ANALYSIS OF MICRO COIL GEOMETRICAL

FEATURES FOR MEMS-BASED FLUXGATE

MAGNETOMETER

BY

MOHAMMED THAMEEMUL ANSARI M.H

A dissertation submitted in fulfilment of the requirement for the

degree of Master of Science

(Electronics Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

JANUARY 2017

iii

ABSTRACT

This dissertation presents a multi variant structure of fluxgate magnetometer. The core

of fluxgate magnetometer is made of soft iron material. It also consists of sensing and

driving coils made of copper having conductivity of 5.8*10^7[S/m]. Magnetic flux

density of fluxgate sensors is simulated by considering different core structures that

include E-shaped core (adjacent coils), square shaped core, rectangular shaped core,

E-shaped core (centre tapped coil) and triangular shaped core. These designs consist

of primary and secondary coils, which are used as driving coil and sensing coil

respectively. In addition, these different types of cores have been analysed by varying

the successive coil turns through which magnetic flux flow is measured. All these

structures are designed and simulated by using a FEM (Finite Element Method) tool

known as COMSOL multiphysics. Furthermore, results of all assumed structures are

compared to finalise the better design among all the chosen structures. Consequently,

triangular shaped structures result in a good sensitivity range of ±0.02mT regardless

of its size. The fluxgate magnetometer is suitable for various applications including

power transformer and inverter for interior magnetic core fault detection and high

sensitivity.

iv

ملخص البحث

يقدم هذا البحث نموذج لهيكل شبكة مجال مغناطيسى. تتكون نواة هذه الشبكة من مادة ي المصنوعة من النحاس ذو الموصليةتتكون ايضاً من ملفات الاستشعار والقيادة الحديد اللين.و

8.5 *01 ^7 [S /m كثافة التدفق المغناطيسي لجهاز الاستشعار يتم محاكاتها من .] Eخلال النظر في البنية الأساسية المختلفة للمستشعر التي تشمل البنية الأساسية على شكل

ستطيلة الشكل الأساسية و على )ملفات متجاورة( و البنية الأساسية على شكل مربع و مالأساسية )نقطة تفرع ملف( والبنية الأساسية على شكل مثلث. هذا التصميم Eشكل

يتكون ملفات ابتدائية وثانوية التي تستخدم كملفات تحكم واستشعار. بالإضافة إلى ذلك، ا يتم قياس فقد تم تحليل هذه الانواع المختلفة من خلال تغيير لفائف الملف التي من خلاله

FEMاستمرار التدفق المغناطيسي. محاكاة كل هذه النتائج وتصميمها يتم باستخدام متعددة الفيزياء. وعلاوة على COMSOL)طريقة العناصر المحدودة( أداة تعرف باسم

ذلك، يتم مقارنة نتائج جميع الهياكل لاختيار أفضل تصميم بين جميع الهياكل المختار. بغض 0.02mT±ياكل ثلاثية الشكل تدد إلى مد سساسية ييدة ونتيجة لذلك، اله

النظر عن سجمها. إن يهاز الاستشعار المقترح يعتبر مناسب لمختلف التطبيقات بما في ذلك محول القدرة والعاكس واكتشاف الاعطال المغناطيسية الداخلية وله سساسية عالية،

وفقدان مغناطيسي منخفض.

v

APPROVAL PAGE

I certify that I have supervised and read this study and that in my opinion it conforms

to acceptable standards of scholarly presentation and is fully adequate, in scope and

quality, as a dissertation for the degree of Master of Science (Electronics

Engineering).

................................................

Ahmad Zamani

Supervisor

.................................................

Nadzril Bin Sulaiman

Co-supervisor

I certify that I have read this study and that in my opinion it conforms to acceptable

standards of scholarly presentation and is fully adequate, in scope and quality, as a

dissertation for the degree of Master of Science (Electronics Engineering).

.................................................

Siti Noorjannah

Internal Examiner

.................................................

Anis Nurashikin

Internal Examiner

This thesis was submitted to the Department of Electrical and Computer Engineering

and is accepted as a fulfilment of the requirement for the degree of Master of Science

(Electronics Engineering).

................................................

