Final Report
IntelliBed Hospital Bed Add-On Kit
For Improved Patient Safety
ECE4884 Senior Design
Section L05, Koblasz
Care Taker Team
Bikram Virk
Sujoy Sanyal
Ryan Eiswerth
Wasif Khawaja
Mushfiq Saleheen
Submitted
May 2, 2008
TABLE OF CONTENTS
Executive Summary ......................................................................................................... iii
1. Introduction ..................................................................................................................1
1.1
1.2
1.3
Objective .............................................................................................................1
Motivation ...........................................................................................................2
Background .........................................................................................................3
2. Project Description and Goals ....................................................................................4
3. Technical Specifications ..............................................................................................6
4. Design Approach and Details
4.1
4.2
4.3
Design Approach ..................................................................................................8
Codes and Standards ...........................................................................................20
Constraints, Alternatives, and Tradeoffs ............................................................21
5. Schedule, Tasks, and Milestones...............................................................................25
6. Project Demonstration...............................................................................................29
7. Marketing and Cost Analysis
7.1
7.2
Marketing Analysis .............................................................................................30
Cost Analysis ......................................................................................................31
8. Summary and Conclusions .......................................................................................34
9. References ...................................................................................................................38
Appendix A – Gantt Chart ........................................................................................... A-1
Appendix B – RFID System Schematic.......................................................................A-2
Care Takers (ECE4884L05)
ii
EXECUTIVE SUMMARY
Hospital attendants continually come in contact with all sorts of harmful germs
while providing treatment to patients. This places the attendants and their patients at a
high risk of being infected. Studies have shown that hospital-acquired infections, also
known as nosocomial infections, alone kill more people a year than automobile accidents
and lung cancer combined [1]. Along with nosocomial infections, hospitals have spent
millions of dollars a year to treat bedsores, which result after patients remain immobile
on their bed for extended periods of time [2].
The IntelliBed project was comprised of two systems that worked in solving
nosocomial infections and bedsores. The first was RFID-based and determined whether
an attendant had washed their hands before they came into contact with a patient lying in
the bed. If the attendant did not dispense soap during a specified period before
approaching the patient, then the system reminded the attendant to wash. This reduced
the chances of carrying harmful parasites from one infected patient to another. The other
system used pressure sensors to prevent bedsores. Whenever this system found that the
patient had not moved for a certain amount of time, it suggested the patient to change
position on the bed. Another important feature of IntelliBed was its compatibility with
any existing hospital beds; the IntelliBed was designed as an add-on to any existing bed
in order to attract more customers.
After initial manufacturing expenses, the total cost for the IntelliBed prototype
was $1,304. Once initial sales increase, production can be increased in order to drive
down the end customer cost. The targeted customers for this product were hospitals,
clinic centers, and nursing homes.
Care Takers (ECE4884L05)
iii
IntelliBed Hospital Bed Add-On Kit
For Improved Patient Safety
1. INTRODUCTION
In hospitals and nursing home, attendants frequently forget to wash their hands
before coming into contact with a patient, which increases the likelihood of nosocomial
infections, also known as hospital-acquired infections. Studies have shown the number
of deaths as a result of nosocomial infections is higher than breast cancer and HIV
combined [3]. Another expensive problem hospitals face is bedsores, which develop on a
patient’s body when they do not change position on their bed for an extended period of
time [4]. Both Nosocomial infections and bedsores can be deadly.
To combat Nosocomial infections and bedsores, the IntelliBed was designed with
several safety components that could be easily attached to most hospital beds. The
objective was to provide hospitals, nursing homes, and other healthcare centers with an
inexpensive alternative to purchasing high-end hospital beds built around similar safety
features. A comparison of this project’s design to comparable beds is more thoroughly
discussed in Section 7.1.
1.1
Objective
By having designed safety features that can be installed onto existing hospital
beds, the goal of the IntelliBed project was to provide hospitals, nursing homes, and other
healthcare centers with an inexpensive alternative to purchasing high-end beds built
around similar features. Some of the features proposed, such as the RFID-linked
database (detailed later), can be connected to systems outside the hospital bed, like a
Care Takers (ECE4884L05)
1
hand-washing system that identifies and reports attendants who did not wash their hands
before they approached a patient.
1.2
Motivation
One of the causes of nosocomial infections results after negligent hospital
attendants come into contact with multiple patients without properly cleansing
themselves between visits [2]. The Centers for Disease Control and Prevention (CDC)
estimated that more than 2 million nosocomial infections occur per year, with around
17,500-70,000 death per year. The annual cost to the healthcare industry to treat
nosocomial infections was estimated between $4.5-5.7 billion [5].
In addition to this problem, bedsores are also a serious concern for hospitals and
patients. Bedsores result after parts of the body are subjected to unrelieved pressure for
extended periods of time, cutting off oxygen and blood flow to the area [4]. Relieving
the pressure can be as simple as adjusting the body’s position periodically. However, for
the elderly and bed-ridden who may not be able to feel when parts of their body are under
pressure, bedsores can become a serious risk. The CDC estimated 1 million bedsorerelated cases per year while 60,000 deaths per year were blamed on bedsore-related
complications. Two thirds of cases occurred in people over 70 years old [4]. Bedsores
and nosocomial infections are serious concerns for patients since both increase the length
of hospital stay, the total charges, and the risk of death.
These concerning statistics exist even though high-end hospital beds are available
that have the potential to dramatically reduce the risk of infections and bedsores.
However, no wide-spread adoption of these beds by healthcare centers has occurred.
This is because these high-end beds are extremely expensive (see section 7.2 for more
Care Takers (ECE4884L05)
2
details). The IntelliBed was designed to be a low-cost alternative to these expensive bed
designs. Healthcare facilities that are looking to provide better safety for their patients
but are not willing to replace the beds they already have for more expensive ones can
purchase the IntelliBed equipment (described in Section 2) and attach these parts to their
current beds.
1.3
Background
RFID tag detection is a new technology and is being applied in many fields,
including healthcare applications. Although hospitals have started to use RFID
technology, such as for positive patient identification or equipment tracking, there is no
RFID system currently established whose purpose it is to prevent the spread of hospitalacquired infection.
