System Series 6000 S6500/S6550 Program

Library FECOM Reference Guide, Texas Instruments Incorporated, 2001

[7] S. J. Franke, ECE 453 Radio Communication Circuites Course Notes and

Laboratory Notes Fall2004: Department of Electrical and Computer Engineering,

University of Illinois, 2004

[8] Richard Cantzler and Grant Farrand, “DESIGN OF A WIRELESS

KEYBOARD, AUDIO, VIDEO & MOUSE SWITCH”, Senior Design Project

(ECE345), Department of Electrical and Computer Engineering, University of

Illinois, United States, Fall 2003

[9] Richard Cantzler and Grant Farrand, “APPENDIX A – BLOCK DIAGRAMS”,

Senior Design Project (ECE345), Department of Electrical and Computer

Engineering, University of Illinois, United States, Fall 2003

26