UNIVERSITI PUTRA MALAYSIA

FREE-SPACE MICROWAVE CHARACTERISTICS OF NATURAL RUBBER COMPOSITES FILLED WITH CARBON BLACK FOR

MICROWAVE APPLICATION

AZLINDA BINTI RAMLI.

FK 2004 102

FREE-SPACE MICROWAVE CHARACTERISTICS OF NATURAL RUBBER COMPOSITES FILLED WITH CARBON BLACK FOR

MICROWAVE APPLICATION

BY

AZLINDA BINTI RAMLI

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirements for the Degree of Master of Science

December 2004

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfillment of the requirement for the degree of Master of Science

FREE-SPACE MICROWAVE CHARACTERISTICS OF NATURAL RUBBER COMPOSITES FILLED WITH CARBON BLACK FOR

MICROWAVE APPLICATION

BY

AZLINDA BINTI RAMLI

December 2004

Chairman: Associate Professor Mohd Adzir Mahdi, PhD

Faculty: Engineering

A contactless and non-destructive microwave method has been developed to

characterize natural rubber composites from reflection and transmission

measurements made at normal incidence. Microwave non-destructive testing

(MNDT) using free-space microwave measurement (FSMM) system involves

measurement of reflection and transmission coefficient in free-space. The

measurement system consist of a pair of spot focusing horn lens antenna, mode

transition, coaxial cables and vector network analyzers (VNA). The inaccuracies in

free-space measurements are due to two main sources of errors. 1) Diffraction effects

at the edges of the material specimen. 2) Multiple reflections between horn lens

antennas and mode transitions via the surface of the sample. The spot-focusing

antennas are used for minimizing diffraction effects and we have implemented free-

space TRL calibration technique by establishing three standards, namely, a through

connection, a short circuit connected to each port and a transmission line connected

between the test ports. This calibration along with time domain gating feature of the

VNA can eliminate effects of multiple reflections.

In this method, the free-space reflection and transmission coefficients, S1 and SZ1 are

measured for natural rubber composites sandwiched between two Teflon plates of

10.64 mm thickness which act as a half-wave transformer at mid-band. The actual

reflection and transmission coefficient, S1 1 and SZ1 of the natural rubber composites

are then calculated from measured S1 1 and SZ1 by using ABCD matrix transformation

in which the complex permittivity and thickness of the Teflon plates are known.

From the complex permittivity, loss tangent, conductivity, wavelength, velocity and

skin depth can be obtained. Result for natural rubber composites filled with different

concentrations of carbon black are reported in frequency range 9-1 1 GHz.

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains.

Oleh

AZLINDA BINTI RAMLI

December 2004

Pengerusi: Profesor Madya Mohd Adzir Mahdi, Ph.D.

Fakulti: Kejuruteraan

Penyelidikan yang menggunakan kaedah gelombang mikro yang tidak menyentuh

dan memusnahkan sampel telah dicipta untuk mengenalpasti ciri-ciri elektrik dan

bukan elektrik yang ada didalam sebatian getah asli dengan menggunakan

pengukuran pembalikan dan penghantaran pada laluan terus.

Kaedah gelombang mikro ini telah menggunakan pengukuran koefisien pembalikan

dan penghantaran dalam ruang 'free-space'. Sistem pengukuran terdiri daripada

sepasang horn antenna, pengalih mod, kabel sepaksi dan Vector Network Analyzer

W A )

Ketidaktetapan dalam pengukuran dalam diruang 'free-space' adalah disebabkan

dua sebab utama 1) Kesan pembelauan pada pinggir sample 2) Terlalu banyak

pembalikan signal yang melalui sampel diantara dua horn antenna. Antena fokus

telah digunakan untuk meminimakan pembelauan signal dan kami juga telah

menggunakan kaedah'fiee-space' penentukur TRL. Kaedah penentukur ini akan

digunakan bersama 'time domain gating' daripada VNA untuk mengurangkan kesan

pembalikan signal.

Dalam kaedah ' free-space' pembal ikan dan penghantaran koefisien'hi s;'; din %" "'

telah digunakan untuk mengenalpasti ciri-ciri elektrik dan bukan elektrik sebatian

getah asli. Sampel sebatian getah asli ini diletakkan diantara dua kepingan Teflon

yang bertindak sebagai pemegang kepada sampel dan sebagai laluan 'half-wave'.

Koefisien sebenar S l l dan Szl dapat dikira dengan menggunakan ABCD matrik

transformasi apabila ciri-ciri elektrik , bukan elektrik dan ketebalan Teflon diketahui.