For automated in-bed patient bedsore prevention, products such as MCES’s
calibrated electronic bed and dialysis weighing and motion detection machine, which
effectively uses load cell technology, exist [7]. However, the cost of this machine ranges
from $3000-$4000. Also, special mattresses like the bedsore prevention pad by DuroMed [8] are available on the market. These mattresses are inexpensive but they are not
able to provide a warning when the patient has not moved for a long period of time, and
thus in risk of bedsores. Other comparable hospital beds designed to prevent bedsores
include the Stryker’s Secure II Med/Surg Hospital Bed [9] and the Hill-Rom Total Care
SpO2RT Hospital Bed [10]. However, these beds cost $10,000 and $28,500,
respectively, which is typical for beds that provide their similar features. Also, these
beds do not utilize RFID technology to prevent nosocomial infections.
Care Takers (ECE4884L05)
3
2. PROJECT DESCRIPTION AND GOALS
Figure 1 displays the main components of the IntelliBed. The project’s goal was
to lower hospital-acquired infections by implementing a RFID system to detect
approaching attendants and to reduce the risk of bedsores by using pressure sensors to
detect non-movement. For the RFID system, a 13.56 MHz 1-Watt serial cable RFID
transceiver, which was used to read RFID tags, was placed underneath the bed. The
antennas, which allowed the transceiver to detect tags at a distance, were placed on the
bed within the mattress. The pressure sensors were embedded in the mattress and each of
their outputs was read into the computer for analysis. A more thorough description of the
location of each piece of equipment used in this project is detailed in Section 4.
RFID Antenna
PC Monitor
Passive RFID ID Tag
PC
13.56 MHz RFID Reader
Trossen Robotics
24” Force Sensing Resistor
Figure 1. Main Components of the IntelliBed.
Care Takers (ECE4884L05)
4
The total cost of the IntelliBed equipment was $1,304 with a target selling price
of $2,300 (see section 7.2 for cost and price details). The expected market for IntelliBed
included hospitals, nursing homes, and other healthcare centers involved with patient care
requiring a bed.
A brief description of each component of the IntelliBed project is given:

ID ISC.MR101-USB 13.56 MHz Mid Range Reader (1 unit)
Purpose:
Multi-tag Reader for identification of ISO transponders.
It detected the hand-washing status of the approaching attendants.
Placement:
Next to bed at its base.

RFID Antenna (3 units)
Purpose:
Added range to the RFID reader.
Placement:
One antenna at the head, mid-section, and foot of the bed. A two
inch-thick padding was used to separate the antennas from the
metal frame of the mattress. On top of the antennas, another
padding was placed and used to prevent the patient’s weight from
bending the antennas and for the patient’s comfort.

PicKit II Microcontroller Multiplexing Circuit (1 unit)
Purpose:
Controlled switching between the three different antennas. It
allowed a single reader to poll the separate antennas without the
need for each antenna to have its own reader.
Placement:
Underneath the bed.

HP Pavilion Slimline s7700e PC (1 unit)
Purpose:
Stored attendants’ hand-washing database and displayed GUI.
Placement: Next to bed at its base.

Computer Monitor (1 unit)
Purpose:
Displayed GUI warning of patient non-movement, egress, and
the approach of staff with unwashed hands.
Placement:
Mounted on a stand next to the bed

Trossen Robotics 24 Inch Force Sensing Resistor (FSR) and Voltage Divider Kit
(4 units)
Purpose:
These trimmable pressure sensor strips outputted resistance and
voltage readings. Using the change in these values, movement (or
non-movement) was detected. The voltage dividers connected the
FSR’s to the Trossen Robotics Phidget Interface Kit 8/8/8. Voltage
Care Takers (ECE4884L05)
5
Placement:

dividers attached to the leads of the strips allowed the sensitivity of
their readings to be adjusted.
Lengths of strips were laid out parallel to the patient.
Trossen Robotics Phidget Interface Kit 8/8/8 (1 unit)
Purpose:
Used as an analog-to-digital interface between the FSR’s and PC.
Placement: Next to bed at its base.
3. TECHNICAL SPECIFICIATIONS
The proposed and actual specification values for the RFID and pressure systems
are presented in Table 1. The desired detection range for the RFID antennas of 24 inches
was determined by taking into account normal dimensions of hospital rooms. This range
was large enough for the detection of approaching attendants and would have provided
enough time to warn potential germ-carriers appropriately. This desired range was also
small enough to avoid the detection of a tag unnecessarily when an attendant was present
in the room for a purpose other than to attend to the patient.
A transceiver power of 1-Watt ensured that the proposed antenna range of 24
inches was detectable. The frequency of 13.56 MHz was chosen as it was best for the
detection of multiple tags and was large enough to not be obstructed by objects the size of
a human body. In addition, the availability of equipment was commonplace at this
frequency [11].
The Trossen Robotics FSR’s were used for movement detection, which is
described later in Section 4. One of the advantages of using Trossen Robotics Force
Sensing Resistors was that their sensitivity level could be adjusted with the aid of a
voltage divider. The sensitivity specification of the FSR was chosen to be low, where
low sensitivity was set to have a threshold of 20 percent from the sensor strip’s previous
Care Takers (ECE4884L05)
6
Table 1. Technical Design Specifications
Specification
Proposed
Actual
1W ± 2 dB
1W ± 2 dB
13.56 MHz
13.56 MHz
Max. 0.5 A
Max. 0.5 A
RFID Reader
-
Transmitting Power
- Operating Frequency
-
Current Draw
Antenna Dimensions
-
Head Section
17” x 30”
17” x 30”
-
Mid-Section
9” x 30”
9” x 30”
-
Foot-Section
15” x 30”
15” x 30”
Placed On Wooden Table:
Antenna Detection Range
2 ft (24 in.)
1.5-1.75 ft. (18-21 in.)
Placed On Metal Bed Frame:
0-7 in.
Multiplexer
-
Microprocessor
Not Proposed
Pic18 LF2321
-
Power Supply
Not Proposed
3.3 V
-
Current Consumption
Not Proposed
< 5mA
-
Switching Loop-time
Not Proposed
16 ms
Trossen Robotics 24” FSR
-
Force Sensitivity Range
<100 g to > 10 kg
<100 g to > 10 kg
-
Pressure Sensor Range
< 1.5 psi to > 150 psi
< 1.5 psi to > 150 psi
-
Sensitivity to Vibration
Not Significantly Affected
Not Significantly Affected
-
Lifetime
Allowed Patient Rest Time
(No motion)
Pressure Senor Time Monitoring
Care Takers (ECE4884L05)
Not Proposed
>10 Million Actuations
30 Minutes
30 Minutes
Every Minute
Every Second
7
reading. Too high of a sensitivity level would have detected slight movements, such as
the chest of the patient as he or she breathed. However, movements like this would not
be enough to prevent bedsores. Therefore, the sensitivity of the sensors was set to low in
order to disregard the slight movements made by the patient.
