SIM UNIVERSITY
SCHOOL OF SCIENCE AND TECHNOLOGY
INTELLIGENT CONTROLLER SYSTEM
FOR AN INTRAMEDULLARY NAIL
STUDENT
: MD FUAD (Z0706372)
SUPERVISOR
: STEPHEN LOW
PROJECT CODE : JULY 2009/ENG499
A project report submitted to SIM University
in partial fulfillment of the requirements for the degree of
Bachelor of Electronics
May 2010
ABSTRACT
Modern day technology breakthrough in limb lengthening and strengthening can
enable an individual to gain up to 60mm in height in about two months for the upper
and lower bones extremities of the legs.
This technology also helps those who have had an injury that caused shortened or
deformed limb bones or those that were born with limb length inequality to overcome
their shortcoming.
Compared to current day conventional bone extension surgery method, it is much
simpler and safer to be use and perform. The nail which is a metal steel implant is
inserted into the hollow of a bone that has been cut crosswise. It can be activated by a
wireless control unit to increase in length at 1mm a day and will gradually lengthens
as the bone’s cut ends grow and fuse.
The design for this involves an internal unit which is implanted beneath the skin and
tissues and an external unit.
A reliable communication channel needs to be design for both these units to
communicate so that it will be able to control linear drive movement for the nail and
also sends information back from the nail to the user. At the heart of this design will
be a microcontroller unit with software code using any of the microcontroller
programming language written to suit the needs of this project.
At the same time, the internal unit will be making use of wireless power transmission
(inductive coupling) to obtain its required power supply. However, for this project,
wireless power transmission is only done as a literature study (secondary objective)
and testing out will be done with normal power supply to the internal circuit.
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ACKNOWLEDGMENTS
First and foremost, I would like to thank my tutor Mr. Stephen Low for his guidance,
knowledge sharing and patience that he has given me throughout this period. His
relentless questioning helps me in determining the path to be taken for each and every
step of the project. I am also thankful that he always replies my email promptly and
ever willing to meet up with me despite his hectic schedule.
I would also like to thank Mr. Firdaus Wahid for all the technical knowledge that he
shares with me. He also helps a lot on the logistics side of things, such as purchasing
of components and acquiring lab access where it is conducive for me to work on my
project.
I also greatly appreciate the help and support given by Samson Santosh Nickson (Mr
Stephen’s fellow project student), who’s constant motivation keeps me going. He also
helps me a lot on the assembly language whenever I encounter difficulties with it.
Last but not least, I would like to thank my family for the constant encouragement and
support that they had given me.
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TABLE OF CONTENTS
S/NO
TITLE / DESCRIPTION
PAGE
ABSTRACT
2
ACKNOWLEDGEMENTS
3
TABLE OF CONTENTS
4
LIST OF FIGURES
7
LIST OF TABLES
9
LIST OF APPENDICES
PART 1: INTRODUCTION
10
1.1
Background
11
1.2
Project Objective
12
1.3
Overall Objective
PART 2: MANAGEMENT METHOD
12
2.1
Project Breakdown
13
2.2
System Development Method
PART 3: LITERATURE REVIEW
14
3.1
Basic Circuit Theory
16
3.1.1
Closed and Open Circuit
16
3.1.2
Voltmeters and Ammeters
16
3.1.3
Sources
16
3.1.4
Switches
17
3.1.5
Resistors, Resistance and Conductance
17
Microcontroller Fundamentals
19
Building Block Structure of Microcontroller
19
3.2
3.2.1
3.2.1.1 Central Processing Unit
20
3.2.1.2 Memory
20
3.2.1.3 Bus
20
3.2.1.4 Input/Output Unit
20
3.2.1.5 Serial Communication
20
3.2.1.6 Timer Unit
21
3.2.1.7 Watchdog
21
3.2.1.8 Analog to Digital Converter
21
3.2.2
22
Programming Languages Use for Microcontroller
4
3.3
Background of Intramedullary Nail and Having an Intelligent
22
3.4
Biomedical Material
23
3.4.1
Biomaterials Metals
23
3.4.2
Synthetic Polymers
23
3.5
Circuit Design Implementation to Drive the Motor
PART 4: SYSTEM DESIGN
24
4.1
System Description
25
4.2
Microcontroller Selection
26
4.3
Motor Selection
26
4.4
Motor Driver Selection
28
4.5
Transceiver Selection
29
4.6
Circuit Design
PART 5: IMPLEMENTATION OF IDEAS
30
5.1
Idea Implementation
32
5.2
Software Implementation
PART 6: TESTS AND RESULTS
33
6.1
Motor and Driver
35
6.1.1
Motor Rotates in Clockwise Direction
36
6.1.2
Motor Rotates in Anti-Clockwise Direction
37
Software
38
6.2
PART 7: PROBLEM AND DIFFICULTY
7.1
Problems and Difficulties Encountered
39
PART 8: LITERATURE STUDY OF WIRELESS POWER TRANSMISSION
(SECONDARY OBJECTIVE)
8.1
Introduction
40
8.2
System Overview
40
8.3
Power Transmitting Coil
41
8.4
Coil Driver
41
8.5
Power Receiving Call
42
8.6
Experiments and Results
43
8.7
Human Tissue Safety
44
8.8
Conclusion and Discussion
46
5
PART 9: CONCLUSION AND RECOMMENDATIONS
9.1
Conclusion
47
9.2
Future Recommendations
47
PART 10: CRITICAL REVIEW AND REFLECTIONS
10.1
Critical Review and Reflections
48
GLOSSARY
49
REFERENCES
51
APPENDICES
53
6
LIST OF FIGURES
DESCRIPTION
Figure 1: X-ray showing the portion of a fracture with an
intramedullary nail
PAGE
11
Figure 2: Block diagram of a two way communication between
microcontroller system and nail implant
12
Figure 3: WBS for intelligent controller system for an intramedullary
nail
13
Figure 4: Flow chart of system design
15
Figure 5a: A schematic diagram of a resistor
18
Figure 5b: A pull-up resistor
18
Figure 5c: A pull-down resistor
18
Figure 6: An example of a microcontroller’s building block
19
Figure 7: The inside view of a microcontroller
21
Figure 8: Block diagram of a complete intramedullary nail system
25
Figure 9: PIC16F676 microcontroller pin assignments
26
Figure 10: Dimension of a DC motor
27
Figure 11: Dimension of a DC motor with gear
27
Figure 12: Functional block diagram of the BA6289 driver
28
Figure 13: BA6289 driver pin assignments
29
Figure 14: TRM-433-LT transceiver pin assignments
30
Figure 15: Schematic diagram of external circuit
30
Figure 16: Schematic diagram of internal circuit
31
Figure 17: Schematic diagram of proof of concept circuit
31
Figure 18: Flowchart methodology for nail extension
32
7
Figure 19: Flowchart methodology for nail retraction
33
Figure 20: Algorithm of the software implementation
34
Figure 21: Circuit setup for test
35
Figure 22: Circuit and waveforms for motor clockwise movement
36
Figure 23: Circuit and waveforms for motor anti-clockwise
movement
37
Figure 24: System overview
40
Figure 25: Full-bridge Class D inverter
42
Figure 26: Q values of different coils
42
Figure 27: The power-receiving schematic
43
Figure 28: Result of rotation experiment
44
Figure 29a: Mid-coronal and mid sagittal section display
45
Figure 29b: Whole-body skin and skeletal structure
45
Figure 29c: Coil alignment
45
Figure 30: Distribution map of induced current density
46
Figure 31: Distribution map of SAR
46
8
LIST OF TABLES
DESCRIPTION
Table 1: Comparisons of the commonly used implant metals
PAGE
23
Table 2: Comparisons of the commonly used polymers
24
Table 3: An example of a truth table of a motor driver
24
Table 4: Comparisons of the more commonly types of motors
26
Table 5: BA6289 driver pin descriptions
28
Table 6: TRM-433-LT transceiver pin descriptions
29
Table 7: The truth table of motor driver BA6289F
35
Table 8: Results of second test
38
9
LIST OF APPENDICES
DESCRIPTION
Appendix 1: Relevant US and European standard
Appendix 2: Electrical field strength dependent on fat layer thickness
(Anders J Johansson, June 2004)
Appendix 3: Electrical field strength dependent on fat layer thickness
(Anders J Johansson, June 2004)
Appendix 4: Gantt chart
Appendix 5: Medical implant construction rules (Winfried Mayr,
Manfred Bijak, Dietmar Rafolt, Stefan Sauermann, Ewald Unger,
Hermann Lanmuller, Feb 2001)
Appendix 6: Laboratory equipment application
PAGE
53
53
54
54
55
56
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PART 1: INTRODUCTION
1.1 Background
An intramedullary nail implant is a metal steel rod forced into the medullary cavity of
a bone and has long been used to treat fractures of long bones of the body. In 1939, a
German surgeon call Gerhard Kuntscher inaugurated this method of intramedullar
nailing of bone fractures for those World War II soldiers.