Daripada pengukuran tersebut, ciri, kadar pengaliran elektrik, panjang gelombang

dan kelajuan gelombang didalam sampel dapat diketahui. Kesemua keputusan yang

diperolehi untuk sebatian getah asli dengan konsentrasi karbon yang berlainan ini

adalah pada had frekuensi 9-1 1 GHz.

ACKNOWLEDGEMENTS

My deepest praise to Allah s.w.t for giving me the strength and good health to pursue

and complete my M (Sc) dissertation.

It is with great sincerity to acknowledge my supervisors, Associate Professor Dr.

Mohd Adzir b Mahdi and Associate Professor Dr.Deepak Kumar Ghodgaonkar for

giving me the guidance and knowledge with patience and understanding. I would

also like to extend my sincere appreciation to Dr. Sabira Khatum for giving helpful

suggestions concerning my dissertation.

I would like to thank Puan Noor Hasimah Baba, Cik Aznida, Cik Siti Nurani

Adenan,En. Aziz, En.Haris, En. Shahnan and others who had helped me throughout

the course of this project where without their invaluable help this project could not

have been completed with success.

Special thanks are owed to my parent for their support and understanding from the

very beginning of my work until my M (Sc) studies were completed.

I certify that an Examination Committee met on 1 4 ~ December 2004 to conduct the final examination of Azlinda binti Rarnli on her Master of Science thesis entitled "Free Space Microwave Characteristics of Natural Rubber Composites Filled with Carbo Black for Microwave Application" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 1981. The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows:

Adznan Jantan, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman)

Syed Javaid Iqbal, PhD Faculty of Engineering Universiti Putra Malaysia (Internal Examiner)

Khairi Yusuf, PhD Faculty of Engineering Universiti Putra Malaysia (Internal Examiner)

Kaharudin Dimyati, PhD Associate Professor Faculty of Engineering Universiti Malaya (External Examiner)

~rofessor/I)eputy Dean School of Graduate Studies Universiti Putra Malaysia

vii

This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted as hlfilment of the requirement for the degree of Master of Science. The members of Supervisory Committee are as follows:

MOHD ADZIR MAHDI, PhD Associates Professor Faculty of Engineering Universiti Putra Malaysia (Chairman)

DEEPAK KUMAR GHODGAONKAR,PhD Associates Professor Faculty of Engineering Universiti Teknologi Mara (Member)

SABIRA KHATUM, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Member)

AINI IDERIS, PhD ProfessorDean School of Graduate Studies Universiti Putra Malaysia

Date: 1 2 MAY 2005

viii

DECLARATION

I hereby declare that the thesis is based on my original work except for the quotation and citations which have been duly acknowledged. I also declare that it is not been previously or concurrently submitted for any other degree at UPM or other institutions.

AZLINDA BINTI RAMLI

Date:

TABLE OF CONTENTS

Page

ABSTRACT ABSTRAK ACKNOWLEDGEMENT APPROVAL DECLARATION LlST OF TABLES LIST OF FIGURES LlST OF ABBREVIATIONS

CHAPTERS

INTRODUCTION 1.1 Introduction 1.2 Scope of Work

1.2.1 Study of Measurement Equipment, Dielectric and Magnetic Properties

1.2.2 Choose type of Measurement Technique I .2.3 Calibration using Chosen Measurement Technique 1.2.4 Analysis of Results

1.3 Objectives 1.4 Thesis Organization

LITERATURE REVIEW 2.1 Introduction

2.1 .I Theory of Microwaves 2.1.2 Application of Microwaves 2.1.3 Microwave Non-Destructive Testing (MNDT) 2.1.4 Advantages of MNDT 2.1.5 MNDT Applications

2.2 Transmission Line Theory 2.2.1 Half Wavelength Line 2.2.2 Quarter Wavelength Line

2.3 Free-Space Measurement System 2.3.1 A Free-Space Technique

2.4 Introduction of Scattering Parameters 2.4.1 Introduction 2.4.2 Two-Port Network 2.4.3 S-Parameter

2.5 Electromagnetic Properties 2.5.1 Complex Permittivity

2.5.1 .I Real Dielectric Constant 2.5.1.2 Loss Factor

2.5.2 Loss Tangent 2.5.3 Conductivity

2.6 Propagation of Waves in Media

. . 11

iv vi vii ix ...

