MICROWAVE REFLECTOMETER FOR SOIL MOISTURE AND …eprints.utm.my/id/eprint/78618/1/ThenYiLungPFKE2016.pdfeksperimen makroskopik dan mikroskopik. Sepanjang penyelidikan ini, empat sensor

MICROWAVE REFLECTOMETER FOR SOIL MOISTURE AND

PERMITTIVITY MEASUREMENT

THEN YI LUNG

UNIVERSITI TEKNOLOGI MALAYSIA

MICROWAVE REFLECTOMETER FOR SOIL MOISTURE AND

PERMITTIVITY MEASUREMENT

THEN YI LUNG

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Doctor of Philosophy (Electrical Engineering)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JANUARY 2016

iii

To my beloved family and friends,

iv

ACKNOWLEDGEMENT

I would like to express my deepest gratitude to my main supervisor, Dr. You

Kok Yeow, who made all this possible, for his help, guidance, patient and support

throughout this study. I am grateful to two of my co-supervisors, Assoc. Prof. Dr.

Ngasri Dimon and Dr. Tan Tian Swee, who have given advices and suggestions that

contributed directly to this thesis.

I appreciate Universiti Teknologi Malaysia for providing me with Zamalah

Scholarships for three years and also Ministry of Higher Education Malaysia for

providing research grants in order for our research works to proceed. Many thanks to

the officers in Radar Communication Laboratory, Faculty of Electrical Engineering,

Universiti Teknologi Malaysia.

Finally, special thanks to my family and friends for their continuous

encouragement and support throughout the time.

v

ABSTRACT

Microwave sensors are commonly used for aquametry measurements due to

strong tendency of water molecule in absorbing microwave signals. Nowadays,

meter-based microwave system is in demand as more applications need concept of

being portable and simple. This thesis presents a microwave reflectometer, which

operates between 2.2 GHz and 4.4 GHz. It can measure soil moisture content, m.c.

up to 26 % with mean deviation between predicted and actual m.c. determined at ±

2.0 %. Five common soil samples found in southern region of Peninsular Malaysia,

Johor were characterized based on macroscopic and microscopic experiments.

Throughout the research, four microstrip ring resonantor sensors operating between

2.2 GHz and 4.4 GHz were designed with different angles of microstrip bends.

(Conventional Sensor = 0.98 rad., Sensor A = 1.34 rad., Sensor B = 1.57 rad., and

Sensor C = 1.64 rad.). Sensor B was chosen as the soil sensor. A critical study on the

use of microstrip ring resonator sensors for the determination of both permittivity, εr

and m.c. from the measured scattering parameters (S-parameters) in conjunction with

E5071C vector network analyzer (VNA) was presented. The relationship between the

measured εr and m.c. obtained from the oven drying method was established. From

the results, it was observed that two dielectric relaxation conditions (bound and free

water) exist in soil-water mixture. A semi-empirical equivalent lumped element

model was created based on simulation data obtained from Microwave Office

(AWR) software. The predicted εr results from the model agree with the measured

data using commercial HP85070D dielectric probe. The model successfully

estimated εr for the five common soil types with error of 2.5 %. By using inverse

algorithm from the model, m.c. was predicted and was in good agreement with the

standard oven drying method with its average error within ± 1.5 % for all soil

samples. In general, microwave reflectometer with the proposed MRR sensor,

provide nondestructive measurement for rapid determination of soil m.c. and εr.

vi

ABSTRAK

Sensor gelombang mikro biasanya digunakan untuk ukuran aquametrik

kerana kecenderungan yang kuat pada molekul air dalam serapan isyarat gelombang

mikro. Kini, sistem meter gelombang mikro banyak diperlukan kerana kebanyakan

aplikasi memerlukan konsep mudah-alih dan kurang komplikasi. Tesis ini

membentangkan reflectometer yang beroperasi antara 2.2 GHz dan 4.4 GHz.

Reflectometer ini boleh mengukur kelembapan (m.c.) tanah sehingga 26 % dengan

sisihan minima antara ± 2.0 %. Lima jenis sampel tanah yang biasa ditemui di

kawasan selatan Semenanjung Malaysia, Johor telah dicirikan berdasarkan

eksperimen makroskopik dan mikroskopik. Sepanjang penyelidikan ini, empat sensor

gelombang mikro yang beroperasi antara 2.2 GHz dan 4.4 GHz telah direka dengan

pelbagai sudut selekoh mikrostrip. (Sensor Konvensional = 0.98 rad., Sensor A =

1.34 rad., Sensor B = 1.57 rad., dan Sensor C = 1.64 rad.). Sensor B telah dipilih

sebagai sensor tanah. Kajian kritikal terhadap penggunaan sensor gelombang mikro

untuk menentukan ketelusan (εr) and m.c. tanah dengan ukuran dalam S-parameter

melalui penggunaan E5071C penganalisis rangkaian vektor (VNA) telah

dibentangkan. Hubungan antara εr yang diperolehi dan m.c. yang ditentukan dengan

kaedah pengeringan oven telah dikenalpastikan. Dua keadaan relaksasi dielektrik

(terikat dan bebas) yang berlaku dalam pengukuran tanah telah ditunjukkan daripada

analisa keputusan. Model semi-empirik elemen telah dicipta berdasarkan data

simulasi yang diperolehi daripada perisian Microwave Office (AWR). Keputusan εr

yang diramalkan daripada model bersetuju dengan data yang diukur dengan

menggunakan HP85070D kit dielektrik. Model ini berjaya menganggarkan εr untuk

lima jenis sampel tanah dengan ralat 2.5 %. Daripada formula ekoran model ini,

penganggaran m.c. dapat ditentukan dan bersetuju dengan kaedah pengeringan oven

dengan ralat ± 1.5 % untuk semua jenis sampel tanah. Secara umum, reflectometer

yang bersepadu dengan sensor yang dicadangkan itu dapat memberikan pengukuran

yang tidak memusnahkan sampel dalam penentuan m.c. tanah dan εr.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION

ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xii

LIST OF FIGURES xv

LIST OF ABBREVIATIONS xxiv

LIST OF SYMBOLS xxvi

LIST OF APPENDICES xxix

1

INTRODUCTION

1

1.1 Research Background

1.2 Problem Statement

1.3 Research Objectives

1.4 Scope of work

1.5 Research Contributions

1.6 Thesis Organization

1

4

6

6

8

11

2

LITERATURE REVIEW

13

2.1 Microwave Aquametry Techniques 13

2.1.1 Microwave Sensors 14

2.2.2 Design Art of Microwave Sensors (Soil

viii

Measurement Applications) 15

2.1.3 Design Art of Microwave Sensors (For

Arbitrary Material)