4. DESIGN APPROACH AND DETAILS
The IntelliBed project was divided into two main parts. The first part was the
RFID detection system, which was used to prevent the spread of nosocomial infections.
The second system was the bedsore prevention system, which detected patient nonmovement after a specified period of time by using Trossen Robotics Force Sensing
Resistors.
4.1
Design Details
RFID system
Figure 2 demonstrates the main components of the RFID system used in this
project. This system had five components: passive RFID tags, three antenna receivers,
multiplexing circuit, a 13.56 MHz transceiver, and a hand-wash history database. A
multiplexer was also included in this system but it is detailed in the next section.
Each tag had a unique ID corresponding to the tag’s owner. Upon receiving the
transmitted signal from an antenna, the inner circuitry in the tag returned the unique
signal that represented the binary ID assigned to each attendant. This response signal was
then detected by one of the three antennas.
Figure 3a shows the three antennas that were designed for the IntelliBed
prototype. Separate antennas were needed since the bed had sections that could be
Care Takers (ECE4884L05)
8
Figure 3a. The Three antennas designed for IntelliBed.
Figure 3b. The antennas location on the bed.
adjusted into different angular positions based on the patient’s preferences. The
placement of the three antennas on the bed is shown in Figure 3b. After testing different
positions, the location of the antennas spread out in this layout was found to provide the
best possible orientation for the detection of a tag worn by an attendant on his or her wrist
no matter what direction he or she approached the bed from.
One important thing noted by the IntelliBed designers concerning the placement
of the antennas was that they must not touch the metal frame of the bed. Touching the
metal frame would have severely distorted their magnetic fields, affected their range, and
subsequent impedance-matching circuitry. A padding of 2 inches was used to separate
the antennas from the bed frame to help isolate them from the metal’s distorting effects.
Care Takers (ECE4884L05)
9
On top of the antennas was placed another padding to prevent the patient’s weight from
bending the antennas.
Even with the bed padding acting as a buffer, testing of the antennas’ range
occurred while the antennas were on the bed as opposed to them being on a table or any
location far from the bed. This was to ensure that any effects the metal bed frame had on
the antennas was taken into account when the antennas’ impedance matching circuits
were designed.
Once a tag was detected by an antenna, the serial number of the tag was compared
in a hand-wash history database on the PC. In this database, information such as whose
tag had been detected and whether they had previously washed their hands was stored. If
a tag was linked in the database with an attendant who had not washed their hands, then
the warning shown in Figure 4 requesting for the attendants to not approach the patient
was displayed on a GUI.
WARNING:
DR. SMITH PLEASE
STAND BACK
Figure 4. GUI display Developed for IntelliBed Project.
Care Takers (ECE4884L05)
10
The upper left-hand corner of Figure 4 is the RFID interface. It was based off of a
modified version from ECE 4007 Floor Mat Group [12]. Pressing the “Connect” button
and then the “Start Monitoring” button activated the RFID reader for detection. The
RFID interface in the IntelliBed GUI was programmed in Visual Basic 6 and can be
found on the IntelliBed team website. The bottom half of the GUI, which dealt with the
pressure sensors and bedsore prevention, will be described later.
RFID Antenna Multiplexer
In order to operate the three IntelliBed antennas with a single transceiver, the
multiplexing circuit configuration shown in Figure 5 was needed. This configuration was
created to poll each antenna to see if any had detected a tag. Each antenna had one of its
Figure 5. Multiplexer circuit configuration of the RFID System.
Care Takers (ECE4884L05)
11
two leads connected directly to the transceiver and the other lead connected to a relay
switch designated to it. Once each antenna’s assigned relay completed its connection to
the transceiver, the transceiver would read only that antenna. Which relay was allowed to
complete its connection to the transceiver was controlled by the MUX.
The centerpiece of the MUX was the 15 user-configurable pin Pic18 LF2321
microcontroller shown in Figure 6a, with its pin layout in Figure 6b. Three of the pins,
RA1, RA2, and RA3, were used to generate a sequential output of Boolean high (3.3 V)
and low (0 V) across Relay 1, Relay 2, and Relay 3, respectively.
Figure 6a. Pic18 LF2321 Microcontroller.
Figure 6b. Pic18 LF2321 Pin Layout.
Figure 7 shows that the loop time between successive settings of a relay was 16
ms, which followed one of the internal timers of the microcontroller. This time was short
enough to ensure no loss of tag detection even if the tag was quickly passed by the
antenna. Figure 7 also shows the delay of 5 ms between each setting of a pin and
subsequent activation of a relay and antenna. This allowance in time ensured the
magnetic field of one antenna would not interfere with that of another since multiple
antenna interference would have unforeseen consequences on tag detection.
Care Takers (ECE4884L05)
12
Figure 7. Oscilloscope Waveform Capture of PIC18 Microcontroller MUX.
Note that the output from the PIC microcontroller for relay 1 and 2 shown in
Figure 7 were actually being turned off every 1/3 of a second because the relay devices
used were active-low. The Pic18 LF2321 microcontroller was programmed in C and its
source code appears on the IntelliBed website.
Movement Monitoring System
The goal of the second system of this project was to prevent bedsores by
implementing pressure sensors to detect patient non-movement. As mentioned before,
bedsore prevention could be as simple as having the patient’s body position adjusted
periodically. By placing pressure sensors underneath the patient, movements were
Care Takers (ECE4884L05)
13
Figure 8. Algorithm used for Bedsore Prevention.
Figure 9. GUI display warning after non-movement was
detected 30 minutes.
Care Takers (ECE4884L05)
14
monitored according to the algorithm shown in Figure 8. A 30 minute timer was reset
after each significant movement was detected by the pressure strips. Significant
movement was specified as a 20 percent change from the pressure sensors last read value.
If no movement was detected for a period of 30 minutes, then the warning in Figure 9
was displayed on the GUI.
Figure 10. Trossen Robotics Force Sensing Resistor.
The specific type of pressure sensor used for monitoring movement was the
Trossen Robotics 24 inch Force Sensing Resistor (FSR), shown in Figure 10. FSRs are
detailed more thoroughly in the next section, but for now note that these sensors
exhibited a decrease in resistance with an increase in the force applied to their surface.
The FSRs were attached to Trossen Robotics Phidget Voltage Dividers like that
shown in Figure 11a. These voltage dividers allowed the sensitivity of the sensors to be
adjusted. The voltage dividers were then interfaced with the PC through the Trossen
Figure 11a. TR Phidget Voltage Divider.
