non-ionizing electromagnetic radiation effects on
TRANSCRIPT
NON-IONIZING ELECTROMAGNETIC RADIATION EFFECTS ON THE
ACTION POTENTIAL IN HUMAN ARM ELECTRICAL MODEL
ADIB BIN OTHMAN
A thesis submitted in
fulfillment of the requirement for the award of the
Degree of Master of Electrical Engineering
Faculty of Electrical and Electronic Engineering
Universiti Tun Hussein Onn Malaysia
SEPTEMBER 2015
v
ABSTRACT
The common use of Global System for Mobile Communications (GSM) phones has
initiated research regarding the possible biological hazardous effects of exposure to
electromagnetic (EM) radiation. Therefore, it is essential to study the extent of
interaction of GSM phone radiation towards action potentials (AP) in nerve fibres. In
order to investigate the effects of GSM phone radiation towards human arm AP,
human brain-arm nerve fibres were modeled as wire-type transmission lines; two
wires and one wire. Both models with and without interference source from the
radiation were simulated and the output waveforms have been analysed to detect any
existence of interference. The interference source value was obtained by finding
electric and magnetic fields in nerve layer of simulated human arm model that been
exposed by GSM phone radiation. Robotic arm experiment setup was developed to
measure effects of the radiation towards the electrical signal of robotic arm as
indirect comparison to AP. Simulation results show the radiation is capable of
disturbing the normal AP by introducing bursting spikes on it when distance of the
phone from the human arm model is 9 mm with phone radiation power as low as
0.02 W. Furthermore, large nerve fibre radius with huge exposure area to the EM
waves also adds on to the effect of radiation on the AP. The altered AP might disturb
the normal functions of human arm and hence lead to potential health hazard. The
robotic arm has shown displacement from 0.2 cm to 1 cm from the original location
when placing an object to its required place when there are active GSM phones near
the robotic setup. The measured electrical signal of the robotic arm shows brief
distortion in its signal with distortion magnitude up to 0.58 V. This distortion
observation is quite similar to the AP when there is induced source in the nerve fibre
models. In conclusion, there are significance effects of EM radiation towards the AP
in human nervous system.
vi
ABSTRAK
Penggunaan telefon mudah alih yang beroperasi di dalam mod GSM telah banyak
mencetuskan penyelidikan mengenai kesan biologi berbahaya yang berkemungkinan
terjadi kepada hidupan akibat pendedahan kepada radiasi elektromagnetik. Oleh itu,
adalah penting untuk mengkaji sejauh mana interaksi radiasi telefon GSM terhadap
potensi tindakan dalam gentian saraf. Untuk menyiasat kesan-kesan radiasi telefon
GSM kepada potensi tindakan di dalam lengan manusia, gentian saraf dari otak ke
lengan telah dimodelkan sebagai talian penghantaran berwayar dua dan berwayar
satu. Kedua-dua model dengan dan tanpa gangguan daripada sumber radiasi telah
disimulasikan dan gelombang keluaran telah dianalisis untuk mengesan sebarang
kewujudan gangguan. Nilai sumber gangguan telah diperolehi dengan mencari
medan elektrik dan medan magnet dalam lapisan saraf dari simulasi model lengan
manusia yang telah terdedah dengan radiasi telefon GSM. Ujikaji menggunakan
lengan robotik telah dibangunkan untuk mengukur kesan radiasi ke arah isyarat
elektrik di dalam lengan robotik sebagai perbandingan tidak langsung kepada potensi
tindakan. Keputusan simulasi menunjukkan radiasi mampu menganggu potensi
tindakan di dalam saraf dengan mewujudkan pacak gangguan di atasnya apabila
jarak telefon dari model tangan manusia ialah 9 mm dengan kuasa radiasi telefon
tersebut serendah 0.02 W. Perubahan terhadap potensi tindakan mungkin
mengganggu fungsi normal lengan manusia dan dengan itu membawa kepada potensi
kesihatan yang merbahaya. Lengan robotik telah menunjukkan anjakan di dalam
lingkungan 0.2 cm ke 1 cm daripada tempat asalnya semasa ingin meletakkan objek
apabila terdapat telefon GSM yang aktif berhampiran dengan lengan robotik. Isyarat
elektrik yang diukur dari lengan robotik menunjukkan gangguan di dalam isyarat
dengan magnitud gangguan sehingga 0.58 V. Pengamatan daripada gangguan ini
adalah sama seperti apa yang berlaku kepada potensi tindakan di dalam model
gentian saraf apabila terdapat sumber radiasi berdekatan. Secara kesimpulannya,
terdapat kesan signifikan dari radiasi elektomagnetik kepada potensi tindakan di
dalam sistem saraf manusia.
vii
CONTENTS
TITLE i
STUDENT DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
CONTENTS vii
LIST OF TABLES ix
LIST OF FIGURES x
LIST OF SYMBOLS AND ABBREVIATIONS xxii
LIST OF APPENDICES xxiii
CHAPTER 1 INTRODUCTION 1
1.1 Background studies 2
1.2 Problem statement 4
1.3 Aim of research 4
1.4 Objectives of research 4
1.5 Scopes of research 5
1.6 Thesis organization 5
CHAPTER 2 LITERATURE REVIEW 7
2.1 Relationship between EM radiation and health
hazards 8
2.2 Neurological electrophysiology effects of EM
radiation 9
2.3 Physiology of human nervous system 10
2.4 Neuron electrical circuits and action potential
mathematical models 15
2.5 Simple susceptibility model 26
2.6 OWI-535 robotic arm edge overview 28
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2.7 GSM mobile phone overview 30
2.8 Chapter 2 summary 32
CHAPTER 3 METHODOLOGY 33
3.1 Human arm modeling 34
3.2 Brain-arm nerve fibre modeling 39
3.3 EM radiation interference in brain-arm nerve
fibres modeling 45
3.4 Robotic arm experiments 47
3.5 Chapter 3 summary 54
CHAPTER 4 RESULTS AND DISCUSSION 56
4.1 Radiation fields penetration process into nerve
fibre of human brain-arm 57
4.2 Electric and magnetic fields in nerve layer of
human arm model 63
4.3 AP in nerve fibre of human brain-arm TL model 78
4.4 FFT analysis on AP results 97
4.5 Robotic arm movement results 106
4.6 Review of achievement and contribution 116
CHAPTER 5 CONCLUSIONS 118
5.1 Conclusions 118
5.2 Future recommendations 119
REFERENCES 120
APPENDIX 127
ix
LISTS OF TABLES
Table 3.1: Human arm organs and tissue properties .................................................. 35
Table 3.2: Images of phone orientation ..................................................................... 37
Table 4.1: E, H and W directions for different phone orientations ............................ 61
Table 4.2: Possible induced sources for all phone orientation ................................... 63
Table 4.3: Incident electric field, transmitted electric field and shielding
effectiveness, SE for various phone orientations ...................................... 66
Table 4.4: Electric field and magnetic field in nerve layer for 1 W and
0.02 W radiated powers for various phone orientations ............................ 68
Table 4.5: Phone locations along the human arm model with 0o phone
orientation .................................................................................................. 71
Table 4.6: Phone distances from the human arm model with 0o phone
orientation .................................................................................................. 73
Table 4.7: SAR results from simulation..................................................................... 75
Table 4.8: Summary of defined and calculated parameters ....................................... 96
Table 4.9: Radiation magnitude on AP for both one wire and two wire
TL models ................................................................................................ 105
Table 4.10: Received voltage from Nokia phone at different orientations .............. 107
Table 4.11: Received voltage from Samsung phone at different
orientations ............................................................................................ 107
Table 4.12: Received voltage from U-com phone at different orientations ............. 108
Table 4.13: Received voltage from Sony Ericsson phone at different
orientations ............................................................................................ 108
x
LISTS OF FIGURES
Figure 1.1: Source of EM radiation [5] 2
Figure 1.2: Human nervous system [10] 3
Figure 2.1: Action potential and its phases [35] 12
Figure 2.2: Motor control organization for muscle movement [36] 13
Figure 2.3: Descending tracts for muscle motor neurons [36] 14
Figure 2.4: Hodgkin and Huxley nerve fibre electrical model [11] 15
Figure 2.5: Voltage-gated K+ channel in closed (on left) and opened
(on right) states [36] 17
Figure 2.6: Voltage-gated Na+ channel in closed (on left), opened
(at middle) and inactive (on left) states [36] 18
Figure 2.7: Morris-Lecar electrical circuit model [12] 19
Figure 2.8: Isolated bursting AP produced by Hindmarsh and Rose
model [13] 22
Figure 2.9: Comparison of AP in rat's motor cortex and Izhikevich's
model [15] 26
Figure 2.10: Incident EM wave converted to interference sources in
simple susceptibility model [54] 27
Figure 2.11: Voltage source due to electric field convert into current
source [54] 28
Figure 2.12: OWI-535 robotic arm edge joints [55] 29
Figure 2.13: Dimensions of OWI-535 robotic arm edge [55] 29
Figure 2.14: Radiation from GSM phone towards human body part 30
Figure 2.15: GMSK modulated signal [61] 31
Figure 3.1: Simplest form of human arm in axial view 34
Figure 3.2: Human arm model with a GSM phone in vertical orientation 35
Figure 3.3: Human arm model replace with air 36
Figure 3.4: Nerve fibre of two wires and one wire lossless TL models in
PSPICE 41
Figure 3.5: Typical two wires lossless TL model 41
Figure 3.6: Typical one wire lossless TL model 42
Figure 3.7: Anatomy of human brain-arm nerve fibre [9, 36] 44
Figure 3.8: Actual nerve fibres tracts of two wires and one wire TL
models 45
Figure 3.9: Actual nerve fibres tracts with induced radiation current
sources 45
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Figure 3.10: Actual nerve fibres tracts with induced radiation voltage
sources 46
Figure 3.11: Creation of DC signal by using LabVIEW software 48
Figure 3.12: DC source produced by LabVIEW 48
Figure 3.13: NI 9263 module in NI cDAQ-9178 49
Figure 3.14: Robotic arm experiment setup with GSM phones at 0o
phone orientation 50
Figure 3.15: Radiated wave in parallel with the monopole antenna 51
Figure 3.16: Radiated wave not in parallel with the monopole antenna 51
Figure 3.17: Setup for determining the propagated wave position from
mobile phone 52
Figure 3.18: Mobile phones model 53
Figure 3.19: Methodology flowchart 54
Figure 4.1: Radiated electric and magnetic field from a monopole