22

2.1.4 Microwave Sensor Study Summary 24

2.2 Soil Type and Quality Study 28

2.2.1 Moisture Measurements 28

2.2.2 pH Measurements 30

2.3 Moisture Measurement Technologies and Trends 31

2.3.1 Oven Drying Method 31

2.3.2 Nuclear Method 31

2.3.3 Optical Method 32

2.3.4 Tension Method 32

2.3.5 Electrical Method 33

2.3.6 Microwave Method 33

2.3.7 Summary of Moisture Measurements 34

2.4 Microwave Reflectometer 36

2.4.1 Microwave Signal Generator 38

2.4.2 Power Detector 39

2.5 Microstrip Ring Resonator (MRR) 39

2.5.1 Magnetic Wall Model 40

2.5.2 Wall Admittance Formulation 43

2.5.2.1 Mutual Admittance 43

2.5.2.2 Self-Admittance 45

2.5.2.3 Input Impedance Formulation for the

Dominant Mode

47

2.5.3 Conducting Grounded Plane 50

2.5.4 Four-Legged Element Structure 51

2.5.5 Characteristic Impedance Matching of

Microstrip Line

52

2.5.6 Mitered Bends in MRR 53

2.5.7 Lumped-Element Equivalent Circuit 55

2.6 3-dB Branch-Line Directional Coupler 56

2.6.1 Multi Branch-Line Directional Coupler 57

ix

2.6.2 Miniaturized Multi Branch-Line Directional

Coupler

58

2.7 Permittivity and Conductivity Measurements 61

2.7.1 Resonance and Quality Factor 62

2.7.2 Reflection Scattering Measurement 63

2.7.3 Permittivity and Conductivity Measurements

Using Frequency-variation Method

64

2.8 Chapter Summary 65

3

METHODOLOGY AND DESIGN PROCEDURES

67

3.1 Fabrication of Reflectometer for Soil Measurements 68

3.1.1 Fabrication of Wideband Branch-Line

Directional Coupler

69

3.1.2 Reflectometer Assembly 69

3.1.3 Graphical User Interface (GUI) 70

3.2 Design and Simulation of MRR Sensor 71

3.3 Fabrication of MRR Sensors 72

3.4 Soil Under Test (SUT) 73

3.4.1 SUT Preparation 73

3.4.2 Measurement of pH and Relative Permittivity

of Various Soil Types

75

3.4.3 Determination of Soil Particles and Content 76

3.5 Soil Measurement 77


4

MRR SENSORS AND SOIL REFLECTOMETER FOR

MICROWAVE AQUAMETRY MEASUREMENTS

79

4.1 Characteristics Design of MRR Sensors 79

4.1.1 General Input Impedance Based on

Admittance Model

82

4.1.2 Effects of Mitered Bending Structures 83

4.1.3 S-Parameters Measurements for MRR Sensors 84

4.1.4 Power Loss of MRR Sensors 86

x

4.1.5 Equivalent Distributed Lumped Element

Model

87

4.1.6 Contour Mapping of Magnetic Field for MRR 89

4.1.7 Significant Sample Thickness of MRR Sensors 90

4.2 Soil Reflectometer System 90

4.2.1 Four-Port Branch-Line Directional Coupler 92

4.2.1.1 Implementation of Open Stubs 93

4.2.1.2 S-Parameters Measurements for Four-

Port Branch-Line Directional Coupler

95

4.2.1.3 Phase Difference between Transmitted

and Coupled Port

96

4.2.1.4 Performances of Four-Port Branch-

Line Directional Coupler

97

4.2.2 Simulation and Measurement for Soil

Reflectometer

98

4.2.3 Development of GUI for Soil Reflectometer 99


5

STATISTICAL PROPERTIES OF SOIL QUALITY

FOR MICROWAVE AQUAMETRY APPLICATION

IN MALAYSIA

101

5.1 Physical Tests for Various Soil Types 103

5.1.1 Magnification Images for Various Soil Types

with Respective Bulk Density

103

5.1.2 Trace Element Content for Various Soil Types 108

5.1.3 Soil Moisture and Its Influence on Soil pH 109

5.1.4 Dielectric Properties for Various Soil Types In

Dry Condition

112

5.1.4.1 Resonance Technique (MRR) 112

5.1.4.2 Cavity Perturbation Technique

(Coaxial Cavity Sensor)

114

5.1.4.3 Open-Ended Coaxial Probe Technique

(Dielctric Probe HP85070D)

115

xi

5.1.4.4 Dielectric Properties Determination 116

5.1.5 Soil Sample Classifications 118

5.2 Determination of Bound and Free Water 118

5.3 Determination Permittivity and Conductivity in Soil-

Water Mixture

123

5.4 Lumped Element Modelling for Soil Moisture and

Dielectric Prediction

135

5.4.1 Phase Adjustment and Correction of Return

Loss

136

5.4.2 Prediction Procedures with Objective Function 137

5.4.3 Soil Dielectric Prediction 138

5.4.4 Soil Moisture Prediction (Lumped Element

Model)

141

5.5 Soil Measurement Using Microwave Reflectometer 144

5.5.1 Soil Moisture Measurement Using

Reflectometer

145

5.5.2 Soil Dielectric Measurement Using

Reflectometer

147

5.5.3 Performances of Soil Reflectometer in

Microwave Aquametry Application

149


6

CONCLUSION AND FUTURE WORKS

152

6.1 Conclusion 152

6.2 Future Works 153

REFERENCES 155

Appendices AF 161175

xii

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Characteristics of Microwave Sensor (Soil Measurement

Applications).

26

2.2 Soil separates and their diameter ranges for three soil

types. (Rice, 2002).

28

2.3 pH ranges and influence on plant growth potential

(Whiting et al., 2014).

30

2.4 Moisture Measurement Techniques. 35

2.5 Specification Operation for ZX47-50+ Power Detector. 39

2.6 Characteristics of four port directional coupler (Muraguchi

et al., 1983).

58

3.1 Calculated respective bulk density, ρdrysoil for various soil

types.

75

4.1 Characteristics of open stubs for multi branch-line

directional coupler.

92

4.2 Dimensions for modified four-port branch-line directional

coupler.

95

4.3 Summary of performances of four-port branch-line

directional couplers.

98

5.1 Trace element contents in weight (%) through EDX

scanning analysis.

