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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