specific absorption rate in the presence of...
TRANSCRIPT
SPECIFIC ABSORPTION RATE IN THE PRESENCE OF CONDUCTIVE
METALLIC OBJECTS WITH CLOSE PROXIMITY RADIATING SOURCE
NAZIRAH BINTI OTHMAN
UNIVERSITI TEKNOLOGI MALAYSIA
SPECIFIC ABSORPTION RATE IN THE PRESENCE OF CONDUCTIVE
METALLIC OBJECTS WITH CLOSE PROXIMITY RADIATING SOURCE
NAZIRAH BT OTHMAN
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Master of Engineering (Electrical)
Faculty of Electrical Engineering
Universiti Teknologi Malaysia
MARCH 2015
iii
DEDICATION
To my beloved mom & dad,
Rosadah Abu Bakar & Othman Puteh
my dearest husband,
Aizat Azmi
my supportive sister & brother
Syazwani & Mohd Nizam
iv
ACKNOWLEDGEMENT
Alhamdulillah, Praise to Allah S.W.T for HIS blessing and guidance have
helped me in completing my thesis. I would like to take this opportunity to express
my deepest gratitude to my supervisor, Dr Noor Asmawati Samsuri and my co-
supervisor, Professor Dr. Mohamad Kamal for their advice, guidance, motivation,
suggestions and ideas throughout my study from the beginning to the end of this
research.
My utmost thanks also go to my family, especially my father, my beloved
mother, and my dearest husband to whom I owe my love and gratitude for their
support every moment I need them. I can never thank them so much and tell how
much I appreciate their encouragement.
To all my friends and P18 members who have helped and supported me along
the way, I thank you from the bottom of my heart. Thank you; the most suitable
words for those who keep supporting and be there all the way through my years in
Universiti Teknologi Malaysia.
v
ABSTRACT
This thesis identifies and evaluates the effect of human body and conductive
metallic objects in the vicinity of portable handheld electronic devices on antenna
radiation pattern, antenna performance and Specific Absorption Rate (SAR). The
presences of electronic devices in the vicinity of human body especially close to the
human sensitive part (when the antenna is left inside the trousers pocket) allow the
radiated electromagnetic wave to penetrate inside human tissues. Homogeneous and
realistic body models have been considered in the simulation. The excitation is
provided by means of a simple dipole and PIFA antennas as the radiating source at
four different frequencies (0.4, 0.9, 1.8 and 2.4 GHz). In order to characterize the
variation of SAR due to metallic items, the external metallic item and implanted
medical item are used and modelled as conducting objects with their sizes chosen in
order to coincide with typical sizes available. The results have shown that the
presence of human body near to the antenna detuned the resonant frequency and
significantly distorted the antenna radiation pattern. Nevertheless, the presence of
conductive objects do not have any profound effect on antenna radiation pattern due
to their size which is relatively small compared to the size of human body.
Additional metallic objects close to the human leg could alter the SAR and the effect
varies depending on the size and the position of the objects. In addition, the zip could
significantly increase SAR inside the testicle by 50% at 0.9 GHz due to the position
of zip that is close to the human sensitive organ. Nevertheless, the presence of
conductive medical implant inside the leg could increase the maximum SAR by more
than 400 times at 0.4 GHz. However, the medical implant has only minor effect on
SAR inside the testicle. The simulation results have been validated through
measurement using homogeneous body model at 2.4 GHz.
vi
ABSTRAK
Tesis ini mengenal pasti dan mengkaji kesan kehadiran tubuh manusia dan
objek bersifat konduktif yang berhampiran dengan elektronik mudah alih pada corak
radiasi antena, prestasi antena dan Kadar Penyerapan Spesifik (SAR). Kehadiran
alat-alat elektronik berhampiran badan manusia terutama berdekatan dengan
bahagian sensitif manusia (apabila antena ditinggalkan di dalam poket seluar)
menyebabkan gelombang elektromagnetik menembusi tisu badan manusia. Model
homogen dan model realistik telah digunakan dalam kajian ini. Dwipolar antena dan
PIFA antena digunakan sebagai sumber radiasi pada empat frekuensi yang berbeza
(0.4, 0.9, 1.8 dan 2.4 GHz). Objek luar dan implan yang bersifat konduktif digunakan
dalam simulasi berangka untuk mencirikan kesan objek tersebut terhadap SAR
dengan mengubah saiz objek tersebut berdasarkan saiz yang terdapat di pasaran.