108

5.2 Trace element contents in atomic (%) through EDX

scanning analysis.

108

5.3 Relationship between soil pH and moisture content based

on gravimetric and volumetric methods for various soil

types.

111

xiii

5.4 Calculation of D for each sensor with respective mean

squared error (MSE) values.

117

5.5 Comparison between different measurement techniques for

permittivity of various soil types.

117

5.6 Classifications of soil samples found in southern region of

Peninsular Malaysia, Johor.

118

5.7 Determination of BW and FW conditions based on

gravimetric and volumetric methods.

123


permittivity of white soil at m.c.g level range between 0 %

and 30 %.

124


permittivity of yellow soil at m.c.g level range between 0 %

and 30 %.

125


permittivity of loam soil at m.c.g level range between 0 %

and 30 %.

126


permittivity of peat soil at m.c.g level range between 0 %

and 26 %.

127


permittivity of sand soil at m.c.g level range between 0 %

and 22 %.

128

5.13 Polynomial regression values for the relationship between

εr′ and m.c.g (Top) and relationship between εr′ and m.c.v

(Bottom) of white soil.

130



(Bottom) of yellow soil.

131



(Bottom) of loam soil.

132


xiv


(Bottom) of peat soil.

133



(Bottom) of sand soil.

134

5.18 Relationship between dielectric properties and various

moisture level by using gravimetric m.c.g and volumetric

m.c.v for different soil types.

142

5.19 Parametric RLC in Equation (4.4) as a polynomial

functions of relative permittivity and loss tangent.

143

5.20 Polynomial regression values for Equations (5.10), (5.11),

and (5.12).

146


and (5.15).

147


and (5.18).

149

xv

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 MRR with the strip width, ws and the ring perimeter, l

designed at 0.37 cm and 11.35 cm, respectively

(Sarabandi and Eric, 1997).

15

2.2 (a) Fabricated soil meter, (b) Architecture of microwave

soil meter consisting of a microcontroller, a voltage-

controlled oscillator (VCO), a directional coupler, and a

power detector, and (c) Dimensions and cross sectional

view of the monopole sensor (You et al., 2014).

16

2.3 (a) Fabricated HYMENET probe, with two electrodes’

length measured at 36 cm. Other details include ø = 50

mm in diameter; D = 90 mm between the axes, and h = 45

mm and (b) Dimensions and cross sectional view of the

monopole sensor (Frangi et al., 2009).

17

2.4 (a) Dimensions of the microstrip line sensor (w = 2 mm, h

= 1.6 mm) and fabricated soil moisture sensor consisting

of (b) sensor head (70 mm in length) and (c) electronic

transceiver (Rezaei et al., 2012).

17

2.5 A 1186.55 mm rectangular cavity resonator was attached

to the Vector Network Analyzer (VNA) for oil sands

measurement (Erdogan et al., 2011).

18

2.6 (a) Dimensions and cross sectional view, (b) Sensor with

filled soil sample, (c) In-situ measurement setup, and (d)

Designed helmet with (i) adapter for outer conductor and

(ii) adapter for inner conductor (Lauer et al., 2012).

18

2.7 (a) Cross-section of coaxial transmission lines (Dc = 54

xvi

mm, Hc = 44 mm, and dc = 23.5 mm), (b) Proposed

adapter with the improved Kopecky cylinder, and (c)

Kopecky sensor kits (Kitić and Bergin, 2013).

19

2.8 (a) Lengths of 1, 2, and 3 cm of two wire stainless steel

rod (D = 13 mm and ø = 2 mm in diameter), (b)

specification details of the probe, and (c) the interface

between coaxial and parallel waveguides (Skierucha and

Wilezek, 2010).

19

2.9 The coaxial probe technique for soil measurement as for

reference.

20

2.10 Dimensions for (a) Single resonant patch and (b) Dual-

resonant patch and (c) Acrylic soil holder up to 60 mm on

top of the rectangular antenna patch sensor (You et al.,

2010).

21

2.11 Dimension configurations of band-stop filter type sensors

on 12.7 mm thick Taconic CeR-10 dielectric substrate

with operating frequency at (a) 2.54 GHz and (b) 2.75

GHz (Birgermajer et al., 2011).

22

2.12 Geometry of the microstrip ring resonator on an alumina

substrate (εr = 9.98) with h = 0.0635 cm, Ro = 0.2143 cm,

Ri = 0.1543 cm, w = 0.0635 cm, and S = 0.09525 cm

(Abegaonkar et al., 1999).

22

2.13 (a) Geometry of the monopole sensor and (b)

Measurement set-up (Ansarudin et al., 2012).

23

2.14 The microstrip patch soil sensors with communication

distance of 30 m for (a) a 1.6 mm thick rigid FR4

substrate and (b) a 0.025 mm thick flexible PI substrate

(Toba and Kitagawa, 2011).

24

2.15 The block diagram of reflectometer (Plumb and Ma,

1993).

37

2.16 The cascaded bridged-T attenuators proposed in

improving directional coupler for broadband

measurements (Choi et al., 2005).

37

xvii

2.17 The microwave signal generator by Windfreak, operating

between 137.5 MHz and 4.4 GHz frequency range.

38

2.18 Magnetic wall model of the ring resonator (Chang and

Hsieh, 2004).

41

2.19 Dimensions of MRR (Chang and Hsieh, 2004). 43

2.20 The MRR modeled as radial transmission lines and load

admittances (Chang and Hsieh, 2004).

47

2.21 (a) The equivalent π-network and (b) the simplified circuit

model of the MRR (Chang and Hsieh, 2004).

49

2.22 Electric field leakage for different substrate boards: (a)

Teflon epoxy (εr = 2.55) and (b) Alumina (εr =10) (Pozar,

2012).

50

2.23 Geometry of dielectric substrate plane (a) ungrounded

metal plate and (b) grounded metal plate (Chen et al.,

2004).

51

2.24 Geometry of four-legged element structure (Munk, 2000). 52

2.25 Configuration of structures for the compensation of

MRR’s corner bends.

54

2.26 Configuration of mitered bends of MRR with its

dimensions (Douville et al., 2000).

55

2.27 Lumped element model of MRR for the input impedance,

Zin.

56

2.28 Configurations of a 3-dB four-port directional coupler. 58

2.29 Size reduction scheme using lumped to distributed

elements (Then et al., 2013).

60

2.30 Calculations of half-power bandwidth (Chen et al., 2004). 62

2.31 Determination of half-power width from S11for measuring

quality factor (Chen et al., 2004).

