Final Report
Off the Wire
BRIGHAM YOUNG UNIVERSITY – ECEN 490
2012
Authored by: James Smith, Jorge Conde, Bradford Law
Final Report
Off the Wire
Executive Summary
Freelinc, based in Orem, UT, is the sponsor of this ECE senior project. They design and produce magnetic
inductance wireless systems for law enforcement and military use in on-body sensor networks. This
approach to wireless communications that uses magnetic inductance is also known as NFC (near-field
communication). NFC is an emerging area of research and development and is set to solve some of the
problems that traditional wireless radio networks suffer from, such as security, bandwidth saturation, and
signal degradation through solid objects.
Freelinc’s existing products are limited to just a few channels and are used mainly to transmit audio signals
which have a high tolerance to error. They hope to expand their product line, however, and develop a
system based with much greater bandwidth and much lower bit error rates per channel. Having such a
system would allow many on-body sensors to communicate simultaneously and allow high-bandwidth
applications such as video streaming to be possible.
Our purpose was to take the existing wireless system provided by Freelinc and the work of the project’s
previous student contributors and improve those designs. Our goals were to significantly increase the
bandwidth while keeping the power draw as low as possible.
Final Report: Off the Wire | 4/12/2012
Our first steps in achieving our goals were to construct prototype transmitting antennas that were tuned to
two and three resonant frequencies respectively. We referred to these as “triple-tuned” and “double-tuned”
and they will be identified by those names throughout this report. Our first prototypes were limited to one
coil per ferrite rode, with our final product an extension of this design with each ferrite rod having a
winding for each tuned frequency to make all channels available in each orientation.
1
We found that our initial prototypes of the triple and double-tuned antennas performed remarkably well, a
huge improvement on the work of previous project contributors. We assumed that these improvements
would transfer to the final prototypes with multiple windings per rod. Upon building the final prototypes,
however, we found that our initial assumptions were wrong and the induced currents we thought would
not be present were indeed present and made the entire antenna unusable.
Progress, however, was made on another solution to increase bandwidth: a negative inductance circuit. We
created a schematic and model that properly modeled negative inductance behavior. Unfortunately, we
were unable to demonstrate a working physical circuit.
Despite our failure to produce a working final prototype we made huge leaps in bandwidth and have
uncovered a roadblock that future students and engineers will have to address.
EXECUTIVE SUMMARY ............................................................................................... 1
TABLE OF CONTENTS ................................................................................................ 2
FIGURES AND TABLES ................................................................................................ 4
INTRODUCTION.......................................................................................................5
PROJECT SPECIFICATIONS ........................................................................................... 6
TEST PLAN ............................................................................................................. 7
TEST DESCRIPTION ................................................................................................ 8
ACCOMPLISHMENTS ..................................................................................................9
DOUBLE-TUNED...................................................................................................9
TRIPLE-TUNED .................................................................................................. 10
NEGATIVE IMPEDANCE .......................................................................................... 12
ANALYSIS OF RESULTS.............................................................................................. 13
NEGATIVE IMPEDANCE .......................................................................................... 13
SINGLE-PORT RESULTS ......................................................................................... 13
THREE-PORT RESULTS.......................................................................................... 14
INDUCTIVE COUPLING....................................................................................... 14
POSSIBLE SOLUTIONS............................................................................................... 18
CONCLUSION ....................................................................................................... 18
APPENDIX A: FUNCTIONAL SPECIFICATION DOCUMENT........................................................ 1
CONCEPT GENERATION AND SELECTION ......................................................................1
INTRODUCTION ...................................................................................................2
OVERVIEW ......................................................................................................2
PURPOSE ........................................................................................................2
MATRICES .......................................................................................................2
BODY OF FACTS ................................................................................................ 2
SPECIFICATIONS ................................................................................................ 2
KNOWN FACTS .................................................................................................2
ASSUMPTIONS...................................................................................................2
PROPOSED DESIGN ................................................................................................ 3
CRITICAL DESIGN AREAS ......................................................................................... 3
DIFFERENT CORES ............................................................................................. 3
MULTIPLE CORES .............................................................................................. 3
WIRE............................................................................................................. 4
CONCEPT SELECTION & SCORING .............................................................................. 4
COMPLEXITY....................................................................................................4
BANDWIDTH ....................................................................................................4
RESULTS ............................................................................................................5
DUAL TUNED ...................................................................................................6
APPENDIX B: CONCEPT GENERATION AND SELECTION DOCUMENT ..........................................1
INTRODUCTION ...................................................................................................2
Final Report: Off the Wire | 4/12/2012
Table of Contents
2
Final Report: Off the Wire | 4/12/2012
OVERVIEW ......................................................................................................2
BACKGROUND ..................................................................................................2
PRODUCT DESCRIPTION ...................................................................................... 3
PROJECT REQUIREMENTS ........................................................................................ 3
CUSTOMER NEEDS ............................................................................................. 3
ANALYSIS OF CUSTOMER NEEDS ............................................................................. 4