Care Takers (ECE4884L05)
Figure 11b. TR Phidget Interface Kit 8/8/8.
15
Robotics Phidget Interface Kit shown in Figure 11b. This interface kit provided a
convenient way to interface up to eight FSRs to the PC using a USB cable. It was also
able to run on a number of operating systems, including WindowsXP, which was used in
this project. It also came with extensive written program examples and in a number of
API’s [13], including VB6, which was used to create the IntelliBed’s GUI.
Figure 12. Layout of the Pressure Sensors on the Bed.
Four FSR strips were connected to the Phidget Interface Kit 8/8/8 and placed
parallel to the length of the bed, as shown in Figure 12. The mid-section of the bed was
chosen for the placement of the sensors because the lower back of the patient is one of
the most common areas of the body prone to bedsores [4]. To prevent excessive bending
of the sensors by the weight of the patient, they were attached on top of hardboard and
placed under 2 inch thick bed padding.
The strategic placement of the FSR strips in the mid-section of the bed also
allowed for the detection of egress of the patient from the bed. The egress algorithm
followed by the code is outlined in Figure 13. If one of the outer strips registered a large
force (defined as a >50% from its previous value) while at the same time the other three
sensors registered a negligible force (defined as < 10% of from its previous value) then it
was assumed that the patient was putting all their weight onto one side of the bed and
Care Takers (ECE4884L05)
16
Figure 13. Egress detection procedure.
about to egress. The GUI was programmed to display the warning shown in Figure 14
when such a situation was detected The scroll bars shown in the bottom half of the GUI
were used as visual indicators of the relative amount of pressure registered by each of the
four FSRs. Quantitative values were displayed next to the scroll bars. These values, like
the scroll bars, were used only to show relative comparisons of force and do not reflect
any unit of measurement such as psi. Notice how one of the outer sensors registered an
applied pressure while the other three registered nothing, which signaled egress.
Sensitivity settings appear to the right of the scroll bar. The three sensitivity levels
available for the pressure sensors and controlled by the voltage dividers were low,
medium, and high.
Care Takers (ECE4884L05)
17
The source code for the GUI, which was written in Visual Basic 6 and based off
of example source code provided by Trossen Robotics, can be found on IntelliBed team
website.
WARNING: EGRESS
DETECTED
Figure 14. GUI displaying Egress Warning.
The Trossen Robotics Force Sensing Resistor
As mentioned before, the type of pressure sensors used in the IntelliBed were the
Trossen Robotics 24 inch Force Sensing Resistors, previously shown in Figure 10. FSRs
are paper-thin, durable, flexible, and trim-able to any size required. FSRs are not load
cells or strain gauges, but they function in a similar manner because, as described later,
Care Takers (ECE4884L05)
18
Figure 15 . Diagram of a typical FSR.
they use electrical properties of resistance to measure the force or pressure applied to its
surface [14].
A typical FSR is made up of two parts, as shown in Figure 15. The first part is a
resistive material (type depends on FSR) applied to a film. The second part is a set of
contacts applied to another film. The resistive material makes an electrical path between
the two sets of conductors on the other film. When a force is applied to the sensor, a
better connection is made between the contacts, and so the conductivity increases as
shown in Figure 16a. The behavior of the FSR’s conductance over a wide range of forces
Figure 16a.
Conductance vs. Force (0-10Kg)
Care Takers (ECE4884L05)
Figure 16b. FSR typical force vs. resistance
response behavior (log/log scale).
19
is approximately a linear function of the force.
Viewing the FSR behavior from a different perspective, Figure 16b shows the
typical force vs. resistance response behavior of a FSR on a log scale. This response
generally follows an inverse power law characteristic of 1/R. In other words, FSRs
exhibit a decrease in resistance with an increase in the force applied to their surface.
4.2
Codes and Standards
The RFID functionality of the IntelliBed was constrained by the fact that
electromagnetic interference in hospital settings must be kept to a minimum, and
transmitted signals from antennas must be held to minimal power levels. In order to drive
a larger antenna, a larger amount of power would have been required. However, since
the RFID system would be in such close proximity to medical electronics in practical use,
no additional power was added to the 1-Watt reader used.
Electromagnetic Compatibility (EMC), which requires “the correct operation, in
the same electromagnetic environment, of different equipment which use electromagnetic
phenomena, and the avoidance of any interference effects [16]” was an important
constraint for this project. However, the 13.56 MHz RFID reader used was known to be
standardized so as not to interfere with electronic medical devices, as described in ISO
35.240.80 [17].
The use of a 13.56 MHz transceiver frequency was also important because this
standardized frequency eliminated the need for hard copper wiring in the tags and
allowed for printed ink tags to be implemented with the system. This frequency also
Care Takers (ECE4884L05)
20
complied with ISO standard 14443, which allowed for standardized and cheaper tags
because of their widely manufactured usage [18].
4.3
Constraints, Alternatives, and Tradeoffs
FSRs are not suitable for precision measurements, as they might exhibit as much
as 15% to 25% variation between each other [15]. However, since precise measurements
were not necessary in the role of movement detection, the IntelliBed prototype was not
affected by the FSR’s shortcoming. However, there were alternatives considered to using
Trossen Robotics FSRs in the role of bedsore prevention. Strain gauges, like the foil-type
shown in Figure 17a, were the most likely alternative to the FSRs. These strain gauges
could have been mounted within the bed mattress, just as the FSRs were placed, and used
to measure the compression and tension of the bed surface as the patient moved.
If strain gauges were used in the IntelliBed project then a Wheatstone Bridge
circuit, similar to that shown in Figure 17b, would have been needed. These circuits
magnify the amplitude of the resistance change of the strain gauges, similar to what the
voltage divider devices did for the Trossen Robotics FSR’s. However, the strain gauge
Figure 17a. Foil-type Strain Gauge.
Care Takers (ECE4884L05)
Figure 17b. Wheatstone Bridge Circuit.
21
and Wheatstone Bridge alternatives that were found did not provide as extensive example
computer source code for interacting with the sensors and the PC as the Trossen Robotics
products did.
Several designs for the IntelliBed RFID antennas were considered. These designs
were based on projects of previous semesters and they include a spiral and two variations
of a concentric loop antenna, as shown in Figure 18a. Though no design had a significant
Spiral-Loop
Concentric-Loop
Variation 1
Concentric-Loop
Variation 2
Figure 18a. Alternative Antenna Designs Considered for IntelliBed System.
