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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
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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.
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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.
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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
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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……………………………..
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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
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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.
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I dedicate this research work to my beloved parents, siblings and the ummah...
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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
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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
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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
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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
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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
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Figure 4.22 Flux density in triangular core without external field 51
Figure 4.23 Flux density in triangular core without external field 52
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LIST OF ABBREVIATIONS
FEA Finite Element method
PDE Partial Differential Equation
3-D Three dimensional
2-D Two dimensional
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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
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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
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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).
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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.
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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
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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
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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.
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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
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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.