PROJECT SPECIFICATION ......................................................................................... 5
ANALYSIS OF METRICS ............................................................................................ 6
CONCLUSION ......................................................................................................6
APPENDIX C: PROJECT SCHEDULE ................................................................................. 1
APPENDIX D: NEGATIVE IMPEDANCE CALCULATIONS........................................................... 1
3
Figures and Tables
Figure 1: Triple-Tuned Concept Antenna With Three Ports ......................................................... 5
Figure 2: Black Box Diagram ................................................................................................ 5
Figure 3: Test Bench Transmitter .......................................................................................... 7
Figure 4: Test Bench Receiver .............................................................................................. 7
Figure 5: Full Test Bench .................................................................................................... 8
Figure 6: Double-Tuned Prototype with One Port ..................................................................... 9
Figure 7: Antenna Response Measured by Network Analyzer ........................................................ 9
Figure 8: Double-Tuned Test Results for 13MHz Tuning ........................................................... 10
Figure 9: Double-Tuned Test Results for 13.75MHz Tuning ....................................................... 10
Figure 10: Triple-Tuned Prototype with One Port ................................................................... 11
Figure 11: Triple-Tuned Test Results for 12.75MHz ................................................................ 11
Figure 12: Network Analyzer Results for Triple-Tuned, Single-Port Antenna .................................. 11
Figure 13: Triple-Tune Test Results for 13.5MHz .................................................................... 12
Figure 14: Triple-Tune Test Results for 14.25MHz .................................................................. 12
Figure 15: Negative Impedance Schematic.............................................................................. 12
Figure 16: Negative Impedance PCB Layout ........................................................................... 12
Figure 17: Simulated Inductance For Negative Impedance .......................................................... 13
Figure 18: Double-Tuned, Triple-Port Antenna. ..................................................................... 14
Figure 19: S11, S22, S33 for Double-Tuned, Triple-Port Antenna ................................................ 15
Figure 20: S21, S12 for Double-Tuned, Triple-Port Antenna ...................................................... 15
Figure 21: S32, S23 for Double-Tuned, Triple-Port Antenna ...................................................... 16
Figure 22: S11, S22, S33 for Triple-Tuned, Triple-Port Antenna ................................................. 16
Figure 23: S21, S12 for Triple-Tuned, Triple-Port Antenna ........................................................ 17
Figure 24: S31, S13 for Triple-Tuned, Triple-Port Antenna ........................................................ 17
Final Report: Off the Wire | 4/12/2012
Table 1: Project Specifications Provided by Freelinc ................................................................... 6
4
Introduction
The initial project goal was to create a three port, three polarization system for the company Freelinc (see
Error! Reference source not found.). The design consists of three orthogonal ferrite rods. Depending
n the tuning of the antenna (tuned usually to two or three resonant frequencies, double-tuned and tripletuned respectively), each ferrite rod would have a winding for each tuned frequency. Our goal was to
create the antenna with the most usable channels (assumed to be triple-tuned), with all channels available in
each direction (each ferrite rod holding multiple windings). Error! Reference source not found.
llustrates the final prototype we had in mind.
Ultimately, our antenna would be a “black box” with three inputs and one output as illustrated in Figure 2.
The team operated under the assumption that one signal would be sent through only one port at a time. As
the other ports would be open circuited, it was believed that no unwanted currents would be generated
through inductive coupling.
In addition to the three port system, Freelinc requested our team work to build a matching system that
modeled a negative inductor. Having such a system would theoretically allow an antenna to resonate at all
frequencies and thus maximize BER and SNR
H
M
L
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L
5
1
2
L
3
M
M
H
H
F IGURE 1: T RIPLE -T UNED C ONCEPT A NTENNA W ITH
T HREE P ORTS
F IGURE 2: B LACK B OX D IAGRAM
Output
Project Specifications
The specifications we received from Freelinc emphasized bandwidth and portability. We took the project
specifications provided by Freelinc and prioritized them in order of importance (see Table 1Table 1).
T ABLE 1: P ROJECT S PECIFICATIONS P ROVIDED BY F REELINC
Description
Importance
1
Bandwidth: 12-15MHz
The wireless system should be capable of operating
between 12 to 15 MHz
1
2
Channels: 250kHz stepping
centered at 12.00, 12.25...
MHz
The device must be able to switch between 8 channel
frequencies enabling multiple devices to communicate
simultaneously. Regardless of orientation
2
3
Power Consumption: <40mA
Device should be powered by a 3.7V battery and pull
no more than 40mA.
2
4
Size: Highly portable
The device must be portable and light.
1
5
Cost: Inexpensive
The application is the United States military so the
device scale of production will be huge.
3
Bandwidth was the primary focus of the project and, by extension, the number of usable channels.
Increasing the bandwidth directly increased the number of usable channels. Our goal was to achieve at least
eight channels, where channels were defined as 250kHz wide, starting at 12 MHz continuing to 15MHz
having a bit error rate between 10-5 and 10-6. A total of 12 channels are possible between 12 MHz and 15
MHz.
Power consumption was important, however we included that in our development and testing by using an
amplifier designed and built under these specifications. The amplifier was powered by a battery similar to
the battery Freelinc uses to ensure the results of our testing would accurately represent the performance of
our antenna.
The size of the antenna was important because of the potential applications, so all of our designs were
limited to three ferrite rods. All of our designs were portable and met this specification.
Final Report: Off the Wire | 4/12/2012
Customer Specification
6
The cost is entirely out of our control. We have limited ourselves to basic materials that would be easily
fabricated in the final product such as ferrite rods, capacitors, and wire.
Test Plan
Previous senior project teams as well as graduate students working on the project have developed an
automated testing system that loads a sequence of random binary numbers onto an FPGA and transmits that
bit sequence on each of the 12 channels that are tested. The receiving system is also hooked up to a
computer with an FPGA where it samples the received signal and calculates the power for that channel.
Data from this test can then be imported into Matlab where accurate analysis can be performed.
Final Report: Off the Wire | 4/12/2012
List of Equipment
7

Two Computers With FPGA’s



Power Supply
Network Analyzer
Transmit Amplifier



Transmit Antenna
Receive Amplifier
Receive Antenna


Testing Apparatus
Cables

Automated Testing Program
F IGURE 3: T EST B ENCH T RANSMITTER
F IGURE 4: T EST B ENCH R ECEIVER
Test Description
1. In order to start the test, we have to connect the computers to the network so that they can access
the Automated Testing Program and can communicate with each other we also need to tune the
antennas at certain frequencies using the network analyzer.