Keputusan kajian menunjukkan bahawa kehadiran badan manusia berhampiran
dengan antena menyebabkan perubahan pada frekuensi dan corak radiasi antena.
Walau bagaimanapun, kehadiran objek bersifat konduktif berhampiran dengan
antena tidak memberi sebarang kesan kepada corak radiasi antena kerana saiz objek
adalah lebih kecil berbanding saiz badan manusia. Kehadiran objek bersifat
konduktif berhampiran kawasan kaki manusia boleh mengubah SAR dan perbezaan
kesan bergantung kepada saiz dan kedudukan objek. Selain itu, kehadiran zip bersifat
konduktif juga boleh meningkatkan SAR di dalam testikel sebanyak 50% pada
0.4 GHz adalah disebabkan oleh kedudukan zip yang terletak berhampiran dengan
testikel. Tambahan pula, kehadiran implan bersifat konduktif boleh meningkatkan
SAR maksima lebih daripada 400 kali ganda pada 0.9 GHz. Walau bagaimanapun,
kehadiran implan hanya menyebabkan perubahan SAR yang kecil dalam testikel.
Keputusan simulasi berangka telah disahkan melalui pengukuran menggunakan
model badan homogen pada 2.4 GHz.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF ABBREVIATIONS xviii
LIST SYMBOLS xix
LIST OF APPENDICES xx
1 INTRODUCTION 1
1.1 Introduction 1
1.2 Problem Statement and Significance of the
Research
3
1.3 Objectives 5
1.4 Scope of Research 6
1.5 Organization of Thesis 7
2 LITERATURE REVIEW 9
2.1 Introduction 9
viii
2.2 Thermal Effect on Human Biological Tissue due
to the EM Wave
10
2.3 Specific Absorption Rate (SAR) 11
2.4 The Interaction between the EM Field and Human
Body on Antenna Performance and SAR
13
2.5 The Presence of Additional Metallic Item near the
Human Body
14
2.5.1 The Presence of External Metallic Object
near the Human body
14
2.5.2 The Presence of Conductive Medical
Implant inside the Body
17
2.6 Numerical Modeling and Analysis on the
Interaction between the EM Field and Human
Body
20
2.6.1 Human Body Model and Dielectric
Properties of Biological Body Tissue
20
2.6.2 Computational Modeling using Finite
Integration Technique (FIT)
22
2.7 Summary 23
3 METHODOLOGY 26
3.1 Introduction 26
3.2 Project Flow Chart 26
3.3 Radiation Source 29
3.3.1 Dipole Antenna 29
3.3.2 Planar Inverted–F Antenna (PIFA) 30
3.4 Conductive External Objects 32
3.5 Medical Implants 33
3.6 Homogeneous Cylindrical Body Model 35
3.6.1 The Effect of Cylindrical Body Model on
S11
37
3.6.2 The Effect of Cylindrical Body Model on
Radiation Pattern
40
ix
3.6.3 The Effect of Cylindrical Body Model on
SAR
42
3.7 Realistic Body Model 44
3.8 Simulations in CST Microwave Studio 46
3.9 Summary 48
4 THE EFFECT OF EXTERNAL METALLIC
OBJECT
49
4.1 Introduction 49
4.2 The Effect of Heterogeneous Body Model and
Metallic Object on Antenna Performance
50
4.2.1 The Effect of Different Orientation of
Dipole and PIFA Antenna on S11 in the
Presence of Body Model
50
4.2.2 The Effect of Antenna Orientation on
Radiation Pattern in the Presence of Body
55
4.2.3 The Effect of Metallic Object on S11 59
4.2.4 The Effect of Metallic Object on
Radiation Pattern
62
4.3 The Effect of Metallic Object on Averaged 1g and
10g SAR
65
4.3.1 The Effect of Coin, Ring and Zip on
Maximum 1g and 10g SAR
66
4.3.2 The Effect of Coin and Ring at Different
Size on Maximum 1g and 10g SAR in the
Leg
70
4.3.3 The Effect of Metallic Objects on
Averaged 1g and 10g SAR inside Testicle
71
4.4 Summary 76
5 THE EFFECT OF CONDUCTIVE MEDICAL
IMPLANT
78
5.1 Introduction 78
x