antenna [78] 57
Figure 4.2: Surface current for 0o to 180
o phase 57
Figure 4.3: Surface current for 180o to 360
o phase 58
Figure 4.4: Magnetic field for 0o to 180
o phase 58
Figure 4.5: Magnetic field for 180o to 360
o phase 58
Figure 4.6: Electric field for 0o to 180
o phase 59
Figure 4.7: Electric field for 180o to 360
o phase 59
Figure 4.8: Nerve axial view [79] 62
Figure 4.9: Incident electric field with GSM phone at 0o phone
orientation 63
Figure 4.10: Transmitted electric field with GSM phone at 0o phone
orientation 64
Figure 4.11: Incident electric field with GSM phone at 45o phone
orientation 65
Figure 4.12: Transmitted electric field with GSM phone at 45o phone
orientation 65
Figure 4.13: Electric field in nerve layer with GSM phone at 0o phone
orientation 66
Figure 4.14: Magnetic field in nerve layer with GSM phone at 0o
phone orientation 67
Figure 4.15: Shielding effectiveness comparison for various phone
orientations 69
Figure 4.16: Electric fields comparison for various phone orientations 70
Figure 4.17: Magnetic fields comparison for various phone orientations 70
Figure 4.18: Electric fields comparison for different phone location
along the human arm at 0o phone orientation 72
Figure 4.19: Electric fields comparison for different phone location
along the human arm at 90o phone orientation 72
Figure 4.20: Electric fields comparison for different phone distance
from the human arm at 0o phone orientation 74
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Figure 4.21: Electric fields comparison for different phone distance
from the human arm at 135o phone orientation 74
Figure 4.22: Electric fields comparison for different phone radiation
power at 0o phone orientation 77
Figure 4.23: Electric fields comparison for different phone radiation
power at 270o phone orientation 77
Figure 4.24: Interference of an induced current source on one wire
TL model 78
Figure 4.25: Interference of an induced current source on two wires
TL model 79
Figure 4.26: Interference of an induced voltage source on one wire
TL model 79
Figure 4.27: Interference of an induced voltage source on two wires
TL model 80
Figure 4.28: Interference of an induced current source on one wire
TL model with varied phone orientations 81
Figure 4.29: Interference of an induced current source on two wires
TL model with varied phone orientations 81
Figure 4.30: Interference of an induced voltage source on one wire
TL model with varied phone orientations 82
Figure 4.31: Interference of an induced voltage source on two wires
TL model with varied phone orientations 82
Figure 4.32: Interference of an induced current source on one wire
TL model with varied phone distance 84
Figure 4.33: Interference of an induced current source on two wires
TL model with varied phone distance 84
Figure 4.34: Interference of an induced voltage source on one wire
TL model with varied phone distance 85
Figure 4.35: Interference of an induced voltage source on two wires
TL model with varied phone distance 85
Figure 4.36: Interference of an induced current source on one wire
TL model with varied phone radiation power 86
Figure 4.37: Interference of an induced current source on two wires
TL model with varied phone radiation power 87
Figure 4.38: Interference of an induced voltage source on one wire
TL model with varied phone radiation power 87
Figure 4.39: Interference of an induced voltage source on two wires
TL model with varied phone radiation power 88
Figure 4.40: Interference of an induced current source on one wire
TL model with varied nerve fibre radius 89
Figure 4.41: Interference of an induced current source on two wires
TL model with varied nerve fibre radius 89
Figure 4.42: Interference of an induced voltage source on one wire
TL model with varied nerve fibre radius 90
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Figure 4.43: Interference of an induced voltage source on two wires
TL model with varied nerve fibre radius 90
Figure 4.44: Interference of an induced current source on one wire
TL model with varied h 91
Figure 4.45: Interference of an induced voltage source on one wire
TL model with varied h 91
Figure 4.46: Interference of an induced current source on two wires
TL model with varied s 92
Figure 4.47: Interference of an induced voltage source on two wires
TL model with varied s 92
Figure 4.48: Original AP produced by one unit of Hodgkin and Huxley
model 94
Figure 4.49: AP produced by one unit of Hodgkin and Huxley model
that interfered by induced voltage source 94
Figure 4.50: AP produced by one unit of Hodgkin and Huxley model
that interfered by induced current source 95
Figure 4.51: FFT of AP in one wire TL model affected by induced
current source with phone orientation at 0o 98
Figure 4.52: FFT of AP in one wire TL model affected by induced
current source with phone orientation at 45o 98
Figure 4.53: FFT of AP in one wire TL model affected by induced
current source with phone orientation at 135o 99
Figure 4.54: FFT of AP in one wire TL model affected by induced
voltage source with phone orientation at 90o 100
Figure 4.55: FFT of AP in one wire TL model affected by induced
voltage source with phone orientation at 45o 100
Figure 4.56: FFT of AP in one wire TL model affected by induced
voltage source with phone orientation at 135o 101
Figure 4.57: FFT of AP in one wire TL model affected by induced
current source with phone distance at 9 mm 102
Figure 4.58: FFT of AP in one wire TL model affected by induced
current source with phone distance at 56 mm 102
Figure 4.59: FFT of AP in one wire TL model affected by induced
current source with phone distance at 1000 mm 103
Figure 4.60: FFT of AP in one wire TL model affected by induced
voltage source with phone distance at 9 mm 103
Figure 4.61: FFT of AP in one wire TL model affected by induced
voltage source with phone distance at 56 mm 104
Figure 4.62: FFT of AP in one wire TL model affected by induced
voltage source with phone distance at 1000 mm 104
Figure 4.63: First reading of received voltage from Nokia phone at
0o orientation 106
Figure 4.64: Second reading of received voltage from Nokia phone at
0o orientation 106
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Figure 4.65: Third reading of received voltage from Nokia phone at
0o orientation 107
Figure 4.66: Location of antenna at each mobile phone 109
Figure 4.67(a): Match box placement without radiation source 110
Figure 4.67(b): Match box placement with phones at 0o orientation 110
Figure 4.67(c): Match box placement with phones at 45o orientation 110
Figure 4.67(d): Match box placement with phones at 90o orientation 110
Figure 4.67(e): Match box placement with phones at 135o orientation 110
Figure 4.67(f): Match box placement with phones at 180o orientation 110
Figure 4.67(g): Match box placement with phones at 225o orientation 111
Figure 4.67(h): Match box placement with phones at 270o orientation 111
Figure 4.67(i): Match box placement with phones at 315o orientation 111
Figure 4.68: Robotic arm signal in unmovable state with appearance
of phone at 0o 112
Figure 4.69: Robotic arm signal in unmovable state with appearance
of phone at 45o 113
Figure 4.70: Robotic arm signal in unmovable state with appearance
of phone at 180o 113
Figure 4.71: Robotic arm signal in unmovable state with appearance
of phone at 225o 114
Figure 4.72: Robotic arm signal in movable state with appearance
of phone at 0o 114
Figure 4.73: Robotic arm signal in movable state with appearance
of phone at 225o 115
Figure B - A: Incident electric field with GSM phone at various phone
orientations ....................................................................................... 130
Figure B - B: Transmitted electric field with GSM phone at various
phone orientations ............................................................................ 130
Figure C - A: Electric field comparison for different phone location
along the human arm at 45 degree phone orientation ...................... 131
Figure C - B: Electric field comparison for different phone location
along the human arm at 135 degree phone orientation .................... 131
Figure C - C: Electric field comparison for different phone location
along the human arm at 180 degree phone orientation .................... 131
Figure C - D: Electric field comparison for different phone location
along the human arm at 225 degree phone orientation .................... 132
Figure C - E: Electric field comparison for different phone location
along the human arm at 270 degree phone orientation .................... 132
Figure C - F: Electric field comparison for different phone location
along the human arm at 315 degree phone orientation .................... 132
Figure D - A: Electric field comparison for different phone distance
from the human arm at 45 degree phone orientation ........................ 133
Figure D - B: Electric field comparison for different phone distance
from the human arm at 90 degree phone orientation ........................ 133
xv
Figure D - C: Electric field comparison for different phone distance
from the human arm at 180 degree phone orientation ...................... 133
Figure D - D: Electric field comparison for different phone distance
from the human arm at 225 degree phone orientation ...................... 134
Figure D - E: Electric field comparison for different phone distance
from the human arm at 270 degree phone orientation ...................... 134
Figure D - F: Electric field comparison for different phone distance
from the human arm at 315 degree phone orientation ...................... 134
Figure E - A: Electric field comparison for different phone radiation
power at 45 degree phone orientation ................................................. 135
Figure E - B: Electric field comparison for different phone radiation
power at 90 degree phone orientation ................................................. 135
Figure E - C: Electric field comparison for different phone radiation
power at 135 degree phone orientation ............................................... 135
Figure E - D: Electric field comparison for different phone radiation
power at 180 degree phone orientation ............................................... 136
Figure E - E: Electric field comparison for different phone radiation
power at 225 degree phone orientation ............................................... 136
Figure E - F: Electric field comparison for different phone radiation
power at 315 degree phone orientation ............................................... 136