2. Once we have the computers connected to the network, we have to connect the amplifiers to the
FPGAs. The transmitter amplifier will have a power supply of 3.7 V. according to our
specification. The receiver amplifier will be connected to the other FPGA and will have a power
supply of 15V.
3. Once both the receive and the transmit amplifiers are connected to the FPGAs and their power
supply we connect the transmit and the receive antenna to the corresponding amplifier. This is
done by positioning one of the polarizations of the double or triple tuned antennas parallel to a
receive antenna tuned to the same frequency as the transmit polarization. This process will be
repeated in order to test all the polarizations of the transmit antenna, retuning the receive antenna
each time to resonate with the transmit polarization.
4. Next the antennas are placed 1 m from each other.
5. 5. The automated test is run by selecting it on the program. The software will ask the name of the
antennas and the amplifiers and the distance that the antennas are from each other. This is key to
maintaining consistent data and building a matrix of data that is easy to search through. The test will
transmit frequencies starting at 12 MHz and increment 250 kHz until it tests the 15 MHz channel.
6. Several different tests are conducted at various orientations and positions are accumulated in order
to accumulate a steady average indicative of the reliability of the antenna
Final Report: Off the Wire | 4/12/2012
F IGURE 5: F ULL T EST B ENCH
8
7. Finally, after running different tests, Matlab is used to compile the results and display the mean Bit
Error Rate (BER) as well as Signal to Noise Ratio (SNR) and relative power of received signal and
noise.
Accomplishments
During the course of this project we made a lot of
progress in increasing the bandwidth of previous
designs. We started with a simple double-tuned
antenna with one input port and increased the
complexity by making a triple-tuned antenna with one
port. We hoped to eventually apply the breakthroughs
we made with these single port antennas to the final
three-port antennas.
F IGURE 6: D OUBLE -T UNED P ROTOTYPE WITH O NE P ORT
Final Report: Off the Wire | 4/12/2012
Double-Tuned
Our double-tuned antenna, picture in Error! Reference source not found., was the first antenna we
uilt. It is a simple design with two ferrite rods, each with a single tuned winding. The different tunings are
facilitated by the orange adjustable capacitors shown.
After building our antenna, we measured the response using a network analyzer and compare it to our
model for dual-tuned response using a special Matlab program we created for this purpose (shown in Figure
7). We used these results to finely tune our antennas and help them meet our model response. We found
that our previous prototypes of a
dual-tuned antenna had its ferrite
rods too close together, which
caused an unintended interaction
between the magnetic fields which
hurt the antenna’s performance.
We also found that centering the
windings on the ferrite rods served
to help our antenna’s performance
somewhat. Also, the number of
turns in each winding was
significant. We found that ten
turns provided a good response.
Finally, by using a lower-gauge
F IGURE 7: A NTENNA R ESPONSE M EASURED BY N ETWORK A NALYZER
9
wire (22 ga.) than that provided by Freelinc we improved performance significantly. Our final doubletuned antenna (Error! Reference source not found.) incorporated all of these improvements and
erformed surprisingly well.
We were able to achieve considerable improvements in the number of channels as shown in Figure 8 and
Figure 9. This antenna actually came close to meeting our requirements on the number of channels we
hoped to obtain. Our next step was to build our triple-tune antenna based on the principles learned during
the optimization of this antenna.
Double Tuned 13.75 MHz 50% of tests lie within error bars
Double Tuned 13 MHz 50% of tests lie within error bars
Bit Error Rate
0
-2
-2
10
Bit Error Rate
Bit Error Rate
10
-4
10
-4
10
-6
-6
10
10
11.5
Bit Error Rate
0
10
10
12
12.5
13
13.5
14
Frequency Channel (MHz)
14.5
15
11.5
15.5
Received Signal Power & Noise Floor
12
12.5
13
13.5
14
14.5
Frequency Channel (MHz)
Received Signal Power & Noise Floor
15
15.5
15
15.5
-40
-30
-35
-45
-40
-50
Power (dBm)
Power (dBm)
-45
-50
-55
-60
-55
-60
-65
-70
-65
-80
11.5
12
12.5
13
13.5
14
Frequency Channel (MHz)
14.5
15
15.5
F IGURE 8: D OUBLE -T UNED T EST R ESULTS FOR 13MH Z T UNING
-70
11.5
12
12.5
13
13.5
14
Frequency Channel (MHz)
F IGURE 9: D OUBLE -T UNED T EST R ESULTS
T UNING
14.5
FOR
13.75MH Z
Triple-Tuned
After our success with the double-tuned antenna, we started work on the triple-tune variant. The main
difference was a third ferrite rod for the third tuned coil. It is shown in Error! Reference source not
ound.. This unit still had just a single input port, making this simply an interim step on our way to our
final prototype with three input ports.
Using the lessons learned from the double-tuned antenna, we spaced the ferrite rods well away from each
other. The response recorded by our network analyzer was very encouraging, shown in Figure 11, Figure
Final Report: Off the Wire | 4/12/2012
-75
10
13,
Triple Tuned 12.75 MHz 50% of tests lie within error bars
Bit Error Rate
0
10
-2
Bit Error Rate
10
-4
10
-6
10
11.5
12
12.5
12
12.5
13
13.5
14
14.5
Frequency Channel (MHz)
Received Signal Power & Noise Floor
15
15.5
15
15.5
-30
-35
F IGURE 10: T RIPLE -T UNED P ROTOTYPE WITH O NE P ORT
Power (dBm)
-40
-45
-50
-55
-60
-65
-70
11.5
13
13.5
14
Frequency Channel (MHz)
14.5
Final Report: Off the Wire | 4/12/2012
and Figure 14 . Furthermore, after much
F IGURE 11: T RIPLE -T UNED T EST R ESULTS FOR 12.75MH Z
testing, our antenna seemed to match our
project requirements, giving us between 8 and
10 channels, depending on the environment and orientation. This was better than expected, and so we
moved on to the three-port antennas, assuming that the improvements and performance we observed with
these
single-port
antennas would
translate to the
three-port
prototypes.