5.2 The Effect of Bone Plate on SAR and Antenna
Performance
80
5.2.1 The Effect of Bone Plate on Maximum 1g
and 10g SAR
80
5.2.2 Averaged 1g and 10g SAR within the
Testicle due to Conductive Bone Plate
84
5.2.3 The Effect of Different Size of Bone Plate
and Antenna Orientation on Antenna
Performance
87
5.2.3.1 Effect on S11 88
5.2.3.2 Effect on Radiation Pattern 92
5.3 The Effect of Conductive Rod on Maximum 1g
and 10g SAR
95
5.4 Averaged 1g and 10g SAR within the Testicle due
to Implanted Conductive Rod
99
5.5 Summary 102
6 SAR MEASUREMENT 104
6.1 Introduction 104
6.2 Homogeneous Waist Phantom 105
6.3 Metallic Ring and Medical Implant 107
6.4 Measurement Procedure 108
6.5 Measurement Results and Discussion 110
6.6 Summary 113
7 CONCLUSIONS AND FUTURE WORK
RECOMMENDATIONS
116
7.1 Conclusions 116
7.2 Future Works Recommendation 120
REFERENCES 121
Appendices A - G 130-136
xi
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Basic restriction for frequencies up to 10 GHz 12
2.2 Basic restriction used in Europe and USA 12
2.3 Dielectric properties of human biological tissue 21
3.1 The dielectric properties of average muscle used for
homogeneous body model
36
4.1 Numerical results of antenna performance (efficiency)
for λ/2 dipole antenna at four different frequencies
52
5.1 Relative enhancement ( ),
SARrel of 1g SAR and 10g SAR due to the bone plate
at all tested frequencies, f. The input power is
normalized to 1W
81
6.1 The dielectric properties of muscle equivalent liquid for
measurement
106
implant noimplantith SARSARw
xii
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Orientation and position of external metallic items
metallic ring is pierced to the ear, metallic in front of the
eyebrow and straight metallic pin positioned in front of
the face
16
2.2 SAR distribution at three different cutting plane 16
2.3 The skin closure staple and hemostatic clip that have
been considered in
18
2.4 Metallic implants inside the head; plate, bone plate,
fixtures and earring
19
2.5 The position of ‘hot-spot’ due to the presence of
conductive screws
19
3.1 Project flow chart 27
3.2 SAR measurement set-up 28
3.3 The dimension of half-wave dipole antenna 29
3.4 The λ/2 dipole antenna return loss simulated in free
space
30
3.5 The return loss of PIFA antenna in free space 31
3.6 PIFA antenna used in this research 31
3.7 Geometric of ring, coin and zip 33
3.8 An x-ray image showing the position of intramedullary
nail and bone plate. The dimension of intramedullary
nail, 162 mm bone plate and 213 mm bone plate used in
the simulation
34
xiii
3.9 Simulation set-up of dipole antenna in the presence of
simple cylindrical body model without ring and with
ring
35
3.10 The effect of simple body model on simulated S11 at
0.4 GHz, 0.9 GHz, 1.8 GHz and 2.4 GHz
38
3.11 Simulated S11 with and without the presence of metallic
ring at 0.4 GHz, 0.9 GHz, 1.8 GHz and 2.4 GHz
39
3.12 Simulated radiation pattern (H-plane) in the presence of
cylindrical body model
40
3.13 The effect of ring on antenna radiation pattern (H-plane)
at 0.4 GHz, 0.9 GHz, 1.8 GHz and 2.4 GHz at d = 5 mm
and 1 mm distance between ring and body
41
3.14 10g SAR in the cylindrical body model at four different
antenna-body distance; d=5 mm, d=10 mm, d=15 mm
and d=20 mm at 0.4 GHz, 0.9 GHz, 1.8 GHz and
2.4 GHz
42
3.15 Comparison on the effect of ring on 10g SAR in the
simple body model at 0.4 GHz, 0.9 GHz, 1.8 GHz and
