A STUDY AND DEVELOPMENT OF LOW COST MICROWAVE ABSORBER
MOHD AZIZI BIN ALI SABERI
This report is submitted in partial of the requirement for award of Bachelor of Electronic Engineering (Telecommunication Electronic) With Honours
Faculty of Electronic and Computer Engineering Universiti Teknikal Malaysia Melaka.
“I hereby declare that this report is the result of my work except for quoted as cited in references”
Signature : ………
Author : ………
“I hereby declare that I have read this report and in my opinion this report is sufficient in terms of the scope and quality for award of Bachelor of Electronic Engineering
(Telecommunication Electronics) With Honours.”
Signature : ………
Supervisor’s Name : ………
ACKNOWLEDGEMENT
First of all, endless thanks to the Almighty ALLAH S.W.T, the source of my life, wisdom and hope for giving me the strength and patience to pursue this project.
My warmest appreciation especially is to my supervisor, Mr Imran Bin Mohd Ibrahim for his caring and cooperation towards his protégé. He is very keen in facilitating me during project execution. Also special gratitude for the kindness spending his precious time in supervising me even he was very busy. For that, thank you very much.
I would like to express my sincere appreciation to Mr. Mohammad Zoinol Abidin Bin Abdul Aziz that help me so much in completing this project and also to all lectures for their help and providing me with many positive remarks, which inspired me in becoming a well-rounded engineer. Deeply thanks for giving me the knowledge as well as guidance throughout project accomplishment and this knowledge is valuable in work field as a competence engineer.
My special thanks to panels Miss Nurmala Irdawaty and Pn Zahariah Manap for accessing my performance throughout the presentations.
ABSTRACT
In modern times, telecommunication typically involves the use of electronic
transmitters such as the telephone, television, radio or computer. Nowadays
communication system becomes more sophisticated that involved high frequency to
deliver information. Hence a lot of tool was invented to perform the task. Then the
equipment has to test before widely used. The test must be done perfectly without
interference from the external wave or reflected wave from surrounding objects.
Therefore the wave absorber invented to overcome this problem. But nowadays, all the
chambers for high frequency measurement have use expensive base and material as well
like ferrite or semi conductor elements and it is high in cost. This microwave absorber
based on low cost material to overcome the problem in term of money matter. The
absorber will absorb the electromagnetic wave energy to produce the null reflectivity
environment for interior and free wave from exterior. The purpose of the testing that
done in the chamber is to obstruct the external source from the environment and to avoid
the measurement is influence by uncorrelated noise such as heat or rain. The testing can
be perform in the field or open space but the result taken not as better as testing result in
anechoic chamber. In this project the absorber shape used is pyramidal shape. This is
because of the total surfaces on the shape is high instead of other shape. The low cost
materials that get used in this project are activated carbon powder and water based paint.
The absorber that fabricated by using that the material respectively will be undergoes the
test. From the result obtained, observation will be made on how the material will give
ABSTRAK
Pada zaman moden kini, telekomunikasi biasanya melibatkan penggunaan
pemancar elektronik seperti telefon, televisyen atau komputer. Pada masa kini, bidang
telekomunikasi semakin canggih dan melibatkan frekuensi yang tinggi dalam
penghantaran maklumat. Maka, pelbagai jenis peralatan direka untuk memenuhi
keperluan ini. Peralatan ini perlu diuji terlebih dahulu sebelum digunakan secara meluas.
Pengujian perlu dilakukan tanpa pertindihan sebarang gelombang lain di persekitaran
luar ataupun gelombang yang dipantul balik dari objek sekeliling. Oleh itu, penyerap
gelombang dicipta untuk mengatasi masalah ini. Akan tetapi, pada masa kini, kesemua
bilik kebuk yang digunakan untuk menguji frekuensi tinggi menggunakan penyerap
berasaskan ferit atau bahan semi-konduktor serta mahal. Penyerap ini dibina berasaskan
bahan berkos rendah untuk menyelesaikan masalah dari segi kos bahan penyerap.