F IGURE 12: N ETWORK A NALYZER R ESULTS FOR T RIPLE -T UNED , S INGLE -P ORT A NTENNA
11
Triple Tuned 14.25 MHz 50% of tests lie within error bars
Triple Tuned 13.5 MHz 50% of tests lie within error bars
Bit Error Rate
0
Bit Error Rate
0
10
10
-2
10
-2
Bit Error Rate
Bit Error Rate
10
-4
10
-4
10
-6
10
-6
10
11.5
11.5
12
12.5
13
13.5
14
Frequency Channel (MHz)
14.5
15
12
15.5
12.5
13
13.5
14
14.5
Frequency Channel (MHz)
Received Signal Power & Noise Floor
15
15.5
-30
Received Signal Power & Noise Floor
-35
-40
-40
-45
Power (dBm)
Power (dBm)
-45
-50
-55
-60
-50
-55
-60
-65
-70
-65
-75
-70
11.5
12
12.5
13
13.5
14
Frequency Channel (MHz)
14.5
15
F IGURE 13: T RIPLE -T UNE T EST R ESULTS FOR 13.5MH Z
15.5
-80
11.5
12
12.5
13
13.5
14
Frequency Channel (MHz)
14.5
15
15.5
F IGURE 14: T RIPLE -T UNE T EST R ESULTS FOR 14.25MH Z
F IGURE 15: N EGATIVE I MPEDANCE S CHEMATIC
F IGURE 16: N EGATIVE I MPEDANCE PCB L AYOUT
Final Report: Off the Wire | 4/12/2012
Negative Impedance
At the request of our customer, Freelinc, we worked at building a negative inductance circuit. Though
negative inductance is impossible to achieve with passive components, clever use of active components can
result in the behavior of a negative inductor. Error! Reference source not found. shows a schematic of
he negative impedance circuit. Mathematical derivations of the circuit can be found in Appendix D.
12
One of the difficulties in taking a step from ideal design to implementation was a working model. Using
pSpice, we set out to build a circuit that could demonstrate the desired behavior with the non-ideal
conditions modeled in PSpice. One of the difficulties we encountered in this situation was bandwidth.
Because the behavior of amplifiers generally break down in the 1 MHz range it was difficult to find an
amplifier that demonstrated stable negative inductance between 12 and 14 MHz. In the end, we found two
amplifiers that fit the model.
Negative Inductance Results
0.00E+00
1.00E+00
1.20E+00
1.40E+00
1.60E+00
frequency (MHz)
1.80E+00
2.00E+00
Inductance (H)
-1.00E-06
-2.00E-06
-3.00E-06
-4.00E-06
-5.00E-06
F IGURE 17: S IMULATED I NDUCTANCE F OR N EGATIVE I MPEDANCE . N OTE THE CONSTANT INDUCTANCE
ACROSS ALL RELEVANT
FREQUENCIES
Final Report: Off the Wire | 4/12/2012
Analysis of Results
13
Negative Impedance
Unfortunately we were not able to produce a working negative impedance circuit. Throughout testing
there were several problems associated with oscillation, short and open circuitry, and added resistance.
However, with a working simulation in PSpice, there is still hope that further debugging will lead to a
working model.
Single-Port Results
Single port antennas were built as predecessors to triple port systems. Because coupling was assumed to be
low in the triple tuned network, it was believed that the single port model would be an easy and efficient
way to create functionality that would mirror the behavior of the triple port system. The antennas all had
tuned frequencies attached to the port in parallel. All the single port antennas behaved according to our
model. Furthermore, the single port antennas exhibited great bit error rate (BER) and SNR. The triple
tuned antenna gave us especially outstanding
results. The performance of these two antennas
gave us the confidence to start working on the
triple port antennas.
Three-Port Results
In theory, the double and triple tuned antennas
with three ports should have given us great
results with great bandwidth and multiple
channels. We assumed that by connecting one
port, the other port should not have had any
interference since they were open circuited.
When we connected one port to the network
analyzer, it became obvious that something was
wrong with the configuration. At first we
Inductive Coupling
Inductive coupling is a common phenomenon in circuits where the magnetic field of one coil passes through
a separate coil and induces a current. This behavior can severely disrupt proper functionality or predicted
behavior of a circuit as in the case of the three port antenna systems built during this project. In the case of
the three port system, current going through an active antenna induces a current in an inactive coil that then
travels to all of its parallel antenna partners. The resulting fields interact destructively to create low BER
rates and unpredictable behavior.
Final Report: Off the Wire | 4/12/2012
thought there were mistakes in the wiring or
F IGURE 18: D OUBLE -T UNED , T RIPLE -P ORT A NTENNA WITH
unintentional shorts. After disconnecting all of D ISCONNECTED (G RAY ) P ORTS D ISPLAYING I NDUCED C URRENTS .