63

2.32 Frequency shifting for each soil type with A = fUnload and B

= fLoaded.

65

3.1 The flowchart of the overall research work. 68

3.2 The architecture of the microwave reflectometer with

MRR sensor attached at port 2 of the directional coupler.

70

xviii

3.3 The architecture of the microwave reflectometer system

with PC and DAQ as monitoring and collecting data,

respectively.

70

3.4 The flowchart of designing and simulating MRR sensors. 71

3.5 The proper working steps on fabricating the MRR sensors. 72

3.6 SUT preparation by using (a) Drying oven and (b) Kern

weighing meter.

74

3.7 (a) Cavity cube with filled SUT and (b) Soil weighing

setup. The SUT as shown is sand soil.

74

3.8 Determination of pH and dielectric properties of various

soil types by using (a) HI98127 pH tester, (b) pH meter

buried into soil sample, and (c) HP85070D dielectric

probe, respectively at room temperature (25±1) ˚C.

75

3.9 (a) Hitachi TM3000 tabletop microscopy instrument and

(b) Soil sample was placed on top of a nickel or iron alloy

with thickness 38 nm.

76

3.10 (a) Measurement setup to determine significant sample

thickness. And (b) Soil measurement setup via vector

network analyzer.

78

4.1 (a) Dimensions for the conventional microstrip ring

resonator (MRR) design with red dotted ring, representing

the calculated ring design and (b) Side view for MRR

sensor, which is grounded on an aluminium plate.

81

4.2 Flowchart of the calculation of admittance model for the

calculated ring design with resonant at 3.2 GHz. (w = 4.93

mm and l = 109.6 mm).

82

4.3 General input impedance, Zin of calculated ring design (w

= 4.93 mm and l = 109.6 mm) based on admittance model

with resultant resonance at 3.2 GHz.

83

4.4 MRR configuration structure (a) Conventional Sensor, (b)

Sensor A, (c) Sensor B, and (d) Sensor C.

84

4.5 Proposed MRR sensors with two SMA connectors at both

ends, which were attached later to the Agilent E5071C for

xix

soil measurement. 85

4.6 Simulated and measured S-parameters in response to

operating frequency between 2GHz and 4 GHz for (a)

Conventional Sensor, (b) Sensor A, (c) Sensor B, and (d)

Sensor C.

85

4.7 Simulated and measured (a) power loss and (b) operating

resonance frequency in response to different mitered

bending angles.

86

4.8 Resistor-Inductor-Capacitor (RLC) distributed lumped

element circuit model for the input impedance, Zin of

MRR.

88

4.9 Lumped capacitance values for (a) Capacitor 1, C1 and (b)

Capacitor 2, C2 in response to different mitered bending

angles of the four proposed MRR sensors.

88

4.10 Contour mapping of magnetic field, Hø surrounding

structure designs for (a) conventional sensor, (b) Sensor

A, (c) Sensor B, and (d) Sensor C.

89

4.11 Variation in magnitude of return loss with air thickness, d

at respective operating frequency for four MRR sensors.

90

4.12 (a) Architecture of microwave soil reflectometer and (b)

Microwave sensor system for microwave soil aquametry

measurements.

91

4.13 Simulated S-parameters of the four-port branch-line

directional coupler based on different stub length, Stub A

= 5.8 mm in length; Stub B = 6.4 mm in length and Stub C

= 8.8 mm in length.

94

4.14 Modified four-port branch-line directional coupler design

with the allocation of stub B.

94

4.15 (a) Fabricated directional coupler with size reduction of

40 % and (b) Comparison between conventional and

modified directional coupler.

96

4.16 Simulated and measured S-parameters of the modified

directional coupler.

96

xx

4.17 Simulated and measured phase difference between S21 and

S31 of the modified four-port branch-line directional

coupler at 90˚.

97

4.18 The microstrip design for the combination of 4-port

branch-line directional coupler and Sensor B.

98

4.19 Return loss, S11 for air measurement by using simulated

and actual soil reflectometer at room temperature (25 °C).

99

5.1 The general flow of the investigation results of soil quality

determination for MRR sensors and microwave

reflectometer.

102

5.2 Images taken on the SEM for white soil with three

magnification scales of (a) ×500, (b) ×1000, and (c)

×3000.

104

5.3 Images taken on the SEM for yellow soil with three


×3000.

105

5.4 Images taken on the SEM for loam soil with three


×3000.

106

5.5 Images taken on the SEM for peat soil with three


×3000.

106

5.6 Images taken on the SEM for sand soil with three


×3000.

107

5.7 Relationship between soil pH and soil moisture based on

two methods: (a) Gravimetric and (b) Volumetric.

109

5.8 Frequency shifting for each soil type with MRR sensors:

(a) Conventional Sensor, (b) Sensor A, (c) Sensor B, and

(d) Sensor C; with A = fUnload and B = fLoaded.

113

5.9 Sensitivity, S of the MRR sensors in response to various

soil types at room temperature (25 ± 1) °C.

114

5.10 Coaxial cavity waveguide sensor with (a) Components of

xxi

coaxial cavity sensor, (b) Measurement setup, and (c)

Dimensions of coaxial cavity sensor.

115

5.11 Measurement setup with (a) HP85070D dielectric probe

and (b) soil permittivity measurements setup.

116

5.12 Measured return loss, S11 for each gravimetric m.c.g values

up to 30 % of white soil type for (a) Conventional, (b)

Sensor A, (c) Sensor B, and (d) Sensor C at room

temperature (25 ± 1) °C.

119


up to 30 % of yellow soil type for (a) Conventional, (b)



120


up to 30 % of loam soil type for (a) Conventional, (b)



121


up to 26 % of peat soil type for (a) Conventional, (b)



121


up to 22 % of sand soil type for (a) Conventional, (b)



122

5.17 Variations in relative dielectric constant and loss factor of

white soil. (a) Gravimetric method: 0 – 30 % m.c.g and (b)

Volumetric method: 0 – 25.1 % m.c.v at room temperature

(25 ± 1) °C.

130


yellow soil. (a) Gravimetric method: 0 – 30 % m.c.g and

(b) Volumetric method: 0 – 27.6 % m.c.v at room


131


xxii

loam soil. (a) Gravimetric method: 0 – 30 % m.c.g and (b)


(25 ± 1) °C.

132


peat soil. (a) Gravimetric method: 0 – 26 % m.c.g and (b)


(25 ± 1) °C.

133


sand soil. (a) Gravimetric method: 0 – 22 % m.c.g and (b)


(25 ± 1) °C.