Figure G - A: FFT of AP in one wire TL model affected by induced
current source with phone radiation power at 0.02 W ..................... 178
Figure G - B: FFT of AP in one wire TL model affected by induced
current source with phone radiation power at 0.2 W ....................... 178
Figure G - C: FFT of AP in one wire TL model affected by induced
current source with phone radiation power at 1 W .......................... 179
Figure G - D: FFT of AP in one wire TL model affected by induced
voltage source with phone radiation power at 0.02 W ..................... 179
Figure G - E: FFT of AP in one wire TL model affected by induced
voltage source with phone radiation power at 0.2 W ....................... 180
Figure G - F: FFT of AP in one wire TL model affected by induced
voltage source with phone radiation power at 1 W .......................... 180
Figure G - G: FFT of AP in one wire TL model affected by induced
current source with 10 μm nerve fibre radius ................................... 181
Figure G - H: FFT of AP in one wire TL model affected by induced
current source with 5 μm nerve fibre radius ..................................... 181
Figure G - I: FFT of AP in one wire TL model affected by induced
current source with 2.5 μm nerve fibre radius .................................. 182
Figure G - J: FFT of AP in one wire TL model affected by induced
voltage source with 10 μm nerve fibre radius .................................. 182
Figure G - K: FFT of AP in one wire TL model affected by induced
voltage source with 5 μm nerve fibre radius .................................... 183
Figure G - L: FFT of AP in one wire TL model affected by induced
voltage source with 2.5 μm nerve fibre radius ................................. 183
xvi
Figure G - M: FFT of AP in one wire TL model affected by induced
current source with 10.01 μm h factor.............................................. 184
Figure G - N: FFT of AP in one wire TL model affected by induced
current source with 10.007 μm h factor............................................ 184
Figure G - O: FFT of AP in one wire TL model affected by induced
current source with 10.004 μm h factor............................................ 185
Figure G - P: FFT of AP in one wire TL model affected by induced
voltage source with 10.01 μm h factor ............................................. 185
Figure G - Q: FFT of AP in one wire TL model affected by induced
voltage source with 10.007 μm h factor ........................................... 186
Figure G - R: FFT of AP in one wire TL model affected by induced
voltage source with 10.004 μm h factor ........................................... 186
Figure G - S: FFT of AP in two wires TL model affected by induced
current source with phone orientation at 0o ...................................... 187
Figure G - T: FFT of AP in two wires TL model affected by induced
current source with phone orientation at 45o .................................... 187
Figure G - U: FFT of AP in two wires TL model affected by induced
current source with phone orientation at 135o .................................. 188
Figure G - V: FFT of AP in two wires TL model affected by induced
voltage source with phone orientation at 90o ................................... 188
Figure G - W: FFT of AP in two wires TL model affected by induced
voltage source with phone orientation at 45o ................................... 189
Figure G - X: FFT of AP in two wires TL model affected by induced
voltage source with phone orientation at 135o ................................. 189
Figure G - Y: FFT of AP in two wires TL model affected by induced
current source with phone distance at 9 mm .................................... 190
Figure G - Z: FFT of AP in two wires TL model affected by induced
current source with phone distance at 56 mm .................................. 190
Figure G - AA: FFT of AP in two wires TL model affected by induced
current source with phone distance at 1000 mm .............................. 191
Figure G - BB: FFT of AP in two wires TL model affected by induced
voltage source with phone distance at 9 mm .................................... 191
Figure G - CC: FFT of AP in two wires TL model affected by induced
voltage source with phone distance at 56 mm .................................. 192
Figure G - DD: FFT of AP in two wires TL model affected by induced
voltage source with phone distance at 1000 mm .............................. 192
Figure G - EE: FFT of AP in two wires TL model affected by induced
current source with phone radiation power at 0.02 W ..................... 193
Figure G - FF: FFT of AP in two wires TL model affected by induced
current source with phone radiation power at 0.2 W ....................... 193
Figure G - GG: FFT of AP in two wires TL model affected by induced
current source with phone radiation power at 1 W .......................... 194
Figure G - HH: FFT of AP in two wires TL model affected by induced
voltage source with phone radiation power at 0.02 W ..................... 194
xvii
Figure G - II: FFT of AP in two wires TL model affected by induced
voltage source with phone radiation power at 0.2 W ....................... 195
Figure G - JJ: FFT of AP in two wires TL model affected by induced
voltage source with phone radiation power at 1 W .......................... 195
Figure G - KK: FFT of AP in two wires TL model affected by induced
current source with 10 μm nerve fibre radius ................................... 196
Figure G - LL: FFT of AP in two wires TL model affected by induced
current source with 5 μm nerve fibre radius ..................................... 196
Figure G - MM: FFT of AP in two wires TL model affected by induced
current source with 2.5 μm nerve fibre radius .................................. 197
Figure G - NN: FFT of AP in two wires TL model affected by induced
voltage source with 10 μm nerve fibre radius .................................. 197
Figure G - OO: FFT of AP in two wires TL model affected by induced
voltage source with 5 μm nerve fibre radius .................................... 198
Figure G - PP: FFT of AP in two wires TL model affected by induced
voltage source with 2.5 μm nerve fibre radius ................................. 198
Figure G - QQ: FFT of AP in two wires TL model affected by induced
current source with 50 μm s factor ................................................... 199
Figure G - RR: FFT of AP in two wires TL model affected by induced
current source with 40 μm s factor ................................................... 199
Figure G - SS: FFT of AP in two wires TL model affected by induced
current source with 30 μm s factor ................................................... 200
Figure G - TT: FFT of AP in two wires TL model affected by induced
voltage source with 50 μm s factor................................................... 200
Figure G - UU: FFT of AP in two wires TL model affected by induced
voltage source with 40 μm s factor................................................... 201
Figure G - VV: FFT of AP in two wires TL model affected by induced
voltage source with 30 μm s factor................................................... 201
Figure H - A: First reading of received voltage from Nokia phone at
45 degree orientation ........................................................................ 202
Figure H - B: Second reading of received voltage from Nokia phone at
45 degree orientation ........................................................................ 202
Figure H - C: Third reading of received voltage from Nokia phone at
45 degree orientation ........................................................................ 202
Figure H - D: First reading of received voltage from Nokia phone at
90 degree orientation ........................................................................ 203
Figure H - E: Second reading of received voltage from Nokia phone at
90 degree orientation ........................................................................ 203
Figure H - F: Third reading of received voltage from Nokia phone at
90 degree orientation ........................................................................ 203
Figure H - G: First reading of received voltage from Nokia phone at
135 degree orientation ...................................................................... 204
Figure H - H: Second reading of received voltage from Nokia phone at
135 degree orientation ...................................................................... 204
xviii
Figure H - I: Third reading of received voltage from Nokia phone
at 135 degree orientation .................................................................. 204
Figure H - J: First reading of received voltage from Nokia phone
at 180 degree orientation .................................................................. 205
Figure H - K: Second reading of received voltage from Nokia phone
at 180 degree orientation .................................................................. 205
Figure H - L: Third reading of received voltage from Nokia phone
at 180 degree orientation .................................................................. 205
Figure H - M: First reading of received voltage from Nokia phone
at 225 degree orientation .................................................................. 206
Figure H - N: Second reading of received voltage from Nokia phone
at 225 degree orientation .................................................................. 206
Figure H - O: Third reading of received voltage from Nokia phone
at 225 degree orientation .................................................................. 206
Figure H - P: First reading of received voltage from Nokia phone
at 270 degree orientation .................................................................. 207
Figure H - Q: Second reading of received voltage from Nokia phone
at 270 degree orientation .................................................................. 207
Figure H - R: Third reading of received voltage from Nokia phone
at 270 degree orientation .................................................................. 207
Figure H - S: First reading of received voltage from Nokia phone
at 315 degree orientation .................................................................. 208
Figure H - T: Second reading of received voltage from Nokia phone
at 315 degree orientation .................................................................. 208
Figure H - U: Third reading of received voltage from Nokia phone