Anis Nurashikin

Head, Department of Electrical

and Computer Engineering

This thesis was submitted to the Kulliyyah of Engineering and is accepted as a

fulfilment of the requirement for the degree of Master of Science (Electronics

Engineering)

..................................................

Erry Yulian

Dean, Kulliyyah of Engineering

vi

DECLARATION

I hereby declare that this dissertation is the result of my own investigations, except

where otherwise stated. I also declare that it has not been previously or concurrently

submitted as a whole for any other degrees at IIUM or other institutions.

Mohammed Thameemul Ansari

Signature………………………..…… Date……………………………..

vii

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR

USE OF UNPUBLISHED RESEARCH

ANALYSIS OF MICRO COIL GEOMETRICAL FEATURES FOR

MEMS-BASED FLUXGATE MAGNETOMETER

I declare that the copyright holder of this dissertation is Mohammed Thameemul Ansari.

Copyright © 2017 by Mohammed Thameemul Ansari. All rights reserved.

No part of this unpublished research may be reproduced, stored in a retrieval system, or

transmitted, in any form or by any means, electronic, mechanical, photocopying, recording

or otherwise without prior written permission of the copyright holder except as provided

below.

1. Any material contained in or derived from this unpublished research may only

be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies (print or

electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieval system and

supply copies of this unpublished research if requested by other universities

and research libraries.

By signing the form, I acknowledged that I have read and understand the IIUM Intellectual

Property Right and Commercialisation policy.

Affirmed by Mohammed Thameemul Ansari

………………………… ..……………….

Signature Date

viii

ACKNOWLEDGEMENTS

In The Name of Allah, The Most Beneficent, The Most Merciful The most important

acknowledgement is to our Lord Most Merciful Most Wise by whose mercy we were

able to begin this project. His Mercy is such that unworthy slaves like ourselves are

given the ability to work in His cause through which we remember Him Swt and be

grateful towards all He has given us. Allah states in the Quran 'Then remember Me; I

will remember you. Be grateful to Me, and do not reject Me' (al-Baqarah 2: 152) May

Allah accept our humble project as a effort to remember and thank Him Swt. Ameen. I

would like to express my deepest appreciation to my main supervisor, Dr. Ahmad

Zamani Bin Jusoh, for his guidance, motivation and constant supervision as well as

for providing necessary information in completing the project. I also deeply thank Dr.

Nadzril Bin Sulaiman, my co-supervisor, for his extensive guidance, keen interest and

support in various stages of this project through IIUM Endowment B (EDW B14-141-

1026). I would like to express my gratitude towards my mother, Noorjahan for her

kindness, countless du'a and encouragement which helped me in completing this

project. It is the time to extend my deep sense of gratitude to my dearest friend Mr.

Sheik Fareed for his constant help, support and coordination in completing this project

without whom it's impossible for me to reach this stage. Sincere thanks also go to my

brothers Mr. Mohammed Thahir and Mr. Mohammed Thaiyub for their faith in me.

It's my genuine pleasure to extend my sincere gratitude to my sweet sister Mrs.

Thasneem Bagem and her husband Mohammed Riyaz Ali for their constant support

and motivation. Not forgetting my dad, Late Hyder Ali for his teachings and trainings

to get through the struggles in my life. He is no more in this world, May Allah reward

him with highest ranks of Jannah. Ameen. Furthermore I would also like to

acknowledge with much appreciation the Lab Technician Br Abdul Rahmat for his

support in maintaining the post graduate lab. My thanks and appreciation also goes to

my colleagues from the Electronics and Computer Engineering Department

Postgraduate Lab for their company, advice and motivation during the study. Lastly, I

would like to thank International Islamic University Malaysia for letting me study for

all these years. Not forgetting all the people who remembered us in their prayers, May

Allah give them a high status in Paradise and may He give them the best of this world

and more, may He The Ever-Forgiving (Al-Ghaffar) also forgive all their sins Ameen.

ix

I dedicate this research work to my beloved parents, siblings and the ummah...

x

TABLE OF CONTENTS

Abstract .................................................................................................................................... iii

Abstract in arabic ...................................................................................................................... iv