2.4 GHz when d = 5 mm and body-ring distance is fixed
at 1 mm
43
3.16 Heterogeneous Voxel body model and waist area 44
3.17 Homogeneous body model 46
3.18 The simulation configuration for external metallic
object; coin, ring and zip, intramedullary nail and bone
plate
47
4.1 The orientation of the antenna with respect to the body
vertical and horizontal
50
4.2 S11 for different orientation of dipole antenna 0.4 GHz,
0.9 GHz, 1.8 GHz and 2.4 GHz in the presence of
heterogeneous body model
51
4.3 The position of PIFA antenna with respect to the body
in the simulation vertical orientation and horizontal
orientation
54
xiv
4.4 S11 for different orientation of dual-band PIFA at 0.9
GHz and 1.8 GHz in the presence of heterogeneous
body model
55
4.5 λ/2 dipole radiation pattern in E-plane and H-Plane at
0.4 GHz, 0.9 GHz, 1.8 GHz and 2.4 GHz with d is fixed
at 5 mm
56
4.6 Comparison on the antenna gain without and with the
presence of Voxel body model at 1.8 GHz
57
4.7 The antenna radiation pattern in E-plane and H-plane at
0.9 GHz and 1.8 GHz with and without heterogeneous
body model for PIFA antenna with d is fixed at 5 mm
58
4.8 Simulated S11 of horizontal orientated dipole antenna at
1.8 GHz and 2.4 GHz with d is fixed at 5 mm
59
4.9 Simulated S11 of vertical orientated dipole antenna at
1.8 GHz and 2.4 GHz with d is fixed at 5 mm
60
4.10 Simulated S11 for horizontal orientated PIFA antenna at
0.9 GHz and 1.8 GHz with d is fixed at 5 mm
61
4.11 Simulated S11 for vertical orientated PIFA antenna at
0.9 GHz and 1.8 GHz with d is fixed at 5 mm
62
4.12 Radiation pattern (E-plane) for horizontally orientated
dipole antenna at 0.4 GHz, 0.9 GHz, 1.8 GHz and
2.4 GHz
63
4.13 Radiation pattern (E-plane) for vertically orientated
dipole antenna at 0.4 GHz, 0.9 GHz, 1.8 GHz and
2.4 GHz
64
4.14 Radiation pattern (E-plane) for horizontally and
vertically orientated PIFA antenna at 0.9 GHz and
1.8 GHz
65
4.15 Maximum averaged 1g SAR inside the leg at four
different frequencies for horizontal and vertical
orientation of dipole antenna
66
4.16 Maximum averaged 10g SAR inside the leg at four
different frequencies for horizontal and vertical
xv
orientation of dipole antenna 67
4.17 1g SAR distributions for dipole antenna at 0.4 GHz
body only, in the presence of coin, with ring in the same
position as coin and in the presence of zip with d is
fixed at 5 mm
69
4.18 The position of coin or ring in the simulation 70
4.19 The effect of different size of coin and ring for vertical
orientated antenna for 1g and 10g SAR
71
4.20 Average 1g SAR calculated inside the testicle for dipole
antenna in vertical and horizontal orientation with and
without the metallic object
72
4.21 Average 10g SAR calculated inside the testicle for
dipole antenna in vertical and horizontal orientation
with and without the metallic object
73
4.22 Average 1g SAR calculated inside the testicle for
vertical and horizontal orientated dual-band PIFA
antenna
74
4.23 Average 10g SAR calculated inside the testicle for
vertical and horizontal orientated dual-band PIFA
antenna
75
5.1 The truncated human body structure, fracture of femoral
shaft and the implanted conductive intramedullary nail
79
5.2 SAR distributions within the leg with and without the
presence of conductive bone plate at 0.4 GHz, 0.9 GHz,
1.8 GHz and 2.4 GHz
82
5.3 Electric field distributions within the leg in the presence