xi11

xiv xvi

2.6.1 Propagation of Waves in Lossless Medium 2.6.2 Propagation of Waves in Lossy Medium 2.6.3 Velocity and Wavelength of the Wave inside the Sample 2.6.4 Skin Depth in Lossy Medium Natural Rubber 2.7.1 The Nature of Rubber 2.7.2 Raw Rubber 2.7.3 HAF(N330) Carbon Black as a Filler 2.7.4 The Nature of Carbon Black 2.7.5 Electrical Conductivity 2.7.6 Conductivity Impacted by Carbon Black to Composite 2.7.7 Conductive Carbon Black 2.7.8 Dielectric Measurements 2.7.9 Processing Technique 2.7.10 Mixing 2.7.1 1 Vulcanization, Crosslinking and Compounding

RESEARCH METHODOLOGY 3.1 Free-Space Measurement System Setup 3.2 Measurement Calibration 3.3 Sample Assembly 3.4 Experimental Flowchart 3.5 Experimental Procedure 3.6 Calculation of the Actual S-Parameters from the Measured

S-Parameter. 3.7 Calculation of Complex Permittivity from Measured St,

Only Method 3.8 Flow Chart for Finding Complex Permittivity

RESULT AND DISCUSSION 4.1 Introduction 4.2 Sample Specifications 4.3 Measurement Calibration

4.3.1 Short Circuit Connection 4.3.2 Through Connection

4.4 Verification Results 4.4.1 Teflon 4.4.2 Polyvinyl-chloride (PVC)

4.5 Experimental Results 4.5.1 Natural Rubber without Carbon Black Concentration 4.5.2 Natural Rubber with Carbon Black Concentration

4.5.2.1 Effect of Frequency 4.5.2.2 Effect to Electromagnetic Properties 4.5.2.3 Velocity and Wavelength inside the Sample 4.5.2.4 Skin Depth

4.5.3 Half wavelength and Quarter wavelength Line

CONCLUSION AND FUTURE DEVELOPMENT 5.1 Conclusion

5.2 Future Development

REFERENCES APPENDICES BIODATA OF THE AUTHOR PUBLICATIONS

xii

LIST OF TABLES

Table

2.1 Electromagnetic waves

Commonly used microwave frequency band

Density for each ingredient.

Carbon Black composition for Vulcanization

Cured and molding time

Compounding ingredients and their functions

Thicknesses of the samples

Page

1 1

... Xll l

LIST OF FIGURES

Figure

2.1

2.2

Page

18

20

~ a l f wavelengd Transmission Line

Quarter wavelength Transmission Line

The Z, Y and h descriptions of two port network

Alternative configuration of polyisoperene; left cis (natural rubber); right, trans (gutta percha)

Schematic resistivity-concentration curve for carbon black-polymer composite.

Relationship between z and tan 6 in case of varying carbon black loadings.

Flow Schematic of making the rubber product

Internal mixer (top) and two-roll mill (bottom).

Schematic diagram of free-space measurement setup

Teflon plate-sample-Teflon plate assembly.

Dimension of DUT samples

The flowchart of experimental work

Schematic diagram of Teflon plate-sample-Teflon plate.

Flowcharts for Finding Complex Permittivity

Calibration result for short circuit connected to each port,S1 1

Calibration result for through connection, Szl

Complex Permittivity for Teflon

Complex Permittivity for Polyvinyl-chloride (PVC)

xiv

Dielectric constant of natural rubber with 0% carbon black concentration from 9 GHz to 1 1GHz.

Loss Factor of natural rubber with 0% carbon black concentration from 9 GHz to I 1GHz.

Dielectric Constant of thin samples with different carbon black 79

Dielectric Constant of thick samples with different carbon black concentration at 9GHz to 1 1 GHz.

Real permittivity of natural rubber with different carbon black concentration from 9 GHz to 1 1 GHz.

Loss factor of natural rubber with different carbon black concentration from 9 GHz to 1 1 GHz.

Loss tangent of natural rubber with different carbon black concentration from 9 GHz to 1 1 GHz.

Conductivity of natural rubber with different carbon black concentration from 9 GHz to 1 1GHz.

Microwave velocity of samples with different carbon black concentration at 10 GHz.

Wavelength of samples with different carbon black concentration at 10 GHz.

Skin Depth of thin samples with different carbon black concentration from 9 GHz to 1 1 GHz.

Skin Depth of thick samples with different carbon black concentration from 9 GHz to 1 1 GHz.