Approval page ........................................................................................................................... iv

Declaration................................................................................................................................ vi

Acknowledgement .................................................................................................................. viii

List of tables ............................................................................................................................ xii

List of figures ......................................................................................................................... ixiii

List of abbreviations .................................................................................................................xvi

List of symbols....................................................................................................................... xvii

CHAPTER ONE INTRODUCTION ........................................................................................1

1.1 Background ...................................................................................................................1

1.2 Problem statement .........................................................................................................3

1.3 Research objective ........................................................................................................3

1.4 Research scope..............................................................................................................4

1.5 Research methodology ..................................................................................................4

1.6 Flowchart ......................................................................................................................5

1.7 Dissertation outline .......................................................................................................6

CHAPTER TWO LITERATURE REVIEW ...........................................................................7

2.1 Magnetometer ...................................................................................................................7

2.2 Comparison of magnetometers ......................................................................................8

2.2.1 Nuclear precession magnetometer ........................................................................8

2.2.2 Magnetoresistive magnetometer ...........................................................................8

2.2.3 Magnetotransistor .................................................................................................8

2.2.4 Hall-Effect sensor .................................................................................................9

2.3 Recent work ................................................................................................................ 10

2.4 Comparison of recent work ........................................................................................ 12

2.5 Core Material Property And Selection ......................................................................... 13

CHAPTER THREE SIMULATION SETUP ......................................................................... 17

3.1 Comsol Multiphysics .................................................................................................. 17

3.2 Design Structures ........................................................................................................ 17

3.3 Gating Mechanism ...................................................................................................... 18

3.4 Overview Of Modelling .............................................................................................. 19

3.5 Physics Settings .......................................................................................................... 20

3.5.1 Magnetic Field ................................................................................................... 21

3.5.2 Electric Circuit Coupling .................................................................................... 22

xi

3.6 Mesh Specification ...................................................................................................... 23

3.7 E-Core Structure (Center Tapped Coil) ....................................................................... 24

3.8 E-Core Structure (Side Coils) ...................................................................................... 26

3.9 Rectangular Shaped Core Structure ............................................................................. 27

3.10 Square Core Structure ................................................................................................. 29

3.11 Triangular Shaped Structure ........................................................................................ 31

CHAPTER FOUR RESULTS AND DISCUSSION............................................................... 34

4.1 Parameter influence on the performance of the fluxgate magnetometer ....................... 34

4.2 Outcomes of different designs ..................................................................................... 35

4.2.1 Variation of number of turns in sensing coil ...................................................... 35

4.3 E-shaped core structure (side coils) ............................................................................. 35

4.3.1 Response of sensor with two different cases…....................................................35

4.4 E-shaped core (center tapped coils) ............................................................................. 39

4.4.1 Response of sensor with two different cases.......................................................43

4.5 Square-shaped core structure ....................................................................................... 43

4.5.1 Response of sensor with two different cases…....................................................46

4.6 Rectangular-shaped core structure ............................................................................... 46

4.6.1 Rectangular-core response for magnetic field......................................................50

4.7 Comparison of three types core structures ................................................................... 50

4.8 Triangular shaped core structure.................................................................................. 51

4.8.1 Magnetic response of triangular shaped core ....................................................... 52

4.9 Method of calculation ................................................................................................. 53

4.10 Discussion................................................................................................................... 53

CHAPTER FIVE CONCLUSION AND RECOMMENDATION ........................................ 56

5.1 Conclusion .................................................................................................................. 56

5.2 Limitation, future work and recommendation .............................................................. 57

REFERENCES .................................................................................................................... 58

xii

LIST OF TABLES

Table No Page No

Table 2.1: Magnetic Sensors Comparison 9

Table 2.2: Comparison of recent work 13

Table 3.1: Dimension of the existing and assumed design 33

Table 4.1: Result comparison of different design 53

xiii

LIST OF FIGURES

Figure 1.1 Flow chart of Research Methodology 5

Figure 2.1 Basic structure of fluxgate magnetometer 7

Figure 2.3 Basic structure of ring shaped fluxgate magnetometer 11

Figure 2.4 B-H cure for ferrite P2500 material 14

Figure 2.5 Induced Voltage Vs Driving voltage 15

Figure 2.6 Induced Voltage in secondary coil 16

Figure 3.1. Overall Structure of E-shaped core fluxgate magnetometer 20

Figure 3.2. Electrical coupling circuit 23

Figure 3.3. Mesh structure 23

Figure 3.4. Mesh Specification 24

Figure 3.5 E-shaped core structure 25

Figure 3.6 a) cross sectional view of circular coil, b) top view of the circular coil 25