T HE C ONNECTED P ORT (G OLD WITH G REEN W IRES ) H AS C URRENT
the wires and testing each port, we found that W HICH I NDUCED C URRENT IN THE D ISCONNECTED P ORTS ' L OOPS .
this was not the case. Furthermore, the results matched our model when the other ports and capacitors
were disconnected; but, after connecting all the wires together, the same bad results were observed from
before. After observing the S-parameters, we concluded that we were experiencing inductive coupling. We
did not realize that current was being induced in the open ports from the connected port, as illustrated in
the FIGURE. As shown from the matlab results, this behavior did not match our expected values. This
proved to also be the case for the double-tuned, triple-input antenna.
14
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F IGURE 19: S11, S22, S33 FOR D OUBLE -T UNED , T RIPLE -P ORT A NTENNA
15
F IGURE 20: S21, S12 FOR D OUBLE -T UNED , T RIPLE -P ORT A NTENNA
F IGURE 22: S11, S22, S33 FOR T RIPLE -T UNED , T RIPLE -P ORT A NTENNA
Final Report: Off the Wire | 4/12/2012
F IGURE 21: S32, S23 FOR D OUBLE -T UNED , T RIPLE -P ORT A NTENNA
16
Final Report: Off the Wire | 4/12/2012
F IGURE 23: S21, S12 FOR T RIPLE -T UNED , T RIPLE -P ORT A NTENNA
17
F IGURE 24: S31, S13 FOR T RIPLE -T UNED , T RIPLE -P ORT A NTENNA
Possible Solutions
While the coupling is clearly heavily affecting our system, there are simple ways to eliminate a large portion
of the coupling. One of the ways would be to simply have nine different input ports. This would effectively
separate the antennas so that induced currents could not flow between them, and all antennas would be
effectively open.
Yet another solution would be to have 9 different antennas spaced a reasonable distance from one another
and orthogonal to one another. This configuration could effectively lower the coupling while still having
three input ports.
While these are imperfect solutions, our work has identified a major obstacle to a multi-port, multi-tuned
antenna that is important to recognize for further research on this project.
Conclusion
Although we were not able to construct the three port system we set out for, this project was very
insightful and helpful. Above all we learned the importance of thoroughly checking all assumptions, no
matter how obvious they seem. Had we figured out that the open port assumption discussed earlier was
false, the project would have proceeded very differently. This could have been done by drawing up specific
schematics for the end project and analyzing them before going forward.
In summary, we were successful in demonstrating the specifications we set based off the open port
assumption. With the unfortunate result of our initial assumption, our end product proved to be faulty.
However, the models and progress made in negative impedance was a striking achievement that can result
in great success in the future. Future projects that approach the issues we uncovered regarding inductive
coupling could solve these issues and create a usable broadband pan-directional antenna.
Final Report: Off the Wire | 4/12/2012
This project also reinforced the importance of testing software and set up. Testing would have been
extremely cumbersome without a network analyzer. Furthermore, our test bench and software were just as
important as our antennas. The network analyzer was also pivotal in helping us identify the extent of the
coupling and quantify it.
18
Appendix A: Functional Specification Document
Concept Generation and Selection
Freelinc Project
Bradford Law, James Smith, Jorge Conde
Final Report: Off the Wire | 4/12/2012
2/7/2012
1
Introduction
Overview
Our team has been given the challenge to design a matching network for a short range wireless system that
maximizes transmission efficiency. There are several possible designs and methods to accomplish this goal.
Purpose
The purpose of this document is to lay out all possible design concepts and decisions and to document the
reasoning for our eventual concept selection. Critical design concepts are discussed at great length, and
evaluated using the decision matrices. This document is designed to be easily understood and a powerful guide
to anyone wishing to familiarize themselves with this project and the reasoning behind the critical decisions
made.
Matrices
Decision matrices are the clearest way of illustrating the team design decision process. They show what we
believe to be key factors in a good design, and the rationale behind critical decisions. The numbering system
associated with these matrices also allows for easy changes in case new information or requirements are placed
upon us. Above all these matrices are perfect for achieving the proposed goal of this document.
Body of Facts
The Freelinc group is a team working on building a system that will communicate with different
sensors and devices on the human body without the use of wire to connect them together. Because of this
and the sensitivity of the information that may be communicated, the system will be short ranged or nearfield. We will be working on creating a matching network that will allow the system to efficiently
communicate over short distances.
Specifications
Needs to be able to function at a distance of one meter.
Bit error rate of 10^-5 db.
Functions with 3.7 V battery
Consumes less than40 mW of power.
The bandwidth needs to handle 8 channels (each channel bandwidth 250 kHz).
Operate between 12-15 MHz
Known Facts





The system will broadcast at intervals of .25 MHz from 12- 15 MHz
Previous work has reached very close to theoretical limits for single core antennas
The design may be fabricated and thus able to be shrunk to a small space
System ultimately will be used in harsh environment conditions and awkward orientations
We will need to use Spice and Matlab to model our designs
Assumptions
Final Report: Off the Wire | 4/12/2012






2



The previously built simulations system accurately measures how our system will work in real life
application
There are areas of BYU that will accurately reflect worse case scenarios for our antenna system
Multiple tuned antennas can increase the bandwidth above that of a single tuned antenna
Proposed Design
Past teams and graduate students have developed a semi-functioning system, so our team objective is to improve
this system. We are focusing primarily on building an extremely efficient matching network for the transmit
antenna. Once we have reached our goals regarding power usage and bandwidth we will focus on the receive
antenna. We have two teams, one team focused on developing a system based on negative impedance using
active components and another team building and modeling using dual and tri-tune antenna systems. Following
are some of the concepts and our analysis of them.
F IGURE 1 T RANSMIT S YSTEM D ESIGN
F IGURE 2 R ECEIVE S YSTEM D ESIGN
Final Report: Off the Wire | 4/12/2012
Figure one shows the transmit system design. Our project is focused primarily on the matching network
and antenna portion of the system.