Penyerap akan menyerap tenaga gelombang elektromagnet untuk menghasilkan
persekitaran bebas pantulan bahagian dalam, serta bebas gelombang luaran. Pengujian
yang dilakukan di dalam kebuk bertujuan menghalang gangguan gelombang dari sumber luar dan mengelakkan bacaan dipengaruhi oleh “uncorrelated noise” seperti haba atau hujan. Pengujian juga boleh dilakukan di tempat lapang atau di tempat terbuka
tetapi kedapatan keputusan pengujian tidaklah sebaik keputusan yang dijalankan di
dalam anechoic chamber. Projek ini menggunakan bentuk piramid. Ini kerana bentuk
piramid mempunyai jumlah permukaan yang tinggi berbanding bentuk lain. Bahan yang
berkos rendah yang digunakan dalam projek ini ialah serbuk karbon teraktif dan cat yang
berasaskan air. Penyerap yang telah difabrikasikan menggunakan bahan tersebut akan
dijalankan pengujian. Daripada bacaan yang telah diperolehi, pemerhatian akan dibuat
CONTENT
CHAPTER ITEM PAGE
PROJECT TITLE i
STATEMENT OF VERIFICATION ii
DEDICATION v
ACKNOWLEDGEMENT vi
ABSTRACT vii
ABSTRAK viii
CONTENT ix
LIST OF TABLE xii
LIST OF FIGURE xiii
1 INTRODUCTION
1.1 Introduction 1
1.2 Problem Statement 3
1.3 Project Objectives 3
1.4 Scope of Project 3
1.41 1st Part 4
1.42 2nd part 4
1.43 3rd part 4
2 LITERATURE REVIEW
2.1 Introduction to the Microwave Absorber 5
2.2 Absorber Shape 8
2.2.1 Pyramidal Shape 8
2.2.2 Flat Shape 8
2.2.3 Wedges Shape 9
2.3 Type of Absorber 9
2.3.1 Ferrite Base 9
2.3.2 Carbon Base 10
2.3.3 Hybrid 11
2.4 Types of Absorber 11
2.4.1 Resin and Semi-Conductor Material 11
2.4.2 Foam and Semi-Conductor Material 12
2.5 Methods of Measurement 12
2.5.2.1 TDRM of Large areas of RAM 15
2.5.2.2 TDR of RAM tiles 19
2.5.3 Enclosed Flared Waveguide Measurement 24
2.5.3.1 Low Frequency Coaxial Reflectometer 27
2.6 Simulation Tool 30
3 PROJECT METHODOLOGY
3.1 Introduction 32
3.2 Project Description 35
4 SIMULATION, FABRICATION
4.1 Introduction 38
4.2 Simulation 39
4.3 Absorber Construction 40
5 MEASUREMENT SET UP
5.1 Measurement Setup 43
5.2 Measurement Process 46
6 Result
6.1 Result 48
7 Discussion
7.1 The Arch Method 52
7.2 The Pyramidal Shape 53
7.3 Recommendations 54
7.3.1 The Absorber 54 7.3.2 The Measurement Set-up 54
8 Conclusion
8.1 Conclusion 55
Reference 54
LIST OF TABLE
No. TITLE PAGE
1.1 Microwave Frequency Bands 6
5.1 Reading for Commercial Absorber, Carbon Base Absorber, reflector and simulation result
50
LIST OF FIGURE
No. TITLE PAGE
2.1 Arch Method Setup Measurement 13
2.2 Time Domain Reflectivity Measurement 17 2.3 Example of received waveform of a transmitted short pulse 17 2.4 Example of received waveform after the subtraction process 18 2.5 Typical TEM horn antenna used to measured absorber
reflectivity
19
2.6 Time Domain Reflectivity measurement of RAM tiles 21 2.7 Ferrite tile/urethane hybrid RF absorber structure 22 2.8 Reflection Coefficient of ferrite tile only 22 2.9 Reflection coefficient of ferrite/urethane of Figure 2.7 23 2.10 Flared waveguide measurement procedure test setup 26 2.11 Low-frequency Coaxial Reflectometer 27
2.12 Square Coaxial 28
2.13 Thin Wire Coaxial 28
2.14 Stripline 29
3.0 Project Methodology 34
4.1 Microwave Absorber in Simulation Design 39
4.2 Foam before cut 40
4.3 The foam in the mould 41
4.4 The foam was cut 41
4.5 The pyramidal shape foam 42
4.6 Low cost microwave absorber 42
5.1 UBP Synthesized Signal Generator SG 2100 43
5.2 Spectrum Analyzer R3132 44
CHAPTER I
INTRODUCTION
1.1 Project Introduction
Nowadays, most of the devices around us were electronic
implementation, from the simple device to the complex one. While designing the
new electronic devices, the designer always relies on the specifications and
requirements to produce a new product. One of the requirements is the customer
safety.