at 315 degree orientation .................................................................. 208
Figure H - V: First reading of received voltage from Samsung phone
at 0 degree orientation ...................................................................... 209
Figure H - W: Second reading of received voltage from Samsung phone
at 0 degree orientation ...................................................................... 209
Figure H - X: Third reading of received voltage from Samsung phone
at 0 degree orientation ...................................................................... 209
Figure H - Y: First reading of received voltage from Samsung phone
at 45 degree orientation .................................................................... 210
Figure H - Z: Second reading of received voltage from Samsung phone
at 45 degree orientation .................................................................... 210
Figure H - AA: Third reading of received voltage from Samsung phone
at 45 degree orientation .................................................................. 210
Figure H - BB: First reading of received voltage from Samsung phone
at 90 degree orientation .................................................................. 211
Figure H - CC: Second reading of received voltage from Samsung phone
at 90 degree orientation .................................................................. 211
Figure H - DD: Third reading of received voltage from Samsung phone
at 90 degree orientation .................................................................. 211
xix
Figure H - EE: First reading of received voltage from Samsung phone
at 135 degree orientation ................................................................ 212
Figure H - FF: Second reading of received voltage from Samsung phone
at 135 degree orientation ................................................................ 212
Figure H - GG: Third reading of received voltage from Samsung phone
at 135 degree orientation ................................................................ 212
Figure H - HH: First reading of received voltage from Samsung phone
at 180 degree orientation ................................................................ 213
Figure H - II: Second reading of received voltage from Samsung phone
at 180 degree orientation ................................................................ 213
Figure H - JJ: Third reading of received voltage from Samsung phone
at 180 degree orientation ................................................................ 213
Figure H - KK: First reading of received voltage from Samsung phone
at 225 degree orientation ................................................................ 214
Figure H - LL: Second reading of received voltage from Samsung phone
at 225 degree orientation ................................................................ 214
Figure H - MM: Third reading of received voltage from Samsung phone
at 225 degree orientation ................................................................ 214
Figure H - NN: First reading of received voltage from Samsung phone
at 270 degree orientation ................................................................ 215
Figure H - OO: Second reading of received voltage from Samsung phone
at 270 degree orientation ................................................................ 215
Figure H - PP: Third reading of received voltage from Samsung phone
at 270 degree orientation ................................................................ 215
Figure H - QQ: First reading of received voltage from Samsung phone
at 315 degree orientation ................................................................ 216
Figure H - RR: Second reading of received voltage from Samsung phone
at 315 degree orientation ................................................................ 216
Figure H - SS: Third reading of received voltage from Samsung phone
at 315 degree orientation ................................................................ 216
Figure H - TT: First reading of received voltage from U-com phone
at 0 degree orientation .................................................................... 217
Figure H - UU: Second reading of received voltage from U-com phone
at 0 degree orientation .................................................................... 217
Figure H - VV: Third reading of received voltage from U-com phone
at 0 degree orientation .................................................................... 217
Figure H - WW: First reading of received voltage from U-com phone
at 45 degree orientation .................................................................. 218
Figure H - XX: Second reading of received voltage from U-com phone
at 45 degree orientation .................................................................. 218
Figure H - YY: Third reading of received voltage from U-com phone
at 45 degree orientation .................................................................. 218
Figure H - ZZ: First reading of received voltage from U-com phone
at 90 degree orientation .................................................................. 219
xx
Figure H - AAA: Second reading of received voltage from U-com phone
at 90 degree orientation ............................................................... 219
Figure H - BBB: Third reading of received voltage from U-com phone
at 90 degree orientation ............................................................... 219
Figure H - CCC: First reading of received voltage from U-com phone
at 135 degree orientation ............................................................. 220
Figure H - DDD: Second reading of received voltage from U-com phone
at 135 degree orientation ............................................................. 220
Figure H - EEE: Third reading of received voltage from U-com phone
at 135 degree orientation ............................................................. 220
Figure H - FFF: First reading of received voltage from U-com phone
at 180 degree orientation ............................................................. 221
Figure H - GGG: Second reading of received voltage from U-com phone
at 180 degree orientation ............................................................. 221
Figure H - HHH: Third reading of received voltage from U-com phone
at 180 degree orientation ............................................................. 221
Figure H - III: First reading of received voltage from U-com phone
at 225 degree orientation ............................................................. 222
Figure H - JJJ: Second reading of received voltage from U-com phone
at 225 degree orientation ............................................................. 222
Figure H - KKK: Third reading of received voltage from U-com phone
at 225 degree orientation ............................................................. 222
Figure H - LLL: First reading of received voltage from U-com phone
at 270 degree orientation ............................................................. 223
Figure H - MMM: Second reading of received voltage from U-com phone
at 270 degree orientation ............................................................. 223
Figure H - NNN: Third reading of received voltage from U-com phone
at 270 degree orientation ............................................................. 223
Figure H - OOO: First reading of received voltage from U-com phone
at 315 degree orientation ............................................................. 224
Figure H - PPP: Second reading of received voltage from U-com phone
at 315 degree orientation ............................................................. 224
Figure H - QQQ: Third reading of received voltage from U-com phone
at 315 degree orientation ............................................................. 224
Figure H - RRR: First reading of received voltage from Sony Ericsson
phone at 0 degree orientation ....................................................... 225
Figure H - SSS: Second reading of received voltage from Sony Ericsson
phone at 0 degree orientation ....................................................... 225
Figure H - TTT: Third reading of received voltage from Sony Ericsson
phone at 0 degree orientation ....................................................... 225
Figure H - UUU: First reading of received voltage from Sony Ericsson
phone at 45 degree orientation ..................................................... 226
Figure H - VVV: Second reading of received voltage from Sony Ericsson
phone at 45 degree orientation ..................................................... 226
xxi
Figure H - WWW: Third reading of received voltage from Sony Ericsson
phone at 45 degree orientation ..................................................... 226
Figure H - XXX: First reading of received voltage from Sony Ericsson
phone at 90 degree orientation ..................................................... 227
Figure H - YYY: Second reading of received voltage from Sony Ericsson
phone at 90 degree orientation ..................................................... 227
Figure H - ZZZ: Third reading of received voltage from Sony Ericsson
phone at 90 degree orientation ..................................................... 227
Figure H - AAAA: First reading of received voltage from Sony Ericsson
phone at 135 degree orientation .............................................. 228
Figure H - BBBB: Second reading of received voltage from Sony Ericsson
phone at 135 degree orientation .............................................. 228
Figure H - CCCC: Third reading of received voltage from Sony Ericsson
phone at 135 degree orientation .............................................. 228
Figure H - DDDD: First reading of received voltage from Sony Ericsson
phone at 180 degree orientation .............................................. 229
Figure H - EEEE: Second reading of received voltage from Sony Ericsson
phone at 180 degree orientation .............................................. 229
Figure H - FFFF: Third reading of received voltage from Sony Ericsson
phone at 180 degree orientation .............................................. 229
Figure H - GGGG: First reading of received voltage from Sony Ericsson
phone at 225 degree orientation .............................................. 230
Figure H - HHHH: Second reading of received voltage from Sony Ericsson
phone at 225 degree orientation .............................................. 230