134

5.22 Simulated data for empirical lumped element model for

Sensor B by using AWR simulator for relative dielectric

constant, εr′ (1 to 10) and loss tangent, tan δ (0.01 to 0.2).

135

5.23 Side view of MRR on an aluminium plate with SMA

connector.

136

5.24 (a) Simulated and measured |S11| for Sensor B, and (d)

Simulated, measured, and measured phase shifting by

Equation (5.6) for Sensor B.

137

5.25 The variations in relative dielectric constant, εr′ for (a)

white soil, (b) yellow soil, (c) loam soil, (d) peat soil, and

(e) sand soil with changes in gravimetric moisture content,

m.c.g at room temperature (25 ± 1) oC.

139

5.26 The comparison between predicted and measured

moisture content, m.c.g of white, yellow, loam, peat, and

sand soil at room temperature (25 ± 1) oC.

141

5.27 Variation in return loss, |S11| with frequency, f of various

gravimetric (left) and volumetric (right) m.c. level for (a)

White soil, (b) Yellow soil, (c) Loam soil, (d) Peat soil,

and (e) Sand soil at room temperature (25 ± 1) oC.

144

5.28 The comparison between predicted and measured

moisture content, m.c. of white, yellow, loam, peat, and

sand soil at room temperature (25 ± 1) oC.

146

xxiii

5.29 The comparison between measured dielectric constant, ε′r

using HP85070D dielectric probe and fabricated

microwave reflectometer at room temperature (25 ± 1) oC.

148

xxiv

LIST OF ABBREVIATIONS

BW - Bound Water

CST - Computer Simulation Technology

DAQ - Data Acquisition Unit

DC - Direct Current

DGS - Defected Ground Structure

EDX - Energy-Dispersive X-ray

EM - Electromagnetic

FDR - Frequency Domain Reflectometry

FSS - Frequency Selective Surfaces

FW - Free Water

GDP - Gross Domestic Product

GUI - Graphical User Interface

HYMENET - Hygrometric Measurement Network

ISM - Industrial, Scientific, and Medical

MRR - Microstrip Ring Resonator

MSE - Mean Squared Error

NI - National Instrument

NPK - Nitrogen, Phosphorus, and Potassium Analysis

PC - Personal Computer

PCB - Printed Circuit Board

RF - Radio Frequency

RLC - Resistor-Inductor-Capacitor

RMSE - Root Mean Square Error

SEM - Scanning Electron Microscope

SMA - SubMiniature version A

SUT - Soil Under Test

SWR - Standing Wave Ratio

xxv

TDR - Time Domain Reflectometry

TE - Transverse Electric

TM - Transverse Magnetic

VCO - Voltage Controlled Oscillator

VNA - Vector Network Analyzer

VSWR - Voltage Standing Wave Ratio

xxvi

LIST OF SYMBOLS

m.c. - moisture content

εr - relative permittivity

εr′ - dielectric constant

εr˝ - loss factor

|| - reflection coefficient

m.c.g - gravimetric moisture content

m.c.v - volumetric moisture content

|S11| - return loss

λ - wavelength of electromagnetic wave

tan δ - loss tangent

mwater - weight of water

mdrysoil - weight of dry soil sample

Vwater - volume of water

Vdrysoil - volume of dry soil sample

Vcube - volume of the cavity cube

ρdrysoil - dry soil bulk density

ρwater - density of water

- conductivity

|S21| - transmission coefficient

fr - resonant frequency

GS - antenna gain of the sensor

GM - antenna gain of the transmitter and receiver

Q - quality factor

PRX - power receiver

PTX - power transmiter

LP - conversion loss

εeff - effective relative permittivity

xxvii

r - mean radius of the ring

n - mode number

c - speed of light in vacuum

λg - guided wavelength

a - inside radius of ring

b - outside radius of ring

c - feed point radius of ring

ψ - specific field function

k - propagation constant

ω - angular frequency

µ0 - permeability of free space

ε0 - permittivity of free space

Jn - nth-order Bessel function

Yn - nth-order Neumann function

Ym - mutual admittance

Ea - radial electric fringing aperture fields at a

Eb - radial electric fringing aperture fields at b

Ys - self- admittance

gs - self-conductance

bs - wall susceptances

Zin - input impedance

θi - incident angle

d - thickness of grounded plane

w - microstrip line’s copper width

h - substrate thickness

Ploss - power loss

L - inductance

C - capacitance

R - resistance

Z0 - characteristic impedance of the feed line

θ - electrical length

B01 - susceptance for stubs

θs - degree of freedom

xxviii

βi - coupling coefficients

QL - loaded quality factor

Q0 - unloaded quality factor

fUnload - unloaded resonant frequency

fLoaded - loaded resonant frequency

D - filling factor

VA - reflected voltage

VB - incident voltage

ø - bending angle

Z01 - impedance of open stub

θ01 - electrical of open stub

SR - size reduction

Smax - maximum sensitivity

Smin - minimum sensitivity

S - sensitivity

Rs - resolution

ko - propagation constant

z - distance of transmission line in coaxial cavity

TLoaded - transmission coefficient with sample

TUnload - transmission coefficient without sample

fBW - bandwidth

A - calculated deviation length of MRR

G - relative average error

fs - frequency shifting

xxix

LIST OF APPENDICES

APPENDIX TITLE PAGE

A List of Publications 161

B Graphical User Interface for Microwave

Reflectometer

162

C MATLAB Code for MRR Admittance Wall Model 163

D MATLAB Code for Dielectric Prediction Using

Lumped Element Model

166

E Bound and Free Water Conditions (Volumetric

Methods)

168

F Relationship Between Permittivity and Volumetric

m.c.

171

CHAPTER 1

INTRODUCTION

1.1 Research Background

Microwaves in radio frequency (RF) engineering are a form of

electromagnetic radiation with wavelengths ranging from as long as one meter to as

short as one millimeter. Microwaves as designated in S-band frequency (2 GHz to 4

GHz) are commonly used in human applications, such as microwave oven and

communication devices. Since the discovery and development of microwave

technologies, these technologies have become common in different fields of study,

both commercial and private industries. For this reason, recently, the microwave

electronic components are widespread in the market with affordable price. This

situation becomes an absolute advantage for researchers to apply microwave

technologies to other fields of science, such as food industry, biomedical

applications, and agricultural industry. One of the most common microwave

products, microwave oven has been introduced in our daily life. The concept of using

microwaves in heating the food is due to the polarization of water molecule

contained in the sample which is sensitive, and is showing significant response when

exposed to microwave energy. Besides, the tendency of water molecule to absorb

microwaves, allowing the microwave techniques to be successfully applied in

microwave aquametry research with ideas of determining moisture content, m.c. in a

materials containing water (Troughton, 1969 and Sarabandi and Eric, 1997).