of conductive bone plate at 0.4 GHz, 0.9 GHz, 1.8 GHz
and 2.4 GHz over two different antenna orientation
84
5.4 The averaged 1g SAR, 10g SAR and Point SAR within
the testicle due to the presence of implanted conductive
bone plate over two different size for vertical orientated
dipole
85
5.5 The averaged 1g SAR, 10g SAR and Point SAR within
xvi
the testicle due to the presence of implanted conductive
bone plate over two different size for horizontal
orientated dipole
86
5.6 The antenna return loss at 0.4 GHz, 0.9 GHz, 1.8 GHz
and 2.4 GHz for vertical orientation of dipole antenna
89
5.7 The antenna return loss at 0.4 GHz, 0.9 GHz, 1.8 GHz
and 2.4 GHz for horizontal orientation of dipole antenna
90
5.8 Measurement setup 91
5.9 Measured S11 for vertical and horizontal orientated
dipole antenna at 2.4 GHz with and without the body
and medical implant
92
5.10 The E-plane radiation pattern due to the presence of
body and bone plate at 0.4 GHz, 0.9 GHz, 1.8 GHz, and
2.4 GHz for vertically orientation of dipole antenna
93
5.11 The E-plane radiation pattern due to the presence of
body and bone plate at 0.4 GHz, 0.9 GHz, 1.8 GHz, and
2.4 GHz for horizontally orientation of dipole antenna
94
5.12 1g SAR and 10g SAR inside the leg in the presence of
different length of rod at different frequency
96
5.13 The 1 SAR distributions inside the leg at 0.4 GHz,
0.9 GHz, 1.8 GHz and 2.4 GHz with and without the
conductive rod
97
5.14 Current density inside the leg at 0.4 GHz, 0.9 GHz,
1.8 GHz and 2.4 GHz with and without the conductive
rod
98
5.15 The effect of the different size of implanted conductive
rod at 0.4 GHz, 0.9 GHz, 1.8 GHz and 2.4 GHz on
averaged 1g SAR in the testicle
100
5.16 The effect of the different size of implanted conductive
rod at 0.4 GHz, 0.9 GHz, 1.8 GHz and 2.4 GHz on
averaged 10g SAR in the testicle
101
6.1 The waist body phantom and muscle equivalent liquid at
2.4 GHz for SAR measurement
106
xvii
6.2 Modified Voxel body model 106
6.3 The copper ring with different diameter and bone plate
used in SAR measurement
107
6.4 Measurement setup at 2.4 GHz for external metallic
object, conductive medical implant and dosimetric SAR
probe
109
6.5 Simulation and measurement results of point SAR at
2.4 GHz with and without the copper ring inside leg and
testicle
110
6.6 Simulation and measurement results of point SAR at
2.4 GHz with and without the bone plate inside leg and
testicle
112
6.7 Simulated and measured results on the effect of
separation distance between the antenna and body on
point SAR
113
xviii
LIST OF ABBREVIATIONS
EM - Electromagnetic
RF - Radio Frequency
ICNIRP - International Commission on Non-Ionizing Radiation
Protection
SAR - Specific Absorption Rate
ELF - Extremely Low Frequency
UHF - Ultra High Frequency
SAM - Specific Anthropomorphic Mannequin
FDTD - Finite Difference Time Domain
DASY - Dosimetric Assessment System
MRI - Magnetic Resonance Imaging
FIT - Finite Integration Technique
MOM - Method on Moment
CST - Computer Simulation Technology
PIFA - Planar Inverted–F Antenna
PEC - Perfect Electric Conductor
FCC - Federal Communications Commission
xix
LIST OF SYMBOLS
ρ - mass density of the materials
εr - relative permittivity
σ - tissue conductivity
ηtot - total efficiency
ηrad - radiation efficiency
d - antenna-body distance
r - radius of coin and ring
lr - length of intramedullary nail
xx
LIST OF APPENDICES
APPENDIX TITLE PAGE
A List of Publication 130