Circular-Loop
Figure 18b. Antenna Design Selected for IntelliBed Project.
advantage over the other, the one that was chosen for the IntelliBed is shown in Figure
18b. This design was recommended by Texas Instruments in their technical report
“Constructing a 1000 x 600 HF Antenna [20]”. TI was able to achieve a detection
range of 24 inches using this antenna design but only after setting their transceiver to a 4-
Care Takers (ECE4884L05)
22
Watt output. However, the transceiver used in the IntelliBed was limited to only 1-Watt.
Nevertheless, when the IntelliBed’s antennas were tested on a wooden table, even with a
1-Watt transceiver they were able to consistently detect at a range of 1.5-1.75 feet.
As an alternative to constructing their own antennas, some previous semester
groups opted for purchasing professionally-made antennas instead. The Floor Mat Group,
whose project also dealt with placing RFID antennas on top of a metal-framed hospital
bed, bought the Medium Gateway Antenna made by Dynasys shown in Figure 19. The
advantage of using this antenna is that it comes with what Dynasys calls their De-Q
feature, which automatically re-tunes the antenna if it is detuned after it is placed near a
material with a high moisture or metal content [21]. This feature allowed the antenna to
have a guaranteed detection range of a couple feet, even when next to large metal objects
like a hospital bed. The Floor Mat group used the Medium 20” x 20” and the Large 20” x
63” Gateway antennas successfully in their project. However, the cost for each antenna
was $400 and $800, respectively [17].
Figure 19. Unenclosed medium 20” x 20” High Frequency
(13.56 MHz) ISO 15693 antenna from Dynasys.
Care Takers (ECE4884L05)
23
If three Medium Gateway antennas were purchased instead of constructing the
three IntelliBed’s antennas, it would have been an expensive $1,200 added to IntelliBed
prototype. If a single Large Gateway antenna, which covers most of the area of the bed,
was purchased instead of buying three separate Medium Gateway antennas, then the
savings would have been $400. However, the Large Gateway’s rigid frame would have
prevented the bed from adjusting into its different positions.
Automatic antenna tuners would have provided the most likely source of success
in achieving maximum range from the IntelliBed antennas. However, the price-tag for
these devices easily ranged in the hundreds of dollars. Figure 20 shows the basic
principle behind automatic antenna tuners. As explained by ARRL, the National
Figure 20. Basic Operation Principle Behind Automatic Antenna Tuners.
Association for Amateur Radio:
“In practical terms, all a tuner does is act as a kind of adjustable impedance transformer
between the antenna system and the radio. It takes whatever impedance the antenna
system presents and attempts to convert it to 50 Ohm--or something reasonably close to
that value--for the transceiver. When the transceiver ‘sees’ a 50 Ohm impedance, it is
able to load its maximum RF output into the system. That power is transferred through
the antenna tuner, to the feed line and, ultimately, to the antenna--minus any losses
incurred along the way [23].”
Care Takers (ECE4884L05)
24
Figure 21. KAT100 High Power Automatic Antenna Tuner.
Figure 21 shows the KAT100-1 High Power Automatic Antenna Tuner, the most
likely device that may have aided the IntelliBed prototype antenna detection range. This
tuner operated from as low as 0.2 Watts to 100 Watts, which meant it would have worked
properly with IntelliBed’s 1 Watt transceiver. However, the cost for this device was $239
[24].
5. SCHEDULE, TASKS, AND MILESTONES
The tasks of the IntelliBed project were divided into the following categories:
1. Listed and Acquired Parts/Components:
The entire group met together and made a detailed list of required parts. The
critical parts included pressure sensors with PC connection, pressure sensor
mounts, PC, RFID reader, RFID antennas, and RFID tags.
Assigned Member(s): All members.
Degree of Difficulty: Easy. With the exception of two FSRs that
inexplicably malfunctioned and required several more to be reordered as
Care Takers (ECE4884L05)
25
replacements, no problem was encountered in the ordering of hardware for
this project.
2. Implemented Weight-Shift Detection
After interfacing the pressure sensors with the PC, Visual Basic 6 code was
developed to detect weight-shift detection.
Assigned Member(s): Sujoy, Ryan, Wasif
Degree of Difficulty: Easy. Trossen Robotics provided clear GUI
examples that allowed the FSRs to essentially be plug-and-play. The
IntelliBed GUI was based off of a modified version of example code
provided by Trossen Robotics.
3. Realized Bed Egress Detection
A program was written to detect patient egress from the reading of the pressure
sensors. Once detected, a warning was displayed on the GUI.
Assigned Member(s): Sujoy, Ryan, Wasif
Degree of Difficulty: Easy. Trossen Robotics provided clear GUI
examples that allowed the FSRs to essentially be plug-and-play. The
IntelliBed GUI was based off of a modified version of example code
provided by Trossen Robotics.
4. Constructed RFID Antenna
Three RFID antennas were constructed. A multiplexing circuit was designed in
order for the one reader to poll each antenna to determine which had detected a
tag.
Assigned Member(s): Bikram, Mushfiq
Degree of Difficulty: Hard. The metal bed frame interfering with the
magnetic fields of the antennas made it difficult to find the impedance
matching circuitry for the antennas. Several weeks were devoted to this
task, but to no avail. Final solution was to use the matching circuitry from
professionally made Gateway antennas (see Section 4.3) bought by a
previous semester’s group.
Care Takers (ECE4884L05)
26
5. Created Interaction with Hand-wash Monitoring System
The RFID reader was connected with the antenna and tuned with the tags to the
correct frequency. A hand-wash monitoring database was created and interfaced
with the RFID system.
Assigned Member(s): Bikram, Mushfiq
Degree of Difficulty: Hard. RFID monitoring system was based off of the
Floor Mat Group’s code from a previous semester. Deciphering the
several files in order to make a single working project file was
challenging. Also, the bedsore prevention GUI was originally written in
Visual Basic 2005. The RFID interface was written in Visual Basic 6 and
so in order to combine the two GUIs into one, the pressure sensor GUI,
which was determined as the easier of the two to translate, had to be rewritten in Visual Basic 6.
6. Implemented the Full System
Once all the components of the project were built, they were interfaced with each
other to realize an integrated system. The final system was tested, debugged and
fine-tuned for final demonstration.
Assigned Member(s): All members
Degree of Difficulty: Hard. One week before project was expected to be
completed, two FSRs inexplicably malfunctioned and the antennas were
not achieving the target range of 24 inches. After using the impedance
matching circuits taken out of the Gateway antennas, antenna range was
improved but still not near target. In addition, after several successful tests
with the MUX, the relays stopped working. The relays were replaced but
whether the fault in the original relays had anything to do with the
Gateway impedance matching circuits remained unexplained.