Before that, treatment of such fractures was only limited to traction or plaster, both of
which required long periods of inactivity.
One of the most significant advantages of intramedullary nail implant that stood out
over other methods is that it shares the load with the bone, instead of entirely
supporting it. Because of this, patients are able to use their extremity more quickly
and thus results in earlier return to activity.
However, intramedullary nail implant cannot be used for all fractures, and there are
often complaints of pain and other symptoms at the site where the metal steel rod are
inserted. Due to this, a second operation may be needed to remove them if patients
have these painful symptoms.
Therefore a two way communication system, which is facilitated by a wireless link,
will be able to make real-time adaptations according to patient’s condition without
having to remove the implant.
In 1999, the Federal Communications Commission (FCC) allocates 402-405 MHz of
band frequency to the Medical Communication Implant (MICS). This particular band
frequency was chosen because it enables the design of low power transmitter and
antenna arrangement which is small enough for implanted applications while still
achieving reasonable transmission range. As there are no other radios that operate in
this same band of frequency, there will also be no interference risks. On top of it, this
range also has propagation characteristics that are conducive to transmission within
the human body.
(Federal Communications Commission, 1999. Medical Implant Communication
Service (MICS) Part 95. Available at: www.fcc.gov
[Accessed 23 August 2009])
Figure 1: X-ray showing the portion of a fracture with an intramedullary nail.
(Picture courtesy of Dr Sarbjit Singh, Orthopedic Surgeon, Mount Elizabeth
Hospital, Singapore)
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1.2 Project Objective
The primary objective of this project is to develop an intelligent controller system for
an intramedullary nail that provides a two way communication between the user and
the nail where a microcontroller system will be develop to control a linear drive
movement and at the same time sends information back from the nail to the
microcontroller and eventually the user. An assembly language program will be used to
generate the codes to control the intelligent. Data between the implant and the free air
space surrounding the patient will be transmitted and received via the transceiver.
Based on the allocated budget, careful study for the selection of the components must
be taken into consideration. A very important factor is the size of these components as
some of them will be implanted internally. Thus all possibilities need to be explore so
that it can be inserted into the patient via the 12mm diameter incision that is made. The
grade of the component chosen must also meet medical requirements, such as not
degrade in its properties and not cause any adverse reactions within the human body.
For final assembly and testing out, animal trials shall be used instead of human body.
The secondary objective of this project will be to do a literature study on the feasibility
of using wireless power transmission to transmit power to the implant.
Figure 2: Block diagram of a two way communication between user,
microcontroller system and nail implant
1.3 Overall Objective
The adding of intelligent to an intramedullary nail allows it to be reprogrammed and
changed to suit the needs of the patient without having to make changes to the
electronics hardware. This will simplify the design, resulting in the use of few
components. Through re-programming, it also helps to reduce pain felt by the patient.
Therefore, unnecessary surgery can be avoided.
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PART 2: MANAGEMENT METHOD
2.1 Project Breakdown
In planning a project, it is normal to be momentarily overwhelmed and confused when
the details and scope of a project begins to come into picture. The way to overcome
this is by breaking the project into pieces and organizes them in a logical way using
work breakdown structure (WBS).
WBS is a result oriented family tree that captures all the work of a project in an
organized way. Often portrayed as a hierarchical tree, it can also be a tabular list of
categories of product, data or service and tasks that appears in the Gantt chart
schedule.
(Work Breakdown Structure, Wikipedia. Available at:
http://en.wikipedia.org/wiki/Work_breakdown_structure [Accessed 5 May 2010])
For this project, using WBS, four main tasks are identified and they are research and
planning, circuit design, software development and hardware assembly and testing.
Under each main task, a few sub tasks branches within it.
Figure 3: WBS for intelligent controller system for an intramedullary nail
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2.2 System Development Method
Currently in the industry, there are a few system development methods that are being
practiced such as waterfall, prototyping, spiral and Structured System Analysis and
Design Method (SSADM).
The waterfall model maintains that one should move to next phase only when its
preceding phase is completed and perfected. There is no jumping back and forth or
overlap between them.
(History of the Waterfall Model, Select Business Solutions. Available at:
http://www.selectbs.com/adt/analysis-and-design/what-is-the-waterfall-model
[Accessed 5 May 2010])
(Waterfall Model, Wikipedia. Available at:
http://en.wikipedia.org/wiki/Waterfall_model [Accessed 5 May 2010])
The prototyping model is a system where a prototype is built, tested, and then
reworked as necessary until an acceptable prototype is finally achieved. From there,
the complete product can be developed. It works best in scenarios where not all of the
project requirements are known in detail ahead of time. It is also often call as an
iterative or a trial and error model.
(Prototyping Model, SearchCIO-Midmarket.com Definitions. Available at:
http://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci755441,00.html
[Accessed 5 May 2010])
The spiral model depends on the nature of the project and its associated risks. With
low risks, it is something similar to waterfall. However when with high risks, it is
more of a prototyping model.
(Spiral Model, Wikipedia. Available at: http://en.wikipedia.org/wiki/Spiral_model
[Accessed 5 May 2010])
The SSADM model is very much function oriented and event driven. It is widely used
in the industry as it is simple to use, has clear procedures and high traceability due to
good Quality Assurance (QA) practices such as revision and change control. It also
supports diagrams representation of information and enhances communication
between different parties concerns.
(Structured System and Design Method, Wikipedia. Available at:
http://en.wikipedia.org/wiki/SSADM
[Accessed 5 May 2010])
Specifically for this project, the prototyping model was chosen as many of the project
requirement and specification had yet to be confirmed and thus it needs to be build on
trial and error basis. Furthermore, the initial build up till the proof of concept will
need to build on prototype approach
14
Figure 4: Flow chart of system design
15
PART 3: LITERATURE REVIEW
3.1 Basic Circuit Theory
A circuit consists of circuit elements and wires. Wires appear on schematics as being
straight lines. Nodes appear on a schematic when 2 or more wires connect, and are
usually marked with a dark black dot. Circuit elements are "everything else" in a
sense. Most basic circuit elements will have their own symbols for recognizing factor,
although some will be drawn as a simple box image, with the specifications written
somewhere that is easy to find. Below we look into further details of circuit theory
related to this project.
3.1.1 Closed and Open Circuit
A closed circuit is one in which a series of devices complete a connection between the
terminals, and charge is allowed to flow freely.
An open circuit on the other hand is a section of a circuit where there is no
connection. Current does not flow between the terminals of an open circuit, although
a voltage may be applied between the terminals, and capacitance may exist between
them. At steady state, there is no current flow in an open circuit.
Often the term "shorting" is widely used in circuit analysis. Shorting an element in a
circuit means placing a wire across the terminals of the element. Because current will
take the least resistance path, shorting an element redirects all current around it.
Because the potential difference between the terminals of the device is zero, no
current can flow through it. This must be done carefully, because reducing the
resistance of a certain portion of a circuit to zero can raise the current to infinity, and
this will damage the circuit.
3.1.2 Voltmeters and Ammeters
Voltmeters are used to measure the voltage across an element and ammeters are used
to measure the current flowing through a wire.