Reflection Coefficient ,SI 1 for thin sample at 10 GHz

Reflection Coefficient ,S1 1 for thick sample at 10 GHz

Transmission Coefficient ,S2, for thin sample at 10 GHz

Transmission Coefficient ,S21 for thick sample at I0 GHz

Real Permittivity for thin sample at 10 GHz

Real Permittivity for thick sample at 10 GHz

Loss Factor for thin sample at I0 GHz

Loss Factor for thick sample at 10 GHz

LIST OF ABBREVIATIONS

Y

P S

1

s11

s2 1

HAF

SMR

NR

pphr

MNDT

FSMM

TRL

LRL

FSMS

VNA

DUT

IF

RF

r I l- l GHz

Complex Permittivity

Complex Permittivity

Complex Permeability

Complex Permeability

Angular Velocity, radls

Conductivity

Attenuation Constant

Propagation Constant

Phase Constant

Skin Depth

Wavelength

Reflection Coefficient

Transmission Coefficient

Carbon Black N330

Standard Malaysian Rubber

Natural Rubber

Part per hundred rubber

Microwave Nondestructive Testing

Free-Space Microwave Measurement

Thru, Reflect, Line

Line, Reflect, Line

Free-Space Measurement System

Vector Network Analyzer

Device under Testing

Intermediate Frequency

Radio Frequency

Complex Reflection Coefficient

Magnetic of Reflection Coefficient

Giga Hertz

xvi

CHAPTER 1

INTRODUCTION

Introduction

The measurement of complex permittivity of materials at microwave frequencies can be

performed in many ways. Waveguide methods are popular, where the sample is

precisely machined to fit inside the waveguide. Rectangular and coaxial waveguides are

used, rectangular samples are easier to produce than coaxial ones, and however they can

only be used over a limited frequency range. Coaxial waveguide allows extremely wide-

band measurements but sample preparation is difficult. A vector network analyzer is

generally used to collect the reflected and transmitted signals, and permittivity value can

be extracted from the results.

Waveguide measurements suffer from errors caused by incomplete filling of the

waveguide by the sample. Corrections for this have been proposed with some success

but are not perfect. Sample preparation is destructive and often time consuming. Some

materials are not suitable for waveguide measurements, such as those containing long

fibers, or foams with large voids. High frequency measurements are especially difficult

due to waveguide size. Free space techniques overcome many of these problems [I].

The main objective of this project is to develop a free space measurement system at

microwave fiequencies in the frequency range of 8 GHz to 12 GHz (X-band) for a

measurement of Reflection Coefficient, S1l and Transmission Coefficient, S21 of the

Natural Rubber filled with different concentration of Carbon Black (HAF N330). The

Complex Permittivity (E*) is then calculated from the measured values of Sl and Szl.

A Free-Space Microwave Measurement (FSMM) method is a non-destructive and

contactless; hence, it is suitable for measurements of the complex electric permittivity of

the rubber composites under high-temperature conditions. In the past, free-space

methods have been used by several investigators for the measurement of electrical

properties of materials [I]-[4]. Recently, a new free-space method was developed for the

accurate determination of the dielectric constant and loss tangent of non magnetic

materials such as Teflon and quartz at microwave fiequencies using reflected fields from

metal-backed samples [3]. This paper presents an extension of the free-space method for

simultaneous measurement of complex permittivity of non magnetic materials at

microwave frequencies using reflected and transmitted fields.

FSMM method is used because the reflection and the transmission coefficients (S-

parameters) of planar specimens of rubber composite materials are measured in free-

space instead of coaxial line method. The errors in free-space measurements are

presumed to be due to diffraction effects at the edges of the sample and multiple

reflections between the horn lens antennas and the mode transitions. Diffraction effects

at the edges of the sample are minimized by using spot-focusing horn lens antennas as

transmitters and receivers. In addition, a free-space TRL (Through-Reflect-Line)

calibration technique which eliminates errors due to multiple reflections is developed in

the research work.

A conventional method for E* measurement consist of measuring complex reflection

coefficients of short-circuited and open-circuited (quarter wavelength short-circuited

line) samples [2]. Using this method, the measurements are difficult and time consuming

to make because the open- circuited sample has to be established at each measurement

frequency. In this project, a method for determination of E* from reflection and

transmission coefficients of a planar sample is used. This method is especially suitable

for quick, routine, and broad-band measurement of E* and of high-loss materials. For

materials with dielectric (or magnetic) loss tangent less than 0.025, the loss factor

measurements are found to be inaccurate because of errors in reflection and transmission

coefficient measurements[ I 1 1.