Once the device is an electronic implementation, the device could be
having attenuation on frequencies. So, before the device was marketed, it has to
undergo many tests in the laboratory. One of the purposes of the test is, to
determine the reliability of the product when the product was in various
frequencies area. Some of product might be failed when through this area.
The laboratory that used to test the product is the anechoic chamber.
Every electronic device manufacturer should have the anechoic chamber. The
usage of anechoic chamber is not just to check the reliability of a device or
anechoic and semi anechoic chamber. The fully anechoic chamber is fully
covered with absorber while the semi anechoic chamber is fully covered on
upper part of chamber.
The absorber that used in anechoic chamber is currently was made from
semi conductor materials. Sometime, size for 1 meter length with 1metre width
on 1 meter high will cost around MYR19000. This is extremely high for
constructing a fully anechoic chamber. The anechoic chamber did not have
certain length of size, but it has to be wide enough for future purposes. From the
problem that appeared, this project will come out a solution with Low Cost
Microwave Absorber.
Microwave absorber or frequently called RF absorber already
implemented in our surrounding. The applications that commonly known by
implement microwave absorber are microwave oven, the microwave absorber
use to prevent the wave instead of radiated to outside, and indirectly harm the
people around. In military, the microwave absorber is frequently use in aircraft
manufacturing. It is functioning as to prevent the aircraft from get detected by
enemy radar. Another application that widely use for all over the world is
Anechoic Chamber. The purpose of the anechoic chamber is to test any object
that regard to the frequency and wave as explained previously.
In generally, simple name for microwave absorber is Radar Absorber. It
used to absorb any signal wave or radar wave that emitted on its surface. This
Low Cost microwave absorber was involved frequency range from 1GHz – 10GHz. The main material that uses in manufacturing of pyramidal type RF
absorber is semi-conductor material.
The major aspect that use in selection of the absorber material is activated
semi-conductor. It make the absorber absorbs and the matched the incoming
frequency. So, when there have matching network, there is no reflection on the
system. Beside, the material is low in cost as well.
Normally, in the market nowadays, the absorber was constructed by using
foamed plastic polymers or commonly known as sponge as it base. The polymers
were used because it is ease to shape regard to size and design required. Then,
the absorber was painted with liquid that added by semi-conductor material on
surface top of it. Semi-conductor are use because of it have good conductivity.
This project was still use the pyramidal shape because of its optimum in
absorption but, in term of the novelty, it is using the low cost material.
1.2 Problem Statement
The problem statement of this project is the existed microwave absorber
was high in cost. Most of the price may reach around MYR 500 per feet2. To
construct an anechoic chamber for microwave, it will cost around 2million. The
problem on cost of absorbers was cause on the material that used.
1.3 Objective Project
To design a pyramidal Low cost microwave absorber at frequency range
from 1GHz – 10 GHz. The rational of this study is to discover the new material that can be used to replace the existed costly microwave absorber. Generally, the
absorbers in the market are in pyramidal form shape. So, the novelty of this
project was on the material that used. From this study, the cost of making
microwave absorber can be reduced, and the results obtained were meets the
Scopes of work for this project were divided into 3. All 3 parts have
explained as follow:
1.4.1 Project Identification
The first part was regard on research for absorber. There are 4 steps have
to be done. The first step is to collect information regarding to the absorber from
existed research previously. Secondly is to understand basic of the absorber with
cautiously based on title that given include do some analysis on the information.