Figure 3.7 E-core material specifications 26

Figure 3.8 E-core structure with adjacent coils 27

Figure 3.9: Rectangular shaped core 28

Figure 3.10 a) Top view of coils b) Cross sectional view of coils 28

Figure 3.11 Rectangular core material specifications 29

Figure 3.12 Square Core 30

Figure 3.13 a) Cross sectional view of coil and b) Top view of coil 30

Figure 3.14 Final structure for square core 31

Figure 3.15: Triangular core 31

xiv

Figure 3.16 a) Cross sectional view of coil and b) Top view of coil 32

Figure 3.17 Final Structure for Rectangular Core 32

Figure 4.1 Primary voltage with combination of number of turns 36

Figure 4.2 Voltage induced in drive coil with Ns = 18 36

Figure 4.3 Induced Voltage with Ns = 27 37

Figure 4.4 Induced voltage with Ns = 36 37

Figure 4.5 Induced Voltage with various number of turns 38

Figure 4.6 Induced Voltage E-shaped core without external field 39

Figure 4.7 Induced Voltage with Ns = 18 40

Figure 4.8 Induced Voltage with Ns = 27 40

Figure 4.9 Induced Voltage with Ns = 36 41

Figure 4.10 Induced voltage with the combination of turns 41

Figure 4.11 Primary voltage with combination of number of turns 43

Figure 4.12 Induced voltage with Ns = 180 44

Figure 4.13 Induced voltage with Ns = 270 44

Figure 4.14 Induced voltage with Ns = 360 45

Figure 4.15 Induced voltage with number of turns 45

Figure 4.16 Excitation voltage with different combination of turns 47

Figure 4.17 Induced Voltage with Ns = 18 47

Figure 4.18 Induced voltage with Ns = 27 48

Figure 4.19 Induced voltage with Ns = 36 48

Figure 4.20 Induced voltage with different number of turns 49

Figure 4.21 Hysteresis Loop of Symmetric Structures 50

xv

Figure 4.22 Flux density in triangular core without external field 51

Figure 4.23 Flux density in triangular core without external field 52

xvi

LIST OF ABBREVIATIONS

FEA Finite Element method

PDE Partial Differential Equation

3-D Three dimensional

2-D Two dimensional

xvii

LIST OF SYMBOLS

Symbols Description Unit

B0 or HJ or HX External Magnetic Field Tesla

Iexc Excitation Current Ampere

Vind Induced Voltage Voltage

μ (mu) Permeability of the material (Wb/A-t-m)

μ0 (mu_0) Relative Permeability of free

space

No unit

μr (mu_r) Relative Permeability of

Material

No unit

Σ Electrical Conductivity Siemens per

meter(S/m)

Bexc Excitation Magnetic Field Tesla

H Magnetic field Tesla

B Magnetic flux density Ampere turn per

meter(A-t/m)

M Magnetization No Unit

Φ Magnetic Flux Weber per meter

(Wb/m2)

I Current Ampere

V Voltage Voltage

1

CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND

MEMS (Micro-Electro-Mechanical-Systems) are the technology that can be realized by

using micro fabrication techniques. This could also be defined as miniaturized and electro-

mechanical elements i.e., devices and structures in the most general form (Pieters, 2007). Small

sized sensors are required in many applications such as safety and security. The purpose of this

dissertation is to investigate and analyse the geometrical features of MEMS-based fluxgate

magnetometer that could assist in optimizing the design of the device. Magnetometer is an

instrument for measuring the strength and direction of a magnetic field. There are several types

of magnetometer which had been used in different applications. A magnetometer can indicate the

location of deposits of magnetic ore, such as iron ore, or geological formations associated with

petroleum (Mohri, Kondo, Fujiwara, & Matsumoto, 1983).