Figure H - IIII: Third reading of received voltage from Sony Ericsson
phone at 225 degree orientation .............................................. 230
Figure H - JJJJ: First reading of received voltage from Sony Ericsson
phone at 270 degree orientation .............................................. 231
Figure H - KKKK: Second reading of received voltage from Sony Ericsson
phone at 270 degree orientation .............................................. 231
Figure H - LLLL: Third reading of received voltage from Sony Ericsson
phone at 270 degree orientation .............................................. 231
Figure H - MMMM: First reading of received voltage from Sony Ericsson
phone at 315 degree orientation .............................................. 232
Figure H - NNNN: Second reading of received voltage from Sony Ericsson
phone at 315 degree orientation .............................................. 232
Figure H - OOOO: Third reading of received voltage from Sony Ericsson
phone at 315 degree orientation .............................................. 232
xxii
LISTS OF SYMBOLS AND ABBREVATIONS
GSM - Global System for Mobile Communication
AP - Action Potential
TL - Transmission Line
EM - Electromagnetic
WHO - World Health Organization
EMF - Electromagnetic Field
ICNIRP - International Committee on Non-Ionizing Radiation Protection
IEEE - Institute of Electrical and Electronic Engineering
IEGMP - Independent Expert Group on Mobile Phones
AHP - Afterhyperpolarization
Na - Sodium
K - Potassium
ICF - Intracellular Fluid
ECF - Extracellular Fluid
Ca - Calcium
DC - Direct Current
emf - Electromagnetic Force
PCB - Printed Circuit Board
TDMA - Time Division Multiple Access
FDMA - Frequency Division Multiple Access
GMSK - Gaussian Minimum Shift Keying
CST - Computer Simulation Technology
PIFA - Planar Inverted F Antenna
CNS - Central Nervous System
PNS - Peripheral Nervous System
SE - Shielding Effectiveness
SAR - Specific Absorption Rate
FFT - Fast Fourier Transform
xxiii
LISTS OF APPENDICES
APPENDIX TITLE PAGE
A
MATLAB programming for shielding effectiveness…………..…..127
B Incident and transmitted electric fields for various phone
orientations……...…………...………………………………….....130
C Electric field results base on relationship between phone
orientations and phone location along the human arm 131
D Electric field results base on relationship between phone
orientations and phone distance from the human arm 133
E Electric field results base on relationship between phone
orientations and phone radiation power 135
F
Summary of defined and calculated parameters for
actual nerve fibre tracts circuits considering all parameter
variations…….………….. 137
G FFT results for one wire and two wires transmission line
models considering all parameter variations………..…………… 178
H Received voltage from different phones at various phone
orientations………………………………………………...…… 202
1
CHAPTER 1
INTRODUCTION
The effects of non-ionizing electromagnetic (EM) pollution on humans have been
studied for more than 50 years. The World Health Organization (WHO), through its
International Electromagnetic Field (EMF) Project, has conducted a series of in-
depth international reviews of the scientific literature on the biological and health
effects of exposure to electromagnetic fields. WHO website (www.who.int) contains
more than 3400 entries of which more than 1800 are relevant to health effects of EM
exposure. The studies conclude their findings based on evidence collated from
epidemiological, animal or in vitro studies.
In depth studies showed that, human nervous system is the electrical system
of human body. Neurons are the fundamental unit of the nervous system that carries
electrical pulses known as action potentials (AP). This AP assists the communication
and coordination functions of the nervous system with other systems in human body.
Lots of research in neurons and AP has produced biophysical electrical equivalent
circuits as well as mathematical models representing the behaviour of AP
inside neurons.
2
1.1 Background studies
Non-ionizing radiation is electromagnetic radiation that does not alter atomic
structure [1]. It is well accepted that human exposure to non-ionizing EM radiation
can have multiple effects on the body. Many studies [2, 3, 4] over the years have
positively reported thermal or heating effect and non-thermal effects that cause from
non-ionizing EM radiation. Whilst thermal effect can have adverse health effects due
to heating of the tissue, the consequences of non-thermal effects such as cell
interaction, neuro-stimulation and behavioural changes are still subjected to
differences of opinion amongst researchers, governments and industries.
How the EM energy interacts with the body depends on a number of factors
some of which include frequency, signal strength, exposure time, modulation, and a
person’s natural immune system. The relationship between these and other factors
makes it extremely difficult to determine exact cause effect relationships. This
complexity just adds to the controversy over the carcinogenic effects of EM radiation
from high tension power, computer monitors, mobile phones, base stations and other
equipment as shown in Figure 1.1 which are in common use today.
Figure 1.1: Source of EM radiation [5]
The International Committee on Non-Ionizing Radiation Protection
(ICNIRP), which was established in 1992, published guidelines [6] limiting exposure
to time-varying electric, magnetic and electromagnetic fields to an acceptable level
3
to avoid adverse health effect. Other standards are based on work by IEEE and other
national and international commissions [7, 8]. The guidelines maybe insignificant for
certain attributes of humans because some people do not experience the symptoms
associated with non-ionizing EM radiation as much as others. However, long-term
exposure that does not lead to immediate symptoms can still result in cumulative
physiological effects that may ultimately cause serious disease. Every person is
affected by EM, but some people are more sensitive, less resilient and therefore more
susceptible to health problems.
Our body is a combination of many systems that work simultaneously and
always working relatedly to each other. The human body consists of systems such as
muscular system, cardiovascular system, endocrine system, immune system, nervous
system and few others of them to be name. The nervous system acts as a command
system that coordinate systems in human body, so they can work in an appropriate
manner [9]. A very special part in the nervous system that is so powerful that it
controls other systems in human body is the brain. In support with the spine and also
a very large mesh network so called nerve fibre make the system to become very
sophisticated system in the field of anatomy and physiology.
In electrical engineering point of view, the nerve fibre network is suitable to
be converted into electrical circuits in order to make observation and analyses easier
and results obtain can be relate logically to the real situation. As referring to Figure
1.2, the brain is likely to function as a source which produces the AP, nerve fibre as a
transmission line (TL) circuit that transmit the AP to trigger a movement on finger
muscle which act as a load.
Figure 1.2: Human nervous system [10]
brain
nerve
fibre
finger
muscle
4
The statement in previous sentence is supported by studies from many
researches. Hodgkin and Huxley [11] and Morris and Lecar [12] are researchers
whose responsible in converting nerve fibre to a TL circuit. Hindmarsh and Rose
[13], Wilson [14] and Izhikevich [15] have produced mathematical models that
functioning as similar to brain neural network which produced continuous AP
throughout the nervous system. Details about work been done by these
researchers will be explained briefly in literature review.
1.2 Problem statement
Unawareness of long term pollution from non-ionizing EM radiation to the human
body is a critical issue nowadays. Either thermal effect or non-thermal effect can
bring threats to humans and even any living organism. The EM radiation can easily
penetrate into a human body and thus disturb the harmonious function of systems
inside. The EM radiation propagating the human body will induce currents and
voltages which can interact with APs throughout the body. The interaction of the
interfering currents and voltages with APs over long period of exposure can create
havoc or confusion to the delicate electrical system of the body which is the nervous
system. This might be the starting of potential health hazards. It is extremely
important for research work to be undertaken to quantify the extent of the interaction
and how it could jeopardize the harmonious flow of the signals throughout the
human body.
1.3 Aim of research
The aim of the research is to investigate using circuit simulation and hardware
implementation that action potential in human arm can be disturbed by non-ionizing
electromagnetic radiation.
5
1.4 Objectives of research
The objectives of the research are as follows:-
(i) To model the electrical system of human arm as equivalent to combinations
of voltage sources, capacitors, inductors and resistors by using TL model
method
(ii) To analyse the effect of non-ionizing EM radiation on the AP in human arm
electrical model due to radiation distance, power, orientation and also due to
nerve fibre radius and its exposure area to the EM radiation
(iii) To verify the effect of non-ionizing EM radiation on the AP in human arm
electrical model by performing measurement to robotic arm signal with
appearance of GSM phones nearby
1.5 Scopes of research
Human arm nervous system which converted to electrical model in this research is a
human somatic nervous or peripheral nervous system. Connection of nerve fibres
from brain to arm is considered as equivalent circuit of lossless TL with the source of
the circuit is an action potential inside the nervous system of human body. The
source is modelled as the action potential by using Izhikevich simple spiking model
[15]. The electromagnetic radiation is produce by mobile phone with operating
frequency of 900 MHz. Purpose of using robotic arm to compare with human arm is
not by comparing in physical means, but to compare what will happen to the signal
inside the wires of robotic arm when there is radiation source placed near to the
robotic arm. It is just the same like situation in simulation circuit where the result is
observed on signal behaviour when radiation source appear.