In developing world, agriculture is often seen as a “leading edge” of a region

or country’s early commercial growth which has a multiplier effect on the overall

economy (Miller, 1995). The concern with soil quality and maintaining it under

intensively cropped systems is important. The development of civil engineering due

2

to increase of population in Malaysia has also brought soil quality into significant

research study. Soil quality is important in the fact that building cement blocks are

made up of soil, water, and cement. Therefore, good monitoring of soil quality will

lead to strong building structures. Soil quality is macroscopically and

microscopically determined based on physical properties (soil texture, moisture

content, m.c. and relative permittivity, εr) and chemical properties (pH, base

saturation, and soil acidity).

Soil moisture content, m.c. is categorized as one of the most necessary

physical characteristics in various sectors such as agriculture, civil engineering,

landscaping, irrigation engineering, and hydrology, since the consistency and

workability of a clayey soil strongly depend on its m.c. Moisture content, m.c. is

divided into bound water and free water conditions. You et al., (2013) stated that

different soil types may have different bound water and free water levels. There are

two standard methods of determining m.c. of soil, which are divided into the direct

and indirect methods. Direct method determines m.c. by removing the water

molecules from the soil-water mixture sample with the oven drying technique. This

method is accurate but it is not preferable due to time consuming. On the contrary,

indirect method requires the measurement of the electrical properties in the soil-

water sample by using fabricated instrument, so-called moisture detection meter. The

change in electrical properties will be directly correlated with a change in the actual

m.c. of the respective soil obtained from oven drying method (direct method).

Recently, indirect methods become more popular than the direct method due to well

continuity of testing, real time measurement, good sensitivity, instantaneous results,

and with good user-friendly features (Skierucha and Wilezek, 2010 and You et al.,

2013).

The interaction between agri-foods materials with microwave can be

described by the complex relative permittivity, εr in Equation (1.1).

rrr j (1.1)

where the real part of permittivity which is known as dielectric constant, εr′ is an

important parameter in food and agricultural industries processing using microwave

techniques. On the other hand, the imaginary part, εr″ is the dielectric loss factor

3

which is influenced the energy absorption or attenuation of the material. In fact, εr˝

varies greatly between soil types (Skierucha et al., 2010) due to different trace

elements content in soils, terrain either in vegetative or mountainuous structure

(Lesmes et al., 1999), and moisture content, m.c. (Sarabandi and Eric, 1997, Storme

et al., 1999, and You et al., 2013). Both εr′ and εr″ are highly correlated with

moisture content, since at microwave frequencies, the electromagnetic energy are

mainly absorbed by water and the volume of moisture in the total volume of material

most heavily influences the effective relative permittivity of the material. This is due

to the relative permittivity of water (εr = 80 at DC stage) normally being much

greater than that of the other constituents in soil (mineral soil: 4, organic matter: 4,

air: 1). If the value of the effective relative permittivity changes in the soil sample,

the microwave device will measure a change in reflection /transmission coefficient or

resonant frequency that can be directly correlated with a change in moisture content,

m.c. of the soil, which was obtained from oven drying method. Thus, the dielectric

measurements can be used to monitor the moisture content, m.c. inside the soil under

test. Although measurement of permittivity, εr is well established, there is a lack of

dielectric characterization study based on different soil types and this further gives

great motivation for this overall study. In addition, reliable microwave aquametry

measurement system which appears as a useful tool to investigate and determine

permittivity, εr and moisture content, m.c. level of various soil types also not

diffusely available worldwide.

There are numerous microwave techniques to determine εr′, such as

microstrip ring resonator (MRR) technique, which has different working principles

comparing with the dielectric probe technique, monopole sensing technique, and

coaxial cavity technique. Since soil particles are not uniformly distributed, air gap do

exists in between soil individual particles. Although dielectric probe technique is

fast, but it is less preferred for good measurement technique due to its high

sensitivity toward the presence of air gaps and also the applied pressure, which

contributes to degradation in term of the accuracy (Sarabandi and Eric, 1997).

Generally, monopole structure sensor technique is slightly difficult when burying the

sensor into the soil for measurement. Commonly, measurement by using monopole

sensor is too sensitive and the obtained results often provide large uncertainties (You

et al., 2013). Consequently, decreases the precision and repeatability of the

measurement. Coaxial cavity techniques had been widely used to perform

4

nondestructive dielectric constant measurements of materials. This technique is

accurate but it is related to difficulties in loading and unloading samples (Joshi et al.,

1997). Resonant methods have higher accuracies and sensitivities, and they are most

suitable for low-loss samples; in this case; soil samples (Chen et al., 2004).

As a consequence, permittivity, εr and moisture content, m.c. level of various

soil types remain as interesting research topics to be explored by the microwave

propagation communities. This research work aimed to fill these knowledge gaps by

investigating several physical phenomena and specificities of various soils types

particularly in southern region of Peninsular Malaysia, Johor using microwave

sensing that could possibly lead to agricultural processing industry using microwave

techniques.

1.2 Problem Statement

First problem statement discussed on the necessity for microwave soil

aquametry sensor and such measurement is represented in frequency-domain

analysis. Time-domain reflectometer, which firstly introduced in 1970’s is

commonly applied now in most soil measurement study. However, these DC time-

domain type sensors can only detect the existence of water and no-water conditions

but cannot exactly display a range percentage of moisture content, m.c., which is

required at most. Infrared sensor is less precise and sensitive as compared to

microwave sensor due to soil sample is in-homogenous and infrared sensing is based

on one particular dotted area. Optical technique is also used in soil measurement

study. The optical calculation is based on the change of refractive index of sample, n.

For microwave sensor, it is based on the change of permittivity, εr. As know that, n2=

εr. Thus, principally, microwave sensor is more sensitive as compared to optical-type

sensor. Moreover, this kind of measurement system cannot provide insight and point

out properties that are hard to discern or observe such as the soil permittivity.

Representation of soil characteristics is more convenient and intuitive when working

in the frequency-domain because signal can be represented by magnitude and phase

as functions of frequency.