An ideal voltmeter has an infinite resistance (in reality, several megohms), and acts
like an open circuit. A voltmeter is placed across the terminals of a circuit element to
determine its voltage.
An ideal ammeter has zero resistance (in reality, a few ohms or less), and acts like a
short circuit. Ammeters are placed in-line in a circuit, so that all the current from one
terminal flows through to the other terminal.
3.1.3 Sources
Sources come in 2 basic forms: Current and voltage sources. These sources may be
further broken down into independent and dependent sources.
16
Current sources are sources that output a specified amount of current. The voltage
produced by the current source will be dependent of the output current and the
resistance of the load (ohm's law). Voltage sources produce a specified amount of
voltage. The amount of current that flows out of the source is dependent on the
voltage and the resistance of the load (ohm's law). If a voltage source is shorted (a
resistance-less wire is placed across its terminals), the current output approaches
infinity. No voltage source in existence can output infinity current, thus the source
will usually melt or explode long before it reaches that particular value. This is an
important point to keep in mind. An example of voltage source is a battery, which is
specified as being 6V or 9V. The amount of current that the circuit draws from the
battery determines how long the battery life is.
Independent sources produce current or voltage at a particular rate that is dependent
only on time. These sources may output a constant current/voltage, or they may
output current or voltage that varies with time.
Dependent sources are current or voltage sources whose output value is both
dependent on time and another value from the circuit. A dependent source may be
based on the voltage over a resistor, or even the current flowing through a given wire.
The following are possible;
- Current-controlled current source
- Current-controlled voltage source
- Voltage-controlled current source
- Voltage-controlled voltage source
3.1.4 Switches
A switch then is a circuit element that is an open-circuit for all time t < T0, and acts
like a closed-circuit for all time t ≥ T0.
U (t) = {0, if t < T0
U (t) = {0, if t ≥ T0
Function above provides a mathematical model to describe circuit elements that
change between Boolean states (high/low).
3.1.5 Resistors, Resistance and Conductance
Resistors are circuit elements that allow current to pass through them, but restrict the
flow accordingly to a specific ratio called resistance. Flow that is restricted by
resistors is said to be "lost to the resistor". Resistors are commonly used as heating
elements, because energy lost to the resistor is frequently dispersed into the
surroundings as heat. Each resistor has a given resistance. Implementing resistors on a
design are commonly used either as a pull-up resistor where it is place below VCC
and the short is eliminated or a pull-down resistor where it pulls the signal down to
the ground instead of up to VCC.
17
Figure 5a: A schematic diagram of a resistor
Figure 5b: A pull-up resistor
(Picture courtesy of everything2.com)
Figure 5c: A pull-down resistor
(Picture courtesy of everything2.com)
Resistance is measured in terms of units called Ohms (volts per ampere), which is
commonly abbreviated as Ω. Ohms is also used to measure the quantities of
impedance and reactance. The variable most commonly used to represent resistance is
r or R. It is defined as R = ρL/A, where ρ is the resistivity of the materials, L is the
length of the resistor, and A is the cross-sectional area of the resistor.
Conductance is the inverse of resistance. Conductance has units of siemens (S),
referred to as mhos (ohms backwards, abbreviated as an upside-down Ω).
Conductance can be useful to describe resistors in parallel, since the sum of
conductance is equal to the equivalent conductance. However, this is rarely used in
practice. The variable most commonly used to describe conductance is G. It is defined
as R=1/G.
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3.2 Microcontroller Fundamentals
A microcontroller is a device that integrates various components of microprocessor
system into one single microchip. It interacts with the outside world through on-board
interfaces. Its main function is to co-ordinate the flow of information between
separate memories and peripherals which are located outside it. The connections to a
microprocessor include address, control and data busses which allow it to select one
of its peripherals and send to or retrieve data from it. Therefore, a microcontroller
incorporates the following;
- CPU
- Memory (ROM and RAM)
- Parallel digital I/O
- Serial I/O port
- Timer module
- Analog to digital converter (ADC)
3.2.1 Building Block Structure of Microcontroller
Figure 6: An example of a microcontroller’s building block
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Below we look into details of these blocks.
3.2.1.1 Central Processing Unit
A block that have a built in capability to multiply, divide, subtract, and move its
content from one memory location into another. Its memory locations are called
registers.
Registers on the other hand are memory locations whose role is to help with
performing various mathematical operations or any other operations with data
wherever data can be found. For example, if user wishes to add the contents of two
memory locations and return the result again back to memory, there would be a need
for a connection between memory and CPU. To simply put it, it must have some
"way" through for data to go from one block to another.
3.2.1.2 Memory
This is a part of the microcontroller whose function is to store data. For a certain input
it gets the contents of a certain addressed memory location. However there are two
things to take note which are the addressing and memory location. Memory consists
of all memory locations, and addressing is selecting one of them. This means that user
needs to select the desired memory location, and on the other hand wait for the
contents of that location. Besides reading from a memory location, it must also
provide for writing onto it. This is done by supplying an additional line called control
line. This line is designated as r/w (read/write). It is used in the following way, if
r/w=1, reading is done, and if opposite is true then writing is done on the memory
location.
3.2.1.3 Bus
There are two types of buses, address and data bus.
Address bus consists of as many lines as the amount of memory user wish to address
and it serves to transmit address from CPU memory.
Data bus on the other hand is as wide as data needed and it serves to connect all
blocks inside the microcontroller.
3.2.1.4 Input/Output Unit
When working with I/O port, it is necessary to choose which port user need to work
with, and then to send data to, or take it from. The port acts like a memory location.
Something is simply being written to or read from and it could be noticed on the pins
of the microcontroller.
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3.2.1.5 Serial Communication
It is possible to receive and send data simultaneously at the same time. A full-duplex
mode block which enables this is called serial communication. Unlike the parallel
transmission, data moves bit by bit or in a series of bits. After the reception of data,
user needs to read it from the receiving location and store it in memory. In sending
data, the process is reversed.
3.2.1.6 Timer Unit
In order to utilize serial communication, there is the need to add on few additional
blocks. One of those is the timer block which is significant because it can give user
information about time, duration, protocol etc. The basic unit of the timer is a free-run
counter which is in fact a register whose numeric value increments by one in even
intervals, so that by taking its value during periods T1 and T2 and on the basis of their
difference user can determine how much time has elapsed.
3.2.1.7 Watchdog
This block is a free-run counter where the program needs to write a zero in it every
time it executes correctly. In case that program gets "stuck", zero will not be written
and counter will reset the microcontroller. This will result in executing the program
again, and correctly this time around. That is an important element of every program
so as to be reliable without man's supervision.
3.2.1.8 Analog to Digital Converter
As the peripheral signals are usually different from what microcontroller can
understand (one and zero/high and low), thus they have to be converted into a pattern
which can be understood by a microcontroller. This task is performed by a block for
analog to digital conversion. This block is responsible for converting information
from analog value to a binary number and to follow it through to a CPU block so that
it can then be process further.
Figure 7: The inside view of a microcontroller
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3.2.2 Programming Languages Use for Microcontroller
For all application, a microcontroller alone is not enough. User needs a program that
can be executed. Programming can be done in several languages. Assembler, C and
Basic are the more commonly used. Assembler is a lower level language that is
programmed slowly, but takes up the least amount of space in memory and gives the
best results where the speed of execution is concerned. C is easier to be written and to
be understood but is slower in execution compared to assembler. Basic is the easiest
among all but it is also slower than assembler when it comes to execution. Therefore
user needs to consider carefully the demands for speed of execution and the size of
memory available. After the program is written, user would install the microcontroller
into a device and run it. The microcontroller would then need to be connected to a
power supply. As it detects and receives power supply, microcontroller will perform a
small check up on itself, look up the beginning of the program and start executing it.
3.3 Background of Intramedullary Nail and Having an Intelligent
Intramedullary nail implant was originally intended to correct shortened or deformed
limb caused by injuries, diseases or other causes like congenital defect. However, it is
more popularly use this days for individuals who wants to increase their height. An
individual can gain lengths of up to 60mm for the upper and lower bones of the legs.