B Simulated S11 of horizontal orientated dipole antenna
at 0.4 GHz and 0.9 GHz with d is fixed at 5 mm
131
C Simulated S11 of vertical orientated dipole antenna at
0.4 GHz and 0.9 GHz with d is fixed at 5 mm
132
D Radiation pattern (H-plane) for horizontally orientated
dipole antenna at 0.4 GHz, 0.9 GHz, 1.8 GHz and
2.4 GHz
133
E Radiation pattern (H-plane) for vertically orientated
dipole antenna at 0.4 GHz, 0.9 GHz, 1.8 GHz and
2.4 GHz
134
F The H-plane radiation pattern due to the presence of
body and bone plate at 0.4 GHz, 0.9 GHz, 1.8 GHz,
and 2.4 GHz for vertically orientation of dipole
antenna
135
G The H-plane radiation pattern due to the presence of
body and bone plate at 0.4 GHz, 0.9 GHz, 1.8 GHz,
and 2.4 GHz for horizontally orientation of dipole
antenna
136
1
CHAPTER 1
INTRODUCTION
1.1 Introduction
The extremely fast development in mobile and wireless technologies, along
with the use of radio frequency (RF) as the channel for data transmission has led to
the increase of public concern on the possible adverse health effects due to the
electromagnetic (EM) wave radiated by the antenna while in used. The antenna
periodically emits the EM radiation although it is in standby mode. Generally, a
mobile phone is usually being placed close to the human head when it is in used,
while it is left inside the trousers pocket (especially front trousers pocket) for longer
duration when it is not being operated. In this case, the mobile phone is left in
standby mode and in very close proximity to the human body (waist area). In 2005,
research in [1] has found that 57% of man out of 419 left their mobile phone inside
the trousers pocket. This condition has raised the public concerned due to the vicinity
of the human sensitive organ to the radiation source. Researches in [2-4] have shown
that EM wave could significantly affect the male reproductive system due to the
thermal and non-thermal effects especially on human spermatozoa.
2
In normal practice, there are some conductive metallic items such as coin,
ring, zip, and belt placed inside and in close proximity to the trousers pocket, hence
they have become very close to the mobile phone antenna. Besides, patients who
suffer from bone fracture are having orthopedic implant such as bone plate, screw,
pins, rods implanted inside their body. These metallic implants when exposed to the
radiation source could enhance the current density in nearby body tissue when
compared to the body model without any implant [5]. The finding in [5] has shown
that the significant increase in current density however exceeded the restriction
recommended by International Commission on Non-Ionizing Radiation Protection
(ICNIRP). In recent years, numbers of studies have focused on the effect of metallic
implant inside the head [6-8] and body [9-12]. Research in [6] has found that the
conductive metallic implant notably increases the Specific Absorption Rate (SAR)
inside the head by 162% for 1g SAR and 64% for 10g SAR.
Besides, numerous studies have examined the interaction between the EM
fields radiated by the mobile handset with the human head [13-19], the human head
and hand [19-21], and also with additional conductors such as external objects (wire-
framed spectacles, braces, ring, bangles, hands-free, earring, zip, coin) [22-27] that
may also have effects on the amount of the EM field radiated by the antenna.