7. Deliverables Prepared
At least two weeks before each deadline, the entire team prepared for the
deliverables and worked on the project construction. Group members were
assigned different sections of the deliverables.
Assigned Member(s): All members
Care Takers (ECE4884L05)
27
Degree of Difficulty: Hard. Providing clear and detailed documents of the
IntelliBed project proved time-consuming. The IntelliBed designers
suspected more time was involved in documentation of the project than
the actual construction of the project.
No risk was involved in any of these tasks, with the exception of soldering during
the antenna construction. The team was divided into two groups: bedsore prevention,
which included Sujoy and Ryan, and RFID technology, which included Bikram, Mushfiq,
and Wasif. Ryan prepared the weekly project progress reports and attended to the overall
documentation of the IntelliBed project. Aside from regular scheduled class meetings,
the group met several times a week for discussion and project work. Each member was
held accountable to their assigned tasks by the rest of the group.
Figure 22 shows a timeline chart that outlines the key tasks that had to be
accomplished by the project team. A more detailed Gantt chart of the proposed as well as
the actual project schedule appears in Appendix A. The project was finished on its
expected date of completion of May 2, 2008.
Figure 22. Timeline for project.
Care Takers (ECE4884L05)
28
6. PROJECT DEMONSTRATION
Demonstration of the pressure sensor system of the IntelliBed occurred in one of
the senior design rooms. The GUI created for the project was described and displayed.
The pressure sensors were interfaced with the GUI and then spread out parallel to each
other on a hospital bed in a similar layout to their proposed positioning. An egress
warning was shown on the GUI after one of the IntelliBed designers pressed his hand
against one of the outer sensors, leaving the others untouched. The designer then
simulated patient non-movement across the sensors after he pressed down on all the
sensors and maintained this force until the timer countdown finished and a warning
signaled, which the patient to move, was displayed on the GUI. For convenience during
the demonstration, the GUI displayed a warning when patient non-movement was
detected for a period of 10 seconds and not 30 minutes.
The RFID system demonstration also occurred in the senior design room where
the hospital bed was stored. The three antennas were laid out across the bed and
connected to the MUX circuit, which was connected to the RFID transceiver and
interfaced with the GUI. Multiplexing was demonstrated by holding a tag close to each
antenna in turn until the GUI displayed a message that signaled detection.
Two types of tags were issued for the demonstration. One tag was linked in a
premade database to a person who did not wash their hands and the other tag was linked
to someone who did was their hands. When the tag associated with the unwashed
attendant was detected, the GUI displayed a warning for that person to not approach the
bed. When the tag associated with the attendant that had washed their hands was
detected, the GUI was set to display a greeting.
Care Takers (ECE4884L05)
29
Due to concerns of damaging the antennas and the pressure sensors,
demonstration of either occurred without a person lying on top of them, as a patient
would in a finalized product of this project. The IntelliBed design team believed that the
functionality of both the pressure sensors and the antenna detection systems were
demonstrated properly, regardless.
7. MARKETING AND COST ANALYSIS
7.1
Marketing Analysis
Many medical equipment providers have already created hospital beds that
provide the same services as the IntelliBed offers. In some cases, their beds outperform
the IntelliBed. Other comparable hospital bed designs designed to prevent bedsores
include the Stryker’s Secure II Med/Surg Hospital Bed [9] and the Hill-Rom Total Care
SpO2RT Hospital Bed [10] shown in Figure 23. These beds have pressure sensors that
weigh the patient, detect egress/ingress, and can automatically adjust to a chair position
for safer egress. Other main features of these beds include:
Hill-Rom Total Care SpO2RT:
Stryker’s Secure II Med/Surg:





air mattress system
scale
lateral rotation and percussion
an intuitive bed system that helps
increase caregiver productivity,
IntelliDrive mechanism that offers
power assisted transport and
maneuverability of the bed within
and outside of the patient room.
Features of the Stryker’s bed
Care Takers (ECE4884L05)


BackSmart system design that
helps to significantly reduce the
risk of back injuries through
integrated ergonomics,
smart bed monitoring system
called iBed that communicates
local bed status information to
caregivers to help ensure patient
safety and improve overall
efficiency
patented motorized Zoom drive
that significantly reduces effort
needed for patient transport.
30
Figure 23. IntelliBed Competing Products.
However, beds likes these are expensive and so have not experienced wide-spread
adoption by healthcare facilities. The price for the Secure II Med/Surg and the Total
Care SpO2RT bed were $10,000 and $28,500, respectively, which is typical for beds
offering their similar features. Also, these beds do not implement RFID to prevent the
spread of hospital-acquired infections.
The main selling point of IntelliBed was that healthcare centers do not have to
buy expensive beds like Stryker’s or Hill-Rom’s if they wanted to provide a safer
environment for their patients; they can install the IntelliBed components onto their
existing beds, thereby providing similar services as the high-end beds offer, but without
the expensive cost.
7.2
Cost Analysis
Table 2 gives a list of the required parts for the project and their cost. Two types
of equipment were used: movement monitoring related parts and RFID related parts.
Apart from having been used for movement and hand-wash monitoring, the Slimline PC
and computer monitor were able to be used to interface and display other medical
measurements.
Care Takers (ECE4884L05)
31
Table 2. Project Equipment Costs
Product
Quantity
Unit Cost
Total Cost
Trossen Robotics 24” FSR
4
$24
$96
1
$400
$400
Interface Kit 8/8/8
1
$77.60
$78
Cables
1
$10
$10
TI-FEIG RFID Reader
1
$350
$350
Copper Plating
25 ft.
$20
$100
Antenna Board
1 pair
$20
$20
1
$250
$250
System
and Voltage Divider Kit
System
RFID
Pressure Sensor
Group
HP Pavillion Slimline
s7700e PC
PIC Kit II Microprocessor
Total Equipment Cost
$1,304
Table 3 shows a detailed cost list for the project development. The total one-time
development cost for the IntelliBed was $40,950. The main components of this estimate
included the cost for parts of $1,304, a labor cost of $25,200, and an overhead cost of
$14,490. The biggest contributor to the total project cost was labor related expenses,
where an hourly wage of $30 was used to calculate the labor costs. The labor hours
estimated included research and product design, team discussions, parts purchased,
design implementation, test analysis, and debugging. Fringe benefits at 25 percent of
labor costs and overhead cost at 25 percent of materials, labor, and fringe added to give
the total overhead cost. When the IntelliBed goes into production, the labor related costs
was expected to be significantly lower than those estimated for product development.