As long as they are at least 13 years of age and in good health, this can be done.
(Yeo Hai Teck, 2007. ENG499, Final report)
As compared to conventional bone extension surgery, intramedullary nail implant is
much safer and simpler to perform. The device is inserted into the hollow of a bone
that has been cut crosswise (with a diameter of 20mm). It is than activated by the user
using either a supported GUI or PC to increase the length of their bones with up to
1mm a day. It would then normally takes about three months or more for the bone to
gain its normal strength. (Yeo Hai Teck., 2007. ENG499, Final report)
The hardware design of the intelligent controller system mainly involves a transceiver
and a splatch antenna implanted internally and also externally (for two way
communication). However today, not much is known of the communication channel
between the nail implant and the free air space surrounding it externally.
The Federal Communications Commission (FCC) had allocated 402-405 MHz
frequency band to Medical Communication Implant (MICS). This band range is
suitable for implanted applications as it is small enough and at the same time able to
allow the design of low-power transceiver and antenna arrangement that can achieve
reasonable transmission range. It also does not pose any interference risk.
(Federal Communications Commission, 1999. Medical Implant Communication
Service (MICS) Part 95. Available at: www.fcc.gov
[Accessed 23 August 2009])
(Anders J Johansson1, Anders Karlsson2., 2004 Wave-propagation from medical
implants)
22
Good transceiver and antenna circuit design is a very critical factor in obtaining good
range and stable throughput. As this is for implant application, the size of the
hardware and its circuit will also have to be considered.
Finally, when all the hardware is assemble together, a microcontroller will be
deployed to execute control.
3.4 Biomedical Material
In our daily lives, we often have to depend on biomaterials and biomedical devices
which are used throughout our body. However there are stringent controls placed
upon the application of devices and the materials that can be used. When a medical
implant device is placed into human body, it concerns the effect of the physiological
environment on the material and device. Specifically for this project, any biomedical
material used will not only have to satisfy its design requirements but must also not
degrade in its properties and not cause any adverse reactions within the human body.
Below is an explanation of bio metals and synthetic polymers in further details.
(Yeo Hai Teck., 2007. ENG499, Final report)
3.4.1 Biomaterials Metals
Due to their toughness and strength, metals are widely used as biomaterials. The more
commonly used implant metals such as stainless steel, titanium and cobalt alloys are
generally biocompatible. However there will be some people who are allergic to ions
released from these metals. One of the major problems with metals is the generation
of fine wear particles that can lead to inflammation and implant loosening.
(Tristan Burg., 2001. Owen Standard)
Table 1: Comparisons of the commonly used implant metals
3.4.2 Synthetic Polymers
Polymers have physical properties that are almost similar to natural tissues in human
body and are thus widely used as implant materials. Its usage includes wound
dressings, tendon replacements, intraocular lens replacement and joint linings. The
polymers that are commonly used include polyethylene (PE), polyethylene
terephthalate (PET), polytetrafluoroethylene (PTFE) and polyurethane (PU). These
23
materials are well tolerated in the human body. However, the additives and molecules
released due to polymer breakdown can lead to allergic and inflammatory responses.
(Tristan Burg., 2001. Owen Standard)
Table 2: Comparisons of the commonly used polymers
3.5 Circuit Design Implementation to Drive the Motor
In determining the circuit design that will be able to drive the motor in the nail
implant, the first most important thing is to identify the truth table logic of the motor
driver that will be used. Upon that, these basic factors shall be incorporated into the
circuit design.
- Identifying of the pins on the microcontroller unit that will be assign to the forward
and reverse switch.
- Identifying of the pins on the microcontroller unit that will be assign as the inputs.
- Based on the truth table logic of the motor driver that will be used, the software code
shall be written for the logic (high/low) detection and settings for these pins
accordingly.
- The pins on the microcontroller unit that had been assigned as inputs will have to be
connected to the motor driver so that the appropriate input to output logic conversion
will take place. This conversion will be done by the motor driver itself.
- The pins on the motor driver which had been identified as outputs are to be
connected to the motor.
With proper coordination of these factors in the design set-up and software code
writing, user will be able to drive the motor accordingly.
Table 3: An example of a truth table of a motor driver
24
PART 4: SYSTEM DESIGN
4.1 System Description
Figure 8 depicts a block diagram of the complete system. It includes mainly an
external circuit, user interface, function selector and an implanted internal circuit.
The internal circuit gets its power supply from the receiver coil which will have
power transmitted to it wirelessly via the transmitter coil. It is possible to achieve very
low average power consumption since the entire cycle can be completed in less than a
few seconds.
The transceiver on the external circuit will transmit command from the MCU
commander while the transceiver on the internal units will receive command to the
MCU slave for execution.
This system is to produce linear motion in bi-directional motor drive systems.
Figure 8: Block diagram of a complete intramedullary nail system
25
4.2 Microcontroller Selection
The selection of which microcontroller to be use is very much based on the aspect of
its size and functions. For this project, the width of the microcontroller should
approximately not be more than 10mm due to the 12mm diameter incision that is
made. Some of its necessary specification requirements needed are;
- 8-bits.
- 128 bytes of RAM.
- 4k bytes of on-chip ROM.
- 2 timers, 1 serial port and 4 ports which are 8-bits wide each.
- 2 or 3 16-bits counters and programmable full-duplex serial port with its baud rate
provided by one of its timers.
- Minimum of 32 I/O lines (four 8-bits ports) with RAM.
With all this in mind, Microchip’s PIC16F676 was found to be suitable and thus
chosen as the microcontroller for this project due to its powerful but yet easy to
program (only 35 single word instructions) capability.
Figure 9: PIC16F676 microcontroller pin assignments
4.3 Motor Selection
As with the microcontroller, the diameter of the body of the chosen motor must also
not be more than 10mm. Table 4 looks at the more commonly types of motors that are
available in the market such as DC motor, stepper motor and servo motor.
Comparison details between them need to be reviewed so as to select the most
suitable type of motor to be use.
Table 4: Comparisons of the more commonly types of motors
26
After reviewing all the comparisons and weighing the pros and cons, it was initially
decided that stepper motor is to be use since it is simple and interfaces well to
microcontroller systems. At the same time, the output power needed for this project is
also not very high. However the smallest diameter of the body of a stepper motor that
is available in the market is 12mm. With this, DC motor was the obvious choice left.
In the search for a suitable DC motor, Faulhaber stands out as the world’s largest
consolidated portfolio of miniature and micro drive system technologies. With a
technology focus on the self-supporting, skew-wound, ironless rotor, DC motor and
precision system components such as gearboxes, encoders and motion controllers, it
specializes in complex and high precision area of application such as medical devices,
handling automation, telecommunications and precision optics.
Thus the Faulhaber model of choice of DC motor for this project is 1024 M 003 S
with G10/1 gear due to its size properties.
Figure 10: Dimension of a DC motor
Figure 11: Dimension of a DC motor with gear
27
4.4 Motor Driver Selection
A half amp full bridge driver for small 3V, 5V and 12V DC motor with below
considerations should be selected;
- Split ± voltage power supply option for output drivers.
- Load switching capabilities to 0.5A.
- Operating voltage of +2.5V to 15V.
- Low standby current.
- CMOS/TTL compatible input logic.
- Over temperature shutdown protection.
- Over current limit protection.
- Over current fault flag output.
- Direction, braking and PWM control.
- Width approximately not more than 10mm.
Rohm BA6289 driver is chosen to be the motor driver for this project as it is one of
the few in the market that meets these considerations and at the same time available
for small quantity purchase.
Figure 12: Functional block diagram of the BA6289 driver
Table 5: BA6289 driver pin descriptions
28
Figure 13: BA6289 driver pin assignments
4.5 Transceiver Selection
The key considerations in transceiver selection are;
- Its communication standards protocol.
- Its hardware platform.
- Its communication modes.
- Its application interface.
- Range capability of more than 2m.