Researches [19, 22-26] have found that the presence of additional external
conductors may change the amount of energy absorption inside the human body.
Moreover, researchers in [25] who have investigated the effect of common metallic
items placed inside the trouser pocket (zip, coin, and ring) on SAR suggested that the
small increment of SAR values in the testicles could be very important than the same
increase in the leg.
3
1.2 Problem Statement and Significance of the Research
In recent years, there have been considerable research efforts devoted to the
effect of human head on antenna performance especially for mobile phone and
wireless devices [28-32]. These published researches reported that the presence of
human head in close proximity to the antenna has significantly detuned the antenna
resonance. Part of the energy radiated by the antenna is absorbed by the body hence
modifying the antenna efficiency and radiation pattern. In addition to that, some
researches [6, 26, 33, 34] have shown that the presences of additional metallic
objects near the antenna and the human body have notable effect on the amount of
energy absorbed by the body. Therefore it is expected that this condition will further
modifies the antenna performance. However the effect of human body on antenna
performance in the presence of metallic object has received limited attention in the
literature. Therefore, this research aims to further investigate the effect of additional
metallic items (such as coin, ring and zip) on antenna performance at 0.4 GHz,
0.9 GHz, 1.8 GHz and 2.4 GHz. These frequencies are chosen to represent the
frequency for walkie-talkies, GSM band and ISM band where the operating devices
are used in close proximity to the human body.
In addition, rapid development and usage of mobile devices has raised the
public concern on any possible health effect due to the amount of energy absorbed by
the body. The condition is further worrying as some researchers [22, 26] have found
that the common metallic items worn on the human head enhances the energy
absorbed by 25%. In practice, the mobile phone is placed near the head while in
used, but left for longer duration inside the trousers pocket while not in used.
Therefore, the effect of antenna radiation on the waist part of the body is placed in
doubt, especially when it could consequently affect the human sensitive organ
(testicle). Besides, study in [4] has demonstrated that the presence of EM radiation
increases the temperature inside the testicle and affect the behavior of the normal
sperm.
4
The issue complicates further by the presence of additional metallic items
inside the trousers pocket. The additional metallic items such as key, coin and
keychain ring that are usually left inside the trousers pocket may enhance the energy
radiated by the antenna and thus increases the temperature and the amount of energy
absorbed by the body and the sensitive organ. Very little works have been done on
the effect of EM field on human sensitive organ (testicular) in the presence of any
additional metallic objects [25]. Therefore, this research will further investigate the
effect of common metallic items on the amount of energy absorbed by the body,
focusing on the waist area including the testicle tissues.
On the other hand, as the presence of external metallic objects is expected to
further enhances the energy absorbed by the body and affecting the testicle tissues,
the presence of additional metallic items implanted inside the waist area are also
another concerning matters. Previous researches have shown that the presence of
conductive implant has increased the current distribution and SAR inside the human
body [5, 9, 35]. Research in [9] focuses on small size metallic implant and the
results demonstrated that the effect on SAR is less significant. However, larger size
of conductive implant is expected to have significant effect on SAR. To date, there
is no available research investigating the effect of medical implant near the
reproductive organ. Therefore this research will examine the effect of larger size
conductive implant (bone plate and intramedullary nail) on antenna performance and
SAR focusing on the waist area including the men sensitive organ.
Moreover, most researches have been focusing on the far-field interaction of
the human body in the vicinity of additional metallic objects [11, 16, 26, 36-38]. To
the best of our knowledge, there are very limited number of researches that focused
on the near-filed effect of external metallic objects [25] and conductive metallic
implant [35, 38] especially in the waist area. Such work is crucial and worth further
investigations since the implants, particularly near to the leg area is typically very
close to the human sensitive organ. The presence of the conductive implant in the
near-field exposure is expected to significantly increases the SAR in the testicle since
the position of the testicle is considerably close to the mobile antenna when it is left
5
inside the front trousers pocket. Hence, this research aims to investigate and analyse
the effect of human body, external metallic objects and medical implant on antenna
performance and SAR in near-field exposure.