3
Figure two shows the receive network which will receive more attention upon optimizing the transmit
system.
Critical Design Areas
Different Cores
In a ferrite core coil antenna, the ferrite material used plays a significant role. Different ferrites add
different impedances to the antenna and effectively increase or decrease the bandwidth. The size is also
important as our design can only be so large.
Multiple Cores
As previous projects have reached theoretical limitations on single core antennas, it is now time to explore
the effects of having multiple core antennas to achieve better bandwidth. By having different ferrite rods
tuned to different frequencies, one can achieve a desired bandwidth by switching antennas based on the
broadcasted frequency.
Wire
One of the keys to increasing the bandwidth of the system is to lower the Q of the circuit. Q is a function
of resistance and inductance. By using a larger wire with fewer loops it is possible to decrease the resistance
and inductance of the circuit and therefore lower the Q. This should increase our bandwidth and have a
positive effect on the range because of a higher current transfer. As wire has a significant effect on the
number of turns this is an important aspect in design.
Concept Selection & Scoring
Complexity
Complexity is a very import of the design. We know that the single tuned will be the most simple design. Past
projects, however, have reached theoretical limits, and our sponsor has specifically asked for multiple tuned
antennas. As multiple tuned antennas as well as negative impedance designs are complicated it is important to
decide on a design that can be created in the time allotted. Because of the complicated nature of the alternatives
this is a pivotal point of reason and thus receives a weight of 25%.
Cost
While the majority of our designs will not require expensive parts, it is important to pay attention to cost
regardless of the project. The negative inductance requires wide bandwidth active components and thus will
cost significantly more than other projects. While cost does play a factor, it is not a large concern and thus
receives a weight of 5%.
Our customer Freelinc wishes to have a system whose bandwidth spans 12 different frequency channels. Past
projects have only been able to achieve between 4 and 7.
Our goal is to design a matching network that consistently reaches 8 channels in all environments and
orientations. This is our most important consideration as we decide upon a design we have given it a weight of
50%.
Reliability
The term reliability is this context refers to the capability of the system to do its job right. Our end product will
ideally be able to function in all environments at all orientations. It is important that it can reliably produce the
desired result regardless of location and orientation. This is not quite as important as complexity but far more
important than cost and thus is given a weight of 20%. The reason this is not given as much weight as complexity
is that it would be more desirable to build a system in the right time than have it go over the time allotted but be
more reliable
Final Report: Off the Wire | 4/12/2012
Bandwidth
4
Possible design selection
Single Tuned Antenna- One way to go about building this network is to have one antenna with a matching
capacitor.
Double Tuned Antenna- Another possible solution would be to have two different antennas tuned to two
different frequencies by their respective capacitors. Once we have a double tuned antenna with one coil on each
ferrite, we will move to design the double tuned antenna with three ports.
Triple Tuned Antenna- Another possibility is to have three orthogonal antennas tuned to separate frequencies to
allow the transmitted bits to resonate at three different classes.
Negative Impedance- Recent research has shown the possibility of achieving negative impedance which would
result in an ideal matching network. Once we have the triple tuned antenna working. We will move to design
the triple tuned antenna with three coils on each ferrate tuned to three different frequencies.
Multi-Stage antennas-Using multiple stages, it is possible to create a matching network with wide bandwidth.
Matching
System
Weight
Single
tuned
Dual tuned
triple tuned
Negative
Impedance
Complexity
25
8
6
4
2
Cost
5
5
5
5
1
Bandwidth
50
2
4
6
7
8
8
Reliability
Final Report: Off the Wire | 4/12/2012
Total
5
20
100
2
4
365
455
585
565
Results
After debating each of the designs, we gave a rating for each design in each of the critical design areas. We
wanted to keep in mind what was really important. We used a weight system to help us rate what we felt to be
truly important.
Single Tuned
Single tuned system is the most simple of the system. That is why way gave a 50 points for complexity. But this
system will not provide with the bandwidth that the customer requested, and past projects have already reached
theoretical limits. This was solely considered as a standard to compare the other designs to. The total score was
365.
Dual Tuned
This system is a little more complex. But it will give us a better bandwidth. Theory also states that this system
will be more reliable in harsher conditions, and allows us to deal with orientation problems. The total score for
the dual tuned was 455.
Triple Tuned
In considering multiple tuned antennas, the triple tune appears to be our best bet as far as the bandwidth that we
can have. It is more complex and theoretically it will be reliable and meet the requirements. This is also optimal
for dealing with orientation problems. For this System we had a total score of 585.
Negative Impedance
This system is very different that the other three. It does not require several different tunings but is based on the
theory of negative impedance converters. Theoretically this will give us the best bandwidth, but cost the most
and is clearly the most complex system of those considered here. Our customer, however, has asked us to look
into this system in addition to whatever design we decide upon. This system had a score of 565
Summary
Final Report: Off the Wire | 4/12/2012
After scoring each of the system designs we found that the best system design was to build the triple tuned
system, which had a total score of 585. A stepping stone in achieving the triple tuned antennas, however, is
getting a double tuned antenna to work first. This document has helped us realize that we ultimately want to
create a functional triple tuned system that achieves specifications for the Freelinc system. We will also be
working on the negative impedance matching system as our sponsor requested it. As evidenced above, this
document records and supports that decisions made by team Off the Wire. This document is also subject to
change as the project progresses and other concepts come into play.