After that, to identify the shape of absorber that will be constructs and last one is
to do some calculation regarding to the absorber size.
1.4.2 Project Construction
This second part is absorber’s construction phase. In this period, the activities that involved are constructing the mould of absorber. Then, do cut the
absorber base into pyramidal shape. After that, do prepare the absorber coat paint
and lastly, do paint the absorber with the semi-conductor material. Another
addition construction phase is to prepare the stand for absorber measurement
purposed.
1.4.3 Measurement of Project
The third part is the last phases where this phase will cover the prototype
measurement process. The activities that involve in this part are Near-filed
measurement in lab to obtain the reading of absorption rate, the obtained reading
was converted into graph for observation and the last one is action that taken for
CHAPTER II
LITERATURE REVIEW
2.1 Introduction to Microwave Absorber
The microwave stands from two words. Micro mean extremely small.
And wave means a periodic disturbance of a particle of a substance which
may be propagated without net movement of the particles, as in the passage of
undulating motion or sound. Combining these two words, will resulting the “microwave” that given meaning of an electromagnetic wave with a wavelength in the range 0.001 – 0.3 mm. for this wavelength of frequencies, there are many application regard to the frequency. For a certain ranges, the
Band Name
Freq Range Application
L 1–2 GHz
long range air traffic control and surveillance
S 2–4 GHz
terminal air traffic control, long-range weather, marine radar, Wi-Fi, Wimax C 4–8 GHz Satellite transponders, weather
X 8–12 GHz
Missile guidance, Marine radar, Weather, medium-resolution mapping and ground
surveillance, Airport radar.
Ku 12–18 GHz High-resolution mapping, Satellite altimetry
Ku 18–24 GHz Weather, Speed trap
Ka 24–40 GHz
Mapping, Short range, Airport surveillance, Photo radar, Speed trap
Each of band name given, were regard to the size of the wavelength
itself. For this project, the range of frequencies that focused was on 1 – 10 GHz.
In new era, most of things around us using electronic implementation
equipment, some of them were using frequency. As we know, whenever have a
system, there always have disturbance, or imperfection. The disturbance also
named as noise. The noise was divided by two types. It is correlated noise and
uncorrelated noise. The reflected wave when doing measurement is known as
[image:20.612.145.514.110.448.2]In using frequency implementation equipment, users tend to avoid from
directly emitted with strong frequency, if they know what will cause them for a
long term period. Take an example, household equipment such as microwave oven, the users don’t want the frequency of microwave oven radiated to surrounding and harm the family members around. The concept was same as in
military, but not on health but for war purposes. The pilots do not want the
enemy radar tracking their fleeting aircraft while doing reconnaissance routine
and attacking sortie. Base on that problem, the researcher has done much study to
generate something useful to absorb the radiated frequencies and reflected or
unnecessary incoming frequency. It is named as Microwave absorber or Radar
absorber.
An anechoic chamber is a room that shielded space that design to obstruct
the external incoming electromagnetic signal or sound. Basically, the Anechoic
chamber was used in rational of absorbing acoustic echoes that caused by wave
reflection in the room or covered space, but more recently anechoic chambers
have also been used to provide a shielded environment for radio frequency (RF)
and microwaves. An RF anechoic chamber is designed to restrain the echoes of
electromagnetic wave energy: reflected electromagnetic waves, from the internal
surfaces. Both types of chamber are constructed with echo restraint features and
with effective isolation from the acoustic or RF noise present in the external
environment.
In a well-designed acoustic or RF anechoic chamber, the equipment
under test receives acoustic, mechanical or RF signals from a signal source, a
flawless chamber will not internally reflect these transmitted waves. This ensures
the integrity of the subject being tested is not influenced by external or internal
reflected noise. Furthermore, the shielding of the chamber limits interference
from equipment located outside of the chamber. Anechoic chambers range from
small compartments to chambers as large as aircraft hangars. The size of an
interference (RFI) is the unwanted reception of radio signals. Radio frequency
interference sources include lightning, electrical equipment, fluorescent lighting,
cell phones, and transmitting equipment from radio stations. RFI testing helps
determine which frequencies affect particular electronic systems and provide
clues to mitigating the risks to communication devices or developing measures to
counter the interference.