1.6 Thesis organization
This study is presented in five chapters. The thesis begins with an introduction to
sources of EM radiation and how it could affect various human body systems. This
concern leads to study on electromagnetic radiation effects towards the AP in the
human nervous system. Chapter 2 is basically literature review about past study on
health hazards towards EM radiation, physiology of human nervous system and its
6
similarity with electrical circuit. Methodology on how this study is under taken is
discussed deeply in Chapter 3. This chapter include the modelling of nerve fibres
circuit and the setup of robotic arm experiment. Chapter 4 is focused on discussion of
results obtained from simulation process of nerve fibres circuit in term of its AP and
experimental results from the robotic arm movement and its signal correspond to
mobile phone radiation. Conclusions and future recommendations for this study were
briefly stated in Chapter 5.
7
CHAPTER 2
LITERATURE REVIEW
In this modernization era, people are exposed to EM radiation in their daily life due
to ever increasing usage of wireless communication device such as mobile phones
and base stations which are widely placed in human environment. As a consequence,
human body is continuously exposed to the EM radiation from those devices. Many
literatures came with conclusion that devices that emit microwaves are possible to
create health hazard towards animals and humans.
Deep understanding in physiology of human nervous system is very
important in producing an equivalent circuit of a neuron network. Literature on
previous neuron equivalent circuits has helped in producing new neuron network
equivalent circuit. Furthermore, many researchers that specialize in the field of brain
neural networks have produced different mathematical models that can be simulated
in mathematical software to produce AP that exist in neurons. All of other researches
worked will be discussed in this chapter soon.
Simple susceptibility model in electromagnetic compatibility field is a useful
model to quantify the interaction of EM radiation towards electrical system of human
body. Information from this model is crucial to be stated in the thesis to give better
understanding for readers about works done in this thesis. In addition, some
information about robotic arms and mobile phones that are used as experimental
hardware are listed as they are crucial in proving interaction of EM radiation towards
human body electrical system.
8
2.1 Relationship between EM radiation and health hazards
Mobile phones are one of the most commonly used and carried along by users.
Hence, mobile phones can become extremely effective source of EM radiation since
its usually on.
Bawin, Kaczmarek and Adey [16] and Foster [17] reported that since GSM
phone operates in a pulse mode and its signal is categorised as modulated EM
radiation, the signal may cause neurological effects even at low average power.
The Independent Expert Group on Mobile Phones (IEGMP) in the United
Kingdom has reported that children are more sensitive to EM radiation from mobile
phones compared to adults because of their smaller head and brain size, thinner
cranial bones and skin, thinner, more elastic ears, lower blood cell volume, as well as
greater conductivity of nerve cells [18].
Johansson [19] did an extensive literature review on the non-thermal effects
of EM radiation and concluded that there are a number of strong indications of EM
fields being capable of disturbing the immune system and thus increasing disease,
including cancer risk. He suggested that existing safety limits are inadequate to
protect public health and need to be reviewed to accommodate deployment of
untested technologies.
Guy and Chou [20] reported that a rat which exposed to a very high-intensity
microwave pulses has a temperature rise in its brain and seizures occurred to the rat
and followed by unconsciousness for 4 to 5 minutes. Postmortem revealed damage at
myelin sheaths of the rat nerve fibre.
Blackman [21] raises concerns about the possible health consequences on
non-thermal effects based on recent evidence from epidemiological studies
associating increases in brain and head cancers with increased cell phone use per day
and per year over 8-12 years. Furthermore, two of the studies did by Hardell, Mild
and Carlberg [22], have found that there are correlations between tumor's location
and side of the head where phone were held during a phone call.
Luria et al. [23] did a study on the cognitive functions of humans when
exposed to GSM radiation. 48 healthy right-handed males were given a specific task
and their response times were recorded. The study confirmed the existence of an
effect of the EM exposure on the hand response time and has correlation with
exposure time and location of the phones on the head.
9
Other studies [24, 25] revealed that non-thermal effects of EM exposure
show evidence of potential risk to health. Current EM exposure safety standards are
deemed inadequate to address this issue. Immediate adverse health effects are not
common but there are various other effects which can result in slow death or as silent
killers. The consequences might surface after years or perhaps in future generation.
2.2 Neurological electrophysiology effects of EM radiation
There are several studies mostly involving mobile phones at GSM 900 band as the
source of EM radiation towards the APs in nervous system. The behavioural and
physical changes happened to the APs due to the EM radiation is know as
neurological electrophysiology.
Bolashakov and Alekseev [26] found that non-continuous 900 MHz pulsed
wave radiation increased bursts of firing of Lymnea (freshwater snail) neurons. This
result correlates with finding from Hao et al. [27]. 47 rats exposed to 916 MHz, 10
W/m2 mobile phone EM radiation; 6 hours a day, 5 days a week for 10 weeks. The
neuron signals of one exposed rat and one control rat in the maze were obtained by
the implanted microelectrode arrays in their hippocampal regions. The hippocampal
neurons of exposed rat showed irregular firing patterns and more spikes with shorter
interspike interval during the whole experiment period. Furthermore, results from
rats searching for food in an eight-arm radial maze show the average completion time
and error rate of the exposure group were longer and larger than that of control
group. It indicates that the 916 MHz EM radiation influence learning and memory in
rats to some extent in a period during exposure.
Razavinasab, Moazzami and Shabani [28] did a study on electrophysiological
properties of CA1 pyramidal neurons which exposed to GSM radiation. 8 rats were
exposed to 900 MHz pulsed EM radiation for 6 hours per day. Whole cell recordings
in hippocampal pyramidal cells did show a decrease in neuronal excitability. Mobile
phone exposure was mostly associated with a decrease in the number of APs fired in
spontaneous activity. There was an increase in the amplitude of the
afterhyperpolarization (AHP) in AP of exposed rats compared with the control. The
results of the passive avoidance and Morris water maze assessment of learning and
memory performance showed that phone exposure significantly altered learning
acquisition and memory retention in exposed rats compared with the control rats.
10
Therefore, the study confirmed that exposure to mobile phones adversely affects the
cognitive performance of rats.
Meanwhile study by Partsvania et al. [29] show that after acute exposure of
900 MHz mobile phone radiation on single neurons of mollusk, average firing
threshold of the action potentials was not changed. However, the average latent
period was significantly decreased. This indicates that together with latent period the
threshold and the time of habituation might be altered during exposure. However,
these alterations are transient and only latent period remains on the changed level.
There are also study for different frequency of non-ionizing EM radiation on
action potential in a nerve. An early study from McRee et al. [30] has undergone an
experiment where the spinal cords of cats were directly exposed to 2450 MHz
continuous wave EM radiation in order to study the effect on reflex response and
synaptic function. APs recorded from the ventral root nerve were amplified 500 to
2000 times from its original signal with apperance of EM radiation. Meanwhile,
Seaman and Wachtel [31] observed a different result, which is increased in AP firing
rates of Aplysia (sea snail) ganglia that been exposed to 2.5 GHz continuous wave
EM radiation.
As several studies produce different behavioural and physical changes
towards the AP, the main concern here is the EM radiation do alter the AP.
Therefore, its essential to undertaken a study on EM radiation on AP in order to
quantify the extent of the interaction.
2.3 Physiology of human nervous system
Combination of neurons and brain create a system known as the nervous system.
Neurons are interconnected in a mesh of neural networks and convey information
among them or other target cells by using frequency modulated pulses known as AP
that course along an axon [32, 33]. Intracellular fluid inside of an axon or nerve fibre
is separated from extracellular fluid by a thin layer known as plasma membrane. It is
typically 4 nm to 10 nm in thickness and composed of a lipid bilayer embedded with
various types of protein molecules [34]. Voltage-gated sodium channel (voltage-
gated Na+ channel), voltage-gated potassium channel (voltage-gated K
+ channel),
sodium-potassium pump (Na+-K
+ pump) and leakage sodium channel (Na
+ leakage
channel) and leakage potassium channel (K+ leakage channel) are protein molecules
11
that have an active role in producing and retaining the AP inside the nerve fibre.
Production of AP involved several phases, starting from resting, depolarization,
repolarization, hyperpolarization and lastly return to resting [35].
At rest, nerve fibre intracellular fluid (ICF) voltage is -70 mV which also
known as resting potential. Some transport mechanism helped the axon to maintain
its ICF voltage which involves some protein molecules as mention in paragraph
above. The Na+-K
+ pump actively transports 3 Na
+ out of and 2 K
+ into the nerve
fibre, keeping the concentration of Na+ high in the extracellular fluid (ECF) and the
concentration of K+ high in ICF [30]. This uneven positive ions or cations transfer
resulting in higher concentration of cations in ECF compared to ICF. Furthermore,
the fact that the plasma membrane is permeable to K+ adding to factor of high
concentration of cations in ECF. Inexistence of any protein molecules that can
support transport mechanism for negative ions or anions in ICF and zero
permeability of anions towards the plasma membrane resulting in higher
concentration of anions compared to cations in ICF. Therefore, voltage difference
between ICF and ECF has produced the negative value of resting potential.