1.3 Objectives
The main objective of this research is to evaluate the effect of human body on
antenna performance and energy absorbed by the human body in the presence of
metallic objects (common external metallic objects and medical implants). The
effect on human sensitive organ (testicular) will also be addressed in this research.
This research involves numerical simulation and also measurement for validation
purposes.
The objectives can be summarized as follows:
To evaluate the effect by the presence of human body close to the antenna on
antenna performance and SAR at 0.4 GHz, 0.9 GHz, 1.8 GHz and 2.4 GHz
To determine and analyse the effect by the presence of external metallic
objects and metallic implant closed to the human body on the antenna
performance and SAR
To construct simple measurement set-up in order to measure and validate
SAR in the waist area at 2.4 GHz
6
1.4 Scope of Research
The evaluations on antenna performance and SAR due to conductive metallic
items involve a series of research work. This research is done based on the following
scope:
• Literature review on the interaction between the human body and antenna
performance and also the factor that possibly affect the SAR.
• In order to study the effect of different dielectric properties of body model on
antenna performance and SAR, three types of body models are considered in
this research which are: simple cylindrical homogeneous body model,
realistic Voxel body model and homogeneous Voxel body model.
• Simulate two types of antenna (λ/2 dipole and PIFA) in freespace condition at
four frequencies; 0.4 GHz, 0.9 GHz, 1.8 GHz and 2.4 GHz.
• Then, the body model is included in the simulation and the antenna is place
next to the leg. The orientation of the antenna is varied to vertical and
horizontal orientation with respect to the body in order to study the effect of
human body on antenna performance.
• Additional metallic items (coin, keychain ring and zip) made of copper and
conductive medical implant (bone plate and intramedullary rod) made of
stainless steel are then introduced in the simulation. The antenna
performance and SAR with and without the presence of conductive items are
compared.
• Further investigation and evaluation on the factor that affect the SAR
distributions by varying the radius of ring, r, the length of intramedullary rod,
lr and bone plate.
7
• Measurement system is constructed for validation purpose using body
phantom made of fiberglass. The body phantom is filled with muscle
equivalent liquid at 2.4 GHz . Then, simulations and measurements results
are compared and examined.
• Simulated and measured results are analyzed and discussed the in terms of
S11, antenna radiation pattern, SAR and current density.
1.5 Organization of Thesis
This thesis consists of seven chapters:
Chapter 1 presents a brief introduction of the thesis including the problem statement,
the significance of the research, the objectives, and the scope of research.
Chapter 2 is an overview on the previous work related to this research. The basic
concept of EM wave, the interaction between the EM wave and the human body with
and without the presence of metallic object, the energy absorption by the human
tissues is also discussed in this chapter.
Chapter 3 presents the methodology and the project flow involved in this research.
This project includes simulation and measurements that will be explained in details
in this chapter.
In chapter 4, the effect of external metallic items on antenna performance and SAR
are discussed. The metallic items are designed as a coin, ring and zip. The size of
8
the ring is varied as well as the homogeneity of body model (homogeneous and
inhomogeneous). The results are presented in the form of antenna performance and
SAR.
Chapter 5 analyses the simulation results on the effect of human body in the presence
of medical implants. In order to identify the factors that affect the energy
distribution and absorption, two types of medical implants (intramedullary nail and
bone plate) with different length are considered in this research. The effect of using
different types of body model also have been investigated and discussed in this
chapter.
Chapter 6 discusses the measurement results. All measurements are conducted at
2.4 GHz using dipole antenna as the radiation source. The measured results are
compared and further validate the simulation results.
The conclusions and summary on the research work are stated in Chapter 7 together
with the recommendation for additional study.
References are listed at the end of this thesis.
120
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