In addition, magnetometers are also used in airports to screen boarding passengers for

concealed guns or other metallic weapons. This system works when the passenger walks through

a fluctuating magnetic field which would further set up a secondary magnetic field of various

strengths around metallic objects that he or she may be carrying. If it detects any secondary

magnetic field characteristic of a weapon, then an alarm would alert the security system.

Some magnetometers use a permanent magnet while others use an electromagnet; and yet

others make use of the magnetic properties of the nuclei of atoms. Fluxgate magnetometer is a

device which consists of one or more soft iron cores each surrounded by primary and secondary

windings. It is a device used for determining the characteristics of an external magnetic field

2

from the signals produced in the secondary windings. The intensity and orientation of magnetic

lines of flux can be measured by the fluxgate magnetometer and these are defined by the

magnetic field to be measured (the signal field) that would control the saturable inductor

(fluxgate). The fluxgate magnetometer (or saturable-core magnetometer) was developed during

World War II as an airborne detector of submarines. It has a sensing element of permalloy or a

similar material that becomes magnetically saturated in very low magnetic fields. Due to its

affordability and very low power consumption, fluxgates were used in a variety of sensing

applications.

A coil surrounding the core excites it to near saturation at a frequency of about 1 kHz. If

there is no external magnetic field, the alternating magnetic flux induced in the core is

symmetrical in the two directions, but the presence of external steady magnetic field along the

axis of the core causes it to approach saturation more quickly during half of the cycle, and the

resulting flux is asymmetric (Araki, 1994). A fluxgate magnetometer includes a high

permeability core, an excitation winding for applying a periodically varying magneto motive

force to the core, the incident signal field (usually dc or of much smaller frequency than the

excitation frequency), and an output winding whose induced voltage is a function of the signal

field (Geyger, 1958). Thereupon, geometrical features of fluxgate coils such as width of the coil,

distance between successive coil, and gap between top and bottom coils have an effect towards

device miniaturization.

Eventually, the abovementioned facts such as width, distance and gap between coils are

essential features that can increase the optimum design of the fluxgate magnetometer. Besides

that, simulation work will be conducted to increase the performance design, which could reduce

the possibility of fabrication error by using the Finite Element Method (FEM).

3

1.2 PROBLEM STATEMENT

The problem are to be addressed through this research is the reduction in the size of

the magnetometer and also the ways to improve the performance based on the geometrical

dimension or structure. The main problem in fluxgate magnetometer is to detect the magnetic

field range in the presence of background magnetic field. Another important shortcoming along

with this is the structure of the fluxgate magnetometer. Therefore, the issues are more focused as

follows,

Detection Range of the fluxgate magnetometer

Design Structure of the fluxgate magnetometer

1.3 RESEARCH OBJECTIVE

The objectives of this research are as shown below

1. Investigate the effect of fluxgate micro coil geometrical features towards it detection range.

2. Develop and conduct simulation processes by using a suitable finite element method (FEM)

software.

3. Analyse simulation results to determine the optimum geometrical features of the micro coils

for the MEMS-based fluxgate magnetometer.

4

1.4 RESEARCH SCOPE

The scope of this research is to analyse the detection range of the fluxgate magnetometer by

varying core shape and coil dimensions in micro scale by modelling using the Finite Element

Method (FEM) tool.

1.5 RESEARCH METHODOLOGY

Even though there are advanced techniques to detect earth magnetic field but the

shortcomings in design structure are still present. The issues are more focused on

Increasing the sensitivity of detection range

Making the design more compact

Although there are many design structures that exist for fluxgate magnetometer but still

there is a lacking in analysing geometrical features of those design which could be useful to

improve design compactness and sensitivity. By considering the stated issues, the geometrical

features of the design had been investigated and analysed. The main features that were

considered are as follows,

Number of turns in the coil

Width of the coil and core

Distance between the core and coil

By changing these features, results of the different designs such as rectangular, triangular and

transformer core structures will be verified and justified according to the requirement. The steps

carried out to ensure the flow of this project is described here. First, a thorough review on the

micro coil designs of micro-scaled magnetic devices is given. In addition to that is the

identification of related parameters that are relevant to the micro coils that affected the

5

performance of the micro-scaled fluxgate magnetometer. Furthermore, development of the

simulation process using the finite element method (FEM) software which includes geometrical

modelling of micro coils, modelling of inputs and outputs to the simulations based on the

relevant parameters. Having stated all the relevant parameters, validation of the results had been

made with the help of a developed simulation process. Finally, generation of data from the

simulation results allowed for further evaluation and analysis. Moreover, the overall conclusion

from the work has been published in a journal paper.