Actually, the plasma membrane is slightly permeable to Na+. This
characteristic has helped inward movement of Na+
into the nerve fibre. Inward of Na+
is very important to counterbalance outward movement of K+ from the nerve fibre
[36]. This two way processes have helped the nerve fibre to maintain its resting
potential always at -70 mV, instead of keep decreasing towards K+ equilibrium
potential because of its high permeability towards the membrane. Small portion of
Na+ that enters the nerve fibre will slowly increase the potential value in the nerve
fibre towards threshold potential. As a result, activation gates of some of its voltage-
gated Na+ channels to open. Na
+ starts to enter into the nerve fibre because of
concentration difference. The inward Na+ excites more voltage-gated Na
+ channels to
open its activation gates [36]. More Na+ is rushing into nerve fibre and produces
rapid increase of potential value inside the nerve fibre. The voltage increase process
is known as depolarization phase in AP.
During rapidity of voltage-gated Na+ channels opening its activation gate,
there is counterbalance process from inactivation gate ball that is slowly binding to
the channel opening. Therefore, there is interval of 0.5 ms between processes of
activation gates open and inactivation gates close [36]. This 0.5 ms interval has made
the nerve fibre depolarized until its AP reached the peak of +30 mV which is near to
12
Na+ equilibrium potential. Once the inactivation gate closed, the voltage-gated K
+
channels activation gate starts to slowly open at the peak of the AP [36]. K+ starts to
exit from the nerve fibre because of concentration difference. Consequently, the
potential value inside the nerve fibre is plummeting from its peak back to resting.
The voltage decrease process is known as repolarization phase in AP.
However, characteristics of voltage-gated K+ channels that are slow to close
have resulting in more K+ to leak from the nerve fibre. This process has made the
potential value inside the nerve fibre become more negative that the actual resting
potential. This process is known as hyperpolarization phase in AP. The
hyperpolarization does not last long since voltage-gated K+ channels activation gate
closing process will increase back the excess potential negative value during
hyperpolarization. Once the activation gates closes completely, the AP returns to it
resting phase. The whole phases create the AP as shown in Figure 2.1.
Understanding the creation of AP, has aided many researchers to produce
mathematical model of AP inside the brain which is essential as the source in
designing a neuron electrical circuit in this studies.
Figure 2.1: Action potential and its phases [35]
13
Correlation between central nervous system (CNS) and peripheral nervous
system (PNS) are very important to initiate motor control on muscle, so that the
muscle will moved according to human brain thought. Figure 2.2 illustrate the
organization of motor control for voluntary movement of a human arm. In voluntary
movement, an idea to move an arm is initiated in brain at primary motor cortex area.
The idea or information is carried by propagation of AP in a nerve fibre through
brain stem and spinal cord. Motor neuron that synapses in the spinal cord continues
the propagation of AP until reach muscle fibre to trigger an arm movement. The
movement event is sensed by a peripheral receptor that produces AP. The AP
propagates in an afferent neuron until reach the afferent neuron terminals at spinal
cord. The AP are now transmitted by other nerve fibre through brain stem and
cerebellum until the AP reaches the origin of primary motor cortex to continue the
arm movement. The propagation of AP in the motor control diagram is in a loop
which can be compared to a complete circuit model which will be discussed in next
chapter.
Figure 2.2: Motor control organization for muscle movement [36]
14
There are also movements by skeletal muscle which only involves efferent or
motor neurons. Those neurons form tracts from the brain to the skeletal muscle
which known as descending tracts as shown in Figure 2.3. The process of AP
propagation to realize a movement is same as explained in previous paragraph,
except there is no sensor to detect the movement event. Even though the AP
propagation are point to point movement, but the surrounding substance around the
neurons can be used as grounding in order to introduce a circuit model which also
will be discussed in next chapter.
Figure 2.3: Descending tracts for muscle motor neurons [36]
15
2.4 Neuron electrical circuits and action potential mathematical models
The history of neuro-computational science starts in 1950s when Hodgkin and
Huxley had formulated the nerve fibre AP in a squid giant axon. Earlier studies by
Hodgkin and Huxley [37, 38, 39] have show that, movement of Na+ and K
+ across
the plasma membrane can be represent as continuous time function conductance
because rapid conductivity of those ions across the membrane only happens at their
own specific time. The membrane that separate ICF and ECF can be consider as
capacitance. Adding with conductivity factor of those ions through the leakage
channels, the nerve fibre electrical network can be shown as in Figure 2.4.
RNa RK RL
VK VL
CM
VNa
extracellular fluid
intracellular fluid
Vm
INa IK IL
I
Figure 2.4: Hodgkin and Huxley nerve fibre electrical model [11]
Analysis for circuit in Figure 2.4 by using Kirchhoff’s Current Law produced
an equation of total membrane current during ion transportation process.
LKNa
m
M IIIdt
dVCI (2.1)
where I is the membrane total current density 2/ cmA
INa, IK, IL are the Na+, K
+, leakage ion current density 2/ cmA
Vm is the membrane potential mV
Cm is the membrane capacitance per unit area 2/ cmF
t is time ms
16
The individual ionic currents are presented by the relations:
NamNaNa VVgI (2.2)
KmKK VVgI (2.3)
Llmll VVgI (2.4)
where gNa, gK, lg are the Na
+, K
+, leakage ion conductance 2/ cmmS
VNa, VK, VL are the Na+, K
+, leakage ion equilibrium potentials mV
Hodgkin and Huxley use a theoretical power variables satisfying first order
kinetic equations curves to best fit Na+ and K
+ experimental conductance values
which are obtained from voltage clamp experiments on squid giant axonal membrane
[11, 32]. A part of this process has produced an assumption that K+ conductance is
proportional to K+ activation gating variable. Multiplying the variable by the
asymptotic value of K+ maximum conductance, a K
+ conductance formula is
introduced.
4ngg KK (2.5)
nndt
dnnn 1 (2.6)
where Kg is a constant 2/ cmmS
n is a K+ activation gating variable (unitless)
n ,
n are rate constants (ms -1
)
The first order kinetic equation defines the n gating variable which represents
the closing and opening of the activation gate K+ channels as shown in Figure 2.5.
The variable, n is vary between 0 and 1. The K+ conductance value is maximum
when n is equal to 1 while n equal to 0 indicates no K+ conductance value or no
voltage-gated K+ channels appear on the membrane.
17
Figure 2.5: Voltage-gated K+ channel in closed (on left) and opened (on right) states
[36]
The rate constants, n and
n are functions that dependent on membrane
potential, Vm but not with time even though its unit is inverse of time. As in K+
conductance experimental values, the experimental rate constants points are plotted
to their respective membrane voltage and continuous curves which are clearly a good
fit to the experimental data are applied. Hence, formulas of curves that represent both
rates constant are obtained.
1
5001.0501.0
mV
m
ne
V (2.7)
60125.0125.0
mV
n e (2.8)
Unlike K+ conductance, Na
+ conductance is proportional to two variables
instead of one. Those two variables are Na+ activation gate variable and Na
+
inactivation gate variable. Multiplying the variable by the asymptotic value of Na+
maximum conductance, a Na+ conductance formula is introduced.
hmgg NaNa
3 (2.9)
mmdt
dmmm 1 (2.10)
hhdt
dhhh 1 (2.11)
where Nag is a constant 2/ cmmS
m is a Na+ activation gating variable (unitless)
h is a Na+ inactivation gating variable (unitless)
m ,
m , h ,
h are rate constants (ms -1
)
18
The first order kinetic equation defines the m and h gating variables which
represent the closing and opening of both activation and inactivation gates of Na+
channels as shown in Figure 2.6. The variable, m and h are also varies between 0 and
1. Both gating variables have to be non-zero for the Na+ conduction to occur.
Figure 2.6: Voltage-gated Na+ channel in closed (on left), opened (at middle) and
inactive (on left) states [36]
Figure 2.6 showed that voltage-gated Na+ channels have three states rather
than two states for voltage-gated K+ channels. This is due to Na
+ conductance has
two separate gating variables, m and h. As seen in Figure 2.6, closed and opened
states are determined by the m gating variable that controls closing and opening of
activation gate during AP process. Inactive state is determined by the h gating
variable that controls the hanging ball which represents the inactivation gate in
Figure 2.6 during AP process.
Properties of rate constants, m ,
m , h and
h are the same as n and
n
of K+ conductance. The rate constants points from Hodgkin and Huxley [11]
experiments are plotted to their respective membrane voltage and continuous curves
which are clearly a good fit to the experimental data are applied. Hence, formulas of
curves that represent all of the rates constant are obtained.