- Capability of allowing device to sleep in order to save power.
- Width approximately not more than 10mm.
LINX Technologies transceiver TRM-433-LT meets most of these consideration and
thus is the chosen transceiver for this project.
Table 6: TRM-433-LT transceiver pin descriptions
29
Figure 14: TRM-433-LT transceiver pin assignments
4.6 Circuit Design
Figure 15: Schematic diagram of external circuit
- Emergency: Press the button and the power supply will be cut-off.
- Motor Accordion: Press the button and a command will be send to the MCU slave in
the internal circuit to move the motor in accordion motion.
- Motor Forward: Press the button and a command will be send to the MCU slave in
the internal circuit to move the motor in forward motion.
- Motor Reverse: Press the button and a command will be send to the MCU slave in
the internal circuit to move the motor in reverse motion.
30
Figure 16: Schematic diagram of internal circuit
Due to limitation of time to work on this project, the task was simplified to just proof
of concept of the idea. Thus only one main circuit is to be developed and it is call the
proof of concept circuit to test out workability of the idea implementation and also its
electronics.
Figure 17: Schematic diagram of proof of concept circuit
31
PART 5: IMPLEMENTATION OF IDEAS
5.1 Idea Implementation
As with the specification set out for this project, the nail should only extend or retract
by a maximum of 0.25mm at a time and a maximum of 1mm per 24hrs. As a whole,
the nail should also only be extended or retracted up to a maximum of 60mm.
Therefore, this will be a key aspect of the microcontroller implementation.
Figure 18: Flowchart methodology for nail extension
32
Figure 19: Flowchart methodology for nail retraction
Another thing to take note is that on top of having forward and reverse movement,
accordion movement is also needed for this. This is because the accordion like
pumping action will help to hydrate and increase the fluid circulation to the tissues
around the nail.
(Kane M., 1985. Journal of Orthopedic and Sports Physical Therapy)
5.2 Software Implementation
Therefore, with all these in mind, the software implementation for this project had
been set out to have below intelligent.
- Forward/Reverse movement should not be more than 0.25mm (13 secs) extension
/retraction per each time.
- Accordion movement moves forward than reverse continuously, with that 13 secs
for each direction.
- Counter 1 set a count of (N+1) every time the forward switch is pressed.
- Counter 1 set a count of (N-1) every time the reverse switch is pressed.
- Timer starts timing once it detects the first switch being activated (N+1 or N-1). This
timer together with counter 1 will get refresh every 24hrs.
33
- The forward switch will not be able to be activated if the counter 1 reads a value of
> 4 for (N+1) so as to prevent an extension of more than 1mm per 24hrs.
- The reverse switch will not be able to be activated if the Counter 1 reads a value of <
-4 for (N-1) so as to prevent a retraction of more than 1mm per 24hrs.
- After 24hrs and counter 1 gets refresh, whatever value the count is reading is to be
stored in another counter (Counter 2). Whenever Counter 2 reads a value of > 240 or
< -240, it will prevent any movement from taking place. This is to ensure the nail can
only be extended or retracted to a maximum of 60mm. (60/0.25 = 240)
Figure 20: Algorithm of the software implementation
34
PART 6: TESTS AND RESULTS
6.1 Motor and Driver
The first test to be carried out pertains to the motor and driver. The tests are;
- Motor rotates in clockwise direction.
- Motor rotates in anti-clockwise direction.
Figure 21: Circuit setup for test
Table 7: The truth table of motor driver BA6289F
35
6.1.1 Motor Rotates in Clockwise Direction
Figure 22: Circuit and waveforms for motor clockwise movement
Channel A (Output 1): Display the enable signal was pull to high logic with a voltage
of 4.265V. The current reading taken was 0.046A.
(Minimum current needed for Faulhaber 1024 M 003 S DC motor is 0.016A)
Channel B (Output 2): Display the enable signal was pull to low logic.
36
6.1.2 Motor Rotates in Anti-Clockwise Direction
Figure 23: Circuit and waveforms for motor anti-clockwise movement
Channel A (Output 1): Display the enable signal was pull to low logic.
Channel B (Output 2): Display the enable signal was pull to high logic with a voltage
of 4.234V. The current reading taken was 0.044A.
(Minimum current needed for Faulhaber 1024 M 003 S DC motor is 0.016A)
37
6.2 Software
The second and final test to be carried out pertains to the software. The tests are;
- Per every time motor rotates in clockwise direction, ~0.25mm of extension takes
place.
- Per every time motor rotates in anti-clockwise direction, ~0.25mm of retraction
takes place.
- Within 24hrs, when 1mm of extension has taken place, motor will not carry out any
movements.
- Within 24hrs, when 1mm of retraction has taken place, motor will not carry out any
movements.
With the help of the mechanical jig of the nail implant that comes with a distance
reader which was provided by the school, the test for the above was able to be carried
out.
Table 8: Results of second test
38
PART 7: PROBLEM AND DIFFICULTY
7.1 Problems and Difficulties Encountered
One of the main problems encountered while doing this project was the inability to
get the Faulhaber 1024 M 003 S DC motor to work even though the entire circuit up
to the motor driver portion was working fine. After further debugging, the main
problem identified was;
- The motor driver pin 2 (motor voltage) was connected to a 1K resistor which was
connected to VCC.
- This connection was done based on examples from the BA6289 driver datasheet.
- Conclude that the reason for a need for this 1K pull-down resistor was to protect the
motor from receiving a very high current input from the driver if the VCC use is very
high since the driver has an operating voltage capability of up to 15V.
- However, since the VCC use in this case is only 5V, the pull-down resistor causes
the current to be of a very low value. (< 0.005A)
- The Faulhaber 1024 M 003 S DC motor on the other hand needs a minimum current
of 0.016A.
Thus, the 1K resistor was removed and the motor driver pin 2 was connected directly
to VCC. With that, the Faulhaber 1024 M 003 S DC motor manage to work.
39
PART 8: LITERATURE STUDY OF WIRELESS POWER TRANSMISSION
(SECONDARY OBJECTIVE)
8.1 Introduction
In order to deliver stable and sufficient power supply to a human tissue safely, a
wireless power transmission system based on inductive coupling is presented. The
system consists of a primary coil outside and a multiple secondary coils inside the
body. The primary coil is driven to generate a uniform alternating magnetic field
covering the whole of the alimentary tract and the multiple secondary coils receive
energy regardless of the position and orientation relative to the generated magnetic
field. The human tissue safety of the electromagnetic field generated by transmitting
coil was evaluated, based on a high-resolution realistic human model.
8.2 System Overview
Wireless power transmission comprises two subsystems, the power transmitter and
the power receiver. The power transmitter generates alternating magnetic field
through the transmitting coil, driven by the power amplifier. Energy is delivered by
inductive coupling between the transmitting and receiving coils. The received AC
voltage is rectified and regulated to DC voltage. The transmitting coil is normally the
primary side and the receiving coil is the secondary side. Because there is a large air
gap between them, they form a loosely coupled transformer. In order to improve the
power transmission efficiency, the primary and secondary side coils should be
compensated by capacitors, thus forming serial or parallel resonant circuits on each
side. The serial resonant circuit is preferable in this weakly coupled system because of
its better load performance. The power transmitter and receiver work in resonant state,
in which the resonant frequency of both sides must be identical. The frequency of the
alternating magnetic field is determined by the resonant circuit of the power
transmitter. Selection of the magnetic field frequency is critical and is determined
mainly by the characteristics of the receiving coil, which must be designed for highpower transmission efficiency.