Care Takers (ECE4884L05)
32
Table 3. Project Development Costs
Component
Labor
Labor
Equipment
Total
Hours
Cost
Cost
Component
Cost
Movement Measurement
Movement Detection
310
$9,300
Egress Detection
96
$2,880
FEIG RFID
50
$1,500
RFID System
124
$3,720
Class lecture/meetings
260
$7,800
Total Labor
840
$25,200
$250
$12,430
$1,010
$6,230
$0
$7,800
RFID
Interface
Total Equipment Cost
Fringe Benefits, 25% Of
$1,260
$6,300
Labor
Overhead, 25% Of
$8,190
Material, Labor & Fringe
Total Overhead
$14,490
Total Project Cost
$40,950
A detailed product cost and profit analysis is shown in Table 4. In a mass
production facility, each unit was expected to cost $2,065. Based on market evaluations,
it was estimated that 2,000 units would be sold every year for five years. An initial profit
margin of 10.22 percent was used that resulted in each unit expected to be sold for
$2,300. Selling 10,000 units over a five year period was expected to generate
$23,000,000 of revenue with a total profit of $2,350,600.
Care Takers (ECE4884L05)
33
Table 4. Selling Price Estimation
Equipment Cost
$1,226
Assembly Labor
$10
Testing Labor
Subtotal, Labor
Fringe Benefits, 25% of Labor
Subtotal, Labor & Fringe
Overhead, 25% of Material, Labor & Fringe
Subtotal, input Costs
$6
$16
$4
$1,280
$320
$1,600
Sales & Marketing Expense, 15% of Selling Price
$345
Support & Warranty Expense, 5% of Selling price
$115
Amortized Development Costs
Subtotal, All Costs
Profit, 10.22%
Selling Price
Total Revenue, Based on 10,000 Units
Total Profit
$5
$2,065
$235
$2,300
$23,000,000
$2,350,600
8. SUMMARY AND CONCLUSIONS
The prototype of the IntelliBed ended in mixed results. The pressure sensor
system was fully functional within the early design stage of the project. The GUI that
was created properly displayed the pressure sensor data, as well as a warning when nonmovement persisted for any time limit specified by the user.
However, the RFID system did not fully meet expectations. The MUX functioned
properly, switching the connection from the transceiver to each of the three antennas in
turn, and a warning was displayed on the GUI whenever one of the antennas detected a
tag. Unfortunately, the actual antenna detection range was limited (see Table 3).
Care Takers (ECE4884L05)
34
The main factor that was suspected of making it difficult to find the proper
antenna matching network to allow the greatest possible detection range was the
antennas’ proximity to the metal frame of the bed. The proximity to metal is among one
of the top concerns for RFID antenna designers. It is known to greatly alter antenna
design, as explained by Bob Scher, CEO of Dynasys Technologies, Inc.:
“Altered performance of the RFID system can be expected when metals are in close
proximity of the radiation field. Proximity to metals effectively lowers the antenna's
inductance. Lower inductance causes an increase in resonant frequency and also a
reduction in "Q". Designers may consider starting with a higher-than-needed "Q" "in the
lab" to start with, expecting it to be lowered when it is installed in its intended location.
External capacitance may be required to tune the modified antenna system back to
resonance. These types of situations can be experienced around conveyor belt structures
and also embedding antenna loops on concrete driveways where metal re-bar absorbs
some of the radiated energy. [22]”
The proximity of the antennas to the metal bed frame was one of the first
concerns for the IntelliBed design team. The design team proposed during the
Preliminary Design Report to separate the antennas from the metal bed frame using a 2
inch thick bed padding. However, during the testing phase once the detection range for
the antennas were found to be poor, it was quickly determined that a much larger
separation between the antennas and the bed may have been required. Further tests with
the antennas then proceeded with a padding of 7 inch thickness between them and the bed
frame.
The impedance matching networks for all three antennas were first built on a
single Protoboard out of convenience for the designers when fine-tuning the networks.
Wires connecting the matching networks to the antennas were originally around 10” long
and of 2 mm thickness. However, these wires acted as antennas themselves and were
able to detect tags held extremely close to them. Twisting these wires to form something
Care Takers (ECE4884L05)
35
similar to a coaxial cable prevented them from acting as antennas, but did little to have
any noticeable effects on the detection ranges. Wires of larger diameters were also
tested, but ended in inconclusive results.
Nevertheless, based on the already seen side-effect the length of the wires
between the Protoboard and antennas had on generating its own antenna, it was
concluded by the design team that the length and not the width of these wires had a more
significant role on the antennas’ detection ranges. Thus, the lengths of these wires were
continuously reduced and the antenna range continuously tested, with mixed results, until
eventually the matching network was taken off the Protoboard and built directly on the
antenna. However, not only did such a move make it difficult for fine-tuning the
matching network of each of the antennas, but it also ended again with inconclusive
results.
The solution presented itself not in the wires but in the impedance matching
circuitry. After all, in theory a properly tuned matching network would have been able to
take into account any effects the length of the wires would have had on the antenna
range. However, to create a matching network was itself a challenging task, even with
the aid of a VSW meter. For the difficulties to be compounded by the proximity of the
antennas to the bed, the IntelliBed designers could not find stable matching networks for
all the antennas.
The IntelliBed designers then replaced the IntelliBed matching circuitry with the
two matching networks that were in the Dynasys antennas. Recall from Section 4.3 that
the Dynasys networks were able to return themselves in the proximity of metal.
Immediately, results could be seen as a stable detection range of >7 inches was achieved.
Care Takers (ECE4884L05)
36
It is important to note that when the matching network is to be connected to the
antennas, they were not connected directly to the antennas but rather to the opposite end
of the wiring where the MUX was located. This was so the matching network took into
account any loss due to the wiring lengths leading from the transceiver to the separate
antennas spread out across the bed.
Though no further testing on the wires were done, the IntelliBed designers believe
that had 50 ohm coaxial cables been used instead of the standard 2 mm wiring, the
antennas may have achieved more stable results even without the aid of the Dynasys
matching circuitry. 50 ohm coaxial cables are widely used in radio transmitter
applications and may have prevented any loss frequently seen when 2 mm wiring was
used. Also, 50 ohm cables theoretically could have allowed the matching circuitry to be
built directly on the antenna as opposed to nearer the transceiver, since the minimal loss
in the cables would not have to have been taken into account.