6
Appendix B: Concept Generation and Selection Document
Near Field Wireless Communication System
Functional Specification Document
Final Report: Off the Wire | 4/12/2012
26 January 2012
1
Presented by:
James Smith
Bradford Law
Jorge Conde
Introduction
Overview
Our team goal is to build a matching network for a near field communication system. Research has been
already started on the this project. We are using some of the results from the research to implement them
with the specification given by our sponsor FreeLinc and our adviser Dr Warnick. Our challenge for this
project is to develop the best design to meet the requirements to satisfy our costumer’s need.
Final Report: Off the Wire | 4/12/2012
Background
As military equipment continues to become more technologically advanced, soldiers find themselves to be
covered in more and more wires. For example a common soldier could find himself with radios, bullet
impact monitors, and other communication systems. The transfer of these systems is so sensitive and
important that common wireless technology, which has a history of problems and malfunctions, just won’t
cut it. If wireless technology is to be trusted it must be developed with very low error rates and able to
transfer efficiently over short distances regardless of terrain orientation or circumstance. This was the birth
of the Freelinc project. Our job is to build the wireless future of military equipment.
2
Product Description
We will be working on designing a low-frequency high-bandwidth transceiver. It will have the operational
parameters of performing within the 12-16 MHz spectrum and be capable of having multiple channels that
operate at 250 kbps. In our design wants provide 1 to 1 ratio of frequency modulation to bandwidth. It will
then stream the data through a waveform generator that will be sent to a matched antenna. This signal will
then be transmitted and received by another antenna. This antenna will then pass the signal to an A/D
converter that will then convert the information to a file. As part of the system we will develop a protocol
for handshaking between the two antennas as well as error correction coding. The end product will allow
the user to connect multiple devices to one master device that will allow instantaneous communication
between the devices.
Project Requirements
Customer Needs
The customer provided us with the following list of requirements. We have assigned a point-value system
to the requirements with an associated key to sort them in order of importance.
Final Report: Off the Wire | 4/12/2012
1.
2.
3.
4.
3
Critical
Very Important
Important
Optional
Customer Specification
Description
Imp.
1
Bandwidth: 12-15MHz
The wireless system should be capable of operating
between 12 to 15 MHz with a Q factor large enough to
ensure a good transmitted signal.
1
2
Channels: 250kHz stepping
centered at 12.00, 12.25...
MHz
The device must be able to switch between 13 channel
frequencies enabling multiple devices to communicate
simultaneously.
3
3
Power Consumption:
<40mA
Device should be powered by a 3.7V battery and pull no
more than 40mA.
2
4
Size: Highly portable
The device must be highly portable and light.
1
5
Cost: Inexpensive
The application is the United States military so the device
scale of production will be huge.
3
Table 1
Freelinc, the customer, can currently only transmit using single frequency. Obviously this is a huge
limitation as it limits the the number of concurrent signals to one. Our main emphasis is to increase the
number of devices that can concurrently communicate. The ideal goal is to have 13 total channels spaced
every 250kHz, however our first milestone is 6-8 different channel operations.
Our top priorities of bandwidth and size will allow Freelinc to have many devices communicating
simultaneously while remaining small enough that having many devices won’t introduce a significant burden
on the people who will be carrying these devices.
Power consumption is our second priority. The system should be run on a small 3.7V battery. The system
needs to be efficient to keep the size (and weight) of the power supply down. If, however, the bandwidth
Final Report: Off the Wire | 4/12/2012
Analysis of Customer Needs
The customer’s needs aren’t limited solely to the list they provided. The device must function properly and
be reliable under extreme conditions.
4
and size requirements are met, this project will be considered a provisional success, regardless of the
battery used.
Further specifications provided by the customer include channelization (and by extension, number of
channels), and cost. These requirements factor into the overall goals that Freelinc has for the device but are
outside the scope of our involvement. Ultimately, the device will achieve 13 channels between 12 MHz and
15 MHz, spaced every 250 kHz. Since Freelinc currently has a model with only one channel, they would be
satisfied with a working prototype that functioned on 4-6 channels (with more channels being added later).
The implementation is also intended to be mass produced, implying the need for the device to be costeffective. Once again, this is a specification that would have but that could ultimately be added later on by
replacing expensive parts on a working model with less expensive ones.
Project Specification
Final Report: Off the Wire | 4/12/2012
The following metrics were set to help us have a quantitative measure of the advance of our project. These
metrics go in accordance with the customer need and they are outlined on the table below.
5
Metric
#
Need
#(s)
Metric
Baseline Value
Ideal Value
1
1
Bandwith
12-13.5MHz or 13.515MHz
12-15MH
2
5
Size
<=6 cu in
3 cu in
3
4
Power
Consumption
(anything above 3.7 V)
3.7 V Battery and
<=40mW
4
2,3
channels
4-6 channels spaced at 250
kH
13 channels spaced at 250
kHz
5
6
Cost
<=$100
$1
Analysis of Metrics
As mentioned before. Our metrics are in accordance with the needs of the customer. We arranged these
metrics in order of priorities. The number one metric, bandwidth, corresponds to the number one
customer need. In order for the system to function properly and in order to accommodate the number of
desired channels while maintaining a low bit rate error rate, the signal must have a high enough bandwidth.
This ideally will be achieved with a bandwidth from 12-15MHz.
The second metric that we have established is the size of the device. Even though we did not receive
specific dimensions for the device from Freelinc; we know that the device needs to be small enough to fit on
the uniform of a soldier and lightweight enough to be carried around in combat.
The third metric involves power consideration. Ideally we want the product to function on a 3.7 volt
battery draw low current to prolong battery life. Freelinc would like the battery to last 10 hours and in
order to do so the prototype should pull no more than 40mW. This is already a limitation that we have. we
have decided that we might initiate testing with higher power sources. Ultimately, however, the 3.7V at
40mW is essential for the implementation of the product for its intended use with the military.