(Robert Huston., 2000. International Journal of Medical Robotics)
Figure 24: System overview
40
8.3 Power Transmitting Coil
The function of the power-transmitting coil is to generate an alternating magnetic
field compatible with the power receiver. A solenoid coil with an inner diameter
greater than the transverse dimension of the human body is simple and easy to
implement, but it has a serious drawback. The magnetic field is not uniform in such a
coil. In positions near the coil, the magnetic field is much stronger than that in the
central positions. This will make the received power too excessive in one position but
too weak in another, causing instability when the power receiver works in different
positions. Another problem is the potential adverse health effect to the tissues near the
coil, because the magnetic field would go beyond the safety threshold. A uniform
magnetic field should be adopted to avoid these two problems. A uniform magnetic
field can be generated by having two identical circular coils that are placed
symmetrically on each side of the experimental area, along a common axis and
separated by a distance equal to the radius of the coil. Each coil carries an equal
current flowing in the same direction. The magnetic field generated can be static,
time-varying DC or AC, depending on applications. The current in each coil should
be the same phase in order to generate a low-frequency magnetic field.
(Robert Huston., 2000. International Journal of Medical Robotics)
8.4 Coil Driver
To drive the transmitting coil, an inverter that can change the DC power to AC power
is needed. In order to achieve a high efficiency, a Class D inverter should be selected.
The DC input voltage is converted to a quasi-square wave by full-bridge switches to
excite the transformer primary coil. In order to reduce over-voltage and switching
losses of Q1, Q2, Q3 and Q4 (MOSFETs) in conventional Class D inverters, a
snubber network is implemented. A square wave signal with a duty cycle of 50%,
produced by the timing generator, is fed to the driver to generate a sinusoidal driving
current in the LC tank. An adjustable inductor, Lr, is serially connected with the LC
tank formed by the transmitting coil, L, and the resonant capacitor, C. Because the
inductance of the power-transmitting coil and the capacitance of the resonance
capacitor may change, the adjustable inductor acts as a regulator to maintain the
specified resonance frequency through the variation of its inductance. The resonant
capacitor must resist a high AC voltage up to several KV, because of the high Q value
of the transmitting coil. The capacitor should have a Q value as high as possible to
reduce heat generation. A ceramic vacuum capacitor with a capacitance of 250pF and
a high-frequency peak working voltage of 21KV is adopted.
(Robert Huston., 2000. International Journal of Medical Robotics)
41
Figure 25: Full-bridge Class D inverter
8.5 Power Receiving Coil
In order to deal with the orientation problem, a multiple receiving coil orientated in
three different directions is design. The winding wire should be able to reduce the
skin effect and proximity effect losses in coils. In addition, the quality factor of the
receiving coil should be optimized through appropriate design parameters to reduce
the power loss and increase the power link efficiency. The most important design
parameter is the number of turns of each coil. Because the usable space is restricted,
the number of turns determines the number of strands. In order to find the optimized
configuration, tests are performed on one-dimensional coils with different turns and
strands wound on cubic ferrite cores with the same size of 6.6 × 6.6 × 5.5mm. The Q
values of each coil were tested at different frequencies as illustrated in Figure 26. In
the testing, the Q of one coil was measured when the other coils opened. Test results
shows that the configuration of more strands and fewer turns is preferable.
Figure 26: Q values of different coils
A schematic of the power-receiving circuit is shown in Figure 27. Three LC series
resonant circuits, formed by 3D coils L1, 2, 3 and their resonant capacitor C1, 2, 3,
were power receiving front-ends. A series resonant circuit, rather than a parallel
resonant circuit, was selected because its impedance was lowest at the resonant
42
frequency. A large current instead of a high voltage can be acquired to drive the load.
A full-bridge rectifier, rather than a full-wave rectifier, was used in the receiving
circuits. The full-wave rectifier has the features of the same efficiency as a full-bridge
rectifier while few diodes are needed, but it needs twice the number of turns than that
of the full-bridge rectifier, which means more space is required when same power is
retrieved. From the point of view of space, a full-bridge rectifier is more suitable as it
can provide mover power when the given space is fixed, which is essential to the
wireless power link. The extra space occupied by the diodes can be counteracted by
adopting smaller packages. A Schottky barrier diode with low forward voltage was
adopted to reduce power loss in the rectification process. Parallel connection, rather
than serial connection, was selected to summarize the contributions of three coils after
rectification. In parallel connection, only the coil which produces the maximum
voltage among the three will contribute its power to the load; the other two cannot
form a return circuit because of the clamping of the diode. In serial connection, the
receiving power may increase because all the three coils may contribute their power,
but the power loss from the diode also increases. In addition, the receiving circuits
may operate out of resonance because of interference when all the three coils form the
return circuit; this would result in a remarkable drop of the receiving power. After the
parallel connection, a filter capacitor, Cf, and a zener diode, DZ, were adopted. The
filter capacitor was used to smooth the rectified voltage and the zener diode to protect
against possible over-voltage. Because there is a need for a fixed voltage for its
operation, a regulator should be connected after rectifier. For the sake of conversion
efficiency, a switching mode DC converter was adopted instead of a conventional
linear regulator. The DC converter, designed with a step-down converter chip and a
few other chip components, was demonstrated to have an efficiency of 85–90%. All
the power receiving circuits except the receiving coil could be implemented in a
circular double-sided PCB.
(Robert Huston., 2000. International Journal of Medical Robotics)
Figure 27: The power-receiving schematic
8.6 Experiments and Results
In order to investigate the performance of the designed wireless power transmission
system, position and orientation stability tests is necessary. In these tests, receiving
power was acquired by measuring the voltage of the load resistance, Rd which was
temporarily connected with Cf in the receiving circuit shown in Figure 27. The DC
converter and zener diode were removed during the tests to get rid of the influence of
these components. The load resistance was set to 15R, approximating the series
resistance of the power-receiving coils. The magnetomotive force of the power
transmitting coil was 39 ampere-turns. The frequency of the magnetic field was
43
400KHz. In the position stability test, receiving power was recorded on a mesh grid of
20 × 20mm on a plane across the axis of the power-transmitting coil, and the
receiving coil was maintained in a fixed orientation, with the electromagnetic field
perpendicular to one of the three coils. An orientation stability test had to be carried
out, using a rotatable stage located at the centre of the transmitting coil. The rotation
mode was adopted for all possible orientations that would be covered in the rotation
when ϕ was kept at 45◦. The receiving power was acquired every 10◦ in 360◦
rotation, and the result is illustrated in Figure 28. According to the analysis of
orientation stability above, the optimal orientation in power receiving occurs when θ
= 0◦ and 180◦ in rotation, and the worst orientations are 54◦, 126◦, 234◦ and 306◦. The
experimental result in Figure 28 also shows that it is in accordance with the
theoretical analysis, and the maximum and minimum receiving power was 790 and
310mW. From the theoretical analysis and experiments, it was revealed that some
degree of orientation stability could be achieved by using a 3D power-receiving coil.
Because the orientation stability was tested in the centre of the transmitting coil,
which is the worst position in the power transmission, the power of 310mW in the
orientation stability test was thus the minimum power received.
(Robert Huston., 2000. International Journal of Medical Robotics)
Figure 28: Result of rotation experiment
8.7 Human Tissue Safety
The concern for human tissue safety of power transmission could not be avoided in
this study, since an excessive electromagnetic field generated by the transmitting coil
might damage the human body. According to the 1997 guideline of international
commission on non-ionizing radiation protection (ICNIRP), for the frequency range
100KHz–10MHz, electromagnetic influences on biological tissue include thermal
effects and stimulant action. The thermal effect is a result of the generation of Joule
heat, while the non thermal effect involves exciting neurons and muscles by the
induced current. The specific absorption rate (SAR, W/Kg) is often used as an index
of the thermal effect and current density (A/m2) is often used as an index of the non44
thermal effect. Since the SAR and the current density in human tissues cannot be
acquired by experiment, a numerical simulation method, based on a high-resolution
human anatomical model, was adopted in the study. A semi-automatic image
segmentation technique was performed to identify and segment the image into regions
of different tissues or organs, based on sectional image and anatomical knowledge.