1.6 FLOWCHART

Figure 1.1 Flow chart of Research Methodology

Start

Literature Review

Develop Simulation Model

Are the simulation

Ok?

Evaluate Data

End

No

Yes

Modify

6

1.7 DISSERTATION OUTLINE

Chapter 1 contains the introduction of fluxgate magnetometer that exploits the background in

section 1.1, followed by problem statement in section 1.2, which further extends to Research

objective in section 1.3.

Moreover chapter continues with research scope in section 1.4, and finally detailed Research

Methodology and flowchart in section 1.5 and section 1.6, respectively.

Chapter 2 covers all previous work related to fluxgate magnetometer and also the comparison of

most recent research in this field to choose the selected designs. Chapter 3 presents the

simulation setup using the Finite Element method (FEM) tool for different structures of the

fluxgate magnetometer.

Chapter 4 states the results and discussion part which are derived for different fluxgate

magnetometer designs. Eventually, Chapter 5 summarizes the whole research work, which

extends to the advantages and limitations throughout this research. Finally, the discussions part

discusses on the recommendations for future work.

7

CHAPTER TWO

LITERATURE REVIEW

2.1 MAGNETOMETER

Mankind uses magnetic sensors in analysing and controlling thousands of functions. Magnetic

sensors play a very important role in computer with the use of magnetic storage disks and tape

drives. In addition, it is also used in aeroplanes because of the high reliability of noncontact

switching with magnetic sensors. Magnetic fields can be detected in many ways but most of

them are used between the magnetic and electric phenomena (Lenz, 1990).

Fig 2.1 depicts the fluxgate magnetometer that consists of a ferromagnetic material wound with

two coils. It also shows the magnetic induction with the hysteresis exposed by all ferro magnetic

materials. Dependence of the state of a physical system on its previous history is described using

the hysteresis loop.

Figure 2.1 Basic structure of fluxgate magnetometer

DRIVE COILS SENSE COILS

FERRO MAGNETIC MATERIAL

SATURATION

OUT OF SATURATION

8

2.2 COMPARISON OF MAGNETOMETERS

2.2.1 NUCLEAR PRECESSION MAGNETOMETER

Geomagnetic field measurement is the main application where the nuclear free precession

magnetometers played a vital role. Packard and Varian discovered the principles of operation for

the steps of magnetic polarization and observation of nuclear induction in 1953 (Grivet &

Malnar, 1967). In addition, its sensitivity lies between 10-6 and 106 Gauss. However, unlike the

fluxgate magnetometer, its field of detection is high which gives more significance to the

fluxgate sensors.

2.2.2 MAGNETORESISTIVE MAGNETOMETER

In the presence of external magnetic field, the reluctance of ferromagnetic material would

change. This has been used to check the sensitivity of the magnetoresistive sensors (MR).

Among the different kinds of magnetoresistive (MR) sensors, some can be fabricated in a thin

film such as anisotropic, giant and tunnelling magnetoresistive (TMR) (PBrown, 2012).

Obviously, it is clear that only selected groups of magnetoresistive sensors are fabricated in

micro scale.

2.2.3 MAGNETOTRANSISTOR

Complementary Metal oxide semiconductor (CMOS) has been involved in fabricating

magnetotransistor (MTS) devices for magnetic field detection. Additionally, batch fabrication,

miniaturization, and cointegration of circuitry are key features of this sensor. Furthermore, MT’s

could sense non alternating signals that come from the linear magnetic response (Metz & Balres,

2001). Although it has several good features, it is still lacking in sensing weak fields.