Due to the mixed results concerning the RFID antennas, the IntelliBed design
team has concluded its prototype is not ready for mass production. It is recommended
that if any future design group whose project relies heavily on RFID antenna range then
they should purchase professionally-made antennas with automatic impedance matching
networks built in, similar to that made by Dynasys mentioned earlier (see sec. 4.3). If
cost is a concern for the group, then a separate automatic impedance matching network
device that can be attached to antennas could be purchased instead.
Also, the design team suggests to any future project groups whose goal it is to
prevent patient bedside falls for them to utilize the Trossen Robotics 24 inch Force
Sensing Resisters in their design. As described earlier in Section 4, the IntelliBed
Care Takers (ECE4884L05)
37
designers were able to detect patient egress based on registering a large force on either
side of the bed where a sensor was located.
9.
REFERENCES
[1]
WebMD, “Cellultis,” [Online]. Available: www.webmd.com [Accessed: Jan. 29,
2008].
[2]
Dr. Tamer Fouad, M.D., “Study Shows hospital staph infections cause 12,000
deaths, cost $9.5 billion,” www.doctorslounge.com. para. 11, Aug. 2005.
[Online].
Available:http://www.doctorslounge.com/infections/articles/nosocomial/staph_ho
spital. [Accessed Jan 30, 2008].
[3]
MedicineNet, “Staph Infection (Staphylococcus Aureus)” [Online]. Available:
http://www.medicinenet.com/staph_infection/article.htm [Accessed Feb. 20,
2008].
[4]
Health A to Z, “Bedsores,” Health A to Z, 14, [Online].
Available: www.healthatoz.com. [Accessed Jan. 28, 2008].
[5]
Quoc V Nguyen, MD., “Hospital-Acquired Infections,” www.emedicine.com.
Aug. 21, 2007. [Online].
Available: http://www.emedicine.com/PED/topic1619.htm.
[Accessed Jan. 30, 2008].
[6]
CISCO, “CISCO Unveils WiFi RFID Tracking and Multi-Function Box,”
www.cbronline.com. May 4, 2005. [Online]
Available: http://www.cbronline.com/article_news.asp?guid=3B2D6FC7-1041475E-B798-EDC57DA1DC56/ [Accessed Feb 14, 2008].
[7]
Medical Supplies and Equipment Co. {MSEC}, “Calibrated Electronic Bed and
Weighing Machine,” [Online]. Available: www.medical-supplies-equipmentcompany.com. [Accessed Jan. 25, 2008].
[8]
Amazon, “Decubitus Pad Bedsore Prevention”, [Online]. Available:
http://www.amazon.com/Decubitus-Pad-Sore-Prevention-hite/dp/B000PY2EUA.
[Accessed Jan. 31, 2008].
Care Takers (ECE4884L05)
38
[9]
Stryker, “Medical Equipment: Our Products”, Stryker. [Online]. Available:
http://www.stryker.com/enus/products/PatientHandlingEMSandEvacuation
Equipment/Beds/MedSurgBeds/SecureII/index.htm [Accessed March 1, 2008].
[10]
Hill-Rom, “Hill-Rom Products,” Hill-Rom. [Online].
Available: http://www.tradekey.com/selloffer_view/id/1447563.htm [Accessed
March 1, 2008].
[11]
Thomasnet, “RFID Integrated Circuits Operate at 13.56 MHz,” [Online].
Available: http://news.thomasnet.com/fullstory/452444 [Accessed March 2,
2008].
[12]
RFID Floor Mat Group, Available: http://www.ece.gatech.edu/academic/
courses/ece4007/07fall/ece4007l03/group03/
[13]
Trossen Robotics “Phidget 8/8/8 manual” [Online]. Available:
http://www.pdfdownload.org/pdf2html/pdf2html.php?url=http%3A%2F%2Fwww
.phidgets.com%2Fdocumentation%2FPhidgets%2F1018.pdf&images=yes –
[Accessed April 2, 2008].
[14] Trossen Robotics, “24 Inch Force Sensing Resistor Strip”, [Online].
Available: http://www.trossenrobotics.com/store/p/3223-24-Inch-Force-SensingResistor-FSR-Strip.aspx [Accessed March 15, 2008].
[15] William Putnam, R. Benjamin Knapp. “Input/Data Acquisition System Design for
Human Computer Interfacing”. [Online].
Available: http://ccrma.stanford.edu/CCRMA/Courses/252/sensors/node8.html
[Accessed April 28, 2008].
[16] Wikipedia.org, “Electromagnetic Compatibility”. [Online].
Available: http://en.wikipedia.org/wiki/Electromagnetic_compatibility
[Accessed April 1, 2008].
[17]
ISO, “ISO 35.240.80” [Online]. Available: ISO.org.
[Accessed April 16, 2008].
[18]
O. Bashan, “ISO 14443: An Introduction to the Contactless Standard for Smart
Cards and its Relevance to Customers,” On Track Innovations, ltd (OTI). Report.
[19] Wikipedia, “Strain Gauge” [Online]. Available: http://en.wikipedia.org/wiki/
Strain_gauge. [Accessed April 10, 2008].
[20]
Texas Instruments, “Constructing a 1000 x 600 HF Antenna” [Online].
Available: www.ti.com/rfid/docs/manuals/appNotes/HF1000x600AntennaRev2
.pdf
Care Takers (ECE4884L05)
39
[21]
RFIDUSA, “Featuring Dynasys de-Q Tuning” [Online].
Available: http://rfidusa.com/superstore/index.php?cPath=37_30
[Accessed April 20, 2008].
Bob Scher, “Antenna Considerations for Low Frequency RFID Applications,”
Dynasys.[Online]. Available: http://209.85.165.104/search?q=cache:860_
iBxDXPYJ:rfidusa.com /superstore/pdf/Antenna_Considerations_for_LF
.pdf+proximity+to+metals+%2B+rfid&hl=en&ct=clnk&cd=6&gl=us [Accessed
April 20, 2008].
[23] ARRL, the National Association for Amateur Radio, “Antenna Tuner Operation”.
Available: http://www.hamuniverse.com/tuner.html [Accessed May 1, 2008].
[22]
[24]
Elecraft, “KAT100 High Power Automatic Antenna Tuner”, Elecraft. [Online].
Available: http://www.elecraft.com/kat100/kat100_page.htm
[Accessed: May 1, 2008].
Care Takers (ECE4884L05)
40
APPENDIX A
PROJECT GANTT CHART
Care Takers (ECE4884L05)
41
PROPOSED SCHEDULE
ACTUAL SCHEDULE
Care Takers (ECE4884L05)
42
APPENDIX B
MULTIPLEXER SCHEMATIC
Care Takers (ECE4884L05)
43
Care Takers (ECE4884L05)
44