The physical properties of the tissues or organs, such as conductivity, permittivity and
density were specified to the corresponding tissues after identification. The
conductivity, permittivity of human tissues comes from parametric models for the
dielectric spectra of tissues and the tissue densities were based on Reference Man of
the ICRP, for some tissues whose densities were not included in the references, a
homologous density was assigned. When these two steps were finished, a human
electromagnetic calculation model was achieved. This model was imported into a
commercial software package by the format of voxel data; after setting the parameters
of the transmitting coil, current density and SAR that can be calculated by finite
integration technique. Figure 29a-c shows the display of the human model that was
established. The model consists of 56 kinds of tissues or organs, with a resolution of
0.33mm in transverse section and 2mm between slices. The maximum current
densities in the cutting plane for a frequency of 400KHz are shown in Figure 30 for a
current density distribution of an x–z plane at y = 0 cm and an y–z plane at x =
16.1cm, respectively. The results showed that current density was large at places near
the transmitting coils and in tissues consisting of muscle. The maximum current
density, calculated as above, was 3.82A/m2, below the ICNIRP basic restrictions
(4A/m2). The maximum SAR distributions in the cutting plane as an average value of
10g for a frequency of 400KHz are shown in Figure 31, for a SAR distribution of an
x–z plane at y = 4.8cm and a y–z plane at x = 0cm, respectively. SAR was large at
places near the coils and in fat and muscle tissues. The maximum SAR, calculated as
above, was 0.329W/Kg, far below the ICNIRP basic restrictions (10W/Kg).
(Robert Huston., 2000. International Journal of Medical Robotics)
a
b
c
Figure 29a: Mid-coronal and mid sagittal section display
Figure 29b: Whole-body skin and skeletal structure
Figure 29c: Coil alignment
45
Figure 30: Distribution map of induced current density
Figure 31: Distribution map of SAR
8.8 Conclusion and Discussion
At least 310mW of usable powers can be transmitted under the worst geometrical
conditions. The maximum specific absorption rates (SAR) and current density of
human tissues are 0.329W/Kg and 3.82A/m2, respectively, well under the basic
restrictions of the ICNIRP. The designed wireless power transmission is shown to be
feasible and potentially safe in a future application.
(Robert Huston., 2000. International Journal of Medical Robotics)
46
PART 9: CONCLUSION AND RECOMMENDATIONS
9.1 Conclusion
The main approach taken for this project had been to design and develop a
microcontroller system that controls a linear drive system for an intramedullary nail
that meets a set of technical specifications according to the user requirements. Studies
and classification of biomedical implantable devices and wireless power transmission
were also undertaken.
The motivation behind this was being able to play a part in helping those who desire
to gain additional heights or those who have had an injury that caused shortened or
deformed limb bones or were born with limb length inequality to overcome their
shortcoming.
The main advantage of this project is that it allows the system to be reprogrammed and
changed to suit the needs of the patient without having to make changes to the
electronics hardware. Therefore, through re-programming, it helps to reduce pain felt
by the patient and unnecessary surgery can be avoided.
One of the main achievements of this project is in the implementation of ideas. Even
though the concept and design is not entirely original, the idea implemented was
unique and not done before.
Looking back to the project objective earlier, testing out on animal trials was not
carried out as project was developed more on the basis of proofing of concept due to
time limitations. Thus, the transmitting and receiving portion was left out and the
physical circuit develop was also not according to specific size requirements as
miniaturization of hardware was not look into.
9.2 Future Recommendations
Up to this point, there remain a few things where future work can be done to bring
this project to a higher level and fully complete it. They are;
- Physical development of the transmitting and receiving portion.
- Physical development of the internal circuit according to specific size requirement
with proper miniaturization of hardware.
- Physical development of wireless power transmission.
- Look into the possibility of enabling the user to use their handphone via sms to
control the nail, with the help of a GSM module.
47
PART 10: CRITICAL REVIEW AND REFLECTIONS
10.1 Critical Review and Reflections
In the beginning of this project, I was very lost and low in confidence of getting it
done. The overall picture of the project looks to be very daunting. Other than having a
good knowledge of electronics engineering and microcontroller programming,
biomedical knowledge is also needed especially in the biomechanics of the upper and
lower extremities.
Thus, a lot of biomedical research needs to be done. There were also many electronics
and circuitry knowledge which I wasn’t sure of and I was also not highly proficient in
microcontroller programming languages.
However, through those initial meetings I had with Mr. Stephen and Mr. Firdaus,
slowly but surely I begin to clear my doubts and build up my confidence.
Along with all the research and learning that I done through this period, the skills,
knowledge and experienced obtained during my studies in Unisim through these
subjects (HESZ331, TZS323, ENG311, ENG327 and ENG328) do comes in handy as
backbones for the project.
As a whole, it had been a very good experience and an eye opener for me as to what
research, development and project planning is all about. It has truly been beyond
classroom learning.
48
GLOSSARY
Linear drive system: Movable machine element, such as slide, carriage or the like,
and relative movement between the guide element and the base element is obtained by
a toothed or gear belt engaging into a rack, in which, for example, the rack is located
on the base element and the gear belt is driven by a drive motor or the like located on
the movable machine element, slider or carriage.
Microcontroller: A type of microprocessor emphasizing self-sufficiently and costeffectiveness, in contrast to a general-purpose microprocessor.
Potential difference: The amount of energy per unit charge needed to move a
charged particle from a reference point to a designated point in a static electric field;
voltage.
Pull-up resistor: A resistor that is connected between the power-supply line and a
logic line and ensures that the line is normally pulled up to the supply potential. Opencollector logic devices may be connected to the logic line and each device is then
capable of pulling the line low to the ground.
Pull-down resistor: A resistor that is connected between the ground and a logic line
and ensures that the line is normally pulled down to the ground potential. Opencollector logic devices may be connected to the logic line and each device is then
capable of pulling the line up to the power-supply line.
Full-duplex mode: Capable of transmitting and receiving over the same channel
simultaneously. In pure digital networks, this is achieved with two pairs of wires. In
analog networks or in digital networks using carriers, it is achieved by dividing the
bandwidth of the line into two frequencies, one for sending, and the other for
receiving.
Transceiver: A device that has both a transmitter and a receiver which is combined
and share common circuitry or a single housing. If no circuitry is common between
transmit and receive functions, the device is a transmitter-receiver.
Antenna: Also known as an aerial, a transducer designed to transmit or receive
electromagnetic radio waves.
Interference: Any disturbance that interrupts, obstructs, or otherwise degrades or
limits the effective performance of electronics and electrical equipment. It can be
induced intentionally, as in some forms of electronic warfare, or unintentionally, as a
result of spurious emissions and responses, intermodulation products, and the like.
Stepper motor: A brushless, synchronous electric motor that can divide a full
rotation into a large number of steps. When commutated electronically, the motor’s
position can be controlled precisely, without any feedback mechanism.
DC motor: An electric motor that runs on direct current (DC) electricity.
49
Servo motor: A motor used for motion control in robots, hard disc drives and etc.
Generally designed more like an alternator than a standard motor, most servos need
special control circuitry to make them rotate electrically. Some can be used in reverse
to generate alternating current.
MOSFETs: A special type of field-effect transistor (FET) that works by
electronically varying the width of a channel along which charge carriers (electrons or
holes) flow. The wider the channel, the better the device conducts. The charge carriers
enter the channel at the source, and exit via the drain. The width of the channel is
controlled by the voltage on an electrode called the gate, which is located physically
between the source and the drain and is insulated from the channel by an extremely
thin layer of metal oxide.
Resonant frequency: A frequency at which some measure of the response of a
physical system to an external periodic driving force is a maximum. Three types are
defined, namely, phase resonance, amplitude resonance, and natural resonance, but
they are nearly equal when dissipative effects are small.
Vacuum capacitor: A capacitor with separated metal plates or cylinders mounted in
an evacuated glass envelope to obtain a high breakdown voltage rating.
Filter capacitor: A capacitor used in a power-supply filter system to provide a lowreactance path for alternating currents and thereby suppress ripple currents, without
affecting direct currents.
Full-bridge rectifier: A full-bridge device, such as a diode, that converts alternating
current to direct current.
Full-wave rectifier: A full-wave device that converts the whole of the input
waveform to one of constant polarity (positive or negative) at its output. Full-wave
rectification converts both polarities of the input waveform to direct current (DC), and
is more efficient.