Malaysia has been a successful developing country, excellent in agriculture

5

and civil construction sectors. Agriculture sector is the main economic supporter in

Malaysia. Nearly twenty four percent of Malaysia’s land area is composed of land

dedicated to agriculture alone. Palm oil is the main commodity in Malaysia’s

agricultural sector and contributes nearly 9 percent to the Gross Domestic Product

(GDP). Malaysia is the second largest producer of palm oil in the world and is

responsible for one third of the world’s rubber exports. Other agriculture products

including rice, cocoa, timber, coconut, and pineapple also contribute to the

economics’ growth. Soil provides proper nutrition, growth, and life of plants. The

optimal soil moisture level is the main factor that affects plants’ growth and well

development. Recently, civil construction is rapidly developed in Malaysia to

provide more homes due to increased of population. Soil is important ingredients in

the cement mixture and water defines the soil quality. Consistency in mixing and

moisture is the key to good quality concrete block. Maintaining right quantity usage

of soil and water in cement block mix not only produces good quality blocks but also

cost savings in long term. Therefore, proper control and monitor of soil quality is

significant for strong fundamental of buildings. Since water is an important

characteristic of many natural and man-made products or is introduced during

technological processes, it is quite obvious that measurement and control of moisture

content, m.c. have great economic contribution and technical importance. Hence, in

order to estimate reliable specific moisture content, m.c. values of soils for some

plantations and constructions, it is therefore of key importance to carefully assess the

relationship between soil quality and moisture content, m.c. rates from times to

times.

Third factor is due to inconsistent soil classifications for every country. The

first classification, the International System, was first proposed by Albert Atterberg

in 1905, and was based on his studies in southern Sweden for that time agricultural

purposes. The soil classification may differ from our country due to different climatic

regions. Till today, there is still no uniform data for soil classifications in Malaysia

yet. Through the macroscopic and microscopic testing on various soil types in

Malaysia, it is possible to find out the interaction between the measurement data and

establish the relationship between soil particle sizes and soil dielectric properties. By

determining the particle sizes based on soil dielectric properties is considered a novel

and non-destructive technique for soil research industry. This is another milestone

for us to determine our own particle sizes classifications for Malaysia based on

6

tropical climate. Even though the collected soil database may not applicable for

universal use but it is possible to be used as references for current ongoing and future

soil research studies.

1.3 Research Objectives

In regards to recent technological advances and problems mentioned above,

the main goal of this study is to provide critical information for the moisture

variation and permittivity of various soil types, particularly in southern region of

Peninsular Malaysia, Johor by developing the reflectometer with resonator type of

sensors. More specifically, the main research objectives are listed below:

i. To construct a reflectometer for microwave aquametry measurement

at S-band and develop a distributed element model to suite the

microstrip resonator ring (MRR) sensor for m.c. and εr measurements

of various soil types in Malaysia.

ii. To investigate the relation between m.c. and εr of various soil types as

well as resonant frequency shifting of reflection coefficient, || and

propose a soil quality classification using microwave measurement

techniques. This database can also be applied for soil in tropical

regions around the world.

1.4 Scopes of work

The scope of this research is given as follow:

(1) Review on influence of moisture content, m.c. on soil permittivity, εr

with assumption that higher m.c. value will result in higher soil εr.

Next, investigate frequency-variation method by using microstrip ring

resonator (MRR) sensor to differentiate various soil types based on

7

respective soil dielectric constant, εr′ and determine moisture content,

m.c. of respective common soil types. The proposed sensors are

designed to operate from 2 GHz to 4 GHz (cover the industrial,

scientific and medical (ISM) band) with resonance frequency range

between 2.9 GHz and 3.3 GHz.

(2) Design a four-port branch-line directional coupler for the remote

sensing S-band soil reflectometer. Next, develop the PC controllable

configuration for the reflectometer with NI LABVIEW as Graphical

User Interface (GUI). MRR sensor is attached together with the meter

device for sensing purposes. The calibrated equations are programmed

in MATLAB for rapid and real-time determination of soil m.c. and

soil permittivity, εr for various soil types in this study.

(3) Analyze the suitable microstrip ring resonant (MRR) sensor via

empirical resistor-inductor-capacitor (RLC) distributed element model.

The model is developed by applying basic fitting method with

simulated values obtained using the microwave office (AWR)

simulator from 0.5 GHz to 4.5 GHz over a wide range of relative

dielectric constant, εr′ (1 to 10) and loss tangent, tan δ (0.01 to 0.2).

The values for the seven elements (three inductors, two capacitors,

and two resistors) are expressed as polynomial functions of εr′ and tan

δ and by using the inverse algorithm with an objective function

computed in MATLAB program, the model is sufficient to predict soil

permittivity, εr and consequently, determining moisture content, m.c.

of respective soil samples.

(4) Macroscopically testing analysis on respective soil samples for

physical properties determination, such as soil’s relative permittivity,

pH, and moisture content, m.c. is performed by using experimental

tools, such as HP85070D dielectric probe, HI98127 pH meter, and

designed sensors via Keysight 8071C Vector Network Analyzer. On

the other hand, microscopic analysis by magnifying the texture of soil

8

sample using scanning electron microscope (SEM) is carried out to

observe the particles’ shape and sizes of respective soil samples in

different bulk samples. From the captured images, the trace elements

contained in respective soil samples can be obtained.

(5) Describe the relationship for relative dielectric properties, εr and soil

pH based on different moisture content, m.c. for various soil types and

perform polynomial regression analysis to establish these two

relationships.

i. Develop calibration equations which relate both dielectric

properties and various moisture levels by using gravimetric

m.c.g and volumetric m.c.v for different soil types for the

designed sensors.

ii. Develop calibration equations which relate which relate both

soil pH and moisture content, m.c. of various soil types by

using gravimetric and volumetric methods for the designed

sensors.

(6) Determine bound water and free water conditions based on

relationship between measured return loss, |S11| and moisture content,

m.c. for various soil types. Consequently, develop a concise soil

quality classifications based on these dependant factors, together with

(4) and (5) for agricultural purposes in Malaysia. Due to time

constraint, the measurements will be done on five common soil types

(white, yellow, loam, peat, and sand soil) in southern Peninsular

Malaysia, Johor. Limitations such as environment and temperature

change were excluded because measurements were done inside lab

with room temperature (25°C).