2.2 Absorber shape.
There have a few types of absorber shape. Each of shape have own rate
absorption
2.2.1 Pyramidal Shape
Commonly, there have 2 shapes of RF absorber, where most of the
materials of the absorber were made using flat thin piece from foam absorber
type and covered around by carbon dust or light solid in pyramidal shape. Both
of it are various multilayer types and foam for single layer are used in this type
of product. Individual cone is divided to some feet of length on their base. The
unit will be able to install in RF or anechoic chamber.
The pyramidal shape has much more surface area rather than other
surface with the same dimension of length and width.
2.2.2 Flat Shape.
Flat Laminate Absorber is a thin broadband microwave absorber with a
graded material that has been widely accepted in the microwave and antenna
impregnated foam. By using a front layer with a small loss tangent, a center layer
with a median loss tangent, and a bottom layer with a large loss, an electric taper
is achieved that yields a material with an average reflection coefficient of -20 dB
over a wide frequency range.[7]
2.2.3 Wedge Shape
Low-density rigid polystyrene foam is used to encapsulate a standard
pyramidal or wedge absorber. A thin sheet of semi-rigid polyvinyl chloride foam
is adhered to the top to provide a walking surface, which is smooth and
impervious to water, and dirt. The Walkway Absorber fabricated in this manner
will support up to 90.7 kg per .3 meter (200 pounds per square foot) and is
durable and easily maintained. Reflections will occur at any foam surface, the
magnitude of the reflection being dependent on the density of the material. [7]
2.3 Types of Absorber
There are many types of absorber. The types was depend on
semi-conductor material. Each of material give different rate of absorption.
Commonly, the Microwave absorber that existed in the market nowadays is
using ferrite base type.
2.3.1 Ferrite Base
Ferrites are usually non-conductive ferromagnetic ceramic compounds
derived from iron oxides such as hematite (Fe2O3) or magnetite (Fe3O4) as well
as oxides of other metals. Ferrites are, like most other ceramics, hard and brittle.
Ferrite absorbers provide high performance at low frequency, providing excellent
absorption from 30 MHz to 1 GHz. They are very thin allowing chambers to be
cubic crystal structure. While some ferrites did have similar Km and Ke over a
narrow frequency range, it turned out that both the real and imaginary parts of Ke
and Km varied so rapidly with frequency that their utilization as absorbers was
limited. Subsequent development of a much wider range of ferrite compositions
gave rise to absorber types which are commonly used today. Ferrite-based
absorbers offer the remarkable feature of being able to provide reflection
reductions of 10 to 25 dB in the 30 to 1000 MHz range with a thickness of only
about a quarter of an inch. Since ferrite is inorganic, it cannot burn, has good
outgassing properties, can be operated to elevated temperatures, and is capable of
dissipating incident power by as much as 20 watts per square inch. Pure ferrite
absorbers are employed primarily to create anechoic chambers and absorbing
antenna caps for use at frequencies from 30 through 1000 MHz. [12]
2.3.2 Carbon Base
Activated carbon, also called activated charcoal or activated coal, is a
form of carbon that has been processed to make it extremely porous and thus to
have a very large surface area available for adsorption or chemical reactions. The
word activated in the name is sometimes substituted by active. Due to its high
degree of micro-porosity, just one gram of activated carbon has a surface area of
approximately 500 m² (or about 2 tennis courts), as determined typically by
nitrogen gas adsorption. Sufficient activation for useful applications may come
solely from the high surface area, though further chemical treatment often
enhances the adsorbing properties of the material. Activated carbon is usually
derived from charcoal.
Activated carbon is the generic term used to describe a family of
carbonaceous adsorbents with a highly crystalline form and extensively
developed internal pore structure. A wide variety of activated carbon products is
