final paper
TRANSCRIPT
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
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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
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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.
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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.)
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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.
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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
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