In this method, the free-space reflection and transmission coefficients, S1l and S2] of a

planar sample are measured for a normally incident plane wave. The complex

constitutive parameter E* is calculated from the measured S1 1 and S2]. For flexible

samples of non-magnetic materials, the accuracy of measurement of S11 and S2] is poor

because of sagging of the sample when mounted on the sample holder. Hence, the

sample had to be sandwiched between two half-wavelength (at midband) Teflon plates,

to eliminate the effect of sagging. The actual reflection

and transmission coefficients, S1 1 and of the sample are calculated from the measured

S1l and Szl of the Teflon plate-sample-Teflon plate assembly from knowledge of the

complex electric permittivity and thickness of the Teflon plates.

The key components of the measurements system consists of transmit and receive spot-

focusing horn lens antenna, and the vector network analyzer. Because of the far-field

focusing ability of horn lens antennas free-space measurement can be made at

microwave frequency in a relatively compact and simple measurement setup

Scope of Work

The scopes of work that have been studied and done are listed below:

1.2.1 Study of Measurement Equipment and Dielectric Properties

The study is including the basic theory on microwave to improve skills and knowledge

in doing a calibration and choose a better method to given a better result for the

calibrations. This study is also including the basic theory on the rubber materials to give

some ideas.

1.2.2 Choose Type of Measurement Technique

The Free Space Measurement System (FSMS) at microwave frequencies in the

frequency range 8 GHz to 12 GHz was chosen to measure the Reflection Coefficient, S11

and Transmission Coefficient,. S2, of the natural rubber filled with different

! concentration of carbon black.

@MAEAM WL SAhfAD

1.2.3 Calibration using Chosen Measurement Technique

Implement two-port TRL (Through-Reflect-Line) calibration technique along with time

domain-gating to remove the effect of multiple reflections.

1.2.4 Develop Computer Programs

To develop computer programs for the calculation of complex permittivity of the

composite.

1.2.5 Analysis of results

Analyze the data using FORTRAN Software to reduce the effect of Teflon permittivity

on the Reflection Coefficient S1l and Transmission Coefficients S2, of the samples.

The Fortran 77 programming is used to determine the complex permittivity E* of the

sample by using measured S2, only.

Objectives

1. To measure dielectric properties of natural rubber with different

concentration of carbon black using microwave non-destructive technique.

2. To establish a correlation between the dielectric properties of natural rubber

composites evaluated from microwave non-destructive technique with the

electrical properties.

3. To develop computer programs for the calculation of complex permittivity.

Thesis Organization

To achieve the objectives mentioned earlier, a microwave non-destructive measurement

system using free-space method has been developed. Natural rubber with various

parameters were cast and prepared.

The parameters are the concentration of the carbon black as filler and the thickness of

the samples. The system was used to measure the electromagnetic properties of natural

rubber with different concentration of carbon black in frequency range 8-12 GHz. The

effects of the carbon black concentrations to the electromagnetic properties of natural

rubber were investigated.

Finally, the relationship between the electromagnetic properties and the basic properties

was established.

Chapter two describes the theory of microwaves which are related to this measurement

and investigation. It discuss the S-parameters, two-port network, transmission line and

electromagnetic properties of the sample.

Chapter three discuss about the theory of natural rubber and the effect of the carbon

black to the dielectric materials.

Chapter four focuses on the experimental program. It describes the material used in this

research and the methods of the testing. Also, this chapter describes the measurement

system developed for the purpose of this research, calibration system and methods of

calculating the properties of the composites from measured reflection and transmission

coefficient.

Data analysis and results together with their interpretation are presented in chapter five.

Chapter six summaries the findings , provides conclusions and future development.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

The first free-space method for measurement of dielectric constant using transmission

technique was proposed by R.M Redheffer in 1966 [4],who reported that free-space

methods are non-destructive and contactless techniques which are suitable for dielectric

measurement of material.

Harrold L.Basset [5 ] was the first researcher to measure complex permittivities of fused

silica as a function of temperature from ambient to 2500 '~ in free-space employing

spot- focusing horn lens antennas at a frequency at 9.4 GHz [2],[3]. This technique has

been used for dielectric, reflection and transmission coefficient measurements of

material such as cement, bricks, textile, wood and human skin in the frequency range of

8-40 GHz by Ghodgaonkar and others [24],[25].

A free-space method by Ghodgaonkar and others [3] was developed for accurate

measurement of dielectric constants and loss tangents of metal-back planar samples in

microwave frequencies. For low-loss materials the accuracy of this method is better than

+ 2% and 20 x lo4 for dielectric constants and loss tangents measurement respectively.