Regulator: Device or circuit that maintains a desired output under changing
conditions.
Zener diode: A silicon semiconductor device used as a voltage regulator because of
its ability to maintain an almost constant voltage with a wide range of currents.
Linear regulator: A voltage regulator based on an active device operating in its
"linear region" or passive devices like zener diodes operated in their breakdown
region. The regulating device is made to act like a variable resistor, continuously
adjusting a voltage divider network to maintain a constant output voltage. It is very
inefficient since it sheds the difference voltage by dissipating heat.
Magnetomotive force: Force that produces a magnetic field.
50
REFERENCES
1. Yeo Hai Teck., 2007. ENG499, Final report
2. ISO 14155-1., 2003. Clinical investigation of medical devices for human subjects_
Part 1
3. ISO 14155-2., 2003. Clinical investigation of medical devices for human subjects_
Part 2
4. Federal Communications Commission, 1999. Medical Implant Communication
Service (MICS) Part 95. Available at: www.fcc.gov
[Accessed 23 August 2009]
5. Work Breakdown Structure, Wikipedia. Available at:
http://en.wikipedia.org/wiki/Work_breakdown_structure [Accessed 23 August 2009]
6. Waterfall Model, Wikipedia. Available at:
http://en.wikipedia.org/wiki/Waterfall_model [Accessed 23 August 2009]
7. Prototyping Model, SearchCIO-Midmarket.com Definitions. Available at:
http://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci755441,00.html
[Accessed 23 August 2009]
8. Spiral Model, Wikipedia. Available at: http://en.wikipedia.org/wiki/Spiral_model
[Accessed 23 August 2009]
9. Structured System and Design Method, Wikipedia. Available at:
http://en.wikipedia.org/wiki/SSADM
[Accessed 23 August 2009]
10. Circuit Theory, Wikipedia. Available at:
http://en.wikibooks.org/wiki/Circuit_Theory/All_Chapters
[Accessed 27 January 2010]
11. Pull-up/Pull-down Resistor, Everything2.com. Available at:
http://everything2.com/title/Pull-up+resistor [Accessed 10 February 2010]
12. Microcontroller, PIC Tutorial. Available at:
http://www.pictutorials.com/what_is_microcontroller.htm
[Accessed 27 January 2010]
13. Anders J Johansson1, Anders Karlsson2., 2004 Wave-propagation from medical
implants
14. Tristan Burg., 2001. Owen Standard
15. Microcontroller PIC16F676 datasheet, Farnell. Available at:
http://www.farnell.com/datasheets/19068.pdf [Accessed 23 August 2009]
51
16. DC motor 1024 M 003 S datasheet, Faulhaber. Available at:
http://www.faulhaber.com/uploadpk/EN_1024S_MIN.pdf [Accessed 23 August 2009]
17. Motor driver BA6289 datasheet, Digikey. Available at:
http://media.digikey.com/pdf/Data%20Sheets/Rohm%20PDFs/BA6289F,6417F.pdf
[Accessed 23 August 2009]
18. Transceiver TRM-433-LT datasheet, LINX Technologies. Available at:
http://www.linxtechnologies.com/Documents/TRM-xxx-LT_Data_Guide.pdf
[Accessed 23 August 2009]
19. Kane M., 1985. Journal of Orthopedic and Sports Physical Therapy
20. Robert Huston., 2000. International Journal of Medical Robotics
21. Glossary search, Answers.com. Available at: http://www.answers.com/
[Accessed 8 May 2010]
22. Anders J Johansson., 2004.Wireless communication with medical implants:
Antennas and propagation
23. Winfried Mayr., 2001. Basic design and construction of the Vienna FES implants
52
APPENDICES
Standard
United States FCC Title 47
CFR 95.601-95 Subpart E
European Union En 301
839 (Part 1 and 2)
European Union EN301
489-27
Description
Title 47 of the Code of Federal, Part 95 explains
operational rules and technical regulations
applicable to MICS transmitters.
Deals with RF aspects of implants in the 402
405MHz band, including unique test methods such
as the use of a human torso simulator to recreate the
effect of implantation in the body when measuring
radio emissions. Also includes an RF interference
avoidance specification for accessing the 402405MHz band to provide interference free
operation in this band.
Deals with EMC issues for 402-405MHz
equipment. Aligns with EU Active implantable
Medical Devices Directive so that manufacturers
that comply with the standard can satisfy both
directives without duplicating their testing for
EMC.
Appendix 1: Relevant US and European standard
Appendix 2: Electrical field strength dependent on fat layer thickness
(Anders J Johansson., 2004.Wireless communication with medical implants:
Antennas and propagation)
53
Appendix 3: Electrical field strength dependent on fat layer thickness
(Anders J Johansson., 2004.Wireless communication with medical implants:
Antennas and propagation)
Appendix 4: Gantt chart
54
1.
All surfaces have to be of proven biomaterials that do not cause excessive tissue
reactions even in the presence of slight inflammation of the adjacent tissue. The
surfaces must not react chemically with resulting corrosion products.
2. The mechanical design of the implant has to be kept small in size and weight. Its
surface has to be shaped as far as possible to the assigned anatomical site and it
must not present corners and edges that could cause pressure damage.
3. All electrical conductors carrying direct current (DC) have to be sealed
hermetically; consequently all electrical conductors that are exposed to moisture
have to be kept DC-free. This requirement applies especially to the electrode
outputs and the electrodes themselves, which directly interface with an
electrolytic medium and are in danger of being destroyed rapidly if there is DC.
4. Antenna coils for transmission of energy and/or for data transmission have to be
positioned inside a hermetic capsule or if that is not possible constructed in a
manner that avoids both leakage current and change of electrical capacity
between different windings of the coil. The coil is usually part of a resonant
circuit that is susceptible to detuning or loss of efficiency.
5. Special care has to be taken when connecting metal parts. They must not differ
excessively in electrochemical contact voltage. Electrochemically equivalent
materials are to be preferred, alloys should be avoided if possible and welding
techniques are preferable to soldering techniques. For soldering, acid-free flux
and careful removal of residues are required.
6. Plastic materials, including the usual medical grade silicone and epoxy polymers,
do not provide hermeticity. DC-loaded parts of the electric circuit have to be
enclosed in a metal or ceramic case.
7. Metals that can be used to enclose implant electronics are made of the reactive
metals titanium, tantalum or niobium with glass-to-metal-seals made from
sodium-free borosilicate glass. Stainless steel is not suitable, because the alloy is
decomposed during the welding process that seals the case.
8. For data transmission with a limited data rate it is possible to position the antenna
coil inside a metal case. The carrier frequency is a compromise between the
shielding factor of the case and the required data rate. To power an implant
circuit via an RF-carrier the antenna has to be placed outside, and distant to, the
metal case to achieve an acceptable efficiency. An alternative is to choose a
ceramic case, but these are difficult to seal hermetically at low temperatures.
9. The usual strategy of combining a hermetic case with some external components
embedded in a polymer requires additional care to avoid or at least to elongate
leakage paths as far as possible. They originate normally where the electrodes
penetrate the surface, and inside the implant they follow all the surfaces of
embedded components.
10. Clean all surfaces before embedding them to avoid residual ions that cause
corrosion as soon as they come into contact with moisture. The mould with the
liquid sealing compound has to be evacuated at the very beginning to remove air
bubbles, and the rest of the curing procedure has to be done under high purity
nitrogen. Rapid temperature changes have to be avoided during polymerization
to prevent homogeneities, strain and cracks within the cured material.
Appendix 5: Medical implant construction rules
(Winfried Mayr., 2001. Basic design and construction of the Vienna FES implants)
55
Equipment
Portable DC Power Supply
Oscilloscope
Multimeter
Soldering Station
Application
Provide the necessary DC power to
the microcontroller and any other
integrated circuits or other devices
that require their own power supply.
It is indispensable for this project in
designing and debugging circuits.
It is indispensable for this project in
getting necessary measurements.
Basic tool for building electronics
circuit and PCB.
Appendix 6: Laboratory equipment application
56