Conclusion
Final Report: Off the Wire | 4/12/2012
To satisfy our customer’s needs we need to design and build a error proof ultra-efficient matching
network for a near field communications antenna network. As ultra-efficient and low power often doesn’t
go together these different will be the areas of focus for our project. We will be working on these areas
concurrently in our simulation and designs for matching networks.
6
Appendix C: Project Schedule
Final Report: Off the Wire | 4/12/2012
Project Schedule
1
Duration
36 days?
36 days?
32 days?
64 hrs?
8 hrs?
2 hrs?
1 day?
1 hr?
1 hr?
1.25 days?
2.5 hrs?
2.5 hrs?
2 hrs?
15 days?
15 days?
1 day?
3 hr?
3 hr?
3 days?
2.5 hrs?
2.5 hrs?
2 hrs?
21.5 days?
21.5 days?
8.5 days?
8 hrs?
9 hrs?
2 hrs?
1 day?
1 hr?
1 hr?
2.5 days?
2.5 hrs?
2.5 hrs?
2 hrs?
15 days?
15 days?
1 day?
3 hr?
3 hr?
Start
1/16/2012
1/16/2012
1/16/2012
1/16/2012
1/23/2012
1/30/2012
1/31/2012
1/31/2012
2/1/2012
3/8/2012
3/8/2012
3/8/2012
3/16/2012
3/17/2012
3/17/2012
3/19/2012
3/19/2012
3/19/2012
3/23/2012
3/23/2012
3/23/2012
4/9/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/27/2012
3/19/2012
3/20/2012
3/20/2012
3/21/2012
3/21/2012
3/21/2012
3/23/2012
3/26/2012
3/17/2012
3/17/2012
3/19/2012
3/19/2012
3/19/2012
Finish
3/16/2012
3/16/2012
3/10/2012
3/10/2012
1/27/2012
1/30/2012
2/1/2012
1/31/2012
2/1/2012
3/9/2012
3/9/2012
3/9/2012
3/16/2012
4/9/2012
4/9/2012
3/20/2012
3/20/2012
3/20/2012
3/25/2012
3/25/2012
3/25/2012
4/9/2012
3/27/2012
3/27/2012
3/5/2012
2/24/2012
3/5/2012
3/19/2012
3/21/2012
3/20/2012
3/21/2012
3/26/2012
3/23/2012
3/26/2012
3/27/2012
4/9/2012
4/9/2012
3/20/2012
3/20/2012
3/20/2012
Names
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Final Report: Off the Wire | 4/12/2012
Task Name
Double-Tuned Antenna
Medium-Core
Simulate
Simulate in Matlab
Simulate in P-Spice
Build Medium-Core Prototype
Tune
Tune Capacitors
Tune Using Testing System
Test
Test Under Various Conditions
Test in Various Orientations
Compare Test Results
Double-Tuned Antenna Three Ports
Medium-Core
Tune
Tune Capacitors
Tune Using Testing System
Test
Test Under Various Conditions
Test in Various Orientations
Compare Test Results
Triple-Tuned Antenna
Medium-Core
Simulate
Simulate in Matlab
Simulate in P-Spice
Build Medium-Core Prototype
Tune
Tune Capacitors
Tune Using Testing System
Test
Test Under Various Conditions
Test in Various Orientations
Compare Test Results
Triple-Tuned Antenna Three Ports
Medium-Core
Tune
Tune Capacitors
Tune Using Testing System
2
Test
Final Report: Off the Wire | 4/12/2012
Test Under Various Conditions
Test in Various Orientations
Compare Test Results
Negative Impedance Circuit
Simulate Designs in P-Spice
Order Proper Amplifiers
Board Design
Design Board Layout in Altium
Mill Board
Solder Board
Debug Board With Network Analyzer
Board Design
Design Board Layout in Altium
Mill Board
Solder Board
Debug Board With Network Analyzer
3
3 days?
2.5 hrs?
2.5 hrs?
2 hrs?
43 days?
1 wk?
1 wk?
22.5 days?
2 days?
1.5 days?
21 hrs?
10 days?
13.5 days?
2 days?
1 day?
1 hr?
10 days?
3/23/2012
3/23/2012
3/23/2012
4/9/2012
1/9/2012
1/9/2012
1/16/2012
1/20/2012
1/20/2012
1/23/2012
1/24/2012
2/10/2012
2/29/2012
2/29/2012
3/2/2012
3/5/2012
3/6/2012
3/25/2012
3/25/2012
3/25/2012
4/9/2012
3/22/2012
1/13/2012
1/20/2012
2/28/2012
1/23/2012
1/24/2012
2/10/2012
2/28/2012
3/22/2012
3/2/2012
3/5/2012
3/5/2012
3/22/2012
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
Jorge,Bradford,James
James
James
James
James
James
James
James
James
James
James
James
James
James
The first task we wanted to work on was the double tuned antenna. We had the plan to finish it in 36 days.
We were able to get ahead of schedule and conducted a great amount of testing. After we had a working
double tuned antenna we started to work on the triple tuned antenna. Even though this one was a little
more complex than double tuned, we were able to get ahead of schedule as well since we gained experience
building double tuned.
Final Report: Off the Wire | 4/12/2012
Our biggest trouble was building double tuned three ports in parallel with triple tuned three ports. We had
to work on both antennas at the same time and we were able to finish it just in time. Something very
important to understand is that while we working on double and triple tuned antennas, James was also
working on the negative impedance circuit. Since negative impedance is a very complex circuit it took too
much time to finish and when finished we found that there is still a lot of debugging to do. The same is the
case for the double and triple antennas with the three ports.
4
Final Report: Off the Wire | 4/12/2012
Appendix D: Negative Impedance Calculations
1