1.5 Research Contributions

Different climatic regions and inadequate sensor system result in poor soil

9

study and measurement. In order to establish reliable soil measurement model in

tropical climatic regions, accurate significant soil study model with respect to the

local climatic study is required. To this aim, this work mainly focused on the

characterization of five common soil types specifically devoted to their physical and

chemical behavior. The following has been identified to be the main contribution for

the requirement of significant soil study model:

i. The main contribution is the development of a frequency domain

reflectometer. In electronics, a four-port branch-line directional

coupler contains power detectors in both arms of the auxiliary line

(Incident and Reflected ports) so as to measure the electrical power

flowing in both directions in the main line. From incident and

reflected voltages, reflection coefficient, || of the sample under test

can be determined. This fabricated microwave reflectometer is a PC

controllable measurement system, which attached with suitable

microstrip ring resonator (MRR) acting as sensor device that is

capable to determine soil gravimetric moisture content, m.c.g up to 26

% m.c.g with mean deviation between actual and predicted within ± 2

% m.c.g.

ii. The second contribution is the design and fabrication of microstrip

ring resonator (MRR) sensors, operating at S-band frequency range.

MRR sensor was applied in microwave aquametry measurements due

to its highest sensitivity towards the presence of water. The designed

MRR sensors were successfully used in this study to characterize

various soil types, with average error values of less than 5 %, which

are in fine agreement with commercial dielectric probe and cavity

perturbation technique. In this study, Sensor B chosen as the suitable

sensor for soil measurement via proposed microwave reflectometer.

iii. The third contribution is the application of distributed element model

for the characterization of the microstrip ring resonator (MRR) sensor

in different operating frequencies. This study also utilizes this model

according to its microstrip bending angle for every sensor design and

10

determines the suitable operating frequency for suitable agriculture

products and also various soil types. By using the inverse algorithm

from polynomial functions of εr′ and tan δ with an objective function

computed in MATLAB program, the model is sufficient to predict soil

permittivity, εr and thus, the prediction of m.c. can be done. The mean

deviation between actual and predicted was calculated within ± 1.5 %

m.c.g. The main advantage of this model lies in its adaptability to the

local soil measurement. For this case, the soil samples are commonly

found in Malaysia. This model is specifically applicable to soil types

in tropical countries. Besides, the flexibility of this model may

contribute to more sensor designs for other agriculture products, such

as pineapple, palm oil, rice, and cocoa.

iv. The forth contribution is the determination of relationship between

soil complex relative permittivity, εr and soil moisture content, m.c.

and also the relationship between soil pH and soil moisture content,

m.c. The relationships were expressed into polynomial regression

equations to determine actual soil moisture content, m.c. and soil pH

in the absence of the actual moisture and pH measurement.

v. The fifth contribution concerned the soil quality determination. Five

common soil samples (white, yellow, peat, loam, and sand) in

southern region of Peninsular Malaysia were identified through the

soil analysis based on macroscopic and microscopic experimental

testing. The physical properties (soil texture, moisture content, m.c.

and relative permittivity, εr) and chemical properties (pH and soil

acidity). Statistical significant bound and free water conditions were

investigated for each soil type. These parameters are particularly

important for proper irrigation process and stored as soil database for

future references.

11

1.6 Thesis Organization

This thesis is presented in six chapters. This chapter introduces the

background of the investigated research study, followed by identifying the problem

statements and motivations which have led to narrow study into this research. The

scientific objectives and significant contributions from this research work are

outlined and highlighted with a clear identification of the novel content in the work.

Chapter 2 reviews study on past, recent, and ongoing microwave aquametry

research studies with various microwave measurement techniques and applications,

followed by the history of evolution and development in agriculture sectors. Some

research gaps on the past techniques and sensors are reviewed with relevant data and

proofs. It continues with the soil type and quality study based on two main dependant

factors, such as moisture content, m.c. and pH measurements. Next, study on the

reflectometer and architecture of the development, following by the design of

microstrip ring resonator (MRR) and also modified design of MRR based on four-

legged element structure with different mitered bending angles are reviewed.

Besides, study on MRR sensor based on wall admittance calculation and lumped

element equivalent circuit formulations are presented. This chapter also presents

procedures of modification in lumped element circuit with open stub technique at

conventional branch-line directional coupler to achieve smaller branch-line

directional coupler and with better performances. Finally, resonant method based on

MRR sensor with reflection technique and frequency variation method to determine

permittivity and conductivity for respective soil types are presented.

Chapter 3 describes on the research methodology for the design of the

proposed MRR sensors and development of microwave soil quality meter for soil

quality measurement. It begins with detailed explanation of the research

methodology, which consists of five main stages. Section 3.1 describes on MRR

sensors’ design and simulation, while Section 3.2 presents the fabrication of MRR

sensors. Section 3.3 explains on fabrication of the soil meter system, which includes

the design of four-port miniaturized branch-line directional coupler. Section 3.4

includes soil under test (SUT) preparation procedures and setup instruments. Last

section presents the soil measurement process.

Chapter 4 presents MRR sensor with investigations on admittance model,

mitered angle bending’s effects on MRR design, power loss and sensitivity, as well

12

as contour mapping of magnetic field. Lumped element modelling consisting of

resistor, R inductor, L, and capacitor, C on MRR sensors was presented as follows.

The second section discussed on the design of four-port branch-line directional

coupler based on performances of coupling, return loss, bandwidth, phase angle

between ports as to produce a reliable microwave reflectometer for soil quality

determination. Besides, discussions on the assembly of microwave reflectometer and

initial results, together with the development of graphical user interface (GUI) for the

meter were presented.

Chapter 5 describes the physical and chemical properties of the five common

soil samples in Malaysia, namely white, yellow, loam, peat, and sand soil. Besides,

the relationships for relative dielectric properties, εr and soil pH based on different

moisture content, m.c. are presented with implementations of polynomial regression

equations for the respective soil types by using proposed microwave MRR sensors

via vector network analyzer. A lumped element prediction model for suitable

microwave MRR sensor based on some key concepts of the distributed elements

(resistor, R, inductor, L and capacitor, C) circuits was proposed to estimate the

respective soil dielectric constant, εr′ and consequently, the soil m.c. determination.

Such predictions are found to be in good agreement with dielectric measurements

obtained from a commercial dielectric probe (HP85070D) and actual m.c.

determination using oven drying technique. This chapter continues with discussions

on the results for determining soil εr′ and m.c. by using fabricated microwave soil

quality reflectometer. The relationship between shifting frequency, fs of soil samples

and various moisture levels is presented and programmed in MATLAB for results

study and analysis. Finally, a soil database based on the above dependant factors for

the five common soil types is established and can be used as reference for agriculture

sectors and civil engineering in Malaysia.

Chapter 6 discusses the conclusion and future works. The major works in this

thesis are concluded and summarized, followed by some constructive

recommendations on the further work are given.

155

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