1
351.0351.0
mV
m
me
V (2.12)
18/604
mV
m e (2.13) 6005.0
07.0
mV
h e (2.14)
1
1301.0
mVhe
(2.15)
One per unit circuit as shown in Figure 2.4 only can produce an AP when I=0
in Equation (2.1). Therefore, by solving Equation (2.1) until Equation (2.15) in a
19
simulation package such as PSPICE or MATLAB, an AP as in Figure 2.1 will be
obtained.
Analysis by Keynes et al. [40] towards their data in voltage clamp
experiments on barnacle muscle fibre, shows that two voltage dependent
conductance exist in muscle fibre membrane which are calcium (Ca2+
) conductance,
gCa and K+ conductance, gK. Both conductances are in function of membrane voltage.
Morris and Lecar [12] did a further studies based on Keynes findings in order to
produce a muscle fibre electrical as shown in Figure 2.7 which is quite similar with
Hodgkin and Huxley circuit except, the Ca2+
conductance is used instead of Na+
conductance.
RNa RK RL
VK VL
CM
VCa
extracellular fluid
intracellular fluid
Vm
ICa IK IL
I
Figure 2.7: Morris-Lecar electrical circuit model [12]
The equations describing the muscle fibre membrane behavior are obtained
from analysis of circuit in Figure 2.7 by using Kirchhoff’s Current Law.
LmLCamCaKmKm
M VVgVVMgVVNgdt
dVCI (2.16)
MMdt
dMM (2.17)
NNdt
dNN (2.18)
where I is the membrane total current density 2/ cmA
Vm is the membrane potential mV
CM is the membrane capacitance per unit area 2/ cmF
t is time ms
20
gCa, gK, gL are the Ca2+
, K+, leakage ion conductance 2/ cmmS
VCa, VK, VL are the Ca2+
, K+, leakage ion equilibrium potentials mV
M, N are the Ca2+
, K+ opening gating variable (unitless)
M∞, N∞ are the Ca2+
, K+ steady state opening gating variable (unitless)
M , N are rate constants (ms
-1)
The variables M and N are analogous to the Hodgkin and Huxley [11] “m”
and “n” parameters [12]. M is gating variable that controls Ca2+
channels opening at
any given time while N is gating variable that controls K+ channels opening at any
given time.
Elementary statistical arguments in Lecar, Ehrenstein and Latorre [41] and
Ehrenstein and Lecar [42] have produced formulae for rate constants, M and N
and also steady state opening gating variable, M∞ and N∞.
21 /tanh15.0 VVVM m (2.19)
21 2/cosh VVVmMM (2.20)
43 /tanh15.0 VVVN m (2.21)
43 2/cosh VVVmNN (2.22)
where M , N are maximum rate constants (ms -1
)
V1, V3 are potential at which M∞ = N∞ = 0.5 (mV)
V2, V4 are M∞, N∞ reciprocal of slope of voltage dependence
Note: Values for the parameter in Equation (2.19) until equation (2.22) are
obtained from Morris and Lecar [12] voltage clamp experiment data.
21
At early stage of mathematical modelling by Hindmarsh and Rose [13] in
order to produce isolated bursting AP, they proposed two simultaneous first order
differential equations that can produce the bursting AP.
Ibxaxydt
dx 23 (2.23)
ydxcdt
dy 2 (2.24)
where x is the membrane potential (mV)
y is a recovery variable (unitless)
t is time ms
a, b, c, d are time constant (ms) [positive real number]
I is a stimulus current (nA)
Those equations are obtained through modification and transformation of
variables in earlier Hindmarsh and Rose model [43]. The drawback in model from
equations above is inexistent of hyperpolarization state on the produced AP.
Furthermore, an AP produced by the model has longer duration than actual AP. In
order to overcome the problems, they introduced another first order differential
equation that produces slow current. The slow current equation can give an ample
time for the AP to enter hyperpolarization state before reaches a resting state.
zIbxaxydt
dx 23 (2.25)
ydxcdt
dy 2 (2.26)
zxxsrdt
dz 1
(2.27)
where z is the membrane adaption current (nA)
x1 is the initial membrane potential (mV)
r, s are time constant (ms) [positive real number]
All the time constants have very important role in producing the required AP.
As a result, they have produce the isolated bursting AP that existing
hyperpolarization state as shown in Figure 2.8.
22
Figure 2.8: Isolated bursting AP produced by Hindmarsh and Rose model [13]
Subsequent investigations after Hodgkin and Huxley findings, have found
that the AP in nerve fibre of human are diverse in their spike patterns. Furthermore,
there are many ionic currents other than IK and INa that contributing to the AP
creation in the nerve fibre. Connors and Gutnick [44], Gutnick and Crill [45] and
Gray and McCormick [46] have categorized the diversity of neocortical neurons
spike patterns into four distinct classes which are regular spiking, fast spiking,
continuous bursting and intrinsic bursting neurons. Gutnick and Crill [45] and
McCormick [47] investigations have shown that approximately 12 ionic currents are
involved during AP propagation through the nerve fibre.
Analysis of the diversity of neurocortical ionic currents and AP spike patterns
has triggerd a development of simplest plausible mathematical model that is
consistent with dynamical behaviour of neocortical neurons [14]. The Wilson model
consist of four first order differential equations that are modified from original
Hodgkin and Huxley model with some reasonable approximation and with addition
of two more dominant ionic currents from others ionic current as mentioned in
Gutnick and Crill [45] and McCormick [47]. At early stage of Wilson model
development, the Hodgkin and Huxley model is modified and simplified until only
two first order differential equations are left.
23
IVVRgVVmdt
dVC KmKNam
m
m (2.28)
RRdt
dR
R
1 (2.29)
where I is a stimulus current (nA)
Vm is the membrane potential mV
Cm is the membrane capacity per unit area (nF)
t is time ms
Kg is the K
+ maximum conductance S
VNa, VK are the Na+, K
+ equilibrium potentials mV
R is the K+
activation function (unitless)
m∞, R∞ are the Na+, K
+ steady state activation function (unitless)
R is a time constant (ms)
Voltage-gated Na+ channel activation time constant, τm is much smaller
compared to voltage-gated Na+ channel inactivation time constant, τh and also
voltage-gated K+ channel activation time constant, τn [11]. This means that the
activation of the Na+ channels is quite fast in reaching their steady state value.
Therefore Wilson takes this advantage by taking the activation m function is always
equal to steady state activation m∞ function by assuming the τn is too small until its
effects can be neglected. This approximation is supported by Rinzel [48] that
produced AP mathematical model by assuming Na+ channels activation are
sufficiently fast enough to be described by its steady state value m∞.
In order to reduce computation time in Wilson model, Na+ channels
inactivation gating variable, h is ignored. Again, according to Hodgkin and Huxley
[11] investigation, roughly same numerical value between τh and τn has triggered
Wilson to replace the effect of Na+ inactivation gating variable, h with the
comparable effect of K+ activation gating variable, n. Furthermore, observation of
human and mammalian neocortical neurons does not contain any inactivation Na+
currents [49, 50].
The final assumption by Wilson is the τr is chose to be independent of Vm or
in other words, τr is a real number rather than a function. This is possible because
Wilson used second order polynomial curve fit approximations that follow the
exponantial behaviour of activation gating variable n and m in Hodgkin and Huxley
24
model which are analogus to activation gating variable R∞ and m∞ in Wilson model
respectively.
Among other currents that responsible for creation of AP instead of IK and
INa, a low threshold Ca2+
current, IT and a slow afterhyperpolarizing (AHP) K+
current, IH are also dominant factor in AP propagation process. Therefore, by taking
into account IK, INa, IT and IH effects in AP creation and propagation, Wilson [14] has
proposed a mathematical model that consists of four first order differential equations
with each steady state activation functions are represent by second order polynomial
equations.
IVVHgVVTgVVRgVVmdt
dVC HmHTmTKmKNam
mm
(2.30)
RRdt
dR
R
1 (2.31)
TTdt
dT
T
1 (2.32)
THdt
dH
H
31
(2.33)
8.176.478.33 2 mm VVm (2.34)
24.17.32.3 2 mm VVR (2.35)
205.46.118 2 mm VVT (2.36)
where HT gg , are the Ca
2+, AHP K
+ dynamic conductance S
VT, VH are the Ca2+
, AHP K+ equilibrium potentials mV
T, H are the Ca
2+, AHP K
+ activation function (unitless)
T∞ is the Ca2+
steady state activation function (unitless)
T ,
H are time constants (ms)
Izhikevich [15] has produced a simple model of spiking neurons that is as
biologically plausible as the Hodgkin and Huxley model which it can produce
various firing patterns of neurons. Furthermore, it is computationally efficient with
very low number of floating point operation are needed in order to simulate it in
required duration if compared to real Hodgkin and Huxley model [51]. The first
version of this model was published in [52] but in trigonometric form in order to ease
the mathematical analysis. Then, Izhikevich transform the model so it can perform
large-scale simulations.
120
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